Hiroshi Higashiyama

Design Equation for Punching Shear Capacity of SFRC Slabs

In this paper, a design equation for the punching shear capacity of steel fiber reinforced concrete (SFRC) slabs is proposed based on the Japan Society of Civil Engineers (JSCE) standard specifications. Addition of steel fibers into concrete improves mechanical behavior, ductility, and fatigue strength of concrete. Previous studies have demonstrated the effectiveness of fiber reinforcement in improving the shear behavior of reinforced concrete slabs. In this study, twelve SFRC slabs using hooked-ends type steel fibers are tested with varying fiber dosage, slab thickness, steel reinforcement ratio, and compressive strength. Furthermore, test data conducted by earlier researchers are involved to verify the proposed design equation. The proposed design equation addresses the fiber pull-out strength and the critical shear perimeter changed by the fiber factor. Consequently, it is confirmed that the proposed design equation can predict the punching shear capacity of SFRC slabs with an applicable accuracy.

SHEAR CAPACITY EVALUATION OF RC BEAMS STRENGTHENED BY UNDERSIDE OVERLAY METHOD USING HIGH-PERFORMANCE POLYMER CEMENT MORTAR

In this study, the new strengthening method of spraying high-performance PCM (polymer cement mortar) onto the underside of existing beams was adopted. The underside of the RC (reinforced concrete) beams was strengthened between two support points except 50mm nearly the supports. This experiment assumed application to a RC highway bridge slabs and beams. These RC beams were tested to determine the shear capacity and shear failure mode of this overlay method. Loading tests were carried out on the RC beams with changes in the reinforcement ratio, effective depth, and shear span-to-effective depth ratio. As a result, RC beams without web reinforcement strengthened by the underside sprayed-on overlay method using high-performance PCM reached diagonal tension failure without any slip in the interface between the existing concrete and PCM. Based on the test results, it was considered that the mechanism of shear resistance of the beams strengthened by this overlay method was supported by two compressive paths; one was the path toward main reinforcement in the existing concrete, the other was toward reinforcement in the PCM from a macroscopic perspective. An experimental formula for shear capacity considering two compressive paths has been proposed by modifying existing Niwas formula of shear capacity for normal reinforced concrete beams without web reinforcement. This formula facilitates the design for beams strengthened using the overlay spraying method using high-performance PCM. It is necessary to examine the value of safety factor as a future problem more. In addition, it was revealed that the high toughness of PCM did not contribute to the improvement of the shear capacity.高靭性ポリマーセメントモルタルを用いた吹付け施工により下面増厚補強したRCはりの補強効果とせん断耐力について実験的に検討した。RCはり供試体は道路橋のRC床版やRC桁への適用を想定し、RCはりの支点手前50mmの範囲は下面増厚を施していない。有効高さ、せん断スパン比、主鉄筋比、補強鉄筋比をパラメータとする下面増厚補強RCはりのせん断耐力実験を行い、補強効果を検証するとともに、せん断破壊過程から土木学会（二羽式）のせん断耐力式における有効高さの取り扱いを考察し、せん断耐力の評価法について検討した。