Fracture in Steel Bridge Piers due to Earthquak

Chitoshi Miki,Eiichi Sasaki 한국강구조학회 2005 International Journal of Steel Structures Vol.5 No.2

In recent years, the use of cold-formed steel rof truss has been increased in steel houses and high-rise apartments. The designexperimental research on the structural behavior of anchor connections is described. Roof truss and connection members couldbe jointed directly with self-driling screw fasteners or simple shaped connection members, which are excellent in workabilityand structural capacity. They could also be used to connect roof truss and sub-structure. The conecting method has beenselected according to the construction material of sub-structures: chemical anchor for reinforced concrete structures and weldingstrength and the stiffness, and the test results have been compared with AISI (1996) and AISC (1989) specifications. Simpleformulas for the ultimate shear strength of the screw fastener connections are proposed and compared with conection tests.

Fatigue Damage in Orthotropic Steel Bridge Decks and Retrofit Works

Chitoshi Miki 한국강구조학회 2006 International Journal of Steel Structures Vol.6 No.4

and improvement of details on these fatigue cracks are presented in this paper. Local stresses at the fatigue crack initiationpoints, fatigue behaviors and the effectiveness of retrofiting works are examined by applying FEM, field measurements andwheel running fatigue tests. The effective notch concept is also used to study the possibility of fatigue crack initiation at therot of welds. The cause of fatigue crack in the longitudinal welds between deck plates and trough ribs is local bending stresseschange to composite deck system by placing fiber concrete on deck plates.

Design of Rupture Strength of Side Blocks in Elevated Steel Girder Bridges with Elastomeric Bearings

Samim Mustafa,Chitoshi Miki 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.3

Elastomeric rubber bearings with side blocks have been extensively used as a seismic response-control device in steel girder bridges in Japan. In real scenarios, the behavior of the girder bridges with elastomeric bearings are usually complex because of the complex mechanism by which the seismically induced inertia forces at concrete deck transmits to the girder bearings. Therefore, it is important to carry out seismic response analysis of a whole bridge system considering the interaction between diff erent structural components in order to check the performance of the side blocks during an event of severe earthquakes. The objectives of the present study are to develop a detailed three-dimensional fi nite element (FE) model of an elevated girder bridge system and to propose a design rupture strength for the side blocks. The FE-model is constructed based on an existing plate girder bridge considering the eff ect of concrete slab, girders, stiff eners, rubber bearing, pier and the damage control by the side blocks. A sequence of seismic response analysis is then performed using four diff erent rupture forces of the side blocks by considering the Level-2 design earthquake, the 1995 Kobe earthquake and the 2016 Kumamoto earthquake. The analytical investigation reveals that the side blocks should be designed to withstand a horizontal force of at least 1200 kN in order to prevent the rupture of the side blocks and to mitigate damage of bridge piers. Moreover, the damage to the critical parts of bridge superstructure can be mitigated by strengthening the side blocks. Based on the analysis results, a retrofi t plan to strengthen the side blocks of existing girder bridges is proposed.

Experimental Study on Low Cycle Fatigue Strength of Beam-to-column Connections in Steel Bridge Bents with Different Plate Assembling and Material Mismatching

Kawin Saiprasertkit,Eiichi Sasaki,Chitoshi Miki 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.3

This study examined the effects of inherent defects due to plate assembling and material mismatched condition between base and weld metal on the fatigue strength of beam-to-column connections. Low cycle fatigue tests were carried out on specimens with different plate assembling systems and material mismatched conditions. The test results revealed that the global loaddisplacement relationships from specimens with different plate assembling systems and material mismatched conditions are similar, meaning these effects involve only local behavior of specimens. However, the fatigue strength of the specimens strongly depends on the location of defects resulting from plate assembling and mismatched conditions. The specimen with the undermatched conditions and the existing defect located closer to the corner of beam-to-column connection tends to have lower fatigue strength. The fracture surfaces indicated that failure patterns of specimen are different regarding mismatched conditions. While the crack propagated through the weld metal for the undermatched condition, it propagated towards the boundary between base and weld metal for overmatched condition. Elasto-plastic shell analysis was performed under the same condition as the experiments. And it is found that when evaluating fatigue strength of beam-to-column connections, the effects of plate assembling system and material mismatched condition should be considered.

Low- and High-cycle Fatigue Behavior of Load-carrying Cruciform Joints with Incomplete Penetration and Strength Under-match

Takeshi Hanji,Kawin Saiprasertkit,Chitoshi Miki 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.4

The fatigue strengths of load-carrying cruciform joints with incomplete penetration and a strength mismatch between the base metal and the deposit metal were studied. Low- and high-cycle fatigue tests were performed on specimens with five matching conditions and two sizes of incomplete penetration. The test results revealed that the failure life was governed by crack propagation in both the low-cycle and high-cycle fatigue regions, and the crack propagation paths differed according to the matching and loading conditions. In addition, the fatigue strengths of the joints were compared for the degree of strength matching and the size of incomplete penetration in the low- and high-cycle fatigue regions. It was found that the effect of strength matching on the fatigue strength is negligible in the high-cycle fatigue region, but it becomes large in the low-cycle fatigue region and significantly reduces the fatigue life of the specimen in the under-matched joints.

Effects of Redecking from RC Deck to Orthotropic Steel Deck on Seismic Resistance of Elevated Girder Bridges

Samim Mustafa,Hidehiko Sekiya,Mizuki Hayama,Chitoshi Miki 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

Due to the rapid deterioration of reinforced concrete decks (RCD) under the combined eff ects of deck overloads, weather and salts, the orthotropic steel decks (OSD) that are light weight and require less construction time are being used increasingly to replace old deteriorated decks. In this paper, a numerical investigation was carried out to study the eff ect of reduction in superstructure weight on the earthquake resistance of elevated girder bridges when an existing RCD was being replaced by an OSD. Firstly, an eigenvalue analysis was carried out to study the eff ect of superstructure weight on the global vibrational characteristics of the bridge and then, the evaluation of seismic performances of both the bridge models were carried out by performing a series of non-linear dynamic analysis with input earthquake data in the longitudinal and transverse directions separately and simultaneously. The behavior of the pier bases was examined by monitoring the displacement responses and plastic strains during earthquakes. It was found that the bridge model with OSD exhibits a shorter period of vibrations and a huge improvement in the seismic performance of the bridge was observed by replacing the existing RCD with the OSD. The analysis results could be useful in fi nding a solution for seismic retrofi t of existing girder bridges.