Minimum clamping reinforcement across construction joints in walls of DCH

An additional requirement for DCH walls is to provide across all construction joints clamping reinforcement at a minimum ratio:


where NEi is the minimum axial force from the analysis in the seismic design situation (positive when compressive). Equation (D5.50) is derived from the requirement that the combination of cohesion, friction and dowel action at such a joint is not less than the shear stress that may cause shear cracking at a cross-section nearby. According to Eurocode 2, cohesion and friction provide at a naturally rough, untreated interface between concretes cast at different times a design shear resistance equal to

-Pvfy yd

where /ctd =/ctk 0 Q5/jc = 0.7/ctm/7c is the design value of the tensile strength of concrete and pv the ratio of wall vertical reinforcement providing clamping at the interface. It may be assumed that at the displacements associated with the shear resistance given by equation (D5.51), 50-60% of the design shear resistance due to dowel action may be mobilized as well. As for a single bar of diameter dbL, this latter shear resistance is equal to 1 -3<ibL2(/,d/cd)l/2, dowel action may be considered to add to the right-hand side of equation (D5.51) the term 0.9pv(fydfcd)m. The so enhanced design shear resistance of the interface should not be less than the shear stress causing concrete cracking, which, for pure shear conditions, o-j = -<7n = r, and the linear biaxial strength envelope for concrete between al =/cl and au = -fck ~ -10/cl, is equal to rcr = 0.9/ct. Taking, for simplicity, rcr= 0.9/ctd, gives equation (D5.50) for the minimum ratio of clamping reinforcement across construction joints.

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