Takumi Ito

Timber Health Monitoring using piezoelectric sensor and machine learning

The Timber Health Monitoring System, which enables constant monitoring of wooden buildings by artificial intelligence based analysis of the signals of a piezoelectric sensor attached to a piece of timber, is proposed. Basic verification was carried out by modeling timber damage and performing vibration tests. Analysis of the obtained waveform data using the k-nearest neighbor (k-NN) method and a support vector machine revealed that the proposed system has a strong classification performance. We also tried reducing the data dimensions by using principal component analysis and found that the classification rates barely decreased even if dimensional reduction was adopted. These results are promising for the realization of our proposed system.

Study on Ultimate Seismic Behavior and Repair Method of Damaged SteelFrames

Recently, there are many discussions about repairability and recovery on damaged buildings. It is desirable to establish the design manuals for recovery considering continuous use of structures. In our previous researches, the damaged steel members of H-shaped and square tube section were reproduced by loading test. From the loading test results, the inelastic behavior and restoring force characteristics were clarified, and also the analytical model were proposed which can chase test results well. It means that we have already conducted the member based research on repairability. So, in this study, to investigate the inelastic behavior and restoring force characteristics of repaired steel frames, the loading test is performed on half size scaled - partial frame model as parameters with strength ratio of column-beam and panel-beam. It is assumed that the various type of failure mode is generated on original state and repaired state. During loading test on original state, local buckling is observed on H-shaped steel beam. Therefore, the damaged area is repaired by welding cover plates method which is recommended by Japanese restoration manual for damaged building structure by severe seismic disasters. And also, the loading tests on repaired state is performed, and it is confirmed that the strength is restored at the same or high level compared with original state. However, in case of beam failure mode on original state, different failure mode is observed on repaired state. Furthermore, a finite element analysis is performed, and the resistant mechanism during ultimate state is investigated analytically in detail.

Study on Ultimate State and Mechanical Characteristics of Connection Joint of Damaged H-Shaped Bracing Structure

In Japan, various kinds of failure modes in steel structures have been reported in severe past earthquake disasters. Also, the various type of repair method for damaged building structure is suggested, and it has been published as restoration manual and guideline. However, it is guessed that these repair methods have some difficulties related to construction technique and estimation of recovery of seismic resistant performance after repair. This study focuses on the seismic ultimate state of steel brace connection of original state and repaired state after damaged, and the effective restoration method is suggested herein. In our past researches, new repairing method for damaged steel bracing joint which has angle-section brace member has been suggested already, and its applicability and feasibility were investigated experimentally. Herein, H- shaped section brace members are focused which are adopted on middle-rise or high-rise steel building structures, and also, various kinds of failure modes of these bracing structure has been reported after past terrible seismic disasters in Japan. So, the effective restoration method is proposed here. First, to reproduce the seismic ultimate state, the vertical loading test on H-shaped bracing test specimen are performed as parameters with bolt layout, thickness of gusset plate, that is, out-of-plane rigidity of joint. Next, the damaged bracing joints are repaired. Finally, the loading test is done on repaired specimen again. From test results, the restoring force characteristics after repair can be recovered, and any type of failure modes are observed. So, 3D model of damaged bracing joint is constructed by using 3D scanner, and it helps to identify the failure mode and yield lines on gusset plate. Furthermore, the plastic limit analysis is performed by reference of 3D model, and it can predict the ultimate state of test results well.

A Study on Ultimate Seismic States of Multi-story Horizontally MixedStructural System and Feasibility on Connection Joints

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.

The Repair Method of Damaged H-shaped Steel Members and Experimental Study on Recovery after Repair

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.

An Experimental Study of Embedded Connection for Lightweight SteelSquare Tube Filled with Adhesives

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.

Repair Method of Damaged Steel Framed Structures and Ultimate SeismicState of Repaired Steel Frames

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 a²¯ Resilience a²° 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.

Repair Method of Damaged Steel Braced Structure and Restring ForceCharacteristics after Repair State

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 [1]. 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.

AN EXPERIMENTAL STUDY ON REPAIR METHOD AND RECOVERY OF STRUCTURAL PERFORMANCE FOR DAMAGED RHS STEEL MEMBERS

There are many discussions about repairability and recovery on damaged building structures. In considering sustainable use of damaged building structures, it is required to apply suitable repair methods for each damaged component members. Several repair methods for damaged RHS steel members have been proposed in technical guideline. However, the specific work procedure and the relationship between repair method and recovery have not been well reported in past researches. This study focuses on a repair method for RHS steel members. The detailed repair procedure is validated based on actual examples. Furthermore, the recovery of structural performance after repair is clarified.

An Experimental Study on Bearing Strength in Compression for Bolted Joint of Plywood

In recent years, in the field of wood industry, especially in Japan, it is required that planed raw materials switch from import materials to domestic lumber and development of new usage suitable for domestic lumber is strongly demanded. To promote and increase the demand of domestic cedars, the various types of products or building members by use of plywood has been suggested in Japan. We suggested the combined structure which sandwiched a steel material in plywood. And also, to investigate the structural resistant mechanism and performance under compression, the loading test of the sandwiched members has been conducted. Furthermore, we assume that the combined structural system would apply to sheet lightweight section steel structures, and the examination about the stiffening effect with the system is done, too. In addition, it is thought that it is necessary to establish enough clearance between the hole of plywood and bolt because of the accuracy of finishing of materials and precision of constructions. On the other hand, it is desirable that the clearance becomes small as much as possible, because the excessive clearance causes a drop of the structure unity of the combined material and invites the paths for thermal air environmental and humidity. Then, the moderate clearance around the joint would be inevitable, it is necessary to clarify the influence on the stress transfer mechanism and modification quality by the bearing pressure of the circumference of a bolt joint, and the above. In this research, the two types of filling up method for the clearance are studied; the first is a wet construction method by use of filler, and the other is a dry construction method with steel hardware. Herein, to develop and propose the above filling up methods, the structural resistant performance is not only evaluated, the difficulties of production, the costs and the human body effects are estimated. To select the suited filler materials, the construction examination and material testing were carried out. Form this selection, an urethane, an epoxy and a cement were picked up. And the bearing pressure experiment tests with the parameter of materials, the size of clearance, i.e. the thickness of filler, and the procuring period were conducted. The next, the steel hardware is designed with consideration the absorbing the gap resulted from construction and production errors. And the bearing pressure experiment study is conducted. From the experimental result, the relations of rigidity and strength with the parameters of fillers are clarified. And also, from the comparison of the results of filler and the ones of steel hardware, it can be said the steel hardware becomes the one of the most suitable methods.