Experimental Research On Mechanical Properties Of Timber Structural Members With Shrinkage Cracks In Historic Buildings

As a kind of building material, the lumber has been widely used in the traditional historical architecture, the ancient settlement of existing mostly are timber structure building. However, due to the unique anisotropic characteristics of lumber, the timber structure is easy to be affected by temperature and humidity, and the longitudinal shrinkage cracks are commonly observed especially in the historical building. Therefore, it’s of great significance to study the structural behavior of timber structure with longitudinal shrinkage cracks for the purpose of evaluating its safety.In order to study the influence of longitudinal shrinkage cracks on the mechanical properties of wood, the experiments on eight timber columns of the circular section with different crack size subjected to axial compression and the experiments on eight timber beams of the rectangular section with different crack size in bending were conducted. Test results show that:the specimens with deeper longitudinal shrinkage cracks exhibited smaller load carrying capacity and when the crack depth reaches 64% of the timber column diameter, it would reduce the axial compression bearing capacity by 20%.Longitudinal shrinkage cracks on the influence of wooden beams flexural bearing capacity is to change the bearing capacity calculation control condition. The cracks could weakened the shear area parallel to grain, with the increase of crack depth, wooden beams flexural bearing capacity calculation control condition by bending control would change into shear control. In this paper, a crack limit indicators calculation method was proposed to consider the longitudinal shrinkage crack on the influenced of wooden beams flexural bearing capacity. When the crack depth is equal to the limit value, wooden beams’ bending strength and shearing strength run out at the same time; When the crack depth is less than the limit value, the flexural bearing capacity is controlled bending control conditions, so the influence of the crack can be ignored; When the crack depth is greater than the limit value, wooden beam bending control condition would change to the shear bearing capacity, and it’s time to consider the influence of the cracks.With the aid of the finite element software ABAQUS, numerical simulation is carried out to investigate the effect of longitudinal shrinkage cracks on the mechanical performance of timber structural components. By comparing the numerical simulation data and test results verify the correctness and reliability of the finite element model so that it can be used to study the complex parameters of longitudinal shrinkage cracks.According to the results of numerical simulation on longitudinal shrinkage crack of wood mechanical properties analysis, the component bearing capacity reduction coefficient was two times polynomial relations the relative crack depth and the relative crack length, was linearly correlated with the width of crack, and when crack width is less than 3mm, the effects of longitudinal shrinkage cracks can be ignored. A model for calculation of load carrying capacity of wood columns with longitudinal shrinkage cracks was proposed. By comparing the results of the formula and test values, the correctness of the calculation method is verified.