This research is concerned with vibration control system with passive friction dampers equipped at the bottom of a steel frame. Sliding of friction dampers give the frame the base-isolation effect. There is a problem of a large residual displacement of the building after a strong earthquake. In order to make the residual displacement conservative, the outer columns in the first story of the frame are directly connected to the foundation. Therefore, the base of the frame with friction dampers could get back to the original position by the spring back-force. Eventually, the system solves the problem of the residual displacement after an earthquake. In this paper, dynamic behavior of this base-isolation system is examined with four types of frame.

Fatigue damage of bellows damper due to girder deformation caused by temperature change is examined. The bellows damper is connected between girders and abutments to reduce damage of superstructures and substructures. A design method to develop the compact and high-performance seismic dampers was proposed by the authors in which the bellows dampers are permitted to be subjected local inelastic cyclic strains due to temperature expansion and contraction of girders. In this paper, low-cycle fatigue properties of the bellows designed by the proposed design method are investigated based on P/V difference method as one of cycle-counting methods through fatigue analysis and low-cycle fatigue tests of the bellows. Fatigue strength of the bellows is examined using the equation of Manson-Coffin and the Miner's cumulative damage law. In addition, the validity of the proposed damage evaluation method for low-cycle fatigue of the bellows dampers is verified by variable amplitude loading fatigue tests of the bellows.

There are many discussions about repairability for damaged building. In previous study, it is reported that strength and rigidity of steel members are improved after repair. However, it is worried that the predominate failure mode of repaired frame is changed. In this study, the repairability of damaged steel subassemblage are investigated experimentally. From the test results, it is confirmed that the predominate failure mode of repaired frame is changed, but it may make the performance deterioration. Furthermore, a finite element analysis is conducted to clarify effectiveness of repair method expansion plan. From these results, it is capable of making the same failure mode as the original.

Steel framed houses consist of wall and floor panels made of structural boards and light-gauge cold-formed steel frames that are fastened with drilling screws. We had already made clear that the conventional shear walls show poor ductility and low damping ability and we developed a new type of shear wall with a few built-in friction-type dampers. Through the static loading tests results, we confirmed that this wall exhibits high energy absorbing capacity as well as high ductility. In this study, we first give general information on conventional and newly developed shear walls. Then, an analytical study to evaluate ductility reduction factor of the buildings designed using this wall will be conducted by Incremental Dynamic Analysis (IDA). Finally, we confirm that this wall has higher effects on suppressing seismic response compared with conventional shear walls.

For examining lateral-torsional buckling behavior of H-shaped steel beam with concrete floor slab，numerical model with springs，which are considered with restraint effect by slab，on the beam upper flange is often used. This paper describes the restraint effect by slab on the beam，e.g.，torsional stiffness，lateral stiffness，maximum strength，and so on. First，loading test with slab-beam subassemblies was conducted to confirm the effects of some kinds of parameters on the stiffness and strength at the connection between beam upper flange and concrete slab. Second，prediction results by past researches and test results are compared，and in a part，new methods are proposed to enhance accuracy of prediction results.

Welded joints in steel structures are subjected to high strain amplitude during earthquake, which could cause a low cycle fatigue crack. To assess low cycle fatigue strength of welded joints, an estimation method based on local strain range at a crack initiation point has been established. In this method, an FE model with extremely-fine mesh is needed to obtain the local strain range accurately. In this paper, a prediction method of the local strain range from a model with relatively coarse mesh was proposed. Strain ranges obtained from coarse-mesh models were related to the local strain ranges from fine-mesh models. A prediction formula of the local strain range which is applicable to T-shaped joints, cruciform joints and out-of-plane gusset joints was established.