Q$1-($Problem $4\mathrm{.}6-$ modified$)$ A simply$-$supported foot bridge $(L=60ft)$ uses a standard precast pretensioned double$-$T concrete beam in its inverted position. Typical cross sections and available dimensions are given in the figure and table shown below. These are normal weight concrete beams.

Given:

o $f_c^{\text{'}}=7,800$

o $f_{ci}=4,600$

o $f_{\text{t}\text{i}\text{a}\text{l}\text{l}}=-150$

o $f_{\text{t}\text{a}\text{l}\text{l}}=-375$

o$.f_{\text{c}\text{i}\text{a}\text{l}\text{l}}=3,000$

o$.f_{c,\text{a}\text{l}\text{l}}=4,000$

o $f_{pe}=180$ksi

Losses $=16\%$

Select the least weight bean that satisfies the flexural stress requirements from the available sections if the design live load is $w_{LL}=600plf.$

Table P$4\mathrm{.}6$ Properties of bean sections $($nernal welght cencrete$).$

$\backslash$table$[[\backslash$table$[[$h$],[$in$]],\backslash$table$[[b_1$