Keweenaw County may consider adding a new ATV $($all$-$terrain vehicle$)$ trail, but the

Montreal River is in the way. The solution is a narrow timber bridge, spanning $30$ feet,

and subjected to two load combinations.

$$ Load combination $1$: DL $=250$ plf $($dead load$),$ LL $=150$ plf $($LL $=$ pedestrian load

for $6$ months$).$

$$ Load combination $2$ is DL $=250$ plf $($dead load$),$ SL $=520$ plf $($snow load$),$ VL $=$

$2200$ lbs $($VL is the vehicular $($ATV$)$ load$).$ Assume VL is a moving concentrated

load with an accumulative duration of $1$ day.

Determine the controlling load combination and corresponding load duration factor for

a$.$ Bending b$.$ She