Embedment Analysis of Lag Screw Connections in Timber Concrete Composite (TCC) Slab

Lag screw connections in timber-concrete composite (TCC) slabs are evaluated with respect to the embedment depth using push-out-shear tests. Nine different trials are performed on embedment depths of 5.08 cm, 7.0 cm, and 8.9 cm. The specimens are studied to observe the modes of failure, and to develop a good understanding of the effect of embedment depth on TCC slabs. Then, wood crushing fiber strength is evaluated at 6.6 cm and 7.0 cm embedment to analyze the wood fiber crushing load, yielding of lag screws, and modes of failure of lag screw. A study of the relationship observed between the embedment depth and shear capacity of TCC slabs demonstrated that there is a clear increase of shear strength between 5.08 cm and 7.0 cm, but no significant changes between 7.0 cm and 8.9 cm. The wood crushing fiber strength results showed that the experimental fiber strength can be as much as twice the theoretical values. Based on the study outcomes, it is strongly recommended that the penetration depth of the lag screw into the timber specimen should be at a minimum of 7.33d (d=diameter of the lag screw). Multiplying the diameter of the lag screw by this factor would provide the required embedment depth to resist the applied loads with lower deflection and displacement of the lag screws. Based on the work done in this research, TCC behavior could be governed by three constraint limits: Double bending of lag screws, bearing strength of concrete on lag screw, and wood crushing fiber strength. As the connection goes through each of these modes successively, each lag screw with an embedment of 7.0 cm could safely uphold loads of 12,704 N.