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

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.