CIVIL ENGINEERING FORMULAS

CONCRETE FORMULAS 149

whereVutotal design shear force
capacity reduction factor0.85
d0.8lw
hoverall thickness of wall
lwhorizontal length of wall

The shear Vccarried by the concrete depends on whether Nu, the design axi-
al load, lb (N), normal to the wall horizontal cross section and occurring simul-
taneously with Vuat the section, is a compression or tension force. When Nuis
a compression force, Vcmay be taken as , where is the 28-day
strength of concrete, lb/in^2 (MPa).WhenNuis a tension force, Vcshould be tak-
en as the smaller of the values calculated from

(5.113)

(5.114)

This equation does not apply, however, when Mu/Vu lw/2 is negative.
When the factored shear Vuis less than 0.5Vc, reinforcement should be
provided as required by the empirical method for bearing walls.
WhenVuexceeds 0.5Vc, horizontal reinforcement should be provided with Vs
Avfyd/s 2 , where s 2 spacing of horizontal reinforcement and Avreinforcement
area. Also, the ratio hof horizontal shear reinforcement to the gross concrete area of
the vertical section of the wall should be at least 0.0025. Spacing of horizontal shear
bars should not exceed lw/5, 3h, or 18 in (457.2 mm). In addition, the ratio of vertical
shear reinforcement area to gross concrete area of the horizontal section of wall does
not need to be greater than that required for horizontal reinforcement but should not
be less than

(5.115)

wherehwtotal height of wall. Spacing of vertical shear reinforcement should not
exceedlw/3, 3h, or 18 in (457.2 mm).
In no case should the shear strength Vnbe taken greater than at
any section.
Bearing stress on the concrete from anchorages of posttensioned members with
adequate reinforcement in the end region should not exceed fbcalculated from

(5.116)

fb0.6 2 fc (5.117)

B

Ab

Ab

 fc

fb0.8fc

B

Ab

Ab

0.2 1.25fci

10 fchd

(h0.0025)0.0025

n0.00250.52.5

hw

lw

Vchd0.6 2 fc

lw(1.25 2 fc0.2Nu/lwh)

Mu /Vulw /2 

Vc3.3 2 fchd

Nud

4 lw

2 fchd fc