Structural engineers are often tasked with making modifications to existing floor or roof structures to accommodate new equipment or changes in use loads that were not considered in the original structural design.  Many options exist to alter steel joists and joist girders to increase their load carrying capacity, however the alterations can be complex.  Are you aware that the Steel Joist Institute offers a useful tool to aid in the design of reinforcing existing steel joists and joist girders?

In the August 2026 SEU session, Bruce Brotherson, PE, SE, an Innovation Architect from Vulcraft, and Walter Worthley, PE, SE, from SEQ Engineering, LLC, presented Evaluation, Modification, Retrofit: Steel Joists, Roof, and Floors.  Bruce demonstrated examples of joists that can be retrofitted and those that should not be retrofitted.  He also identified key characteristics of in-place joists and explained how to determine who the original manufacturer was and whether they can provide additional documentation.  Bruce described how to verify the original design loads and evaluate the joists for new loads.  Walt then covered methods and practices to modify existing joists to increase the load carrying capacity and shared some commonly used details to increase the load capacity of a joist component.

Walt highlighted a useful tool offered by SJI as a free download on their website.  The Joist and Joist Girder Reinforcement Tool was developed by SJI to assist the engineer and steel fabricator with the complex task of reinforcing open web steel joists and joist girders to accommodate additional loads for which they were not originally designed.  As you can see in the slide below, one of the 17 available spreadsheets in this tool helps to calculate the distribution of an added load between 3 or 4 adjacent joists.  The additional spreadsheets offer options for reinforcing the top chord, bottom chord, and webs with various combinations of rods, angles, and plates.  The design tool is based on the guidance provided in SJI Technical Digest 12 – Modification of Open-Web Steel Joists and Joist Girders, the SJI 45th Edition Catalog, and the AISC 360-16 Specifications.  Be sure to check out this useful tool on your next retrofit project to assist in the reinforcement of existing joists and joist girders.