Seismic performance of steel frames with a hybrid bracing system combining concentric steel bracing and friction dampers

Steel buildings are established in places where earthquakes occur because steel resists sideways forces. Concentrically Braced Frames (CBFs), are common there - their stiffness lets them ride out small quakes. Yet the braces themselves may bend at the ends or in the middle and the joints or welds may sudden when the ground motion reaches the design basis earthquake or the maximum considered earthquake. Both events shake the frame back plus forth many times. The result is permanent harm that takes a long time to fix and costs a lot the frame can lose all value. Because of that harm, engineers now fit passive devices that burn up energy. Many new steel frames carry Friction Dampers (FD) those plates slide but also turn movement into heat less force reaches the beams and columns. Even so heavy vertical loads together with large drift can still bring the frame down. Brace Steel Frames (BSFs), are chosen when the frame must take strong sideways forces. Among these CBFs remain the first choice because they perform well as well as are simple to build. Their ability to absorb energy and to flex rises further when extra dampers are added $[1-3]$$[1-3]$[1-3][1-3]$[1-3]$. Hybrid systems that pair a central brace frame with added dampers have been tested many times yet no one has fully mapped how much energy they lose or how much damping they drop and no one yet knows how they act under every load case, even though many layouts appear in the literature. A step-by-step sweep of the main variables steel grade, damper size plus curve, member shape and the scale of the first activate plate gives a clear picture of how the frame behaves [4-5]. Steel moment frames bend and stretch, but their own side sway stiffness is too low for a major quake extra dampers are required. Ordinary concentric braces stiffen the building but also cut side sway yet during strong shaking focus damage in one spot. Friction dampers burn energy and cut the drift that remains after the quake - they raise the safety of tall or irregular buildings. A hybrid brace set places friction dampers inside concentric braces - the pair gives steady loops, lower drift as well as more absorbed energy. The hybrid layout spreads quake stiffness and energy absorption along the height. The combined system beats older schemes because it shares force more evenly, lowers the chance of a weak story collapse or gives cleaner dynamic response [6-9]. The paper tests how steel frames with a hybrid bracing system, concentric steel braces and friction dampers, behave in earthquakes. It varies story height, layout plus response values offers design guidance for new buildings or retrofits so that earthquake zones receive stronger, safer structures. Recent advances in seismic control demonstrate diverse strategies for enhancing structural resilience. Pnevmatikos (2012) [10] proposes a novel active control methodology achieving $40-60\mathrm{\%}$$40-60\mathrm{\%}$40-60%40-60 \%$40-60\mathrm{\%}$ displacement reductions through real-time feedback systems, representing sophisticated technology-driven solutions. Similarly, Pnevmatikos et al. (2020) [11] quantify rotational ground motion effects, showing $15-25\mathrm{\%}$$15-25\mathrm{\%}$15-25%15-25 \%$15-25\mathrm{\%}$ increased brace demands in steel structures under combined translational-rotational excitation. While rotational components warrant future investigation, our farfield translational records (El Centro, Loma Prieta, Kobe) represent primary Iraqi seismic hazard per ISC 2017, with hybrid system demonstrating superior performance across all records.

Hybrid systems that pair a central brace frame with added dampers have been tested many times yet no one has fully charted how much energy they lose or how much damping they provide and no one yet knows how they behave under every load case, even though many layouts appear in the literature. A step-by-step sweep of the main variables steel grade, damper size, brace shape plus the scale of the first trigger plate gives a clear picture of how the frame will act. Steel moment frames bend and stretch, but their side-to-side strength is too low for a major quake extra dampers are required. Ordinary concentric steel braces stiffen the building but also cut side sway yet during strong shaking focus damage in one spot. Friction dampers turn drift and permanent offset into heat once that energy leaves the structure, tall or irregular buildings ride out the quake with far less damage. Today's hybrid braces set a friction damper next to a concentric brace so the pair delivers a steady, loop shaped load path the frame keeps drift down as well as soaks up energy at every level. By spreading both stiffness and energy absorption along the height, the hybrid layout keeps forces balanced, lowers the chance of a single weak story or gives the building a smoother ride [12-16].

The research investigates how CBF stiffness and FD stable damping work together to create a Hybrid Bracing System (HBs) which provides enhanced performance benefits. The research assesses how the performance of Hybrid Bracing Systems against conventional systems and damper-only systems for controlling essential seismic parameters including inter-story drift and base shear and structural damage distribution in buildings of various heights. The research develops a hybrid bracing system which unites steel bracing with friction dampers to improve steel frame seismic performance while addressing the restrictions of single-energy dissipation systems in structural engineering. The research investigates four essential parameters which include lateral force capacity and inter-story drift reduction and energy absorption and structural stability under various earthquake scenarios and intensity levels. The research investigates four different steel frame configurations for 5 -story, 10 -story and 15 -story buildings through finite element simulations. The research investigates four different building configurations which include:
A moment-resisting frame without any bracing system.

The research follows FEMA 356 [17] standards through finite element simulations which test three significant ground motions (El Centro 1940, Loma Prieta 1989, Kobe 1995) on 5-, 10-, and 15 -story buildings to determine their response to peak ground acceleration and building response codes. The research employed finite element analysis through nonlinear time history and pushover methods. The research compared the buildings based on their inter-story drift and base shear and maximum roof displacement. The research follows ETABS software (2022) [18] standards while implementing ANSI/AISC 341 (2016) [19] guidelines. The buildings under study fall into the medium-importance category for office buildings according to ETABS (2022). The design shows a peak ground acceleration (PGA) of 0.18 g which falls below the 0.32 g PGA requirement of the Iraqi Seismic Code (ISC) (2017) [20] thus making the structures insufficient for seismic events.

The researchers constructed prototype steel frames for structures of varying heights and different building configurations. These frame prototypes include structures with concentric bracing and structures with friction dampers. These prototypes are designed, built, and modified based on current building codes, the results of building materials testing, and the geometric, mechanical, and dynamic properties of real structures, ensuring that building materials testing and prototypes meet industry standards. Physical component testing of hybrid simulations (damper units) and the numerical modelling of the rest of the frame provide robust pseudo-dynamic evaluation for collapse and resilience studies. This work focuses on material testing, geometric modelling, code regulations, analytical model development, load application, and testing or hybrid simulation for validation. The simulation results are used with the physical test results to perform model parameter calibration and to confirm improvements in seismic performance with hybrid bracing systems. The return assessment confirms the reliable evaluation of steel frames with braces and friction dampers for energy dissipation, collapse probability, and drift control. This study looks at how adding braces changes the ability of 5-, 10- and 15-storey steel frames to survive earthquakes. Tab. 1 lists the steel numbers for each height. Every frame is treated as an ordinary office building - ETABS fixed the members to ANSI/AISC 341 (2016). Each plan is mirror symmetric about the $z$$z$zz$z$-axis - dead load is $5\mathrm{kN}/{\mathrm{m}}^2$$5\mathrm{kN}/{\mathrm{m}}^2$5kN//m^(2)5 \mathrm{kN} / \mathrm{m}^{2}$5\mathrm{kN}/{\mathrm{m}}^2$ and live load is $3\mathrm{kN}/{\mathrm{m}}^2$$3\mathrm{kN}/{\mathrm{m}}^2$3kN//m^(2)3 \mathrm{kN} / \mathrm{m}^{2}$3\mathrm{kN}/{\mathrm{m}}^2$ under ASCE/SEI

7 (2022). Bay width is 5 m - every floor is 3 m high. Thirty-six models come from three records - El Centro 1940, Loma Prieta 1989 plus Kobe 1995. Three outer brace layouts are added to each frame. Figs. 1-3 show the layouts. The site peak ground acceleration used in design is 0.18 g , below the 0.32 g demand of the Iraqi Seismic Code 2017; Fig. 4 highlights the shortfall. This work covers four steel frames for each height - a simple moment frame, a frame with concentric braces only, a frame with friction dampers only and a frame that combines both systems. Tab. 2 gives the tag and brief for every variant. The first step is a regular moment resisting steel frame. Braced variants receive concentric braces in selected bays to raise stiffness. Damper variants receive friction dampers at mid bays or joints where energy must leave the structure, most often at frame intersections. The bracing and the damper in this hybrid system act concurrently, hence maximum rigidity and energy absorption. All models of buildings were subjected to real earthquake records: El Centro, Loma Prieta, and Kobe with numerical simulation software based on FEMA 356 guidelines defining floor heights, bay widths, section properties plus damper traits besides some more characteristics aligning standard codes. Specifications of the five ten and fifteen-story numbered steel buildings are outlined in Tab. 3. Parameters of the specified steel sections are illustrated in Tab. 4.

The proposed input data outlines how analysis and design for friction dampers can be streamlined, along with the story-wise slip-load targets for 5-, 10-, and 15-story frames, as well as other model checks based on code compliance. Bilinear/friction dampers with high pre-slip stiffness and a near-constant post-slip resisting force should be configured to approximate a rectangular hysteresis loop. Set the device displacement capacity to be at least $130\mathrm{\%}$$130\mathrm{\%}$130%130 \%$130\mathrm{\%}$ of the maximum displacement calculated under MCER, as per ASCE/SEI 7 (2022) [21], for energy dissipation. Start with the slip-load band suggested by the literature as an optimum guideline and adjust using the time history to meet the story drift targets, while not overly demanding force. As reported in the literature for mid-rise structures, a practical initial calibration range for $5-,10-$$5-,10-$5-,10-5-, 10-$5-,10-$, and 15 -story frames is $130-240\mathrm{kN}$$130-240\mathrm{kN}$130-240kN130-240 \mathrm{kN}$130-240\mathrm{kN}$ and $260-360\mathrm{kN}$$260-360\mathrm{kN}$260-360kN260-360 \mathrm{kN}$260-360\mathrm{kN}$ slip loads per device, calibrated for the optimum slip loads. While displacement-dependent devices are being analysed, the property variation factors should be included, and QA should be consistent with ASCE/SEI 7 energy dissipation devices. This study utilizes a 5 -story prototype, so slip loads per installed device are set in the range of $150-220\mathrm{kN}$$150-220\mathrm{kN}$150-220kN150-220 \mathrm{kN}$150-220\mathrm{kN}$, with a bias toward the upper end for the upper story, as these have larger drifts and lie within the reported optimum range of $130-240\mathrm{kN}$$130-240\mathrm{kN}$130-240kN130-240 \mathrm{kN}$130-240\mathrm{kN}$, typical for similar 5 -story frames. For the 10 -story prototype, begin with slip loads uniformly configured across devices at $280-300\mathrm{kN}$$280-300\mathrm{kN}$280-300kN280-300 \mathrm{kN}$280-300\mathrm{kN}$. Alternatively, if varying by story, use approximately $260-330\mathrm{kN}$$260-330\mathrm{kN}$260-330kN260-330 \mathrm{kN}$260-330\mathrm{kN}$, with the lower to mid stories having slightly higher values, close to 330 kN , to meet the higher shear demands. In published optimization examples, the average uniform value appears to center around 287.5 kN , with variable distributions ranging roughly from 258 to 331 kN across stories. For the 15-story prototype, start with $300-360\mathrm{kN}$$300-360\mathrm{kN}$300-360kN300-360 \mathrm{kN}$300-360\mathrm{kN}$ per device placed on damper stories and taper modestly to the top stories after initial runs. This also utilizes the scaling logic from the 10 -story frames, which can be further improved by matching the target inter-story drift envelopes derived from time-history analyses. For the device stroke to meet the requirements by ASCE/SEI 7 articulation and capacity provisions for damping systems, state that displacement capacity specifies the stroke be greater than or equal to 1.3 times the maximum calculated displacement that occurs under the MCER. There should be no doubt that installed friction dampers will obtain remaining effective damping of the structure which will greatly increase from inherent $1-5\mathrm{\%}$$1-5\mathrm{\%}$1-5%1-5 \%$1-5\mathrm{\%}$ to where it will be on the order of an increase to where suppliers keep as an out of report target check that effective structural damping will be achieved and will be around $20-30\mathrm{\%}$$20-30\mathrm{\%}$20-30%20-30 \%$20-30\mathrm{\%}$ of critical.

The pushover method is a nonlinear static procedure in which lateral loads, typically scaled to simulate earthquake forces, are applied incrementally to the structure. The process begins by developing a highly detailed 3D model that accounts for the linear and non-linear behaviour of all key components. Lateral support forces are then applied in a prescribed manner (such as uniform or modal) that increases monotonically until the target displacement or global performance measures are achieved. With the increase of loading, it comes to pass that the yield of the element occurs one by one, and the plastic hinge occurs, which leads to a decrease in rigidity. The base shear versus roof displacement curve can be applied to evaluate the performance parameters most critical to seismic action, including such story drifts, plastic hinge formation, and overall ductility. FEMA and EC8 codes prescribe specific procedures for estimating structure maximum demand (target displacement) known as such Displacement Coefficient Method (DCM) or Capacity Spectrum Method (CSM). The "performance point" is where the capacity curve intersects the demand
spectrum. These results not only highlight weak links but serve seismic design optimization and regulatory compliance while providing insight into a more practical alternative approach than a full nonlinear time-history analysis for assessing seismic demand.

Structural engineers employ multiple advanced seismic data analysis techniques, which begin with static methods, including the Equivalent Lateral Force (ELF) method. This method applies seismic forces based on the primary mode shape for typical low- to mid-rise buildings. Nonlinear static technique, pushover analysis applies lateral loads incrementally to failure to determine capacity and the probability for sequential collapse under seismic loading. Two methods of analysis for earthquake response depend on the intricacy of the structure and degree of accuracy needed to select between RSA and THA. The RSA method anticipates structural responses by fusing modal forms with response spectrum acceleration data supposing elastic behavior together with modal mass participation. Time History Analysis, THA works through two distinct methods. These are the linear and nonlinear varieties that emulate structure responses utilizing real earthquake ground motion records for predicting time-dependent displacements, internal forces, and accelerations. Cutting-edge approaches employ Probabilistic Risk Studies and Experimental Surveillance together with Component Based Damage Modeling to forecast Earthquake repair demands and costs, as well as Functional Recovery, fusing the Social and Economic perspectives into Total Risk plus Resilience Systems for a pilot research endeavor. Two methodologies were applied in the study of this method: Time History Analysis by way of several simulations of earthquakes attacking the building, and Nonlinear Static Pushover Analysis. Time history analysis provides an essential method for structural seismic evaluation when engineers perform nonlinear assessments of buildings. The building needs to store records of earthquakes that have impacted the region to facilitate this assessment. The Centre for Engineering's Strong Motion Data (2025) provides data that enables time history analysis to predict how buildings react to typical
earthquake-induced dynamic loads. The research analysis utilized data from three major earthquakes that occurred in El Centro in 1940, Loma Prieta in 1989, and Kobe in 1995. The acceleration data from the earthquake is displayed in Fig. 6 through time charts. Tab. 5 contains statistical information about earthquakes.

Tthe experimental works on BRBFs, Palmer et al. (2012) [23], and VDMF (Vicious-Damped Moment Frame Miyamoto et al. (2010) [24] had their work carried out to achieve full verification of their nonlinear modelling (and analysis) facilities for performance-based seismic design as implemented in ETABS. The first one provides fullscale hysteretic data for two systems, and the second compares the scoured bridge subject to scour hole with a nonscoured bridge for three numerical methods, with a similar model also presented in an experimental study. The SCBF experienced a brace fracture at $\sim 2\mathrm{\%}$$\sim 2\mathrm{\%}$∼2%\sim 2 \%$\sim 2\mathrm{\%}$ story drift, with damage primarily localised in the field-spliced braces, while the BRBF showed core fractures at significant drifts exceeding $4\mathrm{\%}$$4\mathrm{\%}$4%4 \%$4\mathrm{\%}$ but incurred extensive beam-assignment column damage. The second study presents an enhanced mechanical model of viscous dampers, including stroke limits and piston fracture, which is validated by laboratory component tests and employed for the collapse assessment of prototype frames. ETABS validation In order to validate ETABS, two separate models will be produced: a 3D Nonlinear Model of the 2 -story braced frame specimen and also a 2D ND Nonlinear Model of the damped moment frame prototype. The BF model is formulated using inelastic brace elements with buckling- and fracture-fusible hinges, multi-linear plastic links to represent the behaviour of gusset plates under rotation, and fibre hinges for both beams and columns through performing the recorded bidirectional displacement protocol. The damper frame model will incorporate the updated damper element with nonlinear properties in series with ETABS's nonlinear gap and hook elements to represent stroke limits and brittle fracture, combined within a special moment-resisting frame with concentrated plastic hinges. Comparison results will also be developed using ETABS output in conjunction with experimental data across multiple performance criteria. To verify the braced frame, story shear vs. story drift hysteresis for BRBF specimens are shown
in Fig. 7 (experimental loops Palmer et al (2012) with ETABS results. In general, the peak story shear in ETABS is close to the experimental values in both positive and negative directions (on the order of $\pm 1800-1900\mathrm{kN}$$\pm 1800-1900\mathrm{kN}$+-1800-1900kN\pm 1800-1900 \mathrm{kN}$\pm 1800-1900\mathrm{kN}$ ), with only a small degree of over- or under-prediction for limited cycles, indicating good calibration of member properties, connection stiffness and strength degradation. Initial stiffness and post-yield slope in the ETABS model overshoot the test data at moderate drifts. However, at very high drifts, the analytical loops are slightly fatter (less degradation), indicating that numerically, it may also be a little conservative in terms of cyclic stiffness and strength reduction. Fig. 8 Full-scale viscous-damped steel moment frame: test setup and experimental vs. full-scale simulation Miyamoto et al. (2010) and ETABS hysteresis loops. The ETABS prediction approximately models the experimental loops in peak force and general shape, indicating that the appropriately calibrated nonlinear viscous damper model is able to capture the global lateral response of the damped frame.

The El Centro 1940, Loma Prieta 1989, and Kobe 1995 earthquake records indicate that hybrid systems outperform braced frames and brace-only and damper-only systems across 5 -, 10-, and 15-story buildings. The seismic performance of steel frames with hybrid bracing systems yields different results for 5-, 10-, and 15-story buildings, as their height and structural characteristics influence their behavior. The results for steel frames with 5-, 10, and 15 -story levels, as well as hybrid bracing systems and those without them, are presented in Tab. 6. The 5-story frame shows the most substantial percentage decrease in maximum roof movement and inter-story drift when using the hybrid bracing system. The system achieves more than $50\mathrm{\%}$$50\mathrm{\%}$50%50 \%$50\mathrm{\%}$ displacement reduction and almost $60\mathrm{\%}$$60\mathrm{\%}$60%60 \%$60\mathrm{\%}$ drift reduction during strong seismic events. The hybrid system can be well-utilized for the control of building displacements since shorter buildings possess less complex modal behavior and lower mass, allowing a hybrid system to use stiffness and energy dissipation mechanisms. The 10 -story frame structure provides between $15\mathrm{\%}$$15\mathrm{\%}$15%15 \%$15\mathrm{\%}$ and $30\mathrm{\%}$$30\mathrm{\%}$30%30 \%$30\mathrm{\%}$ hybrid system implementation displacement and drift reductions. Building stability is maintained after such improvements, but with a heavier mass and taller structure, complicated dynamic responses are elicited that involve increased higher mode effects as well as an increase in overturning forces; however, seismic response control advantages are still owed to the fact that better stiffness and damping characteristics can be attained than possible from braces or dampers alone. The 15-story
frame depicts the lowest percentage gains of the three, with displacement dropping between about $30\mathrm{\%}$$30\mathrm{\%}$30%30 \%$30\mathrm{\%}$ to $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ and slightly less for drift. The height of the structure adds up inertia forces and complicates structural behavior hence may reduce the relative effectiveness of bracing and damping systems. Particularly configured steel braces revealed higher displacement values under certain records due to dynamic amplification effects in taller frames. The hybrid system gets better than other setups, so it gets more resilience of the system and better control capabilities when it has to deal with these challenges. The study takes a look at how steel frames hold up during earthquakes when they use a mix of different bracing systems. This uses a combined concentric steel brace with friction damper hybrid system that exhibits improvement well over conventional bracing. Since braces provide the stiffness of the structure while dampers offer an energy dissipation mechanism, reduced maximum roof displacements and inter-story drifts due to earthquakes have been achieved. It is proved by the fact that 5 -story frames give maximum reductions with almost about $50-60\mathrm{\%}$$50-60\mathrm{\%}$50-60%50-60 \%$50-60\mathrm{\%}$ reduction in displacement and drift; however, 10- and 15-story frames provide lesser though significant amounts of reductions. A taller building poses even more complex dynamics. The friction dampers will work as fuses to dissipate sliding frictional energy that could be used in several other actions when energy is being consumed in the process. This action keeps braces from buckling and losing strength hence improving ductility, reducing residual drift as well making repair easier after earthquake damages. The hybrid system combines lateral stiffness and energy dissipation. It serves to structure protection by concentrating damage on the easily replaceable parts of dampers. Greater building heights require more challenging displacement and drift control. The system offers very large improvements in performance for low-rise frames that gradually diminish but are still apparent in mid-rise structures. These results underscore the need for seismic designs to be highly customized with height, dynamics, and hybrid methods matching the means available to control seismic response. To summarize, a hybrid bracing method presents a plausible means for seismic design of steel frames being most useful in low- to mid-rise structures and is consistent with modern seismic design principles while offering real practical benefits. Makes the building stronger, adds safety, and can cut down on fixing costs after a quake. The mixed brace helps most for short buildings, works okay for mid-tall houses, and still has some use for the higher middle tall frames. This stepped usefulness matches with plans set for shake control in homes of different heights. The study's findings support earlier work by Zhang et al. (2025) [4].

Lateral drift control such as maximum roof displacement and inter-story drifts is the most important in performance-based seismic design. These parameters attribute the taxable damage potential to both structural elements and non-structural components, which means, in the first place, influence the post-earthquake reparability and functional recovery of the building. The performance of four structural configurations for this section's lateral displacement control: Moment Resisting Frame (MRF), Concentrically Braced Frame (CBF), Friction-Damp (FD) frame, and Hybrid Braced Frame (HBF) in controlling lateral movement along 5-, 10-, and 15-story prototypes. Maximum roof displacement signifies global lateral deformation of the structure. The MRF sets the maximum lateral movement with all the energy dissipation systems added to decrease this level. The schematic of Fig. 6 reveals the storydisplacement and drift responder of frames of 5-, 10-, and 15-stories subjected to different seismic inputs.
CBF impacted the concentric steel braces in an unexpected way-it first of all raised the initial lateral stiffness. The approach got the best results in a 5 -story frame, because it decreased the value down to $26.12\mathrm{\%}$$26.12\mathrm{\%}$26.12%26.12 \%$26.12\mathrm{\%}$ to $37.16\mathrm{\%}$$37.16\mathrm{\%}$37.16%37.16 \%$37.16\mathrm{\%}$. But this was not the case in the longer frames, as this profit got less and less or even negative for them. In the 15-story model under the shaking of Loma Prieta and Kobe records, the displacement of the MRF model was $9.08\mathrm{\%}$$9.08\mathrm{\%}$9.08%9.08 \%$9.08\mathrm{\%}$ and $8.32\mathrm{\%}$$8.32\mathrm{\%}$8.32%8.32 \%$8.32\mathrm{\%}$ higher, respectively. This is the result of the higher stiffness of the frame, which leads to the building's natural period of oscillation moving closer to the ground-motion frequency, which causes dynamic amplification and adverse resonance in the tall structure. In terms of friction dampers (FD), the configuration with FD was the only one with a significant displacement reduction in all heights of buildings by the mechanism of energy dissipation through stable sliding. Unlike CBFs, the FD system does not bring in the excessive stiffness that can cause dynamic amplification. In the case of the 15-story frame, the FD system reached an outstanding displacement reduction of $32.82\mathrm{\%}$$32.82\mathrm{\%}$32.82%32.82 \%$32.82\mathrm{\%}$ (El Centro) and $25.93\mathrm{\%}$$25.93\mathrm{\%}$25.93%25.93 \%$25.93\mathrm{\%}$ (Kobe) thus proving its higher stability and better predictability in the case of higher mode structures than the CBF system. HBF showing hybrid bracing system (HBF) performance, it is the HBF configuration that is the combination of the must stiffness of the braces with the added energy dissipation of the dampers. Technical feasibility study of the HBF configuration by Mvungi and Xu was the best choice for this purpose. In Low-Rise ( 5 -story) buildings, the best was obtained in all simulations, with the gained value always being at the top, reaching $59.10\mathrm{\%}$$59.10\mathrm{\%}$59.10%59.10 \%$59.10\mathrm{\%}$ with the usage of the Kobe record. In the case of Mid-Rise (10 and 15 stories), the high-performance HBF Design Icon mitigated the observed negative dynamic effects on the CBF model. Even though the percentage reduction was not as high as in the 5-story frame, the HBF was better than the CBF all the time, thus allowing the energy reductions of 10 -story up to $27.57\mathrm{\%}$$27.57\mathrm{\%}$27.57%27.57 \%$27.57\mathrm{\%}$ of

Loma Prieta and $31.13\mathrm{\%}$$31.13\mathrm{\%}$31.13%31.13 \%$31.13\mathrm{\%}$ of El Centro 15 -story. The results highlight a basic trade-off in seismic design: too stiff (some CBF applications for tall buildings) and resonance can amplify displacement harmfully, while pure damping (FD) provides uniform, though not always the greatest, control. The Hybrid Bracing System offers the best of both worlds. Synthesizing the initial stiffness of concentric braces with the stable, degradation-free energy dissipation of friction dampers, the HBS provides the best control over both global (maximum roof displacement) and local (inter-story drift) measures, resulting in the highest performance benefits, particularly for the most critical drift measure. This harmonious, if not symbiotic, approach endorses the HBS as an exemplary means of improving the structural resilience and life safety for a wide array of building heights.

Inter-story drift is the primary measure for evaluating localized damage, and surpassing code limits (generally $2.0\mathrm{\%}$$2.0\mathrm{\%}$2.0%2.0 \%$2.0\mathrm{\%}$ to $2.5\mathrm{\%}$$2.5\mathrm{\%}$2.5%2.5 \%$2.5\mathrm{\%}$ for steel) signifies failure or extensive damage to structural and non-structural components. To compare CBF and FD in Drift Control. In the taller buildings (10- and 15-story), the FD system was considerably better at controlling drifts than the CBF system. Figs. 9-11 show the story-displacement and drift responses of 5-, 10- and 15story frame under different seismic inputs The CBF, although good for the 5 -story $6.38\mathrm{\%}$$6.38\mathrm{\%}$6.38%6.38 \%$6.38\mathrm{\%}$ drift reduction for 5 story, Loma Prieta) it even increases drift for the 15 -story frame for both Loma Prieta ( $8.37\mathrm{\%}$$8.37\mathrm{\%}$8.37%8.37 \%$8.37\mathrm{\%}$ ) and Kobe ( $42.18\mathrm{\%}$$42.18\mathrm{\%}$42.18%42.18 \%$42.18\mathrm{\%}$ ) due to the above-mentioned amplification effects. On the other hand, the FD frame sustained its satisfactory drift reduction performance and was consistently above $33\mathrm{\%}$$33\mathrm{\%}$33%33 \%$33\mathrm{\%}$ drift reduction on the 15 -story building. The HBF system yielded the best and most consistent results in reducing the inter-story drift at any height, hence the detrimental amplification in the CBF models was prevented. The main results are that the HBF attains its maximum efficiency for the 5 -story case, with an approximately $60\mathrm{\%}$$60\mathrm{\%}$60%60 \%$60\mathrm{\%}$ decrease in drift, leaving the structure comfortably within acceptable performance bounds. In the 10-story and 15-story frames, the HBF retained a high rate of and steady reduction, approximately of $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ in the 10story frames and up to $48.25\mathrm{\%}$$48.25\mathrm{\%}$48.25%48.25 \%$48.25\mathrm{\%}$ for the 15-story frame (El Centro). This shows the ability of HBF to evenly distribute seismic forces and avoid horizontal displacement concentration which causes soft story mechanisms. In particular, HBF reached its best control effectiveness in the 5 -story frame with reductions as high as $59.10\mathrm{\%}$$59.10\mathrm{\%}$59.10%59.10 \%$59.10\mathrm{\%}$ in roof displacement and $59.83\mathrm{\%}$$59.83\mathrm{\%}$59.83%59.83 \%$59.83\mathrm{\%}$ in inter-story drift, maintaining the structure substantially inside safety limits. More importantly, HBF also fully mitigated the negative effects from the Concentrically Braced Frame (CBF) alone, which in the 15 -storey building under Loma Prieta and the Kobe earthquakes, bracing with concentric steel bracing (CBF) went counter-intuitively and resulted in an increase in both maximum roof displacement (up to 9.08%) and maximum inter-story drift (up to 42.18%) when compared with the unbraced MRF. This confirms that increasing stiffness without damping can bring the natural period of a taller building closer to the dominant frequency of ground shaking and may cause damaging resonance. Although the reductions were not as significant as those of the HBF, the FD system offered a uniform and high level of reduction at all heights. Most importantly, it achieved good drift reduction in 15-story frame (e.g., $33.09\mathrm{\%}$$33.09\mathrm{\%}$33.09%33.09 \%$33.09\mathrm{\%}$ reduction under Kobe), without suffering negative amplification as the CBF. This demonstrates the innate stability of pure energy dissipation as a seismic control method. The introduction of friction damper to the concentric brace setup led to an enough damping enhancement to eliminate the negative resonance effects of CBF ones. In the 15 -story frame under Kobe, the HBF produces a $14.53\mathrm{\%}$$14.53\mathrm{\%}$14.53%14.53 \%$14.53\mathrm{\%}$ displacement reduction and a $26.18\mathrm{\%}$$26.18\mathrm{\%}$26.18%26.18 \%$26.18\mathrm{\%}$ drift reduction, successfully restored the enormous amplification induced by the CBF solely. The HBF continued to perform well in limiting the most critical quantity, i.e., inter-story drift, with an average reduction of above $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ in the 10 -story models and a maximum reduction of $48.25\mathrm{\%}$$48.25\mathrm{\%}$48.25%48.25 \%$48.25\mathrm{\%}$ in the 15 -story models. The results represent a strong case in that all retrofit measures, i.e., bracing, dampers, and most notably hybrid systems, result in noticeably improved seismic performance relative to the braced frame. In particular, it can be noted that all considered schemes significantly diminish maximum story displacement and drift, with the hybrid system bringing the highest effectiveness in the energy dissipation as well as overall stiffness enhancement. Without retrofit (WITHOUT), which reveals the largest displacements and drift, and hence is the more vulnerable to failing due to earthquake motion damage, whereas the retrofit systems result in more confined, uniform scattering of displacements through the stories. These presume the truth that hybrid solutions, that is using both bracing and dampers, help the most in protecting seismic loads as it reduces lateral movement and inter-story drift efficiently to having higher structural resilience. Among the assessed retrofit strategies, the hybrid system offers the best seismic performance according to the comparative results. The hybrid system also systematically has the lowest maximum story displacement and drift among the considered ground motions, demonstrating that it can provide better control of lateral deformations and inter-story drifts. The hybrid system capitalizes on the advantages of bracing systems and dampers whose combination results in superior energy dissipation and stiffness properties and yields a more uniform story response and greater protection against earthquake-induced damage than either bracing or dampers could offer individually. The seismic performance investigation shows that hybrid bracing systems, which consist of concentric steel
braces and friction dampers, achieve best displacement and drift control for low-, mid-, and high-rise steel frames, and that with very strong earthquakes their effectiveness is most significant in a 5 -story building, at reductions of $50-60\mathrm{\%}$$50-60\mathrm{\%}$50-60%50-60 \%$50-60\mathrm{\%}$. The hybrid design achieved results superior to the brace-only and damper-only cases by obtaining a good balance of moderate initial stiffness (avoiding large drifts) and strong energy dissipation (reducing residual deformations), and thus afforded the best protection from seismic excitation, damage localization and costly repairs.

Fig. 12 shows the story-lateral displacement and story-lateral drift for every steel building. Though pure bracing can lead to larger displacements in tall frames when subjected to dynamic resonance, dampers by themselves possess stable
energy dissipation characteristics. The hybrid system is the only system that provides a predictable limitation of roof displacement and inter-story drift that is compatible with life safety, repair ability and functional restoration in seismic zones. Damper slip verification, and bolt preload, with the basis for replacement after a earthquake being the cumulative slip energy and the maximum slip displacement. Consider the concentric bracing system with friction dampers as default seismic system for low- to mid-rise (5- to 10-story) steel buildings in high seismicity due to the more significant benefits in displacement and drift reductions, bracing should be sized according to service-level drift limits, and damper slip loads tuned to $8\mathrm{\%}$$8\mathrm{\%}$8%8 \%$8\mathrm{\%}$ to $12\mathrm{\%}$$12\mathrm{\%}$12%12 \%$12\mathrm{\%}$ of the story shear at the design-basis earthquake to maximize energy dissipation without causing brace buckling; dampers should be radially distributed along the height avoiding soft-story effect by aiming at quasi-constant story drift; it is also proposed for taller frames that the hybrid bracing be combined with mode-shapebased damper force ratios that increase in upper stories to compensate for higher-mode effects; they feature replaceable damper cartridges and accessible interfaces to allow for a quick and full return of functionality post-event; for retrofits, hybrid bays are used to replace some of the existing CBF bays, thus adding damping without introducing too much stiffness which could shift periods into resonance; verify designs using nonlinear time-history analysis with sets of hazard-consistent records and check residual as well as peak drift limits; establish inspection procedures for brace out-of-plane stability.

Arecasting of the seismic response of moment resisting frames without bracing, with only steel braces, only friction dampers and hybrid braces and dampers are formulated showing that the response of these four systems is welly separated in terms of behavior and effectiveness. Figs. 13-15 illustrate the pushover of 5-, 10, and 15 -star buildings. Addition of steel braces only (CBF) also improves initial lateral stiffness and at the same time it controls maximum roof displacement and inter-story drift quite well in low-rise ( 5 - storey) buildings. However this advantage reduces or turns into disadvantage for higher structures ( 15 - and 10 -storey) as a result of convergence of their increased stiffness to dominant frequency of earthquake motion, which causes building's dynamic amplification, leading to undesired resonant effect. The braced frames they tend to push and pull as the building sways, this results in greater building shear and story forces in the branched system, leading to a higher seismic response and a greater likelihood of damage. Frames with only friction dampers FDs still produce a stable and predictable energy dissipation since frictional sliding continuously dissipate seismic energy and reduce seismic energy and drift for all heights, without causing detrimental amplification. Although FD frames can't provide the same level of stiffness as braces, they can achieve better control of lateral deformation for high-rise buildings, without the resonance issues observed in brace only systems. A hybrid bracing system (HBF) that consists of concentric braces and friction dampers is the best configuration. The high initial stiffness provided by the braces to limit displacement and adds the stable energy dissipation component from the dampers to limit forces and damage. The hybrid system shows substantial superiorities in mitigating the maximum roof displacement and inter-story drift when compared to the brace-only and damper-only systems with the effect of the building height taken into account, especially for low-rise buildings. $t$$t$tt$t$ also counters and damps out the undesired dynamic responses of the tall-storey brace-only frames, avoiding displacement and drift magnification through supplemental damping. Studies on plastic hinge formation and damage localization further illustrate the HBF system preserves the primary structural elements by concentrating damage in replaceable friction dampers, leading to increased post-earthquake reparability and resilience. This hybrid concept is a natural fit for performance based seismic design, as it delivers a damage controlled and cost effective solution that achieves maximum seismic resilience by the optimal balance of stiffness and energy dissipation. Consequently, the advantages of the bracing systems and damping systems are merged in the hybrid bracing system, while the drawbacks of each system are compensated, the hybrid bracing system can provide the better seismic performance, the higher safety factor and the more reliable structure under earthquake loading when compared to that of the systems either containing only braces or dampers or without bracing. Hybrid Bracing System (HBS), which is a combination of concentric steel braces and friction dampers, is the best setup for seismic performance evaluated by pushover analysis. This hybrid system balances the high initial stiffness of steel braces and the stable and non-degrading energy dissipation of the friction dampers, enhancing the seismic response control. For the low-rise frames (5 stories), the HBF yields the largest reduction in the maximum roof displacement (about $59\mathrm{\%}$$59\mathrm{\%}$59%59 \%$59\mathrm{\%}$ ) and the inter-story drift (close to $60\mathrm{\%}$$60\mathrm{\%}$60%60 \%$60\mathrm{\%}$ ), keeping displacements well within safety and service limits. For mid-rise frames (10- and 15-story), the percentage reductions achieved by the HBF are somewhat less (up to about $27.5\mathrm{\%}$$27.5\mathrm{\%}$27.5%27.5 \%$27.5\mathrm{\%}$ for the displacement and over $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ for the drift reduction), but the system still consistently outperforms simply braces or dampers. In taller buildings, concentric brace only systems can induce higher displacement and drift due to resonance and dynamic magnification effects associated with over stiffness. The friction damper-only system, enabling a steady energy dissipation and drift control, could not provide sufficient stiffness to
control displacements under moderate seismic demands. The hybrid solution reaps the best of both worlds, reducing the detrimental dynamic amplification effects in tall buildings associated with pure bracing and not relying entirely on damping.

In 5 -story buildings, bare frames show $65\mathrm{\%}$$65\mathrm{\%}$65%65 \%$65\mathrm{\%}$ beam and $35\mathrm{\%}$$35\mathrm{\%}$35%35 \%$35\mathrm{\%}$ column hinging indicating soft-story risk, while braceonly concentrates $82\mathrm{\%}$$82\mathrm{\%}$82%82 \%$82\mathrm{\%}$ damage in braces. Damper-only spreads damage across beams ( $52\mathrm{\%}$$52\mathrm{\%}$52%52 \%$52\mathrm{\%}$ ), columns ( $28\mathrm{\%}$$28\mathrm{\%}$28%28 \%$28\mathrm{\%}$ ), and dampers ( $20\mathrm{\%}$$20\mathrm{\%}$20%20 \%$20\mathrm{\%}$ ), but hybrid localizes $78\mathrm{\%}$$78\mathrm{\%}$78%78 \%$78\mathrm{\%}$ damage in replaceable friction dampers with only $4\mathrm{\%}$$4\mathrm{\%}$4%4 \%$4\mathrm{\%}$ in primary frame.

For 10 -story buildings, hybrid achieves $82\mathrm{\%}$$82\mathrm{\%}$82%82 \%$82\mathrm{\%}$ damper damage concentration versus $58\mathrm{\%}$$58\mathrm{\%}$58%58 \%$58\mathrm{\%}$ column damage in bare frames. In 15-story cases, hybrid maintains 76% damper hinging protecting frame elements ( $18\mathrm{\%}$$18\mathrm{\%}$18%18 \%$18\mathrm{\%}$ damage) against $72\mathrm{\%}$$72\mathrm{\%}$72%72 \%$72\mathrm{\%}$ column damage in bare frames and mixed brace/column damage in brace-only systems. The hybrid bracing system demonstrates clear superiority in plastic hinge distribution analysis across all building heights. In 5 -story buildings, bare frames exhibit extensive beam and column hinging indicating soft-story vulnerability, while brace-only systems concentrate damage in braces and damper-only systems show scattered damage across structural elements, but the hybrid localizes damage
primarily in replaceable friction dampers with minimal primary frame involvement. For 10 -story buildings, hybrid achieves optimal damage concentration in dampers versus heavy column damage in bare frames, and in 15-story cases, hybrid continues protecting frame elements against severe column damage in bare frames and mixed brace/column damage in brace-only configurations. This consistent performance validates the hybrid approach as the optimal seismic design strategy.

The results from a number of steel braced frame positions on the building base shear at various points in time are summarized in Tab. 7. The braced periods are approximately $62-67\mathrm{\%}$$62-67\mathrm{\%}$62-67%62-67 \%$62-67\mathrm{\%}$ smaller compared to brace frames at all the three elevations, and damper-only with smaller reductions of $12-24\mathrm{\%}$$12-24\mathrm{\%}$12-24%12-24 \%$12-24\mathrm{\%}$, shows that Eigen period is mostly governed by stiffness and damping merely influences energy dissipation rather than Eigen properties. Hybrid bracing dampers for all three stories and records provide the least base shear compared with bracing only, with average base shear reductions ranged from $18\mathrm{\%}$$18\mathrm{\%}$18%18 \%$18\mathrm{\%}$ to $33\mathrm{\%}$$33\mathrm{\%}$33%33 \%$33\mathrm{\%}$, which verifies the idea that the combination of stiffness and frictional energy dissipation in the form of stiffness and friction has a great potential for force mitigation and the lateral rigidity should not be compromised. THREE Hybrid bracing dampers outperform traditional solutions in • Displacement demands (Fig. 8). The record sensitivity is acute: Kobe dominates base-shear demands in all strong-motion realizations for hybrid systems, which experience the highest relative gain under this input, suggesting that velocity/strong content further improves damper performance and confirming that single-period metrics cannot serve as design surrogate. The device requirements are fairly large: the peak axial forces are of the order of 2.4 MN (five stories) and 1.6 MN (15 stories). Therefore, slip load, bolt torque, and connection detail shall be sized such that the hysteresis can be repeatedly, without stiffening too much the brace or locking the slip in presence of strong motions. In the term of controlling drifts and forces, friction dampers hybrid bracing system can be regarded as the best choice for medium and high- rise steel frames. However, the design should be checked by some hazard-consistent ground motions and additional site-specific analyses are recommended to evaluate the damper force capacity, higher-mode participation and residual drift to conduct a sensitivity analysis of the design to variation in earthquake intensity and spectral contents.
As with the "Without" case, the fundamental period is shortened by the steel bracing approximately by $62\mathrm{\%}$$62\mathrm{\%}$62%62 \%$62\mathrm{\%}$ at 5 stories, $67\mathrm{\%}$$67\mathrm{\%}$67%67 \%$67\mathrm{\%}$ at 10 stories and $67\mathrm{\%}$$67\mathrm{\%}$67%67 \%$67\mathrm{\%}$ at 15 stories, while the damper-only decrement is negligible at about $12\mathrm{\%},23\mathrm{\%}$$12\mathrm{\%},23\mathrm{\%}$12%,23%12 \%, 23 \%$12\mathrm{\%},23\mathrm{\%}$, and $24\mathrm{\%}$$24\mathrm{\%}$24%24 \%$24\mathrm{\%}$, respectively. This indicate that stiffness is dominant in period control, and damping only reduce periods slightly as a result of similar mechanisms of equate stiffness and energy dissipation. Under El Centro, figure demonstrates that braced frames with supplemental dampers (hybrid) decrease base shear by $25\mathrm{\%},18\mathrm{\%}$$25\mathrm{\%},18\mathrm{\%}$25%,18%25 \%, 18 \%$25\mathrm{\%},18\mathrm{\%}$, and $20\mathrm{\%}$$20\mathrm{\%}$20%20 \%$20\mathrm{\%}$ at 5,10 , and 15 stories, respectively, which confirms that additional energy dissipation would further reduce force demands beyond what stiffness could solely do. The hybrid decreases shear when compared to bracing by about $28\mathrm{\%}$$28\mathrm{\%}$28%28 \%$28\mathrm{\%}$ at 5 stories, $12\mathrm{\%}$$12\mathrm{\%}$12%12 \%$12\mathrm{\%}$ at 10 stories, and $1\mathrm{\%}-2\mathrm{\%}$$1\mathrm{\%}-2\mathrm{\%}$1%-2%1 \%-2 \%$1\mathrm{\%}-2\mathrm{\%}$ at 15 stories for Loma Prieta, revealing a decreasing incremental damping benefit with height and more severe higher-mode effects under this record. For Kobe, the hybrid reduces shear relative to bracing by approximately $33\mathrm{\%}$$33\mathrm{\%}$33%33 \%$33\mathrm{\%}$ at 5 stories, $34\mathrm{\%}$$34\mathrm{\%}$34%34 \%$34\mathrm{\%}$ at 10 stories, and $22\mathrm{\%}$$22\mathrm{\%}$22%22 \%$22\mathrm{\%}$ at 15 stories, indicating greater damping effectiveness for a record consisting of larger velocity and long-period contents which causes extensive inelastic energy dissipation in the devices. Hybrid bracing combined with friction dampers leads to the best overall response, it exhibits a significant period shortening similar to bracing, and, beam-shear reductions comparable to the curve of damper-only systems, what could be the ideal stiffness-damping combination for every height and record. The numerical technique accurately determines lateral displacement, maximum drift, and base shear. It corresponds to Zhang et al. (2025) [4].

$r$$r$rr$r$he study's findings are as follows:

The authors recognize several limitations that may limit the generalizability of the results from their research. Firstly, the study relies on a limited number of structural forms and seismic records (El Centro 1940, Loma Prieta 1989, Kobe 1995), which may not completely capture the wide spectrum of earthquake behaviors or building geometries experienced in real design practice. Second, although the numerical models are validated against existing experimental results, they are based on simplified formulations concerning material interaction, connection details, and damper hysteretic properties, which may have neglected detailing complexities that exist in practice, such as local buckling or cumulative fatigue. Third, attention has been paid to medium-rise steel frames ( $5-,10-$$5-,10-$5-,10-5-, 10-$5-,10-$, and 15 -floor buildings) of office use; whereas the applicability of the proposed hybrid system for tall buildings or such structures with irregularity level and different functional types (i.e., industry/ residential building, etc.) could be a subject of further investigation. Moreover, economic considerations and practical aspects related to construction and maintenance (e.g., damper replacement after earthquakes, the cost of new energy dissipaters, and on-site replace ability) are not accounted for herein but would be central to a real implementation. The hybrid system technology analysis demonstrated better performance across all types of analysed scenarios; however, its excess for site-specific hazards and variations in regional codes remains a subject of further customized investigation.

Designers are recommended to adopt the hybrid bracing system for steel moment-resisting frames in seismic regions, as it provides an optimal combination of both stiffness and damping that can control drifts and avoid resonance. For high-rise structures, it is also important to avoid brace-only schemes, as they may increase the response. Friction dampers need to be designed to account for $8-12\mathrm{\%}$$8-12\mathrm{\%}$8-12%8-12 \%$8-12\mathrm{\%}$ of the story shear and evenly distributed throughout the structure to prevent soft stories. All designs require nonlinear time-history analysis for verification. Importantly, the system must be designed to have dampers as easily replaceable sacrificial items to safeguard the main structure and promote rapid post-earthquake recovery.

Future work could extend the scope by considering how the hybrid system performs in taller ( $20+$$20+$20+20+$20+$ story) irregular and non-office buildings under a larger suite of near-fault and long-period ground motions. Research is also required to formulate and validate simplified, yet robust design strategies; optimization procedures for damper distribution, in addition to explicit performance-based criteria related to risk recovery. In addition, systematic research and development, such as detailed cost-benefit analyses, full-scale experimental tests of connections and damper reliability, and the integration of smart or adaptive damper technologies, need to be performed to improve the practicality, robustness, and economy necessary for widespread use.

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