To read the full-text of this research, you can request a copy directly from the authors.
Dual structural systems with structural fuse such as linked column frame system (LCF) have two main performances, including the resistance to lateral seismic loads and the proper function of structural fuse to control deformation of the other members to remain in elastic phase. The achievement of these two functions is necessary for appropriate seismic design of these systems. Undoubtedly, despite the practical complexity, displacement-based seismic design methods are generally the best method for this purpose. In contrast, conventional force-based methods are relatively simple, but it cannot easily guarantee the desired performance. In this paper, a simplified force-based seismic design method is presented for linked column frame system based on parametric studies on different structures, which are designed with displacement-based method. In addition to simplicity, the proposed method has an appropriate accuracy in terms of achieving the performance objectives. For the parametric study, 18 prototype structures with various relative lateral stiffness of moment frame and linked column system are designed with the displacement-based method. Based on the results of the structures designed with desirable performance, the criteria are proposed for the force-based design method. Based on evaluating results, the structures designed by the proposed simplified force-based method properly reached the performance objectives.
To read the full-text of this research, you can request a copy directly from the authors.
... Current design methods of building structures, such as the force-based design (FBD) method , are based on the basic design information to determine the seismic influence coefficient and calculate the seismic load effect according to the acceleration response spectrum. The bearing capacity of the structure is required to be greater than the seismic load combinations. ...
The steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is a new seismic lateral resistant component. This paper outlines the performance requirements of the steel frame-shear plate shear wall with self-centering energy dissipation braces (SF-SCSPSW) structure and presents a direct displacement-based seismic design method for the structure. A combined strip model of the SPSW-SCEDB that considers the effect of the bolted connection on the wall plate is established. The comparison of the simulated and experimental results shows that the model can accurately predict the strength and hysteretic behavior under cyclic loading. The 8- and 15-story prototype buildings were designed using the presented method. The results of nonlinear dynamic analysis showed that larger inter-story deformations occurred on the lower floors, and the inter-story ratios gradually decreased with an increase in the number of floors. The maximum inter-story drift ratio (1.73%) of the 8-story structure under mega earthquakes and the maximum residual drift ratio (0.018%) of the 15-story structure under large earthquakes were less than the limit values (2% and 0.5%). Local yielding occurred between the brace connection and the column under mega earthquakes, but the columns remained in an elastic state. The seismic responses of the SPSW-SCEDBs in the two structures met the performance requirements of being elastic and suffering light and moderate and serious damage under frequent, medium, large, and mega earthquakes, respectively. The effectiveness of the proposed design method was verified.
... Shoeibi et al.  proposed a force-based method for the seismic design of the LCFs. Using a parametric analysis on 18 structures with various lateral stiffnesses, found that the system has been appropriately designed. ...
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%.
... A design algorithm for the system was proposed; by reducing the over-strength factor, an optimised system was obtained. Shoeibi et al. (2019) presented an algorithm for the design of LCF systems, which was based on a moment frame to a linked column interaction. ...
Linked Column Frame (LCF) is a seismic load resisting system with ductile behavior. In this system, the link beam, operating as a shear fuse, reduces or eliminates damages to other components of the structure under various hazard levels. In this study, by combining the rocking motion and changes in the linked column pattern, an innovative seismic-resistant system is presented. This paper aims to improve the performance of the LCF system and reduces damage in the flexural beams and the columns and to concentrate damage to the link beams. For this means, a three-story model based on the SAC building has been designed based on story drift demands. The models were evaluated by incremental dynamic analysis according to FEMAP695 instructions in the open Sees program. Results of changes in the linked column pattern from the incremental dynamic analysis indicate a 20% increase in the structural capacity of the prevalent LCF model. The model with rocking motion results in reduced structural capacity, shear and horizontal acceleration of the story, and maximum drift compared to the model without rocking motion. This novel linked column frame seismic system provides self-centering and damage control by using features such as rocking motion.
... Shoeibi et al.  proposed a force-based method for the seismic design of the LCFs. Using a parametric analysis on 18 structures with various lateral stiffnesses, found that the system has been appropriately designed. ...
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. To this end, these structures are designed based on plan of SAC buildings using SAP2000 and then, nonlinear time-history analyses were carried out on them. 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. Unlike, in the case of soft soils (type IV), drifts values increase by 6.85% subjected to both far and near-field earthquakes.
Moreover, in contrast to the stiff soil, roof acceleration has decreased more in the case when resting on soft soil whose value is nearly 6.12%. Analysis of maximum inter-story drift ratios of the structures founded on soil type II, illustrates that under average of near-field earthquakes, drift ratios of 3 and 6-story structures have raised by 3.2% but the 9-story structure has encountered a decrease by 5.17%. in the case of soil type IV, under average of near-field earthquakes, drift ratio of 3 and 6 as well as 9-story structures have grown up to 5.11 and 11.2%, respectively when compared to the fixed-base models. Subjected to far-field earthquakes, drift values of 3 and 6-story structures have been reduced by 6.2% and the 9-story structure has experienced an increase by 8.79%.
Modern earthquake engineering has to evolve toward resilient-based design, where structures are expected to survive major earthquakes with reduced or null damage that could be easily reparable in a reasonable time. With such design strategy, three important goals are warranted: a) life safety of people, b) preserve building property within a reasonable investment to repair light damage, and c) minimize economic losses because of building´s usage interruption. One way to achieve such goal is using hysteretic energy dissipation devices as structural fuses. Although any global strategy could be used for the successful resilient design of buildings with structural fuses, the authors have work extensively to define global design parameters to introduce resilient-based design in the current force-oriented format of most seismic building codes worldwide. Then, global design parameters obtained from very comprehensive parametric studies for special moment-resisting steel frames with hysteretic fuses are presented and discussed. Also, it is shown that the proposed code-oriented methodology is successful to achieve resilient seismic design when subjected to strong earthquake records that may even surpass those considered in their design spectra.
Linked column frame system, as a new seismic load-resisting system, has a proper seismic behavior in various performance objectives due to ductile behavior of replaceable link beams. Thus, returning to occupancy after moderate earthquake is rapid and low-cost. Performance-based seismic design methods should be used for this system in order to have proper seismic behavior. In this study, by using performance-based plastic design method, a highly accurate and simple design procedure is proposed for this system. 9 prototype structures with 3, 6 or 9 stories and with 3, 4 or 5 bays are selected for parametric design and assessment. For assessment of the designed structures, nonlinear static and dynamic analyses with models according to experimental test results of the members and recommended ground motion records of FEMA P695 are used. According to analyses results, the designed structures in three hazard levels meet the performance objectives.
In this paper the authors summarize the results of a parametric study devoted to evaluate, using static nonlinear analyses (pushover), the seismic behavior of low to medium rise regular special moment-resisting steel frames (SMRSFs) with hysteretic energy dissipation devices mounted on chevron steel bracing. Frame models ranged from 5 to 25 stories were designed using different elastic stiffness ratios (α) between the moment frame system and the whole structure (frame-bracing-hysteretic device system). Also, different elastic stiffness balances (β) between the hysteretic device and the supporting braces were considered. Post to pre yielding stiffness ratios (k 2 /k 1) of 0.0 (elastic-perfectly plastic), 0.03 and 0.05 for the hysteretic devices were considered. Two angles of inclination of the chevron braces with respect to the horizontal axis (θ) were considered: 40 0 and 45 0 , taking into account typical story heights and bay widths used in Mexican practice. From the results obtained in this study, optimal stiffness balances α and β are defined to achieve a suitable mechanism where the hysteretic devices yield first and develop their maximum local displacement ductility μ, whereas in the moment frame incipient yielding is only formed at the beam ends. Finally, additional comments are made with respect to: (a) relations between global ductility capacity and local displacement ductility capacity for the hysteretic devices for a given combination of α, β, k 2 /k 1 and θ, (c) story drifts at yielding and their relation with the selected α balance and, (d) overstrength factors (Ω) for design purposes.
In this paper, the authors summarize the results of a parametric study devoted to evaluate the seismic behavior of low to medium rise regular special moment-resisting steel frames with hysteretic energy dissipation devices mounted on chevron steel bracing. For that purpose, 270 different building models were designed considering typical story heights and bay widths used in Mexican practice. The parameters under study were (1) number of stories: 5, 10, 15, 20, and 25, (2) elastic stiffness ratios (α) between the moment frame system and the whole structure (frame-bracing-hysteretic device system): α = 0.25, 0.50, and 0.75, (3) different elastic stiffness balances (β) between the hysteretic device and the supporting braces: β = 0.25, 0.50, and 0.75, (4) post-to pre-yielding stiffness ratios (K2/KELD) for the hysteretic devices of 0.0 (elastic-perfectly plastic), 0.03, and 0.05, and (5) two angles of inclination of the chevron braces with respect to the horizontal axis (θ): 40° and 45°. From the results obtained in this study, optimal stiffness balances α and β are defined to obtain a suitable mechanism where the hysteretic devices yield first and develop their maximum local displacement ductility μ, whereas incipient yielding is only formed at beam ends of the moment frame. Observations are done with respect to: (a) the global ductility capacity for the structure and its relationships with the local displacement ductility capacity for the hysteretic devices for a given combination of α, β, K2/KELD, and θ and (b) overstrength factors (Ω) for design purposes.
It became possible to predict and trace elasto-plastic behaviors of unbonded braces by the finite elements method taking the material and geometrical non-linearity into considerration in which unbonding effect was modeled by "tying method". (1) Regarding the relationship of the load and the axial displacement and of the load and the horizontal displacement, there is good agreements between analytical and experimental results in the characteristics of hysteresis curves, although analytical values eive larger values than experimental values because (1)Bauschinger's effect of steel was disregarded, (2)stiffness of mortar after the occurrence of cracking was evaluated on the stiffer side, (3)local fracture of end mortal was disregarded, and (4)steel's yield point after large cyclic strain was evaluated on the high side in the mixed hardening rule of steel material. (2) There is good agreement between analytical and experimental results regarding the characteristics in stress and strain distribution and hysteresis charachteristics of core steel plates.
It is well recognized that structures designed by current codes undergo large inelastic deformations during major earthquakes. However, lateral force distributions given in the seismic design codes are typically based on results of elastic-response studies. In this paper, lateral force distributions used in the current seismic codes are reviewed and the results obtained from nonlinear dynamic analyses of a number of example structures are presented and discussed. It is concluded that code lateral force distributions do not represent the maximum force distributions that may be induced during nonlinear response, which may lead to inaccurate predictions of deformation and force demands, causing structures to behave in a rather unpredictable and undesirable manner. A new lateral force distribution based on study of inelastic behavior is developed by using relative distribution of maximum story shears of the example structures subjected to a wide variety of earthquake ground motions. The results show that the suggested lateral force distribution, especially for the types of framed structures investigated in this study, is more rational and gives a much better prediction of inelastic seismic demands at global as well as at element levels.
Some results are highlighted in this paper from a research effort being undertaken to identify ground motion and structural characteristics that control the earthquake response of concentrically braced steel frames and to identify improved design procedures and code provisions. The focus of this paper is on the seismic response of three and six story concentrically braced frames utilizing buckling-restrained braces. A brief discussion is provided regarding the mechanical properties of such braces and the benefits of their use. Results of detailed nonlinear dynamic analyses are then examined for specific cases as well as statistically for several suites of ground motions in order to characterize the effect on key response parameters of various structural configurations and proportions.
In structural systems combined with structural fuse system, the replaceable fuse elements, with their ductile behavior, are an adequate solution for protecting main structural members and reducing the destructive effects of earthquakes, during and after the event. Relatively low cost and easy repair process in these systems leads to rapid return to occupancy after an earthquake. Performance-based design of these systems is a complicated process because of the interactions between two systems, and so far, no simplified method is introduced for this purpose with adequate accuracy. In this study, by using the performance-based plastic design method (PBPD), an iterative, simple and highly accurate procedure is introduced for designing these dual systems. This method is based on separating the two structural systems considering their interactions. There are three performance objectives in this method: first, elastic behavior in low earthquake hazard level for immediate occupancy, second, inelastic behavior of fuse in moderate earthquake hazard level for rapid repair, and third, inelastic behavior of the whole structure in very high earthquake hazard level for collapse prevention. As design examples, structures with linked column frames (LCF) were chosen. Three structures with 3, 6 and 9 stories, were designed with this method. To evaluate the proposed method, nonlinear static and dynamic analysis was applied, and structures were modeled according to experimental results of the members and ground motions representing various seismic hazard levels. Analyses results showed that the designed structures achieved the performance objectives. Moreover, in moderate earthquake hazard level, only fuse members yielded and other structural members remained elastic.
Previous research has proposed the Linked Column Frame (LCF) as a lateral load-resisting system capable of providing rapid return to occupancy for buildings impacted by moderate earthquake events and collapse prevention in very large events. The LCF consists of flexible moment frames (MF) and linked columns (LC), which are closely spaced dual columns interconnected with bolted links. The linked columns (LC) are designed to limit seismic forces and provide energy dissipation through yielding of the links, while preventing damage to the moment frame under certain earthquake hazard levels. The proposed design procedure ensures the links of the linked column yield at a significantly lower story drift than the beams of the moment frame, enabling design of this system for two distinct performance states: rapid repair, where only link damage occurs and quick link replacement is possible; and collapse prevention, where both the linked column and moment frame may be damaged.
Here, the seismic performance factors for the LCF system, including the response modification factor, R, the system over-strength factor, Ω0, and the deflection amplification factor, Cd, are established following the procedures described in FEMA P695 . These parameters are necessary for inclusion of the system in the building code. This work describes the development of archetype structures, numerical models of the LCF systems, incremental dynamic analyses, and interpretation of the results. From the results, it is recommended that R, Ω0, and Cd values of 8, 3, and 5.5 be used for seismic design of the LCF system. A height limit of 35 m (115ft) is recommended at this time as taller LCFs are not considered in this study.
The Linked Column Frame (LCF) is a new brace-free lateral structural steel system intended for rapid return to occupancy performance level. LCF is more resilient under a design level earthquake than the conventional approaches. The structural system consists of moment frames for gravity that combines with closely spaced dual columns (LC) interconnected with bolted links for the lateral system. The LC links are sacrificial and intended to be replaced following a design level earthquake. The centerpiece of this work was a unique full scale experiment using hybrid testing; a combination of physical test of a critical sub-system tied to a numerical model of the building frame. This paper outlines the experimental setup, testing and validation of the LCF steel frame system. Hybrid testing allows for full scale study at the system level accounting for the uncertainties via experimental component and having the ability to model more conventional behavior through numerical simulation. The experimental sub-system consisted of a two story LCF frame with a single bay while the remainder of the building was numerically modeled. Two actuators per story were connected to the specimen. The LC links have been designed to be short and plastically shear dominated and the LCF met the design intent of 2.5% inter-story drift limits. For evaluating the LCF response, hybrid testing was performed for ground motion at three different intensities; 50%, 10% and 2% probability of exceedence in 50 years for Seattle, Washington ground motions. The system overall had exhibited three distinct performance levels; linearly elastic, rapid return to occupancy where only the replaceable links would yield, and collapse prevention where the gravity beam components also became damaged. Experimental results demonstrated a viable system under seismic loading, offering a ductile structural system with the ability to rapidly return to occupancy.
A parametric study was devoted to evaluate, using static nonlinear analyses (pushover), global seismic design parameters for low to medium rise regular reinforced concrete moment-resisting braced frames (RC-MRBFs) with hysteretic energy dissipation devices mounted on chevron steel bracing. Frame models with range from five to twenty five stories were designed using different elastic stiffness ratios between the moment frame system and the whole structure (frame-bracing-hysteretic device system). Also, different elastic stiffness balances between the hysteretic device and the supporting braces were considered. Different post to pre yielding stiffness ratios for the hysteretic devices were considered. Two angles of inclination of the chevron braces with respect to the horizontal axis were considered, taking into account typical story heights and bay widths used in Mexican practice. From the results obtained in this study, stiffness balances are defined to achieve a suitable mechanism where the hysteretic devices yield first and develop their maximum local displacement ductility, whereas in the moment frame incipient yielding is only formed at the beam ends. Finally, additional comments are made with respect to: (a) relations between global ductility capacity and local displacement ductility capacity for the hysteretic devices for a given combination of the studied stiffness parameters and angles of inclination, (b) story drifts at yielding and their relation with the selected elastic stiffness ratio between the moment frame system and the whole structure and, (c) overstrength factors for design purposes.
Current approaches to building design for large lateral seismic demands typically involve the use of ductile structural systems, which in most cases utilize the gravity load-carrying members to resist the lateral movement. The resulting inelastic behavior reduces the design base shear while preventing collapse and allows for economic design of the structural components. However, inelastic behavior leads to structural damage, which in most ductile frame lateral systems means damage to the gravity load-carrying members. The loss of occupancy and the difficulty associated with repairing the gravity system economically burdens the owners and occupants. A structural steel framing system free of diagonal bracing and intended for rapid return to occupancy is outlined. The lateral system consists of dual columns interconnected with replaceable link beams and a secondary moment frame. The linked columns provide inelastic behavior to the system by having the links yield primarily in shear under predetermined levels of lateral load, while protecting the columns and beams that carry the gravity loads. Non-linear pushover analyses were used to investigate the performance of the proposed lateral system. Under increasing drift, a ductile system response was obtained with inelasticity initiated in the links. The structural system exhibited three levels of performance: 1) elastic, 2) rapid return to occupancy and 3) collapse prevention. The rapid return to occupancy can be achieved prior to yielding of the gravity beams by replacing the damaged links, offering an improved level of performance over conventional moment frames. The linked column contribution toward system stiffness and strength was found to depend on the link strength and the secondary moment frame connectivity. The system behavior was ductile with drift levels exceeding special moment resisting frames, but with reduced demand on the beam moment connections. The closely spaced linked columns can develop large axial forces that need to be addressed at the foundation level, but also resist significantly lower moments than the special moment resisting frames. In general, the non-linear analyses showed the linked column frame system to be viable under seismic loading, offering the designers and owners a ductile structural system with specific target performance levels.
A new type of seismic resistant structural steel braced-frame system is introduced that employs controlled rocking, elastic post tensioning, and replaceable fuses to resist earthquake shaking with limited structural damage. Through the use of capacity design principles, inelastic energy dissipation is confined to replaceable fuses while the controlled rocking and elastic post tensioning provide self-centering action to eliminate residual drift. Quasi-static cyclic tests and dynamic shake table tests of large-scale specimens confirm that the system can sustain extreme earthquake ground shaking with story drift ratios up to 3 % without structural damage. Owing to the well-defined rocking mechanism, analysis and design of the system is straightforward. Work is ongoing to develop design criteria and guidelines to facilitate practical implementation of these system in building design and construction.
Extended end-plate moment connections are one alternative to fully welded connections that has been considered for use in seismic force resisting moment frames. As a part of the SAC Steel Project, a research program to investigate the behavior and design of extended end-plate moment connections under cyclic loading was conducted at Virginia Polytechnic Institute and State University. Six bare steel beam-to-column connection specimens and one composite slab beam-to-column connection specimen were tested. An overview of the design, fabrication, and testing of the specimens is presented. The test results show that extended end-plate moment connections can be designed to provide the strength, stiffness, and ductility required for use in seismic force resisting moment frames. The effects of the composite slab are discussed, and it is recommended that the effects of the slab be considered in the design of beam-to-column extended end-plate moment connections.
Seismic design relies on inelastic deformations through hysteretic behavior. However, this translates into damage on structural elements, permanent system deformations following an earthquake, and possibly high cost for repairs. An alternative design approach, proposed in the past, is to concentrate damage on disposable and easy to repair structural elements i.e., "structural fuses", whereas the main structure is designed to remain elastic or with minor inelastic deformations. The implementation of the structural fuse concept into actual buildings would benefit from a systematic and simple design procedure. Such a general procedure is proposed here for designing new or retrofitted structures. The proposed structural fuse design procedure for multi-degree-of-freedom structures relies on results of a parametric study presented in the paper, considering the behavior of nonlinear single degree of freedom systems subjected to synthetic ground motions. Nonlinear dynamic response is presented in dimensionless charts normalized with respect to key parameters. The proposed design procedure is illustrated as an example of application using Buckling-restrained braces as metallic structural fuses. This example is used in an experimental project which is described in a companion paper as a proof of concept to the developed design procedure.
Non-linear dynamic analyses examining the seismic response of moment resisting (MR) steel frames enhanced with low-yield steel shear panels are presented. Shear panels, which act as damping and stiffening devices, are schematised as equivalent bracing elements having a suitable hysteretic behaviour. For this purpose, an analytical model is set up and calibrated on the basis of available experimental tests. A parametric analysis is therefore carried out varying several parameters of shear panels, namely strength, stiffness, ductility and hysteretic behaviour, aiming at determining those factors having the major impact on the seismic response of the frame. Obtained results show that the considered design procedure is really effective and convenient, low-yield steel shear panels providing an apparent reduction of storey deflection and damage level of the primary structure.
Seismic behavior of frames with innovative energy dissipation systems (FUSEIS1-2)
Unbonded braces in the United States—Design studies, large-scale testing, and the first building application
Investigation of replaceable sacrificial steel links
Performance-based plastic desig (PBPD) method for earthquake-resistant structures