Northeastern University Department of Civil and Environmental Engineering THERMAL BREAK STRATEGIES FOR CLADDING SYSTEMS IN BUILDING STRUCTURES Report to the Charles Pankow Foundation Kara D. Peterman, Justin Kordas, Julieta Moradei, Kyle Coleman, and Jerome F. Hajjar, Department of Civil and Environmental Engineering, Northeastern University James A. D’Aloisio, Klepper Hahn & Hyatt Mark D. Webster, Jason Der Ananian, Simpson Gumpertz & Heger, Inc. May 2017 Executive Summary This research explores approaches for developing thermal breaks to reduce loss of energy for heating and cooling in steel building structures. Structural steel elements that pass through the building envelope potentially act as thermal bridges due to their ability to conduct heat, transferring interior heat or cooling to the exterior and thus increasing building energy consumption. Condensation and reduced building occupant comfort can also result from thermal bridging. The key goal of this project is to explore and validate several concepts and develop associated design recommendations for mitigating the loss of energy via thermal bridging and other related issues in steel building structures by using a variety of possible solutions. By introducing thermal break strategies to various components throughout the detailing in a structure, we identify practical solutions geared for gaining acceptance and codification as needed for use within the steel construction industry. The scope of this work involves only snug-tight connections. The scope of this work includes investigation of structural steel shelf angle details to support building cladding, structural steel roof posts to support dunnage on building roofs, and cantilevered structural steel beams to support light canopies. Experimental testing, structural analysis, and thermal analyses were conducted to explore a variety of solutions including different fiber-reinforced polymer (FRP) shims, FRP shapes, and manufactured structural thermal break assemblies (MSTBA). In addition, a methodology is put forward to conduct creep testing on FRP plates loaded in compression through the thickness, and the creep properties of FRP plates used as shims is documented. Thermal modeling described herein demonstrates the efficacy of the proposed thermal break mitigations strategies. For continuous cladding elements (i.e., shelf angles), the proposed solutions can reduce the thermal conductivity of a system by approximately 50% when compared to an unmitigated broken wall segment. When compared to the conductivity of the unbroken wall element, these solutions result in an improvement of approximately 75%. For discrete cladding details (i.e., roof posts and canopy beams), the improvement is smaller when compared to an unmitigated detail (10-14%, depending on strategy), but more significant when compared to unbroken wall and roof details with no penetrations (60-70%). Experimental and computational studies on the most successful thermal break strategies provide structural validation of the proposed solutions. The proposed solutions were often seen to impact the failure mode; however, this behavior was not evident until well beyond the design range of the component. In the shelf angles, members with FRP shims were seen to have a decrease in strength compared to members with steel shims. However, shelf angles with FRP shims showed no significant decrease in strength compared to shelf angles without shims due to beneficial changes in the connection geometry. In roof posts and canopy beams, shim mitigation strategies have little to no impact on component behavior. While small differences in strength can be observed (~5%) between mitigated details, this difference is typically due to a difference in shim material properties, and not a system effect. This report concludes with possible analysis and design recommendations for including thermal breaks in the detailing of shelf angle cladding supports, roof posts, and canopy beams. ii Acknowledgements This material is based upon work supported by the Charles Pankow Foundation, the American Institute of Steel Construction, the American Composites Manufacturers Association (ACMA), the ACMA-Pultrusion Industry Council, the National Science Foundation under Grant No. CMMI-0654176, Simpson Gumpertz & Heger, Inc., and Northeastern University. In-kind support was provided by ArmadilloNV, Bedford Reinforced Plastics, Capone Iron, Creative Pultrusions, Fabreeka, Fastenal, Inframetals, and Strongwell. This support is gratefully acknowledged. Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors. For their contributions to this project, the authors would like to thank project team members Mehdi Zarghamee, James Parker, Pedro Sifre, Sean O’Brien, Mariela Corrales, Nathalie Skaf, Elisa Livingston, and Jessica Coolbaugh of Simpson Gumpertz & Heger, Inc., Yujie Yan, Dennis Rogers, Michael MacNeil, and Kurt Braun of Northeastern University, and the members of the Industrial Advisory Panel and the ACMA-Pultrusion Industry Council Technical Advisory Team for this project: INDUSTRY ADVISORY PANEL Fiona Aldous Wiss, Janney, Elstner Associates, Inc. Glenn Barefoot Strongwell Corporation Todd Berthold Strongwell Corporation Craig Blanchet LeMessurier Associates John P. Busel American Composites Manufacturing Association Rodney Gibble Rodney D. Gibble Consulting Engineers Robert Haley ArmadilloNV Robert Kistler The Façade Group Adrian Lane Owens Corning Andrea Love Payette Alex McGowan Levelton Consultants, Ltd. Steve Moore Fabreeka International, Inc. Larry Muir American Institute of Steel Construction Rick Pauer CCP Composites Thomas Schlafly American Institute of Steel Construction Tabitha Stine American Institute of Steel Construction Dustin Troutman Creative Pultrusions, Inc. ACMA-PULTRUSION INDUSTRY COUNCIL TECHNICAL ADVISORY TEAM Glenn Barefoot Strongwell Corporation Todd Berthold Strongwell Corporation Stephen Browning Strongwell Corporation John P. Busel American Composites Manufacturing Association Alfred D’Sousza Fibergrate Composite Structures, Inc. Ellen Lackey University of Mississippi Bhyrav Mutnuri Bedford Reinforced Plastics, Inc. Kevin Spoo Owens Corning Jim Tedesco AOC LLC Dustin Troutman Creative Pultrusions, Inc. iii Table of Contents Executive Summary ........................................................................................................................ ii Acknowledgements ........................................................................................................................ iii Table of Contents ........................................................................................................................... iv 1 Introduction ............................................................................................................................. 1 1.1 Archetypal building .......................................................................................................... 1 1.2 Archetypal cladding details .............................................................................................. 3 1.2.1 Slab-supported shelf angle ........................................................................................ 3 1.2.2 Canopy Beam ............................................................................................................ 5 1.2.3 Rooftop Dunnage Post .............................................................................................. 5 1.3 Thermal break mitigation strategies ................................................................................. 6 1.3.1 Post/beam systems .................................................................................................... 6 1.3.2 Roof Post Prototype Structures – Mitigation with FRP Shims ................................. 6 1.3.3 Roof Post Prototype Structures – Replacement with FRP Structural Sections ........ 8 1.3.4 Canopy beam prototype structure – manufactured structural thermal break assembly (MSTBA) solutions ................................................................................................................. 9 1.3.5 Horizontal Beam Prototype Structure – Substitution with FRP Structural Members 9 1.3.6 Slab-supported shelf angle ...................................................................................... 10 1.4 Organization of the Report ............................................................................................. 15 2 Background ............................................................................................................................ 16 2.1 Overview ........................................................................................................................ 16 2.2 Morrison Hershfield (2008) ........................................................................................... 16 2.1.1 Relieving Angle Models ......................................................................................... 16 2.1.2 Cantilever Beam Model .......................................................................................... 19 2.3 The Corus Group (2011) ................................................................................................ 20 2.1.3 Local Insulation ...................................................................................................... 21 2.1.4 Slotted Steel Sections .............................................................................................