International Journal of Earthquake and Impact Engineering (4 papers in press)
Dual hysteretic damper system effective for broader class of earthquake ground motions
by Takuma Shiomi, Kohei Fujita, Masaaki Tsuji, Izuru Takewaki
Abstract: This paper aims to develop a Dual Hysteretic Damper (DHD) effective for a broader class of ground motions, which includes two level-oriented hysteretic dampers and a gap element. To reveal the influence of DHD parameters on the earthquake structure response, a closed-form solution is used of the maximum response of a single-degree-of-freedom system with DHD under the critical double impulse. An energy balance approach plays a central role in the derivation of such closed-form solution. A design process of DHD in a multi-degree-of-freedom system is proposed which is based on the sensitivity analysis. The transformation of earthquake ground motions into the double impulse overcomes the difficulty in the emergence of sensitive response variation to design parameters and the closed-form expression makes the proposed system efficient. It is demonstrated that DHD is effective both for small and large-amplitude input motions and the proposed system is applicable to recorded ground motions approximately. It is also verified through the comparison with the designs obtained by the Monte Carlo simulation and the genetic algorithm (GA) that the proposed design method is more effective and efficient than conventional methods.
Keywords: damping; hysteretic damper; dual use; double impulse; gap element; optimal design.
Evaluating Seismic Response Modification Factor of Steel Frames with Different Bracing Systems
by Yousef Al-Qaryouti, Besan Alagawani
Abstract: This paper aims to evaluate seismic response modification factor, overall ductility factor, and overstrength factor of ordinary moment steel frames with different concentrically bracing systems (X-bracing, V-bracing, and inverted V-bracing). The effect of bracing type and number of stories have been considered in the course of this study. Such factors effects on seismic parameters are not considered in seismic codes such as International Building Code (IBC) and European standards (EN). Linear time history analysis has been performed using multiple earthquake records selected to include the variability in ground motion characteristics for four-, eight-, twelve-, and sixteen-story steel frame buildings. Nonlinear pushover analysis was then carried out by assigning nonlinear material behaviour and plastic hinges to steel elements according to code. It has found that each bracing system has a unique behaviour as well as different seismic parameters than other types, which are not differentiated in seismic codes such as IBC and EN. Also, it was found that the overall ductility factor, decreased with increasing the number of stories, while response modification factor (except for the inverted V-braced system) and overstrength factor increased with increasing the number of stories.
Keywords: earthquake engineering; seismic behaviour factors; response modification factor; ductility factor; overstrength factor; moment steel frames; steel bracing system; static pushover analysis; time history analysis; plastic hinges.
Fragility curves for steel-concrete hybrid tall buildings
by Huanjun Jiang, Yanfeng Duan, Huan Zuo
Abstract: Fragility curves of steel-concrete hybrid tall buildings designed according to the current Chinese seismic design code were derived by analytical methods, taking into account the uncertainty of earthquake ground motions. Totally, 45 analytical models were analyzed considering all combinations of three design parameters, i.e., seismic protection intensity, site soil type and design group. On the basis of a large number of nonlinear time history analyses, fragility curves were derived reflecting exceeding probabilities corresponding to each performance level. The influence of different engineering demand parameters (EDPs) and design parameters on fragility curves was analyzed. The result showed that fragility curves based on different EDPs varied significantly, indicating that different structural components played different roles in seismic performance of the structure. While seismic protection intensity had little impact on seismic vulnerability, structures tended to be more vulnerable on the site with softer site soils and longer characteristic periods.
Keywords: steel-concrete hybrid tall buildings; fragility curves; seismic protection intensity; site soil type; design group; engineering demand parameters; fragility curves; exceeding probability; performance-based seismic design; performance objective; incremental dynamic analysis.
Finite element analysis for estimating steel structure responses under a variety of marine-collision actions
by Aditya Rio Prabowo, Seung Jun Baek, Jung Hoon Byeon, Dong Myung Bae, Jung Min Sohn, Ahmad Fauzan Zakki, Gunawan Dwi Haryadi, Bangun I.R. Harsritanto
Abstract: The risks to human life, the ocean environment, and ship structures in accidental collisions have been a concern for shipbuilding since the occurrence of several remarkable historic maritime disasters. This has resulted in growing demands for increased safety assessments, as ship collisions may occur with ships and other marine structures that are affected by various factors. Many studies have worked to quantify these complex events, and classification of ship collisions has indicated that external dynamics and internal mechanics are important elements. The mass of the ships and the attacking angle during collision vary, and these are also critical parameters for the external dynamics. This study conducted a series of ship collision analyses to observe the effect of external parameters on the responses of steel structures. Variations in mass are represented by using different ship types as the striking ship, while an oblique collision was conducted initially and was compared to a perpendicular collision scenario. The other involved ship was denoted as the struck ship, and the side structures of a roll-on/roll-off (RoRo) passenger ship were designated as the target. Reliability of the numerical method was taken as the background to conduct this study using finite element (FE) analysis. Crashworthiness criteria produced by the FE analysis can be summarised to illustrate the trends in structural responses for the selected parameters. Based on this summary of the FE solutions, satisfactory results were obtained, as the rigid striking ship successfully produced a higher internal energy. In terms of the damage extent, the larger dimensions of the cargo carrier as the striking ship (compared to the struck ship) significantly crushed the target structure. Finally, a comparative analysis of the structural responses subjected to varying attacking angles was conducted to evaluate the absorbed strain energy and structural crushing process.
Keywords: Ship collision; side structure-striking bow interaction; nonlinear finite element method; crashworthiness criteria; response contours; progressive failure sequences.