Self-centering Research Articles

Experimental study of a self-centering prestressed concrete frame subassembly

This paper presents the experimental investigation of the behavior of a 0.5-scale, one-bay, one-story self-centering (SC) moment resisting concrete frame subassembly under cyclic loading. The SC frame utilizes post-tensioned (PT) beam–column connections and column–foundation connections to provide the re-centering capabilities after earthquakes. Beam web friction devices are included in the beam–column connections to provide the adjustable energy dissipation capacity, and steel jackets are used at the beam ends and column bases to avoid concrete crushing at the contact interfaces. The influence of various parameters (i.e. initial PT forces in the beam and columns, friction forces, etc.) on the seismic behavior of the SC frame is experimentally examined, and it is observed that the frame subassembly performed well up to a 2.5% drift with only minor damage in concrete cover of the beam, and the column remained damage free. To avoid the stiffness reduction upon unloading and to achieve desirable energy dissipation, the stiffness of the friction devices and connecting bolts should be properly enhanced in future study.

Development of a novel self-centering buckling-restrained brace with BFRP composite tendons

Buckling-restrained braces (BRBs) have excellent hysteretic behavior while buckling-restrained braced frames (BRBFs) are susceptible to residual lateral deformations. To address this drawback, a novel self-centering (SC) BRB with Basalt fiber reinforced polymer (BFRP) composite tendons is presented in this work. The configuration and mechanics of proposed BFRP-SC-BRBs are first discussed. Then an 1840-mm-long BFRP-SC-BRB specimen is fabricated and tested to verify its hysteric and self-centering performance. The tested specimen has an expected flag-shaped hysteresis character, showing a distinct self-centering tendency. During the test, the residual deformation of the specimen is only about 0.6 mm. The gap between anchorage plates and welding ends of bracing tubes performs as expected with the maximum opening value 6 mm when brace is in compression. The OpenSEES software is employed to conduct numerical analysis. Experiment results are used to validate the modeling methodology. Then the proposed numerical model is used to evaluate the influence of initial prestress, tendon diameter and core plate thickness on the performance of BFRP-SC-BRBs. Results show that both the increase of initial prestress and tendon diameters can obviously improve the self-centering effect of BFRP-SC-BRBs. With the increase of core plate thickness, the energy dissipation is improved while the residual deformation is generated when the core plate strength exceeds initial prestress force.

Residual Drifts of Self-Centering Systems Including Effects of Ambient Building Resistance

There has been widespread interest in the development and use of self-centering (SC) lateral resisting systems that eliminate residual drifts after large earthquakes. SC systems often include a restoring force component and a component that dissipates seismic energy. Typically, it is assumed that the criterion for self-centering is satisfied if the restoring force is proportioned to be greater than the force required to yield the energy dissipating component. A parametric SDOF study was conducted using time-history analyses on several prototype buildings to quantify the effect of varying system parameters on structural response including residual drifts. The ambient resistance of the rest of the building was considered, as well as proportioning the system with less restoring force than the yield capacity of the dissipative component. In addition, the probabilistic mechanism that creates a propensity for reducing residual drifts in systems with little or no restoring force is explored and quantified. It was found that a restoring force that is at least one-half of the force required to yield the dissipative component will still reliably eliminate residual drifts in a non-softening system.

Analytical model validation and influence of column bases for seismic responses of steel post-tensioned self-centering MRF systems

The first generation for the post-tensioned (PT) self-centering (SC) system, which incorporates the PT technology to beam-to-column connections, exhibits good seismic performance with small residual deformations except for the first floor. Instead of using the fixed column base, the column PT to the base affects the seismic performance of frames, especially for residual deformations. Recently, the seismic response of a SC frame subassembly, which applied the PT technology to the connection and column base, was verified in shake table tests. In this paper, a three-dimensional analytical model with rotational springs in the PT connection and PT column base was introduced to capture shake table test results of the frame subassembly. The same modeling approach was adopted to one MRF and three SC frames to study the effects of column bases on the seismic responses of frames under the design-based and maximum-considered earthquakes. The monotonic, cyclic pushover, and time–history analyses were conducted for these frames. Analytical results showed that (1) the residual drift of the first floor could be significantly minimized by using the PT column base but the maximum interstory drift in the SC frame increased with decreasing fixity at the column base, (2) the largest maximum interstory drifts of the SC frames were larger than those of the MRF due to the low-to-medium structural period and high yield strength, and (3) the SC frame with the PT column base effectively decreased column restraining forces to the first floor compared to that with the fixed column base.

Tests and analyses of a full-scale post-tensioned RCS frame subassembly

A series of cyclic tests of a full-scale one-story two-bay specimen frame, a substructure of a three-story post-tensioned (PT) self-centering (SC) building using reinforced concrete columns and steel beams, were conducted in the Taiwan National Center for Research on Earthquake Engineering. The objectives of the tests were: (1) to examine the connection performance, progress of damage, and strength degradation of the frame, (2) to assess the hysteretic responses of the frame subjected to various loading patterns, and (3) to study the effects of column restraints on the frame expansion. Time-history analyses of the three-story PT building subjected to the design basis earthquake (DBE) and the maximum considered earthquake (MCE) were conducted to investigate seismic demands of the proposed system. These tests confirmed the SC response of the PT frame and explored failure of the beam compression toe, which was never observed in prior tests of beam–column subassemblages. The nonlinear structural analysis computer program PISA could be used to simulate the experimental results well; time-history analyses of the three-story building showed that the proposed frame can meet seismic demands by MCE level ground motions.