Variable friction cladding connection for multi-hazard mitigation

Safety and serviceability design of civil infrastructure, including buildings and energy, lifeline, communication, and transportation systems, is critical in providing and maintaining services and benefits to our communities. In modern society, new constructions tend to be more flexible due to advances in material science and construction technologies. A key challenge in the design of these structures is to meet the motion requirements under operational and extreme loadings. The purpose of a motion-based design (MBD) approach is to ensure that motion requirements are met under the design loads, after which strength requirements are verified and met. A popular method under MBD is the inclusion of supplemental damping systems. For instance, several passive damping systems were introduced over the last decades, demonstrating high effectiveness at reducing seismic vibrations for buildings. These traditional passive control systems, although capable of mitigating targeted loads, are restricted to single hazard one-at-a-time due to their limited performance bandwidth. It follows that they become difficult to implement when multiple excitation inputs are considered either combined or individually, termed multi-hazards. Alternatively, one can use high-performance control systems that include active, semi-active and hybrid control systems, to adapt structural responses under different types of hazards. This work proposes and characterizes a novel high-performance control system termed variable friction cladding connection (VFCC). The VFCC leverages the motion of cladding elements to dissipate energy. It consists of friction plates upon which variable normal force is applied through an adjustable toggle system controlled by a linear actuator. When locked, the device acts as a traditional rigid cladding connection with high stiffness for daily operation and also provides maximum friction force to passively dissipate blast energy transferred to the structure. A rubber bumper is integrated to avoid collision between the structure and cladding elements under high impact loads. The VFCC, once activated under wind and seismic hazards, performs as a semi-active damping device that leverages cladding mass to reduce structural vibrations via a feedback control system. Here, a device prototype is fabricated and tested in laboratory to identify and validate its dynamic behavior. Experimental results show that the device prototype functions as designed and demonstrates its high promise for multi-hazard mitigation. In order to effectively implement the VFCC, an MBD procedure is developed and demonstrated on building examples subjected to multi-hazards. The MBD procedure includes the analytical quantification of hazards, identification of structural motion objectives, and iterative design of cladding connection parameters. The MBD approach is first developed for each hazard individually and then extended to multi-hazard design for blast, wind, and seismic loads. Numerical simulations are conducted on several building examples where the VFCC is simulated under a linear quadratic regulator controller (semi-active case) for wind and seismic loadings, and under a locked position (passive-on case) under blast load. An uncontrolled case with a traditional rigid cladding connection is used to benchmark results, and a passive-on case is simulated under wind and seismic loads also for benchmark purposes. Simulation results show that the designed VFCC is capable of reducing the response of the uncontrolled structures under the prescribed performance objectives under multi-hazard loadings. Overall, this work demonstrates the VFCC\u27s high capability of mitigating multi-hazards by leveraging motion of the cladding system, and the promise of the developed MBD approach enabling its holistic integration at the design phase