The members of the steel highway bridges have been designed by analyses with the grillage model based on the elementary beam theory. On the other hand, actual damage of bridges due to fatigue or accidents such as earthquake is investigated by finite element analysis focusing on local stresses or secondary stresses. In this study, the analytical design method for steel highway bridges mainly using the constant shear flow panels is proposed to achieve those two results from one analytical model rationally.

On beam-to-column connections used in steel frames, site welded non-bracket type connections with weld access holes are becoming popular. In order to make up for less deformation capacities due to the presence of weld access holes, beam flanges are commonly widened. Although such doing leads to the improvement of structural characteristics, it restricts architectural plans and results in higher costs. This paper reports on the achieved improvement as to the deformation capacities of connections with weld access holes when the holes are filled up with welding, without beam flange widening.

In this study, we aim to design the bolted joints for ultimate state such as the earthquake of Hanshin Awaji. The main consideration is the capacity of bolted joints for friction type with clearance between bolt and hole after slipping. We carry out the experimental study of the behavior and performance of bolted joints, which involves the slipping and break. We have already examined bolted joints for friction type with main plate whose thickness is 9 mm. In this study, we scrutinize the joints with main plate whose thickness is 19 mm．

Fatigue Design Guideline for Steel Highway Bridges was issued in 2002. Requirements for standard structural details of orthotropic steel decks (OSDs) are specified to ensure the fatigue resistance. After identifying various types of fatigue cracks observed in existing OSDs, it is important to evaluate fatigue strength of present structural details and propose fatigue-resistant structural details with long-term performances. This paper discusses local stress behaviors at welded connections around cutouts between crossbeam and U-shaped rib. Analytical studies using a whole bridge model were conducted based on FEA. Effects of structural dimension of the OSDs to local stresses around the cutouts were clarified.

Various studies have been performed on improving fatigue strength of out-of-plane gusset welded joints because their fatigue strength is very low in the case of as-welded condition. Grinding the weld toes of the joints with burr grinder is the most common method for fatigue strength enhancement. In this study, for the purpose of sugesting appropriate grinding depth for out-of-plane gusset joints, fatigue tests and FEM analyses have been performed.

In the Electro-slag welding(ESW) joint, under severe earthquakes, it is worried about an early brittle fracture in the tip of a slit between a skin plate and a backing strip. According to the previous experimental and analytical studies, between the fracture toughness where the fractures initiate and the equivalent maximum principal stresses (MPA) obtained by the finite element analysis (FEA) was roughly positive correlated. It suggests that the required fracture toughness to prevent the brittle fracture of ESW joint can be estimated if the MPA around the tip of a slit in ESW joint is obtained. Therefore, in this paper, the method of calculating the MPA of ESW joint without carrying out FEM, by converting the macro stress of interior diaphragm, is proposed.

Beam-to-column connections of steel pier is tend to have stress concentration and causes fatigue crack in welding connects flange and web steel plate of beam and pier which is difficult to keep good welding quality. In 1982, crack damage on beam-to-column connection of a T-shape steel pier in Hanshin Expressway is detected for the first case. The damage was repaired by attaching ribs by welding. Another crack was detected on the welding of the ribs and repaired in 1995 but it was cracked again in 2002. In this study, finite element method analysis and stress frequency measurement are conducted to evaluate former and newly proposed retrofit method. Finally, retrofit existing stiffening ribs and patching steel plate with bolt was adopted.

Fatigue damage due to large cyclic strains is one of the main failure modes of steel structures during earthquake. This study investigated fatigue crack propagation behavior of structural steels under large cyclic strains. Crack propagation tests for plain material and deposited metal were performed with a compact tension type specimen. Besides, as an index for crack propagation, cyclic J-integral range was defined based on fracture mechanics concept and calculated by finite element analysis. Based on the results, a fatigue crack growth curve under large cyclic strains was proposed by using the cyclic J-integral range. Then, the applicability of the proposed curve was verified through fatigue tests of corner welded joints.

This paper investigates the bending performance and design applicability of I-girders with Steels for Bridge High Performance Structure 400 (SBHS400). Though SBHS400 can reduce the construction cost, the effect of its high yielding ratio on bending performance has not been fully investigated. In this study, maximum bending resistance and rotation capacity of SBHS400 girders were evaluated and compared to existing design curve and girders with a conventional material by experiments and finite element analyses. Parametric study was conducted with varying width-thickness ratios and strain hardening characteristics. It was clarified through this research that bending capacities of SBHS400 girders are almost same as with conventional steel girders and satisfy criterion of current AASHTO LRFD bridge design specifications and Japanese design specifications for highway bridges.