Hybrid cross-laminated timber plates with beech wood cross-layers

A hybrid, three-layered, softwood-hardwood cross-laminated timber build-up with outer layers of European spruce (Picea abies) and a center cross-layer of European beech (Fagus sylvatica) has been investigated with regard to out-of-plane bending. The determination of the rolling shear properties of the beech cross-layer performed by different test and measurement methods comprising bending and compression shear tests was of primary interest. The shear capacity of the composite is significantly influenced by the spruce longitudinal shear strength at the beech-spruce interface. The characteristic values of rolling shear modulus and strength of the beech cross-layer from the bending tests were Gr,mean = 350 N/mm2 and fv,r,05 = 2.6 N/mm2, respectively. Direct strain gauge measurements and compression shear tests resulted in 10-20% higher values. The high rolling shear properties render the shear lag implications of the softwood CLTs to a negligible quantity. The hybrid build-up can be designed as a rigid composite with small error versus a more exact analysis. The novel investigations reveal the great potential of mixed softwood-hardwood CLT build-ups for structural elements in the building sector.