Manual for standard pile caps has been updated
February 17, 2021 08:08 CET 6 min read
The manual contains ready calculated concrete pile caps for 2, 3, 4 and 5 piles. Calculations have been done according to Finland’s National Annexes to Eurocodes.
Different pile sizes and types included in the manual are driven piles RR115/8 – RR400/12.5 and RRs115/8 – RRs245/12.5 and drilled piles RD90 – RD320/12.5 and RDs115/8 – RDs3230/12.5. Pile caps having 3, 4 or 5 piles include all mentioned piles, but pile caps for 2 piles have slightly limited selection.
Calculations according to Eurocodes and FE analysis
This new version utilizes strut-and-tie analysis more accurately. Special care has been given for stresses in concrete on top of the piles, in location shown in Figure 1. This point is critical due to two reasons; reduction of concrete strength because of two-axial tension stresses (Ft) in node and high concentrated compression stresses (Fc) from column.
Figure 1. Often critical node in strut-and-tie model of pile cap is on top of piles (Pieksemä 2019)
EN 1992-1-1, Eurocode design standard for concrete structures, doesn’t give exact methods for designing this particular detail in concrete pile caps. Therefore a considerable number of FE analyses were made to model the stress distribution in pile cap and especially on top of the piles. The work started with M.Sc. thesis (Pieksemä M., Teräspaaluanturan solmupisteen jännitysten analysointi paalun ja anturan liitoksessa, Saimaan ammattikorkeakoulu, 2019) to define the model type and the boundaries for analysis. Example of a stress distribution is shown in Figure 2. Based on the results of M.Sc. thesis the calculations were widened to cover all pile sizes and pile cap types in the manual.
Due to reduced concrete strength just above piles there is often need for increase the size of bearing plate at the top of the pile. The size of bearing plate has also been considered in the manual and it contains also information on bearing plate size required for every situation.
Figure 2. An example of a stress distribution in pile cap (Pieksemä 2019)
Content of the manual
Manual contains several tables giving necessary information on concrete grades, reinforcements and dimensions of the pile caps, part of Table 5 in the manual is shown in Figure 3. Beside the manual, also readymade DWG files are available for all pile caps in the manual.
Figure 3. Table 5 in the manual included pile caps having 3, 4 or 5 RR piles
Manual contains also graphs showing resistances of pile caps under combined normal force and bending moment. These graphs give designers an easy and fast tool to estimate whether the piles will remain as compressed with different N and M loadings and also whether the pile cap will withstand the loadings. An example of a resistance graph is shown in Figure 4.
Figure 4. An example of a resistance graph for combined N and M loadings.
You can download manual in Finnish from here: SSAB Perustukset - Teräsbetoniset vakiopaaluanturat RR- ja RD-paaluille
DWG files for all pile caps in the manual can be downloaded from here: SSAB Vakiopaaluanturat DWG
Tekla component for 3D modeling of the pile caps still follows the old manual version. Update of the components is starting and the component will be available from Tekla Warehouse site.
More information on RR® and RD® piles www.ssab.com/infra