SHEAR CHECK FOR RETAINING WALLS

Shear check for retaining walls

The check sections of the stem and footing of retaining walls are verified to shear without transverse reinforcements to shear (brackets, pins, bent bars) in general for massive structures but also for the purpose to simplify the execution on site. The computation of the shear check is based on the following:

(1) V_Rd ≥  V_Ed  

The shear resistance V_Rd is as follows:

(2) V_Rd = {0,18 ∙ k ∙ (100 ∙ ρ_l ∙ f_ck)^1/3 / γ_c  + 0,15 ∙ σ_cp} ∙ b_w ∙ d   ≥  ( v_min + 0,15 ∙ σ_cp) ∙ b_w ∙ d

In essence the shear strength depends strongly on the effective height d of the section, but also on the concrete class f_ck and the rate of tensile longitudinal reinforcement to deflection ρ_l = A_sl /b_w ∙ d. In our case it is marginal or null the increment of the normal stress constituted by the term  0,15 ∙ σ_cp .

The software MDC makes a first sizing of the bending reinforcements obtaining an initial value for ρ_l.

If applying (2) the correspondent shear strength V_Rd  does not satisfy (1) further bending longitudinal bars are added increasing ρ_l until a maximum of 1% (ρ_l = 0,01). If with the 1% of tensile reinforcement the section is not verified to shear it is necessary to proceed with the increase of the effective height d of the section and/or to the use of a concrete with a higher characteristic resistance f_ck.

Generally the increase of the number of tensile longitudinal bars occurs only in restricted areas that are in proximity of the convergence node of the stem with the foundation. If in these area the shear check is positive, the designer should consider a significant difference between the design moment and the resistant moment (sign of a significant increase in the tensile longitudinal bars), might consider appropriate to increase, by own judgement, the transverse dimension d of the element in question (and/or use a higher class concrete) in order to reduce the above mentioned increment.