Deep beams with web openings - Reinforced Concrete Deep Beams - page 83

Figure 3.14 Stress-block for flexure strength of deep beams (mid-section) (Ray, 1980; 1982; 1985).

where F s is total force in tensile steel, F wt is total force in web steel below
NA, A wt is sectional area of individual web steel below NA, F ct is total force
of concrete in the tensile region, f r is modulus of rupture strength of
concrete, C is total compressive force and K parameter as defined in Figure
3.14. From statical equilibrium of forces, we obtain
C = F ct + F s + F wt
on substitution of the values of equations in 3.26 into Eqn 3.27 and solving
for K we obtain

(3.27)