Shrestha K.C.,Kyoto University |
Nagae T.,Hyogo Earthquake Engineering Research Center |
Araki Y.,Kyoto University
Journal of Disaster Research | Year: 2011
This paper focuses on finite element (FE) modeling of the out-of-plane response of retrofitted masonry walls subjected to quasistatic cyclic loading. Retrofitting involves inserting inclined stainless steel bars on the plane perpendicular to the wall face, already practiced in several historical masonry structures in Japan. The FE model for masonry walls, in which continuum elements represent brick units, interface elements the brick unit/mortar interface, and truss elements reinforcing bars, is demonstrated in comparisons with experimental results. A simplified FE model we also propose represents reinforcing bars by an equivalent vertical bar to facilitate convergence and reduce the computational burden. A study evaluating numerical result sensitivity to modeling parameters demonstrates both modeling stability and retrofitting robustness.
Hikino T.,Nippon Steel and Sumikin Engineering Co. |
Okazaki T.,Hokkaido University |
Kajiwara K.,Hyogo Earthquake Engineering Research Center |
Nakashima M.,Kyoto University
Journal of Structural Engineering (United States) | Year: 2013
Abstract Large-scale shake table tests were performed at E-Defense to examine the out-of-plane stability of buckling-restrained braces (BRBs). Two specimens were subjected repeatedly to a near-fault ground motion with increasing amplification. The test specimens comprised a single-bay, single-story steel frame and a pair of BRBs placed in a chevron arrangement. The specimens were not braced at the brace-to-beam intersection in order to produce a condition where the BRBs were susceptible to out-of-plane instability. Standard BRBs were used in the first specimen, while BRBs with a flexible segment at each end of the steel core were used in the second specimen. A simple stability model predicted the BRBs in the second specimen to fail because of out-of-plane buckling. The first specimen exhibited excellent ductility during the shake table tests, while the second specimen developed severe out-of-plane deformation that compromised the ductility of the BRBs. Based on the experimental observations and the stability model, a methodology is proposed to evaluate bracing requirements at the brace-to-beam intersection. © 2013 American Society of Civil Engineers.
Kim Y.,University of Tokyo |
Kabeyasawa T.,University of Tokyo |
Matsumori T.,Hyogo Earthquake Engineering Research Center |
Kabeyasawa T.,Building Research Center
Earthquake Engineering and Structural Dynamics | Year: 2012
A full-scale shake table test on a six-story reinforced concrete wall frame structure was carried out at E-Defense, the world's largest three-dimensional earthquake simulation facility, in January 2006. Story collapse induced from shear failure of shear critical members (e.g., short columns and shear walls) was successfully produced in the test. Insights gained into the seismic behavior of a full-scale specimen subjected to severe earthquake loads are presented in this paper. To reproduce the collapse process of the specimen and evaluate the ability of analytical tools to predict post-peak behavior, numerical simulation was also conducted, modeling the seismic behavior of each member with different kinds of models, which differ primarily in their ability to simulate strength decay. Simulated results showed good agreement with the strength-degrading features observed in post-peak regions where shear failure of members and concentrated deformation occurred in the first story. The simulated results tended to underestimate observed values such as maximum base shear and maximum displacement. The effects of member model characteristics, torsional response, and earthquake load dimensions (i.e., three-dimensional effects) on the collapse process of the specimen were also investigated through comprehensive dynamic analyses, which highlighted the following seismic characteristics of the full-scale specimen: (i) a model that is incapable of simulating a specimen's strength deterioration is inadequate to simulate the post-peak behavior of the specimen; (ii) the torsional response generated from uniaxial eccentricity in the longitudinal direction was more significant in the elastic range than in the inelastic range; and (iii) three-dimensional earthquake loads (X-Y-Z axes) generated larger maximum displacement than any other loading cases such as two-dimensional (X-Y or Y-Z axes) or one-dimensional (Y axis only) excitation. © 2011 John Wiley & Sons, Ltd..
Ji X.,Tsinghua University |
Hikino T.,Hyogo Earthquake Engineering Research Center |
Kasai K.,Tokyo Institute of Technology |
Nakashima M.,Kyoto University
Earthquake Engineering and Structural Dynamics | Year: 2013
A series of large-scale dynamic tests was conducted on a passively controlled five-story steel building on the E-Defense shaking table facility in Japan to accumulate knowledge of realistic seismic behavior of passively controlled structures. The specimen was tested by repeatedly inserting and replacing each of four damper types, that is, the buckling restrained braces, viscous dampers, oil dampers, and viscoelastic dampers. Finally, the bare steel moment frame was tested after removing all dampers. A variety of excitations was applied to the specimen, including white noise, various levels of seismic motion, and shaker excitation. System identification was implemented to extract dynamic properties of the specimen from the recorded floor acceleration data. Damping characteristics of the specimen were identified. In addition, simplified estimations of the supplemental damping ratios provided by added dampers were presented to provide insight into understanding the damping characteristics of the specimen. It is shown that damping ratios for the specimen equipped with velocity-dependent dampers decreased obviously with the increasing order of modes, exhibiting frequency dependency. Damping ratios for the specimen equipped with oil and viscoelastic dampers remained constant regardless of vibration amplitudes, whereas those for the specimen equipped with viscous dampers increased obviously with an increase in vibration amplitudes because of the viscosity nonlinearity of the dampers. In very small-amplitude vibrations, viscous and oil dampers provided much lower supplemental damping than the standard, whereas viscoelastic dampers could be very efficient. © 2012 John Wiley & Sons, Ltd.
Nakamura I.,Hyogo Earthquake Engineering Research Center |
Otani A.,IHI Corporation |
Shiratori M.,Yokohama National University
Journal of Pressure Vessel Technology, Transactions of the ASME | Year: 2010
Pressurized piping systems used for an extended period may develop degradations such as wall thinning or cracks due to aging. It is important to estimate the effects of degradation on the dynamic behavior and to ascertain the failure modes and remaining strength of the piping systems with degradation through experiments and analyses to ensure the seismic safety of degraded piping systems under destructive seismic events. In order to investigate the influence of degradation on the dynamic behavior and failure modes of piping systems with local wall thinning, shake table tests using 3D piping system models were conducted. About 50% full circumferential wall thinning at elbows was considered in the test. Three types of models were used in the shake table tests. The difference of the models was the applied bending direction to the thinned-wall elbow. The bending direction considered in the tests was either of the in-plane bending, out-of-plane bending, or mixed bending of the in-plane and out-of-plane. These models were excited under the same input acceleration until failure occurred. Through these tests, the vibration characteristic and failure modes of the piping models with wall thinning under seismic load were obtained. The test results showed that the out-of-plane bending is not significant for a sound elbow, but should be considered for a thinned-wall elbow, because the life of the piping models with wall thinning subjected to out-of-plane bending may reduce significantly. Copyright © 2010 by ASME.