Experimental analysis and structural modelling of the punching behaviour of continuous two-way CLT flat slabs

摘要

A newly developed bonding technology makes it possible to rigidly connect timber elements parallel to the grain. This technology allows to build two-way and point-supported flat slabs in cross-laminated timber (CLT). In such a structure high loads have to be transferred from the slab into the columns. This paper presents punching tests on different CLT plates. The results of these tests allow for a better understanding of the important parameters of a point-supported CLT slab and should help create the basic design criteria for these connections. To transfer vertical forces from higher storeys through the CLT slab without subjecting it to stresses perpendicular to the grain, the columns are directly connected to each other through an opening in the slab. Even though the opening leads to a stress concentration in the CLT plate, the rolling shear failure was the governing failure mode during the tests. With numerical models the behaviour of the tested plates was simulated and the strains around the opening were calculated. The results show good correlation with the measured strains. After the punching tests, every plate was cut in cubes and the visible failures were recorded. In addition, material samples were cut out of the plates and tested to determine the rolling shear strength of single boards. The achieved shear resistance in the punching tests was 1.4 times higher, than the rolling shear strength determined in shear tests on single boards would allow. An additional rolling shear test series showed that an anchoring effect contributes to the increased rolling shear resistance in punching tests. The results of the punching tests confirm the potential of CLT slabs to be used as biaxial, continuous, point-supported floor slabs.