Mitsumasa Midorikawa

Earthquake response reduction of buildings by rocking structural systems

We are developing the rocking structural systems that can reduce earthquake responses of buildings by causing rocking vibration. This paper aims to examine the effects of the rocking system. To cause rocking vibration under appropriate control, weak base plates are attached at the bottom of each steel column at the first story. When the weak base plates yield during a strong earthquake, the building causes rocking vibration. In this paper, the earthquake responses of this rocking system (the base plate yielding system) are examined comparing with those of the simple rocking system and the fixed-base system by nonlinear time history analyses. The results are summarized as follows: 1) Story shear forces of the base plate yielding systems are reduced as much as those of the simple rocking system. The roof displacements and axial forces are less than those of the simple rocking system. 2) The roof displacements and axial forces of the base plate yielding systems are almost similar to those of the fixed-base system under a certain input level. It is concluded that the rocking system with weak base plates can reduce earthquake responses of buildings.

Development of smart systems for building structures

Building Research Institute, Japanese Ministry of Construction, initiated a 5-year research and development project of Smart Materials and Structural Systems in 1998 as a part of U.S.-Japan cooperative research efforts. The U.S. Counterpart is the National Science Foundation. Smart Structural Systems (also called as Autoadaptive Media) are defined as systems that can automatically adjust structural characteristics, in response to the change in external disturbance and environments, toward structural safety and serviceability as well as the extension of structural service life. The research and development of (1) concept and performance evaluation of smart structure system, (2) sensing of structure performance, and (3) development and evaluation of structural elements using smart materials will be conducted.

Seismic response control tests and simulations by fuzzy optimal logic of building structures

This paper outlines shaking table tests and their results for an active seismic response control system that uses fuzzy optimal logic (FOL). The test results confirmed the validity of the vibration control effect of this seismic response control system. The results of this study lead to two conclusions, that the effectiveness of this FOL control system can be increased by modifying the membership function, and that the results of seismic response control tests can be qualitatively evaluated by simple simulation methods.

FINITE ELEMENT SIMULATION OF A STEEL BRACED FRAME STRUCTURE DAMAGED BY THE 2011 TOHOKU EARTHQUAKE

Abstract. During post-earthquake reconnaissance after the March 11, 2011 Tohoku Earthquake, the writers examined a damaged parking ramp structure. The structure was a twostory steel structure with a 52.5 by 48.5-m floor plan which relied on chevron braces for lateral load resistance. The earthquake damaged nearly all first-story braces in their connection to the beam. The majority of bracing connections had fractured in the east-west frame while many bracing connections were distorted, but none of them fractured, in the north-south frame. The cause of the observed damage was examined by detailed finite element simulations. Planar models of the structure, one extracted from the east-west frame and another extracted from the north-south frame, were subjected to static cyclic loading and to a ground motion record obtained within 800 meters from the structure. The simulation captured the main features of the observed damage. The results suggest that the bracing connections in the eastwest frame failed under a compressive force much smaller than the buckling load of the brace. Although they failed similarly, the bracing connections in the north-south frame were almost strong enough to develop the compressive strength of the brace. This difference may explain the reason why the damage differed in severity between the two loading directions. While fracture was not explicitly modeled in the simulation, the computed plastic strain indicated that the observed fracture in the bracing connections was due to severe cyclic deformation produced while the brace was in compression.

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