Double Friction Pendulum Bearings Research Articles

Shaking table tests of base-isolated reinforced concrete frame by double friction pendulum bearings

The effectiveness of seismic isolation by friction pendulum bearings (FPBs) in protecting structural and non-structural components from damage was evaluated by shaking table tests. A base-isolated reinforced concrete frame model by double friction pendulum bearings (DFPBs) with 1/5 scale was considered in the experimental program. A non-isolated model was also tested for comparison. The models were subjected to ground motions with incremental earthquake intensities. This paper presents a comprehensive overview of the test results in terms of peak inter-story drifts, peak floor accelerations, floor acceleration response spectra, hysteretic behaviors, seismic responses of the DFPBs and damage mechanisms of the structures. The results demonstrated that the base-isolated system can effectively protect both structural and non-structural components even under earthquakes larger than maximum considered intensities. The residual displacements of DFPBs remained small after multiple inputs and showed no direct correlation with the maximum sliding displacement and earthquake intensities. The effects of vertical earthquake shaking on the displacement responses of DFPBs were negligible for the test model.

An adaptive friction isolation system for seismic response control of buildings

This paper proposes an adaptive friction isolation system (AFIS) composed of shape memory alloy (SMA) cables and double friction pendulum bearings (FPBs). Double FPBs with different friction coefficients enable two-level response characteristics that are advantageous at frequent and design basis hazard levels, while SMA cables with initial slack provide adaptive response at maximum considered earthquake hazard level. SMA cables are arranged vertically and they limit excessive isolation displacement by providing hardening effects and additional energy dissipation capacity. They also improve the stability of FPBs under severe earthquakes. Based on the experimental response of FPB and SMA cables, a high-fidelity finite element model of AFIS is first established in ABAQUS. Then, to study the effectiveness of the AFIS in controlling seismic response of structures, a simplified model of the AFIS is developed in OpenSees and nonlinear time history analyses of a seven-story steel frame building isolated with AFIS are conducted. The results show that the AFIS can satisfactorily meet displacement demands under frequent and moderate earthquakes, while it effectively reduces the excessive displacement of the building under severe earthquakes. In particular, the AFIS considerably improves the performance of the isolated building under pulse-like near-fault earthquakes.

Comparative response assessment of base-isolated braced-frame buildings considering effects of ductility design

This paper evaluates seismic responses of steel concentrically bracing frames isolated by double friction pendulum bearings with two levels of ductility. The seismic responses of base-isolated buildings are compared to their comparable fixed-base buildings. For this purpose, two isolated and two conventional concentrically braced-frame low-rise buildings are seismically designed, and their three-dimensional finite element models are developed in OpenSees. To investigate the impact of ductility, seismic responses of both ordinary and special levels of ductility are computed and analyzed. The results indicate that the ductility levels significantly affect seismic responses of base-isolated buildings. The superstructure with special level of ductility decreases the peak floor acceleration compared to the ordinary ones. The maximum reduction is calculated by about 20%. Moreover, special ductility level increases peak drift demand compared to the ordinary ones up to 75% in base-isolated buildings. Furthermore, the results show that the ordinary superstructure reduces the maximum and residual displacement of double friction pendulum bearings compared to the special ones. • Effects of level of ductility on seismic responses of isolated concentrically braced-frame buildings. • Seismic assessment of buildings with double friction pendulum bearings. • Comparative response evaluation of base-isolated and conventional steel frames. • Considering different hazard levels in assessment of base-isolated buildings.

On the Influence of the Vertical Earthquake Component on Structural Responses of High-Rise Buildings Isolated with Double Friction Pendulum Bearings

The double friction pendulum (DFP) bearing is adapted from the well-known single friction pendulum (SFP) bearing. This type of bearings has been widely used for structural vibration controls. The main advantage of the DFP is its capacity to accommodate larger displacements as compared with the SFP one. This paper aims to assess the effect of the vertical earthquake component on the seismic behaviour of a base-isolated high-rise building. In this respect, the mathematical model of the building subjected to earthquake excitations with an implementation of a DFP bearing system is established. The model presented herein considers earthquake excitations in horizontal (X and Y) and vertical (Z) directions. A series model of two friction elements is presented for the bearing, where the friction load of the bearing surface is governed by a modified Bouc-Wen model, which is dependent on the sliding velocity and the contact pressure. The numerical results of an example of a base-isolated 9-story steel building subjected to near-source and far-field earthquakes show the high effectiveness of the bearing system in reduction of the seismic response of the building, especially in the near-source region, as well as exhibit considerable effectiveness of the vertical earthquake component on the bearing and structural behaviour.

Optimizing the seismic response of base-isolated liquid storage tanks using swarm intelligence algorithms

Large-scale liquid storage tanks are used worldwide for storing water, chemicals and fuels, such as liquefied natural gas (LNG) and oil. Any major damage due to man-made or natural hazards, such as earthquakes, to these critical infrastructures would cause serious socio-economical losses and devastating environmental consequences. Moreover, they should remain functional even after a severe earthquake to support restoration actions, thus, their robust and optimal seismic design is deemed necessary. For this reason, base isolation is generally considered as a highly efficient technique for their seismic protection. Elastomeric bearings, such as lead-rubber bearings (LRB), high damping rubber bearings (HDRB) and friction bearings: single friction pendulum bearings (SFPB), double friction pendulum bearings (DFPB) and triple friction pendulum bearings (TFPB) have been used. In this work, the focus is given on the sizing optimization of the main parameters of SFPB and TFPB isolators. For this reason, efficient swarm intelligence optimization algorithms are used to derive optimal friction coefficient and radius of curvature values that enhance the dynamic performance of a base-isolated liquid storage tank. The main objective of the proposed formulation is to minimize the accelerations transmitted to the superstructure, while constraints related to damping and vibration period of the system are imposed.