Static Experimental Testing to Define Force-Deformation Relationships of Precast Concrete Cladding Building Façade Systems

Six full-scale experimental studies of precast concrete facade have been completed in 2011/12 to evaluate the seismic performance of nonstructural building components. Experimental testing of cladding panels was completed at the nees@berkeley lab facility. Research findings are particularly relevant to seismic regions of the United States and other countries. The paper is targeted toward engineers directly responsible for façade design as well as the Engineer of Record for a building project. Researchers involved in code development and expansion of Performance Based Earthquake Engineering will also benefit from the paper. Specimens included full-width, half-width, and return column covers supported by an articulated steel test jig simulating a building structural frame. Steel connections between the panels and the supporting frame included slotted connections at the tops of panels and welded connections at the base of panels. The static loading protocol compared cyclic loading with increasing amplitude to a seismic loading protocol based upon the nonlinear time history drift of the prototype structure. The horizontal slotted connection at the top of panels allowed inter-story drift matching the building code requirements to occur with minimal damage to the panels. However, once the inter-story drift increased above a point where the slotted connection reached the allowed travel, damage to the panel occured in the form of severe cracking at embedded connections. Force-deformation graphs of the global specimen and individual connections quantify the hysteretic behavior. Horizontal slotted connections clearly show minimal resistance to lateral movement while the displacement remains below the maximum allowance of the slot. Once this free clearance is reached, bearing of the slot significantly increases and the connection quickly increases lateral resistance. Welded connections show very little hysteretic behavior due to low levels of relative displacement. The concrete embeds of the weld plates show more pronounced hysteretic behavior as this is the main location of damage and cracking at the base connections. The primary goal of evaluating the connection force-deformation relationships is to develop suitable analytical models for use in nonlinear studies of the façade system. The presentation will clarify performance of modern façade systems and define the analytical modeling input data for researchers exploring holistic building performance.