This program quickly designs a steel girder system given bay sizes, steel properties, and gravity loading. The girders selected satisfy both strength and deflection requirements while being as cost effective as possible by using the lightest weight results.

Notes: The strength properties used are yield moments. The girder self weight is not included in the demand calculation, so the dead load input should include a factor for beam weight. The program incorporates live load reductions.

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A detailed explanation is provided later in this submission

The Dynamo script is shown below.

The dimension inputs outline the distances between each bay and the number. Fy is a property of the steel. The dead loads and live loads must be calculated by the engineer and input. Note that the dead load does not include girder self weight, so a factor should be added, and the live load is reducible.

This section calculates the moment demands for each case. The maximum of the standard LRFD load combinations is taken. Live load reductions from ASCE 7-22 are used, based on the tributary area of each girder. The psf loads are converted to line loads using tributary areas once again. Last, the moment demands are calculated with the uniform line loads.

Live load and total load drifts are found and used to find required moments of inertia. These loads are not from the load combinations and are just the service loads (with reduced live load). The equation from the calculation is for a uniform load, and solves for I using the deflection limits. The limits are L/360 for live loads and L/240 for the total dead and live loads.

This block reads an excel file with section data for 132 common I beams. The beams are sorter by weight. The yield moments are found by multiplying Sx by Fy. This value is compared with the moment demands from the strength calculation section. The Ix values are compared with the Ireq values from the deflection calculation section. The properties on the right are used later for drawing the beams.

This block compares all the values. The “larger” function creates lists of booleans that determine which beam sizes have yield moments over the moment demand (top 4) and moments of inertia over Ireq (bottom 4). Then, for each case the boolean lists are combined to find the beams that satisfy both requirements. Finally, the first size (the lightest) is taken as the girder size to use.

The outputs gathered from the previous steps are shown here for each case.

This section creates the layout in Rhino. A grid is generator by creating lines for each of the four cases. Using the selected section properties for each case, the I beam shape is drawn and then swept along the respective lines.

The output color coding is Light Blue for EW interiors, Dark blue for EW Exteriors, Pink for NS Interiors, and Magenta for NS Exteriors.

Rhino, Grasshopper, Table of I beams (attached in ACC folder).