Experiment Research Of Masonry Wall’s Double Underpinning Structure’s Mechanical Performance

With country economy and people living standard continuous improve, the urban construction are speeding up. But problems appeared at the new city construction, old city reconstruction and road widen, such as the contradiction between new buildings and adjacent buildings. In order to solve these contradictions, protect those excellent ancient buildings’ historical valuation and cultural valuation, people began to use overall building translation technique.The underpinning structure is the core link in the process of building translation, it also determines the success of translation. In the ancient times, masonry structure accounts for a large proportion, and most of the buildings have been build for a long time. Because of masonry structure buildings’ poor integrity and poor Seismic performance, the underpinning design of masonry structure becomes particularly difficult, so the study of composite masonry structure is important.This experiment takes beam height and longitudinal reinforcement into consideration, design nine 1:1 full scale specimen. The specimens’design and construction, also the strain gauge’ paste and dial indicator’ placement should meet the test purpose and requirements. This experiment using one 200t hydraulic jack to supply the static load,Each grade provide 50 Kilonewtons, and keep the load for three minutes each additional level, when the dial indicator reading stay unchanged,exert the next level loads until the underpinning beam or joint surface come to damage. During the experiment, we should observe the phenomenon, including the crack position, crack length, crack width and crack spacing, take steel and concrete strain value, record the dial indicator reading. At last draw the load-strain curve and load-displacement curve.Through experiment analysis and study, we can easily come to the following conclusions. First, the 200 and 300 millimeter beam height specimen occur the joint surface punching shear failure, the masonry wall rushed out suddenly and come to brittle failure, combined with experiment data and masonry specification, we can come to the experience formula of the punching shear bearing capacity of joint surface; the 400 millimeter beam height specimen occur underpinning beam failure or local wall bearing failure. Second, with the beam height increase, the specimen failure pattern and force mechanism is more close to the wall beam. This experiment concluded that the premise of occur wall beam failure is that the beam height should be equal or greater than 400 millimeter, also beam height is the main factor to affect specimen failure pattern and bearing capacity. Third, in the whole loading process, the height of underpinning beam’ compressive zone is small and the longitudinal reinforcement is in tension state, when specimen come to failure, the virtually crack run through cross section and distributed uniformly.