# Structural Behaviour of Aluminium-Timber Composite Beams with Partial Shear Connections
## 1 Introduction
The bolted shear connections were classified as brittle because the value of the characteristic ultimate slip was below 6 mm. [PERSON] [48] investigated two types of demountable shear connectors that can be applied in precast steel-concrete composite bridges. Locking nut shear connectors and friction-based shear connectors had an important advantage--they facilitate replacing concrete slabs in the steel-concrete composite bridge. [PERSON] et al. [49] pointed out that demountable connectors should be replaceable due to the fact that damage of the connector tread could occur during transportation. If the connectors are not replaceable and they are damaged during transportation, not only the connectors but also the concrete slab is lost. For this reason, the authors demonstrated two shear connection types (the coupler system and the cylinder system). The initial stiffness of the systems was high (i.e., 70-100 kN/mm in the case of the coupler system and 250-500 kN/mm in the case of the cylinder system). Demountable connectors were not only suggested for steel-concrete composite structures, but they were also applied in steel-timber composite structures and aluminium-timber composite structures. In the case of steel-timber composite structures, several types of demountable connectors were analysed (i.e., screws [50; 51], bolts [52; 53], and bolted shear connectors embedded in the grout [54]). Bolted shear connectors embedded in the grout had high ductility and energy-dissipating capacity when an adequate edge distance between the bolted shear connectors and the edge of the grout pocket in the timber slab were provided. In the case of aluminium-timber composite structures, similar demountable connectors were investigated (i.e., screws [25; 55; 56; 57], bolts [26], screws with toothed plates [58], and bolts with toothed plates [59]). A comparison of the bolted and screwed connections was presented in [59]. In the case of both types of connections, the increase in the fastener diameter provided for the increase in the connection strength and its slip moduli. The bolted connection had a lower slip modulus \(k_{0.6}\) than the screwed connection due to the hole clearance. The bolted connections had an 80% higher shear strength than the screwed connections. The structural performance of the composite floors significantly depends on the shear connection as it provides composite action. Recently conducted theoretical, experimental, and numerical investigations have focused on aluminium-timber composite beams with almost full shear connections. However, experiments on aluminium-timber composite beams with partial shear connections have not yet been conducted. In this paper, the composite action in composite beams with different screw spacing was studied. The analysed elements comprised aluminium beams and timber slabs to form T-shaped composite beams. Ten mm hexagon head wood screws were used to combine the composite beam components. Four-point bending tests were conducted on composite beams with different screw spacing. The degree of composite action was calculated taking into account the shear resistance of connectors investigated in the previous push-out tests. The method used for the steel-concrete composite beams with partial shear connection was adopted to estimate the load bearing capacity of the investigated aluminium-timber composite beams. The accuracy of this method was evaluated by comparing the results from the theoretical analysis with the results of three experiments. In addition, four numerical models of the composite beams were developed.