Cross laminated timber walls with glued-in ultra-high-performance concrete lamellas

The combination of ultra-high-performance concrete with timber results in a novel high-performance composite material that appears promising for use in multi-story building construction. The intention is to replace single- or multiple- timber lamellas in the core layer of cross laminated timber wall elements with prefabricated ultra-high-performance concrete lamellas. Hereby the load bearing capacity of cross laminated timber walls is increased, and the cross-section is optimized according to local load concentrations. This paper describes the two-step development process of these structural elements. First, the feasibility of bonding timber to ultra-high-performance concrete was investigated with small scale shear-, delamination-, and bond tests. Second, centric and eccentric load bearing tests were performed on wall segments with composite cross section. During the tests, strains and the horizontal deflections were measured and compared with calculated values. For the calculation, the differential equation for theory of second order problems was solved with an effective bending stiffness based on the shear analogy method. Based on the results of the small-scale tests, it seems feasible to bond timber to ultra-high-performance concrete with adhesives used in standard cross laminated timber production and the connection may be considered rigid. The centrically loaded wall samples exhibited elastic buckling behaviour and the eccentrically loaded samples mostly exhibited a ductile load bearing behaviour where the outermost timber lamella showed compression failure. The calculated deflections and strains show good correlation with the measured test values.