Steel truss design


I’ve written a paper (not yet online) about graphical statics. In order to demonstrate that the “form-finding” objectives of such techniques are often superficial and flawed, I needed to provide a case study of an actual structural design problem, using real materials and real design methods, that accounts for things (like the buckling of bars in compression, or shear lag and effective net area of bars in tension, or deflection issues) that graphical statics ignores. So I created an enormous spreadsheet to find the optimal (lightest) steel double-angle Pratt or Warren truss for any given span, spacing, and loading condition. The spreadsheet actually designs 105 different trusses (with aspect ratios ranging from 2:1 to 16:1; and with from 2 to 14 “panels,” as shown in Figure 1) in order to find the optimal combination of aspect ratio and panel geometry for a given span, spacing, and loads.

Figure 1. Trusses are designed with from 2 to 14 panels

Figure 1. Trusses are designed with from 2 to 14 panels

Well, the spreadsheet had well over 1,000,000 cells and couldn’t be converted to an online calculator using the software I have. Therefore, I made a smaller version of the same spreadsheet — this one only designs a single truss (rather than 105 versions) and only considers whatever aspect ratio and panel geometry have been selected. However, this calculator can also be used to find the lightest truss, but only by trying out numerous geometries while keeping track of the truss weight.

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