Check compression strut

The internal forces which are calculated in direction of concrete strut have to be also checked. The internal forces in direction of concrete strut have to be carried by the concrete.

The of depth of the compression zone will be calculated for each surface as  average values from depth of compression zone for statically required reinforcement from both directions :

x_c,_avg± = 0.5*(x_c,1± + x_c,2±)

where

xc,1±	depth of the compression zone calculated from statically required reinforcement in the first direction
xc,2±	depth of the compression zone calculated from statically required reinforcement in the second direction

Design value of resistance of concrete compressive strut is calculated according to formula:

where

Acc±	the compression area at upper(lower surface)  Acc± = xc,avg±∙1m
h	it is coefficient for reduction design compressive strength of the concrete from concrete setup, see chapter "General"
Redfcd	coefficient for reduction strength of the concrete in compressive concrete strut from concrete setup, see chapter "General"
fcd	design compressive strength of concrete

Check compression strut is fulfilled, if  the conditions below is fulfilled:

n_Ed,sc+ ≤ n_Rd,sc+ and n_Ed,sc- ≤ n_Rd,sc-

with unity check

If conditions below is not fulfilled (it means UC > 1), the calculation finishes with error E0/1. The check of compression strut is done only, if:

• statically required reinforcement is designed in both directions (A_s1± > 0 and A_s2± > 0)
• the depth of compression zone is nonzero (x_c,_avg± > 0)

Otherwise, check of compression zone is not necessary and calculation finishes with note N0/3