Seismic Performance Of Structures Research Articles

SLIM‐FLOOR BEAM‐TO‐COLUMN JOINTS FOR SEISMIC‐RESISTANT STRUCTURES: JOINT PERFORMANCE AND CASE STUDY ON MOMENT‐RESISTING FRAMES

AbstractThe current seismic design of steel and composite frames relies on lateral frame stiffness and on the controlled failure mechanism of dissipative members or connections. The implementation of the slim‐floor solution in practice results in several advantages. But due to the reduced height of the slim‐floor beam – generally considered to result in lower flexural stiffness – the current practice disregards the usage of moment‐resisting slim‐floor beam‐to‐column joints in seismic applications. However, a previous study of the authors has experimentally and numerically confirmed the possibility of expanding the application of composite beams by developing inelastic behaviour in slim‐floor beams. The test results allowed the definition of the slim‐floor beam's mechanical characteristics and the evaluation of the structure's seismic performance through nonlinear static and dynamic analyses. The usage of the slim‐floor system resulted in a vertical space gain ‐ due to its reduced height ‐ and demonstrated the solution's effectiveness when implemented in seismic‐resistant structures.

Upgrading framed structure seismic performance using steel Lever-Armed dampers in the Braces

This study evaluated the performance of frames equipped with novel lever-armed dampers in the braces (LAD-Brace). Cyclic loading tests and time-history response simulations using various earthquake ground motions were conducted on framed structures with and without LAD-Braces. The experimental results confirmed that the LAD-Braces effectively enhanced the strength of the structures. Significant achievements in elastic and inelastic stiffness of LAD-Braced frames over the SMRF justified the adequacy of the proposed design in deformation control and stability assurance. Simultaneous yielding on entire energy dissipation plate length incurred effective energy dissipation mechanism and efficient damping characteristics of the LAD-braced frames. LAD-Brace structural applicability was further evaluated by multi-bay-multi-story framed structural simulations using 11 different earthquake excitations. The simulation included the comparison of LAD-Braced frames to SMRFs and CBFs structure. The time-history structural responses revealed that the maximum story drifts and residual drifts of LAD-Braced frames were significantly reduced when compared with the corresponding SMRFs. In contrast to CBFs, analytical results showed that the LAD-Braced frame base shears were maintained at magnitudes equal to or less than the values of the corresponding SMRFs. This phenomenon combined with the effective reductions in story drifts and residual drifts validated the applicability of LAD-Brace in framed structural performance upgrading.

A Simplified Method for Evaluating the Diaphragm Flexibility for Frame-Shear Wall Structure under Earthquake Load

The rigid floor assumption is commonly used in structural design, but it is not applicable to buildings with a large plane aspect ratio. This study designed nine frame-shear wall structures with the story of 3, 6, and 12, with a plane aspect ratio of 2, 3.33, and 4. Based on the design results, the finite element models were set up by ETABS. Both the rigid diaphragm and the flexible diaphragm cases were considered in each model. The effect of elastic diaphragm deformation on structural seismic performance was investigated, including fundamental period, top displacement, inter-story drift, and base shear force. The results indicate that the diaphragm deformation on 3-story structures is more significant than that on 6-story and 12-story structures. The diaphragm in-plane deformation increases with the aspect ratio. On the basis of the analysis results, a simplified formula to calculate the internal force amplification factor and a quantitative assessment method for evaluating the diaphragm flexibility were proposed, which can provide a reference for engineering design.

Preventive Structural Risk Assessment of Buried Gas Pipelines in Liquefaction of Ground

Recently, a number of earthquakes have been detected in Korea and damage has been reported. Actually, ground liquefaction was reported due to the earthquake that occurred in the Pohang. In Korea, the risk of liquefaction in the event of an earthquake is relatively higher as there are many landfill areas such as Busan's coastline, Incheon, and Cheongna International City. In this study, the effect of underground structures when liquefaction occurs is evaluated by dividing it into stages of liquefaction. Moreover, detailed evaluation methods for buried gas pipelines are presented in case of regional liquefaction that can be used in all regions. For the risk assessment of liquefaction, the Standard Penetration Test (SPT) result or Cone Penetration Test (CPT) result of the borehole is used. To evaluate buried gas pipelines, Finite Element (FE) analysis is performed using the subsidence calculation method linked with the borehole data. By defining ground and gas pipe variables, structural analysis is conducted in several cases, and the desired area is evaluated based on this. A Winkler foundation spring-based optimal finite element analysis model is developed to evaluate the structural seismic performance of gas pipelines across areas where liquefaction is expected.

Design, manufacturing, and testing of a hybrid self‐centering brace for seismic resilience of buildings

AbstractThis study explores the development of a shape memory alloy (SMA)‐based hybrid self‐centering brace that combines NiTi superelastic cables with viscoelastic dampers. First, the behavior of individual components of the hybrid self‐centering brace, that is, SMA cables and viscoelastic damper is characterized under various experimental conditions. Then, three prototype hybrid self‐centering braces with a maximum force capacity of 172 kN are designed and fabricated. The experimental tests are conducted to reveal the response of the hybrid self‐centering braces under increasing loading displacement amplitude. The effect of loading rate and training loading cycles on the mechanical response of the braces are also analyzed. Furthermore, the low‐cycle fatigue behavior of the hybrid self‐centering braces is evaluated by testing two of the braces for up to 30 loading cycles at a relatively large displacement amplitude. For each experimental condition, the variation of certain mechanical properties such as equivalent stiffness and equivalent viscous damping are evaluated and analyzed. Three case‐study frames with various bracing systems (i.e., SMA brace, viscoelastic brace, and hybrid self‐centering brace) are designed and modeled in OpenSees. Nonlinear dynamic analyses are carried out under 44 far‐field ground motion records to illustrate the advantages of hybrid self‐centering brace on structural seismic performance. The results indicate that the developed SMA‐based hybrid self‐centering braces provide an average of 9% equivalent viscous damping at different loading amplitudes with a complete self‐centering characteristic. The response of the bracing system is not affected considerably by loading rate, but it is found to be sensitive to cyclic loading. The steel frame with hybrid self‐centering braces is capable of leveraging the benefits of self‐centering ability and energy dissipation capacity.

Performance-Based seismic design and evaluation of out-of-code structure on Nanjing Financial City

The main scope of performance-based seismic design and evaluation study focuses more on the seismic performance of the simple structure or the regular structure, instead of out-of-code structure. The C1 tower in Nanjing Financial City is taken as an engineering case study. Many design indexes of the original design scheme of the structure exceed the requirements of the existing Chinese specifications, such as the height exceed the limits, the torsional irregularity, the partial floor slab discontinuity etc., which are summarized in detail in this paper. Then, several special structural design strategies are adopted to improve the overall seismic performance of this out-of-code structure. For example, multiple lines of seismic defences are set and the outrigger trusses are strengthened to solve the height overrun. For torsion irregularity, the influence of the bidirectional seismic torsion effect is considered in the calculation. Finally, according to the results of dynamic elastoplastic time history analysis under rare earthquakes, the seismic performances of the out-of-code structure are evaluated in detail. The analysis results show that the overall seismic performances of the structure are all within a reasonable range, and the seismic performance of the main components in the structure all meet the specification requirements.

Integrating push-over analysis and FEMA guidelines for building vulnerability assessment

An earthquake has impacted the existing buildings around the area where the earthquake occurred. To maintain the safety of building occupants, it is necessary to evaluate the building's vulnerability. The most frequently used assessment methods are the Rapid Visual Screening (RVS) from FEMA and the push-over. FEMA can assess the exposure of a building quickly through visual observation but cannot provide a structural response. The push-over can explain the structural response seismic capacity and performance, collapse identification, and building strengthening strategies. However, the push-over has weaknesses; the analysis depends on modelling and structural analysis. This study aims to integrate push-over with FEMA to obtain the most appropriate assessment of buildings in earthquake vulnerability. Both assessment models have been applied to mid-rise buildings of flats after the earthquake. The building received a final score of 2.3 in the FEMA screening evaluation, indicating that it is secure. The push-over analysis shows the damage to the structure is Immediate Occupancy, which means only slight damage occurs. Overall, both methods give the same results and can be integrated to develop RVS and push-over assessments mutually when new modes of building failure are identified and as tools to assess fast, precise and accurate structural failure.

Conceptual design of anti-seismic devices with metal foam core for CBFs

Metal foam is a relatively new and potentially revolutionary material due to its properties such as the low weight-to-stiffness ratio, high damping and energy dissipation capacity. Even if this material is widely used in mechanical, aerospace and automotive industries, it is still not frequently used in civil engineering applications. The large energy dissipation capacity that metal foams possess could be exploited to control the seismic performance of structures, but only few research investigations have been focused on this matter. Within this context, the present paper investigates a possible solution to realize dissipative aluminium foam dampers to be applied in X-braced steel structure resembling a concentrically braced steel frame (CBF). The bracing system consists of a steel rod or tube linked to the aluminium foam damper. The damper device is constituted by aluminium foam that provides the structure with dissipation capacity when activated under compression. The permanent deformations of the aluminium foam are absorbed by a wedge device, avoiding a pinching behaviour in the global response. Analytical equations governing the global behaviour of the bracing system are herein developed. An X-braced steel frame complying with Eurocode 8 provisions is designed and considered as case-study. The structure is subsequently upgraded by introducing the dissipative device into the bracings. The results of preliminary experimental and numerical tests on the components of the device are herein presented, showing the potentiality of the solution.

Development of Steel Yielding Seismic Dampers Used to Improve Seismic Performance of Structures: A Comprehensive Review

Seismic excitation can cause significant energy to be released within structures. By using special devices, this energy can be consumed and dissipated without deforming structural members significantly. Due to this, structural damage is minimized, casualties are prevented during earthquakes, and structures are extended in their useful life. Over the past five decades, it has been widely acknowledged that steel yielding dampers are among the best energy dissipation devices. It has been stated that the hysteretic behavior of steel yielding dampers could vary slightly depending on their geometry. From a practical point of view, they are suitable for the improvement of seismic safety in new and existing structures. The purpose of this paper is to present a review related to steel yielding dampers, their development, various types, and applications, in order to help understand the role of these dampers in improving the seismic performance of structures. In terms of their shape, steel yielding dampers can be categorized as steel plate dampers, pipe dampers, curved dampers, and slit dampers. The most common use of steel plate, such as ADAS and TADAS, and pipe dampers is within braced frames, whereas U-shaped, J-shaped, and S-shaped dampers are mostly seen in frames with chevron bracing. Steel curved dampers with a 60° angle in a steel-braced frame, on the other hand, provide the best energy dissipation and frame strength. In this direction, until today, steel slit dampers have been found to be the most commonly used steel yielding dampers.

Development and experimental verification of self-centering disc slit damper for buildings

The damage avoidance design (DAD) philosophy is oriented towards the low-damage design of building structures compared to the previous conventional ductile design. Low-damage structures with supplemental damping and self-centering ability are one of the main aspects of the DAD philosophy to decrease irreparable damage and enhance the seismic performance of structures. This research proposes an efficient, double-acting self-centering hysteretic damper by combining the widely used steel slit dampers and prestressed disc springs for building structures. The proposed seismic protection device is called Self-Centering Disc Slit Damper (SC-DSD), which consists of two square standard hollow steel sections, nested together with an assembly of prestressed disc springs within the steel sections. The performance of SC-DSD is assessed experimentally through a static cyclic loading test to evaluate the global system's dissipation capacity, self-centering ability, and hysteresis loop. A simplified numerical model is developed to predict the self-centering force-displacement relationship of the proposed device. Finally, the seismic force bearing capacity of the proposed damper is compared with the conventional slit damper.

Accounting for earthquake‐induced ground‐motion duration in building‐portfolio loss assessment

AbstractEarthquake‐induced ground‐motion duration can have a non‐negligible impact on the nonlinear seismic performance of structures. However, in current seismic risk assessment practice, hazard and vulnerability analyses generally only consider ground motion's amplitude and frequency‐content features, often relegating duration to implicit considerations. This study introduces a simulation‐based framework to explicitly quantify the impact of ground‐motion duration on building‐portfolio direct economic losses. Case‐study synthetic building portfolios located at different distances from a case‐study seismic source (i.e., fault) are assembled considering – individually and in combination – three building typologies representing distinct vulnerability classes in Southern Italy. Such typologies correspond to non‐ductile moment‐resisting reinforced concrete (RC) infilled frames designed to only sustain gravity loads (i.e.,pre‐codeinfilled frames), and ductile moment‐resisting RC infilled and bare frames designed considering seismic provisions for high‐ductility capacity (i.e.,special‐codeinfilled and bare frames). Event‐based probabilistic seismic hazard analysis is performed explicitly simulating duration jointly with spectral‐shape‐related intensity measures (IMs), accounting for their spatial and cross‐correlation. Sets of ground‐motion records are selected to conduct cloud‐based nonlinear time‐history analyses (NLTHAs) and derive fragility models for each considered building typology through archetype structures, simulating their structural response using computational models that account for stiffness and strength cyclic and in‐cycle deterioration as well as destabilising effects. Fragility models are derived using average pseudo‐spectral acceleration (in a range of periods of interest) as the primary IM and alternatively: (1) the dissipated hysteretic energy as an engineering demand parameter (EDP), implicitly accounting for duration given the cumulative nature of such an EDP and the adopted nonlinear modelling strategy, in a scalar format; (2) the dissipated hysteretic energy as an EDP, as before, explicitly considering duration as an IM together with spectral shape, in a vector‐valued format. Vulnerability models are then derived using the fragility models and appropriate building‐level damage‐to‐loss models. The portfolio loss exceedance curves and expected annual losses computed for each combination of exposure, hazard, and vulnerability models are critically assessed and discussed. Depending on the portfolio's size, exposure composition, location relative to the fault, site conditions and the seismic source model, the impact of duration on the loss estimates can be significant. For the considered settings, relative variations up to 200% between the scalar‐ and vector‐valued‐based portfolios expected annual losses are observed, attaining the highest discrepancies as the fault‐to‐portfolio distance increases.

Evaluation of the seismic performance of structures equipped with novel multi-level TADAS dampers

Evaluation of the seismic performance of structures equipped with novel multi-level TADAS dampers

Mechanical properties of curvature-consistent frictional pendulum bearings and isolation performance of spherical reticulated shells

With the increasing demand for isolated long-span spatial structures, the seismic performance of structures during rare earthquakes should be improved. In this study, we proposed a type of curvature-consistent frictional pendulum bearing (CC-FPB) that may induce notable seismic isolation effects in long-period and long-span spatial structures during rare earthquakes. Hysteresis tests were performed on the structure with the CC-FPB, and a refined numerical simulation method was established to analyse the isolation performance of the CC-FPB was established. The accuracy of the simulation method was verified by comparing the simulation results with experimental results. Based on the refined numerical simulation method, the CC-FPB was applied to a single-layer spherical reticulated shell structure, and the dynamic time history response of the structure was analysed. Furthermore, the seismic isolation effect was compared with that of the classical friction pendulum bearing (C-FPB). Parametric analysis was performed for structures with different roof qualities and input ground motions. We also analysed the seismic isolation effect and isolation influence mechanism of the structure with the CC-FPB. The results indicated that the CC-FPB had high isolation performance and energy dissipation capacity. Although the isolation performance had negligible influence on the loading frequency, the energy dissipation capacity and isolation performance increased with the increase in the loading frequency and loading displacement. The isolation efficiency of the isolation structure with the CC-FPB improved in comparison with that of the structure with the C-FPB. The isolation performance and energy dissipation capacity of the isolation structure increased with the increase in the seismic amplitude. The energy dissipation and damping capacity of the CC-FPB improved under high-frequency excitation.

Theoretical and experimental analyses of structures with supplemental clutching inertia devices

AbstractClutching inertia device (CID) is a novel device that incorporates the function of an inerter and the clutching effect that can be provided by a ratchet. In this paper, the performance of an SDOF system with supplemental clutching inertia is investigated through theoretical analyses and experimental tests. First, the dynamic equation for a structure with a CID is built in the form of multi‐body motion. Second, an inertia device (ID), a CID, and an inertia‐enhanced CID (ECID) by reducers are designed for dynamic testing in a small‐scale steel structure. Third, the influence of clutching effect, flywheel inertia and accessory damping of the CID on the structural response is analyzed through a comparative study of numerical simulation and shaking table tests under harmonic and seismic excitation. The results confirm previous predictions that the clutching effect helps to reduce the resonant response of the structure and that the increase in flywheel inertia can further mitigate the resonant response when considering certain accessory damping in the CID. The increase in accessory damping, either viscous damping or friction damping, will obviously reduce the resonant response and resonant frequency of the controlled structure, and the structure with the ECID shows better performance than that of CID when considering the same accessory damping. It is confirmed that the tested CIDs improved the structural seismic performance by slightly prolonging the fundamental structural period and prominently controlling the response in resonant frequency and high frequency owing to the effect of supplemental clutching inertia and accessory damping.

Numerical Study on Optimal Design and Seismic Capacity of Double-Span RC Frame Structures with Exterior Verandahs

Frame structures with exterior verandahs, which are mostly built in densely populated areas such as teaching buildings and dormitories in southern China, are a special form of frame structure that must continue to be developed. However, compared with other frame structures in many post-earthquake fields, this type of building designed following the Chinese code has demonstrated poor seismic performance, leading to a significant number of casualties and property losses. Therefore, to complement the design requirements of this structural type in the present Chinese code, the seismic performance of this structural type needs to be improved and optimized. A typical double-span RC frame structure with an exterior verandah in the Lushan Earthquake as the structure prototype was selected in this paper. PKPM software is used to obtain design information for the structure prototype, and the finite element model is established by utilizing ABAQUS software for simulation and analysis. A series of various optimal conditions are created at the base of the structure prototype’s simulation results, and a thorough investigation of the structural seismic performance under each condition is performed. Eventually, suggestions and proposals for future Chinese codes concerning the structurally optimum design of this structural type are provided.

Prediction of the Yield Strength of RC Columns Using a PSO-LSSVM Model

Accuracy prediction of the yield strength and displacement of reinforced concrete (RC) columns for evaluating the seismic performance of structure plays an important role in engineering the structural design of RC columns. A new hybrid machine learning technique based on the least squares support vector machine (LSSVM) and the particle swarm optimization (PSO) algorithm is proposed to predict the yield strength and displacement of RC columns. In this PSO-LSSVM model, the LSSVM is applied to discover the mapping between the influencing factors and the yield strength and displacement, and the PSO algorithm is utilized to select the optimal parameters of LSSVM to facilitate the prediction performance of the proposed model. A dataset covering the PEER database and the available experimental data in relevant literature is established for model training and testing. The PSO algorithm is then evaluated and compared with other metaheuristic algorithms based on the experiment’s database. The results indicate the effectiveness of the PSO employed for improving the prediction performance of the LSSVM model according to the evaluation criteria such as the root mean square error (RMSE), mean absolute error (MAE) and coefficient of determination (R2). Overall, the simulation demonstrates that the developed PSO-LSSVM model has ideal prediction accuracy in the yield properties of RC columns.

Unscented Kalman filter with performance recovery strategy for parameter estimation of isolation structures

After a strong earthquake, it is crucial to evaluate accurately the health of structures in order to decide whether they can continue to be used. Isolation techniques are well known for enhancing the seismic performance of structures; however, a large response displacement anticipated in the design will likely impact the expansion joints. The occurrence of any damage or impact involves a large disturbance in the system or measurement equations. The Kalman filter (KF) is effective and reliable under proper conditions, but a simple simulation may show disrupted stability conditions after a large disturbance, causing a temporary filter divergence. If the filter design cannot be rapidly adjusted, an overall filter divergence may occur, preventing an accurate evaluation of structural health. This study proposes a performance recovery strategy for the unscented KF (UKF). Rather than identifying optimal parameter estimates at the current instant, the filter meets the stability conditions and asymptotically approaches the true estimates. The measurement noise is adaptively adjusted to bound the true noise covariance. Once the filter divergence is identified based on the expected measurement residual error, the state covariance is adjusted by a covariance-matching technique to bound the true error covariance. After sufficient measurements are obtained, the state covariance is reduced to a low level, indicating filter convergence and a reliable estimation. The effectiveness of the proposed approach is numerically validated for an isolation bridge and building under several scenarios, and two existing UKF variants, which adaptively estimate the system and measurement noise covariances, are compared.

Longitudinal seismic fragility analysis of long tunnels under multiple support excitation

Probability-based seismic fragility analysis can quantitatively evaluate the seismic performance of structures. This study proposes a longitudinal fragility analysis method for long tunnels under multiple support excitation (MSE). Firstly, 10 MSEs are synthesised based on the spatially correlated ground motion simulation method. Then, the two-dimensional free-field model is established, and incremental dynamic analysis under MSE is performed. On the basis of the generalised response displacement method, the soil–tunnel model is established and the seismic response is analysed. The maximum opening width of the tunnel circumferential joint and the peak ground acceleration (PGA) are selected as the damage measure and the intensity measure in the fragility analysis, and fragility curves are generated. The obtained results are compared with the identical support excitation (ISE) results. Findings show that the proposed method is suitable for fragility assessment. The seismic response under MSE is larger than that under ISE, and the results of the former are more accurate. The fragility results further indicate that the damage probability of the tunnel is higher under MSE. The seismic design safety of the tunnel can be improved with more reliable MSE results.

Experimental Study on Seismic Behavior of Precast Bolt-Connected Steel-Members End-Embedded Concrete (PBSEC) Beam-Column Connections

With the rapid development and research of precast concrete frame structures, it is not difficult to find that the structural form and seismic performance of dry-connected precast joints have always been the focus of research. Since this type of structural system is complex, the construction is inconvenient in practical application, and many additional parts need to be installed, this paper develops a kind of precast bolt-connected steel-members end-embedded concrete (PBSEC) beam-column connection to solve the shortcomings of the current dry-connected precast joints. There is no wet work in the assembly process, and all-dry construction and assembly methods are used. There is no need to pour concrete and support formwork, which significantly improves construction efficiency compared to wet and cast-in-situ connections. Low cyclic reversed loading tests were conducted to obtain test data, such as failure mode, hysteresis curve, skeleton curve, stiffness, ductility, and deformation capacity of the precast concrete joint. The failure mode of the PBSEC joints is the buckling failure of the connecting steel plate, leading to a perfect seismic capacity and collapse resistance of the structure. The hysteresis curves of the PBSEC joints are bow-shaped and full in shape, showing high energy dissipation capacity. The bearing capacity of the joints begins to rise rapidly at the initial loading stage and then decreases slowly after reaching the peak, which is an ideal shape. By summarizing the average peak load, strength degradation coefficient, loop energy per cycle, loop energy per level, and cumulative energy damping coefficient, it is found that the joint using 10 mm thick Q235 steel can obtain the most suitable failure mode and obtain the best energy dissipation performance. When the strength of the steel plate material increases, the energy dissipation performance of the joint drops.

Optimal Design of Failure Mode Control for Semi-rigid Steel Frame Based on Elitist Retained Genetic Algorithm

The post-earthquake reports show that failure mode control design is of great significance to improve the seismic performance of structures. To realize the optimal design of failure mode in semi-rigid steel frame, a failure mode optimisation design method based on an elite retained genetic algorithm was developed in this study. Firstly, a database of 96 extended end-plate connections was established using the ABAQUS finite element software to obtain the initial rotational stiffness and yield moment under failure criteria. Secondly, with section size as the optimisation variable, failure mode as the constraint condition, and total steel consumption as the objective function, elite gene transfer was realized through gene sequence replication, hybridisation and mutation. With a 10-story, 3-span, semi-rigid steel frame as an example is proposed to demonstrate the application of the proposed semi-rigid design method, and pushover and time history analyses were conducted on the optimized results to verify the accuracy of the proposed method. The analysis results showed that the stable and reliable optimal design results were obtained through 1317 generation genetic iterative calculations, and the energy consumption ratio of the semi-rigid connection (including the beam ends) was 95.82% and that of the column was 4.18%; in addition, 76% of the beam ends had plastic hinges to dissipate energy in the pushover analysis. This finding indicates that the optimized frame can achieve the global failure mode during earthquakes, and the design method can effectively improve the seismic performance of the frame.