Performance Based Strengthening And Repairing Study For Masonry Structures

There are massive existing old masonry buildings over the country, which have no or insufficient seismic fortification measures. To avoid serious damage under earthquakes, it is thus necessary to enhance these buildings. In recent earthquakes, such as Wenchuan and Lushan earthquakes, many masonry structures were damaged seriously, but not collapsed.It needs to be answered whether these buildings are able to be repaired, how to repair, and what’s the seismic performance after repair, and there’s nothing to refer to. This paper, within the framework of performance-based seismic engineering, proposes the enhancement and retrofitting techniques for typical Chinese masonry residential buildings, and evaluates the seismic performance through quasi-static tests. Major contents are as follows:1. The quasi-static test was conducted on a full-scale two story masonry building enhanced by use of post-tensioned rebars. The post-tensioned stress is determined as 20% of the design compressive strength of the masonry assembly, which is supposed to advance the shear strength capacity while not result in compressive shear failure. The enhancement progress, loading scheme and measurement were introduced in detail. The damage level of the masonry building was analyzed and evaluated finally.2. The enhanced masonry building was analyzed by a sophisticated finite element model and a macroscopic model. MSC. Marc and OpenSEES were used respectively. The sophisticated model employs a continuum modeling method and a plastic damage material model to reproduce the damage progress, while a shear spring was adopted to represent a piece of wall in the macroscopic model where the skeleton curve is determined by use of recursive parameters from 56 existing experiments of masonry walls strengthened by post-tensioned rebars. Both models provide similar results as those obtained from experiments.3. The quasi-static test of masonry structure without enhancement was conducted to provide a reference to the enhancement effect. In the first round test, the damage of the second story was found very limited. It is thus treated as the building without enhancement by adjusting the post-tensioned stress. Steel beams were used to fix the first story, while three actuators were used to load the second story quasi-statically. By comparison, it is observed that the post-tensioned rebars can improve bearing capacity of structure by two times and significantly advanced the energy dissipation capability.4. Performance based retrofitting study on masonry structures. After the damage assessment, the repairing goals are determined by costs, construction period and bearing load.This paper chooses supplement constructional column and reinforced cement mortar plasters to repair the damaged structure. By quantifying costs and construction period of the repair process, it is derived that the reinforced structure save costs and reduce construction period by contrast of the new construction. Through quasi-static tests, it is concluded that the peak strength of the reinforced structure is about 2.84 times as much as that of the unreinforced structure, and about 1.32 times as much as that of the reinforced structure by post-tensioned rebars. It satisfies all the pre-determined retrofitting objectives.