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2011 – 2012ASPIREMaster EngineeringStructural Design Project
ASPIRE PROJECT TEAM
ASPIRE designed the gravity, lateral, and foundation systems, utilized finite element software for structural optimization, designed steel and concrete connections, and studied the effects of creep and shrinkage during a year-long analysis of the Chicago Spire. Preliminary analysis included research of different lateral load resisting systems in order to select the system that would best suit the needs of the structure. The lateral system chosen was a central concrete core with outriggers and belt trusses connecting the core with the exterior steel columns. The gravity design of the structure explored the use of non-composite and composite beams and columns in the Spire. ASPIRE selected steel beams with a composite metal decking system. A column load takedown based on tributary areas was used for the preliminary column design. The Chicago Spire was modeled using MIDAS Gen, a structural finite element software, to accurately understand the lateral behavior of the building. A sensitivity analysis was performed to resize the concrete core, the outriggers, and the belt truss members from the initial hand calculation sizes. Core wall thicknesses were optimized across the height of the building. Vertical columns and transfer columns were redesigned as a series of steel built-up shapes through energy optimization methods. The foundation system featured the design of a seven level below-grade parking garage and a retaining wall along the site perimeter. Rock-socketed caissons were designed to support the tower, extending from the base of the building to the bedrock 119 feet below grade. There are hundreds of connections in the Chicago Spire ranging from standard steel connections to complex designs for the outriggers and the lobby level mega-columns. Several steel-to-steel and composite connections were designed throughout the tower. A study of concrete creep and shrinkage estimated differential settlement between the concrete core and the exterior steel columns using the GL2000 model. Creep and shrinkage are dependent on variables such as loading schedule, curing period, and material properties, making it difficult to predict the actual amount of creep and shrinkage. However, failure to acknowledge these effects leads to cracks in the concrete and uneven floors. Through the course of the project, ASPIRE faced many challenges that required the design team to seek guidance from outside sources, including weekly meetings with our faculty advisor and bi-weekly conference calls with our professional advisors from Thornton Tomasetti. The structural design of the Chicago Spire was a collaborative effort of eighteen students and the advisors. The project provided a realistic design experience incorporating team management, iterative design, and professional reporting. For the final deliverable ASPIRE has prepared a cumulative design narrative, calculation book, and final structural drawing set.
designed steel and concrete structures; Outriggers and belt trusses; Gravity and lateral load resisting systems; Foundation systems