In recent years, many new buildings have been designed for low-damage seismic performance in order to achieve earthquake resilience, contrary to seismic design codes, which primarily focus on life safety (ASCE/SEI 7-10, 2010). Many researchers have investigated a variety of approaches to increase the resilience of buildings against wind or earthquake loads. Supplemental passive damper systems such as viscous and visco-elastic dampers are considered effective and affordable means of improving seismic resilience. However, these rate-dependent dampers may unintentionally overstress the columns of the building since their force output depends on inter-storey velocity. One way of reducing the aforementioned detrimental effect is to control the peak damper force using a hybrid damper system. This paper evaluates the seismic performance of steel frames equipped with visco-plastic dampers. The visco-plastic damper is realised by the in-series combination of a viscoelastic damper and a friction device. The main goal of exploiting the visco-plastic damper in resilience-based seismic design is the reduction of storey drifts without increasing the base shear force, i.e., a design objective that is difficult to achieve with conventional viscous or viscoelastic dampers. 

A prototype steel building is designed as a high ductility steel momentresisting frame (MRF). This MRF is then equipped with viscoelastic or viscoplastic dampers to achieve high seismic performance. Parametric designs are carried out by designing visco-plastic dampers with different activation forces for their friction devices. Non-linear dynamic analyses for a set of 20 earthquake ground motions scaled to the design and maximum considered earthquake intensities are carried out in OpenSees. The response results highlight the advantages of the visco-plastic damper. Moreover, they provide the basis to identify the appropriate range of activation force values for the visco-plastic damper’s friction device so that drift reduction and control of the peak base shear force can be simultaneously achieved. Also, peak residual drifts that are directly related to the earthquake resilience of the building are compared between the frames with viscoelastic and visco-plastic dampers under DBE and MCE levels. Furthermore, IDA (Incremental Dynamic Analysis) are carried out on the MRFs with viscoelastic and visco-plastic dampers using a set of 20 far-field seismic records to evaluate vulnerability to collapse. 

The results highlight the effectiveness of the visco-plastic damper in controlling drifts, residual drifts, and the base shear force, while also providing adequate seismic collapse resistance.

Seismic design and assessment of resilient steel frames with visco-plastic dampers

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High-performance braces for seismic design

In the performance-based design, determination of performance and evaluating the structure and its components requires to assess the seismic capacity and demand. In order to achieve these goals, analytical methods with high capabilities of modeling the structure and seismic excitations are required. Linear and non-linear approaches were introduced as analytical methods for rehabilitation pre-standard, where both of them can be done statically or dynamically. Among nonlinear methods, usage of nonlinear static analysis (Pushover analysis) for evaluating the structures is proliferated. This analysis aimed on evaluating the expected performance of structural system and estimating the resistance and deformation demands of it in design earthquake. These demands are compared to the existed capacities of target performance levels. In order to calculate the target displacement or performance point, different methods such as Capacity Spectrum Method (CSM) in ATC-40 [1] and Coefficient Method in FEMA-356 [2] were introduced. However, based on previous researches, the observed results of applying these methods for identical structures were dissimilar. Therefore, FEMA-440[3] proposed two enhanced methods to modify these methods and convergence of their outcomes. The aim of this study is to investigate and compare the accuracy of capacity spectrum method introduced by ATC-40 with modified capacity spectrum method of FEMA-440 for evaluating the seismic performance of Buckling Restrained Braced Frame (BRBF).

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Evaluation of Capacity Spectrum Method for Estimate of Seismic Performance in Buckling-Restrained Braced Frame