島田 侑子

Abstract For safer structural design, a simple index that describes the plastic deformation capacity of composite beams is needed, similar to the connection coefficient in the case of strength. In this study, the relationships between the plastic deformation capacity and strength under varying material properties and geometric shapes of concrete and steel members were considered through finite element analyses. Based on the obtained results, the plastic deformation factor was defined as the ratio of two rotation angles. The minimum value of the connection coefficient in composite beams corresponding to the ductility factor under severe earthquakes was determined because the plastic deformation factor can be used similar to the ductility factor. In addition, the minimum value of the connection coefficient in bare steel beams that will be safe even if a concrete slab is added was determined; therefore, the design of bare steel beams and composite beams are connected by the connection coefficient.

<title>Abstract</title> Submerged arc welding, which is generally used for the corner joint of box-section columns, is a welding process with a high heat input. The influence on the strength and toughness of the heat-affected zone is an important concern, especially when used with a high-performance steel that may be more susceptible to heat input. The ductility of the welded corner joint is one of the important factors to ensure safety against external forces, such as during severe earthquakes. In this study, a series of material and cyclic loading tests of the corner joint comprising SA440C high-performance steel fabricated by submerged arc welding were conducted. The experimental results indicated that the welded corner joint comprising SA440C steel is ductile enough to dissipate input energy caused by the strong ground motion from an earthquake.

The aim of this study was to validate the reinforcement method used for joints connecting a steel roof and a reinforced concrete (RC) frame in existing buildings based on a series of cyclic loading tests. Three reinforcement methods were investigated in the study: one using a steel jacket and high-strength steel rods (Type-1), another using a steel jacket and post-installed adhesive anchors (Type-2), and a third using a steel plate and post-installed adhesive anchors (Type-3). The results obtained show that the Type-1 method is most effective in increasing force, because shear force can be transferred from the RC frame to the steel roof; thus, a steel jacket can support the entire top of the RC column and integrate the roof joints into the RC frame. The Type-2 and Type-3 methods, however, are not effective in the reinforcement of RC columns because shear force cannot be transferred, and concrete failure occurred easily.

This paper is a fundamental study of quantitatively relationship between plastic deformation capacity and strength in composite beam. First, analytical method of composite beam based on the previous experiment results is shown. Specifically, there are three steps in the analysis; invalid area of beam web near scallop is set according to previous experiment results, stress balance between tension and compression in the section is kept under monotonic loading, and deformation of a section is calculated assuming Bernoulli-Euler theory. Secondly, the relationship between plastic deformation of composite beam and geometric condition of beamto-column connection or material characteristics by parametrical study. In this paper, the effect of steel strength and width-to-thickness ratio of column is focused. All composite beam in this paper is presupposed fracture of lower beam flange. Thus, the strain near scallop at lower flange is used as an index that shows progression of plastic deformation.

Investigation on the relationship between seismic damage to non-structural elements and structural characteristics is one of important issue to consider mitigation method of seismic damage to non-structural elements. In this paper, relationship between structural characteristics of school gymnasiums and seismic damage to non-structural elements due to the 2011 Tohoku earthquake and aftershocks is reported. In the investigation, seismic damage of ceilings, windowpanes, outer walls, and inner walls were observed. Such damage is directly linked with serious damage to a human body.

In old low rise steel buildings which need seismic retrofit, pin-type column bases are widely used. Under severe earthquake, anchor bolts in pin-type column base easily fail. Once anchor bolts fail, column base lose its shear transferring capacity. In case of steel building in a urban city, it is difficult to reinforce column base as semi-rigid or rigid connection because of shortage the space around column base and shortage of bending capacity of foundation. In this paper, a new seismic retrofit method for pin-type column base is proposed. The main feature of this method is that only shear transferring capacity is developed without changing the conditions of pin connection. Effectiveness of proposed method is verified by cyclic loading test under bi-axial horizontal force.

In seismic design, moment resisting frame is designed to form the overall sway mechanism under severe earthquake. However, it is possible to form the weak column mechanism with the rise of strength of beams and panel zone due to strain hardening. The causes to collapse the weak column type frame are strong bi-axial seismic force, P-δ effect and deterioration of restoring force. In this study, a series of response analyses of weak column type multi story steel frames under bi-axial ground motion are carried out. In the analysis, realistic hysteresis model of story including deteriorating range is used. From analytical results, collapse behavior and ultimate earthquake resistance of steel frames governed by deterioration of columns are evaluated. © 2012 ASCE.