evo Philly at Cira Centre South in Philadelphia. The structural design had to solve the problem of how to work around three sets of railroad tracks at ground level. Our engineers settled on full-story-height (35-foot) steel “delta frames” encased in concrete that carry the building loads to massive, reinforced-concrete columns proportioned as “crash walls” between the tracks.
Thornton Tomasetti provided structural engineering services for a 33-story mixed-use tower with a footprint of 60 feet by 230 feet. The building’s slender lateral system has a core height-to-depth ratio of more than 18. Built by a developer, the building combines independent student housing as well as office space with a green roof deck, multipurpose space and parking.
The structure is located on a complex site with nearly 50 percent of the building’s floor plate situated over three sets of active railroad tracks that enter or exit Amtrak’s 30th Street Station. The team considered several structural schemes and ultimately settled on a solution that was low-cost and would serve the architectural needs of the street-level amenity spaces, including 35-foot ceiling heights. The team designed steel “delta frames” encased in concrete to carry the building loads to massive, reinforced-concrete columns proportioned as “crash walls” between the tracks.
Slender building columns, with ratios of up to 36 and a minimum thickness of 14 inches, were required to fit into demising walls between units. The width of these narrow columns varied from 36 to 44 in order to achieve the necessary arial capacity and to improve the building’s lateral stiffness under wind loads.
By specifying precast filigree slabs, the engineers reduced the cost of labor on site and increased the pace of construction, enabling the contractor to achieve a three-day cycle for concrete floor construction.
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