Research On Seismic Performance Of UHPC-strengthened Masonry Walls In Historical Buildings

Masonry walls are the one of the major load-bearing members in many architectural heritages.With the long-term load and environmental effect,the shear resistance,rigidity and energy dissipation capacity of these walls have become weakened in varying degrees.Therefore,strengthening of historical building masonry walls is critical for heritage reservation.Currently,bar-mat reinforcement cement mortar and polymer mortar are mainly used for the strengthening of historical building masonry walls.Compared with the previous ones,Ultra-High Performance Concrete is a higher-strength material,which may have more advantages on the strengthening.In order to study the strengthening effect of the UHPC on historical building masonry walls,the dissertation designed the experiment.Three pieces historical building masonry walls in low strength were designed and produced with the bricks and mortar obtained from the historical building site.One piece was not strengthened as confrontation,but the single side of another two pieces were strengthened.The single side of comparative wall was strengthened with the 40 mm thick UHPC after the destruction in the experiment,another two pieces were strengthened with 40 mm UHPC and 50 mm polymer mortar respectively.The strengthening effect of UHPC to the historical building masonry walls was studied from the aspects of hysteretic curve,horizontal bearing capacity,rigidity and energy dissipation.The following conclusions were made:(1)The UHPC can strengthen the historical building masonry walls with severe damage.Compared with the wall before strengthening,the UHPC improved the wall's bearing capacity by 147%,the total area of the hysteresis loop by 120%,and the ultimate deformation by 113%.The UHPC can fill internal damage of wall and form a new entirety with the wall.Therefore,it indicates that the UHPC can be used for strengthening historical building masonry walls with severe damage and the performance of the walls strengthened by UHPC was great.(2)The historical building masonry walls which was strengthened with UHPC was slipped and damaged on the bottom mortar in the action of horizontal and vertical load,but the UHPC did not separate from the walls,which indicates that the UHPC did not fully exert the strengthening effect.The weak part of the bottom of the wall bore the maximum shear force and bending moment,and the UHPC was not fixed to the foundation.The bearing capacity of the strengthened walls were affected by the strength of the original brick and mortar.Therefore,the nodes should be fully fixed to prevent the walls from being damaged early at the weak bottom when using the UHPC.(3)Compared with the historical building masonry walls strengthened by steel mesh polymer mortar,the wall strengthened by the UHPC improved the wall's bearing capacity by 57%,the ultimate deformation by 13% and the ductility by 94%.The construction of the UHPC without steel mesh would not cause second damage to the walls.Because of the small thickness of the UHPC,new strengthening materials can be directly applied on the top of the UHPC layers in the future.The UHPC has more advantages than steel mesh polymer mortar in strengthening the historical building masonry walls.In conclusion,the UHPC can be used to strengthen historical building masonry walls with better effects than steel mesh polymer mortar.It can provide a certain reference for engineering.The dissertation proves the feasibility of UHPC in strengthening the historical building masonry walls,which can make further study on the strengthening effect of UHPC to the historical building masonry walls from the aspect of structure.