Fragility assessment and optimum design of a steel–concrete frame structure with hybrid energy-dissipated devices under multi-hazards of earthquake and wind

Highlights

• A multi-hazard protective frame structure with hybrid energy-dissipated devices of BRB and VD is proposed.

• The effectiveness of the HDF in the vibration control against the multiple hazards of earthquake and wind is studied.

• The multi-hazard fragility surfaces of the HDF under combined earthquake and wind loads are generated.

• The optimal design schemes of the HDF under multiple hazards are suggested.

Abstract

Engineering structures may inevitably be subjected to earthquakes and winds during their life cycles, furthermore, with the probability of simultaneous occurrence, the hit of combined earthquake and wind shall pose a stiffer threat to the structural functionality and safety. Passive control technique is a practical and effective method to mitigate earthquake and wind hazards for new or existing engineering structures. This paper develops a multi-hazard protective system with the hybrid energy-dissipated devices of buckling-restrained braces (BRBs) and viscous dampers (VDs), and investigates the effectiveness and optimum design parameters of different supplemental devices using the fragility function method. The OpenSees platform is employed to establish the finite element (FE) models of bare steel–concrete moment resisting frame (MRF), buckling-restrained braced frame (BRBF), viscous damped frame (VDF) and hybrid damped frame (HDF) with both BRBs and VDs. In total 120 groups of combined “earthquake-wind” events with a wide range of hazard intensities are developed using the Monte Carlo simulation, which are applied to the dynamic time history analyses of the aforementioned four frame structures. The multi-hazard fragility surfaces, which depict the exceeding probability of structures under simultaneous earthquake and wind loads, can be generated for different damage states. The numerical results indicate that the HDF is an effective structural system against the multiple hazards attacks, and the energy dissipation contributions of BRB and FVD vary with the hazard intensities of earthquake and wind. To further identify the optimum design scheme for the HDF system, the parameters of hybrid passive control devices are extensively investigated by evaluating the hazard intensities required when achieving specified damage states in the fragility surfaces. The findings can provide a practical guide for the design of structure with energy-dissipated devices against the multi-hazard scenarios of earthquake and wind.

Introduction

Recently, due to the development of construction technology and utilization of high-performance materials, modern buildings become higher and larger, which makes them vulnerable to severe multi-hazard environments of earthquakes and strong winds. During an extreme earthquake or wind event, high-rise building structures are liable to exceed the code specified deformation or acceleration limits, which may further affect their functionality and safety. Moreover, as investigated and revealed by previous study [1], the coupling effects of earthquake and wind may generate more serious structural damage than the sum of the individual effect of each hazard. Although the probability for simultaneous occurrence of earthquake and wind is limited, as generally deemed and adopted in almost all the current literature that earthquake and wind are independent hazard events [2], [3], considerable economic losses and catastrophic casualties may be caused to the society and human beings once the high-rise structures are struck by the low-probability but high-consequence event of concurrent earthquake and wind. Thus, it is of great significance to investigate the performance of high-rise structures under the combined effects of earthquake and wind hazards [4].

Considering the significant risk posed by multi-hazard scenarios during structural life-cycles, the engineering community has been devoting to mitigate the adverse responses against multiple threats by developing efficient and advanced protective techniques [5]. Passive control technique is a viable and effective strategy providing the multi-hazard protection to building structures [6]. The supplemental energy-dissipated devices play a vital role in modifying the structural dynamic properties, controlling the structural response, and absorbing the input energy caused by multiple hazards of earthquakes and winds. In addition, these devices have the advantages of cost-saving, easy maintenance and non-necessity of external power supply over other control approaches, which greatly promote their application in designing new buildings or retrofitting existing structures. According to their mechanical behavior, the energy-dissipated devices can be classified as displacement-dependent and velocity-dependent devices. Friction dampers [7], metallic yielding dampers [8] and buckling-restrained braces (BRBs) [9], [10] are typical displacement-dependent devices which provide substantial elastic stiffness and enhance energy dissipation capacity after slipping or yielding of the device. They are reliably adopted to absorb input energy and reduce structural displacement under moderate and major earthquakes. The velocity-dependent devices include viscoelastic dampers (VEDs) [11] and viscous dampers (VDs) [12], [13] which dissipate energy primarily by relative velocity between the device attachment ends. Regardless of structural deformation, such devices are effective for vibration control in tall buildings against minor earthquakes and strong winds [14]. Although the energy-dissipated devices have been prevalently applied for protecting structures due to their economy and efficiency, there are still some disadvantages for each kind of device. As a matter of fact, the displacement-dependent devices may be inactive during mild earthquakes since they do not supply sufficient supplemental damping to the structure [15]. Furthermore, the added structural stiffness may increase seismic forces and floor accelerations, which negatively affect the functionality of the nonstructural components [16]. For the velocity-dependent devices, they may fail to reduce structural responses effectively during the early stages of earthquake events [17].

Combining the displacement-dependent and velocity-dependent devices is an effective and economical way to exploit the strengths and minimize the shortcomings of the individual dampers [18], [19]. The hybrid systems consisting of two or more energy-dissipated devices offer promising means to balance the stiffness, strength and energy dissipation against multiple hazards. Some researchers had devoted efforts to investigate the efficiency of hybrid damped systems under earthquake or wind hazards [20], [21], [22], [23], [24]. Kim and Shin [25] carried out performance assessment of a frame structure with various steel-friction hybrid damper schemes, and results proved that the seismic performance of structure with the hybrid dampers are superior to that of structure with individual damper device. Marshall and Charney [26] numerically studied hybrid passive control systems with BRBs and either viscous fluid dampers or high-damping rubber dampers in steel structures subjected to seismic hazards. The hybrid passive control structure proved to be an effective seismic protective system and was practically applicable for the performance-based seismic design. Kim et al. [27] conducted the time-history analyses to investigate the wind-induced vibration control performance of a hybrid damping system which consists of VEDs and BRBs. The proposed hybrid system showed an excellent capacity in improving both the lateral stiffness and serviceability of tall building under wind hazards. Addala et al. [28] presented an innovative hybrid passive control device including friction dampers and a VED in parallel, which was available to control a wide range of structural vibrations from wind and minor to major earthquakes. Actually, given the intricate condition and significant risk posed by the concurrent occurrence of earthquake and wind, the exploitation of hybrid system is an effective approach to protect the engineering structure from multi-hazard threats which deserves delving investigation.

As mentioned before, previous work in a hybrid system has showed the capability to improve the structural behavior compared with conventional individual damper system for the structures subjected to winds and earthquakes. Yet, the system performance is closely related to the distribution, number and size of dampers installed in the structure. Many researchers have put forward different approaches to solve the optimization problem, such as simplified sequential search algorithm [29], [30], exhaustive single point substitution [31], steepest descent search algorithm [32], stochastic control approach [33], genetic algorithm [34] and fragility function methodology [35]. For example, Furuya et al. [36] acquired a proper damper placement for a 40-story building under wind-induced vibrations using the genetic algorithm. Du et al. [37] proposed a multi-performance optimization design method for a hybrid damping system with VDs and BRBs against the seismic hazard. Agrawal and Yang [38] employed combinatorial optimization method to obtain the optimal placement of passive dampers for the seismic and wind excited linear buildings. More recently, some researchers also studied the efficiency of retrofitted damper devices by optimizing the life-cycle cost of the system subjected to multiple hazard scenarios [39], [40]. However, very few studies have been reported about the optimum design of hybrid energy-dissipated devices for the structure against the multiple hazards, especially for the concurrent earthquake and wind. In addition, as revealed by Roy and Matsagar [41], [42], a remedial measure for a particular hazard may worsen the consequence of the structure under the other hazard. As a consequence, to develop an efficient and optimized hybrid system achieving the performance target against the severe multi-hazard scenario of simultaneous earthquake and wind, it is vital to conduct comprehensive performance assessment and parametric study to identify the optimal design of the frame structure with hybrid energy-dissipated devices.

The organization of this paper is overviewed as follows. In Section 2, four types of frame structure with various damper devices are introduced in details, and the corresponding finite element models are numerically established employing the OpenSees platform. The time-history dynamic analyses under simultaneous earthquake and wind hazards are carried out in Section 3, and a series of structural responses including roof displacement, roof acceleration, story drift ratio and force–deformation relationship of damper devices are systematically investigated. Meanwhile, the control effects of various damper devices are comprehensively discussed. Based on the adopted multi-hazard fragility surface method, the fragility surfaces and performance assessments for different energy-dissipated frame structures are presented in Section 4. Section 5 provides a parametric study on the optimal design scheme of the frame structure with hybrid energy-dissipated devices. Using the fragility function method, various design parameters are suggested for the hybrid damped frame structure at different multi-hazard areas. At the end of this paper, relevant conclusions and recommendations are summarized in Section 6.