Redundancy of Exodiagonal Building Structures

Abstract

Exodiagonal building structures are defined as those having a regular series of intersecting diagonal members, completely or partially encompassing the building's exterior face, that carry both gravity and lateral loads. Exodiagonal building structures normally lack vertical members on the exterior walls. The highly redundant exodiagonal structural system facilitates the immediate redistribution of internal forces away from damaged portions of the shell in the case of an extreme loading event. Structures of this type are uniformly resilient without any inherent vulnerabilities. Several completed buildings utilizing this type of structural system are in use today around the world. The general performance characteristics of exodiagonal building structures with respect to redundancy are examined in this study. In this study, two hypothetical building structures, a high-rise and a low-rise, each using a three-dimensional, exodiagonal structural grid, are analyzed. For purposes of this study, the exodiagonal members in the models are sized to meet the minimum requirements of the ASCE 7-02 Code for gravity and moderate lateral loads. Both of the building models are then subjected to the removal of a vertical support and reanalyzed in a manner similar to standard progressive collapse procedures. A vertical support for an exodiagonal structure is judged to be a pair of adjacent diagonal members. Redistributed loads are calculated for pertinent members and compared to the original Code-based member designs. Next, additional exodiagonal members are removed from the model, adjacent to those previously removed. The models are reanalyzed and the loads are recalculated for pertinent members so that the redistribution of internal forces can be considered. This process is repeated through numerous member removal steps. The results of the above redundancy analysis is summarized and presented.