As with the verifications for shear resistance, punching shear verifications for reinforced and pre-stressed concrete structures in nuclear installations must be conducted to DIN 25449 [15]. Under these verifications, which are also based on DIN 1045-1 [54], punching shear reinforcement is required if, along the critical circular section to DIN 1045-1, the shear force vEd to be absorbed per unit of length is greater than the shear resistance vRd, i. e. if:

vEd > vRd;ct

Shear resistance vRdct is obtained from DIN 1045-1. Like VRdct, vRdct reflects the different requirement categories A1, A2 and A3 by a factor (cf. Section 6.3.2: 1.0 for A1, 1.15 for A2 and 1.50 for A3).

To find the punching shear reinforcement required, we distinguish between

— structural members subject to indirect effects of action, as covered in DIN1045-1 (e. g. supports in slabs or foundations), and

— structural members subject to direct effects of actions, as they occur in nuclear engineering construction as structural members subject to extraordinary actions in requirement categories A2 or A3, such as airplane crash or jet forces.

The reinforcement of structural members subject to indirect effects of actions must be obtained to DIN 1045-1. Should no more precise calculation and design procedure be used, the reinforcement required for structural members subject to direct effects of actions may be calculated in accordance with DIN 25449, which is based on DIN 1045­1 and additional experimental studies. The upper bound vRd, max to DIN 1045-1, which is intended to prevent the concrete cover palling at column faces, is irrelevant here, although the concrete strut resistance must be verified to ensure that the stirrup reinforcement is activated, i. e.

VEd ^ VRd, max = °-25 ‘ fcd ‘ uload ‘ d (6.11)

Where

fcd is the design value of concrete compression strength [N/mm2]; fcd = fck/gc (gc in

Table 6.2)

uioad is the circumference of the load area Aload (equivalent circle with radius Rioad; see Figure 6.1)

d is the static effective depth of the flexural reinforcement of the side facing away from the load in the cross-section considered

In calculating the punching shear reinforcement, the decisive shear force VEd is taken as the maximum load resulting on the load area Aload. The verification may assume as the failure figure a punching shear cone with an effective surface area Acw = p x (rL — rn) and angle of inclination of the punching shear cone fir (generally cot fir = 1.25) (Figure 6.1).

For the reinforcement, it must be shown that the relationship

VEd < VRd, sy (6.12)

is satisfied.

The design value for the required shear force reinforcement VRd, sy consists of a contribution of concrete load-bearing VRdc (with the contribution of longitudinal reinforcement) and a contribution of punching shear reinforcement, i. e.

VRd, sy VRd, c T ks ‘ Asw ‘ ftd (6 13)

= [cd • 0.17 • k • (100 • P!)1/4 • f^k^3] • d • uex + asw • ks • Acw • ftd

Where

(average useful height in mm) cd Prefactor reflecting requirement category

Pi Degree of longitudinal reinforcement in tension area