# Structural Behaviour of Aluminium-Timber Composite Beams with Partial Shear Connections
## 1 Introduction  
Aluminium and timber have a lower number of applications in civil engineering than in steel and concrete. Due to a new trend--sustainability in construction--new applications of these materials may gain in popularity. Both aluminium and timber have high strength-to-weight ratios. Aluminium is corrosion resistant and recyclable whereas timber is fully renewable and largely recyclable [1, 2]. Aluminium elements are often extruded, which makes it possible to obtain any cross-section [3]. Recently, it has been demonstrated that aluminium can be combined with magnesium in one composite material to enhance the desired properties of both metals such as the strength-to-weight ratio [4, 5]. Timber is produced in a wide range of shapes [6]. Furthermore, new engineered products made of wood such as laminated veneer lumber (LVL) [7], glued-laminated timber (glulam) [8] and cross-laminated timber (CLT) [9, 10, 11] have made it possible to overcome the size limitations of sawn timber. The use of engineered wood products also reduces the impact of naturallyoccurring wood defects (e.g., knots) [12]. Timber structural elements are easy to reinforce (e.g., by using glued wood-steel joints, glued wood-wood joints or carbon fibre reinforced polymer tapes) [13; 14; 15; 16; 17]. Aluminium and timber can be used together in one structure. Aluminium-timber composite mullion was developed by [PERSON] et al. for building facades [18]. In this solution, timber was used to improve the thermal performance of facade systems. Aluminium girders and timber slabs can be joined to obtain light composite floors. The lightness of this type of floor may speed up the construction process. The cooperation of timber slabs and aluminium girders eliminates stability problems (i.e., the local buckling in aluminium girder cross-sections and the lateral buckling of aluminium girders, in the case of simply supported beams). Slabs of aluminium-timber composite beams can be made of plywood, laminated veneer lumber or cross-laminated timber. Slabs and girders can be joined with self-drilling screws and adhesive epoxy materials [19], hexagon head wood screws, or bolts [20; 21; 22]. Adhesive epoxy materials should be used together with screws to avoid slab separation from girders at the high load value. This failure mode was observed at the ultimate load in the tests of steel-concrete composite beams with an adhesive material used as shear connection, as conducted by [PERSON] [23]. The load-bearing capacity of aluminium girders increases significantly when they are joined with timber slabs (e.g., the load-bearing capacity of the unrestrained aluminium girders increased 6.3 times when they were attached to LVL slabs using screws) [24]. [PERSON] and [PERSON] demonstrated that it was possible to use screws or bolts as shear connectors to obtain composite beams with full shear connections [25; 26]. An important advantage of these connectors is that they are demountable. The authors conducted four-point bending tests and investigated the failure load, mode of failure, load versus deflection, and load versus slip responses of the aluminium and timber composite beams. The shear resistance and stiffness of the bolted and screwed connections were studied in the accompanying push-out tests. The analysed connections were ductile and flexible. A theoretical method to calculate the load-carrying capacity of aluminium-timber composite beams with full shear connections was suggested and verified against the experimental results. The stress block method for steel-concrete composite beams from the EN 1994-1-1 standard [27] was improved to take into account the timber subjected to tension. However, some problems connected to aluminium-timber composite beams remain to be solved. The suggested connections are flexible. In the case of flexible connections, the slip between the girder and the panel is not negligible and its influence on the ultimate load and the stiffness of a composite beam should be evaluated [28; 29; 30].