Abstract
The effectiveness of slightly reinforced thin U-shaped cementitious mortar jacketing for the repair of damaged shear-critical reinforced concrete beams is experimentally investigated. The test project includes two parts. In the first one, five concrete beams over-reinforced against flexure and under-reinforced against shear with different ratio of closed stirrups were initially subjected to monotonic loading until failure. The initially tested beams have been designed to fail in shear after wide diagonal cracking and to exhibit various strength and deformation capacities along with different levels of damages. In the second experimental part, the heavily damaged beams were jacketed with mild steel small diameter U-shaped transverse stirrups and longitudinal reinforcing bars. The retrofitted specimens using the proposed jacketing technique were tested again following the same four-point-bending load scheme. Based on the overall performance of the beams, it is deduced that the shear strength and deformation capability of the jacketed beams were substantially increased compared to the corresponding capacities of the initial beams. Further, although all beams failed in a shear abrupt manner, the retrofitted ones exhibited reduced brittleness and higher deflections at failure up to six times with respect to the initially tested specimens. The level of the initial damage influences the efficiency of the jacketing. Additional test data derived from relative shear-damaged beam specimens and retrofitted with similar thin jackets is also presented herein in order to establish the effectiveness of this repair system and to clarify the parameters affecting its structural reliability. Comparisons indicated that jacketed beams can alter the failure mode from brittle shear to ductile flexural under certain circumstances.
Highlights
A considerable amount of existing reinforced concrete (RC) buildings that were designed based on old code provisions and, in many cases, only for gravity loads can be found worldwide
The experimental program presented and discussed includes five shear-critical beams with various ratios of stirrups tested under monotonic loading until failure in order to exhibit a different level of damage
The heavily damaged beams were retrofitted by U-shaped jackets made of cementitious mortar and reinforced with small-diameter mild steel bars and U-shaped open stirrups
Summary
A considerable amount of existing reinforced concrete (RC) buildings that were designed based on old code provisions and, in many cases, only for gravity loads can be found worldwide. These buildings have usually under-reinforced members against shear, which are vulnerable to brittle failure as their strength and deformation ability is limited [1,2,3]. The first strengthening attempts in RC frame structures with long spans and increased bending moment demands were mainly focused on the enhancement of their flexural capacity [4,5] This way, existing stirrups are not proportioned to prevent. Shear retrofit is deemed necessary in order to eliminate the propensity for shear-critical members, which is derived from the above considerations
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