Search Results (32)

To improve the seismic performance of buildings and reduce earthquake-related disaster risks, this study employs the MIDAS finite element analysis platform to establish a numerical model of a 15-story concrete-filled steel tube frame-shear wall structure. Recorded natural ground motion data are used as the primary input, and a main shock-aftershock sequence is constructed using an attenuation-based method. On this basis, a seismic fragility analysis framework is adopted to derive structural fragility curves, which are subsequently assembled into a comprehensive seismic fragility matrix. The results indicate that, under identical main shock-aftershock sequences, aftershock effects increase the collapse probability of the unretrofitted structure by approximately 17–37%. Furthermore, when buckling-restrained braces are introduced, the structural strength at the same damage state increases by about 8% under the action of the main shock alone and by nearly 24% when both the main shock and aftershocks are considered. Full article

The use of dissipative bracing systems by hysteretic dampers represents one of the most efficient innovative techniques for the seismic retrofitting of existing structures, especially for reinforced concrete (RC) frame buildings. Many studies on design approaches and case studies have been developed in recent decades and are still in progress; however, the importance of the relation between the properties of the existing structure and of the damper system has not been analyzed, and the influence of the type of arrangement inside or outside the structure, has not been pointed out. In this paper, an innovative dimensionless approach is proposed to describe the dynamic structural properties of the retrofitted structure introducing ratios between the properties of the existing structure and damper system. Therefore, indications to optimize the design of the passive energy dissipation (PED) system can be clearly established for each case. Furthermore, a generalization of the design approach considering different solutions with internal and external bracings is proposed. The application of the dimensionless parameters to the design of a dissipation system for a single-bay three-story RC frame building and points out that damping can be reduced by two times if the capacity of the existing structure is used, further reducing the base shear transmitted to foundation. This result is also obtained by mounting the PED system on an external structure. The effect of infill walls on the stiffness of the existing structure requires an increment of the stiffness of the PED system with double the stiffness of the devices further than the buckling-restrained braces (BRBs). Full article

This paper examines the hysteretic behavior of the buckling restrained braces (BRBs) in the steel frame. Both experimental and finite element (FE) studies were conducted. The experimental results showed that the well-detailed buckling restrained braced frame (BRBF) withstood significant drift demands, while the BRB exhibited significant yield without severe damage. Although the BRB inside the steel frame was subjected to 2.69% strain of the CP under the axial compression demands, the local and global deformations were not observed. The FE model was developed and validated. The numerical investigations of hysteretic behavior of the BRBF in the literature are generally focused on the friction between the core plate (CP) and the casing member (CM). The results suggest that the behavior of the BRBF is significantly affected not only by the friction between CP and CM but also by the pretension load on the bolts and the friction between the contact surfaces of steel plates of slip-critical connections in the steel frame. The FE analysis showed that pretension loads of 35 kN and 75 kN gave accurate predictions for cyclic responses of BRBF under tension and compression demands, respectively. Moreover, the FE predictions were in good agreement with the test results when the friction coefficient is 0.05 between CP and CM and it is 0.20 between steel plates. Full article

The process of seismic retrofitting for inadequate RC frames is vital for enhancing structural integrity in areas susceptible to earthquakes. This research investigates a novel tube-in-tube (TnT) buckling restrained brace (BRB) system aimed at improving the seismic performance of these substandard RC frames. By targeting significant weaknesses inherent in older RC constructions, the TnT BRB introduces a lightweight, all-steel configuration that eliminates the need for traditional mortar or concrete infill materials. Experimental shake table testing on two one-third scaled RC frame models was conducted to compare the seismic performance of an unretrofitted control frame and a frame retrofitted with the TnT BRB system. Results indicate significant enhancements in lateral strength, ductility, and energy dissipation capacity in the retrofitted frame, demonstrating stable and symmetrical hysteresis loops and reduced stiffness degradation compared to conventional X-braced systems. Analytical modeling corroborated these experimental findings, confirming the TnT BRB’s superior capability in absorbing seismic energy and preventing premature structural failures. This investigation emphasizes both the practical and financial benefits of integrating the TnT BRB into seismic retrofitting strategies while recommending further research to optimize the system, specifically addressing issues related to local denting, frictional wear, and alignment to bolster its effectiveness in practical applications. Full article

Addressing the critical seismic vulnerabilities of reinforced concrete (RC) beam-column joints remains an imperative research priority in earthquake engineering. This study presents an experimental and analytical investigation into the seismic performance enhancement of non-ductile RC frames using an innovative all-steel Tube-in-Tube Buckling-Restrained Brace (TnT BRB) system. Shake table tests were performed on one-third scale RC frame specimens, including a baseline structure representing conventional substandard design and a counterpart retrofitted with the proposed TnT BRBs. Experimental results revealed that the unretrofitted specimen experienced pronounced brittle shear failures, excessive lateral deformations, and significant degradation of beam-column joints under cyclic seismic loading. In contrast, the TnT BRB-retrofitted specimen exhibited substantially improved seismic behavior, characterized by enhanced energy dissipation, controlled inter-story drifts, and preserved joint integrity. Advanced fiber-based finite element modeling complemented the experimental efforts, accurately capturing critical nonlinear phenomena such as hysteretic energy dissipation, stiffness degradation, and localized damage evolution within the structural components. Despite inherent modeling limitations regarding bond-slip effects and micro-level cracking, strong correlation between numerical and experimental results affirmed the efficacy of the TnT BRB retrofit solution. This integrated experimental-analytical approach offers a robust, cost-effective pathway for upgrading seismically deficient RC structures in earthquake-prone regions. Full article

Earthquakes, as a common natural disaster, frequently occur in close proximity to human activities. Researchers have developed a series of techniques to enhance the seismic performance of typical reinforced concrete frame structures, thereby improving these buildings’ ability to protect human life. How to retrofit and upgrade existing reinforced concrete frame structures with insufficient seismic performance in accordance with current codes and policy requirements, and how to appropriately incorporate new seismic isolation and energy dissipation technologies to enhance their seismic performance, are the focus of this study. This study adopts a data-driven approach that combines both quantitative and qualitative analyses. Relevant literature was collected from the Web of Science database using specific search criteria. This study visualizes both the historical and recent trends within the scientific field and analyzes keyword frequency to identify key areas for future research. Based on frame structures, the paper reviews novel seismic enhancement techniques for structural systems, including frame–shear wall systems, energy-dissipating buckling-restrained braces (BRBs), and seismic isolation bearings. By integrating traditional structural systems with new technologies, a novel structural system is established to ensure the safety of buildings in high-intensity seismic hazard zones. The results indicate that compared with traditional reinforced concrete frame structures, the new structural system increases energy dissipation by approximately 45% on average. Among these techniques, seismic isolation technology, although more costly, exhibits the best seismic performance and is suitable for new high-priority projects; BRB technology offers a balance between economy and effectiveness, making it the first choice for retrofitting existing buildings; and the frame–shear wall system requires an optimized layout to enhance its cost effectiveness. Full article

The increasing demand in structural engineering now extends beyond collapse prevention to encompass business continuity planning (BCP). In response, energy dissipation devices have garnered significant attention for building response control. Among these, buckling-restrained braces (BRBs) are particularly favored due to their stable hysteretic behavior and well-established design provisions. However, BCP also necessitates the prevention of furniture overturning—an area that remains quantitatively underexplored in the context of buckling-restrained braced frames (BRBFs). Addressing this gap, this research designs BRBFs using various design criteria and performs incremental dynamic analysis (IDA) with artificially generated seismic waves. The results are compared with previously developed fragility curves for furniture overturning under different BRB design conditions. The findings demonstrate that the fragility of furniture overturning can be mitigated by a natural frequency shift, which alters the threshold of critical peak floor acceleration. These results, combined with hazard curves obtained from various locations across Japan, quantify the mean annual frequency of furniture overturning. The study reveals that increased floor acceleration in stiffer BRBFs can lead to a 3.8-fold higher risk of furniture overturning compared to frames without BRBs. This heightened risk also arises from the greater hazards at shorter natural periods due to stricter response reduction demands. The probabilistic risk analysis, which integrates fragility and hazard assessments, provides deeper insights into the evaluation of BCP. Full article

Previous research has indicated that buckling-restrained braces (BRBs) increase the lateral story stiffness, resulting in a shortening of the natural period, which leads to an increase in the seismic input into the buildings, especially in high-rise buildings. Additionally, research has also revealed that the long-period seismic motions with a long duration possibly induce a difficulty to ensure the toughness of the BRB members, owing to the large cumulative strains caused by the repeated axial forces. To overcome these issues, this paper proposed a displacement-restraint buckling-restrained brace (DR-BRB) in which no axial force appears initially, and the axial force occurs with a delay under the designated vibration amplitude. Therefore, the natural period can maintain the same level as the moment frame. This study performed five cyclic loading tests to reveal the delayed-action mechanism of BRBs, using gusset plates with multiple slot holes. The test results confirmed that the designated starting point of the brace action is accurate, and the hysteretic behavior of the brace is good. Furthermore, the design equations of the joints were formulated and verified through the test results. Finally, the joint behavior and validity of the proposed design equations were verified by finite element analyses for the single bolt model and the overall joint model. Full article

Rocking walls can control the overall deformation pattern and the distribution of plastic energy dissipation in structures, suppressing the occurrence of weak layers. In the case of step-terrace frame structures, issues such as severe lateral stiffness irregularities, abrupt changes in floor-bearing capacity, and concentrated deformation in upper ground layers exist. To improve the yielding and failure modes of step-terrace frame structures in mountainous regions, this paper proposes a structural system combining step-terrace frame structures with energy dissipation rocking walls attached to their bottoms, aiming to control the yielding mechanism of the structure, further reduce the seismic response, limit residual deformation, and propose a structural system of step-terrace frame structures with buckling-restrained braces (BRBs) and energy dissipation rocking walls. Two sets of numerical models for step-terrace frame structures with different numbers of dropped layers and spans were established. Through simulating low-cycle repeated loading tests on step-terrace frame structures, the rationality of the models and parameters was verified. Incremental dynamic analysis (IDA) was employed to systematically investigate the vulnerability of step-terrace frame structures with energy dissipation rocking walls under different dropped layer and span configurations. This investigation covered aspects such as IDA curve clusters, percentile curves, seismic demand models, fragility functions, failure state probabilities, vulnerability indices, collapse resistance factors, and safety margins. The results indicated that the change in dropped layer numbers had a far greater impact on the vulnerability of step-terrace frame structures with energy dissipation rocking walls than the change in dropped span numbers. Under seismic excitations with the same peak ground acceleration (PGA), rocking walls can limit the depth of structural plasticity development, reduce the dispersion of peak responses, and lower the probability of exceeding various performance levels, thereby exhibiting good collapse resistance. The addition of buckling-restrained braces (BRBs) can further enhance the seismic performance and collapse resistance of the rocking wall frame structure. By analyzing the correlation between seismic intensity measures and peak structural responses, the validity of using peak ground acceleration as a scaling indicator for incremental dynamic analysis (IDA) has been verified. Full article

This paper describes the development of a dual hazard spectrum for use in the dynamic analysis of steel frames subject to the combined effects of earthquakes and wind. The proposed spectrum is obtained by combining the power spectra of earthquakes and wind using the square root of the sum of squares (SRSS) combination method. An equivalent time excitation function is then computed using an inverse fast Fourier transform (IFFT) and serves as input for the dynamic analysis. Using time-history analysis on the OpenSees platform, the dynamic responses expressed in terms of peak and residual inter-story and roof drifts for two multistory steel frames located in two US cities (Los Angeles and Charleston) are obtained to demonstrate that designing these buildings based on just one hazard may not be adequate. For frames that are considered under-designed, an energy-based design procedure that uses buckling-restrained braces (BRBs) to dissipate the excess energy imparted to these frames is proposed so they will satisfy the FEMA 356 recommended drift limits for the performance levels of immediate occupancy and life safety. Full article

Earthquakes are often followed by higher-intensity aftershocks, which tend to aggravate the accumulated and more severe damage to building structures. The seismic vulnerability of concrete-filled steel tube (CFST) structures under major aftershocks is more complex. In this paper, a CFST frame and a frame with buckling-restrained braces (BRBs) are studied, and the finite element analysis software Midas 2022 is used to analyze the seismic vulnerability of the two types of structures under main shock and main–aftershock. The results show that the structural vulnerability of the two structures is significantly higher under the main–aftershock sequences than under the main shock alone. Compared with the CFST structure, the structure with BRBs can effectively reduce the structural displacement and the hysteretic energy, decrease the plastic deformation risk of the structural components, and improve the seismic performance. The structure with BRBs can significantly reduce the probability of structural collapse under the main–aftershock sequence and can provide a reliable guarantee of the stability of the building. Full article

In order to enhance the self-centering capacity of steel frame structures after earthquakes and reduce the tubes of traditional double-tube or triple-tube SC-BRB, an innovative single-tube self-centering buckling restrained brace (ST-SC-BRB) is proposed in this paper. Firstly, the structural configuration of the ST-SC-BRB component was described. Then, cyclic tests were conducted on one small-scaled BRB and one ST-SC-BRB with the same core steel plate. The test results indicate that the ST-SC-BRB specimen exhibits an excellent self-centering ability compared to the conventional BRB. However, their energy-dissipation capacities are still determined by the core steel plate. In addition, time–history analyses were conducted to evaluate the seismic performance of steel frame structures with BRBs and ST-SC-BRBs. The results suggest that the ST-SC-BRBs can effectively reduce the residual deformation of steel frame structures after earthquakes and contribute to the self-centering capacity of the steel frame structures. Finally, the influence of design parameters of ST-SC-BRB components on the seismic performance of steel frame structures was discussed. It is confirmed that the initial stiffness of the ST-SC-BRB component significantly influences the seismic response of the structure, while the self-centering ratio of the ST-SC-BRB component is a crucial factor in determining the residual deformations of the structure. Full article

As a no-disturbance integrated-retrofitting technique, an external rocking frame was widely used on reinforced concrete (RC) structures. Yet, with the increasing demand for seismic strengthening of existing buildings, it has become a concern to evaluate the seismic strengthening schemes based on seismic resilience. Firstly, the dynamic equation of the structural system was derived, and the deformation control mechanism was revealed; thus, the corresponding design method was put forward for the rocking frame reinforcement. Secondly, after soft-first-floor structures were reinforced by rocking frames, the evaluation method of the reinforcement scheme was investigated based on seismic resilience. Finally, the feasibility of the assessment method was verified by a soft-first-floor frame structure, and a comparison was made between the method proposed in this paper and the conventional method. The results find that the soft-first-floor structure reinforced by the rocking frame increased by 10% in the inter-layer displacement and improved by 55.6% and 63.0% in the injury and mortality rates, compared to the buckling-restrained brace scheme. This indicates that the reinforcement scheme of soft layer structures with rocking frames is feasible and effective, and the reinforcement evaluation method proposed in this paper can quantitatively reflect the improvement in seismic performance. Full article

Previous studies have demonstrated that the inclusion of tire-derived aggregate (TDA) enhances the damping, ductility, and toughness of concrete mixtures. The effectiveness of tire-derived aggregate as a ductile material with a higher damping ratio and lower density in buckling-restrained braces has been examined at California State University’s Structures Laboratory (CSU). Through experimental and theoretical investigations, this study compares the structural application of buckling-restrained braces with TDA and with conventional concrete infill subjected to various ground motions as well as artificial excitations. The evaluations include modeling a full-scale experimental setup equipped with a single-leg BRB utilizing ETABS 2016 and OpenSees 2000 software. The effectiveness of the application is demonstrated through a comparison of accelerations, displacements, stiffness, and damping ratios between TDA and concrete filling. Additionally, a design guideline for TDA-filled buckling-restrained braced frames is provided. Full article

Buckling restrained brace frames (BRBFs) exhibit exceptional lateral stiffness, load-bearing capacity, and energy dissipation properties, rendering them a highly promising choice for regions susceptible to seismic activity. The precise and expeditious prediction of seismic demands on BRBFs is a crucial and challenging task. In this paper, the potential of artificial neural networks (ANNs) to predict the seismic demands of BRBFs is explored. The study presents the characteristics and modelling of prototype BRBFs with different numbers of stories and material properties, utilising the OpenSees software (Version 2.5.0) for numerical simulations. The seismic performance of the BRBFs is evaluated using 91 near-fault pulse-like ground motions, and the maximum inter-storey drift ratio (MIDR) and global drift ratio (GDR) are recorded as a measure of seismic demand. ANNs are then trained to predict the MIDR and GDR of the selected prototypes. The model’s performance is assessed by analysing the residuals and error metrics and then comparing the trend of the results with the real dataset. Feature selection is utilised to decrease the complexity of the problem, with spectral acceleration at the fundamental period (T) of the structure (S_a), peak ground acceleration (PGA), peak ground velocity (PGV), and T being the primary factors impacting seismic demand estimation. The findings demonstrate the effectiveness of the proposed ANN approach in accurately predicting the seismic demands of BRBFs. Full article