For pier cap and strut, Substructure carries out the design for flexure, shear and torsion, cracking and fatigue for the selected design code. If Seismic load groups/limit states are included, program carries out the check for flexure and shear for seismic responses considering the plastic hinging moment as well. Apart from the specific details discussed later in this section for different design codes, following common approach is adopted for design of cap and strut.

For integral piers if integral cap with flanges is specified, program carries out the flexure design taking flanges into account. Therefore design/check may result in a tee section design. Similar is done for cracking and fatigue. For hammerhead and multiple column pier, program uses rectangular section for all design.

Using the auto design feature, all sections are considered. The steel requirement at each section is determined first by taking the section as single reinforced. However, if the section cannot be design as a single reinforced section, Substructure computes both tension and compression reinforcement required resulting in a double reinforced design. Geometrically, the cap beam is divided into spans that are considered to extend from each column centerline to next column centerline with supports at the column centerline. Cantilevers, if present, are considered separate spans. The reinforcement provided over each support is selected when it is at least equal to the required reinforcement in 1/4 of the span on each side of the support. The bars are extended beyond the 1/4 points in accordance with the development length, so the reinforcement is fully developed at 1/4 point. For moment in the middle section of the beam, the provided reinforcement is calculated as the largest requirement for the middle half length of the span (from 1/4 to 3/4 in each span). The bars are then extended outwards to a length equal to the development length. If the span length is less than 11 ft (3.4 m), Substructure provides continuous reinforcing bars and does not compute separate detailing for reinforcement over the column and midspan. The calculated area of steel is transformed into required rebar quantity, using the selected rebar sizes.

When calculating the number of reinforcing bars, clear spacing of at least 1.5 times the bar diameter or 1.5 inch and specified side clear cover is maintained. By auto design feature, up to three layers of reinforcement for top and bottom can be created. If a section requires more than three layers, those must be manually input and capacity checked.

To manually input a design (design check), input the appropriate reinforcing pattern and Substructure will compute the required reinforcement for all sections and the section capacity with provided reinforcement. Substructure uses the development length to compute the effective steel at each section at top and bottom and then calculates the capacity based on both top and bottom effective reinforcement.

Program can do the design of cap either for cap moments at centerline of columns or at face of support. For round columns, Substructure converts the round column section to the equivalent square section. The face of the equivalent square will become the critical section. For rectangular chamfered, rectangular filleted, hexagonal, and octagonal columns Substructure determines the size of an equivalent rectangular section maintaining the overall section aspect ratio. When the face of support option is chosen, program ignores moments at all the check points between faces of supports including the centerline of the column values. Such designs mostly result in fewer number of bars at supports.

Following sections provide more detail about specific design and capacity criteria for various code and design options. More details specific to seismic design of cap are listed in the Seismic Design section.