Three dimensional nonlinear analysis of buried box culvert

Abstract

Reinforced concrete box culverts (RCBC) are widely used throughout the world to provide safe and economical structures for conveyance of water, vehicles, utilities or pedestrian. So far, its design approach is based on 2-D plain strain consideration. Previous studies show that bending moment along longitudinal axis (direction of stream) is significant due to the differential settlement along that direction, which developed a considerable amount of stresses on the culvert and may lead to a structural failure. There is no clear suggestion available in the codes and specifications to consider this effect and 2-D plain strain consideration is also incapable to deal with this. In this study 3-D finite element model of reinforced concrete box culvert buried under fill soil is created and its behaviors are observed. A 3-D finite element model of box culvert buried under fill soil is developed with ABAQUS. Soil is modeled with solid elements considering its nonlinear material behaviors, box culvert is modeled with sell elements and interaction between soil and culvert is simulated by isotropic coulomb’s frictional model. FE models of two types of box culvert, one box culvert with embankment installation and other with trench installation, are developed to study their behaviors. It is shown that the differential settlement creates significant amount of stress along the longitudinal direction (direction of stream) of the buried box culvert in embankment installation. However differential settlement is not observed in case of trench installation and stress is also found insignificant. Hence, 2-D plain strain consideration is adequate for trench installation and 3-D analysis should be carried out for embankment installation. In the design of buried box culvert with embankment installation bending moment of the box culvert along the longitudinal direction should be considered. But the axial tension involves due to the frictional drag is significantly low and can be ignored in case of box culvert without wing walls. Based on the behavioral study a detailed parametric study on buried box culvert with embankment installation is performed using the developed 3-D FE model. It is found that fill height, embankment width, culvert size, side slope, modulus of elasticity of original site soil and thickness of culvert slabs and walls have significant influence on the maximum bending moment along the longitudinal direction of the culvert. In contrast pparameters, such as coefficient of friction between soil and concrete, internal frictional angle of soil, dilation angle of soil and modulus of elasticity of fill soil have found little effect on the maximum bending moment along the longitudinal direction of the culvert. On the basis of the findings of the parametric study an empirical equation is proposed to calculate the design moment for designing a buried box culvert avoiding complex numerical analysis.