CES部材の終局せん断耐力に関する研究

抄録

 1. INTRODUCTION

 Steel reinforced concrete structures are typical composite structural systems comprising steel and reinforced concrete (RC), which exhibit excellent resistance against earthquake through high capacities and deformability. The design process and construction work for such structures are technically more complicated than those for RC and steel structures. To overcome these limitations, concrete encased steel (CES) structural system comprising fiber reinforced concrete (FRC) and encased steels have been proposed herein as a new composite structural system. CES has been a subject of continuous and comprehensive studies to make its use practical. Herein, the seismic behaviors of CES members are experimentally investigated to evaluate the ultimate shear strength. A summary of the corresponding test results are laid and a discussion is presented for an approach of evaluating the required characteristics, namely cracking, yield, and ultimate strength and deformation of CES members, for structural design practices.

 2. TEST PROGRAM

 Six specimens were tested under monotonic loading to investigate the effects of the section shape of encased steels and the sectional width of the FRC cover on the shear strength of CES members.

 3. EXPERIMENTAL RESULTS AND DISCUSSIONS

 All specimens showed considerably ductile and stable behaviors. Brittle failure was not significant during testing, although flexural and shear cracks propagated at small deformation. The steel shape affected the observed cracking patterns of the CES members. As revealed by a comparison of the deformation behavior and damage situations of these specimens, the FRC improved the structural performance and reduced the damage in composite members.

 4. SHEAR STRENGTH EVALUATION

 An existing study 3), 4) was referred to for the numerical evaluation of the shear strength results. All specimens displayed larger maximum strengths than those obtained through the formulas; therefore, their strength was evaluated within the safety limits. Moreover, the sectional width of the FRC cover was found to display an influence on the ultimate strength of the CES members; thereby, a design formula was proposed taking into account this influence. Consequently, the formula provided numerical results that showed good agreement with those obtained from the experiment.

 5. CONCLUSIONS

 Specimens with different built-in steel shape and member widths were subjected to beam-column tests, after which the structural performance of CES members with shear failure was examined. The main findings of this study can be generalized as follows:

 1) Shear failure occurred in each specimen. The basic data of shear behavior of CES members were obtained.

 2) Shear cracking occurred in each specimen. After bending, cracks were noticeable in the FRC cover, although there was no indication of a significant decrease in strength or major falling of the cover.

 3) Regardless of the built-in steel shape, such as H- or cross-H-shaped steel, the maximum shear strength increases with an increase in the sectional width.

 4) The ultimate shear strength of CES members was proposed by taking the effective width of the FRC into account. This improves the evaluation accuracy of the ultimate shear strength of the CES members.