| The strengthening and retrofitting of existing buildings become a future development trend in the building construction industry.Due to changes in functionality or improvements of the seismic fortification level of buildings,seismic strengthening method is one of the most common technical issues encountered during the retrofitting process of existing buildings.Moreover,there exist cases that the concrete strengths in new RC shear wall constructions do not meet the design requirements,which also requires structural strengthening.Reinforced concrete shear wall structure is one of the most common structural systems used in buildings and widely employed in high-rise constructions.Therefore,devising effective strengthening solutions for RC shear wall structures is of great significance.In response to the cases of poor-quality concrete with low strength in shear walls and considering their structural characteristics under horizontal seismic actions,this paper proposed a seismic strengthening method that utilizes Modified Reactive Powder Concrete(MRPC)to locally replace two side ends of shear walls.In doing so,the seismic performance of RC shear wall structures was expected to be enhanced so that the losses caused by earthquakes could be effectively reduced.The feasibility and effectiveness of this strengthening method were validated through experiments.Three groups of nine shear wall specimens,with each group consisting of three,were designed and constructed in this study.The specimens in the first group had a concrete strength grade of C15,whereas the ones in the second group had a concrete strength grade of C30.In the third group,the specimens with a concrete strength grade of C15 were locally strengthened using MRPC at two side ends of shear walls with a replacement length of 200 mm.Quasi-static tests were perfomed on all nine shear wall specimens to investigate their seismic performance with focuses on the effectiveness of the MRPC local strengthening method.The influences of axial compression stress level on the seismic performance of the strengthened shear walls were also studied.By analyzing and comparing test results,the effectiveness and feasibility of the local strengthening method using MRPC for shear walls were confirmed and following conclusions were obtained:(1)The locally strengthened shear wall specimens using MRPC exhibited the same flexural failure mode as the ones with a concrete strength grade of C30 under low-cycle repeated loadings.The replaced concrete bonded well with the undisturbed concrete,enabling them to co-work effectively.(2)When the shear wall specimen had a lower concrete strength and experienced a high axial compression stress level,progressive crushing and spalling of the concrete in the compression zone at the side ends of the specimen occurred under cyclic horizontal seismic loading.This led to a reduction in effective cross-sectional area and a decrease in the vertical load-carrying capacity of the specimen.Ultimately,a sudden failure similar to axial compression failure happened.In comparison,the specimens strengthened using MRPC did not exhibit such a brittle failure(3)The shear wall specimens strengthened using MRPC exhibited significantly improved lateral load-carrying and deformation capacities.Compared to the specimens of the same concrete strength grade without strengthening,the lateral load-carrying capacity of the strengthened specimens with three different axial compression ratios increased by 23.5%,33.8%,and 42.5%.When compared to the specimens with a concrete strength grade of C30,the strengthened specimens with three different axial compression ratios showed an increase in the lateral load-carrying capacity of 20.5%,23.7%,and 21.0%.(4)For the specimens having a low concrete strength grade,the effectiveness of the local strengthening method using MRPC becomes more pronounced in those ones with larger axial compression ratios.(5)The strengthened specimens using MRPC exhibited a significant improvement in the seismic performance which was better than the original design.In conclusion,the local strengthening method using MRPC can significantly improve the seismic performance of shear walls and is an effective technique for shear wall strengthening.After a preliminary research on the seismic performance of strengthened shear walls with local replacement using MRPC,this study offers design guidelines for the rational retrofitting of shear wall structures in practical engineering applications.Furthermore,it provides a theoretical basis for further exploration of the seismic performance of strengthened shear walls using MRPC. |
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