Hideaki Azu, Akinobu Kano, Takumi Ito, Donghang Wu, Takashi Nagumo and Haruhiko Hirata
The innovated vibration control device called as “Scaling Frame” (abbreviated as “SF”) structure is proposed by the author. SF structure consists of beam-column frame, diagonal bracing, and SF device (abbreviated as “SFD”) made of Aluminum or Steel. And, vibration energy is absorbed by plastic behavior of diagonal deformation of SFD. SF structure has been already adopted for low-rise wooden buildings in Japan. In this study, SF structure is assumed to apply on multi-story steel frames, that is, in which high strength and rigidity are required. So then, a hybrid SFD (abbreviated as “HSFD”) which consist of various shapes of SFD is developed herein. And also, to clarify the fundamental restoring force characteristics of HSFD, horizontal static cyclic loading test is conducted. From tests results, it is confirmed that the rigidity and strength of devices is expressed in the sum of each SFD which constitutes HSFD, and the stable hysteresis behavior is presented. It means that the strength and rigidity can be adjusted easily by combination of SFD. Furthermore, the analytical study is done by use of restoring force characteristics model of each shapes of SFD. From the comparison between test results and analysis results, it is observed that the proposed analytical model of HSFD can pursue the test result during cyclic loading well. And also, by use of various type of SFD in substitution for normal type of SFD, it is possible to decrease the number of necessary device more.
Takumi Ito and Kenjiro Mori
Recently, a lot of building structures have been experienced severe natural disasters, and it was reported that various types of terrible collapse mode were occurred. And also, there are many discussions about repairability and recovery on damaged buildings over the world. In particular, there has been focused on new keyword à²¯ Resilience à²° in any field including structural engineering. In Japan, a technical guideline for repairing damaged buildings has been established. However, the applicability and feasibility of repair method and recovery has not been well reported. Herein, to investigate the recovery and ultimate seismic state of repaired steel framed structures, experimental and analytical studies are conducted. Herein, the actual repairing technique for steel framed structure is suggested. During experimental study, the damaged steel member is reproduced by loading tests with consideration of past reports of mega-earthquake disasters. The next, the damaged portion is repaired by proposed method by use of steel-cover plate technique. After this repair process, the loading test is done again. And the recovery of structural performance is estimated by comparison of original and repaired state. From the test results, it is confirmed that the strength and ductility are improved after repair. Furthermore, the analytical model and restoring force characteristics of repaired steel member are suggested by observation of ultimate behavior during loading test. Here, the purpose on seismic design is to guarantee the overall failure mode formation on frames. So, the structural demand of strength and rigidity and column-to-beam strength ratio on repaired state are discussing analytically.
Kento Mori, Takehiro Takahashi and Takumi Ito
This study is concerned with horizontally mixed structure system that an existing old R/C structure is seismically retrofitted by addition of exterior steel frame. This system is suggested as seismic retrofitting method in Japan. And some previous studies related to its seismic response mitigation effects were conducted analytically. This study focuses on ultimate seismic state on its multi-degree of freedom system, and the feasibility study of connection joint between exterior steel frame and existing R/C building is investigated. To determine the design point which estimates the ultimate seismic performance, monolithic load patterns considering seismic load effect are adopted on pushover analysis under structural design procedure. Herein, this composite system consists of two various structural systems, and it is assumed that the complicated elasto-plasticity behaviors are presented during inelastic response. So this study suggests the envelope curve model which approximates the inelastic seismic response domain, and the load pattern is obtained by reference of this model. From comparison of proposed model and seismic response analysis, the predicted design points are corresponded each other. And also, it is observed that the predominant failure mode is changed on original and retrofitted state. So this paper suggests the retrofitting strategy which overall failure mode formation is guaranteed. Moreover, the actual connection method between steel frame and R/C building has been suggested. Herein, the required strength is calculated by reference of design points, and ultimate strength of this proposed connection compares with the requirement. From comparisons, it is confirmed that this joint shows sufficient strength.
Itsuki Yagi, Mana Kitahonoki and Takumi Ito
Recently, a various type of steel connection technique has been developed, which aims to possess the multidemands on steel structures. In this study, a new fitting connection technique for steel square tube is suggested, and this joint consists as follows; lightweight steel square tube is just embedded to steel connector, and an adhesive is filled to the clearance between each member as filler, and a pin is inserted as a fail-safe mechanism against the uplift of the column. The adhesives adopted on this connection are widely used to adhere nonstructural members such as tiles and marbles in Japanese architectural building field. The advantage of this connection is not only improvement of workability due to needless of bolting and welding but also the adjustment of the bending strength and rigidity by filling methods and materials. This study investigates the resistant mechanism subjected to bending experimentally. Herein, the loading test is conducted as parameters with the existence of adhesives, pin and loading path. From test results, it is confirmed that the bending strength and rigidity are improved by the filling effect of adhesives, and the maximum bending strength is enhanced by the resistance of a pin during the ultimate state. Furthermore, the stress diagram subjected to bending is investigated from the test results, and a kinematic model of this connection considering the exfoliations of adhesives is suggested. It can almost evaluate the strength of the test results well.
Takayuki Kinoshita and Takumi Ito
In recent years, the terrible earthquake events that are not expected in the design process have occurred in the world. So, it is necessary to estimate the seismic performance accurately. This paper focuses on the energy absorbing efficiency of steel braced frames. Steel brace members in frames show the complicated and unstable behavior because many kinds of buckling and fractures are combined. And evaluation method of restoring force characteristics and capacity have been studied in enormous past researches, however, there are some problems to adopt for seismic design procedure. Also the response characteristics of steel braced frames are affected by the interaction between frames and braces. This paper suggests the analytical method to evaluate the energy absorbing efficiency of steel braced frames as equivalent strength. The equivalent strength is formulated with yield shear coefficient of the frame and slenderness ratio of the brace. Also, to verify the applicability of multi-story steel braced frames response analysis of two types of 5-story steel braced frames (X bracing, inverted-V bracing) is conducted. As compared with energy absorbing efficiency of the response analysis result, it is confirmed that the equivalent strength can be accuracy of plus or minus 20 percent or so.
Ryotaro Arai, Hanako Satoh, Kenta Aoki, Takumi Ito and Changhoon Choi
A lot of steel structures have experienced severe earthquake disasters in Japan, and its various kinds of failure mode have been reported. Especially on steel braced structure, the failure modes are generally categorized into two modes; buckling and fracture of brace member, and yielding of joints and fasteners. After a lot of earthquake disasters, the technical manual has been published to repair and recover the damaged building structures in Japan . The manual suggests the actual repairing method for damaged steel braced structures; however, it is guessed that a few of these methods have some difficulties related to construction technique and estimation of recovery after repair. In this paper, new repairing method for joints on damaged steel brace structure has been proposed, and its applicability and feasibility are investigated experimentally. Herein, the horizontally loading test on diagonal steel brace are performed with parameters as follows; thickness of gusset plate, layout of bolts, slenderness ratio of brace and the method of joint. At first, the damaged state of gusset plate is reproduced by horizontally loading test. Next, the damaged gusset plate is repaired. Finally, the loading test is done to the repaired specimen again. From the test results, the strength is reinforced after repair, and the rigidity is almost same. The change of failure mode and slenderness ratio is presented, and which is related to eccentric distance and torsional parameters. Furthermore, the evaluation method of the failure mode and buckling strength are proposed, and this estimation method shows good utility.
Akinobu Kano, Hideaki Azu, Takumi Ito, Donghung Wu, Takashi Nagumo and Haruhiko Hirata
The innovated vibration control device called as scaling frame à²¯SFà²° structure has been proposed by the authors, and the SF structures are applied to low-rise wooden structures already. This paper aims to investigate the applicability of SF structure on steel frames. Herein, SF structure consists of beam-column frame, diagonal bracing, and SF device à²¯SFDà²° installed, and SFD is made of Steel or aluminum. And vibration energy is absorbed by the plastic behavior of the diagonal deformation of SF device. In previous study, the experimental study on SFD and steel frame specimen with SFD installed were conducted to clarify the seismic response and seismic mitigation effect. And also, from observation of test results, analytical method has been suggested. From the comparison of test results, the proposed method shows good agreements with test results. Furthermore, the enormous past studies have suggested prediction method of maximum seismic response of vibration control frames. So this study aim to develop the prediction method of seismic response on vibration controlled steel frames with SFD installed, and the simple design procedure can be provided. The first, the simplified restoring force characteristics which can chase the test results is applied on prediction method procedure. So the prediction method is reformulated to adapt the bilinear model and strain hardening rule. The time history response analysis is performed to investigate the applicability and effectiveness. From the comparison of analysis results and predictions, it is confirmed that the proposed prediction method shows enough accuracy.
Tomoe Onoda, Takumi Ito, Kenjiro Mori, Hiromu Fuse and Changhoon Choi
Recently, there have been many discussions about repairability for damaged building structures after severe disasters. In japan, a technical manual for repairing damaged buildings has been established; however, its repair abilities have not been reported sufficiently. In this study, the Box-Shaped Repair Method which has been suggested on Japanese technical guideline is adopted for the damaged steel members, and its applicability and feasibility are investigated experimentally. Herein, the damaged portion on steel member such as plastic hinge or local buckling occurrence is covered with steel plate by welding. So the loading test is performed as parameters with section size of steel members, thickness of cover plate and welding size during repair process, and loading path. The procedure of this study is as follows; the first, the damaged test specimens of H-shaped steel member with local buckling are reproduced by initial loading test. Next, the damaged specimens with plastic residual deformation are returned to the original position. Finally, the loading test is done after repair. From test results, it is confirmed that the fundamental structural performance such as the rigidity, maximum strength, and absorbed energy after repair are improved by comparison of original state. And also, this performance can be controlled by adjusting the thickness of cover plate and welding condition. Furthermore, from the observation of test results, the analytical model of repaired steel member is suggested. From the comparison of test results, it can be said that the proposed model shows good agreements both test results and theoretical figure.