In Tampa, Florida, high winds create a precarious setting for a skyscraper. To impart lateral stability to the One Tampa City Center, a 517-foot office building, Lev Zetlin Associates, New York, used a slipformed concrete core. H-frames, embedded at stories 6, 11, 12, 18, 19, and 20, impart strength to the core where the building exterior steps, at floors 10 and 18. The H-frames, of ASTM A36 steel I-beams fillet welded, offset stress concentrations arising from the reduction in building cross-section at those floors.