Experimental and Analytical Investigation of Steel Hardened Curtain Wall Mullions

Abstract

Glass facade/curtain wall assemblies are commonly used in modern building construction as part of building envelop. This system has a number of advantages, including pleasant architectural appearance, building energy optimization, acceptable fire resistance and low maintenance. However, they pose tremendous risk towards maliciously intended acts of terror in the form of bomb blasts. The literature review conducted revealed lack of previous research on mullion strengthening/hardening. The present study has the objective of developing hardening techniques for curtain wall mullions to withstand high-intensity impulsive blast loads. Combined experimental and analytical research was conducted for the development of mullion retrofit techniques using the Shock Tube Facility of the University of Ottawa. The test program involved retrofitting existing, commercially used aluminum mullions with steel plates and subjecting them to different levels of blast loads. The mullions were retrofitted with three techniques with the help of steel L shaped angles, steel plates and with a combination of steel HSS sections and plates. The results indicated an increase of load carrying capacity of the mullions up to a factor of 2.2 with up to 30% reduction in mid-height displacements. It was shown that the steel hardening components developed full composite action with the existing aluminum section, indicating the effectiveness of the hardening technology. The analytical research followed the experimental research with the main objective of validating experimental results, as well as validating the assumption of full composite action between the core aluminum mullion and the hardening plates. The first step was to develop resistance functions followed by the validation of main analytical tool RC-Blast and the UFC charted solution. Following excellent agreement between these two analytical tools, RC-Blast was further validated against the experimental results. In addition, Pressure-impulse (P-I) diagrams were developed as design aids for different pressure-impulse combinations. The retrofit techniques developed were applied to a selected prototype building to assess their feasibility for use in practice. Two different blast threats were considered for this application. Conclusions were drawn regarding the effectiveness of the curtain wall hardening techniques for use in practice.