Link Length Ratio Research Articles

Investigation on laminated steel slit shear walls with low yield steel

To improve the energy dissipation capacity of steel slit shear walls made of thin plates and mitigate the adverse effects from the large out-of-plane deformation and potential local buckling failure, a novel laminated steel slit (LSS) shear wall assembled from two single-layer steel slit (SSS) shear walls is proposed in this study. First, the theoretical analysis method for predicting the shear strength and stiffness of the LSS shear walls is proposed. To validate the theoretical method as well as investigate the hysteretic performance of the LSS shear walls, two specimens made from different materials, common carbon steel and low yield steel, are designed and tested experimentally under quasi-static cyclic loading. Refined finite element models are developed to simulate the hysteretic behaviors of the LSS shear walls, which show good agreement with the test results. Further, the performance differences between the LSS shear walls and SSS shear walls are analyzed using the validated numerical simulation approach. The strength and stiffness of the LSS shear walls are greater than the summation of the individual SSS shear walls, attributed to the interaction between the different layers in the LSS shear walls. The energy dissipation efficiency of the LSS shear walls is improved and the stiffness degradation is effectively delayed, thanks to the incorporation of the low yield steel material. Finally, to evaluate the effects of the contributing factors on the seismic performance of the LSS shear walls, a series of parametric analyses are performed. Parametric analysis results show that the use of the low yield steel helps to improve the ductility and energy dissipation capacity of the LSS shear walls and delay the stiffness degradation. A large link width ratio, small link length ratio and large link thickness ratio can all contribute to a large strength, stiffness and absolute energy dissipation of the LSS shear walls, but the former two at the same time deteriorate the stiffness degradation.

Floor slab composite action effects on hysteresis behaviors of steel-framed-tube structures with shear links

The utilization of spandrel beams with a low span-to-depth ratio in a Steel-Framed Tube (SFT) structure can potentially diminish its ductility and energy dissipation characteristics. Conversely, integrating an SFT with end-plate-connected, replaceable low-yield-point steel shear links (SFT-RLYPSL) may significantly enhance its seismic response. This study introduces a prototype SFT-RLYPSL configuration designed to mitigate the premature separation of a reinforced concrete (RC) slab from the spandrel beams, a phenomenon observed in prior research. A series of finite element (FE) models were established, utilizing the prototype structure as a basis, to systematically investigate the impact of various parameters, including the presence and thickness of the RC slab, concrete strength, shear link length, and initial spandrel beam stiffness, on the cyclic behavior of an SFT-RLYPSL substructure module. Additionally, the failure mechanisms of the substructure module were assessed. The findings of this study reveal that the utilization of T-shaped connectors can effectively delay the pull-out of studs from the RC slab, especially under substantial vertical displacement of the spandrel beam. The initial elastic stiffness and load-carrying capacity of the substructure module can be significantly enhanced through the promotion of RC slab composite action. An optimal shear link length ratio falls within the range of 0.95 to 1.25, and given the assumption of LYP225 steel shear links with length ratios of 0.95 to 1.25 in the SFT-RLYPSL, the recommended minimum thickness and concrete grade for the RC slab, based on numerical simulation results, are 120 mm and C30, respectively. It is further recommended to employ C30 concrete for an RC slab with a thickness of 120 mm. Finally, a restoring force model is proposed, accurately reflecting the observed mechanical behaviors of the SFT-RLYPSL substructure module.

Simple Truss Model to estimate the shear strength of short links in the Eccentrically Braced Frame (EBF) steel system

The measured-to-estimated shear force ratio (Overstrength ratio) is an important metric for the capacity design of a shear link’s adjacent elements and connections. However, some investigations found that short links had an abnormally high overstrength ratio if the shear strength of short links is estimated by the provisions of the American Institute of Steel Construction (AISC 341-16). This study assesses the AISC 341-16 equation’s precision in estimating the shear strength of short links and suggests a Simple Truss Model (STM) for this purpose. The proposed STM considers the strain hardening of flanges and the web due to cyclic loading, where the STM was derived from the end links to reach the plastic moment strength (Mp). An experimental database of 109 specimens from the literature was gathered, screened, and preprocessed to assess the performance of these models. This research found that the overstrength ratio for built-up and rolled W-shape short links is underestimated by the AISC 341-16 provisions; only 4% and 13% of built-up and rolled W-shape specimens, respectively, meet the suggested AISC overstrength value of 1.25. The proposed STM model beat the AISC equation in predicting the overstrength values, with mean values of 1.21 and 1.15 for the built-up and rolled W-shape specimens, respectively. Additionally, for the built-up and W-shape specimens, respectively, 58% and 73% of the overstrength determined by STM conform with the recommended AISC overstrength value of 1.25. Since the STM considers the link length and cross-sectional area, contrary to what the AISC predicted, the calculated overstrength values are less susceptible to the link length ratio, flange width-to-thickness ratio, and the ratio of the flange-to-web areas. This study recommends switching from the current AISC equation to the STM because the STM predictions have statistical metrics that are noticeably better than the AISC equation, with Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) of 0.27 and 18.6%, 0.22 and 14.6%, and built-up and rolled W-shape links, respectively.

Reconfiguration characteristic revelation of multiple metamorphic mechanisms based on geometric morphology of screw systems

The design and analysis of reconfigurable mechanisms is a hot topic in the current research, but few studies discuss the impact of geometric parameter changes on the mechanism's reconfiguration characteristics. In this paper, for a family of 6R single-loop multiple metamorphic mechanisms, the evolution of reconfiguration characteristics under the change of geometric parameters is analyzed, including the link length ratio and the orientation characteristics of revolute joints. Based on the geometric morphology of screw system, the reconfiguration characteristics of the mechanism under different parameters are revealed, and the influence of parameter changes on the reconfiguration characteristics of the mechanism is discussed. Meanwhile, the effect of double parameter changes on mechanism reconfiguration is studied, and the reconfiguration characteristics of mechanisms under different parameter ranges are divided into seven different types.

Machine Learning Algorithm for Shear Strength Prediction of Short Links for Steel Buildings

The rapid growth of using the short links in steel buildings due to their high shear strength and rotational capacity attracts the attention of structural engineers to investigate the performance of short links. However, insignificant attention has been oriented to efficiently developing a comprehensive model to forecast the shear strength of short links, which is expected to enhance the steel structures’ constructability. As machine learning algorithms was successfully used in various fields of structural engineering, the current study fills the gap in estimating the shear strength of short links using sophisticated machine learning algorithms. The deriving factors such as web and flange slenderness ratios, the flange-to-web area ratio, the forces in web and flange, and the link length ratio were investigated in this study, which is imperative to formulate an integrated prediction model. Consequently, the aim of this study utilizes advanced machine learning (ML) models (i.e., Extreme Gradient Boosting (XGBOOST), Light Gradient Boosting Machine (LightGBM), and Artificial Neural Network (ANN) to produce accurate forecasting for the shear strength. In this study, publicly available datasets were used for the training, testing, and validation. Different evaluation metrics were employed to evaluate the prediction’s performance of the used models, such as Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), and Coefficient of Determination (R2). The prediction result displays that the XGBOOST and LightGBM provided better, and more reliable results compared to ANN and the AISC code. The XGBOOST and LightGBM models yielded higher values of R2, lower (RMSE), (MAE), and (MAPE) values and have shown to perform more accurate. Therefore, the overall outcomes showed that the LightGBM outperformed the XGBOOST model. Moreover, the overstrength ratio predicted by the LightGBM showed an excellent performance compared to the Gene Expression and Finite Element-based models. The developed models are vital for practitioners to predict the shear strength accurately, which pave the road towards wider application for automation in the steel buildings.

Experimental study on the cyclic behaviour of shear links made of BLY160 steel

The cyclic behaviour of shear links made of a new type of low-yield-point (LYP) steel BLY160 is intensively investigated. A total of twelve specimens are designed to evaluate the influence of material type, web compactness, link flange, web stiffeners, restraining ribs of the web panel and link length ratio on force transfer mechanism of shear links. Based on the analysis of the failure mode and process, hysteretic performance, strain distribution and development of test specimens, it is found that the excellent mechanical properties of the BLY160 steel have enabled the shear link to yield at a lower strength and reach an inelastic rotation capacity as large as 0.16 rad. Introducing the link flange and reducing the link length ratio can effectively improve the seismic performance of the shear link. Due to the strain-hardening phenomenon of BLY160 steel, the overstrength factors of shear links have reaches 1.70 to 2.02, and is gradually increasing with the reduction of link length ratio. The current design provisions can be applied to calculate the yield strength of shear links with a link length ratio smaller than 2.0. Except for the shear links with diagonal web stiffeners or composed of traditional steel, all the shear links have reached an equivalent damping coefficient exceeding 0.50. Finally, an isotropic–kinematic combined hardening restoring force model is proposed to simulate the cyclic behaviour of shear links made of BLY160 steel, the feasibility and accuracy is verified by comparing the predicted hysteretic curves and test results of shear links with different forms.

Interaction of flange and web slenderness, overstrength factor and proposed stiffener arrangements for long links

This paper is aimed to investigate the interaction of flange and web slenderness ratio, overstrength factor and also to improve the behavior of long links. Pursuant to these goals, 150 numerical models of different long links were developed and exposed to cyclic loading protocol mandated by AISC 341. Link length ratio, flange and web slenderness and stiffener configurations are selected as parameters. The results revealed that the flange slenderness ratio can be relaxed to 0.38(E/Fy)0.5 for long links if the web slenderness ratio is <1.5 (E/Fy)0.5. The shear capacity of long links decreases as the link length ratio increases. The results of shear capacity showed the overstrength factor required by AISC 341 overestimates the shear capacity; therefore, two different equations to predict the overstrength factor for long links are proposed. The stiffener configuration recommended by AISC 341 limits the potential of long links. To mitigate this drawback, different stiffener configurations are proposed to empower the behavior of long links. Using additional one stiffener at each link ends can enhance shear strength, energy dissipation and plastic rotation capacities by 25%, 447% and 322%, respectively. When two additional stiffeners are introduced, these ratios modify to 29%, 479% and 332%. Moreover, rupture index values are utilized to verify proposed stiffener configurations further.

Gene expression model to estimate the overstrength ratio of short links

Short links are used as fuse members in Eccentric Braced Frames (EBFs), hybrid coupled-wall systems, and self-anchored suspension steel bridges. Compared to the intermediate and long links, short links have superior performance such as high strength and plastic deformation capacity. However, several researchers observed a considerably high overstrength ratio for short links. This study found that the AISC Seismic Provisions underestimate the plastic shear strength of short links, the experimental results of 103 specimens showed that only 8% of the specimens comply with the recommended AISC Seismic Provisions overstrength value of 1.25. The average of all data is 1.67 with COV 17.6% and RMSE 0.732. Therefore, a genetic expression-based model (GEP) was proposed to estimate the plastic shear strength of short links. A 96% of the overstrength ratio calculated by GEP of the 103 specimens comply with the recommended AISC overstrength value of 1.25. The average of the GEP overstrength values is 1.00 with COV 13.6% and RMSE 0.136. The GEP model considers the contribution of six variables such as the flange slenderness ratio (bf/tf), the web slenderness ratio (d/tw), the flange to web area ratio (Af /Aw), the flange force (Af fyflange), the web force (Awfyweb), and the link length ratio e/(M/V). Unlike the AISC overstrength ratio estimates, the GEP predictions are not sensitive to the variables. This is evidence that the GEP model is an inclusive and efficient equation to estimate the overstrength ratio of short links.

Fundamental study of optimum design of physical pendulum type of centrifugal pendulum vibration absorber in automatic transmission for cars

The centrifugal pendulum vibration absorber (CPVA) is developed to suppress the torsional vibration of automatic transmission. However, the natural frequency of the CPVA varies due to the nonlinear when the vibration amplitude of CPVA is large. To overcome this problem, a new physical pendulum type of centrifugal pendulum vibration absorber is developed. Physical pendulum type of centrifugal pendulum vibration absorber is possible to rotate depending on the control angle. In this study, the optimal design for the physical pendulum type of centrifugal pendulum vibration absorber is discussed by changing the parameters such as the link length ratio and the control angle.

Stability of laterally unsupported shear links in eccentrically braced frames

AbstractI‐shaped links in eccentrically braced frames (EBFs) are susceptible to lateral or lateral torsional buckling when subjected to cyclic link rotations. Lateral bracing should be provided at the ends of the I‐shaped links in order to prevent these failures. Requirements for such braces are available in widely used design specifications such as the AISC Seismic Provisions for Structural Steel Buildings (AISC341‐16) and EC8. These requirements limit the use of I‐shaped links in bridge piers and elevator shafts. A combined experimental and numerical study was undertaken to investigate the behavior of laterally unsupported I‐shaped links under cyclic loading. The experimental study consisted of testing of six nearly full‐scale EBFs where the link length, link length ratio, and presence of lateral supports were considered as the prime variables. The test results demonstrated that short links with link length ratios less than 1.22 can experience inelastic link rotations greater than the codified limit of 0.08 rad even without lateral bracing. A numerical parametric study was conducted to develop more generalized design recommendations for laterally unsupported I‐shaped shear links. Stability of one‐story one‐bay EBFs was studied using geometrically and materially nonlinear finite element analysis including imperfections. The numerical results showed that I‐shaped links without lateral bracing can provide a stable response when the link length ratio is less than 1.15. In addition to this limit, the ratio of the elastic critical buckling capacity to the plastic shear capacity should be greater than 3.5 and 2.5 for links with and without axial force, respectively.

Path-Constrained Points synthesis of symmetric mechanisms for prescribed higher-order curvature features

The kinematic synthesis of higher-order path generator mechanisms is herein addressed. Assuming mechanisms in a symmetric configuration, a coupler path sharing up to eight infinitesimally separated points with the ideal curve can be achieved. The novel design methodology is based on “Path-Constrained Points” (PCPs) for the characterization of the coupler motion. In particular, given the higher-order curvature features of the curve to be mechanically approximated, the mechanism link length ratios are analytically computed. The PCPs approach has been herein developed for the four-bar and the swinging-block linkages, but can be extended to a wide class of mechanisms. To speed-up computations, design charts solutions have been also prepared. Finally, the numerical examples and the coupler path plots allow to evaluate the accuracy of the proposed procedure.

Experimental Validation of Detachable Links for Eccentrically Braced Frames

AbstractEccentrically braced frames (EBFs) subjected to seismic actions dissipate energy through yielding of link members. Other members of the framing are on the other hand designed to remain mainly elastic during a seismic event. The framing can be reused after an earthquake if the link members can be replaced. In line with this, the last decade has witnessed development of replaceable links. However, most of the proposed details are not well suited for replacement under residual drift conditions. Consequently, this paper presents details of an experimental validation of a detachable link concept where a splice connection is introduced at the mid‐length of the link to facilitate replacement under residual frame drift. The concept was studied by conducting six nearly full scale EBF tests under quasi‐static cyclic loading. Different splice details employing bolted connections with vertical slotted or site drilled holes and welded connections were developed. The link length ratio, type of mid‐splice connection and the amount of residual drift were considered as the variables of the testing program. The specimens were subjected to the loading protocol recommended in AISC Seismic Provisions for Structural Steel Buildings (AISC‐341). The experimental results suggested that the detachable links with the proposed connection details can satisfy the link rotation capacity limits of AISC‐341. The detachable links performed similar to conventional links while their replaceability under residual drift was demonstrated.

An experimental study on the seismic behavior and replaceability of the replaceable steel shear links

The reinforced concrete columns and steel beams (RCS) composite frames have received popularity in low to moderate seismic regions due to advantages of the system. However, the poor repairable capacity and deteriorating pinched hysteretic behaviour of the traditional RCS framed structure limit the application in practice under earthquakes. This study presents a modified RCS framed structure with replaceable members aiming to enhance the energy dissipation and resilience capability. The structural configuration character and the general predetermined levels of lateral response of the proposed RCS framed structure with replaceable members is first introduced. Seven quasi-static loading tests were subsequently conducted to evaluate the seismic behavior and replaceability of the replaceable shear links. Parameters including the link length ratio, stiffener configuration and link-to-column connection were examined. The test results depicted that the specimens exhibited the shear dominated behavior. The major failure features of the shear links included web-to-stiffener weld tear, web buckling and web fracture. All tested specimen showed a stable bearing strength, large inelastic rotation capacity and excellent energy dissipation behavior. The same link length ratio of the specimens with different specialized connections presented the similar behavior. Noted that end plate and web stiffeners connection can alleviate the stress concentration on the fillet weld of the flange-to-end plate weld and optimize the performance of the shear link. The average overstrength factor and inelastic rotation capacity of the test specimens were 1.9 and 0.087 rad significantly exceeding 1.5 and 0.08 rad provided by the AISC 341-16 provisions for the EBF links, respectively. In addition, the replaceability of the specimens was evaluated underwent the entire loading process. Compared with the T-shaped and Π-shaped plate connections, replacement of the shear link with the end plate demanded the least effort and time.

Overstrength factor of short low-yield-point steel shear links

Owing to the relative uncertainty of previous numerical and experimental studies on the behavior of short and very short shear links, this article considers the overstrength factor of short and very short low-yield-point (LYP) steel shear links with or without stiffeners. To this end, 147 I-shaped shear links with link length ratio in the range 0.34–1.83 and made from LYP steel with a nominal yield strength of 100 and 225 MPa are numerically analyzed and compared. The obtained nonlinear finite element results indicate that classifying short links based on the link length ratio, which has been used as a convenient measure of yield behavior, doesn't represent the actual characteristics and behavioral differences between short links. Accordingly, an effective parameter, namely non-dimensional plate slenderness, is introduced in this research to investigate the behavior of short links. Finally, the finite element results are used to derive a new equation for predicting the overstrength factor of short and very short LYP steel shear links. The findings based on the proposed equations are compared to the results of existing experimental studies, indicating a good agreement between the two approaches.

Optimized stiffener detailing for shear links in eccentrically braced frames

Eccentrically braced frames (EBFs) are utilized as a lateral resisting system in high seismic zones. Links are the primary source of energy dissipation and they are exposed to high deformation, which may lead to buckling. Web stiffeners were introduced to prevent buckling of shear link. AISC 341 provides the required vertical stiffeners for a shear link. In this study, different stiffener configurations were examined. The main objective is to improve the behavior of short links using different stiffener configurations. Pursuant to this goal, a comprehensive numerical study is conducted using ABAQUS. Shear links with different stiffener configurations were subjected to cyclic loading using loading protocol mandated by AISC 341. The results are compared in terms of energy dissipation and shear capacities and rupture index. The proposed stiffener configurations were further verified with different link length ratios, I-shapes and thickness of stiffener. Based on the results, the stiffener configuration with two vertical and two diagonal stiffeners perpendicular to each other is recommended. The proposed stiffener configuration can increase the shear capacity, energy dissipation capacity and the ratio of energy/weight up to 27%, 38% and 30%, respectively. Detailing of the proposed stiffener configuration is presented.

Seismic design of elements outside of the short low-yield-point steel shear links

This paper relies on the finite element method to find the safe factor considering the economical aspect to design members outside the short shear links with/without stiffeners constructed from low-yield-point (LYP) steels with nominal yield strength of 100 and 225 MPa. To this end, 147 I-shaped shear links with link length ratios in the range of 0.34–1.83 were numerically analyzed and compared. According to nonlinear finite element results, the classification of short links based on the link length ratio parameter, which has been used in past researches as a convenient measure of yield behavior, does not represent the actual characteristics and behavioral differences between short links. Accordingly, an effective parameter, namely non-dimensional plate slenderness, is introduced in the article. This parameter is employed to investigate the behavior of short links. Finally, the finite element results were used to modify the AISC341-16 design equation for predicting the maximum shear forces generated by the fully yielded and strain hardened shear links.

Experimental and numerical evaluation of innovated T-resisting frames with haunched horizontal plate girders

In this article, a novel configuration for innovated T-resisting frames is proposed. New configuration uses haunched beams with three configurations as horizontal plate girders with prismatic link beam. Using haunched beams confirms T-resisting frame main concept with shear yielding which results in better seismic performance. Haunch configuration leads to achieve any link length ratio especially for very short links. To evaluate seismic response of the haunched beam, a half scale T-resisting frame specimen with haunched configuration at side column face is subjected to a proper cyclic loading protocol. In addition, the same frame is modeled in ABAQUS software to validate the modeling techniques. Results of verification showed good conformity between numerical analysis and test result. Finally, several numerical examples are studied to investigate the effect of height and span length on T-resisting frames with different haunch locations and various link lengths in seismic response. It was found that shear yielding of haunched beams results in high ductility and more energy dissipation and a proper behavior in comparison with prismatic ones.

Impact of Kinematic Structure on the Force Displayability of Planar Passive Haptic Devices.

Haptic devices containing passive actuators, such as controllable brakes or dampers, are an attractive alternative to their motor-driven counterparts due to intrinsic stability and improved impedance bandwidth. Passive actuators cannot generate energy and, therefore, the output force can only oppose the applied velocity. In the same way the kinematic structure of traditional manipulators is designed to maximize dexterity and manipulability, one must consider adapting the device topology to optimize force displayability when designing passive actuators. This article introduces a set of metrics to evaluate and compare the performance of 2-degree-of-freedom (DOF) serial and parallel passive haptic devices. These metrics consider the impact of the kinematic structure on the force displayability according to the directions of the device velocity and desired force. Applying these metrics to nine manipulators revealed that: 1.) serial manipulators can generate passive forces in all directions equally regardless of the link length ratio; 2.) the base link length of five-bar parallel manipulators strongly influences passive force displayability; 3.) five-bar parallel manipulators with the base link length of zero can generate the widest range of passive forces when all links have the same length. The novel performance metrics presented in this paper can aid in the design of 2-DOF passive haptic devices.

Development of detachable replaceable links for eccentrically braced frames

SummaryEccentrically braced frames (EBFs) can be repaired after a major earthquake by replacing the links. The link replacement is not a straightforward process and is influenced by the type of the link and the amount of residual frame deformations. The past decade has witnessed the development of different types of replaceable links such as end‐plated links, web connected links, bolted flange and web spliced links, and collector beam and brace spliced links. All of the developed replaceable link details, except the web connected links, are not suitable for link replacement under residual frame drift. In this paper, a detachable replaceable link detail which is based on splicing the link at its mid‐length is proposed. The detail is well suited for installation under residual frame drifts. In addition, the weight and size of the members to be transported and erected are reduced significantly, thereby facilitating the replacement procedure. Performance of this proposed replaceable link is studied by conducting six nearly full scale EBF tests under quasi‐static cyclic loading. The link length ratio, type of end‐plated mid‐splice connection, and the amount of residual drift are considered as test variables. The test results revealed that the inelastic rotation capacity of the detachable replaceable links exceeds the requirements of the AISC Seismic Provisions for Structural Steel Buildings. No failures are observed in the end‐plated mid‐splice connections demonstrating the potential of the proposed details. The detachable replaceable links are investigated by numerical analysis as well to further validate their applicability and to develop design recommendations.

Replaceable links with gusseted brace joints for eccentrically braced frames

Various replaceable link details were developed for use in steel eccentrically braced frames (EBFs) during the past decade. These details include but are not limited to bolted flush end-plated links, bolted extended end-plated links, web connected replaceable links, and bolted flange- and web-spliced links. Another detail which is based on splicing the beam outside the link and braces was recently proposed by the authors. The performance of this detail when used with directly connected braces was studied through experimental testing and acceptable performance was demonstrated. In practice gusseted attachments are widely used for connecting the braces to the beams in EBF systems. In this paper, the proposed detail by the authors is extended to replaceable links with gusseted brace attachments. The use of gusset plates enables to tailor the geometry of the replaceable link and allows different details to be developed. Three replaceable link details are proposed herein. The first detail employs standard gusset plated detail where splicing the beam is performed outside the connection region. The second detail develops a more compact replaceable link by connecting the beam to the link within the brace connection panel. The third detail is a pin connected detail where minimal amounts of bending moments are transferred to the brace member. The proposed details are studied by conducting nine nearly full-scale EBF tests under quasi static loading. The type of replaceable link, link length ratio, connection type, gap size of splice connections, demand-to-capacity ratio of members are considered as the prime variables. The inelastic rotation capacity provided by the replaceable links satisfied the requirements of the AISC Seismic Provisions for Structural Steel Buildings (AISC341-16). The links failed mainly due to fracture of the link web or flange. No failures were observed in the gusseted joints demonstrating the potential of the proposed details.