The load-carrying capacity of the composite material reinforced concrete lies in the ability of the concrete to resist (primarily) compressive forces and of the reinforcement to resist tensile forces after cracking of the concrete. Research on reinforced concrete under the influence of fluctuating loads, however, indicates that the integrity of both materials as well as their interaction through bond [1] deteriorates under repeated loading. The CEB state of the art report [2] provides an insightful overview of previous work on this phenomenon of fatigue of structural concrete. Concrete members subjected predominantly to cyclic flexural loading typically exhibit increases in the width of existing cracks through a progressive deterioration of bond; disproportionally large deflections result and failure ensues through rupture of individual reinforcing bars or spalling of the concrete in the flexural compressive zone [3]. This failure mode has been observed in numerous experimental investigations [4–۶]. Fehlmann and Vogel [7] investigated the fatigue performance of a typical frame type bridge in a large-scale test with the prescribed fatigue load model according to the current Swiss standard [8]. Virtually no changes in the load-carrying response, apart from the formation of some new cracks, was observed during approximately 90% of the fatigue life. Fatigue damage to the structure remained mostly undetected by conventional methods until shortly before failure. Furthermore, some investigations have shown that concrete members subjected to cyclic loading can exhibit different failure modes to those predicted under static loading. Chang and Kesler [9] conducted a large number of tests on beams in which specimens failed in flexure under static loading and due to fatigue shear modes under cyclic loading. It is currently neither possible to establish the present state of damage in a structural concrete member, nor to predict the remaining fatigue life for future loads [7]. The deck slabs of concrete bridges have been identified to be susceptible to fatigue [10]. Slabs are in direct contact with the wheel loads of heavy vehicles and typically exhibit small ratios of own weight to live loads. A numerical investigation of the stress range in various bridge cross-sections under traffic loads indicates that particularly the transverse deck slab direction at the cantilevers and between the webs is fatigue critical in the absence of prestressing [11]. Due to the highly statically indeterminate nature of slabs and considerable capacity to redistribute stresses, loads are resisted through combinations of bending and torsional moments. Such bending action is typically resisted by layers of finely spaced reinforcing steel bars in an orthogonal layout. As a result, the direction of principal moment will deviate from the reinforcement directions under certain loading and support conditions. A scarcity of experimental data considering the fatigue performance of slabs under clearly defined combinations of bending and torsional moments prompted the tests described in the present paper.