March 17, 2011
Tilt that Sucker Up!
by Hinman Team
Use of tilt-up reinforced concrete panels has proven to be very efficient when applied to the “right" type of building. This mode of construction has long been typical of industrial/warehouse type structures whose design is dictated by functionality and constructability and discounted when aesthetic design needs are more profound. However, recent trends in the architecture and engineering world are beginning to encourage a wider use of tilt-up construction as a result of aesthetic improvements of this building system. Specifically, Hinman has noticed recent trends related to new federal building projects to explore the level of blast protection offered by tilt-up walls.
In a recent project, Hinman used existing tools to develop a new analysis and design approach that efficiently predicts the behavior of exterior reinforced concrete tilt-up wall panels when exposed to project specific air-blast loading. Hinman constructed a 3-D building model using SAP software (Structural Analysis Program), developed by Computers and Structures Inc., which accounted for material strengths, building geometry, gravity loads, and blast pressures. This modeling technique allowed for two-way wall panel behavior to be captured in response to blast pressures applied as a time-history function. Additionally, the wall model allowed us to capture loading eccentricities resulting from varying wall panel thickness. The figures below display graphical samples of analysis results, indicating the positive and negative moments in the wall panels, in each primary direction. Rectangular areas of zero moment are indicative of window locations as well as modeling input to prevent moment transfer across joints to adjacent panels. The design stresses were extracted from the model to determine minimum panel reinforcing requirements. Additionally, wall displacements were reviewed and wall support reactions were coordinated with the structural engineer to be properly resolved into the floor diaphragms.
The analytical methods developed helped minimize unnecessary conservatism inherent in more simplified computational methods (i.e. – single degree of freedom analysis) and yielded design results that are consistent with conventional wall design. We look forward to more opportunities to use these innovative techniques and be a part of the trend to explore new engineering solutions to address and exceed project specific performance goals.