The upturned concrete beam system : an investigation of structural, environmental, and constructability performance

Abstract

While the recently completed U.S. Federal Building in San Francisco features numerous sustainable aspects that reduce energy demand, the most impressive feature required a distinctive structural floor system. Designers applied a non-linear, integrative approach between varying disciplines whose systems are typically mutually exclusive to construct a high-performance building system. Through the use of upturned concrete T-beams, designers created a naturally ventilated workspace that employs the thermal mass of an exposed concrete ceiling. This concrete absorbs heat during the day and is purged at night by cool breezes. This study investigates the inherent structural and constructability properties associated with upturned concrete beam systems in conjunction with its environmental performance so as to better understand its feasibility. A design case study is conducted to evaluate the related construction material and labor costs using ACI 318 practices. The results confirm the innate structural and construction properties while reasons for efficiencies and detriments of the upturned concrete beam system in comparison to a standard T- beam system are discussed. A payback period for the time in which the initial investments in potentially more expensive construction practices is calculated applying average energy saving data. Improvements to the design of upturned concrete beam system are also proposed as well as improvements to the role of the structural engineer in designing for energy minimization.