Seismic collapse simulation of existing masonry buildings with different retrofitting techniques

Masonry buildings are primarily constructed out of bricks and mortar which become discrete pieces and cannot sustain horizontal forces created by a strong earthquake.The collapse of masonry walls may cause significant human casualties and economic losses.To maintain their integrity,several methods have been developed to retrofit existing masonry buildings,such as the constructional RC frame which has been extensively used in China.In this study,a new method using precast steel reinforced concrete(PSRC)panels is developed.To demonstrate its effectiveness,numerical studies are conducted to investigate and compare the collapse behavior of a structure without retrofitting,retrofitted with a constructional RC frame,and retrofitted with external PSRC walls(PSRCW).Sophisticated finite element models(FEM)were developed and nonlinear time history analyses were carried out.The results show that the existing masonry building is severely damaged under occasional earthquakes,and totally collapsed under rare earthquakes.Both retrofitting techniques improve the seismic performance of existing masonry buildings.However,it is found that several occasional earthquakes caused collapse or partial collapse of the building retrofitted with the constructional RC frame,while the one retrofitted by the proposed PSRC wall system survives even under rare earthquakes.The effectiveness of the proposed retrofitting method on existing masonry buildings is thus fully demonstrated.

Collapse simulation of a super high-rise building subjected to extremely strong earthquakes

In recent years, super high-rise buildings (>500 m) are developing very quickly and become an important frontier of civil engineering. The collapse resistance of super high-rise buildings subjected to extremely strong earthquake is a critical problem that must be intensively studied. This paper builds up a nonlinear finite element model of the tallest building in China, Shang- hai Tower (632 m), and proposes the modeling method and failure criteria for different structural elements. The dynamic char- acters of this building are then analyzed, and the possible failure modes and collapse processes due to earthquakes are pre- dicted, as well as the corresponding collapse mechanism. This work will be helpful in collapse prevention and the seismic design of super high-rise buildings.

Influence of soil——structure interaction on seismic collapse resistance of super-tall buildings

Numerous field tests indicate that the soilestructure interaction （SSI） has a significant impact on thedynamic characteristics of super-tall buildings, which may lead to unexpected structural seismic responsesand/or failure. Taking the Shanghai Tower with a total height of 632 m as the research object, thesubstructure approach is used to simulate the SSI effect on the seismic responses of Shanghai Tower. Therefined finite element （FE） model of the superstructure of Shanghai Tower and the simplified analyticalmodel of the foundation and adjacent soil are established. Subsequently, the collapse process of ShanghaiTower taking into account the SSI is predicted, as well as its final collapse mechanism. The influences ofthe SSI on the collapse resistance capacity and failure sequences are discussed. The results indicate that,when considering the SSI, the fundamental period of Shanghai Tower has been extended significantly,and the collapse margin ratio has been improved, with a corresponding decrease of the seismic demand.In addition, the SSI has some impact on the failure sequences of Shanghai Tower subjected to extremeearthquakes, but a negligible impact on the final failure modes. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Performance assessment of innovative seismic resilient steel knee braced frame

Buckling restrained knee braced truss moment frame （BRKBTMF） is a novel and innovative steel structural system that utilizes the advantages of long-span trusses and dedicated structural fuses for seismic applications. Steel trusses are very economical and effective in spanning large distance. However, conventional steel trusses are typically not suitable for seismic application, due to its lack of ductility and poor energy dissipation capacity. BRKBTMF utilizes buckling restrained braces （BRBs） as the designated structural fuses to dissipate the sudden surge of earthquake energy. This allows the BRKBTMF to economically and efficiently create large span structural systems for seismic applications. In this paper, a prototype BRKBTMF office building located in Berkeley, California, USA, was designed using performance-based plastic design procedure. The seismic performance of the prototype building was assessed using the state-of-the-art finite element software, OpenSees. Detailed BRB hysteresis and advanced element removal technique was implemented. The modeling approach allows the simulation for the force-deformation response of the BRB and the force redistribution within the system after the BRBs fracture. The developed finite element model was analyzed using incremental dynamic analysis approach to quantify the seismic performance of BRKBTMF. The results show BRKBTMF has excellent seismic performance with well controlled structural responses and resistance against collapse. In addition, life cycle repair cost of BRKBTMF was assessed using the next-generation performance-based earthquake engineering framework. The results confirm that BRKBTMF can effectively control the structural and non-structural component damages and minimize the repair costs of the structure under different ranges of earthquake shaking intensities. This studies conclude that BRKBTMF is a viable and effective seismic force resisting system.

Numerical investigation of the time-resolved bubble cluster dynamics by using the interface capturing method of multiphase flow approach

The present paper proposes a multiphase flow approach for capturing the time-resolved collapse course of bubble clusters in various geometrical configurations.The simulation method is first verified by computing the dynamic behavior of an isolated vapor bubble placed in a uniform ambient pressure.The comparison between the numerical result and the theoretical solution indicates that the method can accurately capture the bubble shape,the characteristic time and the extremely high pressure induced by the collapse.Then the simulation method is applied to investigate the behavior of two kinds of bubble clusters in hexagonal and cubic geometrical configurations.The predicted collapsing sequence and the shape characteristics of the bubbles are generally in agreement with the experimental results.The bubbles transform and break from the outer layer toward the inner layers.In each layer,the bubbles on the corner first change into a pea shape and cave before collapsing,then the bubbles on the sides begin to shrink.It is also found that,in comparison with the case of an isolated single bubble,the central bubble in the cluster always contracts more slowly at the early stage and collapses more violently at the final stage.