Various stresses in jointed plain concrete pavement slab of size 3.5 m x 4.5 m are denoted as follows:
Wheel load stress at interior = Sⁱ_wl
Wheel load stress at edge = S^e_wl
Wheel load stress at corner = S^c_wl
Warping stress at interior = Sⁱ_t
Warping stress at edge = S^e_t
Warping stress at corner = S^c_t
Frictional stress between slab and supporting layer = S_f
The critical stress combination in the concrete slab during a summer midnight is _______.