Analysis

The structural model defined for pile cap abutment and stem wall abutment are slightly different as follows. Two types of frame analysis are offered for pile cap abutment

1. Pile cap abutment (Piles integral with cap): Program assumes the piles are fixed at the bottom. The restraints can be changed by defining spring at the bottom. The frame model defined in this case is similar to the frame that is generated when cap and multi column are defined.
   
2. Pile Cap abutment (Cap as continuous beam): If user selects this option, program defines pinned connections between cap and piles, and analyzes the pile cap as a continuous beam seating on the knife edge support.
   

   Stem Wall: Program treats stem wall as a column with a very thin, rigid cap on top of the stem. So the structural modal of stem wall is like a T-shape frame as shown below.

   

Design

Design tabs will be different depending on which method is selected in the Abutment Configuration.

1. Pile Cap (Piles Integral with cap)

   If user has selected this option in the abutment configuration, Cap and Pile tab will be available.

   Cap design: The program generates the flexure and shear and torsion design checks for cap.

2. Pile Cap (Cap as continuous beam)

   If user has selected this option, program will analyze the cap as a continuous beam and generates the pile reactions. Cap will be designed as single or double reinforcement beam. Pile reaction table is available under Pile tab.

3. Stem Wall Design

   If user has selected this option, only Stem and Footing tab will be available.

   Stem wall design: The stem will be designed at two locations, i.e., at the bottom and top of the stem. Program generates the design using the same approach as column design in pier design module.

   Footing design: Depending on whether piles are defined, the different design method will be selected. If piles are not defined, the footing will be designed as spread footing. If, piles are defined, program will design as pile cap.

Pile Reactions

Pile Reactions are calculated using the bolt group theory in which cap is assumed to be infinitely rigid. The total vertical load (P), longitudinal moment (Mxx), and the transverse moment (Mzz) are applied at the center of gravity of pile group. The resultant axial force in each pile is calculated using the following equation:

where

N	=	No. of piles
xi	=	Distance in X-direction of Pile (i) from the C.G. of the Pile Group
zi	=	Distance in Z-direction of Pile (i) from the C.G. of the Pile Group