Tetsuhiro Asari

Story Drift Response of R/C Buildings with Hysteretic Dampers

This paper investigates the story drift response of reinforced concrete (R/C) building structures with hysteretic dampers subjected to ground motions. Specifically, it focuses on the effect of the stiffness of the main structure on the story drift demand. The yield story drift of the hysteretic dampers is determined according to the drift ratio and the strength ratio A parametric study is performed by using a multi-degree-of-freedom (MDOF) system model and through a series of non-linear time-history analyses for different values of number of stories, story drift limits at the design phase, and different input ground motions. The results of the earthquake response indicate that there is a strong dependency on the stiffness of the main structure in increasing or decreasing the story drift demand, when installing hysteretic dampers. Dependency on the characteristics of the input ground motion, input energy and response period was also observed.

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 Performance of Story Drift-Controlled RC Frames with Hysteretic Dampers

This paper investigates the seismic performance of story drift–controlled reinforced concrete (RC) frames with hysteretic dampers. The frame models include a wide range of mechanical properties of dampers, which are defined according to a proportion rule in order to explicitly control the yield story drift of dampers. The story drift response, hysteretic energy dissipation and other parameters are examined to evaluate the effectiveness of dampers. The influence of the global flexural deformation of the frame on the response of dampers is also examined, and an analytical procedure to account for this phenomenon is developed. The obtained results indicate that the seismic performance of the structure is improved by reducing the story drift demand and seismic damage uniformly over the building height. Regarding the global flexural deformation, the proposed analytical procedure can be used for a preliminary estimation of the story number up to which dampers yield before the RC frame.

ACTUAL CONCRETE STRENGTH AND SEISMIC DAMAGE PREDICTION OF EXISTING REINFORCED CONCRETE BUILDINGS IN HOKKAIDO BASED ON SEISMIC DIAGNOSIS

In this paper, we investigate the seismic performance of existing reinforced concrete buildings, the damage prediction and the actual concrete strength based on the seismic diagnosis results from 1996 to 2006 in Hokkaido. The following conclusions are obtained: (1) 79% of buildings built before 1971 do not satisfy the sesmic capacity index Is≥0.6; (2) The average ratio of actual concrete strength by core tests to design basis one is 1.39; (3) The seismic retrofit of buildings reduces the predicted seismic damage ratio over moderate damage rank to approximately one fourth as compared to the non-retrofit buildings under the earthquake ground motion level of JMA seismic intensity of 6.