Experimental Study On Shear Behavior Of Concrete Block Masonry In Bed Joints

Masonry construction has a long history worldwide, which makes a great contribution to human reproduction and cultural heritage. However, the shortcomings of traditional unreinforced masonry, such as brittle characteristics, lack of tensile capacity and shear capacity, especially easy to collapse under earthquake, are the obstacles when its application in seismic region. Under the circumstance of promoting the industrialization of low-rise concrete masonry building in villages and small towns, the present paper mainly studies basic mechanic properties of concrete block masonry under direct shear in bed joints as prescribed by the test standard, and this is to supply technical support for code revision and engineering applications.An experimental research under direct shear in bed joints was carried out on 24 groups of block masonry, including 36 hollow specimens and 36 grouted ones. The influence of masonry mortar strength, grouted concrete strength, loading method and axial compression was analyzed and the basic mechanic property parameters such as failure mode, shear strength, cracking strength, peak displacement and ideal loaddisplacement curve were obtained. In addition, studies on 8 groups compressed block masonry, including 15 hollow specimens and 9 grouted ones, were also completed with the purpose of obtaining compressive strength, elastic modulus and Poisson’s ratio.The results showed that the measured elastic modulus of concrete hollow block masonry was larger than the value suggested by the current Code for Design of Masonry Structures. The calculated shear modulus with compression test results was similar to that got through experiments of direct shear in bed joints. The different loading methods had a direct influence on test results of shear strength. The level of axial compression could improve shear strength, peak displacement and ductility of grouted block masonry. Due to the un-compatible deformation between mortar and grouted concrete, the mortar would crack and fail to resist shear stress before peak strength, which made the grouted concrete bear the shear load. This phenomenon explained the reason of the un-conservative shear strength prediction by entirely considering contributions of mortar by the current design code. The grouted masonry had a high stiffness before the crack of mortar layers, and stiffness degradation were also observed after cracking. The crack strength had a positive correlation with mortar strength, grouted concrete strength and axial compression.Based on the analysis of experimental results and collecting literatures, a fitting formula for calculating masonry shear strength made by concrete solid brick, perforated brick and hollow block is obtained, which considering the influence of void ratio. As the value of coefficient of friction suggested in the current code is not suitable for hollow block masonry under low axial compression ratio, it was suggested according to present study. In addition, the influence of axial compression on shear capacity show large discrepancy between test specimens and grouted masonry walls. The calculation formula for coefficients of residual shear strength on prestressed hollow and grouted masonry is obtained by statistical analysis of test data, and the fragment expressions of normalized load-displacement curves are fitted well with the deformation properties of prestressed hollow, grouted and prestressed grouted masonry under direct shear in bed joints.