Design of reinforced concrete foundations by varghese pdf. Free Pdf Download. I still loved the phone. Design of reinforced concrete foundations by varghese. Design of ReinConcrete Foundation - Ebook download as PDF File .pdf), Text P.C. VARGHESE DESIGN OF REINFORCED CONCRETE FOUNDATIONS. download Design Of Reinforced Concrete Foundations by VARGHESE, P. C. PDF Online. ISBN from PHI Learning. Download Free Sample and Get.

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Design of Reinforced. Concrete Foundations. P.C. VARGHESE. Honorary Professor, Anna University, Chennai. Formerly, Professor and Head, Department of. Design of Reinforced Concrete Foundations - site edition by P.C. Varghese. Download it once and read it on your site device, PC, phones or tablets. Find Design Of Reinforced Concrete Foundations by Varghese, P C at Biblio. Uncommonly good collectible and rare books from uncommonly good booksellers.

download This product. Snapshot About the book. Table of Contents: Foundation Structures 2. Wall Footings 6. Combined Footings for Two Columns 8. Balanced Footings 9. Strip Footings under Several Columns Raft Foundations Beam and Slab Rafts Circular and Annular Rafts Under-reamed Pile Foundations Design of Pile Caps Design of Cantilever and Basement Retaining Walls Method 1: We can find it from the fundamentals.

SP 16 gives table see Table B. If the depth is limited. From the theory of limit state design. An alternative method to find La is to read off from a graph constructed for MJfckbd1 vs La. In this method we calculate the length of the lever arm. This graph has to be plotted for a range of values 0.

It is good to remember that for Fe steel and M20 concrete. For this purpose.

For theory regarding this practice. The diameters of the reinforcement should be carefully chosen to satisfy this requirement. This bond is very important in foundation structures as they are short members and the loads to be carried are heavy. This simply means that the length of the reinforcement rod buried in concrete from the point of maximum tension will have the development length Ld. Members Table B.

For beams and narrow slabs. C design [1]. In all R.

Table B. In most cases we use smaller diameter bars to increase the perimeter area for bond. For slabs. The required length can also be made less if we increase the area of steel required and thus reduce the stress level in steel. The diameter of the rods chosen should satisfy this requirement. In fact. This gives values for a depth of section of mm or more.

It has also been observed in tests that in places where the face of support is in compression. It is interesting to note that in BS for footings the one-way shear is considered BS The allowable stress in shear depends on the percentage of tension steel as shown in Table B.

In order to simplify matters. For the design of footings and bases. The value can be increased as shown in Table B.

As the allowable shear stress tc is a function of the tension steel at the section. The maximum values allowed are given in Table B.

Figure 2 bd 2. It is also mandatory that the specified tension steel percentage should be available for a distance equal to effective depth d on both sides of the section.

Where the face of support is in compression as in simply supported or continuous beams and slabs. Where the face of support is in tension as in the case of a bottom slab of an elevated water tank. Section for one-way shear also called beam shear. For slabs thinner than mm thick.

IS allows an increased shear also as given in Table B. If the shear r exceeds Tc in beams. In foundations. Definition of I and b in Eq. Definition of a and b in Eq. For minimum shear reinforcement in beams. In beams even if the shear is less than allowable. The allowable value is. This type of shear occurs around columns in footings and flat slabs.

To design for shear we proceed as follows.

Step 2: The nominal shear steel can be obtained by one of the following methods. In any case. For shear design of a section b x d in shear. For details. For Fe steel. Step 1: Calculate the shear stress at distance d from face of support. T should not be greater than rmax as given in Table B. It is also called two-way shear. Step 4: Slfyd IS Let it be r. If it is equal to or greater than the value of load P. Taking P as column load. IS takes only effective depth d as resisting this shear as shown in Figure 2.

Clause See Example 2. In foundation slabs. They are mostly used in flat slab construction and rarely used in foundation slabs.

Earlier and in some modern codes other than IS. If the shear value is high. For nominal steel we assume that the nominal shear to be taken by section is 0. For design of shear in beams. For depth of footing slab in one-way shear.

For punching shear. To find the required steel. A slab of depth mm and width mm with factored moment kNm. Example 2. The required bond length for Fe steel and M20 concrete is Altp [Eq. The following are some of the important ones: A minimum percentage steel of about 0. It also recommends that the thickness of slabs should be so designed that the shear is less than that is allowed in concrete for the given percentage of tension steel so that no extra shear steel is provided for slabs.

IS recommends that the shear V be considered at a section equal to the effective depth of the slab from the column face. Reference Calculation Step 1.

S code 3 Increased value slabs less than mm of Tc for IS also recommends increased value of in depth as given in Table B. It can also be noted that IS values in shear are very conservative compared to BS values as shown below. The shear to be considered is at l. S code BS is more liberal in shear consideration in footing slabs. Derive an equation for the determination of depth of foundation slab in bending shear for a single footing.

Find the depth required for a footing 3x3 with a factored load of kN on a x mm column. Reference Calculation Step 1 Eq. Find the approximate depth of the slab required to resist one-way shear. Calculation of slab depth for one-way shear for given data 1 Find q. The column is at the centre of the footing. We may also multiply the area of footing A.

Under a load and moment. Assume the depth of the slab obtained from bending shear and use Eq. Check whether this is ample for two-way shear punching shear also. The first and third methods are easier than the second method.

Find depth from the following equation Eq. The depth required for one-way shear is mm. Hence safe. Provide nominal steel Method I: Find the bending moment of the pressures at the face of the column with base pressure as shown in Figure E2.

Footings are structural elements carrying the loads from walls, columns, etc. They can be made of simple lime concrete, plain cement concrete or reinforced concrete, depending on the loading and site conditions. Pedestals are short compression members whose height is usually less than three times their lateral dimensions. They are usually placed at the base of steel columns to transfer their load to the foundation [see Sec.

In this chapter, we deal with the general principles of design of simple footings and pedestals given in IS [1J. More detailed discussion about the design of the various types of footings and examples of design will be given in subsequent chapters of this book.

Loads for determination of size of foundation. The condition to be satisfied by the subsoil in the design of foundation is that its safe bearing capacity which is based on both strength and settlement should not be exceeded by the loads from the structure. Accordingly, the loads to be used to determine the size of the foundation should he the service loads, and not the factored loads.

The three combinations of loads to be used are as follows:. Loads for limit state design of foundations. For reinforced concrete structural design by limit state design, we use factored load. IS , Table 18 gives the four combinations of loads to be used as follows: In multi-storeyed buildings, one should also consider the allowable reduction in live load for residential and office buildings as given in Table 3.

TABLE 3. The first step in the design of footings is to calculate the necessary area from the formula using service loads. Service load on the column or wall above [loads in Eq. In the next step, its structural design is carried out by using factored loads and principles of limit state design as already discussed in Chapter 2.

The main items to be designed are the. It is also important to remember that the percentage of steel provided should not be less than 0.

This is only minimum shrinkage steel. However, many authorities recommend 0. The 0. In most designs of foundations, especially in individual footing design, the soil is considered elastic and the R. Hence, if foundation pressures on these rigid structures are to be assumed as uniformly distributed on the base, it is necessary that the CG of the external load system should always coincide with the CG of the loaded area.

Otherwise, there will be a variation of pressure on the base of the foundation which, for rigid foundations, may be assumed as linearly varying. In all layouts of foundations, these basic. As already discussed in Chapter 1 and shown in Figure 1.

As already mentioned, two different cases can arise. Case 1: The centre of gravity of the foundation and the line of application of P the vertical loads coincide and M due to external forces such as wind forces. The values of qx and q2 with moment M are given by Figure 3. As explained in Chapter 1 Section 1. Case 2: If the moment produced is by the resultant vertical load P acting with an eccentricity e, the resultant base reaction will counteract the applied moment.

The moment M produced is. They should be small under dead load. In the case of small eccentricities due to P and M, the centre of gravity of the foundation itself may be offset from the line of action of the load P to produce uniform resultant distribution on the base as described in Chapter 6.

We always try to avoid this condition. When the base is not fully in contact with the ground, the maximum soil pressures q on the foundation can be calculated from the following equation see Figure 3. The value of the eccentricity e is given by the equation. IS , CI. The main recommendations are the following:. There can be three types of reinforced concrete individual footings: They may rest on soil, rock or on piles. The minimum thickness of the edge of the footing on soil and rock should be mm and that on top of piles should not be less than mm [IS CI.

Types of isolated footings: The column transfers the load on top of the footing by bearing. In limit state design, the value of the pressure allowed under direct compression on an unreinforced loaded area of same size is to be limited to 0.

Reinforced Concrete Shells and Folded Plates by P.C.Varghese.

If the above permissible stresses are exceeded, the transfer of forces should be with steel reinforcement, by extending the reinforcement into the footing or by providing dowel starter bars. According to IS , if dowel bars are provided, they should extend into the column a distance equal to the full development length of the column bars IS , CI.

However, this requirement for the development length has been relaxed in BS According to BS code, compression bond stress that develops on starter bars within bases need not be checked, provided the starter bars extend down to the level of the bottom reinforcement.

The application of this clause can reduce the depth required in footings and save on steel requirement. When the depth of the footing required to satisfy the above development length of the starter bars or because of any other causes is very large, it is more economical to adopt a stepped or sloped footing so as to reduce the amount of concrete that should go into the footing.

According to IS , CI. The diameter of the dowels should not exceed the diameter of the column bars by 3 mm. As seen from the above discussions, the depth of the footings needs to be generally taken as that obtained from the point of shear and bending moment only.

In all cases, the depth should be such that extra shear reinforcement or compression steel for bending can be. The sections to be taken for design are the following as shown in Figure 3. Rectangular footings are generally used with rectangular columns.

The most economical proportions of the footing are given if the rectangular base projects the same distance beyond all the column faces so that the footing requires the minimum amount of materials.

Both one-way shear wide-beam shear and two-way shear punching shear requirements are prevalent as discussed now see Figure 3. One-way shear wide-beam shear. One-way shear is similar to shear in bending in slabs. Considering the footing as a wide beam, the shear is taken along a vertical plane extending the full width of the base located at a distance equal to the effective depth of.

The allowable shear stress is the same as in beams.

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The tension reinforcement to be considered for estimating the allowable shear should continue for a distance equal to the full effective depth beyond the section. For routine design, the lowest value of allowable shear in Table 19 of IS , i. In one-way shear, the shear force to be resisted is the sum of the upward forces in the foundation area from the critical section to the edge of the footing.

The consequent shear per unit area is given by. Design depth. We generally find the depth required from shear consideration before we find the depth required from bending moment consideration in pad footings. In sloped footing we may first find a safe depth for bending as in. Example 4. In both IS and BS , the value of allowable shear in bending Tc is a function of the percentage of steel on the tension side Table B.

As we usually place tension steel of about 0. We will use this approach in our design procedure. Note that the shear force at both ends of L is nil and that in Eqs. Checking for two-way or punching shear. Punching shear indicates the tendency of the column to punch through the footing slab, as illustrated in Figure 3.

As it has twoway section, it is also called two-way shear. This type of shear is similar in flat slabs around the supporting columns. As already stated, it is easier to check than design a section for two-way shear.

The method of checking for punching shear has been explained in Sec. The formula to be used is Eq. Taking P as load from the column, the shear to be resisted is obtained as.

It should be noted that the British practice in punching shear is to use the same design values for punching shear as those for one-way shear.

This will result in larger perimeter length and reduced requirement for shear strength. Both these approaches are found to give safe values for design, especially in footings.

At the face of the column for footings supporting a reinforced concrete column as shown in Figure 3. Half-way between the centre line and the edge of the wall for footings under masonry walls. Half-way between the face of the column and the edge of the gusseted base for footings under gusseted bases.

It should be specially noted that moments should be considered both in X and Y directions and the necessary areas of steel provided in both directions. The steel for the above bending moment is placed as detailed under placement of reinforcement IS , Sec. The footing is to be considered as a slab and the rules for minimum reinforcementfor solid slabs should apply to these slabs also IS , CI.

This recommendation is very important as in many cases of design of footings, the reinforcement calculated from bending moment consideration can be less than the minimum required as a slab of 0. As already pointed out, the depths of footings should be such as to make them rigid.

These are governed by the following considerations:. The depth should be safe in one-way shear without shear reinforcements. The depth should be safe in two-way shear without any shear reinforcement.

The depth should be safe for the bending moment without compression reinforcement. The depth, according to IS , should develop the necessary transfer bond length by the main column bars or dowel bars if it is necessary see Sec. If the column bars are bent at the bottom and properly extended into the footing. In a long footing as in combined footings.

In a sloped footing. Figure 3. In two-way square reinforced column footings. But as regards the steel in the short direction. The steel required in the X. The maximum spacing is 3d or mm. In two-way rectangular column footings.

Design of ReinConcrete Foundation

Details of placing steel in a footing is shown in Figure 3. According to IS The portion of the reinforcement to be placed at equal spacing in this band is determined by the equation IS. Main reinforcement bent upwards if required. IS Bar marks.

For M20 concrete. As bond in compression is 25 per cent higher. Their design is discussed in Sec. The diameter or the sizes of the bars selected should have the required surface area to develop the full development length in the available dimension of the footing. Individual footings are small sized members with large bending moments. But this is not an economic solution.

For Fe and M For column bars of 36 mm. The chart is for Fe steel and M20 concrete. The minimum steel for columns is 0. The diameter of dowels should not exceed that of columns.

Started bars or dowels equal to at least 0. Another method is to increase the number of bars steel area and thus reduce the stress in the steel. For preliminary design of columns. For these reinforcements only. We also examined the detailing to be followed in joining columns to the footings.

If the bearing capacity of the soil is 7. For column to carry 50 tons Table in Chart D. Indian Concrete Institute.

Advanced Reinforced Concrete Design

A column is to carry a load of 45 tons. Reference Calculation Step Case 1: For column to carry 45 tons Table in Chart D. Fe steel Bottom layer 14 Y 10 14 Nos. A column is to carry a load of 50 tons.

Special Publication. Bureau of Indian Standards. Fe steel 2 Chart D. Code of Practice for Plain and Reinforced Concrete. Examples of design are given in Chapter 4.

Common Building Frame Design. Charts D. Use Fe steel and M20 concrete. Determine the plan area from the allowable bearing capacity and service loads from the column. Step 3: Determine the depth for one-way shear. In this chapter. For circular or square columns. Taking the factored dead and live loads. Step 8: Check the development length required and choose the proper diameter of bars. Calculate the reinforcement required in the X. Choose the largest depth required considering steps 3.

Step Verify design by charts given in Appendix D. Provide the necessary cover to reinforcement and find the total depth of footing required. Check the depth adopted for safety against punching shear.

Soil reaction for limit state design. Step 9: Detail the steel as specified in the code see Sec. The steel provided at the section for maximum moment should not be less than the minimum specified for slabs.

Service load Area. By considering one-way shear. Step 5: Step 6: Find plan size of footing. L2 I Find the depth for one-way shear. As seen in Sec. If it is not sufficient. Let the data for design be as follows Figure 3. The actual value of Tc will depend on the percentage of main steel present at the section continued for a distance d on both sides of the section. Find the depth for resistance in the building. Step 7: Considering equilibrium of forces. The depth from bending moment consideration is obtained by taking moments at the face of the column XX.

Some recommend adopting the lowest value of Tc namely.

Take the larger of the depths as obtained from steps 3 to 5. Provide the cover. Distribution steel may be only 0. S is equal to or greater than P. In most cases. Check the development length. Detail steel as discussed in Sec. The slope should not exceed one vertical to three horizontal if top forms are to be avoided. Select the size of the bar whose development length is less than II2 L.

This is due to the fact that there have not been many large-scale tests on sloped footings. Calculation of bending moment and shear for design Example 4. Moment Mxx denotes the bending moment for which steel is placed in the X direction. The procedure for the design of sloped footings varies among designers. Sloped footings generally require more depth.

Figure 4. One of the methods to decrease steel in footings is to adopt a liberal depth for the footing. It is very important to remember that as the strength of the footing depends on the compressive strength of this concrete along the slope. As also stated in Sec. This depth is to be checked for shear and is used for the calculation of the steel area. Y-direction [Note: The bending moment is taken at the face of the column and any of the following three procedures can be used for this purpose.

A less conservative method. In order to get a liberal value for depth. Determination of the required depth in bending: The aim here is to find a reasonable value which will be larger than that required for a block footing. Method a: The first method is to assume that the bending moment is the same as that due to a pad footing in the XX and YY planes.

The expressions are simple and can be derived as follows: One-way shear is checked by taking a section at a distance equal to the effective depth as obtained from step 1 from the face of the column.

The area of concrete resisting the shear is taken as the breadth of the quadrant bx at the section multiplied by the depth of the concrete at that section dx. The shear force to be resisted. We find bx and dx corresponding to the quadrant to that section.

As the first method gives very conservative results. We assume that the column dimensions a and b only resist the bending. The area of the steel required is to be calculated from moment considerations by any of the following methods. The depth of the column should also be enough to resist two-way punching shear. The condition to be satisfied is V2 Step 4: Myy for steel in the 4.

The shear force Vx to be resisted is taken as that acting in the corresponding quadrant into which the slope footing is divided as shown in Figure 4. The considerations are the same as already derived before for sloped footings.

This value will be less than the above two. Pedestals become essential in the layout of steel columns for many reasons. We assume this moment is taken by the full length of the section on which the moment acts see Figure The IS specifications have already been discussed in Sec. Typical detailing of steel in footings is shown in Figure 3. The principles of design are explained in Chapter 5. Design of Short Columns with Moments. Effective Length of Columns. Design of R.

Slender Columns. Design for Torsion. Members in Tension. Design of Staircases. Design of Corbels, Brackets and Nibs. Design of Footings, Pedestals and Pile Caps.It can also be seen from the expression that if we place the footing eccentrically so as to produce a moment opposite in direction to the acting moment. Reference Step Refer Chart D. Please feel free to contact us for any queries. As a rule it is made at least three times the width of the wall. Figure E4.

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