Uncertainties of shear forces and bending moments in retaining wall due to earthquake loading

The section design of a cantilever retaining wall stem requires factored shear forces and bending moments. Conventional design philosophies have adopted pseudostatic force based approach for the design of wall stem under seismic loading. This approach depends upon the selection of a suitable horizontal seismic coefficient (k<inf>h</inf>). The primary aim of this study is to develop understanding of the uncertainties involved with respect to this seismic coefficient. A non-linear finite element model of cantilever retaining wall placed on medium dense sand has been developed in GiD and dynamic analysis has been performed in OpenSees. Four different earthquake motions with peaks concentrated over a certain time interval and peaks distributed for a larger duration of time have been selected for the analysis. These ground motion records have been scaled to 0.36 g PGA consistent with zone V. The forces and moments computed from dynamic analysis have been compared with those calculated using conventional pseudostatic force based methodologies to understand the influence of inappropriate selection of k<inf>h</inf> value in design. Also, the uncertainty involved with respect to the location of the point of action of the dynamic increment has also been studied. The influence of this uncertainty has been reflected in the prediction of design moments. The study aims to evoke the need for modification in the current design philosophy which can efficiently capture these uncertainties with respect to seismic loading.