In recent years, there has been a permitted need for buildings that ensure robust and safety for earthquakes that exceed normal scope of assumptions. To achieve this, it is necessary to make advanced predictions including the collapse of buildings. Therefore, each member is essential to have a high demand such as a deterioration gradient and a repetitive behavior prediction, but no method has been proposed for predicting the load deformation relationship regardless of the load and boundary conditions.
In this study, we propose a new method for determining the shape of a member from the load deformation relationship. Using the MIEC method, we are able to confirm to determine the shape of beams from a load-displacement relationship.
With the aging of civil infrastructures, it is urgent to propose more efficient and simple maintenance and management methods. Higher strength bolts have been known to lose axial force due to relaxation, so that a bolt pre-tension of +10% of the designed axial force was introduced at the time of bolt tightening to compensate for the axial force decrease. Therefore, in this research, focus is placed on high strength bolts under long-term service condition. The residual bolt axial force survey of high strength bolts is carried out on steel bridges after 30 to 50 years of construction in order to know whether the bolt’s axial force remains in design level as required in the design specification.
For TMCP steel of high-rise building frame, an electroslag welding (ESW), which is welding with high heat input, is adopted for the joints between interior diaphragms and plates of steel box columns. Recently, structural steel become to thicker and corresponding higher heat input. The problem is the softening of the heat affected zone(HAZ) of the ESW; the softening is inevitable due to coarsening of grains by TMCP, and the softening may result in lower ESW joint strength than that of estimated by base material strength. In order to quantitatively grasp the influence of HAZ softening part on joint strength, experimental investigation and analysis were carried out.
The complex multi-axial stress field in various parts of buildings is created during a big earthquake. To evaluate the safety of buildings, the constitutive model with high reproducibility against the complex hardening behavior under the multi-axial stress field has been required. In this study, a constitutive model i s proposed to reproduce the hardening behavior u nder the multi-axial cyclic loading. In particular, we focus on the saturation of stress amplitude and the hardening effect under non-proportional cyclic plasticity. The proposed model is developed based on t he concept of the non-hardening strain region. A few additional parameters are employed and the method for identification of the material constants is proposed for the practicality of the model. The proposed model is validated through the comparison between the numerical and experimental results of the tension-torsion testing.
1700 MPa-class ultra-high strength bolts were fabricated through quenching and tempering process after cold forming of a prototype steel with a chemical composition of Fe-0.5%C-2%Si-1%Cr-1%Mo (in mass%). Bolt shape and dimensions were optimized to enhance tensile deformation capacity. The developed bolt has a waisted shank and a thread form that are developed for reducing stress concentration at thread roots. Due to its shape and dimensions, the waisted shank precedingly yields and plastically deforms, resulting in higher bolt elongation. The specification of nut was also determined for the 1700 MPa-class shank preceding yield type bolt.
In steel roof gymnasiums with RC substructures, space frame roof members are damaged by out-of-plane response of Cantilevered RC walls and vertical response of roof. In this paper, numerical analysis models are constructed for two gymnasiums that have suffered damage such as buckling, post-buckling fracture and fallings of truss members in the 2016 Kumamoto earthquake. For the roofs, bearings, and RC substructures, various design methods such as the old design method, the current design method, and the design method using the guidelines are applied. The seismic response of each model is analyzed by time history response analysis, and the damage of the truss members is evaluated.
Damages due to corrosion occur at girder end of rolled H-beam bridge which is managed by municipalities of Japan. Necessity of their repair or renewal should be rationally judged by their remaining strength under limited budget of municipalities. This study aims to experimentally clarify remaining strength of rolled H-beam end with partial cross-section loss at the web and end stiffener. For this reason, residual stress distribution of the web and end stiffeners, which affects the ultimate strength, are shown based on the measurement. Also, the effect of volume loss amount on the ultimate behavior and strength are exhibited by compression test. Moreover, applicability of existing estimation equation for I-shaped girder end with volume loss due to corrosion into rolled H-beam end are demonstrated.
For examining the applicability of Leeb hardness test to the estimation of echanical properties of steel bridge members, a series of experiment was carried out. The plate thickness, support conditions, and surface treatment conditions assuming the application to existing steel bridge members had little effect on the measurement accuracy. Although the mechanical properties of general rolled steels could be estimated by the Leeb hardness, those of TMCP steels could not be estimated. The experimental results suggested that the chemical compositions and steelmaking method of target steel materials might affect the applicability of Leeb hardness to the estimation of mechanical properties of steel bridge members.
Riveting was mainly used in the assembly of steel members and steel plates of bridge prior to the establishment of bolting and welding. To preserve the aged bridges with riveting, it is assumed that the damaged rivets are removed and replaced with new rivets. When a rivet is placed on the existing structural members for repair, the member expands and shrinks caused by heat input during placing the rivet. Although this heat input generates the residual stress, the features of residual stress by riveting is not clear. In this study, a series of experiment and analysis was performed for investigating the generation mechanism of residual stress by rivet joining.
This paper proposes a prediction method of maximum in-plane response of flexible floor in single-story elastic structures with eccentricity. The relative lateral displacement between parallel plane frames and the in-plane shear force sustained by the floor are targeted as requirements for the floor against earthquake using a six-degree of freedom model considering masses distributed on the floor. It is revealed that the predicted results well correspond with the results of time history response analysis, and also the effect of eccentricity on in-plane response is negligibly small.
According to the Japanese specifications for highway bridges, the flange and web joints of the girder connections are designed individually and the applied force in the flange joints is derived from the stress in a flange. On the other hand, it is known that the applied force in the flange joint is determined by both the stress in a flange and the stress in the bearable flange area of a part of the web clearance. Furthermore, the design method adopting the bearable flange area was also proposed under the limited girder shape. In this study, FE analysis was conducted to evaluate the effect of the shape of a girder and connecting plates on the moment sharing ratio and the bearable flange area of a part of the web clearance. It is concluded that the bearable flange area of a web is calculated by the geometrical moment of area, the width of the web joint, and the thickness of the web.