|主題||Path-Dependent Computational Model for RC/Soil System|
|筆頭著者||Ashraf Shawky（The University of Tokyo）|
|連名者1||Koichi Maekawa（The University of Tokyo）|
In the frame of seismic design, dynamic inertial forces as equivalent static loads are determined with references to seismicity of construction cites, ground characteristics, structural ductility and an associated limit state of reinforced concrete. This simplified way of design works well for particular types of structures but is no longer versatile for structures of complexity having interaction with surrounding media. Dynamic forces which arise in underground RC have much to do with the deformation of soil. At the same time, dynamic soil pressure applied to RC is also affected by the stiffness reduction of RC members and the ductility of structures. Thus, the entire system of RC/soil has to be treated as being coupled for rationalization of design. This paper aims to present reversed cyclic models of coupled reinforced concrete - soil foundation system. The nonlinear interaction of RC and soil is an authors' main concern and induced damage of underground RC having no attached superstructures is investigated. Full path-dependent constitutive laws of reinforced concrete, soil and their interfacial zones are of interest in a FEM program named "WCOMRSJ"developed in The University of Tokyo. This computational tool was systematically verified through coupled RC-soil interacting systems subjected to static reversed cyclic loads.
The seismic earth pressure to underground structures predominantly influences on the practical design. However, its dependency on RC structural ductility has been neglected or simply idealized in practical design. Nonlinear characteristics of soil foundation have been of main concern and investigated in view of geotechnical problems. As a matter of fact, dynamic analysis serving practical design is conducted mostly in consideration of nonlinear soil but elasticity of underground RC structures or equivalent reduced stiffness. Based on these recent background, the following development and discussion were attempted and the following tentative conclusions are obtained.
(1) Path-dependent RC/soil model for dynamic finite element analysis
Based on RC nonlinear finite element analysis applicable to reversed cyclic loads, a simple soil model which can fully trace path-dependency and interfacial one was installed in computer code WCOMRSJ. The advantage of full path-dependent model was exhibited such that hysteresis damping and restoring force characteristics of both structures and foundation are intrinsically taken into account, and that residual deformation, which have much to do with remaining functions of RC to be designed, can be quantitatively evaluated.
For examining reliability of a computational tool of multi-functions, systematic experimental verification is indispensable. The item discussed in this paper is RC-soil system under static reversed cyclic forces. The experimental verification was aimed to check the specific item of assumed nonlinearity described by each constitutive law used. Reasonable accuracy was confirmed.
(3) Kinematic interaction of coupled RC/soil system
lt was clarified that nonlinear characteristics of both RC and soil cannot be ignored for simplicity. The degrading stiffness of RC will tend to lessen the shear force under large strain. In most cases, owing to coupled nonlinear kinematics, structural safety will be sustained. From parametric studies, reinforcement ratio was understood as crack control agent but it does not sensitively influence on the shear force of section induced through the soil deformation.