Design for serviceability of prestressed concrete - Concrete Structures: Stresses and Deformations - page 423

Figure 12.7 Choice of the non-prestressed steel ratio, ns to limit characteristic crack
width w k res for variable maximum transient stress ∆ . The charts can also
give the mean residual crack width ( = w k res /1.5) for given values of ns and
∆ ; (a) to (e) ∆ = 2, 3, 4, 5 and 6 MPa, respectively. 1 MPa = 0.145 ksi.

force N < 0 (compressive) and variable M . The graph AED in the same
fi

gure represents the case when N = 0 (same as AED in Fig. 12.9(a)). It can

be seen tha t t he e ff ect of prestressing is to move ED upward to FG ; thus the

value M r √ 0.5 the upper limit of the noncracked state is increased; also, after

cracking, ψ m is reduced. We recall that M r is the value of the moment just

su cient to cause a virgin section to crack; M r can be determined from the

equation: