Torsion Ring Case Study


A concrete contractor needed to pour a 20’ diameter x 30’ tall concrete skirt that was cast out-of-round for a steep tank but did not have the proper forms.


The contractor proposed to repair the problem and enlisted AMG, Inc. to determine the best engineering solution. Both the efficacy of the repair as well as the time required to execute the fix were taken into consideration as the client was on a tight schedule. The contractor and AMG concluded that the best solution was to use a built-up tubular Torsion Ring to receive the tank load from the short steel skirt at the outer edge of the concrete wall and transfer it to the middle of the wall where the resulting stresses could be handled by the concrete.


Since there were various options which could be used to complete the repair, AMG provided a palate of solutions and let the contractor choose the one that could be executed most expeditiously and at the lowest cost. The contractor had in-house structural steel fabrication and erection capabilities as well as expertise in concrete work. Therefore three repair schemes were developed working with just concrete, two of which required some existing concrete removal and replacement. The third involved adding new concrete designed to make the transition from the round tank to the oblate shape of the existing concrete skirt. Two steel alternatives were also provided, both using an 8" thick by 16" wide Torsion Ring, one solid and one made of a built-up tube with 2" thick top and bottom plates and 1" thick side plates. The ring was to be field assembled from eight shop fabricated segments subtending 45° of arc and connected by full penetration field welding. According the contractor, the steel solutions were the fastest and least expensive of the available options. And the solid ring was the least costly of them all because of the reduced labor. But ultimately the built-up tubular ring was used because the 8" thick stock was not immediately available.