Type Of Structural Steel PDF

TYPE OF STRUCTURAL STEEL THE TERM STRUCTURAL STEEL REFERS TO A NUMBER OF STEELS THAT, BECAUSE OF THEIR ECONOMY AND DESIRABLE MECHANICAL PROPERTIES, ARE SUITABLE FOR LOAD-CARRYING MEMBERS IN STRUCTURES. THE CUSTOMARY WAY TO SPECIFY A STRUCTURAL STEEL IS TO USE AN ASTM ( American Society for Test...

TYPE OF STRUCTURAL STEEL THE TERM STRUCTURAL STEEL REFERS TO A NUMBER OF STEELS THAT, BECAUSE OF THEIR ECONOMY AND DESIRABLE MECHANICAL PROPERTIES, ARE SUITABLE FOR LOAD-CARRYING MEMBERS IN STRUCTURES. THE CUSTOMARY WAY TO SPECIFY A STRUCTURAL STEEL IS TO USE AN ASTM ( American Society for Testing and Materials) DESIGNATION. FOR FERROUS METALS, THE DESIGNATION HAS THE PREFIX LETTER “ A “ FOLLOWED BY TWO OF THREE NUMERICAL DIGITS ( e.g. ASTM A36,ASTM A514) Three Groups of Hot-rolled Structural Steels for use in Buildings: 1. Carbon steels used carbon as the chief strengthening element with maximum yield stresses ranging from 220 Mpa to290 Mpa. An increase in carbon content raises the yield stress but reduces ductility, making welding more difficult. 2. High-strength low-alloy steels (HSLA) have yield stresses from 480 Mpa to 840 Mpa. In addition to carbon and manganese, these steels contain one or more alloying elements such as columbium, vanadium, chromium, silicon, copper, and nickel. 3. Quenched and tempered alloy steels have yield stresses of 480 Mpa to 690MPa. These steel of higher strength are obtained by heat-treating low-alloy steels. The heat treatment consist of quenching ( rapid cooling)and tempering (reheating) ASTM DESIGNATION Material conforming to one of the following standard specifications is approved for use according to Section 501.3.1.1 of NSCP: Structural Steel , ASTM A36 Pipe, Steel, Black and Hot-dipped, Zinc-coated Welded and Seamless Steel Pipe, ASTM 53, Grade B High-strength Low-alloy Structural Steel, ASTM A242 High-strength Low-alloy Structural Manganese Vanadium Steel, ASTM A441 Cold-formed Welded and seamless Carbon Steel Structural Tubing in Rounds and Shapes, ASTM A500 Hot-formed Welded and Seamless Carbon Steel Structural Tubing, ASTM A501 High-yield Strength , Quenched and Tempered Alloy-Steel Plate, Suitable for Welding, ASTM 514 Structural Steel with 290 Mpa Minimum Yield Point, ASTM A529 Steel, Sheet and Strip, Carbon, Hot-rolled, Structural Quality, ASTM A570 Grade 275, 310 and 345 High-strength, Low-alloy Columbium-Vanadium Steels of Structural Quality , ASTM A572 High-strength Low-alloy Structural Steel with 345 Mpa Minimum Yield Point to 100mm thick, ASTM A588 Steel, Sheet and Strip, high-strength, Low-alloy and Cold rolled, with Improved atmospheric Corrosion Resistance, ASTM A606 Hot-formed Welded and Seamless High-strength Low- alloy Structural Tubing, ASTM A618 Structural Steel for Bridges, ASTM A709 Quenched and Tempered Low-alloy Structural Steel Plate with 483 Mpa Minimum Yield strength to 100 mm thick, ASTM a852 Certified mill test reports or certified reports of test made by the fabricator or testing laboratory accordance with ASTM A6 or A568, as applicable and the governing specification must constitute sufficient evidence of conformity with one of the above ASTM standards. Additionally, the fabricator must provide an affidavit stating structural steel furnished meets the requirement of the grade specified. PROPERTIES OF STEEL Yield stress, Fy is that unit stress at which the stress-strain curve exhibits a well-defined increase in strain (deformation)without an increase in stress. Tensile strength is the largest unit stress that the materials achieves in a tension test.( max. stress that material can bear before breaking) Modulus of Elasticity, E, is the slope of the initial straight-line portion of the stress-strain diagram. It is usually taken as 200,000 Mpa for design calculation for all structural steel. Ductility is the ability of the material to undergo large inelastic deformations without fracture. Toughness is the ability of material to absorb energy and is characterized by the area under a stress-strain curve.(Amount of energy per unit volume that material can absorb before rupturing. Weldability is the ability of steel to be welded without changing its basic mechanical properties. Poisson’s ratio is the ratio of the transverse strain to longitudinal strain. Poisson’s ratio is essentially the same for all structural steels has a value of 0. in the elastic range. Poisson’s ratio=lateral strain/longitudinal strain Shear modulus is the ratio of the shearing stress to shearing strain during the initial elastic behavior. Typical Properties of A36 Steel Modulus of Elasticity, E 200,000 Mpa Yield strength, Fy 248 Mpa Tensile strength 400Mpa Endurance Strength 207 Mpa Density 7780kg/m³ Poisson’s ratio 0.3 Shear modulus 77,200 Mpa Coefficient of thermal expansion 11.7 x 10⁻⁶/˚c STRUCTURAL STEEL SHAPES Structural shapes are available many shapes. The dimension and weight must be added to the designation to uniquely identify the safe. For example W 40 x 436 refers to W-shape with an overall depth of approximately 40 inches (1000 mm) that weighs 436 lb/ft ( 640 kg/m) Structural Shape Designation Shape Designation Wide Flanges W American Standard Beam S Bearing Pile HP Miscellaneous( those that cannot be M classified as W, S, or HP Channel C Angle L Structural Steel Tee ( cut from W or S or M WT or ST Structural Tubing TS Pipe pipe Plate PL Bar Bar TYPE OF CONSTRUCTION There are three basic types of construction and associated design assumptions permitted and each will govern in the specific manner the size of members and types and strength of the connection. Type 1. Rigid-frame ( continuous frame)- assumes that beam- column connections have sufficient rigidity to hold virtually unchanged the original angles between intersecting members. Type 2. Simple framing ( unrestrained, free-ended) assumes that insofar as gravity loading concerned ends of beams and girders are connected for shear only and are free to rotate under gravity load. Type 3. Semi-rigid Framing ( partially restrained) assumes that the connections of beams and girders posses a dependable and known moment capacity intermediate in degree between the rigidity of Type 1 and flexibility of Type 2. Loads and Stresses Structures are designed to resist many types of loads, live loads, wind loads, earthquake loads. The complete design must take into account all effects of these loads, including all applicable load combination. Dead Load and Live Load The dead load to be assumed in design consist of the weight of steelwork and all material permanently fastened or supported by it. The live load must be stipulated by applicable code under which the structure is being design or that dictated by conditions involved. Impact Loads For structures carrying live loads which include impact, the assumed live load must be increased sufficiently by the percentage provided by Impact Loading Factors. Impact Loading Factors Supports for: Live load increased Elevators 100 % Cab-operated travelling crane support 25% girders & their connections Pendant-operated travelling crane 10% support girders & their connections Light machinery, shaft or motor driven 20% Reciprocating machinery or power 50% driven units Hangers supporting floors and 33% balconies Wind and Seismic Stresses Allowable stresses may be increased 1/3 above the values otherwise provided when produced by wind or seismic loading, acting alone or in combination with the design dead and live loads, provided the required section computed of this basis is not less than that required for the design dead and live load and impact ( if any) computed without 1/3 stress increased and further provided that the stresses are not otherwise required to be calculated on the basis of reduction factors applied to design loads in combination.