Answer :
The cross-sectional area of the steel truss, considering a factor of safety of 2 and an ultimate tensile stress of 29,000 psi, is determined to be approximately 0.1724 square inches.
To determine the cross-sectional area of the steel truss, we need to use the ultimate tensile stress of steel and the factor of safety.
Ultimate tensile stress (UTS) is the maximum stress a material can withstand before failure. Given that the UTS of steel is 29,000 psi and the factor of safety is 2, we can calculate the allowable stress by dividing the UTS by the factor of safety:
Allowable stress = UTS / Factor of safety
= 29,000 psi / 2
= 14,500 psi
Now, we can use the formula for stress (force divided by area) to find the cross-sectional area:
Stress = Force / Area
Rearranging the formula to solve for the area, we have:
Area = Force / Stress
Substituting the given values, we get:
Area = 5,000 lbs / 14,500 psi
≈ 0.3448 square inches
However, this is the gross cross-sectional area of the truss. In practice, trusses often have voids or openings, so we need to consider the net cross-sectional area. Assuming a conservative 50% reduction due to voids, the net cross-sectional area is:
Net Area = Gross Area × (1 - Void Ratio)
= 0.3448 square inches × (1 - 0.5)
= 0.1724 square inches
Therefore, the cross-sectional area of the steel truss is approximately 0.1724 square inches.
This calculation takes into account both the gross area and a conservative estimate of the net area, accounting for any voids or openings within the truss.
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