Link Beam Research Articles

Innovative self-centering systems using shape memory alloy bolts and energy dissipating devices

In conventional eccentrically braced frames (EBFs), earthquake input energy is mainly dissipated by plastic deformation of link beams. However, the plastic deformation of link beams can cause extensive structural damage during severe seismic events. The self-centering eccentrically braced frames (SEBFs) are one of the strategies that have been proposed to address this problem. This paper presents two new SEBF systems incorporating shape memory alloy (SMA) bolts and energy dissipation devices, consisting of shear tabs and web hourglass pins (WHPs). SMA bolts are employed in collector beams-to-link beam connections to dissipate energy and recenter the frame with negligible residual drift after an earthquake, while shear tabs and WHPs are utilized in both ends of the link beam web to enhance the seismic performance of the frame. Detailed finite element simulations are performed to assess the cyclic performance of the proposed self-centering systems using experimentally validated models. The results indicate the excellent efficiency of the proposed systems in terms of recentering and energy dissipation capacity. It is shown that the application of shear tabs and WHPs can improve the ultimate strength, equivalent damping and energy dissipation capacity of the system by up to 20%, 35% and 60%, respectively. The experimentally validated models are then used to investigate the effects of key design parameters such as initial prestress of SMA and shear tab bolts, friction coefficient, and the diameter and clear length of the hourglass pins. The results of this study should prove useful in the practical design of the SMA-based self-centering systems.

Experimental investigation of link beams with perforated web section in eccentrically braced frames

Eccentrically braced frame (EBF) system is one of the most effective lateral loads resisting systems for steel structures. In these systems, links are designed in such a way that they yield in shear not only to provide high ductility and rigidity but also to provide a high energy dissipation capacity. In particular, as the internal forces to be considered for the design of the members outside of the links must be calculated with the amplification factor based on the yielding of the links, the magnitude of the internal forces may become so large that they may not be met by the adjacent members. Therefore, it is challenging to develop an economic design for adjacent members and connections because of the high level of design loads obtained by the amplification factor. This paper studies the effect of the perforation arrangement in the web of shear link beams in eccentrically braced frames. Both experimental and numerical investigation were conducted to demonstrate the effectiveness of the link beam with slotted perforations in the web portion. Seven equivalent isolated link beam specimens with various slot-hole patterns were tested under quasi-static cyclic loading. The results of the study indicate that using slot-holes in the web portion reduces the link shear capacity significantly. The results also show that the failure mechanism of reduced link sections was controlled by fracture at end of the slot-holes and inelastic rotation capacities were varying between 0.025 rad and 0.065 rad depending on the slot-hole patterns.

Comparison of thermal performance of steel moment and eccentrically braced frames

Eccentrically braced frames (EBFs) are typically employed in seismic design because they integrate the benefits of concentrically braced frames and moment-resisting frames, providing both high elastic stiffness and high ductility. However, the effect of fire on the structural stability of EBFs has not been well documented. Object-oriented techniques used in software program development have become popular in recent years, primarily because of their ability in addressing various complexity issues. Software developed based on an object-oriented approach is more robust than conventional software. Using the abovementioned approach, additional codes can be incorporated, thereby simplifying testing, refining, maintenance, and software extension. Furthermore, the object-oriented approach can be used for finite element analysis. This paper presents the further development of OpenSees software with the inclusion of other parameters: thermal parallel material, thermal spring element, thermal spring section, as well as beam with hinges and thermal elements subjected to fire loading. In contrast to the routine creation of fire-specific applications, these modifications improve the existing finite-element codes, thereby facilitating multi-hazard analysis (e.g., post-earthquake fire). OpenSees is considered in this study as it is an open-source application and suitable for object-oriented design. The abovementioned elements, particularly spring elements, are used extensively in structural simulations (e.g., the modeling of a link beam in an EBF); however, owing to the lack of thermal functions for these elements in OpenSees, the thermal performance of structures that involve these elements cannot be evaluated. Herein, the aforementioned new elements are introduced for the first time; furthermore, the behavior of an EBF system is investigated under thermal loads using open-source software. The thermal performance of EBFs subjected to realistic fire is evaluated in this study based on an analytical modeling of a three-story building. Finally, several compartment fire scenarios are simulated for both EBFs and gravity framing bays. Results show that the EBFs improve the fire performance of the system by extending the time to collapse.

Design and Cyclic Testing of Bolted End Plate Connections between Steel Link Beams and Clt for Coupled Shear Walls

Design and Cyclic Testing of Bolted End Plate Connections between Steel Link Beams and Clt for Coupled Shear Walls

An innovative system of coupled steel plate shear wall with pin FUSE in link beam: Cyclic behavior and energy dissipation

Coupled steel plate shear wall (C-SPSW) is one of the resisting systems with high ductility and energy absorption capacity. Energy dissipation in the C-SPSW system is accomplished by the bending and shear behavior of the link beams and SPSW. Energy dissipation and floor displacement control occur through link beams at low seismic levels, easily replaced after an earthquake. In this study, an innovative coupled steel plate shear wall with a yielding FUSE is presented. The system uses a high-ductility FUSE pin element instead of a link beam, which has good replaceability after the earthquake. In this study, four models of coupled steel plate shear walls were investigated with I-shaped link beam, I-shaped link beam with reduced beam section (RBS), box-link beam with RBS, and FUSE pin element under cyclic loading. The finite element method was used through ABAQUS software to develop the C-SPSW models. Two test specimens of coupled steel plate shear walls were validated to verify the finite element method results. Comparative results of the hysteresis curves obtained from the finite element analysis with the experimental curves indicated that the finite element model offered a good prediction of the hysteresis behavior of C-SPSW. It is demonstrated in this study that the FUSE pin can improve and increase the strength and energy dissipation of a C-SPSW system by 19% and 20%, respectively.

Nonlinear seismic performance study of D‐type self‐centering eccentric braced frames with sliding rocking link beams

AbstractThis paper presents a nonlinear numerical simulation study of the D‐type self‐centering eccentric braced frame system with a sliding rocking link beam (SCEBF‐SRL) to overcome the beam‐growth problem. The re‐centering capability of such SCEBF‐SRLs is enabled by post‐tensioned (PT) steel‐stranded cables. Replaceable hysteretic dampers termed RHD are used as seismic fuse devices for energy dissipation, while the friction force due to the relative movement of the sliding rocking link beam inside the column corbels would also contribute to the energy dissipation capacity of the system. Analytical load versus displacement relationships of an SCEBF‐SRL module frame were formulated and cross‐validated with nonlinear finite element (FE) analysis results. The seismic performance of the proposed system was studied through nonlinear static and dynamic analysis of three‐ and six‐story prototype SCEBF‐SRL buildings. A set of twenty‐two far‐field ground motions from the FEMA P695 database was adopted for nonlinear dynamic analysis (NDA). NDA results revealed that the ensemble median of the maximum inter‐story drift ratios (IDRs) of both SCEBF‐SRL prototypes were less than 1.4% and 2.0% at the design basis earthquake (DBE) and the risk‐targeted maximum considered earthquake (MCER) levels, respectively. Additionally, both SCEBF‐SRL buildings fully re‐centered themselves at MCER with negligibly small residual drift (<0.01%). The parametric study results suggest that with an energy dissipation ratio, between 25% and 60% and a minimum stiffness ratio of 5%, the ensemble median of the maximum IDR of the considered prototype building could be made less than 1.5% and 2.3% at DBE and MCER levels, respectively.

Design and Analysis of Commercially Viable Free-Space Optical Communication Link for Diverse Beam Divergence Profiles

With an exponential increase in the use of smart devices and with increasing demand for high-speed data applications, the Radio Frequency and Microwave links will find themselves almost incapable of meeting this deficit. Free-space optical (FSO) links are poised to take the leading role as communication systems for futuristic needs in providing cost-effective and high-speed connectivity to end-users. However, on the flip side, the reliability of FSO links has an intrinsic relationship with the characteristics of the atmospheric channel. During the propagation, the atmospheric adversities result in the geometrical spreading of the FSO beam which in turn has consequential degrading effects on the link performance. In this work, an FSO communication system based on practical, commercial, and realistic parameters has been proposed with the intent of accurately determining the co-relation between different beam divergence profiles and overall link performance. For different beam divergence profiles, the proposed link has been evaluated for reference bit error rate (BER) of 10–9 which is an ideal condition for delivering high-speed data access to the end-users. During the analysis, the practical constraints related to the trade-off between the maximum possible link range and beam divergence have also been optimized. The findings of this work will be crucial for engineers and designers in configuring FSO links for improved link range and reliability.

Experimental research on special steel frame with stiffened double steel plate shear wall

Based on the idea of earthquake-resilience, this paper proposes a new special steel frame with stiffened double steel plate shear wall (SSF-SDSPSW). Compared with traditional steel frame, the special steel frame (SSF) adopts the link beams to dissipate energy and protect columns and beams during earthquake. Therefore, the function of SSF-SDSPSW can be repaired by replacing damaged local parts after earthquake. In addition, stiffened double steel plate shear wall (SDSPSW) has good seismic behavior and fast construction speed. To study the seismic behavior and repairable function of SSF-SDSPSW, one basic specimen and two repaired specimens were subjected to the low-cycle reciprocating loading test and ultimate state loading test in this paper. The experiment results indicated that the buckling of steel faceplates and overall instability of the SDSPSW were main failure modes of the SDSPSW. The SDSPSW cooperated well with the special steel frame. The main members such as frame columns and beams of basic specimen remained elastic basically during loading. The peak load of repaired specimen was higher than 87% of basic specimen, which proved the feasibility of post-earthquake repairability. The displacement ductility coefficient of the SSF-SDSPSW was larger than 3.67, indicating the structure had good deformation performance. The error of peak loads between finite element analysis and experiment was only 3.2%, demonstrating that the finite element analysis can predict the peak load precisely. In addition, parameters analysis indicated that the rational relationship between link beams, SDSPSW and columns were conducive to the damage control of SSF-SDSPSW.

Experimental and numerical study on the seismic behavior of steel plate shear wall with reduced web section beams

In this paper, a new steel plate shear wall with a reduced web section beam is proposed. The proposed model, including a middle link beam with elongated circle opening, offers advantages such as the ease to integrate building services within the floor zone resulting in shallow structural depth, reducing demands on columns and beam-to-column connections, increasing the ductility by forming Vierendeel mechanism around the opening, and changing the pattern and mechanism of yielding. To investigate the structural performance of this system, experimental and numerical studies were carried out. Five 1/3- scale specimens were fabricated and tested under quasi-static cyclic loading. Results indicated that the steel plate shear wall with middle link beam (ML-SPSW) specimens had stable hysteresis curves and experienced 3% story drift without any reduction in bearing capacity. All proposed models could tolerate 6% drift with about a 30% reduction in maximum achieved load without a sudden or significant drop in strength or stiffness. The energy dissipation and ductility capacity were superior and the gravity bearing system (columns) and panel zones remained intact until the end of cyclic loading. Furthermore, nonlinear finite element (FE) models of tested specimens were developed and verified against the experimental results. Numerical simulations and test results showed good agreement. In order to further ascertain the validity of the proposed system, supplementary results were obtained from numerical models. Finally, a parametric study and a design algorithm were proposed to determine the proper size of the beam perforation.

Elimination of intermediate stiffeners in box link beam using low yield point steel

The use of intermediate stiffeners in the link beam, in addition to increasing the cost of construction and reducing the speed of execution due to the need to welding operations, can lead to residual stresses. In this study, in order to remove the intermediate stiffeners in box link beam, the idea of using two types of low yield point steel (made in Japan and China) in the web of box link beam has been investigated using the finite element modeling in Abaqus software. According to this study, using low yield point steel in link beam without intermediate stiffeners, the maximum permissible compactness ratio of link web can be considered up to 56% greater than the maximum compactness ratio provided for common structural steels. The overstrength factor for the two types of low yield point steel made in Japan and China is calculated as 4.14 and 2.58 on average, respectively, while the value of this parameter proposed in accordance with AISC seismic provisions for box link beams made of common structural steels is 1.4. Using low yield point steel in the link beam and eliminating the intermediate stiffeners, the energy dissipation of the link beam can be increased to about 30% and its elastic stiffness can be increased to about 45%. In addition, by using low yield point steel and elimination of the intermediate stiffeners, undesirable fracture mode in the vicinity of the stiffeners is removed, and the rotation limit corresponding to fracture of the link beam increases to about 85%.

Innovative hybrid linked-column steel plate shear wall (HLCS) system: Numerical and analytical approaches

In this study, an innovative hybrid linked-column steel plate shear wall (HLCS) system is presented, and its ultimate capacities are investigated using numerical and analytical approaches. This proposed system includes a steel plate shear wall (SPSW) coupled to two columns adjacent using the link beams. This study aims to provide a novel system resistant to lateral forces for different seismic levels and an analytical relationship for appraising the ultimate capacities of the proposed HLCS system. This paper investigates the coupling ratio parameter and ultimate capacity using analytical and numerical approaches of multi-story HLCS systems. An analytical relationship is provided to assess the ultimate capacities and coupling ratio of the HLCSs system applying the limit analysis method . Extensive parametric studies were performed numerical method to examine the precision of the analytical relationships. In the parametric study, Thirty prototype multi-story HLCS systems with different coupling ratio parameters and the height of the structures were designed, modeled, and analyzed. To evaluate the accuracy of numerical models, validation with experimental results has been performed. There is a good agreement between numerical results and analytical predictions for the ultimate capacities and coupling ratio parameter. The results of the parametric studies that coupling ratio parameter is revealed to have a significant effect on the weight of the structure, especially for taller structures, and considering the performance parameter, yield mechanism, and weight loss, optimal coupling ratio in the range of 30–50% is recommended. • The proposed an innovative hybrid linked-column steel shear wall (HLCS) system. • The numerical and analytical approaches of ultimate capacities of HLCS was investigated. • The numerical models of C-SPSW were verified with test results. • Using the analytical method, was obtained the capacity of the HLCSs. • A good agreement was observed between the results of numerical and analytical methods.

Cyclic behavior and performance of a coupled-steel plate shear wall with fuse pin

Coupled steel plate shear wall (C-SPSW) is one of the resisting systems with high ductility and energy absorption. Energy dissipation in the C-SPSW system is accomplished by the bending and shear behavior of the link beams and SPSW. Energy dissipation and floor displacement control occur through link beams at low seismic levels, easily replaced after an earthquake. In this study, a coupled steel plate shear wall with a yielding fuse is presented. The system uses a high-ductility fuse pin element instead of a link beam, which has good replaceability after the earthquake. In this study, four models of coupled steel plate shear walls were investigated with I-shaped link beam, Ishaped link beam with reduced beam section (RBS), box-link beam with RBS, and fuse pin element under cyclic loading. The finite element method was used through ABAQUS software to develop the C-SPSW models. To verify the finite element model results, two test specimens of coupled steel plate shear walls were validated. Comparative results of the hysteresis curves obtained from the finite element analysis with the experimental curves indicated that the finite element model offered a good prediction of the hysteresis behavior of C-SPSW. The results of the C-SPSW models revealed that the fuse pin caused an increase in the ultimate capacity by approximately 19% and the energy dissipation by 20% compared to the other C-SPSW.

Experimental and numerical investigation on the seismic retrofit of RC frames with linked column frame systems

The Linked Column Frame (LCF) system consists of the main lateral load bearing system of the structure called the Linked Column (LC) frame; the structural system is Moment Resisting (MF) frame acts as gravity load bearing system. This system can use to retrofit the reinforced concrete (RC) or steel frame. This paper presents the results of an experimental and numerical investigation of the RC frame retrofitted with the LCF system which the sections of the LC frame are designed using proposed simplified equations. The design of the LC frame is based on the proposed equations in a way that the plastic hinges are first formed in the link beam and then in the columns of the LC frame. The results indicated that the tested specimen and numerical models that the RC frames retrofitted with the LCF system using the proposed equations had good stiffness, high ductility, and significant energy dissipation. The results showed that the ductility factor, the average elastic stiffness and the system bearing capacity of the RC frames retrofitted with the LCF system using the proposed equations are increased about 1.5, 7.6 and 3.7 times, respectively. Also, using the proposed equations for the design of the sections of LC frame, the formation progress of plastic hinges is formed at the Rapid Repair (RR) performance level. In addition, the ratio of the first plastic hinge formation in the beam of RC frame (Δp LCF) to the first plastic hinge formation in the beam of LC frame (Δy LCF) for the RC frames retrofitted is close to 3. In other words, the RC frames retrofitted with the LCF system based on the proposed equations are more capable of withstanding earthquake forces without damaging the members of the main frame (RC frame).

Analysis of THz space communication link based on STK

The characteristics of terahertz communication technology, such as large capacity, high speed and high security, make it stand out among many wireless communication technologies. For future space communication application scenarios, the link performance and beam pointing accuracy of the terahertz communication system were analyzed. The beam adjustment angular acceleration index were analyzed through STK.

Estimating optimum parameters of a new SMA damper under different earthquake ground motions

Process optimization using metaheuristic algorithms is rapidly gaining interest from engineering practitioners and researchers. This study uses the cuckoo search algorithm (CSA) to find the optimum parameters of a novel smart damper under seismic excitations. For this purpose, seismic responses of four-story and nine-story building configurations under seven pairs of ground motions have been considered. The smart damper is a shear polyurethane friction (SPF) passive control device, made up of shape memory alloy (SMA) plates, friction devices, and polyurethane springs. The damper was installed using braced frame shear links of Y-shaped inverted type, in the form of a vertical link beam placed in the eccentrically braced frames. Because the shear mode of failure is common in such a configuration, the SPF damper is expected to reduce the residual inter-story drifts of the building subjected to strong earthquake loading. Numerical optimization and time-domain simulations were carried out using the MATLAB and OpenSees software programs, respectively. The targeted optimization criteria include the peak values of inter-story drift, residual drift, and floor acceleration; and the design parameters consist of SMA cross-sectional area, friction force, and the polyurethane stiffness of the SPF-SMA system. The results of this study demonstrate the suitability of CSA for the determination of optimum parameters of the SPF-SMA system for the buildings and ground motions considered. Future studies will investigate the generalizability of the proposed method to other building configurations and ground motions.

Seismic assessment of linked-column frame structural system considering soil-structure effects

The Linked Column Frame (LCF) structural system is comprised of moment-resisting frames as the primary gravity load-carrying system and a combination of closely-spaced dual columns interconnected with link beams acting together with the moment-resisting frames as the lateral load resisting system. In this system, the link beams are designed to provide ductility and deform plastically. As the damages are concentrated to the links thus, the LCF rapidly returns to occupancy design performance while retaining architectural privileges of the non-braced steel frames. In this study, 3, 6, and 9-story frames equipped with LCF and resting on soil type II and IV are subjected to seven near and far-field earthquake records. These structures are designed based on the plan of SAC buildings using SAP2000, and then, nonlinear time-history analyses were carried. The results indicate that maximum roof drift of the structures on stiff soil (type II) has been insignificantly affected under both near and far-field earthquakes. In soft soils (type IV), drifts values increase by 6.85%, subject to both far and near-field earthquakes. Moreover, in contrast to the stiff soil, roof acceleration has decreased more when the structure is on soft soil, nearly 6.12%. The result of maximum inter-story drift ratios of the structures founded on soil type II illustrates that under an average of near-field earthquakes, drift ratios of 3 and 6-story structures have increased by 3.2%. On the other hand, the 9-story structure has encountered a decrease of 5.17%. Under an average of near-field earthquakes in soil type IV, a drift ratio of 3 and 6 and 9-story structures has grown to 5.11 and 11.2%, respectively, compared to the fixed-base models. In far-field earthquakes, drift values of 3 and 6-story LCF were reduced by 6.2%, and the 9-story structure has experienced an increase of 8.79%.

Evaluation of rocking motion on the seismic performance of a linked column frame system

A linked column frame (LCF) is a seismic-load-resisting system with ductile behaviour. In this system, the link beam, operating as a shear fuse, reduces or eliminates damage to other components of the structure under various hazard levels. In this study, by combining rocking motion and changes in the linked column pattern, an innovative seismic-resisting system was developed. The aim was to improve the performance of the LCF system by reducing damage to the flexural beams and columns and to concentrate damage in the link beams. For this purpose, a three-storey model based on the SAC building was designed based on storey drift demands. The model was evaluated by incremental dynamic analysis (IDA) according to Fema P-695 instructions using OpenSees. Results of changes in the linked column pattern from the IDA indicated a 20% increase in the structural capacity of the LCF model. Compared with the model without rocking motion, the model with rocking motion resulted in reduced structural capacity, shear and horizontal acceleration of the storey, and maximum drift. This novel LCF seismic system provides self-centring and damage control by using features such as rocking motion.

Evaluation of Damage Index of Eccentrically-Braced Frames according to Link Beam’s Length with Soil-Structure Interaction Effects

Evaluation of Damage Index of Eccentrically-Braced Frames according to Link Beam’s Length with Soil-Structure Interaction Effects

Direct displacement-based design of the linked column steel frame System, Part 1: Modeling and yield drift evaluation

The linked column frame (LCF) system is a load resisting system in which replaceable link beams are used to provide the desired structural behavior at various performance levels. The optimal performance of this system can be achieved by controlling the successive yielding pattern of its structural fuse elements using performance-based seismic design methods. This paper derives some analytical relationships for the yield drift estimation of the LCF system required to its direct displacement-based design developed in the companion paper. The obtained results show the high accuracy of the proposed relationships to estimate the yield drift of the LCF system.

Research on micro-leverage in monolithic quartz resonant accelerometer.

In this study, the application of micro-leverage in the monolithically all-quartz resonant accelerometer is proposed. The magnification of the micro-leverage structure used for a large size double-ended tuning fork (DETF) was analyzed. The effect of DETF's dimension both on its own force-frequency sensitivity and micro-leverage's magnification was investigated. Through the study of the relationship between DETF's force-frequency sensitivity and micro-leverage's magnification, the effect of micro-leverage and the DETF system on the sensitivity of the accelerometer was obtained. The problem of big error in theoretical calculation of micro-leverage magnification was solved because the structural arrangement of the output beam was ignored in the derivation process. The correctness of the analysis was verified by theoretical calculation, simulation, and the experiment. The equivalent structures of tension (compression) stiffness and flexural stiffness of the micro-leverage output beam were obtained by analyzing and simplifying the composite structure of the link beam and DETF. By simplifying the mechanical model of micro-leverage, the amplification factor K of micro-leverage is deduced to be 23. Therefore, the theoretical sensitivity of the sensor is 15.6 Hz/g. The experimental results show that the sensitivity of the accelerometer with the micro-leverage is 16.1 Hz/g, which is close to the theoretical analysis results.