No abstract

Cyclic mobility occurring prior to the liquefaction in sands is a peculiar phenomenon exhibiting a butterfly-shaped stress path and a S-shaped stress-strain curve under undrained cyclic loading. Accurate prediction of this phenomenon is of great importance for the earthquake-resistant design of soil structures. However, it has not been achieved, even though near a half century has passed since it became the object of public attention after the Chile (2010.12.27 受付)

2007�������������������������������������� Though the Kashiwazaki-Kariwa Nuclear Power Station was subjected to significantly strong ground motions of the Niigataken Chuetsu-oki Earthquake in 2007, the main facility buildings had almost no damage. Since a large amount of land subsidence was observed near the buildings, the soil around the buildings was expected to be in the strong nonlinear state during the earthquake. In this paper, the authors tried to clarify actual behavior of Unit No.7 reactor building during the earthquake through the simulation analyses using the finite element method. In our analyses, nonlinear effects were considered in contact conditions between the buildings and the surrounding soil by employing joint elements in addition to soil materials.

This study investigates the failure characteristics of reinforced concrete slabs subjected to moderate-velocity impacts by conducting impact tests and numerical simulations. In a series of tests, a spherical steel projectile with a mass of 8.3 kg and a diameter of 80 mm is collided with an reinforced concrete slab at an impact velocity of 65-90 m/s. To investigate the failure characteristics of the reinforced concrete slab, impact motion of the projectile, reaction force, and strain-time history on the back surface and reinforcing bars of the reinforced concrete slab were measured. Failure modes obtained experimentally were compared with the Central Research Institute of Electric Power Industry formula proposed for the local damage of reinforced concrete slabs. Test results revealed that a circular scabbing crack on the back surface of the reinforced concrete slab was completed while there is a sharp increase in the reaction force. Numerical simulations using a high-fidelity concrete model reasonably reproduced the failure characteristics of an reinforced concrete slab. Numerical results demonstrated that the scabbing failure of an reinforced concrete slab subjected to a moderate-velocity impact was initiated by the penetration of the projectile and was completed during the reaction force response.

The description of the cyclic mobility observed prior to the liquefaction in geomaterials requires the sophisticated constitutive formulation to describe the plastic deformation induced during the cyclic loading with the small stress amplitude inside the yield surface. This requirement is realized in the subloading surface model, in which the surface enclosing a purely elastic domain is not assumed, while a purely elastic domain is assumed in other elastoplasticity models. The subloading surface model has been applied widely to the monotonic/cyclic loading behaviors of metals, soils, rocks, concrete, etc., and the sufficient predictions have been attained to some extent. The subloading surface model will be elaborated so as to predict also the cyclic mobility accurately in this article. First, the rigorous translation rule of the similarity center of the normal yield and the subloading surfaces, i.e., elastic core, is formulated. Further, the mixed hardening rule in terms of volumetric and deviatoric plastic strain rates and the rotational hardening rule are formulated to describe the induced anisotropy of granular materials. In addition, the material functions for the elastic modulus, the yield function and the isotropic hardening/softening will be modified for the accurate description of the cyclic mobility. Then, the validity of the present formulation will be verified through comparisons with various test data of cyclic mobility.