Foundation DesignFoundation is the base of any structure. Without a solid foundation, the structure would not hold for long. We have to be very cautious with the design of foundations because our entire structure rests on the foundation. The job of a foundation is to transfer the loads of the building safely to the ground.

Laying of Column Footing Reinforcement | Foundation DesignThe strength of the foundation determines the life of the structure. As we discussed in the earlier article, design of foundation depends on the type of soil, type of structure and its load. Higher the load bearing capacity of the soil, the larger the load it could safely carry.Foundations are basically divided into Shallow Foundations and Deep Foundations.In this article, we are going discuss the step by step guide to Column Footing Design for a shallow foundation.Reinforced Concrete FootingsFootingcomprises of the lower end of acolumn, pillar or wall which i enlarged with projecting courses so as to distribute load.Footings shall be designed to sustain the applied loads, moments and forces and the induced reactions and to ensure that any settlement which may occur shall be as uniform as possible and the safe bearing capacity of soil is not exceeded.In sloped or stepped footings, the effective cross-section in compression shall be limited by the area above the neutral plane, and the angle of slope or depth and location of steps should be such that the design requirements are satisfied at every section.

Design Procedure of Column Footings | Foundation DesignHere is a step-by-step guide to Column Footing Design:

Column Footing Plan and Section | Foundation DesignStep 1Area required for footingSquare = B = (w+w1)/P0Where, Po = safe bearing capacity of soilw1 = self weight of footingw = self weight of footingFor Rectangle = b/d = B/DA = b x dNet upward pressure on the footingq/p = W/AStep 2Bending MomentCritical section for maximumbending momentis taken at the face of the columnFor a square footing,Mxx= q x B/8 (L a)2Mxx= q x L/8 (B b)2Myy= q x B/8 (L a)2Step 3To fix the depth of the footing shall be greater of the following:Depth from bending moment considerationd =(M/Qb)where, Q = moment of required factorDepth from shear considerationCheck for one way shearCheck for two way shear or punching shearCritical shear for one way shear is considered at a distance d from face of the column.Shear force, V = qB [ (B b) d]Nominal shear stress, Tv= k . TcTc= 0.16fckStep 4Check for two way shearCritical section for two way shear is considered at a distance at a distance d/2 from all the faces of the column.SF, V = q [ B2 (b + d)2]SF, V = q [L x B (a + d)(b + d)]Nominal shear stress, Tv= V/2((a+d)(b+d)d) - {for a rectangleTv= V/4((b+d)d) - {for a squareTv= k . Tck = 0.5 + > 1 ; [Beta = ratio of sides of the columnTc= 0.16fckArea of steel, Ast = M/(()stjd)

Column bases are structural elements used in the design of steel structures to transfer the column load to the footings.Types of Column bases1. Slab base2. Gusseted baseSlab Base

Slab basesare used where the columns have independent concrete pedestals.A thick steel base plate and two cleat angles connecting the flanges of the column to the base plate.In addition to these, web cleats are provided to connect the web of the column to the base plate.These web cleats guard against the possible dislocation of the column during erection.The ends of the column and also the base plate should be mechanized so that the column load is wholly transferred to the base plate.Area of base plate= (load of column)/(permissible bearing stress in concrete)Gusseted baseGussetted basesare provided for columns carrying heavier loads requiring large base plates.A gusseted base consists of a base of reduced thickness and two gusseted plates are attached one to each flange of the column.

Gusseted Column BaseThe gusseted plates, cleat angles and fastenings (bolts, rivets) in combination with bearing area of shaft shall be sufficient to take all loads.

RCC structuresRCC (Reinforced Cement Concrete) is a construction technology which evolved with the evolution of different structural materials in the 18th century during the Industrial Revolution.Industrial Revolution brought in new technology which helped in the manufacture of various materials. The Architect Le Corbusier used RCC for various constructions. He believed that any shape and form was possible; if RCC is to be used.For example,Notre Dame Du Haut, Ronchamp, FranceThis is an example ofLe CorbusierProject where he used RCC like plastic.

Notre Dame Du Haut, Ronchamp, France | RCC StructuresWhat is RCC?RCC means Reinforced Cement Concrete, i.e., cement concrete reinforced with steel bars, steel plates, steel mesh etc to increase the tension withstanding capacity of the structure.Cement Concrete can take up immense compression but weak in tension whereas steel is good in withstanding both tension and compression.Here are some of the advantages of RCC construction:1. Materials used in RCC construction are easily available.2. It is durable and long lasting.3. It is fire resisting and not attacked by termites.4. It is economical in ultimate cost.5. The reinforced concrete member can be cast to any shape because of the fluidity of concrete.6. Its monolithic character gives much rigidity to the structure.7. Cost of maintenance is nil.Here are some of its disadvantages:1. Scrap value of reinforced members is almost nil.2. Constant checking is required.3. Skilled labour is engaged in the work.4. The advantages of RCC outweigh its disadvantages.This is one construction technique that made construction very easy and brought a boom to the field of construction.Components of RCC structuresWe have already discussed and studied the design procedures for the Components of RCC structures.Design of RCC beamsDesign of RCC columnsDesign of RCC staircaseDesign of FoundationsDesign of Simply Supported SlabsEvery component is designed according to the load it carries and its position in the structure. The study of the design of RCC components will help in understanding the basics of RCC design and the method of its implementation.We will study more about different construction techniques in our successive articles

RCC BeamsRCC beams are cast in cement concrete reinforced with steel bars. Beams take up compressive and add rigidity to the structure.Beams generally carryverticalgravitationalforcesbut can also be used to carryhorizontalloads (i.e., loads due to anearthquakeor wind). The loads carried by a beam are transferred tocolumns,walls, orgirders, which then transfer the force to adjacent structuralcompression members. InLight frame constructionthejoistsrest on the beam.

Doubly Reinforced BeamIn this article, we are going to discuss types of beam construction and RCC design of Doubly reinforced beamRCC beam construction is of two types: Singly reinforced beam Doubly reinforced beamSingly reinforced beamA singly reinforced beam is a beam provided with longitudinal reinforcement in the tension zone only.Doubly reinforced beam Beams reinforced with steel in compression and tension zones are called doubly reinforced beams. This type of beam will be found necessary when due to head room consideration or architectural consideration the depth of the beam is restricted. The beam with its limited depth, if reinforced on the tension side only, may not have enough moment of resistance, to resist the bending moment. By increasing the quantity of steel in the tension zone, the moment of resistance cannot be increased indefinitely. Usually, the moment of resistance can be increased by not more than 25% over the balanced moment of resistance, by making the beam over-reinforced on the tension side. Hence, inorder to further increase the moment of resistance of a beam section of unlimited dimensions, a doubly reinforced beam is provided.Besides, this doubly reinforced beam is also used in the following circumstances: The external live loads may alternate i.e. may occur on either face of the member.For example: A pile may be lifted in such a manner that the tension and compression zones may alternate. The loading may be eccentric and the eccentricity of the load may change from one side of the axis to another side. The member may be subjected to a shock or impact or accidental lateral thrust.Design procedure for doubly reinforced beamStep 1Determine the limiting moment of resistance for the given c/s(Mulim) using the equation for singly reinforced beamMulim= 0.87.fy.Ast1.d [1 0.42Xumax]OrBalanced sectionAst1= (0.36.fck.b.Xumax)/(0.87fy)Step 2If factored moment Mu> Mulim, then doubly reinforced beam is required to be designed for additional moment.Mu Mulim= fsc.Asc(d d) [fscvalue from page no. 70]Step 3Additional area of tension steel Ast2Ast2=Asc.fsc/0.87fyStep 4Total tension steel Ast, Ast = Ast1+ Ast2

RCC ColumnA column forms a very important component of a structure. Columns supportbeamswhich in turn support walls andslabs. It should be realized that the failure of a column results in the collapse of the structure. The design of a column should therefore receive importance.Supporting the slabs is the main function of the columns Such slabs are calledSimply Supported Slabs. Simply supported slabs could be either one way slab or a two-way slab. It depends on the dimensions of the slab.

Reinforced Cement Concrete Column Plan and SectionA column is defined as a compression member, the effective length of which exceeds three times the least lateral dimension. Compression members whose lengths do not exceed three times the least lateral dimension, may be made of plain concrete.In this article, we are going to discuss in detail the basis of classification of columns and different types of reinforcement required for a certain type of column.A column may be classified based on different criteria such as:1. Based on shape Rectangle Square Circular Polygon2. Based on slenderness ratio Short column, ??12 Long column, ?> 123. Based on type of loading Axially loaded column A column subjected to axial load and unaxial bending A column subjected to axial load and biaxial bending4. Based on pattern of lateral reinforcement Tied columns Spiral columnsMinimum eccentricityEmin> l/500 + D/30 >20Where, l = unsupported length of column in mmD = lateral dimensions of columnTypes of Reinforcements for columns and their requirementsLongitudinal Reinforcement Minimum area of cross-section of longitudinal bars must be atleast 0.8% of gross section area of the column. Maximum area of cross-section of longitudinal bars must not exceed 6% of the gross cross-section area of the column. The bars should not be less than 12mm in diameter. Minimum number of longitudinal bars must be four in rectangular column and 6 in circular column. Spacing of longitudinal bars measures along the periphery of a column should not exceed 300mm.Transverse reinforcement It maybe in the form of lateral ties or spirals. The diameter of the lateral ties should not be less than 1/4thof the diameter of the largest longitudinal bar and in no case less than 6mm.The pitch of lateral ties should not exceed Least lateral dimension 16 x diameter of longitudinal bars (small) 300mmHelical ReinforcementThe diameter of helical bars should not be less than 1/4ththe diameter of largest longitudinal and not less than 6mm.The pitch should not exceed (if helical reinforcement is allowed); 75mm 1/6thof the core diameter of the columnPitch should not be less than, 25mm 3 x diameter of helical barPitch should not exceed (if helical reinforcement is not allowed)Least lateral dimension 16 x diameter of longitudinal bar (smaller) 300mm

RCC Staircase DesignRCC Structures are nothing but reinforced concrete structures. RCC structure is composed of building components such as Footings, Columns, Beams, Slabs, Staircase etc.These components are reinforced with steel that give stability to the structure. Staircase is one such important component in a RCC structure.

Dog Legged Stair | Staircase designIn this article, we will discuss different types of staircases and study the dog-legged reinforced cement concrete staircase design.StairsStairs consist of steps arranged in a series for purpose of giving access to different floors of a building. Since a stair is often the only means of communication between the various floors of a building, the location of the stair requires good and careful consideration.In a residential house, the staircase may be provided near the main entrance.In a public building, the stairs must be from the main entrance itself and located centrally, to provide quick accessibility to the principal apartments.All staircases should be adequately lighted and properly ventilated.Various types of Staircases Straight stairs Dog-legged stairs Open newel stair Geometrical stairRCC Dog-legged Staircase designIn this type of staircase, the succeeding flights rise in opposite directions. The two flights in plan are not separated by a well. A landing is provided corresponding to the level at which the direction of the flight changes.Procedure for Dog-legged Staircase designBased on the direction along which a stair slab span, thestairsmaybe classified into the following two types.1. Stairs spanning horizontally2. Stairs spanning verticallyStairs spanning horizontallyThese stairs are supported at each side by walls. Stringer beams or at one side by wall or at the other side by a beam.Loads Dead load of a step = x T x R x 25 Dead load of waist slab = b x t x 25 Live load = LL (KN/m2) Floor finish = assume 0.5 KN/mStairs spanning LongitudinallyIn this, stairs spanning longitudinally, the beam is supported ay top and at the bottom of flights.Loads Self weight of a step = 1 x R/2 x 25 Self weight of waist slab = 1 x t x 25 Self weight of plan = 1 x t x 25[(R2+ T2)/T] Live load = LL (KN/m2) Floor finish = assume 0.5 KN/mFor the efficient design of an RCC stair, we have to first analyse the various loads that are going to be imposed on the stair.The load calculations will help us determine, how much strength is required to carry the load. The strength bearing capacity of a staircase is determined on the amount of steel and concrete used.The ratio of steel to concrete has to be as per standards. Steel in the staircase will take the tension imposed on it and the concrete takes up the compression.These are the essential steps that are to be followed for the RCC Stair Design.

What are Simply Supported Slabs?Before we discuss the technical design rules of Simply Supported slabs, lets just go through its definition and learn why they are named soAs the name suggests, simply supported slabs are supported on columns or stanchions

Simply Supported SlabSimply supported slabs dont give adequate provision to resist torsion at corner to prevent corner from lifting.The maximum bending moment will be given if the slabs are restrained. But atleast 50% of the tension reinforcement provided at the mid span should extend to the support. The remaining 50% should extend to within 0.1Lx or Ly at the support as appropriate.RCC Slab Design depends on the on the dimensions of the slab after which the slab is termed as a one-way slab or a two-way slabIn the design of RCC structures,Column DesignandBeam Designare to be done before we start with RCC Slab DesignBasic Rules followed in the design of simply supported SlabThickness of slabl/d ratio should be less than the following: Simply supported slab Continuous slab, l/d = 26 Cantilever slab, l/d = 7In any case of the above, the thickness should not be less than 100mmEffective span Distance between centre to centre of support Clear span plus effective depthMinimum main reinforcement 0.15% gross c/s of slab for MS bars 0.12% gross c/s of slab for HYSD barsSpacing of main barsThe spacing or c/c distance of main bars shall not exceed following: Calculated value 3d 300mmDistribution or Temperature reinforcementThis reinforcement runs perpendicular to the main reinforcement in order to distribute the load and to resist the temperature and shrinkage stresses.It should be atleast equal to; 0.15% gross c/s of slab for MS bars 0.12% gross c/s of slab for HYSD barsSpacing of distribution barsThe spacing or c/c distance of distribution bars shall not exceed the following Calculated area 5d 450mmDiameter of barsThe diameter of the bars varies from 8mm to 14mm and should not exceed 1/8thof the overall depth of the slab.For distribution steel, the diameter varies from 6mm to 8mm.CoverThe bottom cover for reinforcement shall not be less than 15mm or less than the diameter of such bar.

Bending Moment and Shear Force diagramsWhat is Bending Moment?The element bends when a moment is applied to it. Every structural element has bending moment. Concept of bending moment is very important in the field of engineering especially Civil engineering and Mechanical Engineering.Unit of measurement: Newton-metres (N-m) or pound-foot or foot-pound (ft.lb)Bending moment is directly proportional to tensile and compressive stresses. Increase in tensile and compressive stresses results in the increase in the bending moment. These stresses also depend on the second moment of area of the cross section of the element.What is Shear stress?Shear stress is defined as the measure of force per unit area. Shear stress occurs in shear plane. There are many planes possible at any point in a structure which can be defined to measure stress.Stress = Force/Unit areaExample: Bending Moment and Shear Force Calculations

Frame diagrams | Bending moment and shear force calculationsSimply supported bending momentMab= wl2/8 = (224.144.14)/8= 47.13 KN-mMbc= wl2/8 = (224.144.14)/8= 47.13 KN-mFixed MomentsMoment about Bwl2/12 = (224.144.14)/12= 31.4 KN-mSupport reactionsRA+RB+RC= 2(224.14)= 182.16 KN3RA= 182.16RA= 60.72KNRA= RB= RC= 60.72 KN

Load Calculations | Types of LoadsStudents find it difficult to understand the concept of loads although it is a very simple concept. We are going to write a series of articles on Load Calculations and help you all in understanding different types of loads that are to be considered for structural designing and also how to calculate them.In this article, we will discuss different types of loads with examples.In our next article, we will cover the following points: Design principle assumption and notation assumed Design Constant Assumptions regarding Design Loads on Beams Loads on slabsAn object is subject to mainly two types of forces:1. Live loads2. Dead loadsBasically, an object subject to any type of force which could be gravitational force (weight), pressure or anything affects the object is called a load.This concept is used in Mechanical and structural engineering. Lets take in terms of Structural Engineering. Whenever a structure is designed, these concepts are taken into consideration because real world objects are analyzed in order to design the structure. This is very important in terms of structural stability.What are Dead loads?As the name itself suggests, dead loads could be termed as self weight of the non-living objects. It could be the weight of the materials, equipments or any other components in the structure that will remain permanent throughout the life of the structure.Dead load has to be considered in order to make the structural design accordingly. Dead loads vary from structure to structure. Every building is unique and has different considerations.An additional load is considered in case additional forces build up in a structure in case of settlement or due to secondary effects of pre-stress construction or due to shrinkage of concrete.For the calculations of dead loads, we could also consider, Columns Beams Footings Lintels Furniture Machinery and other equipment Walls Floors Roofs Ceilings Stairways Built-in partitions Finishes (POP Plaster of Paris) Cladding (Use of various materials which increase the self weight of the structure) etc.Basically, all the permanent loads are to be considered.What are Live loads?Unlike dead loads, live loads are variable. We could term them as probabilistic loads. Live load varies from time to time.As the name suggests, live load is the load of human beings living in the building. Their movement is not fixed. The number of people at a time in a structure can also vary.For example:A person lives in a 4BHK apartment with his wife and two kids. If he happens to throw a party for 50 persons, the live load on the structure increases considerably for that period of time.As soon as the guests leave, the number of persons reduces from 50 to 4.So, heres what I mean by variable force.Lets take another example:Live load to be considered while designing a staircase: Pressure of the feet Wind load on the stair in case the staircase is located outside the houseLive load to be considered while designing the roof:Movement of workers on the roof during construction, maintenance along with their materials and equipmentsAlso, if the owner of the house plans to make a terrace garden on the roof, that adds additional load to it.For dwelling houses to a 10KN/m2. In any building project, slabs are assumed to be 100m thick from stiffness/deflection consideration.Beams are taken separately and the self-weight is calculated and added separately on the frame. The net weight of the above load is multiplied by a load of 1.5 for concrete.

Load Calculations | Design of BuildingsIn our earlier article, we discussed Different types of loads and their importance in Structural design.Now we will move on with our further discussion on the following points: Design principle assumption and notation assumed Design Constant Assumptions regarding Design Loads on Beams Loads on slabsDesign principle assumption and notation assumed:The notations adopted throughout are same as given in IS:456:2000Density of material used in accordance with reference to IS:857-1987sSr.noMaterialDensity

1Plain concrete24 KN/m3

2Reinforced cement concrete25 KN/m3

3Flooring material (cement mortar)1.00 KN/m3

4Brick masonry19 KN/m3

Design constantUsing M20 and Fe415 grade of concrete and steel respectively for columns and footingsTherefore:Fck i. e. Characteristic strength for M15 15 N/mm2Fck i. e. Characteristic strength for M15 15 N/mm2Fck i. e. Characteristic strength for M20 20 N/mm2Fy i. e. Characteristic strength for steel 415 N/mm2Assumption regarding Design1. Slab is assumed to be continuous over interior support and partial fixed on the edge, due to monolithic construction of walls over it.2. Beams are assumed to be continuous over interior support and they frame in to the column at the ends.Load on BeamsDescription of load of slab on beamThe load of slab is dispersed on to the supporting beams in accordance with clause 23.5 of IS:456-1978, which states that the load on beams supporting solid spans, spacing in two directions at right angles and supporting uniformly distributed loads.Self weight of beamsThis load acts on the beams as a UDL, this is calculated after assuming the suitable cross section (by stiffness/deflection consideration) of the beam.Load due to brick masonry wallIn a framed structure, brick masonry are used to construct curtain walls. They do not carry or transfer any load. Hence, the masonry walls do not have to thick.Point load from intersecting beamIf there is any beam meeting the beam then the load of that beam is considered as point load.Loads on slabsThree types of loads are to be considered for the design of slabs:1. Dead load of the slab2. Live load of the slab3. Floor finish loadDead load of the slabSelf weight of slab acts:This load acts as UDL, this is calculated after assuming the 1m wide square strip and suitable thickness consideration.Floor finish loadThis load also acts as UDL and this is calculated after assuming suitable intensity over 1m wide strip.Live load on the slabThis is the temporary load on its intensity depends on type and occupancy of building.The intensity can vary with the type of building.

Singly reinforced Sections | Design of RCC StructuresIn our series of articles for singly reinforced sections, we have covered the following: Basic definitions and formulas Understanding stresses and modular ratios Assumptions for singly reinforced sections Design procedure for Singly reinforced section I Solved Numericals for Singly reinforced beam | Method I Design of Singly reinforced sections | Design Method 2 Solved Numericals for Singly reinforced beam | Method 2 Moment of Resistance for Singly reinforced sections Solved numerical example | Moment of resistance Solved numerical example 2 | Guide to singly reinforced sectionsNow, we will move on with our discussion on assumptions for singly reinforced sections.

The equivalent stress-strain diagram is developed with respect to the mentioned assumptions in the post.1. The sections that are plane before bending remain plane after bending, at any cross-section.2. All tensile stresses are taken up by steel reinforcement and none by concrete.3. The stress to strain relationship of steel and concrete under working load is a straight line.4. The modular ratio m has the value 280/3cbc5. There is a perfect adhesion between steel and concrete and no slip takes place between steel and concrete.

Design of RCC Structures | Basic definitions and formulasIn this article, we will go through the basic definitions of Stress, strain, elastic materials and modulus of elasticity. This will be our first step towards understanding the design of Singly reinforced sections.What is stress and how does it develop?When an object is subjected to an external force, the object tends to build up internal resistance within itself (material). This resistance is termed as stress.In short, stress can be defined as load per unit area.Stress can be classified into four types:1. Compressive stress2. Tensile stress3. Bending stress4. Shear stressStress = Load/Area = W/A = N/mm2Where, N = NewtonWhat is Strain?To make it easier for you to understand, lets merge the definition of stress with strain.When an object is subjected to an external load, the internal resistance which is built up with the object itself is not enough to withstand the external load results into deformation of the object. This alteration or deformation of the object is called strain.The formula for strain is given as follows:Strain = Change in length/Original lengthStrain has no unit.What are elastic materials?Elastic materials have the capacity to regain their original shape on removal of the load applied on the material.For example:When a rubber band is stretched, it deforms in shape but as soon as the pressure is released, the rubber band returns back to its original shape and size. This property of the material is called elasticity.What is Modulus of elasticity?We know that stress is directly proportional to strain within the elastic limit. The ratio of stress to strain is a constant which is denoted as k.Stress/Strain = KThis constant is the measure of the elasticity of the material, hence called modulus of elasticity.The formula for modulus of elasticity is given by,E = modulus of elasticity = Stress/Strain = N/mm2Denotations and their values: Modulus of elasticity for concrete = Ec = 2 x 105 N/mm2 Modulus of steel = Es = 5700 (square root of fck) N/mm2Where, fck = characteristic compressive strength of concreteIn our next article, we will discusspermissible stresses (steel, concrete) and modular ratio.

Stresses in Steel and Concrete |Building ConstructionIn one of our previous articles, we discussed Basic definitions and formulas.Now we will move on with our discussion on Permissible stresses in concrete and steel and Understanding Modular ratio.Permissible Stresses in ConcreteReinforced concrete designs make use of M15 grade concrete. The permissible stresses for different grades of concrete is different.They are given below:Sr. No.Concrete GradeM15M20M25M30

1.Stress in compression1. Bending578.510

1. Direct4568

2.Stress in bond (average) for plain bars0.60.80.91.0

3.Characteristics compressive strength15202530

Also refer for other values in IS:456-1978Permissible Stresses in SteelThe permissible stresses for different grades of steel are given in the table above.The different grades steel available in the market with their market names are as follows:Mild SteelGrade I steel is known as mild steel. The abbreviation used for Mild steel is (m.s.)High Tensile deformed steel has two types. They are as follows:1. Grade Fe415 (Tor-40 or Tistrong I)2. Grade Fe500 (Tor-50 or Tistrong II)The names of the high tensile deformed steel have been derived from their manufacturers.For example: Tor-Isteg Steel Corporation in Calcutta manufactures Tor-40 and Tor-50. Hence, the name. Tata Iron and Steel Co. Ltd, Calcutta manufactures Tistrong I and Tistrong II.(Being aware of the names of the manufacturers is important for students especially those studying Civil and Structural Engineering.)Understanding Modular RatiosIt is defined as the ratio of moduli of steel to the moduli of concrete. It is denoted by the letter m.m=Es/EcThe modular ratio is not constant for all grades of concrete. It varies with the grade of concrete. Es/Ec is generally not used to calculate modular ratio for reinforced concrete designs.As per IS: 456-1978;m is calculated by the following formula:m = 280/3cbcwhere,cbc= permissible compressive stress in concrete in bending.Calculation of Modular ratio values for different grades of concreteGrade of concreteModular ratio

M15m = 280/35 = 18.66

M20m = 280/37 = 13.33

M25m = 280/38.5 = 10.98

M30m = 280/310 = 9.33

It should be remembered that rounding off the modular ratio values is not permitted by Indian Standard.We shall discuss the following in our succeeding articles: Assumptions for singly reinforced sections Design procedure for Singly reinforced section I Solved Numericals for Singly reinforced beam | Method I Design of Singly reinforced sections | Design Method 2 Solved Numericals for Singly reinforced beam | Method 2 Moment of Resistance for Singly reinforced sections Solved numerical example | Moment of resistance Solved numerical example 2 | Guide to singly reinforced sections

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Causes of cracks in BuildingsIn the previous article, we discussed the occurrence of cracks in buildings due to climatic factors and cracks occurred due to problem at the time of construction of the building. These fall under the category ofMinor causes of Cracks in Buildings.Now we will go ahead with our discussion on Major causes of Cracks in a Building.Major causes of cracks in a building1. Movements of the ground2. Over loading3. Effect of gases, liquids and solids4. Effect of changes of temperature5. General causes such as vibrations etc

Unrestrained Movement of Building MaterialsMovements of the groundMining subsidence, land slips, earthquakes, moisture changes due to clay shrinkable soils (for example, Black cotton soil).Cracks occur because a part of the building is displaced from the rest without any change in the actual size of the material.Overloading Overloading of the ground Overloading of the building itself Overloading of the building parts result in cracksFor example; Cracks under a floor due to overloading of slab.

Overloading forced may be due to1. External (excessive wind/snow loads)2. Internal (from heavy machinery etc.)Effect of Gases, Liquids and SolidsGases Only gas likely to produce cracks is carbon dioxide (CO2). Causes carbonation of porous cement products Leads into an overall shrinkage showing crazing cracksLiquids Water is the most commonly used liquid when not taken care of can prove hazardous for the structures. Construction water i.e., that is utilization of water during the construction process Water in the usage of the buildingEffects of water1. Physical (i.e. due to change in water content)2. Chemical (directly or indirectly affecting other materials)For example, Volumetric increase due to chemical changes or Steel corrosion, sulphate attack with water.SolidsSoluble sulphates are most common and are found in various materials and soil.They are a great cause of concern. They attack the cement products which in turn result in the deterioration of the structure.Effect of changes in TemperatureVarious building materials are used for the construction of a building and all the materials have different coefficient of expansion. Due to changes in the temperature, the expansion and contraction of the building components takes place which result in the changes in the size and shape of the components.Smaller buildings are less affected.In larger buildings, the change in size of one part causes cracks although not in expanded part.For example; Crack below the slab/beam in RCC frame Brick pin buildings. These cracks can close up completely as a result of changes of temperature.General VibrationsVibrations cause cracks in buildings only when their amplitude of vibrations is high.Apart from vibrations caused due to earthquakes, the vibrations caused due to heavy machinery, traffic, sonic booms are also responsible for the occurrence of cracks in buildings.

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