Effect of web openings on timber composite beams: Testing and analytical modelling

Abstract

This study aims at evaluating effect of the web openings on the structural behaviour of the timber-timber-composite (TTC) beams. In total, twenty-two TTC beams (in eleven groups with two replicates of each group) were fabricated by connecting the CLT slab to laminated veneer lumber (LVL) or glued laminated timber (GLT) beams (webs) with or without openings. Effect of shape (square or circular) and size of the openings in the web, timber beam type (LVL or GLT), size of shear connectors (8- or 12 mm coach screws), continuity/discontinuity of the CLT slabs on the service stiffness, load carrying capacity and failure modes of the TTC beams were evaluated experimentally. Results of the tests were compared with additional bending tests performed on bare timber beams (without slab) to demonstrate effect of the slabs and coach screw shear connectors on the failure mode and peak load of the TTC beams with web openings. Lastly, an analytical solution to a Timoshenko composite beam was utilised to determine the distribution of shear force and bending moment between the timber slab and joist (web) and accordingly develop a mechanistic model for predicting the load carrying capacity of the TTC beams with web opening (and reinforcing effect of the screw shear connectors).