Experimental and numerical study of long-term behaviour of timber-timber composite (TTC) connections

Abstract

Long-term sustained load (push-out) tests under an indoor uncontrolled environment were conducted on twelve specimens (in seven groups/types) of Timber-timber composite (TTC) joints with up to two identical specimens of each TTC joint type. The TTC joints were fabricated by connecting either Laminated veneer lumber (LVL) or Glued laminated timber (GLT) joists to Cross laminated timber (CLT) slab panels. Types of joists (LVL and GLT), size of coach screw shear connectors, type of shear connection (screws with or without adhesive) between the joists and CLT slab thickness and orientation (i.e., lengthwise, or crosswise) with respect to the loading direction were the main variables in the experimental program. The laboratory tests revealed that the creep coefficient after 420 days is in the range of 1.05 to 3.90 and the CLT slab orientation has minor and CLT thickness has major influence on the creep coefficient of TTC joints (for a given service load over loading capacity ratio). A creep model was calibrated against the experimental slip-time curves and the model was used to predict the creep coefficient for the 50-year design life of the structure. It was shown that more than 50% of the creep in the TTC joints occur in the first year of loading. Additionally, a 3D coupled Finite element (FE) model implemented as user defined subroutines in ABAQUS/Standard was validated against the long-term test results and accordingly input parameters for coupled long-term FE analysis of the LVL-CLT and GLT-CLT joints (with screw shear connectors) are recommend. The validated FE model was used to further confirm effect of the CLT panel thickness and orientation on the long-term slip-time and creep coefficient of the TTC joints.