Norihide Koshika

Analytical studies on local damage to reinforced concrete structures under impact loading by discrete element method

Abstract This paper proposes a new analytical approach for assessing local damage to reinforced concrete structures subjected to impact load, by applying the discrete element method (DEM). It first outlines the basis concept and analytical formulation of the DEM. Next, it discusses the results of simulation analyses of concrete material tests, uni-axial compression tests and tensile splitting tests conducted to determine appropriate analytical parameters such as material constants, failure criteria and strength increase factors depending on strain rate. Finally, the adaptability of the DEM to local damage to reinforced concrete structures impacted by rigid and deformable missiles is verified through simulation analyses of various types of impact tests. Furthermore, the various impact response characteristics and failure mechanisms, such as impact forces, penetration behavior, reduction in missile velocity and energy transfer process, which are difficult to obtain experimentally, are analytically evaluated by the DEM.

Active tuned mass damper

A new control strategy to improve a tuned mass damper (TMD) is developed for the vibration control of a large structure subjected to external disturbances. The feedback gain of the proposed algorithm is linear to the response acceleration of the primal system and it is optimized in the frequency domain under a harmonic excitation. According to this method both the feedback gain and the TMD parameters are optimized in the frequency domain and they are expressed in a set of closed form solutions. The performance of the proposed control method is discussed and compared with that of a passive TMD.

Experimental verification of bounded-force control method

An efficient and simple non-linear active control method called Bounded-Force Control (BFC) method has been developed. The theoretical development and application examples of the BFC method has been presented in several publications 1-3 where it was shown that the BFC is more efficient than the Linear Quadratic Regulator (LQR) method in terms of maximum control force and power requirements when applied to an Active Tuned Mass Damper (ATMD) system. Following a brief review of the fundamental concept of the BFC and a discussion of its main advantages, the results of an experimental investigation using a three-storey shear building model excited by a shaking table and controlled by an electromagnetic linear motor are presented. The experimental results were in perfect agreement with the analytical results, thus confirming the validity of the proposed BFC algorithm.

Seismic Performance Evaluation of Seismically Isolated Buildings Introduced to the Building Code of Japan

The Building Code of Japan (the Building Standard Law of Japan) has been changed from the former prescriptive type into a performance-based type in June, 2000. This paper presents the evaluation procedures for seismic performance of seismically isolated buildings against major earthquake motions newly introduced to the Building Code of Japan in October, 2000. The evaluation procedures apply the equivalent single-degree-of-freedom (ESDOF) system, equivalent linearization and response spectrum analysis. The basic concept of seismic design spectra for major earthquake motions is (1) basic design spectra defined at the engineering bedrock, and (2) evaluation of site response from geotechnical data of surface soil layers. The principle of evaluation procedures is that the predicted response values should not exceed estimated limit values. The evaluation criteria of each portion of a building are (1) the isolation system shall be designed so that the maximum response displacement does not exceed the design limit displacement, and (2) the structure above the isolation system and the foundation and structural elements below the isolation system shall be designed so that the working stress does not exceed the allowable stress. The scope of application of the evaluation procedures is (I) buildings not exceeding 60 meters in height, and (2) base isolation buildings on the soil layers excluding very soft soils.

Analytical study on active and nonlinear control for large earthquakes

The feasibility of nonlinear control rules consisting of the conventional hybrid mass damper (HMD) method with a control force limiter and of the bounded-force control (BFC) method on an existing building, Kyobashi Seiwa Building, which is equipped with an active seismic response control system, were investigated analytically using the JMA-Kobe ground motion of the Kobe Earthquake as an input. As a result, it has been concluded that the existing system can control the responses to l0cm/s ground motion by changing only the control algorithm. The control system with 10t weight, and HMD-plus-limiter and BFC method are promising up to 50cm/s ground motion. The control force, stroke and control power requirements of the BFC and HMD-plus-limiter method were well within the practical range.

Seismic Evaluation Procedures of Seismically Isolated Buildings Introduced to the Building Code of Japan

The Building Code of Japan (the Building Standard Law of Japan) has been changed from the former prescriptive into performance-based type in June, 2000. This paper presents the evaluation procedures of seismic performance of seismically isolated buildings against major earthquake motions newly introduced to the Building Code of Japan in October, 2000. The evaluation procedures apply the single-degree-of-freedom (SDOF) system, equivalent linearization and response spectrum analysis. The basic concept of seismic design spectra for major earthquake motions is: 1) basic design spectra defined at the engineering bedrock, and 2) evaluation of site response from geotechnical data of surface soil layers. The principle of evaluation procedures is that the predicted response values should not exceed the estimated limit values. The evaluation criteria of each portion of a building are: 1) the isolation system shall be designed so that the maximum response displacement does not exceed the design limit displacement, and 2) the structure above the isolation system and the foundation and structural elements below the isolation system shall be designed so that the working stress does not exceed the allowable stress. The scope of application of the evaluation procedures is: 1) buildings not exceeding 60 meters in height, and 2) base isolation buildings on the soil layers excluding very soft soils.Copyright

FEM Analysis of RC Shear Walls and its Application to a Theoretical Model

In order to calculate the shear capacity of a reinforced concrete (RC) shear wall, some models based on the theory of limit analysis (called “Macro model”) are proposed. These models contains many assumptions which need to be certified, and FEM analysis is considered to be a useful method to examine these assumptions. So, in this study, a nonlinear FEM program to analyze RC shear walls was developed, and the correctness of the macro models was examined by using the FEM analysis.