There are some differences in the steel structures from the view of seismic design and practice between U.S., and Japan. In Japan all columns and beams are the seismic elements in X and Y directions. In U.S. frames in the perimeter zone are only the seismic elements, and the columns inside the building are designed as the gravity columns which support only the weight of the building. In our previous research, it is clarified that such gravity columns can control story drift concentration during an earthquake. We need more study about the effect of damage control for beams and columns by the gravity columns. We will discuss about the seismic limit capacity of the moment resisting frames when the beams or the columns reach their plastic deformation capacities.
Fatigue evaluation of trough rib to deck weld joint failed in weld throat is presented. S-N curve of the joint is determined in term of stress range in weld throat by carrying out plate bending fatigue tests and collecting previous test data. Two approaches are proposed for calculating stress range in weld throat in actual bridge with orthotropic steel deck based on one or two points of measured stress. Both methods give approximate fatigue lives, suggesting one point of stress measurement is also possible in practice. By stress measurement at an actual bridge with orthotropic steel deck, stress range in summer tends to be higher and thus more damaging than in winter.
Steel bridge piers are often used for elevated highway bridges. The Hanshin-Awaji earthquake in 1995 revealed two types of failure mode in the pier, which are local buckling and low cycle fatigue. However, researches on low cycle fatigue of civil structures are limited, and design methods have not been established yet. In this study, low cycle fatigue strength curves for base joints of the steel pier based on nominal strain, which can be calculated by finite element analysis with a beam element, were proposed. Fatigue tests with steel pier specimens demonstrated that the proposed fatigue strength curves could provide fatigue life estimation with enough accuracy.
A new joint system named ‘elastic-hinge joint system’ is proposed. This system shows a non-linear elastic restoring force-rotation relation and can realize origin-oriented frames. These properties can control damage and reduce permanent distortion in structures or in structural elements after a severe earthquake. This paper describes experimental results on a beam-column connection to which this joint system is applied. The purpose of this paper is to clarify the separation and rotation behavior of the elastic hinge joint. Based on the results, a theoretical model of this joint system is proposed.
Sixteen shear-type friction dampers were made and tested under cyclical loading to investigate the effect of the lap gap on the frictional resistance of the damper. The test results have indicated that the frictional resistance of a shear-type friction damper depends not only upon the tensile force by the high-strength bolts that clamp the slipping steel plate but also strongly upon the lap gap. Based on the experimental results, a formula for assessing the effect of the lap gaps on the frictional resistance of the damper was developed. Comparisons between the measured frictional resistances and the predicted ones have indicated that the frictional resistance of a shear-type friction damper with lap gap could be evaluated by the proposed formula very well.
This study describes fracture strength of electro-slag welded (ESW) connections under biaxial loading condition. The discussions are based on model test results of ESW joints and finite element analysis (FEA) results with corresponding analytical models. Case studies are also made where an axial force ratio and a penetration shape are the analytical parameters. Results are summarized as follows; 1) The model test results show roughly positive correlation between the fracture toughness and the fracture strengths of ESW joints; 2) The model test results and the corresponding FEA results correlate the fracture toughness with calculated equivalent maximum principal stress(MPA); 3) In the results of the case studies, the calculated MPA in a heat affected zone highly depends on an ESW fusion line position.
This paper investigates influence of incomplete penetration size on fatigue crack initiation points of load-carrying cruciform welded joints. The investigation was performed by fine meshed FEM using Effective Notch Stress Approach. As a result, to prevent fatigue crack initiated from welded root when the plate thickness is about 34mm, incomplete penetration size should be less than 10% of the plate thickness, and the influences of incomplete penetration size increase with an increase of the plate thickness. Also, a reduction of the stress at the weld root by increasing the weld size is not expected when the plate thickness is thick and welding becomes an unequal leg length welding.
This study is a part of research to introduce load and resistance factor design (LRFD) method to the Japanese Specification for Highway bridges, which is currently based on allowable stress design method. This paper describes outline of design procedures/provisions of steel highway bridges based on the AASHTO LRFD Bridge Design Specifications. And it also discusses the comparison of the design of simply supported plate girders between U.S. and Japan focusing on design live load/dead load.
Recently, many kinds of weathering steel were widely used in steel bridges. 1%Ni-advanced weathering steel is one of new types of weathering steel. It was considered that the quality of this steel has been remarkably improved. However, when it comes to how much, it has not been clarified. In this paper, we investigated the 753 of 1%Ni-advanced weathering steel on the basis of the mill sheet in order to clarify their quality. Investigated items were tensile strength, yield strength, charpy-absorbed-energy, elongation and yield ratio, and these steel mechanical properties were shown. We also showed the degree of improvement in the quality, comparing with the conventional weathering steel data.