# 3-Pile Cap Design Example Using ASDIP FOUNDATION

July 8, 2020

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. This document is a step-by-step 3-pile cap design example using ASDIP FOUNDATION software.

## 3-pile cap design example.

As an example, design a pile cap supported on three piles for the loads shown below. The soils report recommends the use of 100-Ton allowable capacity 10" round piles. The column size is 22" x 22", and it's exposed to dead, live, and wind loads. Design the pile cap size, thickness and reinforcement.

## 3-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 a 3-ft high pedestal, which will create an overturning moment and will impact the pile loads.

The structure is subject to lateral wind loads and moments that will be transferred to the foundation. ASDIP FOUNDATION calculates the pile cap dimensions based on standard pile group layouts. Let's use 3 piles with spacing of 3'-0" and edge distance of 1'-6". The image below shows the pile cap in plan and elevation, with the pile loads for the controlling load combination.

## How do you calculate the thickness?

Enter the pile capacities and other material properties, such as the concrete and reinforcing steel strengths, and the densities of concrete and soil cover. The calculated pile loads are used to check a number of limit states for one-way shear and punching shear. The image below shows the calculated one-way shear forces at the column face limit state, for the controlling load combination.

The shear information is then used to calculate the required pile cap thickness. In this example the pile cap thickness is 38" to comply with the code shear capacity. Note that the design can be optimized based on the immediate results provided by the software. Use the At-a-Glance tab for a quick overview of the limit state checks.

## How do you calculate the bending moments?

ASDIP FOUNDATION calculates the bending moments in the pile cap with the critical section at the column face, as shown below for the controlling load combination. The effective piles considered in the calculation are those falling inside the shaded light blue areas. With this information the software calculates the required area of steel.

ASDIP FOUNDATION considers an accidental pile offset in the calculations. In this example this accidental offset is 3 inches. 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.

## How do you specify the reinforcement?

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 three directions. Note that the required steel area is controlled by the minimum temperature and shrinkage reinforcement. ASDIP FOUNDATION generates a sketch of the pile cap in plan and elevation showing the rebars, similar to the construction drawings.

## Takeaway

ASDIP FOUNDATION includes the design of pile caps, with multiple options to optimize the design in less time. The design of pile caps may be cumbersome and error-prone, with multiple limit states checks. This 3-pile cap design example shows that the task can be completed and optimized with ASDIP FOUNDATION within 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.