Given:

Span length $=70ft$

Both double T section and Bridge section: Superimposed sustained load $(w_{sd})=50l$b$/$ft$2$

For PCI Double T section $($Double T$/$No topping$)$: Superimposed live load $(w_{sl})=10l$b$/$ft$2$

For Caltrans Bridge section: Superimposed live load $(w_{sl})=1950lb/$ft$2$

Concrete $($Class T section$)$:

$f_c^{\text{'}}=5000$ psi $($normal weight concrete$)$

$f_{ci}=3500$ psi

Prestress force $($Grade $270$ low relaxation $7$ strands $=$ one tendon$)$:

The straight pattern of strands is used for all the sections

For PCI Double T section:

Try $n=160($or Try any number$)$

For Caltrans section:

Try $n=60($or Try any number$)$

$A_{ps}=0\mathrm{.}153$ in$.$ in$2($each tendon$)$

$P_1={0\mathrm{.}75}^{*}{n}^{*}{A}_{pa}^{*}$ fpu $($Note: Jacking stress is $75\%$ of $f_{pu})$

$P_o($assumed $10\%$ initial loss$)$

$P_e($assumed $18\%$ total loss$)$

Find: The least weight beam that satisfies the allowable stress limits

Summantiale