Asymmetric Friction Connections Research Articles

Experimental study and numerical simulation analysis of RCS joint with asymmetric friction connection

Based on the seismic design principle of recoverable function and replaceable seismic design, a novel type of reinforced concrete column-steel beam (RCS) joint was proposed, incorporating an asymmetric friction connection in the lower flange of the steel beam. Subsequently, experimental tests, numerical simulations, and theoretical analyses were conducted to evaluate this joint. The test results indicate that the RCS joint with asymmetric friction connection can effectively exert friction slip energy dissipation characteristics, demonstrating good seismic performance in terms of bearing capacity and stiffness. The damage observed in the specimen is primarily focused on the spliced cover plate of the steel beam, with minimal deformation in the core area of the joint. Numerical simulation and parameter analysis were conducted using ABAQUS software. The results demonstrate that the finite element model accurately reproduces the observed phenomena in the test. The parameter analysis reveals that a 10 % increase in bolt preload or a 0.05 increase in friction coefficient can result in a 7 % or 13 % rise in joint bearing capacity, respectively. Finally, a calculation method for determining friction slip in RCS joints with asymmetric friction connection was developed, showing close agreement between the calculated results and finite element outcomes, indicating the accuracy of the formula.

Experimental study on low-damage performance of Sliding Hinge Joint

The Sliding Hinge Joint (SHJ) is a low damage beam-to-column joint primarily for moment resisting steel frames (MRSFs). It is intended to remain rigid during frequent earthquake events, while rotation occurs between the column and beam under design basis earthquake events. At the end of earthquake events, the joint is expected to seize up and become rigid again. However, residual strength and stiffness of the SHJ are considerably reduced even within design-level sliding. The objective of this study is to evaluate resilience and repairability of the SHJ by carrying out cyclic loading on a full-scale beam-to-column assembly considering both design-level sliding and post design-level sliding. Overall, the SHJ exhibited a predictable and stable hysteretic response. It was concluded that the SHJ experienced a 79.5% decrease in average moment resistance and a 59.4% decrease in elastic rotational stiffness with no repair actions taken. Resilience of the joint could be achieved by replacing and retightening the asymmetric friction connection (AFC) bolts to bring the joint back to an as-built condition. Moreover, a detailed finite element model was developed to further investigate the plastic strain distribution, frictional sliding and energy dissipation behaviours of the joint, and the low-damage performance was verified. Finally, a simplified analytical model based on the component method was proposed to predict the joint behaviour.

Seismic performance of a low-damage rocking column base joint along weak axis

This paper presents an experimental and analytical study on seismic performance of a low-damage rocking column base joint equipped with an asymmetric friction connection (AFC). Cyclic loading tests were conducted along weak axis of the column, including INITIAL, AFTERSHOCK and REPAIR cases. Compared with the INITIAL case, the joint exhibited a 2.5% decrease in average moment resistance and a 24.9% decrease in rotational stiffness in the AFTERSHOCK case without any repair taken. By re-installing and tightening the AFC bolts, the moment resistance was completely restored and the rotational stiffness could reach 84.1% of the INITIAL case, achieving resilience and reparability of the joint. Internal forces of the column were effectively limited by frictional sliding of the AFC, and the maximum local equivalent plastic strain at the column base was only 1.0% at a drift ratio of 3%. Axial force, as the main source of restoring forces, provides a favorable tendency for self-centering of the joint. In addition, a finite element (FE) model was developed to quantitatively evaluate damage and sliding behaviors of the joint, and the low-damage characteristics were verified. Finally, a simplified analytical model was proposed to guide the design of this low-damage joint.

Experimental investigation of a novel sleeved member with additional friction dampers

A novel sleeved member with additional friction dampers, which is abbreviated as the frictional sleeved member (FSM) in this paper, was proposed to ensure the stability and greater energy dissipation of compression members in space structures. The FSM consisted of an inner core, an outer sleeve, and additional friction dampers. Two semicircular pipes were fastened by high-strength bolts to obtain the outer sleeve. Friction dampers using composite friction materials were distributed on both sides of the sleeve in the long-axis direction. Cyclic compression-unloading tests of four compression members were completed in this paper. The test results showed that the FSM exhibited the following characteristics compared with an ordinary assembled sleeve member (ASM): comparable lateral-constraint capacity, greater resistance, and greater energy dissipation capacity under tiny axial displacement (0–4 mm). Nonmetallic friction pads had a stable energy dissipation capacity and slight start-sliding displacement, which met the energy dissipation requirements of the FSM under tiny displacements. The additional friction dampers of the FSM had a slight effect on the deformation mode of the inner core, but the resistance and secant stiffness of the specimen were both significantly improved. The outer sleeve of the FSM adopted an asymmetric friction connection, leading to a periodic local increase and an overall decrease in the clamping force of the high-strength bolts. The extrusion between the outer sleeve and the buckling inner core had a negligible effect on the clamping force of the high-strength bolts.

Finite element modelling (FEM) of the asymmetric friction connection (AFC)

Earthquakes occur frequently in New Zealand as the country is situated in the collision zone between the Indo-Australian and Pacific tectonic plates, where many earthquakes and volcanic activities occur. The consequences of severe earthquakes are injury and loss of life of people, the costs of repair for the damage of the structures and contents, and the costs of disruption of business and other activities. In average, 10 000 people are killed in earthquakes every year. Moreover, the damage and disruption caused by earthquakes throughout the world can be considerable. To avoid these undesirable economic effects of earthquakes, the global tendency has been moving towards the development and implementation of low-damage seismic resisting systems. The low damage design philosophy aims to satisfy the well-accepted “life safety” mandate, and minimize the economic losses due to post-earthquake damage repair as well as the downtime. The Sliding Hinge Joint (SHJ) is a low-damage beam-column connection used in steel moment-resisting frames. It allows large beam-column rotation with minimal damage through sliding in asymmetric friction components (AFCs) that are located at the web bottom bolt and bottom flange levels. AFC is friction seismic energy dissipating component of the SHJ. Following a set of experiments and different analytical research carried out on the AFC, there are proposed modifications to improve the performance of the AFC, and in general the SHJ (Clifton et. al., 2007 & Ramhormozian, 2017). One of the key objectives of this project is to provide a complete literature review and background of the friction energy dissipators for seismic applications including the SHJ developments, and to create numerical models to be validated by the previous and ongoing experimental results of the AFC as well as the SHJ. This includes creating finite element model (FEM) of different sizes, capacities, and configurations of the AFC and those of the SHJ, using ABAQUS software.

Probabilistic friction model for aluminium–steel Asymmetric Friction Connections (AFC)

Multiple physical variables potentially affect the friction coefficient of Asymmetric Friction Connections (AFC). This paper discusses the cyclic response of a class of AFC subjected to repeated load protocols. Two phenomena are observed. First, the friction coefficient, initially higher due to wear phenomena and moment-axial force-shear force interaction, stabilizes after multiple cycles. Second, the test repetitions on the same specimen show that the friction coefficient at the beginning of the loading protocol is higher than that observed at the end of the antecedent load protocol. The experimental data prove that the dissipated energy during the current load test, temperature, and the specimen’s history affect the friction coefficient. This paper presents two probabilistic friction models calibrated using a Bayesian approach. The first engineering-oriented model is dependent on the dissipated hysteretic energy. The second includes the measured temperature as a model regressor to estimate its possible role in the response. The proposed probabilistic models can be used to predict with satisfactory accuracy the friction coefficient in Coulomb-like hysteresis models of AFCs.

Experimental and analytical study of Friction Connection for seismic retrofit with Cross‐Laminated Timber (CLT) panels

AbstractWithin the European project e‐SAFE (Energy and Seismic AFfordable rEnovation solutions), this paper presents the experimental tests and modeling attempts for a class of Asymmetric Friction Connections (AFCs) tested in the laboratories of the Norwegian University of Life Sciences. The AFCs are part of the seismic retrofitting solution, called e‐CLT, based on installing Cross‐Laminated Timber (CLT) panels in reinforced concrete structures using friction connections. The authors carried out experimental tests on AFCs fixed with screws to a CLT panel to observe the contribution of timber to the total dissipation performance. The investigation is based on 20 cyclic test data with two different setups. The main one includes a CLT panel and screw connection, while the second one isolates the friction behaviour to evaluate the influence of the screw connection. A modified LuGre hysteresis model for friction is developed to simulate the experimental cyclic response of the tested specimen. The model possesses a direct physical meaning, and it explicitly depends on the slip force and the pre‐slip stiffness. The optimized model is used to assess the performance of the AFC by varying the pre‐slip stiffness and the slip force.

Experimental Cyclic Response of a Novel Friction Connection for Seismic Retrofitting of RC Buildings with CLT Panels

The seismic vulnerability of existing RC framed buildings in seismic-prone areas requires affordable and practice-oriented solutions for their retrofitting. In this paper, the authors present a retrofitting solution for RC buildings based on the combined use of cross-laminated timber (CLT) panels and asymmetric friction connections (AFCs). The AFC connection is activated when the force level reaches the design threshold. The energy dissipation of the AFC increases the structural dissipation capacity and reduces the displacement demand. This research presents the outcomes of an experimental campaign on selected prototypes of these AFC connectors. The authors assess their dissipative capacity from cyclic load tests in four different connector arrangements and examine the contribution of aluminum shim layers. The first results highlight the significant dissipation potential of the AFC, although they also provide evidence of the notable sensitivity on the design and constructive details. The authors present a modeling approach to simulate the experimental results.

Optimization of the structural coupling between RC frames, CLT shear walls and asymmetric friction connections

This paper focuses on the optimum design of the e-CLT technology. The e-CLT technology consists in adding cross laminated timber (CLT) walls to an existing reinforced concrete (RC) infilled frame via asymmetric friction connection (AFC). The authors carried out quasi-static and nonlinear dynamic analyses. The RC frame is modeled in OpenSees by fiber-section-based elements with force-based formulation. The contribution of the infill is simulated using a degrading data-driven Bouc–Wen model with a slip-lock element while the AFC is modelled with a modified Coulomb model. Different types of infill, aspect ratio, scaling, and member size are considered. The benefits of using e-CLT technology are discussed and the ranges of optimum performance of the AFC are estimated. A comparison of the performance of traditional infills with the e-CLT system is presented. The authors provide optimum intervals of the ratio between slip force and in-plane stiffness of the CLT panel, following energy and displacement-based criteria. The seismic displacement demand under various seismic scenario is investigated. Correlations between the RC characteristics and the optimum design ratios bestow possible criteria for the design of the AFC.

Strong axis low-damage performance of rocking column-base joints with asymmetric friction connections

This paper presents an experimental and analytical study on the low-damage performance of a steel rocking column-base joint equipped with an asymmetric friction connection (AFC). The AFC is located at the web of the column base with a frictional sliding surface parallel to the weak axis of the column. Cyclic tests with and without axial forces were carried out along strong axis of the column, including initial, aftershock and repair cases. It was found that in the absence of axial force, the column was completely uplifted after unloading, while in the presence of axial force, the joint could be self-centered. The presence of axial force provided a good tendency for the self-centering capacity of the joint. Resilience of the joint is achieved by simply re-tightening the bolts, and its seismic performance can be well matched to the initial run without loss of strength and stiffness. A finite element model was developed to investigate the stress distribution and frictional sliding behavior of the joint. The low-damage characteristics exhibited by the joint were verified at a high drift ratio of 3%. Finally, a simplified flag-shaped analytical model was proposed to predict the mechanical behavior of this type of column-base joint.

Design of a novel seismic retrofitting system for RC structures based on asymmetric friction connections and CLT panels

Friction-based dampers are a valid solution for non-invasive seismic retrofitting interventions of existing structures, particularly reinforced-concrete (RC) structures. The design of friction-based dampers is challenging: underestimating the slip force prevents the full use of the potential of the device, which attains the maximum admissible displacement earlier than expected. By contrast, overestimating the slip force may cause delayed triggering of the device when the structure has suffered extensive damage. Therefore, designing the appropriate slip force is an optimization problem. The optimal slip force guarantees the highest inter-story drift reduction. The authors formulated the optimization problem for designing a specific class of friction-based dampers, the asymmetric friction connection (AFC), devised as part of the ongoing multidisciplinary Horizon 2020 research project e-SAFE (Energy and Seismic AFfordable rEnovation solutions). The seismic retrofitting technology involves the external application of modular prefabricated cross-laminated timber (CLT) panels on existing external walls. Friction dampers connect the CLT panels to the beams of two consecutive floors. The friction depends on the mutual sliding of two metal plates, pressed against each other by preloaded bolts. This study determines the optimal slip force, which guarantees the best seismic performance of an RC structural archetype. The authors investigate the nonlinear dynamic response of a coupled mechanical system (RC frame-friction damper) under a set of strong-motion earthquakes, using non-differential hysteresis models calibrated on the experimental cyclic responses. The solution of the optimization leads to the proposal of a preliminary simplified design procedure, useful for practitioners.

Experimental study on mechanical behavior of steel-concrete composite beams with friction connections in different structural zones

in order to study the mechanical properties of steel-concrete composite beams with asymmetric friction connections and considering the structural factors, three simple steel-concrete composite beams with friction connections were fabricated, and the uniaxial low cycle cyclic loading sine wave tests were carried out on the steel-concrete composite beams with friction connections. The test results show that the composite beam can get stable two-stage hysteretic curve in structure 1 and structure 3, and has reliable hysteretic energy dissipation capacity. The hysteretic curve of structure 1 is more full and stable, and the strength increases first and then decreases with the loading.

Asymmetric Friction Connection Bolt Lever Arm Effects on Hysteretic Behaviour

ABSTRACT While Asymmetric Friction Connections (AFCs) have been employed as seismic energy dissipation devices in steel structures, development of design guidance based on robust understanding of their behaviour is required. This paper describes the quasi-static testing of 18 AFCs with Bisalloy 500 shims and 2 M16 Grade 8.8 bolts to quantify the effect of bolt lever arm to bolt diameter (l/d) ratio on the AFC sliding performance. Results show hysteresis loop shape remained similar for all l/d. However, increasing l/d from 1.38 to 3.88 reduced the average AFC strength by 42–47%, reduced the hysteresis loop loading stiffness by 33–47%; and reduced the effective friction coefficient from 0.28 to 0.08. For AFCs with l/d ≥3.25, bolts underwent significant flexural yielding, which reduced their performance in future cycles.

Experimental studies on Belleville springs use in the sliding hinge joint connection

The Sliding hinge joint (SHJ) is a low damage beam-to-column connection developed for and widely used in seismic moment-resisting steel frames (MRSFs). The asymmetric friction connection (AFC) is the SHJ's friction sliding energy dissipating component, which has also been used in other seismic resisting structural systems. In current practice, the AFC bolts are yielded at installation by the method of bolt tightening, and they are subjected to moment, shear, and axial force (MVP) interaction during stable sliding. Hence the AFC bolts tension, and as a result, SHJ elastic strength will be reduced after sliding cycles. A remedy to this post-sliding strength reduction could be installing the AFC bolts in the elastic range in conjunction with using Belleville springs (BeSs) to maintain the clamping force, but at the potential cost of deteriorating the SHJ self-centering capability. This paper describes nine real-scale SHJ's AFC component tests at quasi-static and dynamic rates of displacement controlled loading, with bolts either tightened in the elastic range using no BeSs as well as with four different configurations of BeSs which are deliberately not fully deflected at installation, to avoid the system self-centering capability deterioration and to minimize the additional imposed tension on the AFC bolts during stable sliding. It is concluded that using partially deflected BeSs with sufficient axial deformation to reach the installed bolt tension, with these being installed at both head and nut sides of the AFC bolts, will reduce the post-sliding clamping force loss, improve the self-centering capability, increase the system coefficient of friction, reduce the additional imposed tension on the AFC bolts during stable sliding due to prying actions and/or MVP interactions, and reduce the severity of the sliding surfaces' wearing.

Asymmetric Friction Connection (AFC) design for seismic energy dissipation

Asymmetric Friction Connections (AFCs) are used to dissipate seismic energy via friction. AFC strength is affected by moment–axial force–shear force (MPV) interaction. Current MPV models do not consider the increase in bolt tension due to bolt rotation as bolts are assumed to yield axially during AFC assembly. A MPV model is proposed for AFCs considering the increase in bolt axial tension due to bolt rotation, and elastic or elasto – plastic bolt axial behaviour. A parametric study is presented describing the relative impact and effects of bolt rotation, bolt thread, ultimate strength, friction coefficient at the sliding interfaces, and bolt axial relationship. The predicted AFC strength is validated against experimental data from 60 tests of AFCs with Grade 8.8 bolts and Bisalloy 400 shims, and 18 experimental tests with Grade 8.8 bolts and Bisalloy 500 shims. The proposed MPV model considering elasto-plastic bolt axial behaviour better matches the experimental data with average absolute errors of 0–18% for AFCs with M16, M20 and M24 bolts, and of 55–79% for AFCs with M30 bolts. Finally, the model validation indicates the current in practice overstrength and understrength factors of 1.40 and 0.70 can be used with this particular model in design to consider: (i) the variability of the sliding strength due to the bolt fabrication and assembly issues; and (ii) the degradation of sliding surfaces.

Shake table testing of a low damage steel building with asymmetric friction connections (AFC)

This paper describes the shaking table performance of a half-scale two-story steel moment frame with asymmetric friction connections (AFCs) at the column bases and at the beam ends. The dynamic properties of the test structure are determined using snap-back tests. The behavior of the test frame to ground motions was consistent with standard methods to estimate peak displacements, and residual displacements. When beam ends and the base-column joints were modelled by trilinear and bilinear hysteresis loops respectively, the response with time matched numerical simulations well. Residual drifts were <0.2% for peak inter-story drifts up to 3%, and <0.7% for peak inter-story drifts of 6.0% and the structure was able to manually restraightened.

Steel Building Friction Connection Seismic Performance – Corrosion Effects

Asymmetric Friction Connections (AFCs) dissipate energy in structural systems. Surface treatments and severe corrosion effects on AFC strength, and the corrosion mechanism of AFCs have not been explained yet. A total of 12 AFCs were surface treated, exposed to a severe corrosive regime, and cyclically loaded. Surface treatments, such as cleaned, sweep blasted, alkyd coated, and zinc coated surfaces were considered. AFC strength and the stability of the hysteresis loop of the connection were sensitive to both surface treatment and corrosion. AFCs developed general, crevice, and filiform corrosion not only at the external surfaces, but also at the internal clamped surfaces for some surface treatments. As a result of corrosion, connection strength increased at the initial sliding cycles up to 100%, 120%, 130%, and 50% for cleaned, sweep blasted, alkyd coated, and zinc coated surfaces, respectively. After the corrosive product is removed by the sliding of the slotted plate, the connection strength returned to approximately the strength of the non-corroded connections. These results were used to propose a model to predict the maximum and minimum likely AFC strengths when plate surfaces of the plates are treated, and when these four surface treatments are severely corroded. The experimental results, and resulting model, provide significant insight and design tools for the practical use of AFCs in design.

Shake Table Testing of a Low Damage Steel Building with Asymmetric Friction Connections (AFC)

The paper describes the shaking table performance of a half-scale two-story steel moment frame with asymmetric friction connections (AFCs) at the column bases and at the beam ends. The results showed that the beam ends and the base-column joints exhibited bilinear and trilinear response respectively. Residual drifts were less than 0.2% for shake table trials up to 3% peak inter-story drift. Even at a peak inter-story drift of 6.5%, the residual drift response was still only 0.7%.

Numerical Study of Asymmetric Friction Connections (AFC) with Large Grip Length Bolts

A Finite Element (FE) model is used to simulate the experimental behaviour of high strength bolts in asymmetric friction connections (AFC). Two M16 connections tested previously are modelled using ABAQUS and are subjected to cyclic lateral displacements. The numerical results were similar to that from previous experimental studies. It was also shown that hysteresis loop strength and stability reduced for longer bolt grip lengths. Other information, which cannot be easily monitored in experimental tests, such as the bearing stress distribution between plates, component equivalent plastic strain, and bolt tension force, were obtained at different sliding distances. It was shown that bolt and plate plastic deformation tended to occur in bolts with a long grip length to bolt diameter ratio.

Dynamic Friction Coefficient and Performance of Asymmetric Friction Connections

Modern steel structures are increasingly using friction connections to enhance energy dissipation and minimize damage. The Asymmetric Friction Connection (AFC) was developed to create a repeatable, efficient means of dissipating seismic response energy and reducing structural damage without yielding of structural frame elements. Testing has demonstrated stable efficient hysteretic behavior. However, no full characterization of their dynamic friction behavior exists, nor any specific information relating their clamping bolt assembly torque/force to the dynamic friction coefficient during cyclic testing. A deeper understanding of these design and implementation aspects adds greater certainty and precision to design.An experimental evaluation is performed, quantifying the effective dynamic friction coefficient as a function of connection clamping force from clamping bolt torque and input displacement, using torques from 20 to 500Nm and a series of sinusoidal input motions. Bolt elongation and associated clamping force are evaluated with the measured resistive sliding force of the connection to derive a dynamic coefficient of friction for the AFC. Overall results show that friction is weakly dependent on input motion amplitude, but is direction dependent for all torques with larger friction coefficients in the positive, tension direction of input motion, where larger assembly torques over 200Nm had larger direction dependence. Clamping bolt torques over 200Nm result in bolt yielding during input motions, which would necessitate post-earthquake inspection and potential repair, and reduce resistive sliding forces during a subsequent seismic event. The overall results present a generalizable analysis to guide design, which is extendable to similar friction connections or devices. Equally, the results also provide a better understanding to enhance adoption/uptake of these friction connections in steel structures.