ASDIP FOUNDATION is a structural engineering software for the design of concrete footings. It includes the design of pile caps based on the ACI 318 provisions and CRSI Design Guide. Sometimes the lateral capacity of vertical piles is not enough to resist high lateral loads. In those cases the use of batter piles may provide the required lateral capacity to the system. This document is a step-by-step batter pile cap design example using ASDIP FOUNDATION software.
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As an example, consider the pile cap shown below, which supports a steel column on a concrete pedestal for a transmission tower. The soils report recommends the use of 50-Ton allowable capacity 10" round piles. The pedestal size is 30" x 30" x 2'-6". The structure is exposed to dead, live, and wind loads, whose reactions are shown below. Design the number of piles, the pile cap size, thickness and reinforcement.
Pile Cap Design Steps
Enter the information given in the statement of the example, which are the loads and the materials. In this example the analysis of the structure provided the reactions per load case, as shown in the statement above. Note that all loads are applied at the top of the pedestal, therefore additional moments will be produced due to the horizontal reactions. The structure is subject to lateral wind loads that will be transferred to the foundation. The At-a-Glance tab shows a summary of the design for a quick overview of your work as you go. The green check marks indicate that the checks passed.
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Enter the material properties, such as the concrete and reinforcing steel strengths, and the densities of concrete and soil cover. The soils report has provided the allowable pile capacity in compression as 50-Ton, and the lateral capacity of a vertical pile as 5 kips. Note that the service loads will be used to calculate the pile loads, and the program shows the controlling service load combination. The Condensed tab shows a more detailed set of calculations grouped by topic.
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ASDIP FOUNDATION calculates the pile cap dimensions based on standard pile group layouts. Enter the number of piles considering the calculated pile loads. In this example, we could use either 14 or 16 piles, based on the loads and the pile capacity. For illustration purposes, let's use 14 piles with spacing of 3'-0" and edge distance of 1'-3", so the pile cap dimensions are 11.50 ft x 10.70 ft. The pile cap thickness is mostly controlled by shear. In this case a pile cap thickness of 36" provides good results. The Detailed tab shows a complete set of calculations with exposed formulas and with references to the ACI code. An excellent tool for granular checking.
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ASDIP FOUNDATION calculates the axial load per pile, sorted by load combination. This information is used to check a number of limit states for one-way shear and punching shear. In this example eight piles will be battered 14 degrees in order to provide the required lateral capacity, since the vertical piles proved insufficient. Please note that more piles could have been battered easily if necessary.
The first image below shows the calculated pile axial loads for the service load combinations, and it shows the location of the batter piles. The second image below shows the calculated one-way shear forces at the column face limit state for the factored load combinations. The third image below shows the calculated punching shear at a distance "d/2" and at the column face limit states. Note that all these results may be sorted by load combination, for granular checking.
The effective piles considered in the calculation are those falling inside the shaded light blue areas. ASDIP FOUNDATION considers an accidental pile offset in the calculations. In this example this accidental offset is 3 inches.
Enter the reinforcement information for the pile cap. Specify the concrete cover and the bar number and size. In this example we will use #8 rebars bottom in each direction. Note that the top rebars are not required for bending, but they may be required to comply with the minimum temperature and shrinkage reinforcement. In this example only bottom bars were used. ASDIP FOUNDATION generates a sketch of the pile cap in plan and elevation showing the rebars, similar to the construction drawings.
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Takeaway
ASDIP FOUNDATION includes the design of pile caps for vertical and batter piles, with multiple options to optimize the design easily. The design of pile caps may be cumbersome and error-prone, with multiple limit states checks. This batter pile cap design example shows that the task can be completed and optimized with ASDIP FOUNDATION in minutes.
For engineering background, please read the blog post Pile Caps - Structural Design Overview. For our collection of blog posts about foundation design please visit Structural Footing Design.
Detailed information is available about this structural engineering software by visiting ASDIP FOUNDATION. You are invited to download the Free 15-day Software Trial, or go ahead and Place your Order.
Best regards,
Javier Encinas, PE
ASDIP Structural Software
