PROBLEM $1(80$ pts$)$

The stringer & skin shown to the right are made of $7075-$T$6$ Al sheet and are fastened together with a double row of $\frac{1}{4}"$ protruding head rivets spaced every $2"$ along the length of the stringer. The skin$-$stringer combination acts like a column that is $24"$ long between attachments that provide a simple support boundary condition. Given the properties below:

Material: $E=10\mathrm{.}0$Msi,$E_c=10\mathrm{.}5$Msi,$G=3\mathrm{.}8$Msi,$v=0\mathrm{.}33.$

Allowables: $F_{tu}=79$ksi,$F_{cy}=71$ksi.

Stringer: $t={0\mathrm{.}10}^n$

Skin: $t={0\mathrm{.}060}^n$

Cetermine the following:

a$)$ Stringer Euler Buckling Allowable

b$)$ Stiffener Crippling Allowable $($Needham$\text{'}$s Method$)$

c$)$ Effective Width of the Skin $($Corrected for Inter$-$rivet buckling$)$

d$)$ New cross section properties for skin and stringer combination $($Area$,$ Ybar, Ixx, ${}_{,})$

e$)$ What is the dominate failure mode for this section, what do you notice?

PROBLEM $2(20$ pts$)-$ Conceptual

What does a clamped edge fixity and a simply$-$supported edge fixity mean, in terms of Degrees of Freedom?

What is the difference between a crippling failure vs Euler buckling failure?

What is the advantage and disadvantage of having weld reinforcement?

What weld strength $($Tension & Shear$)$ can you assume for a titanium welded joint if the joint is re$-$heat treated?

Given the following cross sections, determine the Gerard Crippling Method's parameter g$.($Show Work$)$