Self-centering Beam Research Articles

Study on seismic performance of prefabricated self-centering beam to column rotation friction energy dissipation connection

Under severe earthquakes, a significant number of unexpected plastic hinges and brittle failure were found in conventional rigid beam to column welded connections of steel frames. To improve the seismic performance of steel frames, an innovative prefabricated self-centering beam to column (SCBC) connection was proposed and experimentally validated in this paper. The SCBC connection consisted of disc springs at the bottom flange of beam and a rotation friction hinge (RFH) at the beam end. The bottom disc springs could not contact with slab systems and provided restoring moment, whereas the RFH was designed to dissipate seismic energy. Firstly, its configuration form and design methodology were introduced. Then cyclic tests of a 1/4 scale SCBC connection specimen was carried out and the responses of the SCBC connection was compared to that of the RFH. Finally, the restoring force model of the SCBC connection was established through theoretical analysis. The experimental and analytical results demonstrated full flag-shaped hysteretic curves of the SCBC connection under cyclic loadings, verifying the desirable energy dissipation capacity and reliable self-centering capability of the SCBC connection. The calculation results based on the restoring force model were in good agreement with the test results, showing that the proposed restoring force model could reasonably predict the hysteretic behavior of the SCBC connection.

Experimental Investigation of a Self-Centering Beam Moment Frame

The self-centering beam (SCB) is a shop-fabricated unit that can be implemented in moment-resisting frames using conventional field construction methods to minimize permanent residual drifts after earthquakes and concentrate seismic damage in replaceable elements. An experimental program was conducted on five SCB specimens that were approximately two-thirds scale relative to a prototype building. The results showed that the beam end moments are not equal, as much as 60% different at peak moment, so total flexural strength, calculated as the sum of the moments at both ends, is a better way to characterize SCB flexural strength. Using this approach, the proposed equation to predict flexural strength exhibited an average error of 5% compared to the tests. The SCB was shown to have exceptional deformation capacity as the specimens were subjected to as much as 6% story drift, and the detailing was shown effective at concentrating inelasticity in the replaceable energy dissipating elements. The proposed design procedure is shown capable of controlling the story drift associated with undesirable limit states, limiting story drifts at zero force (eliminate residual drifts), and producing no observable inelasticity outside the energy-dissipating element at design level drifts.

Seismic performance of steel frame with a self-centering beam

Self-centering moment-resisting frames are capable of returning to their original plumb position after a severe earthquake, having sustained no or only slight structural damage. In this paper, a steel frame composed of a self-centering I-beam is proposed, with its capacities for self-centering and inelastic deformation provided by post-tensioned (PT) strands and energy dissipating (ED) elements, respectively. Based on an analysis of its mechanical properties, an experiment involving this self-centering frame under cyclic loading was conducted to investigate its load transfer mechanism, bearing capacity, hysteretic behaviour, ductility, energy dissipating capacity and self-centering capacity. The results agree well with the theoretical analysis, and it can be concluded that its force-displacement hysteretic curve has a typical flag shape. The plastic deformation of the specimen is concentrated on the ED elements, which can be replaced easily after an earthquake. As the gap-opening of the anchorage plate occurs, the PT strands and ED elements provide the bending stiffness for the structure. When the story drift is loaded to 4%, the skeleton curve does not have a descending section, which means that the structure still has sufficient bearing and deformation capacities. The analysis of the residual story drift and the equivalent viscous damping coefficient shows that the frame has good energy dissipating and self-centering capabilities. A finite element model is established with OpenSees to simulate the seismic behaviour of the self-centering frame. Using the model, the seismic performance of the frame is analysed in terms of its structural parameters, including the section area of the PT strands, initial stress on the PT strands and section area of the ED elements.

Seismic design and performance of self-centering-beam moment-frames

A self-centering beam (SCB) is an innovative shop-fabricated structural member incorporating a gap-opening mechanism into its body. This beam can exhibit self-centering characteristics by using high-strength post-tensioning strands and by dissipating seismic energy by combining pretensioned bolt frictional devices. This paper describes a step-by-step seismic design of self-centering-beam moment frames (SCB-MFs). A series of 3-, 6-, 9- and 12-storey steel frames is designed using this procedure. Fabrication tolerances are included in the model to investigate the effects of beam length tolerance on the seismic responses of SCB-MFs. Nonlinear time history analyses are conducted on these frames under an ensemble of 20 historical earthquakes. The same buildings are designed as ‘special moment frames’ according to ASCE 7–16 for seismic comparison. The results suggest that the proposed SCB-MFs with fabrication tolerances can achieve comparable maximum seismic performance and eliminate residual drifts compared with traditional moment frames of an equivalent beam size and having fully restrained connections.

Experimental Investigation of Self-Centering Beams for Moment-Resisting Frames

AbstractPreviously proposed self-centering moment-resisting frames relied on gap opening and closing in the beam–column interface to achieve recentering capability and energy dissipation capacity. ...

Initial stiffness of self-centering systems and application to self-centering-beam moment-frames

There has been considerable development of self-centering seismic force resisting systems in the past few decades, many of which incorporate gap opening mechanisms. Experiments on these self-centering systems often result in an initial stiffness that is less than the predicted theoretical stiffness. While the discrepancy has often been attributed to uneven bearing surfaces at the gap opening mechanism, the cause of the low stiffness is not well understood and can have critical importance for drift-controlled systems such as moment frames.Concepts related to the initial stiffness of self-centering systems are investigated and the difference between experimental and theoretical initial stiffness is evaluated for a range of previous testing programs on different types of self-centering systems. Seven sources of added flexibility are identified. Then, the concepts for improving initial stiffness are applied to one specific system, the self-centering beam moment frame (SCB-MF). The self-centering beam consists of a two-part beam (upper and lower parts), post-tensioning strands to keep the parts aligned, and bolted friction elements to dissipate seismic energy. The initial stiffness of the SCB-MF is predicted using derived equations and finite element analyses and then the predictions are evaluated against experimental results. It is shown that if the added sources of flexibility are neglected (which is typical practice), the ratio of the average initial secant stiffness from five experiments to the predicted value is 38%, but that if the sources of flexibility are considered, the initial stiffness can be captured. The average ratio of measured to predicted stiffness for the theoretical model including pin flexibility is 59%, while the average ratio for finite element analyses including pin flexibility and beam length tolerance is 102%, demonstrating a significant improvement in accuracy. Using this new understanding about the sources of flexibility in self-centering systems, methods for increasing the stiffness of the SCB-MF are proposed and evaluated.

A simplified numerical model for post-tensioned steel connections with bolted angles

Post-tensioned (PT) self-centering beam–column connections has been developed for its good seismic performance. Many researchers have investigated its mechanical behavior by numerical or experimental method. Prior researches have indicated that the analysis by elaborate FE models is very time consuming. To overcome this disadvantage, a simplified numerical model was established in this paper. The accuracy of results derived by this model was validated against prior investigations on interior PT connections with top-and-seat angles. Influence of initial PT force on mechanical behavior of PT connection was investigated. The Geometric and material nonlinearities, and strands can be considered in the modeling. A planar steel frame structure was established and hysteretic analysis was conducted. Results indicated that the computational cost can be greatly reduced by this model.

Experimental study of the restoring force mechanism in the self-centering beam (SCB)

In the past, several self-centering (SC) seismic systems have been developed. However, examples of selfcentering systems used in practice are limited due to unusual field construction practices, high initial cost premiums and deformation incompatibility with the gravity framing. A self centering beam moment frame (SCB-MF) has been developed that mitigates several of these issues while adding to the advantages of a typical SC system. The self-centering beam (SCB) is a shop-fabricated, self-contained structural component that when implemented in a moment resisting frame can bring a building back to plumb after an earthquake. This paper describes the SCB concepts and experimental program on five SCB specimens at two-third scale relative to a prototype building. Experimental results are presented including the global force-deformation behavior. The SCBs are shown to undergo 5%–6% story drift without any observable damage to the SCB body and columns. Strength equations developed for the SCB predict the moment capacity well, with a mean difference of 6% between experimental and predicted capacities. The behavior of the restoring force mechanism is described. The limit states that cause a loss in system's restoring force which lead to a decrease in the selfcentering capacity of the SCB-MF, are presented.

Cyclic behavior of a prefabricated self-centering beam–column connection with a bolted web friction device

A prefabricated post-tensioned (PT) self-centering beam–column connection using a bolted web friction device (PSC connection) has been proposed. This connection is different from a common self-centering connection using a bolted web friction device (SC connection) in that the beam of a steel frame with a PSC connection is divided into three parts connected with a vertical plate and PT strands, and the beam, including the gap opening feature, can be treated as a normal single beam on site. Eight PSC connections were designed with various combinations of design parameters, which include the initial PT forces, friction bolt forces and loading histories. Low-cycle loading experiments were conducted to study the seismic behavior of the PSC connections and to investigate the effects of the initial PT force and the friction bolt force. Additionally, relevant theoretical analyses were conducted, and the results indicated that the maximum PT force at 5% radians drift with the PSC connection did not exceed the yield force, and the average loss of the PT force was within 10%. The residual rotations of all the specimens were minimal, which indicated that the PSC connection had the same robust self-centering behavior compared to that of the SC connection. Simultaneously, the PSC connection does not require on-site aerial tension in high-rise buildings because the post tensioning can be introduced on the ground or in the factory. The theoretical double-flag models match the experimental results notably well and can be applied in the analysis and design of prefabricated self-centering steel frames.

Experimental Study of a Self-Centering Beam–Column Connection with Bottom Flange Friction Device

A new beam-to-column connection for earthquake-resistant moment-resisting frames is introduced. The connection has a beam bottom flange friction device (BFFD) and posttensioned (PT) high-strength steel strands running parallel to the beam. The BFFD provides energy dissipation to the connection and avoids interference with the floor slab. The PT strands produce self-centering connection behavior. The connection behavior requires minimal inelastic deformation of the connection components and the beams and columns, and requires no field welding. A series of seven large-scale tests were performed to investigate the effect of the BFFD friction force, connection details, and the loading history on the performance of the connection under cyclic loading. The test results indicate that the BFFD provides reliable energy dissipation, and that the connection remains damage-free under the design earthquake.