In light of a generic limiting force profile (LFP), closed-form solutions for laterally loaded free- and fixed- head piles in elastic-plastic media have been developed, and implemented by the first author into a spreadsheet program called GASLFP. The solutions offer an expeditious and sufficiently accurate prediction of response of lateral piles. Conversely, they allow input parameters to be deduced using measured pile response, as has been conducted for over 70 test (elastic) piles to date. Nevertheless, structure nonlinearity of pile body is an important issue at a large deflection.
In this paper, a semi-empirical approach is established to capture pile response owing to structural nonlinearity. Expressions were provided for gaining cracking moment Mcr, flexural rigidity of cracked cross section EpIp, and ultimate bending moment Mult. Against measured response of two laterally loaded single piles, back-estimation indicates that (1) the parameters for elastic piles are quite consistent with the previous findings for piles in sand and clay, (2) The proposed variations of Mcr, EpIp and Mult for nonlinear piles provide good prediction of the pile response against measured data and (3) the modulus of rupture kr of 16.7 (clay) and 33.0(sand) are close to those adopted for structural beams, although a very high kr of 62.7 (thus resulting in higher Mcr) for a pile in sand was deduced (shown elsewhere). The use of the kr for beams would render pile deflections of the later pile to be significantly overestimated. The conclusions may be incorporated into design of laterally loaded piles.