Modified truss analogy for eccentrically loaded pile caps with tension piles

Abstract

The Strut-and-tie models can be utilized to design discontinuity or disturbed regions in reinforced concrete structures where plane sections do not remain plane. Pile caps with a span-to-depth ratio less than two are recommended to be designed using the truss analogy. A number of international standards and design guides have introduced simple truss models for pile caps subjected to a concentric axial load, where all piles are loaded in compression and carry the same load. The present paper discusses extended truss analogy models for eccentrically loaded pile caps of which a pile may be loaded in tension. Compared with the simple truss model, the extended model would require more struts and ties provided at appropriate locations to maintain equilibrium. Numerical examples with plane and space truss models revealed that tension may develop not only in the bottom but also in the top, vertical and diagonal ties of the eccentrically loaded pile cap, depending on the values of the eccentric loads. The reinforcement would, therefore, be provided with adequate area and anchorage length in these ties. It should be noted that the vertical and diagonal tension can not be recognized using the traditional beam method where the pile cap is treated as an inverted beam for flexural design.