### Intended users

The program is meant to be used by structural engineers that are looking to quickly come up with a gravity system for a steel structure.

### Need you’re trying to provide a solution or support for

In the beginning of a building project’s life, a simple task that is always necessary for the structural engineer to do is coming up with the gravity system for the building. This system consists of beams, columns, and girders. The design methodology for this is usually meeting both strength and deflection requirements while using a beam that is as cost effective as possible (usually based on the beam weight).

The program I am developing intends to be able to to calculate the most efficient girder layout for a standard floor plan, depending on the dimensions of the structure, properties of the steel, and gravity loads.

### Inputs

The inputs regarding the structure dimensions include the bay width (east-west dimension), bay length (north-south dimension), and number of bays in either direction.

The second input is the yield strength of the steel. (For structural steel it is typically 50 ksi but it can vary).

The final input is the loading. This consists of both dead and live loads (in psf). The program does not calculate beam self weight, so the user has to be sure to include beam self weight in the dead load. Additionally, the live load is reducible live load.

### Underlying logic of the model you’ll implement

To determine beam size, basic formulas and structural engineering codes are used. These are all based on the inputted loads and the spans. ASCE 7-22 outlines equations for live load reductions and load combinations.

These loads are converted to line loads considering the tributary areas of the girders in each direction. Using uniform load moment equations to determine moment demands for four cases: interior beams spanning the east-west direction, interior beams spanning the north-south direction, exterior beams spanning the east-west section, and exterior beams spanning the north-south direction.

Second, deflection limits are considered. The standard limits are L/360 for live loads and L/240 for total service loads. Using these limits and standard uniform load deflection equations, the required moment of inertia can be found for each case.

Section properties for a collection of common I beams are read from an Excel table, which are sorted by weight. The important properties to compare are the section modulus and moment of inertia. The section modulus is multiplied by Fy, giving yield moment, which is used to compare with the moment demand.

Finally, the lightest beam that meets both requirements is output.

### Outputs

The output of the program are the four beam sizes for each case (interior beams spanning the east-west direction, interior beams spanning the north-south direction, exterior beams spanning the east-west section, and exterior beams spanning the north-south direction).

Lastly, the program displays the beams in a color coded layout.