DSS E-Notes - Design of Steel Structures I - PDF

INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , C...

INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) E-NOTES OF DSS – 1 B.TECH 6th Sem Lesson 1 : Structures and its kinds Lesson 2 : Rolled Structural steel sections Lesson 3 : Loads on structures Lesson 4 : Stresses on structures Lesson 5 : Riveted connections Lesson 6 : Design of Riveted connections Lesson 7 : Welded connection Lesson 8 : Tension members Lesson 9 : Design of Tension member Lesson 10 : Design of columns Lesson 11 : Design of Compression members Lesson 12 : Design of column base – Slab base Lesson 13 : Steel Beams Lesson 14 : Design of steel beams  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 1. Structures and its kinds 1.1 INTRODUCTION The Structural engineering is a branch of engineering which deals with structural analysis and structural design. The structural engineering plays an important role in civil engineering, mechanical engineering, electrical engineering, naval engineering, aeronautical engineering and in all the specialized phases of engineering. The structural analysis deals with the development of suitable arrangement of structural elements for the structures to support the external loads or the various critical combinations of the loads which are likely to act on the structure. The analysis also deals with the determination of internal forces developed in the various members, nature of stresses or critical combination of the stresses at the various points and the external reactions due to the worst possible combination of the loads. The structural design deals with the selection of proper material, proper sizes, proportions and shape of each member and its connecting details. The selection is such that it is economical and safe. The structural design further deals with the preparation of final layout of the structure and the design drawings are necessary for fabrication and construction. 1.2 DEFINITION Construction or framework of structural elements (members) which gives form and stability, and resists stresses and strains. Structures have defined boundaries within which each element is physically or functionally connected to the other elements, and the elements themselves and their interrelationships are taken to be either fixed (permanent) or changing only occasionally or slowly. 1.3 CLASSIFICATION OF STRUCTURES The structures may be classified as statically determinate structures and statically indeterminate structures. When the equation of statics (ΣH=0, ΣV=0 and ΣM=0) are enough to determine all the forces acting on the structure and in the structures are known as statically determinant structures. When the equation of equilibrium are not sufficient to determine all the forces acting on the structures and in the structure, then the structures are known as statically indeterminate  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) structures. The equations of consistent deformations are added to the equations of equilibrium in order to analyze the statically indeterminate structures. The structures are also classified as shell structures and framed structures. The shell roof covering of large buildings, air planes, rail road cars, ship wells, tanks etc are the examples of shell structures. The plates or sheets serve functional and structural purposes. The plates act as a load carrying elements. The plates are stiffened by frames which may or may not carry the principal loads. The framed structures are built by assemblies of elongated members. The truss frames, truss girders, rigid frames etc are the examples of framed structures. The main members are used for the transmission of loads. The structures may be further classified depending on the materials used as plastic structures, aluminium structures, timber structures, R.C.C structures and steel structures. 1.4 ADVANTAGES OF STEEL STRUCTURES 1. Steel has a high strength and so steel components have smaller sections for the same strength compared to corresponding components of other material.The existing steel structures and structural component may be strengthened by connecting additional sections or plates. 2. Steel members are gas and watertight, because of high density of steel. 3. Steel structures can be fabricated at site easily. 4. Steel structures have great durability and serve for many years. 5. Steel members can be readily disassembled or replaced. 6. The existing steel structures and structural component may be strengthened by connecting additional sections or plates. 1.5 DISADVANTAGES OF STEEL STRUCTURES 1. Steel structures are liable to corrosion and need painting frequently. 2. Steel structures have a low fire resistance and are liable to lose their strength and get deformed at high temperature.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 1.6 STRUCTURAL STEEL The structural steel is the steel used for the manufacture of rolled structural steel sections, fastenings and other elements for use in structural steel works. Steel is an alloy of iron, carbon and other elements in varying percentages. The strength, hardness and brittleness of steel increases and ductility of steel decreases with the increase of percentage of carbon. Depending on the chemical composition, the different type of steel are classified as mild steel, medium carbon steel, high carbon steel, low alloy steel and high alloy steel. The mild steel, medium carbon steel and low alloy steel are generally used for steel structures. The copper bearing quality of steel contains small percentage of copper contents. The corrosive resistance of such steel is increased. Mild steel is used for the manufacture of rolled structural steel sections, rivets and bolts. The following operations can be done easily on mild steel 1.Cutting, 2. Punching, 3.Drilling, 4. Machining, 5. Welding and 6. Forging when heated. All structural steels used in general construction, coming within the purview of IS:800-84 shall, before fabrication, comply with one of the following Indian Standard specifications 1. IS : 226-1975 structural steel (standard quality) 2. IS : 1977-1975 structural steel (ordinary quality) 3. IS : 2062-1984 weldable structural steel 4. IS : 961-1975 structural steel (high tensile) 5. IS : 8500-1977 weldable structural steel (medium and high strength qualities) 1.6.1 IS : 226-1975 structural steel (standard quality). The mild steel is designated as St 44-S for use in structural work. This steel is also available in copper bearing quality in which case it designated as St 44-SC. The copper content is between 0.20 and 0.35 per cent. The physical properties of structural steel are given below: 1. Unit weight of steel 78.430 to 79.000 kN/m3 2. Young’s modulus of elasticity, E=2.04 to 2.18 x 105 N/mm2  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 3. Modulus of rigidity, G=0.84 to 0.98 x 105 N/mm2 4. Coefficient of thermal expansion (or contraction) α=12 x 10 -6/˚C or 6.7 x 10-6/˚F. The tensile strength, yield stress and percentage elongation for IS : 226-1975 structural steel standard quality, determined in accordance with IS : 1608-1960. The steel confirming to IS : 226 is suitable for all types of steel structures subjected to static, dynamic and repeated cycles of loadings. It is also suitable for welding up to 20 mm thickness. When the thickness of element is more than 20 mm, it needs special precautions while welding. 1.6.2 IS : 1977-1975 structural steel (ordinary quality). The steel which did not comply with IS : 226, was formerly called as steel of untested quality. The standards for such steel have been laid down in IS : 1977-75 (ordinary quality). There are two grades in this standard which are designated as St 44.0 and St 32.0. The steel St 44.0 is intended to be used for structures not subjected to dynamic loading other than wind loads e.g., platform roofs, office buildings, foot over bridge. The copper bearing quality is designated as St 44.0C. The steel confirming to IS : 1977 is not suitable for welding and for the structures subjected to high seismic forces (earth quake forces). The steel structures using steel confirming to IS : 1977 must not be analyzed and designed by plastic theory. 1.6.3 IS : 2062-1984 weldable structural steel. This structural steel intended to be used for members in structures subjected to dynamic loading where welding is employed for fabrication and where fatigue and great restraint are involved e.g., crane gantry girder, road and rail bridges etc,. it is designated as St 42-W and copper bearing quality is designated as St 42-WC. It is suitable for welding the elements of thickness between 28 mm and 50 mm. when the thickness of elements is less than 28 mm; it may be welded provided the limiting maximum carbon content is 0.22 per cent. 1.6.4 IS : 961-1975 structural steel (high tensile). The high tensile steel forms a specific class of steel in which enhanced mechanical properties and in most of the cases increased resistance to atmospheric corrosion are obtained by the incorporation of low proportions of one or more alloying elements, besides carbon. These steels  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) are generally intended for application where saving in weight can be effected by reason of their greater strength and atmospheric corrosion resistance. Standards of high tensile steel have been given in IS : 961-1975. It has been classified into two grades designated as St 58-HT and St 55- HTW. St 58-HT is intended for use in structures where fabrication is done by methods other than welding. St 55-HTW is intended for use in structures where welding is employed for fabrication. The high tensile steel is also available in copper bearing quality and two grades are designated as St 58-HTC and St 55-HTWC. The steel conforming to IS : 961 is suitable for bridges and general building construction. 1.6.5 IS : 8500-1977 weldable structural steel (medium and high strength qualities) Various medium and high strength qualities of weldable structural steel are, Fe 440 (HT1 and HT2) Fe 540 (HT, HTA and HTB), Fe 570 HT, Fe 590 HT and Fe 640 HT. 1.7 PRODUCTION OF STEEL The steel is produced in the form of ingots and converted to different shapes. In our country, Tata Iron and Steel Company, Indian Iron and Steel Company, Mysore Iron and Steel Company and Hindustan Steel produce steel at their plants 1.8 RECENT DEVELOPMENTS IN MATERIAL A number of developments in material such as steel have been made recently. The weldable qualities of steel (IS : 2062) designated as St 42-W and IS : 961 designated as St-55-HTW are developed with the large scale use of welding. IS : 961 has been developed with high tensile strength and there is saving in weight due to enhanced mechanical properties. Its weldable quality is advantageous for composite construction.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 2. Rolled Structural Steel Sections 2.1 INTRODUCTION The steel sections manufactured in rolling mills and used as structural members are known as rolled structural steel sections. The steel sections are named according to their cross sectional shapes. The shapes of sections selected depend on the types of members which are fabricated and to some extent on the process of erection. Many steel sections are readily available in the market and have frequent demand. Such steel sections are known as regular steel sections. Some steel sections are rarely used. Such sections are produced on special requisition and are known as special sections. ‘ISI Handbook for Structural Engineers’ gives nominal dimensions, weight and geometrical properties of various rolled structural steel sections. 2.2 TYPES OF ROLLED STRUCTURAL STEEL SECTIONS The various types of rolled structural steel sections manufactured and used as structural members are as follows: 1. Rolled Steel I-sections (Beam sections). 2. Rolled Steel Channel Sections. 3. Rolled Steel Tee Sections. 4. Rolled Steel Angles Sections. 5. Rolled Steel Bars. 6. Rolled Steel Tubes. 7. Rolled Steel Flats. 8. Rolled Steel Sheets and Strips. 9. Rolled Steel Plates.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 2.3 ROLLED STEEL BEAM SECTIONS The rolled steel beams are classified into following four series as per BIS : (IS : 808-1989) 1. Indian Standard Joist/junior Beams ISJB 2. Indian Standard Light Beams ISLB 3. Indian Standard Medium Weight Beams ISMB 4. Indian Standard Wide Flange Beams ISWB The rolled steel columns/heavy weight beams are classified into the following two series as per BIS (IS : 808-1989) 1. Indian Standard Column Sections ISSC 2. Indian Standard Heavy Weight Beams ISHB The cross section of a rolled steel beam is shown in Fig. 2.1. The beam section consists of web and two flanges. The junction between the flange and the web is known as fillet. These hot rolled steel beam sections have sloping flanges. The outer and inner faces are inclined to each other and they intersect at an angle varying from 1½ to 8˚ depending on the section and rolling mill practice. The angle of intersection of ISMB section is 8˚. Abbreviated reference symbols (JB, LB, MB, WB, SC and HB) have been used in designating the Indian Standard Sections as per BIS (IS 808-1989) The rolled steel beams are designated by the series to which beam sections belong (abbreviated reference symbols), followed by depth in mm of the section and weight in kN per metre length of the beam, e.g., MB 225 @ 0.312 kN/m. H beam sections of equal depths have different weights per metre length and also different properties e.g., WB 600 @ 1.340 kN/m, WB 600 @ 1.450 kN/m, HB 350 @0.674 kN/m, HB 350 @0.724 kN/m. I-sections are used as beams and columns. It is best suited to resist bending moment and shearing force. In an I-section about 80 % of the bending moment is resisted by the flanges and the rest of the bending moment is resisted by the web. Similarly about 95% of the shear force is resisted by the web and the rest of the shear force is resisted by the flanges. Sometimes I-  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) sections with cover plates are used to resist a large bending moment. Two I-sections in combination may be used as a column. 2.4 ROLLED STEEL CHANNEL SECTIONS The rolled steel Channel sections are classified into four categories as per ISI, namely, 1. Indian Standard Joist/Junior Channels ISJC 2. Indian Standard Light Channels ISLC 3. Indian Standard Medium Weight Channels ISMC 4. Indian Standard Medium Weight Parallel Flange Channels ISMCP The cross section of rolled steel channel section is shown in Fig 2.2. The channel section consists of a web and two flanges. The junction between the flange and the web is known as fillet. The rolled steel channels are designated by the series to which channel section belong (abbreviated reference symbols), followed by depth in mm of the section and weight in kN per metre length of the channel, e.g., MC 225 @ 0.261 kN/m Channels are used as beams and columns. Because of its shape a channel member affords connection of an angle to its web. Built up channels are very convenient for columns. Double channel members are often used in bridge truss. The channels are employed as elements to resist bending e.g., as purlins in industrial buildings. It is to note that they are subjected to twisting or torsion because of absence of symmetry of the section with regards to the axis parallel to the web, i.e., yy-axis. Therefore, it is subjected to additional stresses. The channel sections are commonly used as members subjected to axial compression in the shape of built-up sections of two channels connected by lattices or batten plates or perforated cover plates. The built-up channel sections are also used to resist axial tension in the form of chords of truss girders. As per IS : 808-1989, following channel sections have also been additionally adopted as Indian Standard Channel Secions 1. Indian Standard Light Channels with parallel flanges ISLC(P)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 2. Medium weight channels MC 3. Medium weight channels with parallel flanges MCP 4. Indian Standard Gate Channels ISPG In MC and MCP channel sections, some heavier sections have been developed for their intended use in wagon building industry. The method of designating MC and MCP channels is also same as that for IS channels. 2.5 ROLLED STEEL TEE SECTIONS The rolled steel tee sections are classified into the following five series as per ISI: 1. Indian Standard Normal Tee Bars ISNT 2. Indian Standard Wide flange Tee Bars ISHT 3. Indian Standard Long Legged Tee Bars ISST 4. Indian Standard Light Tee Bars ISLT 5. Indian Standard Junior Tee Bars ISJT The cross section of a rolled steel tee section has been shown in Fig. 2.3. The tee section consists of a web and a flange. The junction between the flange and the web is known as fillet. The rolled steel tee sections are designated by the series to which the sections belong (abbreviated reference symbols) followed by depth in mm of the section and weight in kN per metre length of the Tee, e.g., HT 125 @ 0.274 kN/m. The tee sections are used to transmit bracket loads to the columns. These are also used with flat strips to connect plates in the steel rectangular tanks. A per IS: 808-1984, following T-sections have also been additionally adopted as Indian Standard T-sections. 1. Indian Standard deep legged Tee bars ISDT 2. Indian Standard Slit medium weight Tee bars ISMT  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 3. Indian Standard Slit Tee bars from I-sections ISHT It is to note that as per IS 808 (part II) 1978, H beam sections have been deleted. 2.6 ROLLED STEEL ANGLE SECTIONS The rolled steel angle sections are classified in to the following three series. 1. Indian Standard Equal Angles ISA 2. Indian Standard Unequal Angles ISA 3. Indian Standard Bulb Angles ISBA Angles are available as equal angles and unequal angles. The legs of equal angle sections are equal and in case of unequal angle section, length of one leg is longer than the other. Thickness of legs of equal and unequal angle sections are equal. The cross section of rolled equal angle section, unequal angle section and that of bulb angle section is shown in Fig. 2.4. The bulb angle consists of a web a flange and a bulb projecting from end of web. The rolled steel equal and unequal angle sections are designated by abbreviated reference symbols ∟ followed by length of legs in mm and thickness of leg, e.g., ∟130 x 130 x 8 mm (∟130 130 @ 0.159 kN/m) ∟200 x 100 x 10 mm (∟ 200 100 @ 0.228 kN/m) The rolled steel bulb angles are designated by BA, followed by depth in mm of the section and weight in kN per metre length of bulb angle. Angles have great applications in the fabrications. The angle sections are used as independent sections consisting of one or two or four angles designed for resisting axial forces (tension and compression) and transverse forces as purlins. Angles may be used as connecting elements to connect structural elements like sheets or plates or to form a built up section. The angle sections are also used as construction elements for connecting beams to the columns and purlins to the chords of trusses in the capacity of beam seats, stiffening ribs and cleat angles.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) The bulb angles are used in the ship buildings. The bulb helps to stiffen the outstanding leg when the angle is under compression. As per IS : 808-1984, some supplementary angle sections have also additionally adopted as Indian Standard angle sections. However prefix ISA has been dropped. These sections are designated by the size of legs followed by thickness e.g., ∟200 150 x 15. 2.7 ROLLED STEEL BARS The rolled steel bars are classified in to the following two series: 1. Indian Standard Round Bars ISRO 2. Indian Standard Square Bars ISSQ The rolled steel bars are used as ties and lateral bracing. The cross sections of rolled steel bars are shown in Fig. 2.5. The rolled steel bars are designated by abbreviated reference symbol RO followed by diameter in case of round bars and ISSQ followed by side width of bar sections. The bars threaded at the ends or looped at the ends are used as tension members. 2.8 ROLLED STEEL TUBES The rolled steel tubes are used as columns and compression members and tension members in tubular trusses. The rolled steel tubes are efficient structural sections to be used as compression members. The steel tube sections have equal radius of gyration in all directions. The cross section of rolled steel tube is shown in Fig. 2.6. 2.9 ROLLED STEEL FLATS The rolled steel flats are used for lacing of elements in built up members, such as columns and are also used as ties. The cross section of rolled steel flat is shown in Fig. 2.7. the rolled steel flats are designated by width in mm of the section followed by letters (abbreviated reference symbol) F and thickness in mm, e.g., 50 F 8. This means a flat of width 50 mm and thickness 8 mm. The rolled steel flats are used as lattice bars for lacing the elements of built up columns. The rolled steel flats are also used as tension members and stays.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 2.10 ROLLED STEEL SHEETS AND STRIPS The rolled steel sheet is designated by abbreviated reference symbol SH followed by length in mm x width in mm x thickness in mm of the sheet. The rolled steel strip is designated as ISST followed by width in mm x thickness in mm, e.g., SH 2000 x 600 x 8 and ISST 250 x 2. 2.11 ROLLED STEEL PLATES The rolled steel plates are designated by abbreviated reference symbol PL followed be length in mm x width in mm x thickness in mm of the plates, e.g., PL 2000 x 1000 x 6. The rolled steel sheets and plates are widely used in construction. Any sections of the required dimensions, thickness and configuration may be produced by riveting or welding the separate plates. The rolled plates are used in the web and flanges of plate girders, plated beams and chord members and web members of the truss bridge girders. The rolled steel plates are used in special plate structures, e.g., shells, rectangular and circular steel tanks and steel chimneys. 2.12 RECENT DEVELOPMENTS IN SECTIONS The rolled steel beam sections with parallel faces of flanges are recently developed. These beam sections are called as parallel flange sections. These sections have increased moment of inertia, section modulus and radius of gyration about the weak axis. Such sections used as beams and columns have more stability. Theses sections possess ease of connections to other sections as no packing is needed as in beams of slopping flanges. The parallel flange beam sections are not yet rolled in our country. New welded sections using plates and other steel sections are developed because of welding. The development of beams with tapered flanges and tapered depths is also due to welding. The open web sections and the castellated beams were also developed with the rapid use of welding.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Fig. 2.1 Beam section Fig. 2.2 Channel section Fig. 2.3 Tee section  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Fig. 2.4 Angle section Fig. 2.5 Bar section  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Fig. 2.6 Tube section Fig. 2.7 Flat section  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 3. Loads on structures 3.1 INTRODUCTION The structures and structural members are designed to meet the functional and structural aspects. Both aspects are interrelated. The functional aspect takes in to consideration the purpose for which the building or the structure is designed. It includes the determination of location and arrangement of operating utilities, occupancy, fire safety and compliance with hygienic, sanitation, ventilation, special equipment, machinery or other features, incident to the proper functioning of the structures. In the structural aspect, it is ensured that the building or the structure is structurally safe, strong, durable and economical. The minimum requirements pertaining to the structural safety of buildings are being covered in codes dealing with loads by way of laying down minimum design loads which have to be assumed for dead loads, imposed loads, wind loads and other external loads, the structure would be required to bear. Unnecessarily, heavy loads without proper assessment should not be assumed. The structures are designed between two limits, namely, the structural safety and economy. The structures should be strong, stable and stiff. Estimation of the loads for which a structure should be designed is one of the most difficult problems in structural design. The designer must be able to study the loads which are likely to be acting on the structure throughout its life time and the loads to which the structure may be subjected during a short period. It is also necessary to consider the combinations of loads for which the structure has to be designed. 3.2 TYPES OF LOADS The loads to which a structure, will be subjected to consist of the following 1. Dead loads, 2. Live loads or imposed loads, 3. Wind load, 4. Snow load 5. Seismic load  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 6. Temperature effects In addition o the above loads, following forces and effects are also considered while designing the structures. 1. Foundation movements 2. Elastic axial shortening 3. Soil and fluid pressures 4. Vibrations 5. Fatigue 6. Impact 7. Erection loads 8. Stress concentration effects 3.3 DEAD LOADS Dead load of a structure means the weight of the structure itself. The dead load in a building will consist of the weight of all wall partitions, floors and roofs. Loads due to partition shall be estimated on the basis of actual constructional details of the proposed partitions and their positioning in accordance with plans and the loads thus estimated shall be included in the dead load for the design of the floors and the supporting structures. If the loads due to partitions cannot be actually computed for want of data, the floors and the supporting structures shall be designed to carry in addition to other loads a uniformly distributed dead load per square metre of not less than 33⅓ per cent of the weight per metre run of finished partitions over the entire floor area subjected to minimum uniformly distributed load of 1000 N/m2 in the case of floors used for office purposes. Dead loads can be estimated using the unit-weight of materials used in building construction as per IS : 875 (part I) -1987 3.4 LIVE LOADS OR IMPOSED LOADS  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Live loads are the loads which vary in magnitude and in positions. Live loads are also known as imposed or transient loads. Imposed loads consist of all loads other than dead loads. Live loads are assumed to be produced by the intended use of occupancy in building including the weight of movable partitions, distributed loads, concentrated loads, loads due to impact and vibration and snow loads. Live loads are expressed as uniformly distributed static loads. Live loads include the weight of materials stored, furniture and movable equipments. Efforts have been made at the international level to decide live loads on floors and these have been specified in the International standards (2103 Imposed floor loads in residential and public building and 2633 Determination of imposed floor loads in production buildings and warehouses). These codes have been published in the International Organization. Code IS : 875 (part 2) -1987 defines the principal occupancy for which a building or part of a building is used or intended to be used. The buildings are classified according to occupancy as per IS : 875 (part 2)-1987. 3.5 WIND LOAD The wind loads are the transient loads. The wind usually blows horizontal to the ground at high wind speeds. The vertical components of atmospheric motion are relatively small, therefore, the term wind denotes almost exclusive the horizontal wind. The winds of very high speeds and very short duration are called Kal Baisaki or Norwesters occur fairly frequently during summer months over North East India. The liability of a building or a structure to high wind pressure depends not only upon the geographical location and proximity of other obstructions to airflow but also upon the characteristics of the structure itself. In general, wind speed in the atmospheric boundary layer increases with height from zero at ground level to maximum at a height called the gradient height. The variation of wind with height depends primarily on the terrain conditions. However, the wind speed at any height never remains constant and it has been found convenient to resolve its instantaneous magnitude in to an average or mean value and a fluctuating component around this average value. The magnitude of fluctuating component of the wind speed is called gust, it depends upon averaging time. In general, smaller the averaging interval, greater is the magnitude of the gust speed. The wind load depends upon terrain, height of the structure and the shape and size of structure. It is essential to know the following terms to study the new concept of wind as described in IS : 875 (Part 3) – 1987  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 3.6 SNOW LOAD The snow load depends upon latitude of place and atmospheric humidity. The snow load acts vertically and it is expressed in kN/m2 of plan area. The actual load due to snow depends upon the shape of the roof and its capacity to retain the snow. When actual data for snow load is not available, snow load may be assumed to be 25 N/m2 per mm depth of snow. It is usual practice to assume that snow load and maximum wind load will not be acting simultaneously on the structure. 3.7 SEISMIC LOAD (EARTHQUAKE LOAD) It becomes essential to consider ‘seismic load’ in the design of structure, if the structure is situated in the seismic areas. The seismic areas are the regions which are geologically young and unstable parts and which have experienced earthquakes in the past and are likely to experience earthquakes in future. The Himalayan region, Indo Gangetic Plain, Western India, Cutch and Kathiawar are the places in our country which experience earthquakes frequently. Sometimes these earthquakes are violent also. Seismic load is caused by the shocks due to an earthquake. The earthquakes range from small tremors to severe shocks. The earthquake shocks cause movement of ground, as a result of which the structure vibrates. The vibrations caused because of earthquakes may be resolved in three perpendicular directions. The horizontal direction of vibration dominates over other directions. In some cases structures are designed for horizontal seismic forces only and in some case both horizontal seismic forces and vertical seismic forces are taken in to account. The seismic accelerations for the design may be arrived at from seismic coefficient, which is defined as the ratio of acceleration due to earthquakes and acceleration due to gravity. Our country has been divided in to seven zones for determining seismic coefficients. The seismic coefficients have also been recommended for different types of soils for the guidance of designers. IS : 1893-1962 Indian Standard Recommendations for Earthquake Resistant Design of Structure, may be referred to for actual design. 3.8 SOIL AND HYDROSTATIC PRESSURE The pressure exerted by soil or water or both should be taken in to consideration for the design of structures or parts of structure which are below ground level. The soil pressure and hydrostatic pressure may be calculated from established theories. 3.9 ERECTION EFFECTS  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) The erection effects include all effects to which a structure or part of structure is subjected during transportation of structural members and erection of structural member by equipments. Erection effects also take in to account the placing or storage of construction materials. The proper provisions shall be made, e.g., temporary bracings, to take care of all stresses caused during erection. The stress developed because of erection effects should not exceed allowable stresses. 3.10 DYNAMIC EFFECTS (IMPACTS AND VIBRATIONS) The moving loads on a structure cause vibrations and have also impact effect. The dynamic effects resulting from moving loads are accounted for, by impact factor. The live load is increased by adding to it the impact load. The impact load is determined by the product of impact factor and live load. 3.11 TEMPERATURE EFFECTS The variation in temperature results in expansion and contraction of structural material. The range of variation in temperature varies from localities to localities, season to season and day to day. The temperature effects should be accounted for properly and adequately. The allowable stress should not be exceeded by stress developed because of design loads and temperature effects. 3.12 LOAD COMBINATIONS All the parts of the steel structure shall be capable of sustaining the most adverse combination of the dead loads, prescribed live loads, wind loads, earthquake loads where applicable and any other forces or loads to which the steel structure may reasonably be subjected without exceeding the stress specified. The load combinations for design purpose shall be the one that produces maximum forces and effects and consequently maximum stresses from the following combinations 1. Dead load + Imposed (live) load 2. Dead load + Imposed (live) load + wind or earthquake loads and 3. Dead load + wind or earthquake loads  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 4. Stresses on structures 4.1 INTRODUCTION When a structural member is loaded, deformation of the member takes place and resistance is set up against deformation. This resistance to deformation is known as stress. The stress is defined as force per unit cross sectional area. The nature of stress developed in the structural member depends upon nature of loading on the member. 4.2 TYPES OF LOADS The following are the various types of stresses: 1. Axial stress (direct stress) : i. Tensile stress ii. Compressive stress 2. Bearing stress 3. Bending stress 4. Shear stress A member may be subjected to combined direct and bending stress. Such stress is known as combined stress. The tensile stresses are taken as positive and compressive stress as negative. This sign convention for stresses is convenient as a structural member elongates on application of tensile load and shortens on application of compressive load. 4.3 STRESS-STRAIN RELATIONSHIP FOR MILD STEEL When a mild steel bar is subjected to a tensile load, it elongates. The elongation per unit length is known as strain. The stress is proportional to stain within limit of proportionality. The stress- strain relationship for mild steel can be studied by plotting stress-strain curve. The stress and load may be plotted on y-axis and strain may be plotted on x-axis as shown in Fig. 4.1.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Fig. 4.1 Stress-strain curve When the tensile load increases with increase in strain, stress-strain curve follows a straight line relationship up to ‘Limit of proportionality’. The limit of proportionality is defined as stress beyond which straight line relationship ceases between stress and strain. Beyond the limit of proportionality stress approaches the elastic limit. The elastic limit is defined as the maximum stress up to which a specimen regains its original length on the removal of the applied load. There is hardly any distinct difference in the position of limit of proportionality and elastic limit. Practically, position of limit of proportionality coincides with the elastic limit. When the specimen is loaded beyond the elastic limit, the specimen does not resume its original length on the removal of applied load and a little strain is left in the specimen. This little strain is known as residual strain or permanent set. When the tensile load further increases the stress reaches ‘yield stress’ and material starts yielding. The stress-strain curve suddenly falls showing a decrease in stress. The distinct position from where sudden fall of curve occurs marks the upper yield point and the position up to which fall of curve occurs is known as lower yield point. The material stretches suddenly at constant stress. The adjustment of stress takes place in the elements of material in between upper yield point and lower yield point. On further increase of load, stress increases with the increase of strain. However, strain increases more rapidly. Finally the load reaches the value of ‘ultimate load’. The ultimate load is defined as maximum load, which can be placed prior to the breaking of specimen. The stress corresponding to the ultimate load is known as ‘ultimate  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) stress’. The stress-strain curve suddenly falls with rapid increase in strain and specimen breaks. The load corresponding to breaking position is known as ‘breaking load’. The cross-section of specimen decreases. If actual breaking stress is computed on the basis of decreased cross- sectional area, the breaking stress will be found to be more than the ultimate stress. The boundaries of grains of mild steel are composed of brittle material. This forms a rigid skeleton. The rigid skeleton prevents plastic deformation of the grains at low stress and shows upper yield point in stress-strain curve. At upper yield point, this rigid skeleton breaks down. As a result of this, the stress in material drops down without elongation from upper yield point to lower yield point. This is followed by sudden stretching of the material at constant stress from lower yield point up to strain hardening. 4.4 TENSILE STRESS When a structural member is subjected to direct axial tensile load, the stress is known as tensile stress (σat). The tensile stress is calculated on net cross-sectional area of the member: σat = (Pt/An) Where Pt is the direct axial tensile load and An is the net cross-sectional area of the member. 4.5 COMPRESSIVE STRESS When a structural member is subjected to direct axial compressive load, the stress is known as compressive stress (σac). The compressive stress is calculated on gross cross-sectional area of the member σac = (Pc/Ag) Where Pc is the direct axial compressive load and Ag is the gross cross-sectional area of the member 4.6 BEARING STRESS When a load is exerted or transferred by the application of load through one surface for the another surface in contact, the stress is known as ‘bearing stress’(σ b). the bearing stress is calculated on net projected area of contact  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) σb = (P/A) Where P is load placed on the bearing suface and A is the net projected area of contact. 4.7 WORKING STRESS The working stress is also termed as allowable stress or permissible stress. The working stress is evaluated by dividing yield stress by factor of safety. For the purpose of computing safe load carrying capacity of a structural member, its strength is expressed in terms of working stress. The working stress is the stress which may be developed or set up in the member without causing structural damage to it. The actual stress resulting in a structural member from design loads should not exceed working stresses. This ensures the safety of structural member. The maximum working stresses are adopted from IS : 800-1984. 4.8 INCREASE IN PERMISSIBLE STRESS A structure may be subjected to the different combinations of loads. These loads in combinations do not act for long period. Most of the national codes allow some increase in permissible stresses. Increase in permissible stresses as per IS : 800 is taken as follows: 1. When the effect of wind or seismic load is taken in to account, the permissible stress in steel are increased by 33⅓ percent. 2. For rivets, bolts and tension rods, the permissible stresses are increased by 25 per cent, when the effect of wind or seismic load is taken in to account. The increased values of permissible stress must not exceed yield stress of the material. 4.9 FACTOR OF SAFETY The factor of safety is defined as the factor by which the yield stress of the material is divided to give the working stress (permissible stress) in the material. A greater value of factor of safety results a larger cross-section of the member had to be adopted in design. If the factor of safety is comparatively small, results in appreciable saving in the material. The value of factor of safety is decided keeping in view of the following considerations.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 1. The average strength of materials is determined after making test on number of specimens 2. The value of design loads remains uncertain 3. The values of internal forces in many structures depend upon methods of analysis 4. During fabrication, structural steel is subjected to different operations which causes the structural element are subjected to uncertain erection stress 5. The variations in temperatures and settlement of supports are uncertain 6. The failure of some small or some elements of a structure is less serious and less disastrous than the failure of large structure or main element of a structure 4.10 METHODS OF DESIGN The following methods may be employed for the design of the steel frame work: 1. Simple design 2. Semi-rigid design 3. Fully rigid design and 4. Plastic design 4.10.1 Simple Design This method is based on elastic theory and applies to structure in which the end connections between members are such that they will not develop restraint moments adversely affecting the members and the structures as a whole and in consequence the structure may be assumed to be pin jointed. 4.10.2 Semi-rigid design This method permits a reduction in the maximum bending moment in beams suitably connected to their supports, so as to provide a degree of direction fixity. In the case of triangulated  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) frames, it permits rotation account being taken of the rigidity of the connections and the moment of interaction of members. In cases where this method of design is employed, it is ensured that the assumed partial fixity is available and calculations based on general or particular experimental evidence shall be made to show that the stresses in any part of the structure are not in excess of those laid down in IS : 800-1984. 4.10.3 Fully rigid design This method assumes that the end connections are fully rigid and are capable of transmitting moments and shears. It is also assumed that the angle between the members at the joint does not change, when it is subjected to loading. This method gives economy in the weight of steel used when applied in appropriate cases. The end connections of members of the frame shall have sufficient rigidity to hold virtually unchanged original angles between such members and the members they connect. The design should be based on accurate methods of elastic analysis and calculated stresses shall not exceed permissible stress. 4.10.4 Plastic design The method of plastic analysis and design is recently (1935) developed and all the problems related to this are not yet decided. In this method, the structural usefulness of the material is limited up to ultimate load. This method has its main application in the analysis and design of statically indeterminate framed structures. This method provides striking economy as regards the weight of the steel. This method provides the margin of safety in terms of load factor which one is not less than provided in elastic design. A load factor of 1.85 is adopted for dead load plus live load and 1.40 is adopted for dead load, live load and wind or earthquake forces. The deflection under working load should not exceed the limits prescribed in IS : 800-1984. 4.11 STABILITY OF STRUCTURE According to the stability requirement, the stability of a structure as a whole against overturning is ensured so that the restoring moment is greater than the maximum overturning moment. The restoring moment shall be not less than the sum of 1.2 times the maximum overturning moment due to the characteristic dead load and 1.4 times the maximum overturning moment due to characteristic imposed loads.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) The structure should have adequate factor of safety against sliding due to the most adverse combination of the applied loads. The structure shall have a factor of safety against sliding not less than 1.4 under the most adverse combination of the applied characteristic forces. In case only dead loads are acting, only 0.9 times the characteristic dead load shall be taken in to account. To ensure stability at all times, account shall be taken of probable variations in dead load during construction, repair or other temporary measures. The wind and seismic loading shall be treated as imposed loading. In designing the framework of a building, provisions shall be made by adequate moment connections or by a system of bracings to effectively transmit all the horizontal forces to the foundations.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 5. Riveted Connections 5.1 INTRODUCTION In engineering practice it is often required that two sheets or plates are joined together and carry the load in such ways that the joint is loaded. Many times such joints are required to be leak proof so that gas contained inside is not allowed to escape. A riveted joint is easily conceived between two plates overlapping at edges, making holes through thickness of both, passing the stem of rivet through holes and creating the head at the end of the stem on the other side. A number of rivets may pass through the row of holes, which are uniformly distributed along the edges of the plate. With such a joint having been created between two plates, they cannot be pulled apart. If force at each of the free edges is applied for pulling the plate apart the tensile stress in the plate along the row of rivet hole and shearing stress in rivets will create resisting force. Such joints have been used in structures, boilers and ships. The following are the usual applications for connection. 1. Screws , 2. Pins and bolts, 3. Cotters and Gibs, 4. Rivets, 5. Welds. Of these screws, pins, bolts, cotters and gibs are used as temporary fastening i.e., the components connected can be separated easily. Rivets and welds are used as permanent fastenings i.e., the components connected are not likely to require separation. 5.2 RIVETS Rivet is a round rod which holds two metal pieces together permanently. Rivets are made from mild steel bars with yield strength ranges from 220 N/mm2 to 250 N/mm2. A rivet consists of a head and a body as shown in Fig 5.1. The body of rivet is termed as shank. The head of rivet is formed by heating the rivet rod and upsetting one end of the rod by running it into the rivet  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) machine. The rivets are manufactured in different lengths to suit different purposes. The size of rivet is expressed by the diameter of the shank. Holes are drilled in the plates to be connected at the appropriate places. For driving the rivets, they are heated till they become red hot and are then placed in the hole. Keeping the rivets pressed from one side, a number of blows are applied and a head at the other end is formed. When the hot rivet so fitted cools it shrinks and presses the plates together. These rivets are known as hot driven rivets. The hot driven rivets of 16 mm, 18 mm, 20 mm and 22 mm diameter are used for the structural steel works.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Some rivets are driven at atmospheric temperature. These rivets are known as cold driven rivets. The cold driven rivets need larger pressure to form the head and complete the driving. The small size rivets ranging from 12 mm to 22 mm in diameter may be cold driven rivets. The strength of rivet increases in the cold driving. The use of cold driven rivets is limited because of equipment necessary and inconvenience caused in the field. The diameter of rivet to suit the thickness of plate may be determined from the following formulae: 1. Unwins’s formula d=6.05 t0.5 2. The French formula d=1.5 t + 4 3. The German formula d=(50 t – 2)0.5 Where d= nominal diameter of rivet in mm and t= thickness of plate in mm. 5.3 RIVET HEADS The various types of rivet heads employed for different works are shown in Fig. 5.2. The proportions of various shapes of rivet heads have been expressed in terms of diameter ‘D’ of the shank of rivet. The snap head is also termed as round head and button head. The snap heads are used for rivets connecting structural members. Sometimes it becomes necessary to flatten the rivet heads so as to provide sufficient clearance. A rivet head which has the form of a truncated cone is called a countersunk head. When a smooth flat surface is required, it is necessary to have rivets countersunk and chipped.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.4 RIVET HOLES The rivet holes are made in the plates or structural members by punching or drilling. When the holes are made by punching, the holes are not perfect, but taper. A punch damages the material around the hole. The operation known as reaming is done in the hole made by punching. When the hole are made by drilling, the holes are perfect and provide good alignment for driving the rivets. The diameter of a rivet hole is made larger than the nominal diameter of the rivet by 1.5 mm of rivets less than or equal to 25 mm diameter and by 2 mm for diameter exceeding 25 mm. 5.5 DEFINITIONS OF TERMS USED IN RIVETING 5.5.1 Nominal diameter of rivet (d): The nominal diameter of a rivet means the diameter of the cold shank before driving. 5.5.2 Gross diameter of rivet (D):  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) The diameter of the hole is slightly greater than the diameter of the rivet shank. As the rivet is heated and driven, the rivet fills the hole fully. The gross or effective diameter of a rivet means the diameter of the hole or closed rivet. Strengths of rivet are based on gross diameter. 5.5.3 Pitch of rivet (p): The pitch of rivet is the distance between two consecutive rivets measured parallel to the direction of the force in the structural member, lying on the same rivet line. Minimum pitch should not be less than 2.5 times the nominal diameter of the rivet. As a thumb rule pitch equal to 3 times the nominal diameter of the rivet is adopted. Maximum pitch shall not exceed 32 times the thickness of the thinner outside plate or 300 mm whichever is less. 5.5.4 Gauge distance of rivets (g): The gauge distance is the transverse distance between two consecutive rivets of adjacent chains (parallel adjacent lines of fasteners) and is measured at right angles to the direction of the force in the structural member. 5.5.5 Gross area of rivet: The gross area of rivet is the cross sectional area of a rivet calculated from the gross diameter of the rivet. 5.5.6 Rivet line: The rivet line is also known as scrieve line or back line or gauge line. The rivet line is the imaginary line along which rivets are placed. The rolled steel sections have been assigned standard positions of the rivet lines. The standard position of rivet lines for the various sections may be noted from ISI Handbook No.1 for the respective sections. These standard positions of rivet lines are conformed to whenever possible. The departure from standard position of the rivet lines may be done if necessary. The dimensions of rivet lines should be shown irrespective of whether the standard positions have been followed or not. 5.5.7 Staggered pitch: The staggered pitch is also known as alternate pitch or reeled pitch. The staggered pitch is defined as the distance measured along one rivet line from the centre of a rivet on it to the  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) centre of the adjoining rivet on the adjacent parallel rivet line. One or both the legs of an angle section may have double rivet lines. The staggered pitch occurs between the double rivet lines. 5.6 TYPES OF JOINTS Riveted joints are mainly of two types, namely, Lap joints and Butt joints. 5.6.1 Lap Joint: Two plates are said to be connected by a lap joint when the connected ends of the plates lie in parallel planes. Lap joints may be further classified according to number of rivets used and the arrangement of rivets adopted. Following are the different types of lap joints. 1. Single riveted lap joint (Fig.5.3), 2. Double riveted lap joint: a. Chain riveted lap joint (Fig.5.4) b. Zig-zag riveted lap joint (Fi.5.5)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.6.1 Butt Joint: In a butt joint the connected ends of the plates lie in the same plane. The abutting ends of the plates are covered by one or two cover plates or strap plates. Butt joints may also be classified into single cover but joint, double cover butt joints. In single cover butt joint, cover plate is provided on one side of main plate (Fig.5.6). In case of double cover butt joint, cover plates are provided on either side of the main plate (Fig.5.7). Butt joints are also further classified according to the number of rivets used and the arrangement of rivets adopted. 1. Double cover single riveted but joint 2. Double cover chain riveted butt joint 3. Double cover zig-zag riveted butt joint  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.7 FAILURE OF A RIVETED JOINT Failure of a riveted joint may take place in any of the following ways 1. Shear failure of rivets 2. Bearing failure of rivets 3. Tearing failure of plates 4. Shear failure of plates 5. Bearing failure of plates 6. Splitting/cracking failure of plates at the edges 5.7.1 Shear failure of rivets : Plates riveted together and subjected to tensile loads may result in the shear of the rivets. Rivets are sheared across their sectional areas. Single shear occurring in a lap joint and double shear occurring in but joint (Fig.5.8)  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.7.2 Bearing failure of rivets: Bearing failure of a rivet occurs when the rivet is crushed by the plate (Fig.5.9) 5.7.3 Tearing failure of plates : When plates riveted together are carrying tensile load, tearing failure of plate may occur. When strength of the plate is less than that of rivets, tearing failure occurs at the net sectional area of plate (Fig.5.10) 5.7.4 Shear failure of plates: A plate may fail in shear along two lines as shown in Fig. 5.11. This may occur when minimum proper edge distance is not provided.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.7.5 Bearing failure of plates: Bearing failure of a plate may occur because of insufficient edge distance in the riveted joint. Crushing of plate against the bearing of rivet take place in such failure (Fig. 5.12) 5.7.6 Splitting/cracking failure of plates at the edges: This failure occurs because of insufficient edge distance in the riveted joint. Splitting (cracking) of plate as shown in Fig. 5.13 takes place in such failure. Shearing, bearing and splitting failure of plates may be avoided by providing adequate proper edge distance. To safeguard a riveted joint against other modes of failure, the joint should be designed properly.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.8 STRENGTH OF RIVETED JOINT The strength of a riveted joint is determined by computing the following strengths: 1. Strength of a riveted joint against shearing - Ps 2. Strength of a riveted joint against bearing - Pb 3. Strength of plate in tearing - Pt The strength of a riveted joint is the least strength of the above three strength. 5.8.1 Strength of a riveted joint against shearing of the rivets: The strength of a riveted joint against the shearing of rivets is equal to the product of strength of one rivet in shear and the number of rivets on each side of the joint. It is given by Ps = strength of a rivet in shearing x number of rivets on each side of joint When the rivets are subjected to single shear, then the strength of one rivet in single shear Therefore, the strength of a riveted joint against shearing of rivets =  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Where N=Number of rivets on each side of the joint; D=Gross diameter of the rivet; ps=Maximum permissible shear stress in the rivet(1025 ksc). When the rivets are subjected to double shear, then the strength of one rivet in double shear =. Therefore, the strength of a riveted joint against double shearing of rivets, When the strength of riveted joint against the shearing of the rivets is determined per gauge width of the plate, then the number of rivets ‘n’ per gauge is taken in to consideration. Therefore, 5.8.2 Strength of riveted joint against the bearing of the rivets: The strength of a riveted joint against the bearing of the rivets is equal to the product of strength of one rivet in bearing and the number of rivets on each side of the joint. It is given by, Pb=Strength of a rivet in bearing x Number of rivets on each side of the joint In case of lap joint, the strength of one rivet in bearing = D x t x p b Where D= Gross diameter of the rivet; t=thickness of the thinnest plate; p b= maximum permissible stress in the bearing for the rivet (2360 ksc). In case of butt joint, the total thickness of both cover plates or thickness of main plate whichever is less is considered for determining the strength of a rivet in the bearing. The strength of a riveted joint against the bearing of rivets P b = N x D x t x pb  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) When the strength of riveted joint against the bearing of rivets per gauge widh of the plate is taken into consideration, then, the number of rivets ‘n’ is also adopted per gauge. Therefore, Pb1 = n x D x t x pb 5.8.3 Strength of plate in tearing The strength of plate in tearing depends upon the resisting section of the plate. The strength of plate in tearing is given by Pt = Resisting section x p t Where pt is the maximum permissible stress in the tearing of plate (1500 ksc). When the strength of plate in tearing per pitch width of the plate is P t1 = (p-D) x t x pt The strength of a riveted joint is the least of P s, Pb, Pt. The strength of riveted joint per gauge width of plate is the least of Ps1, Pb1, Pt1. 5.9. STRENGTH OF LAP AND BUTT JOINT The strength of riveted lap and butt joint given in the Fig. 5.14 is summarized as follows: 5.9.1 Strength of lap joint:  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5.9.2 Strength of butt joint: 5.10 EFFICIENCY OR PERCENTAGE OF STRENGTH OF RIVETED JOINT The efficiency of a joint is defined as the ratio of least strength of a riveted joint to the strength of solid plate. It is known as percentage strength of riveted joint as it is expressed in percentage. Efficiency of riveted joint  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Where P is the strength of solid plate = b x t x p t Efficiency per pitch width 5.11 RIVET VALUE The strength of a rivet in shearing and in bearing is computed and the lesser is called the rivet value (R).  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 6. Design of Riveted Connections 6.1 INTRODUCTION The perfect theoretical analysis for stress distribution in riveted connections cannot be established. Hence a large factor of safety is employed in the design of riveted connections. The riveted connections should be as strong as the structural members. No part in the riveted connections should be so overstressed. The riveted connections should be so designed that there is neither any permanent distortion nor any wear. These should be elastic. In general, the work of fabrication is completed in the workshops where the steel is fabricated. 6.2 ASSUMPTIONS FOR THE DESIGN OF RIVETED JOINT Procedure for design of a riveted joint is simplified by making the following assumptions and by keeping in view the safety of the joint. 1. Load is assumed to be uniformly distributed among all the rivets 2. Stress in plate is assumed to be uniform 3. Shear stress is assumed to be uniformly distributed over the gross area of rivets 4. Bearing stress is assumed to be uniform between the contact surfaces of plate and rivet 5. Bending stress in rivet is neglected 6. Rivet hole is assumed to be completely filled by the rivet 7. Friction between plates is neglected 6.3 ARRANGEMENT OF RIVETS Rivets in a riveted joint are arranged in two forms, namely, 1. Chain riveting, 2. Diamond riveting. 6.3.1 Chain Riveting: In chain riveting the rivets are arranged as shown in Fig. 6.1 and in the figure 1-1, 2-2 and 3-3 shows sections on either side of the joint. Section 1-1 is the critical section as compared to the other section. At section 2-2 is equal to the strength of plate in  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) tearing at 2-2 plus strength of three rivets in bearing or shearing whichever is less at 1-1. At section 3-3 is equal to the strength of plate in tearing at 3-3 plus strength of rivets in bearing or shearing whichever is less (6 nos.). Therefore, Strength of plate in tearing at 1-1 = (b-3D).t.pt Where b= width of the plate; D=Gross diameter of the rivet and t=Thickness of the plate. When safe load carried by the joint (P) is known, width of the plate can be found as follows; 6.3.2 Diamond Riveting: In diamond riveting, rivets are arranged as shown in Fig.6.2. All the rivets are arranged symmetrically about the centre line of the plate. Section 1-1 is the critical section. Strength of the plate in tearing in diamond riveting section 1-1 can be computed as follows  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) When the safe load carried by the joint (P) is known, width of the plate can be found as follows Where b=width of the plate, D=gross diameter of the rivet and t=thickness of the plate. At section 2-2: All the rivets are stressed uniformly, hence strength of the plate at section 2-2 is At section 3-3, In diamond riveting there is saving of material and efficiency is more. Diamond riveting is used in bridge trusses generally. 6.4 SPECIFICATION FOR DESIGN OF RIVETED JOINT  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 6.4.1 Members meeting at Joint: The centroidal axes of the members meeting at a joint should intersect at one point, and if there is any eccentricity, adequate resistance should be provided in the connection. 6.4.2 Centre of Gravity: The centre of gravity of group of rivets should be on the line of action of load whenever practicable. 6.4.3 Pitch: a. Minimum pitch: The distance between centres of adjacent rivets should not be less than 2.5 times the gross diameter of the rivet. b. Maximum pitch: Maximum pitch should not exceed 12t or 200 mm whichever is less in compression member and 16t or 200 mm whichever is less in case of tension members, when the line of rivets lies along the line of action of force. If the line of rivets does not lie along the line of action of force, its maximum pitch should not exceed 32t or 300 mm whichever is less, where t is the thickness of the outside plate. 6.4.4 Edge Distance: A minimum edge distance of approximately 1.5 times the gross diameter of the rivet measured from the centre of the rivet hole is provided in the rivet joint. Table 6.1 gives the minimum edge distance as per recommendations of BIS in IS : 800-1984.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) TABLE 6.1 EDGE DISTANCE OF HOLES 6.5 DESIGN PROCEDURE FOR RIVETED JOINT For the design of a lap joint or butt joint, the thickness of plates to be joined is known and the joints are designed for the full strength of the plate. For the design of a structural steel work, force (pull or push) to be transmitted by the joint is known and riveted joints can be designed. Following are the usual steps for the design of the riveted joint: Step 1: The size of the rivet is determined by the Unwin’s formula Where d= nominal diameter of rivet in mm and t= thickness of plate in mm.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) The diameter of the rivet computed is rounded off to available size of rivets. Rivets are manufactured in nominal diameters of 12, 14, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 42 and 48 mm Step 2: The strength of rivets in shearing and bearing are computed. Working stresses in rivets and plates are adopted as per ISI. Rivet value R is found. For designing lap joint or butt joint tearing strength of plate is determined as follows Pt=(p-D).t.pt Where p=pitch of rivets adopted, t=thickness of plate and pt = working stress in direct tension for plate. Tearing strength of plate should not exceed the rivet value R (P s or Pb whichever is less) or From this relation pitch of the rivets is determined. Step 3: In structural steel work, force to be transmitted by the riveted joint and the rivet value are known. Hence number of rivets required can be computed as follows The number of rivets thus obtained is provided on one side of the joint and an equal number of rivets is provided on the other side of joint also. Step 4: For the design of joint in a tie member consisting of a flat, width/thickness of the flat is known. The section is assumed to be reduced by rivet holes depending upon the arrangements of the rivets to be provided, strength of flat at the weakest section is equated to the pull transmitted by  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) the joint. For example, assuming the section to be weakened by one rivet and also assuming that the thickness of the flat is known we have Where b= width of flat, t=thickness of flat, pt=working stress in tension in plate and P=pull to be transmitted by the joint. From this equation, width of the flat can be determined. Example 6.1: A single riveted lap joint is used to connect plate 10 mm thick. If 20 mm diameter rivets are used at 55 mm pitch, determine the strength of joint and its efficiency. Working stress in shear in rivets=80 N/mm2 (MPa). Working stress in bearing in rivets=250 N/mm2 (MPa). Working stress in axial tension in plates=156 N/mm2. Solution Assume that power driven field rivets are used. Nominal diameter of rivet (D) is 20 mm and gross diameter of rivet is 21.5 mm. Strength of rivet in single shear = (π/4) x 21.52 x 80/1000 Ps = 29.044 kN Strength of rivet in bearing = 21.5 x 10 x 250/1000 Pb = 53.750 kN Strength of plate in tension per gauge length = P t=(p-D).t.pt Pt = (55-21.5) x 10 x 156/1000 = 52.260 kN Strength of joint is minimum of Ps, Pb or Pt Therefore, the strength of joint is = 29.044 kN  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Efficiency of joint Example 6.2: A double riveted double cover butt joint is used to connect plates 12 mm thick. Using Unwin’s formula, determine the diameter of rivet, rivet value, pitch and efficiency of joint. Adopt the following stresses; Working stress in shear in power driven rivets=100 N/mm2 (MPa). Working stress in bearing in power driven rivets=300 N/mm2 (MPa). For plates working stress in axial tension =156 N/mm2. Solution Nominal diameter of rivet from Unwin’s formula Adopt nominal diameter of rivet = 22 mm; Gross diameter of rivet = 23.5 mm Strength of rivet in double shear = Strength of rivet in bearing = D x t x pb = 23.5 x 12 x 300/1000 = 84.6 kN The strength of a rivet in shearing and in bearing is computed and the lesser is called the rivet value (R). Hence the Rivet value is 84.6 kN. Let p be the pitch of the rivets. Pt = (p-D) x t x pt = ((p-23.5) x 12 x 156/100) =1.872 (p-23.5) kN  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) In double riveted joint, Strength of 2 rivets in shear Ps = 2 x 86.75 = 173.5 kN Strength of 2 rivets in bearing Pb = 2 x 84.6 = 169.2 kN The pitch of the rivets can be computed by keeping P t = Ps or Pb whichever is less Therefore 1.872 (p-23.5) = 169.2 p-23.5 = (169.2/1.872) = 90.385 p= 90.385 + 23.5 = 113.885 mm Adopt pitch, p= 100 mm Example 6.3: A double cover butt joint is used to connect plates 16 mm thick. Design the riveted joint and determine its efficiency. Solution Nominal diameter of rivet from Unwin’s formula The hot driven rivets of 16 mm, 18 mm, 20 mm and 22 mm diameter are used for the structural steel works. Unwin’s formula gives higher values. Hence, adopt nominal diameter of rivet = 22 mm; Gross diameter of rivet = 22 +1.5 = 23.5 mm In double cover butt joint, rivets are in double shear. As per IS : 800-84, Shear stress for power driven rivets=100 N/mm2 (MPa).  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Bearing stress for power driven rivets=300 N/mm2 (MPa). Strength of plate in tension =156 N/mm2. Strength of rivet in double shear = Strength of rivet in bearing = D x t x pb = 23.5 x 16 x 300/1000 = 112.8 kN The strength of a rivet in shearing and in bearing is computed and the lesser is called the rivet value (R). Hence the Rivet value is 86.75 kN. Let p be the pitch of the rivets. Pt = (p-D) x t x pt = ((p-23.5) x 16 x 156/100) =2.496 (p-23.5) kN The pitch of the rivets can be computed by keeping P t = Ps or Pb whichever is less Therefore 2.496 (p-23.5) = 86.75 (p-23.5) = (86.75/2.496) = 34.756 p= 34.756 + 23.5 = 58.256 mm Adopt pitch, p= 55 mm Adopt thickness of each cover plate t ≈ 5/8 x 16 ≈ 10 mm Example 6.4: Determine the strength of a double cover butt joint used to connect two flats 200 F 12. The thickness of each cover plate is 8 mm. Flats have been joined by 9 rivets in chain  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) riveting at a gauge of 60 mm as shown in Fig. 6.3. What is the efficiency of the joint? Adopt working stresses in rivets and flats as per IS : 800-84. Solution Size of flat used = 200 F 12 Width of flat = 200 mm Thickness of flat = 12 mm Use power driven rivets Nominal diameter of rivet from Unwin’s formula Adopt nominal diameter of rivet = 22 mm; Gross diameter of rivet D = 23.5 mm Strength of rivet in double shear = Strength of rivet in bearing = D x t x pb = 23.5 x 12 x 300/1000 = 84.6 kN Strength of joint in shear, Ps = 9 x 86.75 = 780.75 kN Strength of joint in bearing Pb = 9 x 84.6 = 761.40 kN Strength of plate in tearing Pt = (b-3D) x t x pt  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) = ((200-3x23.5) x 12 x 156/1000) = 242.42 kN Strength of joint is minimum of Ps, Pb or Pt Therefore, the strength of joint is = 242.42 kN Example 6.5: In a truss girder of a bridge, a diagonal consists of a 16 mm thick flat and carries a pull of 750 kN and is connected to a gusset plate by a double cover butt joint. The thickness of each cover plate is 8 mm. Determine the number of rivets necessary and the width of the flat required. What is the efficiency of the joint? Sketch the joint. Take Working stress in shear in power driven rivets=100 N/mm2 (MPa). Working stress in bearing in power driven rivets=300 N/mm2 (MPa). For plates working stress in axial tension =156 N/mm2. Solution  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Nominal diameter of rivet from Unwin’s formula The hot driven rivets of 16 mm, 18 mm, 20 mm and 22 mm diameter are used for the structural steel works. Unwin’s formula gives higher values. Hence, adopt nominal diameter of rivet = 22 mm; Gross diameter of rivet = 22 +1.5 = 23.5 mm Strength of rivet in double shear = Strength of rivet in bearing = D x t x pb = 23.5 x 16 x 300/1000 = 112.8 kN The strength of a rivet in shearing and in bearing is computed and the lesser is called the rivet value (R). Hence the Rivet value is 86.75 kN. Number of rivets required to transmit pull of 750 kN n= (750/86.75) = 8.67 ≈ 9 rivets. Using diamond group of riveting, flat is weakened by one rivet hole. Strength of plate at section 1-1 in teaing Pt = (b-d) x t x pt = ((b-23.5) x 16 x 156/100) = 2.496 (b-23.5) kN Since P = 750 kN, 2.496 (b-23.5) = 750 b=(750/2.496)+23.5 = 323.98 mm Hence provide 400 mm width of diagonal member. The design of joint is shown in Fig. 6.4. Efficiency of the joint  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Example 6.6: A bridge truss diagonal carries an axial pull of 500 kN. It is to be connected to a gusset plate 22 mm thick by a double cover butt joint with 22 mm rivets. If the width of the tie bar is 250 mm, determine the thickness of flat. Design the economical joint. Determine the efficiency of the joint. Adopt working stresses in rivets and flats as per IS : 800-84. Solution Nominal diameter of rivet = 22 mm; Gross diameter of rivet = 23.5 mm Strength of power driven rivet in double shear = Strength of power driven rivet in bearing = D x t x p b = 23.5 x 22 x 300/1000 = 155.1 kN The strength of a rivet in shearing and in bearing is computed and the lesser is called the rivet value (R). Hence the Rivet value is 86.75 kN. Number of rivets required to transmit pull of 500 kN n= (500/86.75) = 5.76 ≈ 6 rivets. Provide six rivets in diamond group of riveting for efficient joint. Let the thickness of flat be t mm Strength of plate at weakest section Pt = (b-d) x t x pt = ((250-23.5) x t x 156/100) = 500 kN Therefore t = 14.151 mm; Adopt 16 mm thickness of flat. Keep 40 mm edge distance from centre of rivet and 85 mm distance between centre to centre of rivet lines as shown in the Fig. 6.5.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) Efficiency of joint  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) LESSON 7. Welded Connection 7.1 INTRODUCTION The development of welding technology in 1940s has considerably reduced the riveted joint applications. Welding is the method of locally melting the metals (sheets or plates – overlapping or butting) with intensive heating along with a filler metal or without it and allowing cooling them to form a coherent mass, thus creating a joint. A typical weld showing various zones of weld is shown in Fig. 7.1. Such joints can be created to make structures, boilers, pressure vessels, etc. and are more conveniently made in steel. The progress has been made in welding several types of steels, but large structure size may impede the use of automatic techniques and heat treatment which becomes necessary in some cases. Welded ships were made in large size and large number during Second World War and failures of many of them spurted research efforts to make welding a better technology. 7.2 ADVANTAGES OF WELDED CONNECTIONS 1. The gross sectional area of the welded members is effective since the welding process does not involve drilling holes. 2. Welded structures are comparatively lighter than corresponding riveted structures. 3. A welded joint has a greater strength sometimes equal to the strength of the parent metal itself. 4. Repairs and further new connections can be done more easily than in riveting.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) 5. Welded joints provide rigidity leads to smaller bending moments than corresponding riveted members. 6. Welded joints are economical to riveted joints due to low maintenance cost. 7. Members of such shapes that afford difficulty for riveting can be more easily welded. 8. A welded structure has a better finish and appearance than the corresponding riveted structure. 9. Connecting angles, gusset plates, splicing plates can be minimized. 10. Steel bars in reinforced concrete structure may be welded easily so that lapping of bars may be avoided. 11. It is possible to weld at any point at any part of a structure, but riveting will always require enough clearance. 12. The process of welding does not involve great noise compared to the noise produced in the riveting process. 7.3 DISADVANTAGES OF WELDED CONNECTIONS 1. Welding requires skilled labor and supervision. 2. Testing a welded joint is difficult. An X-ray examination alone can enable us to study the quality of the connection. 3. Due to uneven heating and cooling, the welded members are likely to get warped at the welded surface. 4. Internal stresses in the welded zones are likely to be set up. 7.4 TYPES OF WELDED JOINTS Welds may be classified into two main types namely butt-weld and fillet-weld. 7.4.1. Butt weld  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) This type of weld is used when the members are in same plane. Butt weld is also termed as groove weld. The butt weld is used to join structural members carrying direct compression or tension. It is used to make tee-joint and butt-joint. The following types of butt welds are in practice. These are named depending upon shape of the grove made for welding. i. Square butt weld. A square butt weld is a weld in the preparation of which the fusion faces lie approximately at right angles to the surfaces of the components to be joined and are substantially parallel to one another (Fig. 7.2 a & b). ii.Single V-butt weld A single V-butt weld is a weld in the preparation of which the edges of both components are prepared so that in the cross-section, the fusion faces form a V as shown in Fig. 7.3.  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) iii.Double V-butt weld A double V-butt weld is a weld in the preparation of which the edges of both components are double beveled so that in cross-section, the fusion faces form two opposing V’s as shown in Fig. 7.4. iv. Single U-butt weld A single U-butt weld is a weld in the preparation of which the edges of both components are prepared so that in the cross section, the fusion faces form a U as shown in Fig. 7.5. v. Double U-butt weld  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem-6th ( Prepared By: Ms Kajal, lecturer , CE) A double U-butt weld is a weld in the preparation of which the edges of both components are prepared so that in the cross section, the fusion faces form two opposing U’s as shown in Fig. 7.6. vi.Single J-butt weld A single J-butt weld is a weld in the preparation of which the edges of one component are prepared so that in the cross section, the fusion faces is in the form a J and the fusion face of the other component is at right angles to the surface of the first component as shown in Fig. 7.7. vii.Double J-butt weld  INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT E-NOTES , Subject : Design of Steel Structures I , Subject Code: CE-304B , Course: B.tech, Branch: CIVIL Engineering , Sem