Design Method
The design method tab provides options to set or control the design for the pile cap. The details of the design method employed are given in the Pile Cap design section above.
Main Article: Beam Theory vs Strut and Tie Methodologies
The layout of the Design Method area is shown below:
Beam Theory (Beam Analogy)
Use the Beam Theory Method only.
This method treats the pile cap as a standard reinforced concrete beam for bending and shear design, relying on the assumptions of Euler-Bernoulli beam theory. It is generally considered valid for "shallow" pile caps where the depth is small compared to the span.
Strut and Tie Method (Truss Analogy)
Use the Strut and Tie method only.
This approach models the complex internal stress patterns as a triangular truss system, where compressive forces flow through concrete "struts" and tensile forces are resisted by reinforcement "ties". This method is specifically recommended for deep pile caps with low span-to-depth ratios (typically less than 3 to 5), where standard beam theory is no longer valid.
Min of Beam & Truss
Use both the Beam Theory and Truss Analogies and use the lesser area of reinforcement required.
This option instructs the software to perform calculations using both Beam Theory and the Strut and Tie (truss) method and then select the lower reinforcement requirement from the two results.
Max of Beam & Truss
Use both the Beam Theory and Truss Analogies and use the greater area of reinforcement required.
Similar to the "Min" option, the software calculates reinforcement using both methods but selects the higher (more onerous) requirement. This is the more conservative design choice.
Design Bending for Net ULS Loads
Design the pile Beam Theory using the applied Column loads only.
Else design the pile Beam Analogy using the total load including self weight and then deduct the self weight.
When using Beam Theory, selecting this option bases the bending reinforcement design on the applied column loads while ignoring the self-weight of the pile cap. While this can slightly reduce reinforcement requirements, designing for gross loads (which include the cap's self-weight) is considered more conservative.
Design truss compression zones
Design truss compression zone for an area equal to the pile diameter.
This is an optional check available when the Strut & Tie (Truss Analogy) method is selected. It verifies that the concrete compression struts and the nodes (the intersections where internal forces meet) have sufficient compressive strength to resist the applied loads. When designing to older codes like BS 8110 or SABS 0100, the software utilizes the C-C-T node check from Eurocode 2 to perform this specific verification.
Deep Beam Theory
Design using Deep Beam Theory if the clear span between supports is less than 2 x Effective depth.
This option is used when Beam Theory is applied to pile caps that have a low span-to-depth ratio, making them behave as deep beams. A deep beam is generally defined as a member with a span less than 3 times its depth. For these cases, the software incorporates the deep beam analysis methodology presented in the Reynolds & Steedman Concrete Designers' Manual to ensure a valid design.
Check Crack Width (EC2-1 7.3.3)
For wmax = 0.3mm.
This parameter enables a serviceability limit state (SLS) check to control cracking in accordance with Eurocode 2 Part 1-1, Clause 7.3.3. This specific clause provides a simplified method for crack control that does not require the direct calculation of a crack width. Instead, it ensures the design is satisfactory by limiting the maximum bar diameters or maximum bar spacings based on the calculated stress in the reinforcement under serviceability load conditions.
Old Manual
Methods
The input options are:
Beam Theory
The pile cap is designed as a rectangular concrete beam for bending.
Strut and Tie method
The pile cap is designed using the truss analogy using tension and compression elements.
Min of Beam & Truss
The pile cap design is carried out using both the Strut and Tie method and the beam method and the smaller reinforcement area required from each method is used.
Max of Beam & Truss
The pile cap design is carried out using both the Strut and Tie method and the beam method and the larger reinforcement area required from each method is used.
Additional Options
There are also three further options to control the design:-
Design Bending for Net ULS loads
The pile loads and bending moments in the pile cap are based on the applied column loadings only, no adjustment is made for the self-weight of the pile cap. This option applies to the beam theory only.
Design truss compression zone
For the strut and tie design to BS 8110 and SABS 0100, the design will use the check for a CCT node taken from the EC2 design code.
Deep Beam Theory
For use with the beam theory method. The design will treat the pile cap as a deep beam, using the method presented in the Concrete Designers’ Manual, Reynolds & Steedman, 10th Edition. This provides an alternative design method for deep beams as an alternative to the strut and tie method.
Check Crack Width
Option to perform rigorous calculation of crack width in accordance with EN 1992-1-1: 2004 7.3.3