Seismic Design and Analysis of Buried Structures with CANDE-2007

Abstract

A method is presented to analyze and evaluate buried culverts and cut-and-cover tunnels for seismic loading in addition to standard static loading from dead and live loads. With CANDE-2007, a plane–strain finite element program, the soil–structure problem is characterized by a cross-sectional slice through the structure and surrounding soil envelope. First, the static design loads are applied with a series of incremental load steps. Next, the seismic loading condition is simulated by specifying quasi-static displacements at the peripheral boundaries of the soil envelope to produce a shear-racking distortion equivalent to the maximum free-field seismic shear strain from the design earthquake. The proposed method is based on two recently completed NCHRP projects and is presented here in detail. An initial linear-elastic study investigates two basic culvert shapes, circular and rectangular, wherein moment and thrust distributions from CANDE-2007 are shown to compare favorably with closed-form solutions. A second study investigates a nonlinear reinforced concrete box culvert installation under the combination of static and seismic loading. Plots of moment, thrust, and shear distributions show how and where the seismic loading alters the response of static loading, including the effect on safety factors for steel yielding, concrete crushing, and shear failure. It is concluded that the proposed seismic method is rational, easy to apply, and fulfills an engineering need heretofore unfulfilled. The procedure applies to any culvert shape, size, and material, and the safety of the culvert installation may be assessed by working either stress or load and resistance factor design.