# Required Zx Calculation for Simply Supported Beam with Uniformly Distributed Load

When dealing with a simply supported beam that is 20 feet long and subjected to a uniformly distributed total factored load of 1kip/foot, the first step is to calculate the maximum bending moment (M) using the formula M = wL^2/8, where w is the load per unit length and L is the span of the beam.

For this scenario, the load per unit length (w) is 1 kip/foot, and the span (L) is 20 feet. By plugging these values into the formula, we can calculate the maximum bending moment (M).

After determining the maximum bending moment, the next step is to ensure that the flexural strength ϕbMn is greater than or equal to the required factored moment. This comparison allows us to calculate the required plastic section modulus (Zx) by rearranging the flexural strength formula to Zx = M/ϕb.

Since A992 steel is assumed for the W-flange member in this case, the specified minimum yield stress of 50 ksi can be used to back-calculate the design factor ϕb according to AISC standards for steel design.

Given the options provided, the correct Zx value will be the one that matches the calculated Zx based on the performed structural analysis, including the use of proper units and design factors. It's important to note that without conducting the actual calculations and considering all relevant factors, the precise correct answer cannot be determined for the required Zx of the simply supported beam.