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Single Pile Cap Design
Are you an Engineering professional? Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. When I have a single pile cap for a column. Is there any parameter or rule of thumb considering the depth of the pilecap and the amount of reinforcement required???
If you analize it theres no punching shear on the pile cap, and there is no moment applied to it, except if there is an eccentricity applied to the pile cap by the column or by misplacement of the pile.Pile under pile cap should be layout symmetrically in both directions. The column or wall on pile cap should be centered at the geometric center of the pile cap in order to transferred load evenly to each pile. Example of pile layout pattern are shown below:.
In general, piles should be spacing at 3 times of pile diameter in order to transfer load effectively to soil.
If the spacing is less than 3 times of diameter, pile group settlement and bearing capacity should be checked. Pile cap thickness is normal determined by shear strength.
For smaller pile cap, the thickness is normally governed by deep beam shear. For large pile cap, the thickness is governed by direct shear. When necessary, shear reinforcement may be used to reduced thickness pile cap.
The edge distance is normally governed by punching shear capacity of corner piles. The punching shear strength according to ACI is. For corner pile, the critical section normally extends to the corner edge of pile cap since it gives less shear area. The critical section of direct shear is at a distance, d, from edge of column or pile. The direct shear shrength according to ACI is. The shear strength is calculated as follows:. Design of flexural reinforcement is the same as spread footing design.
The critical section is at face of column.
Pile Cap Design Assumptions & Recommendations
Pile load can be calculated as. Pile cap design example:. Design Data:. Column size: 18"x18" concrete column. Type of pile: 16 in diameter concrete pile. Estimate number of pile and select pile layout pattern. Check pile capacity:. Column service load moment:.
Maximum pile compression load:. Since the effective depth d is less than 4 ft, check direct shear in the longitudinal direction. Factored pile load:. The factored moment at one d from face of column is. The shear strength of pile cap is.
Check deep beam shear in the short direction. The factored moment face of column is. The deep beam shear strength of concrete is as follows:. The editor made reasonable effort of editing. Nevertheless, the editor does not warrant, and assume no liability for accuracy and completeness of its content. Webmaster: www. Reinforced Concrete Design Design of pile cap General Pile layout pattern: Pile under pile cap should be layout symmetrically in both directions.Foundation Design. A pile cap is one of the types of foundation that consist of a thick concrete pad that is usually supported by piles.
This is commonly used in building foundations with the geographical locations having a very low soil bearing capacity. Pile cap serves to transmit the load of the building into the hard strata of the soil via a pile or group of piles. Design-wise, the pile cap design uses a truss system principle that can be designed using a strut and tie method. Designing a pile cap seems to be complicated because a lot of considerations need to take into account to achieve a safe and sound foundation.
These considerations include the proper spacing of each pile, the pile cap thickness and so on. To achieve this can only be done by understanding its design principles and proper detailing of pile caps. But knowing the correct pile cap dimensions can be considered as a halfway already in design completion.
In this article, we will be dealing with the standards in determining pile cap geometry and dimensions as well as its design considerations. To make it simple, we will break down our design assumption with the following. The first thing to consider in the pile cap design is to determine the shape of the pile cap to use. The shapes vary according to the number of piles in the pile cap that can be deriving according to the load in a column supporting it.
The figure below shows the most common use shapes of the pile cap and the recommended dimensions. One of the important things to consider in a pile cap design is to determine enough thickness. Pile cap thickness must also be sufficient to meet anchorage-bond length requirements of starter bars and normal punching shear requirements. Here is how to assume the thickness of the pile cap:.
Punching shear along the column perimeter should be satisfied according to the standard codes. Also, punching shear due to piles should also be considered in the design check. Further details in punching shear design considerations will soon be published in the succeeding article. Proper detailing of the pile cap is another thing to consider for design completion.
Drawing details should be clear and simple as possible so the contractor can follow it accordingly. Refer to the image below for the recommended typical details of the pile cap. There are so many ways to design a pile cap.
Technically, it can be designed manually using a principle of strut and tie method. But if you are considering a wide pile cap supported by multiple numbers of piles, computer-generated structural design soft wares are available to design a massive pile caps. Kindly select the image to avail!
The above design assumptions and recommendations are considered as guidelines in considering pile cap as your choice of foundation.
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Save my name, email, and website in this browser for the next time I comment. Search for:. The column is reinforced with longitudinal bars of 12 No. Complete pile cap design will be illustrated here; except superimposed load weight of pile cap also exerts some load on piles.
Lets consider cap weight exerts 3 kips load on each pile. Now what can be punched through pile cap? One is pile itself ; another is column o r columns supported by pile cap. Should we check both cases? The basis is to have idea about punching perimeter relative to load.
If a column is heavily loaded and he selects relatively small size of piles cross-section with more pile, the piles can be punched. Again if column load is small and relatively greater cross-section of pile is chosen, pile may not be punched. But calculation for punching of column through pile foundation must be checked for all situations. Consider No. Therefore column will also not be punched. But a partial contribution is considered P u divided by fraction outside the critical section.
Now we calculate beam shear capacity of pile cap. We know critical section lies at a distance d from face of column figure below. The critical section lies N ow distance between column face to pile face inside. If all piles lie inside of critical section for beam shear, no shear is considered to produce shear failure in foundation.
Beam shear is often called flexure shear. The critical section is located at the face of column. For each direction there have three piles to contribute to bending moment. In normal beam section design, the following procedure is followed, if depth is not fixed. We need to establish. In checking moment capacity above procedure based on p max is not valid here as effective depth is governed mainly by shear and required depth 2.
Here in most cases, minimum steel area governs. Lets check required steel area for this moment. Now to check assumed a:. Now check minimum steel area:. The controlling value of minimum reinforcement is 6. As ACI code do not allow plain concrete unreinforced in pile cap, we have to provide minimum steel as calculated above.
Structural engineers sometimes also use shrinkage and temperature steel as minimum steel. These are. Earlier we have assumed cap exerts 3 kips load on each pile.
Now each pile share equal load this is Check for Punching Shear : - As single Pile is provided, the cap has to be checked for punching shear. Provide same at top along perpendicular direction of main reinforcement. Learn more about Scribd Membership Home. Read Free For 30 Days. Much more than documents.
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Design of Single Piles
Single Pilecap Uploaded by tanksaumil. Document Information click to expand document information Date uploaded May 28, Did you find this document useful? Is this content inappropriate? Report this Document. Flag for inappropriate content. Download Now. Related titles. Carousel Previous Carousel Next. Jump to Page.
Search inside document. Related Searches Single pile cap. Documents Similar To Single Pilecap Tee Bun Pin. Khader Abu-dagga. Adilur Rahman. Roda Cadiz. Jie Wu.Pile caps are constructed to hold the pile and superstructure together at the ground level or below the ground level while transferring loads of the superstructure to the foundation.
Generally, pile caps are constructed to connect one pile, two piles, three piles, four piles or a group of files. Dimensions of the pile caps are decided based on the loads and connecting arrangement of the superstructure and the pile foundation.
Pile caps can be designed using the truss analogy or using the bending theories. Mostly, up to the four numbers of piles are connected by a pile cap to support the concentrated load from the superstructure, truss theory is used to design the pile caps.
Equations derived considering the strut and tie model are available to calculate the area of reinforcement. The following figure indicates the typical equations that can be used to calculate the area of tension reinforcements. It was copied from the book Reinforced concrete design to BS When there are more piles, the design could be done using finite element software which makes the analysis easier. In general, the gap between the piles is kept at 2. It is done to avoid the interaction of one pile on others.
In addition to the calculation of the tension reinforcements, different shear checks like punching and vertical line shear shall be done. When there are more than two piles, the selection of the critical shear perimeter shall be done very carefully. The guideline given in BS can be used to select the shear perimeter. Follwing figure extracted from the code BS provide the clear location to be considered for shear design.
Here, a v is the distance from the face of the column to the critical section. Similarly, other types of pile caps can also be designed following the same procedure. However, when the number of piles is increasing in a pile cap, the manual calculation becomes more complicated. Computer packages could be used for ease of design while verifying the design outcome with simple calculations.
November 4, February 17, Skip to content Foundation Design.The design of cast-in-situ bored single piles is discussed in the article. Bored piles are more commonly used in the world as a deep foundation when axial capacity can not be achieved by shallow foundations.
There are different methods available for designing piles.Design of pile caps
In all the methods, skin friction and end bearing calculations are done in the design of piles. If we can calculate the above parameters, we can easily evaluate the capacity of the pile. Calculation of negative skin friction and normal skin friction of soil is not considered in this post.
However, the effect of the soil skin friction can be taken in to account when the pile capacity is evaluated. Especially, when there is negative skin friction, which reduces the pile capacity, it should be considered in the calculation.
Effect of the skin soil skin friction will be discussed in another article on this website. Generally, the allowable end bearing and skin friction is obtained from the geotechnical investigations. If the ultimate end bearing and ultimate skin friction is given in the geotechnical investigation report, they shall be converted into allowable capacities as we compare them with the working loads service loads of the structure. The surface area of the pile in socket length is calculated by multiplying the socketing length length of the pile in the fresh rock by the perimeter length of the pile.
Generally, piles are socketing depth around the diameter of the pile unless it is specified in the geotechnical report. The geotechnical capacity of the pile is compared with the structural capacity of the pile to obtain the load-carrying capacity of the pile. When and piling is done in very soft soils like peat, it is advisable to do a structural check of the pile considering the buckling effect in the very soft medium.
As a rule of thumb, engineers used the following equation to evaluate the structural capacity of piles. The article pile cap design could be referred to get knowledge about pile cap design.
The article pile foundation design has more information related to the pile design. November 4, February 17, December 5, Skip to content Foundation Design.