Unit 1 .pdf

BUILDING DEFINITION: A building can be defined as a structure broadly consisting of walls, floors and roofs, erected to provide covered space for different uses such as residence, education, business, hospitals, manufacturing, worship, entertainment etc. A building may al...

BUILDING DEFINITION: A building can be defined as a structure broadly consisting of walls, floors and roofs, erected to provide covered space for different uses such as residence, education, business, hospitals, manufacturing, worship, entertainment etc. A building may also be defined as a permanent or temporary structure enclosed within exterior walls and a roof, and including all attached apparatus, equipment and fixtures that cannot be removed without cutting into ceiling, floors or walls.  PURPOSE OF BUILDING A building is constructed to achieve the following purposes: (1) The main objective of a building is to provide shelter for the inmates. (2) It helps in providing sufficient accommodation for the purpose for which it is constructed. (3) It helps in providing protection to the inmates from environmental agencies like sun, rain, snowfall, wind etc. (4) It provides protection against burglars and thieves (5) It helps in providing privacy to the people who are residing in them Components of Building 3. Walls The main function of the wall is to enclose or divide the space in desired pattern. In addition, walls provide privacy, security and protect the inhabitants from the weathering agencies like sun, rain, wind etc. Walls are constructed with the help of bricks, stones, concrete blocks (solid or hollow) etc. These building units are bonded together with the help of cement-sand-mortar. 3. Walls Requirements/Functions of load bearing walls in super-structure; They should be strong enough to withstand the dead loads and the superimposed loads. They should provide sufficient stability against overturning and buckling caused by excessive slenderness. They should be weather and fire resistant. They should provide insulation against heat and sound. They should provide security and privacy to the building 4. Columns A column may be defined as an isolated vertical load carrying member, the width of which is neither less than its thickness nor more than four times its thickness.  5. Ground basements and upper floors The primary function of a floor is to provide support to the inhabitants, furniture etc. The building is vertically elevated to provide more accommodation within the limited space. Requirements/Functions of floor: It should provide strength and stability to the building It helps in transferring the dead and live loads It should provide a clean, smooth, durable and impervious surface. It should provide insulation against heat and sound. It should provide a barrier against fire, to travel to the upper floors. 6. Doors, windows and Ventilator The main function of the door is to provide free access to inside and outside a room. It serves as a connecting link between internal parts and also to allow the free movement outside the building. A door mainly consists of two components namely (i) Door frame (ii) Door shutter Ventilators are provided in a building to vent out or exhaust the air from the building 6. Doors, windows and Ventilator Requirements: To perform their basic functions it is required that they should be weather resistant (ie for strength and durability requirements). These members should be strong enough to resist the adverse effects of rain, sun and wind. They must be sound and thermal resistant. They must provide security and privacy to the occupants. 7. Sills, lintel and Sunshades Window sills are provided between the bottom of window frame and the masonry wall below. It is provided to protect the wall from wear and tear. The frame of a door or a window is not strong enough to withstand the weight of the wall above that opening, therefore it is provided with a separate structural element known as lintel A lintel is basically a beam which is provided over the opening. Sun shades or chhajjas are generally combined with lintel of windows to protect them from the adverse effects of weathering agencies like wind, sun, and rain. 7. Sills, lintel and Sunshades Functions/ requirements: Window sills are generally provided to throw away the rainwater. Lintels should be designed properly to carry loads effectively. Length of sunshade projection should be sufficient to protect them from weathering agencies 8.Stairs A stair may be defined as a structure comprising of a number of steps connecting one floor to another. The stair must be constructed in such a manner that it is safe and comfortable to use. The stairs should be centrally located and should have sufficient width to accommodate the inhabitants in case of emergency 8.Stairs Essential requirements/Functions for stairs: Stairs should be comfortable enough to access to the pitch, rise and tread should be properly designed They should be strong enough to carry the anticipated loads safely They should be made from fire resistant materials and provide safe means of escape in case of fire. 9. Roof /Slabs A roof may be pitched or flat type and is the uppermost part of a building and its main function is to cover the space below and protect it from weathering agencies like rain, snow, wind, sun etc. As the roof is directly exposed to the adverse effects of weathering agencies, therefore it should be designed accordingly. 9. Roof /Slabs Essential requirements/Functions of roof: Roof Slabs should be strong enough to withstand the anticipated loads (dead loads and live loads). As it is exposed to atmospheric agencies, therefore it should be weather resistant. Proper drainage arrangements should be provided. It should provide insulation against heat and sound. It should be fire resistant. 10. Building Finishes A building is considered incomplete till the time the surface of its components are given appropriate treatment. Finishing is of several types such as pointing. plastering, painting, white washing, distempering, varnishing, decorative finishing etc. 10. Building Finishes Essential requirements/Functions of finishes: They protect the surface from the adverse effects of the weather. They should provide decorative effect to the building. They should provide true, even and smooth finished surface and also enhance the aesthetic appearance of the building. To some extent they cover the poor or defective workmanship. 11. Building Services Building services include services like water supply, drainage, sanitation, electricity, lighting, acoustics, heating/cooling, fire detection and fire control etc. These built-in items are of immovable nature which are added considerably to the utility of a building and hence, are termed as utility fixtures. 11. Building Services Essential requirements/Functions of utility fixtures: They should be of good quality as per Indian standards. The fittings and other accessories must be as per the guidelines laid down by the 15 codes The guidelines of local authority must be followed Foundation Foundation Every structure consists of two parts The foundation part (also termed as sub-structure) and super-structure. A foundation is that part of the structure which is below the ground level and is in direct contact with the soil. It transfers the load of the structure to the soil below. The load is distributed on a wider area so as to bring the intensity of loading within the safe bearing capacity of the soil. It is desirable that the load of the structure must be allocated to the hard strata. Therefore, sometimes, the foundations are taken deep into the so as to get a hard soil which can take up the loads. Purpose of Foundation Generally, the foundations are placed below the ground level, to increase the stability of a structure. All the engineering structures are provided with foundations at the base. Thus, the object of providing foundation may be outlined as follows: (i) It helps in providing stability to the structure against many disturbing forces like wind, earthquakes etc. (ii) It distributes and transmits the load coming over the structure to a larger area of underlying support. (iii) It reduces the chances of excessive settlement and differential settlement of the structure (iv) It helps in distributing the load evenly on the sub-soil (v) It helps in providing a firm and levelled bed for building operations Shallow Foundation 1. Wall Footing In brick masonry structures, the footing provided below the walls is known as wall footing. It is also known as spread footing because it spreads the load to a wider area below Wider area of footing helps in reducing the stress for a given set of loading. It consists of a number of courses of bricks, the lowest being usually two times the thickness of wall above as shown. The width of the wall may be increased by providing offset of the brick or 50 mm on both sides. Shallow Foundation 2.Isolated Footing This type of footing is used to support individual columns. It can be either stepped type or having projections in the concrete base. In case of heavy RCC columns the steel is provided in both the directions in concrete bed (provided below the footing). The projection of 50 mm is provided uniformly on the four sides Pad isolated Footing Sloped Isolated Footing Shallow Foundation 3. Combined Footing The footing which supports two or more columns in a row is termed as combined footing. The combined footing can be rectangular or trapezoidal in shape as shown. While designing combined footing it should be kept in mind that the location of center of gravity of column loads and the centroid of combined footing should coincide. Shallow Foundation 4. Raft Footing Raft or mat is a type of combined footing that covers the entire area beneath a structure and supports all the columns. This type of footing is provided when the allowable soil pressure is low or the structure loads are heavy, the use of spread footing will cover more than half of the building area, then it is economical to use raft foundation 4. Raft Footing Shallow Foundation 5. Inverted Arch Footing This type of footing is not used now-a-days in buildings. However, it may be used in structures like bridges, reservoirs, supports for drainage lines. Series of inverted arches may be provided along the row of piers, or across the row of piers, or in both the directions as shown.  Deep Foundation These foundations carry loads from a structure through weak compressible soils or fills onto the stronger and less compressible soils or rocks at deeper depths. The foundations are constructed sufficiently below ground level with some artificial arrangements such as piles, wells etc. as their base are known as deep foundations. Deep foundations are further classified into the following types: 1 Pile foundation 2. Well foundation and Caissons  Deep Foundation 1. Pile Foundation Pile foundation is the most commonly used deep foundation in case of buildings as shown. A pile may be defined as a long vertical load transferring element consisting of timber, steel, concrete or a combination of them. Pile foundation is generally used when simple spread foundation at a suitable depth is not possible either because the stratum of required bearing capacity is at greater depth or steep slopes are encountered.  Deep Foundation Suitability of Pile Foundation Pile foundation are advantageous under following conditions When the soil is highly compressible or expansive in nature. For example, in case of black coton soils or man-made landfills, pile foundations are used. Pile found are useful in water logged areas where chances of settlement are more To avoid differential settlement in structures resting on clayey strata or loose pockets. Pile foundations are useful when the provision of grillage and raft foundation becomes very expensive Pile foundations are helpful when structure carries heavy concentrated loads. They are also useful for structures which are not uniformly loading When it is necessary to construct a building along the sea shore or river bed, they are also used as anchors  Deep Foundation Types of Pile Foundation: On the basis of Function On the Basis of Function 1. End Bearing Piles: The piles which rest on hard strata and act as a column to bear the load of the structure are termed as end bearing piles. 2. Friction Piles: When overlay soft soil is present in larger depths and it is not economical or rather practically not possible to rest the bottom end of the pile on the hard strata, the load is borne by the piles through skin friction developed between the surrounding soil and the outer surface of the piles  Deep Foundation Types of Pile Foundation: On the basis of Function 3. Sheet Piles These piles differ from bearing or friction piles because they are never used to provide vertical support but mostly used to act as retaining walls. A series of piles are driven to form a long wall (sheet) and is used to retain soil which is liable to escape laterally when subjected to pressure. They are also used for Retaining walls in docks. Protecting soil erosion of river banks Confining the soil to increase its bearing capacity Isolating the foundations from adjoining soils.  Deep Foundation Types of Pile Foundation: On the basis of Function 4. Anchor Pile When piles are used to provide anchorage against horizontal pull from sheet piling walls or other pulling forces (thrust) they are known as anchor piles. 5. Batter piles: The piles which are driven inclined instead of vertical, to effectively resist horizontal and inclined forces are known as batter piles  Deep Foundation Types of Pile Foundation: On the basis of Material 1. Timber piles The piles made of wood are called timber or wooden piles. The timber to be used as piles should be free from defects. These piles can be circular in shape (of 200 mm - 500 mm in diameter) or square (150 mm to 500 mm side) in cross-section. Timber piles are best suitable at places where there are less chances of moisture variation in soil because they disintegrate. Generally used for building, bridges, coffer dams and not recommended for sea water Use d where timber is easily available. Light in weight and can be easily handled Skilled labour not required  Deep Foundation Types of Pile Foundation: On the basis of Material 2. Cement Concrete Piles The piles which are constructed by using cement concrete are known as cement concrete piles. The concrete piles are of two types: (a) Pre-cast piles (b) Cast-in-situ piles (a)Pre-cast piles: Pre-cast concrete piles are the RCC piles which are manufactured in a factory or space available nearby. They are generally circular, square or octagonal in shape and may be of uniform section throughout its length. Benefits Reinforcement is not disturbed from actual position while concreting. Can be tested before use Can be subjected to loading immediately after driving. Not affected by chemical action of soil  Deep Foundation Types of Pile Foundation: On the basis of Material 2. Cement Concrete Piles b. Cast-in-situ piles These are the piles which are casted in situation ie at site. For making cast-in-situ piles, first of all a bore hole is dug at the site where the pile is to be placed. This can be done by driving a casing pipe into the ground. The loose soil from the casing is taken out and filled with concrete after placing necessary steel reinforcement in it. Advantages Requred number of piles can be casted at site. Pile can be casted in the required length Comparatively less reinforcement is required. Transportation issues are not there as compared to precast piles Required  Deep Foundation Types of Pile Foundation: On the basis of Materail 3. Steel Piles In such piles rolled Steel H and I sections are used to act as pile below the foundation. These can withstand high-impact stress developed during the pile-driving operation. they have a small cross-section area and can be easily driven into the soil. ADVANTAGES Can easily withstand bearing stresses Take impact stresses and lateral loads Can be spliced to increase the length and cut off easily. Bearing capacity of piles is high. Deep Foundation: Well Foundation and Caissons 2. Well foundation and Cassions Well Foundation is the type of deep foundation which is mainly equipped below the water level for bridges. Wells or open caissons are large-diameter foundations obtained in underwater conditions such as bridge foundations in rivers. These types of foundations are suitable for sandy or soft-bearing strata liable to scour and where no firm bed is available for large depth below the surface. The main types of caisson foundation are as follows. 1.Box caisson 2.Open caissons or wells 3.Pneumatic caissons Deep Foundation: Well Foundation and Caissons Well foundation Deep Foundation: Well Foundation and Caissons BOX CAISSON This type of caisson is open at the head and closed at the bottom. It is made of concrete, reinforcement or steel. OPEN CASSION Open caisson or well foundation is also called well. This type of caisson is exposed at the head and bottom. Open caissons come in different shapes. It has a cutting edge at the bottom. So that it is easy to sink the well. Deep Foundation: Well Foundation and Caissons PNEUMATIC CASSION This type of caisson is closed at the top and open (during construction) at the bottom. The water is excluded from the caisson chamber by means of compressed air. Construction details of Spread Foundation 1 Depth of Foundation Construction details of Spread Foundation 1 Depth of Foundation Construction details of Spread Foundation 2. Width of Foundation It should be sufficient enough to take the load of the structure. The width of the foundation is decided according to the following rules: Rule (1). If the wall is directly resting on foundation block as shown in Fig. 2.26, the width of foundation should be equal to 3 times the thickness of wall i.e. B = 3. Construction details of Spread Foundation 2. Width of Foundation Rule 2: The width of foundation should be twice the thickness of the wall of super- structure plus twice the projection of the concrete block from the bottom-most (lower) course of footing as shown in Fig. 2.27 Construction details of Spread Foundation 2. Width of Foundation Rule 3 The width of foundation, B can be obtained by dividing the total load (i.e. sum of LL, EL, WL. etc.) per unit length of foundation by the allowable (i.e. safe) bearing capacity of the soil. B= P/q B= width of the foundation P= total load per unit length of foundation (Kn) q= Safe allowable bearing capacity of the soil (kn/m2) Construction details of Spread Foundation 2. Width of Foundation Summary Note: (a) If the wall is resting on the hard stratum, the value of B (Width) may worked out to be small which may not be safe from stability point of view.In such cases the width of foundation may be taken as the greater of value obtained by Rule (ii) and (iii). (c) For piers, the width of foundation may be taken as Construction details of Spread Foundation 3. Thickness of concrete block The thickness of the foundation concrete block depends wn the following factors: The type of concrete used. The projection of concrete block beyond lowermost course of wall footing. Upward pressure of the soil below Construction details of Spread Foundation 3. Thickness of concrete block (d) A NOTE: Smaller value of A and B is taken adopted as “d” B Construction of Foundation The construction of foundation involves these steps 1 Preparing foundation Plan 2 Setting out (layout) foundation plan on ground. 3 Excavation of Foundation 4 Laying of foundation. Construction of Foundation 1 Preparing foundation Plan On the basis of the sub-soil investigation report, submitted by geotechnical engineer, the structural engineer designs the foundation for the calculated design loads. On the basis of the design, a detailed foundation plan is prepared showing the constructional details required for the effective layout of building. This plan also includes North direction which helps in giving the desired orientation to the building, at site. Before commencing the excavation of trenches, for foundation, a layout plan is prepared on paper Construction of Foundation 2. Setting Out (layout) foundation Plan on Ground Before starting the excavation off foundation, the ground should be cleared of any grass, vegetation, shrubs, trees etc. Then, the position of the building should be carefully marked on ground with center line method. Construction of Foundation 2. Setting Out (layout) foundation Plan on Ground Centre line Method 1. In this method of layout, the centre line of the longest outer wall of building is by stretching a string between wooden pegs driven at ends. 2. This serves as the reference line for marking the centre line of all other walls of the building. 3. The walls perpendicular to long walls are marked by setting up a right angle. 4. Right angle can be set up by forming triangles, with the help of a measuring tape. with sides 3, 4 and 5 units long. 5. For all important and large works, masonry pillars, about 50 mm wider than the proposed width of foundation trenches, are built instead of wooden pegs as shown. Construction of Foundation 2. Setting Out (layout) foundation Plan on Ground 6. In case of rectangular buildings, the diagonals from the opposite corners are checked for their equality. 7.The tops of all the masonry pillars are plastered and should be at the same level. 8.The strings are then stretched over the nails in the pegs and corresponding lines are marked on the wet plaster to have a permanent impression. Construction of Foundation 2. Setting Out (layout) foundation Plan on Ground Construction of Foundation 3. Excavation of Foundation Trenches The foundations of all structures are established below the surface of the ground. The equipments used in excavation are spade, kassi, pick-axe, cave baskets, iron pan,rammers etc., when excavation is carried out by manual labour. In case of large excavation works, the excavation may be done with the help of machines like Ditch Machines (JCB). showels, drag lines etc. Before starting the excavation work the top 15 cm layer of soil is removed as this layer contains vegetation, shrubs, roots, grass etc. The excavation should be commenced over the entire foundation width. Construction of Foundation 3. Excavation of Foundation Trenches Construction of Foundation 4. Laying of Foundation (including Cutting and Filling) The natural topography of the site may be having ups and downs in the proposed site, therefore it is important to utilize the excavated (or cutting) material to fill the lower lying areas. The excavated material (i.e. earth) should be dumped 1-5 m away from the outer edge of the trench, so that it should not fall back in the trench. This excavated soil can be used for backfilling the trenches, after the foundation has been laid Timbering The temporary arrangement of timber planks and bullies erected in a trench to give temporary support to the collapsible sides is termed as timbering process as shown in Figure.  Members used in Timbering 1. Sheething: The planks of timber, which are used vertically and remain in direct contact with the sides of the trench are termed as sheething or poling boards. 2. Wailing: The intermediate timber piece used to transfer the load from sheething to the strut is known as wailing or wale. This timber piece is mostly used horizontally. 3. Strut: It is a timber piece which maintains fixed distance between the sheathings or between the wailing. 4. Bracing: The inclined timber piece used to impart rigidity to the framework of timbering process is termed as bracing. 5. Runners: In case of very loose soils like running sand, long planks called runners are driven along the sides of the excavated trenches. Runners are long wooden planks having iron- shoe at its bottom end Members used in Timbering  Shoring Shoring is the means of providing temporary support to unsafe structures, the stability of which has been endangered due to differential (unequal) settlement of the foundation or due to the removal of adjacent soil in excavating the foundation for adjoining building. The temporary supports for unsafe structure are provided till the time as they have made stable.This method of providing temporary support to structure is adopted when alteration is done in structure itself Types of Shoring 1. Inclined / Raking Shores: It can be defined as the Shoring in which the inclined members are used to provide lateral support to the unsafe structure 2. Horizontal/ Flying shores: Flying shores are used to provide horizontal support to the parallel walls of two adjacent buildings that may collapse without support 3. Vertical / dead Shores: In this system of shoring, the vertical members known as ‘dead shores’ are used to support temporarily the walls, roofs, floors, etc.  De-Watering There are different methods of dewatering, which are explained as 1. Construing Drains This method is generally adopted in shallow foundations in water-logged ground. In this method drains of suitable size are constructed on both the sides of the foundation trench The drains collect sub-soil water from the sides and the enclosed area and convey it into shallow pit called as sump well. In this way the water which would have reached the trench is intercepted by the drains, thus the foundation can be maintained free from waters. These drains are provided with suitable slope and collected to a central place and pumped out from time to time. This method is the cheapest of all the de-watering methods and is useful in case of shallow foundation in water-logged areas. De-Watering Construing Drains De-Watering 2. Construction Deep Well’s In coarse soils, porous rock or in sites where a large quantity of sub- soil water is required to be drained out, 0.30 m to 0.60 m diameter wells are constructed at a spacing of 6 to 15 m centre to centre all around the proposed site for temporary drainage of the ground. The water collected in such wells is pumped out continuously. This method of de-watering is found suitable for depths of excavation more than 16 m. De-Watering 3. Grouting Grouting method is the injecting of grout material effectively into the required position, under high pressure. Grouting solidifies and strengthens the formation so as to increase the bearing capacity and reducing the permeability of the proposed site Grouting process is helpful in reducing the hydrostatic uplift pressure. The materials commonly used for grouts are cement-water, asphalt, chemical admixtures etc. The most commonly used grout in soils is the cement grout (2 Parts of water and 1 Part of cement by volume) and is injected under high pressure into fine seams (cracks) De-Watering 4. Freezing Process This process is useful for excavations in water-logged soils like sand, gravel and silt. This method can be conveniently used for deep excavations (eg. For bridges) specially when excavation is to be made adjacent to an existing structure or near some waterway In this method, the area around the excavation is frozen prior to excavation and the soil is converted into wall of frozen earth. Freezing pipes encasing smaller diameter inner pipes are sink along the periphery of the area to be excavated. Freezing liquid is then supplied to the pipes by refrigeration plant. This makes the ground around the pipes to freeze and form a thick wall of frozen earth surrounding the proposed area of excavation. This method can be used conveniently upto an excavated depth of 30 m. De-Watering 4. Freezing Process De-Watering 5. Chemical Process In this method the soil around the area to be excavated is solidified using chemical solutions or compounds. The chemicals in liquid form can be pumped into the soil, through small openings, where other grouting materials cannot penetrate, This chemical is converted into gel after some time and helps in restricting the entry of water into the proposed excavation. Generally, two chemical solutions of sodium silicate and Calcium chloride are used for the purpose. De-Watering 6. Electro Osmosis Process This method is useful in case of fine soils (like silt and clays) having poor permeability. These soils tend to hold water by capillary action. In this method, stabilization of soft clays and silt is done by passing direct electric current into the soil through two electrodes driven in the saturated soil, water contained in the soil is repelled by positive electrode (known as anode) and is attracted by the negative electrode (i.e. cathode). Now, when cathode electrodes are put into the well-points with an anode at centre (i.e. mid- distance between two well-points) and electric current is passed through them, the flow of groundwater towards well- points (i.e. cathode) is increased. This is an expansive Process. De-Watering 6. Electro Osmosis Process