Structural performance of axially- and laterally-loaded cantilevers with thermally-improved detailing

Abstract

Cladding details that span the building envelope are particularly susceptible to forming thermal bridges, where heat is transferred between interior and exterior, resulting in loss of energy. Steel buildings are particularly susceptible to forming thermal bridges due to the relatively high thermal conductivity of steel compared to that of other structural materials. To mitigate these thermal bridges, thermal breaks may be inserted in the cladding detail connection to the building interior, and have demonstrated promise in previous thermal modeling studies, with up to 65% reduction in thermal bridging. This paper summarizes recent work on the design, validation, and implementation of thermal break strategies that maintain structural integrity. Fiber-reinforced polymer (FRP) shims were used to provide thermal breaks in steel connections of cladding details. Partial replacement of steel structural members with FRP members was also explored. Shims were the focus of the work due to ease of installation, cross-section availability, and thermal performance. While several cladding details were examined in this research, this paper summarizes the cyclic performance of roof posts (under axial and cyclic lateral loads) and canopy beams (under cyclic lateral loads only), representing their anticipated performance during earthquakes and wind events. While roof posts and canopy beams exist in a range of applications in building construction, structural archetypes selected for this work represent lightly-loaded examples that are common in the field. The impact of adding FRP shims at the bolted base plate connection to the building interior is discussed. Recommendations for design and future research are also presented.