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

Performance evaluation of a semi-active cladding connection for multi-hazard mitigation

A novel semi-active damping device termed Variable Friction Cladding Connection (VFCC) has been previously proposed to leverage cladding systems for the mitigation of natural and man-made hazards. The VFCC is a semi-active friction damper that connects cladding elements to the structural system. The friction force is generated by sliding plates and varied using an actuator through a system of adjustable toggles. The dynamics of the device has been previously characterized in a laboratory environment. In this paper, the performance of the VFCC at mitigating non-simultaneous multi-hazard excitations that includes wind and seismic loads is investigated on a simulated benchmark building. Simulations consider the robustness with respect to some uncertainties, including the wear of the friction surfaces and sensor failure. The performance of the VFCC is compared against other connection strategies including traditional stiffness, passive viscous, and passive friction elements. Results show that the VFCC is robust and capable of outperforming passive systems for the mitigation of multiple hazards

Bridge damage detection using spatiotemporal patterns extracted from dense sensor network

The alarmingly degrading state of transportation infrastructures combined with their key societal and economic importance calls for automatic condition assessment methods to facilitate smart management of maintenance and repairs. With the advent of ubiquitous sensing and communication capabilities, scalable data-driven approaches is of great interest, as it can utilize large volume of streaming data without requiring detailed physical models that can be inaccurate and computationally expensive to run. Properly designed, a data-driven methodology could enable fast and automatic evaluation of infrastructures, discovery of causal dependencies among various sub-system dynamic responses, and decision making with uncertainties and lack of labeled data. In this work, a spatiotemporal pattern network (STPN) strategy built on symbolic dynamic filtering (SDF) is proposed to explore spatiotemporal behaviors in a bridge network. Data from strain gauges installed on two bridges are generated using finite element simulation for three types of sensor networks from a density perspective (dense, nominal, sparse). Causal relationships among spatially distributed strain data streams are extracted and analyzed for vehicle identification and detection, and for localization of structural degradation in bridges. Multiple case studies show significant capabilities of the proposed approach in: (i) capturing spatiotemporal features to discover causality between bridges (geographically close), (ii) robustness to noise in data for feature extraction, (iii) detecting and localizing damage via comparison of bridge responses to similar vehicle loads, and (iv) implementing real-time health monitoring and decision making work flow for bridge networks. Also, the results demonstrate increased sensitivity in detecting damages and higher reliability in quantifying the damage level with increase in sensor network density

Variable friction cladding connection for seismic mitigation

Cladding systems are conventionally designed to serve an architectural purpose and provide environmental protection for building occupants. Recent research has been conducted to enhance structural resiliency by leveraging cladding systems against man-made and natural hazards. The vast majority of the work includes the use of sacrificial cladding panels and energy dissipating connectors. These passive protection systems, though effective, have typically targeted a single hazard one-at-a-time because of their limited frequency bandwidths. A novel semi-active friction connection has been previously proposed by the authors to leverage the cladding motion for mitigating blast and wind hazards. This semi-active friction device, termed variable friction cladding connection (VFCC), is designed to laterally connect cladding elements to the structural system and dissipate energy via friction. Its variable friction force is generated onto the sliding friction plates upon which a variable normal force is applied via actuated toggles. Because of its semi-active capabilities, the VFCC could be used over wide-band excitation frequencies and is thereby, an ideal candidate for multiple hazard mitigation. The VFCC in its passive in situ mode has been previously designed to mitigate air-blast effects towards the structure and its semi-active scheme has been applied to wind hazard mitigation. In this paper, a motion-based design (MBD) procedure is developed to apply the VFCC to seismic hazard mitigation, completing its application against multiple hazards. The MBD procedure begins with the quantification of seismic load and performance objectives, and afterwards, dynamic parameters of the cladding connection are selected based on non-dimensional analytical solutions. Simulations are conducted on two example buildings to verify and demonstrate the motion-based design methodology. Results show the semi-actively controlled VFCC is capable of mitigating the seismic vibrations of structures, demonstrating the promise of the semi-active cladding system for field applications

Numerical verification of variable friction cladding connection for multihazard mitigation

The motion of cladding systems can be leveraged to mitigate natural and man-made hazards. The literature counts various examples of connections enhanced with passive energy dissipation capabilities at connections. However, because such devices are passive, their mitigation performance is typically limited to specific excitations. The authors have recently proposed a novel variable friction cladding connection capable of mitigating hazards semi-actively. The variable friction cladding connection is engineered to transfer lateral forces from the cladding element to the structural system. Its variation in friction force is generated by a toggle-actuated variable normal force applied onto sliding friction plates. In this study, a multiobjective motion-based design methodology integrating results from the previous work is proposed to leverage the variable friction cladding connection for nonsimultaneous wind, seismic, and blast hazard mitigation. The procedure starts with the quantification of each hazard and performance objectives. It is followed by the selection of dynamic parameters enabling prescribed performance under wind and seismic loads, after which an impact rubber bumper is designed to satisfy motion requirements under blast. Last, the peak building responses are computed and iterations conducted on the design parameters on the satisfaction of the motion objectives. The motion-based design procedure is verified through numerical simulations on two example buildings subjected to the three nonsimultaneous hazards. The performance of the variable friction cladding connection is also assessed and compared against different control cases. Results show that the motion-based design procedure yields a conservative design approach in meeting all of the motion requirements and that the variable friction cladding connection performs significantly well at mitigating vibrations

Probabilistic performance-based design for high performance control systems

High performance control systems (HPCS) are advanced damping systems capable of high damping performance over a wide frequency bandwidth, ideal for mitigation of multi-hazards. They include active, semi-active, and hybrid damping systems. However, HPCS are more expensive than typical passive mitigation systems, rely on power and hardware (e.g., sensors, actuators) to operate, and require maintenance. In this paper, a life cycle cost analysis (LCA) approach is proposed to estimate the economic benefit these systems over the entire life of the structure. The novelty resides in the life cycle cost analysis in the performance based design (PBD) tailored to multi-level wind hazards. This yields a probabilistic performance-based design approach for HPCS. Numerical simulations are conducted on a building located in Boston, MA. LCA are conducted for passive control systems and HPCS, and the concept of controller robustness is demonstrated. Results highlight the promise of the proposed performance-based design procedure

Development and validation of a nonlinear dynamic model for tuned liquid multiple columns dampers

The tuned liquid column damper (TLCD), a passive damping device consisting of a large U-tube with oscillating liquid, has been shown to be effective at mitigating structural responses under natural hazards. Aside from their bandwidth-limited mitigation capabilities, a key limitation of TLCDs is in their large geometries that occupy large space often at prime locations. A solution is to implement multi-columned versions, termed tuned liquid multiple columns dampers (TLMCDs), which have the potential to be tuned to multiple frequencies and occupy less space by leveraging the multiple columns to allow fluid movement. However, mathematical models characterizing their dynamic behavior must be developed enabling proper tuning and sizing in the design process. In this paper, a new analytical model characterizing a TLMCD as a multiple degrees-of-freedom coupled nonlinear system is presented. The frequencies of free vibration and vibration modes of a TLMCD are identified in closed-form formulations. Results are validated using computational fluid dynamics simulations, and show that the analytical model can predict the damper’s liquid surface movements as well as its capability to reduce structural vibration when the structure is subjected to harmonic excitations. A parametric study is conducted to investigate the effect of head loss coefficients, column spacing, cross-section area ratios, and column numbers on mitigating structural response. It is found that, while TLMCDs are less effective than traditional TLCDs under an equal liquid mass, they can provide enhanced performance under geometric restrictions