Improvement Of Seismic Performance Research Articles

Seismically resistant progressive collapse behavior of infilled frame structures under seismic loads and column loss: A numerical investigation

This research investigated the seismic performance of multi-story reinforced concrete (RC) frames with infilled walls. The study employed a two-step numerical approach: first, a verification process ensured the model's accuracy by comparing it to past experimental results. Following validation, a parametric study explored various factors influencing the frames' behavior. These factors included the number of stories (3, 6, and 12), the earthquake ground motion (Vrancea, El Centro, and Kahramanmaraş), and the effect of removing an internal column. Additionally, the study examined the impact of incorporating polypropylene (P.P.) fibers into different parts of the structure: the RC frame itself, the mortar between infill wall bricks, or both. The findings revealed significant improvements in seismic performance due to the presence of infill walls. In the three-story frame, the wall reduced plastic drift by a remarkable 98.9 %. Furthermore, strengthening with P.P. fibers demonstrated exceptional effectiveness. For example, on the first floor of the three-story frame, the maximum drift value dropped from 0.751 to a 0.004 for the IRCPM model (fibers in the infill wall mortar only) and even lower (0.003) for the IPPM model (fibers in both the RC frame and infill wall mortar). These results highlight the potent ability of P.P. fibers to improve earthquake resistance. The study also assessed the efficacy of strengthened infill walls as partial replacements for lost columns. When an internal column was removed, the presence of a P.P. fiber-reinforced wall (IPRCL model) helped mitigate the structural impact, reducing the base shear force by 11 % compared to the control model without fibers (CIRCL). Similar trends were observed in taller frames. While including fibers in the RC frame of the 6-story model with a removed column resulted in an 11 % decrease in base shear force, models with fibers in the wall components of the 12-story frame exhibited a 31.62 % increase in base shear force after column removal.

Sustainable Seismic Performance of Diagrid Core-Tube Structure with Replaceable Steel Coupling Beam

The diagrid core-tube structure has been widely used in high-rise buildings in recent years, but there are few studies on the sustainable energy dissipation measures and seismic performance improvement of such structural systems. Because the coupling beam is the element connecting the inner tube and the outer tube in the diagrid structure, it is the first seismic defense line and an important energy-dissipation member in the seismic design of the overall structure. Therefore, this paper replaces the traditional reinforced concrete coupling beam of the inner tube of the shear wall with a replaceable energy-dissipation steel coupling beam, and the strength, stiffness, and stability of the replaceable steel coupling beam are designed to improve the sustainability of the structure. By changing the position of the replaceable coupling beam, the relative stiffness of the inner and outer tubes of the diagrid tube structure, and the plane form of the structure, the static elastoplastic analysis and seismic response energy analysis of different diagrid tube structures are carried out, and the influence of the replaceable coupling beam on the sustainable seismic performance of the diagrid tube structure is studied. The results show that the replaceable coupling beams have little effect on the ultimate bearing capacity of the structure, but the ductility and sustainability of the structure are significantly improved, and the whole building layout is the optimal layout scheme. The setting of replaceable coupling beams makes the diagrid tube structure show hysteretic energy-dissipation earlier under the action of large earthquakes, and the proportion of hysteretic energy-dissipation is greatly improved, which reduces the inter-story drift ratios and the damage degree of the diagrid columns under the action of large earthquakes. When the relative stiffness of the outer tube of the diagrid tube structure is small or the plane form of the structure is a regular quadrilateral, the application of replaceable coupling beams is more effective in improving the ductility and sustainability of the structure and reducing the damage to the diagrid column under large earthquakes.

Evaluation of the seismic performance of novel bundled connections precast shear walls under cyclic loading

AbstractThis study proposes a novel precast shear wall connection method for connecting upper and lower wall panels. The vertical steel bars within the lower prefabricated wall panels are bundled and extended into pre‐designed holes within the upper prefabricated shear walls. Subsequently, high‐performance grouting materials are utilized to fill these pre‐designed holes. Cyclic load tests were conducted on all full‐scale specimens to evaluate the seismic performance of the proposed novel connected precast shear walls and compared with the seismic performance of the cast‐in‐place shear wall specimens. The findings reveal that the proposed novel precast shear wall connection method performs comparably to cast‐in‐situ shear walls, exhibiting almost identical results in terms of load‐bearing capacity, stiffness, and ductility. Furthermore, investigations into the removal and retention of metal bellows within the prefabricated holes, as well as the effects of additional reinforcement on the top of these holes, demonstrated no significant improvement in seismic performance. Finally, the reliability of the connection method was verified by analyzing the strain changes of the vertical steel bars in the precast holes of the precast shear wall. This study can provide a reference for promoting new connections in prefabricated structures.

Improvement effects of knee-bracing friction dampers on cyclic behavior of steel joints in antique buildings

To inherit the unique characteristics of historical timber architecture, the steel antique building (SAB) imitating ancient Chinese timber structures has been constructed using contemporary steel materials and fabrication techniques. These buildings typically exhibit premature yielding cracks and weak energy dissipation at the beam ends under seismic loads. To improve the seismic performance of SABs, two different types of friction dampers were deployed at the knee-bracing region around beam-column joints in SABs. First, cyclic loading tests on dampers indicate that both shear friction dampers and rotational friction dampers exhibit full hysteretic behavior, demonstrating an excellent and stable energy dissipation capacity. The friction coefficient of dampers with brass pads was theoretically calculated to be 0.35. Second, the quasi-static test showed that failure of steel joint specimens with knee-bracing dampers primarily occurred at replaceable angles in the beam-column connection region, which demonstrates that the repairability of steel joints in SABs can be greatly improved without overcomplicated labor. Adding knee-bracing dampers effectively postpones damage to the replaceable angles, which improves the strength, stiffness, and energy dissipation capacity of the steel joints significantly. The shear damper exhibits a more pronounced improvement in the overall structural seismic performance compared to the rotational damper with the same frictional sliding force. Moreover, numerical simulations showed that the strength of the proposed joints with knee-bracing friction dampers decreases with an increase in the axial compression ratio, while increasing the thickness of angles or the sliding force of dampers can effectively improve the seismic performance of the steel joints in SABs.

Assessment of Soft-First-Floor Structures Reinforced by Rocking Frame Based on Seismic Resilience

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.

Seismic vulnerability assessment and mechanical – based fragility analysis of a masonry clustered building in South Italy

The paper discusses the seismic behaviour assessment of a masonry clustered building, which is a prevalent typology in historical centres, particularly focusing on a case study located in a small town in Southern Italy. Following the introduction about the historical centre, the main architectural and structural features of the selected aggregate are outlined, based on the CARTIS Form, which was developed as part of the DPC – ReLUIS Italian research project. After establishing the characteristics of the building, its seismic assessment is conducted. Non-linear analyses reveal inadequate seismic behaviour in both longitudinal and transverse directions. A consolidating intervention which foresees the application of a seismic coating system is proposed. This integrated approach aims to improve both the seismic and energy performance of the aggregate. In the final part of the work, a comparison is made between the results obtained before and after the intervention. This includes the evaluation of the seismic safety index, as well as the examination of the fragility curves. The objective is to assess the effectiveness of the coating system on the structural units of the aggregate, thereby determining the overall improvement in seismic performance following the intervention.

Timber-Based Strategies for Seismic Collapse Prevention and Energy Performance Improvement in Masonry Buildings

This study investigates the effectiveness of a range of timber-based solutions for the seismic and energy retrofitting of existing masonry buildings. These solutions are designed not only to prevent structural collapse during earthquakes but also to create integrated interventions that enhance thermo-physical performance and reduce emissions in existing buildings. Various case scenarios were considered and both mechanical and energetic behaviour post-intervention were evaluated. Timber-engineered products serve as foundational components for the retrofit approach, encompassing one-dimensional vertical elements (strong-backs) and various types of panels (cross-laminated timber panels, laminated veneer lumber panels, and oriented strand board panels). The analyzed retrofit techniques share a common principle involving the attachment of these timber-based elements to the building’s wall surfaces through mechanical point-to-point connections. The proposed solutions integrate strong-backs and timber panels with membranes and insulation layers, yielding cohesive, and highly effective interventions. Finite element modeling was employed to analyze the mechanical and thermal responses of the retrofitted walls. A comprehensive comparative analysis of various techniques was conducted to determine the most effective solution for each specific scenario.

Seismic performance improvement of liquid storage tank based on base-isolation and pendulum tuned mass damper

It is necessary to ensure the safety of liquid storage tanks under earthquakes, but the damage probability of the non-damping liquid storage tanks is higher under earthquakes. Based on the damping principle of tuned mass damper (TMD) and the characteristics of the liquid storage tank, a new pendulum TMD (PTMD) system is proposed. Considering the material nonlinearity, the fluid–structure interaction and liquid sloshing characteristics, the three-dimensional numerical calculation models of the non-damping, PTMD, base-isolation (BI) and BI-PTMD liquid storage tanks are established, respectively. The seismic responses of different types of liquid storage tanks under the action of near-field pulse-like earthquakes are investigated, the damping performance of the hybrid control system with the isolation and the PTMD is analyzed, and the influence laws of the mass ratio of PTMD-structure and base-isolation period on the dynamic responses of the liquid storage tanks are discussed. The results show that the BI-PTMD hybrid control system has a significant damping effect on the seismic responses of the liquid storage tank. The damping rate of the base shear is the largest, reaching 86.0%, and the control rate of the PTMD on the displacement of the isolation layer is about 20.0%. The hoop stress, effective stress, liquid pressure and displacement of isolation layer decrease with the increase of the mass ratio of PTMD to structure. With the increase of base-isolation period, the hoop stress, axial compressive stress, effective stress and liquid pressure decrease, and the control effect of PTMD on the liquid storage tank is weakened.

Application of a Deep Learning Method to the Seismic Vulnerability Analysis of Cross-Fault Hydraulic Tunnels Based on MLE-IDA

Rapidly developed deep learning methods, widely used in various fields of civil engineering, have provided an efficient option to reduce the computational costs and improve the predictive capabilities. However, it should be acknowledged that the application of deep learning methods to develop prediction models that efficiently assess the nonlinear dynamic responses of cross-fault hydraulic tunnels (CFHTs) is lacking. Thus, the objective of this study is to construct a rational artificial neural network (ANN) prediction model to generate the mass data and fragility curves of CFHTs. Firstly, an analysis of 1080 complete nonlinear dynamic time histories via incremental dynamic analysis (IDA) is conducted to obtain the mass data of the drift ratio of the CFHT. Then, the hyper-parameters of the ANN model are discussed to determine the optimal parameters based on four examined approaches to improve the prediction capacity and accuracy. Meanwhile, the traditional probabilistic seismic demand models of the predicted values obtained by the ANN model and the numerical results are compared with the statistical parameters. Eventually, the maximum likelihood estimation couping IDA method is applied to assess the seismic safety of CFHTs under different damage states. The results show that two hidden layers, ten neurons, and the ReLU activation function for the ANN model with Bayesian optimization can improve the reliability and decrease the uncertainty in evaluating the structural performance. Moreover, the amplitude of the seismology features can be used as the neurons to build the input layers of the ANN model. It is found through vulnerability analysis that the traditional seismic fragility analysis method may overestimate the earthquake resistance capacity of CFHTs compared with maximum likelihood estimation. In practical engineering, ANN methods can be regarded as an alternative approach for the seismic design and performance improvement of CFHTs.

Performance assessment of steel frame buildings with hybrid self-centering braces under extremely rare far-field earthquakes

This paper investigates the seismic performance enhancement of steel frame buildings using a novel hybrid self-centering braces (HSBs) under extremely rare earthquake events. The hybrid self-centering brace consists of shape memory alloy (SMA) cables and viscoelastic (VE) dampers. A prototype bracing system is designed and fabricated to explore its basic mechanical behavior and working mechanism under cyclic loading, with a focus on its failure modes under large deformation loading condition. A multi-material mechanical model is developed to capture the mechanical behavior and failure of the HSB. Furthermore, five steel frame buildings with different parameterized HSBs are designed and modeled in OpenSees. Nonlinear dynamic analyses and incremental dynamic analyses are conducted on the five case-study frames using 44 far-field ground motions. The risk-based seismic performances of steel buildings with HSB are evaluated to assess the performance of HSB during extremely rare seismic events. The results show that the hybrid self-centering brace exhibits excellent self-centering and energy dissipation capabilities with the maximum equivalent viscous damping ratio reaching 9.4 %. Even under large deformations, VE dampers continue to work effectively after the failure of SMA cables, demonstrating remarkable redundancy. Numerical simulations further reveal that the redundancy of HSB can improve the structural seismic resilience in terms of inter-story drift ratio, residual drift, and floor absolute acceleration. The higher the redundancy of HSB in the case-study frames, the smaller the seismic response and mean annual frequency of exceedance of the engineering demand parameters, thereby indicating a significant improvement in seismic performance.

Correction: Seismic response characteristics and performance improvement of near-fault continuous rigid-frame bridges

Correction: Seismic response characteristics and performance improvement of near-fault continuous rigid-frame bridges

Seismic response characteristics and performance improvement of near-fault continuous rigid-frame bridges

Seismic response characteristics and performance improvement of near-fault continuous rigid-frame bridges

Structural performance study and improvement of Artemio Franchi Stadium in Florence

Artemio Franchi Stadium in Florence is the first world-famous work by Pier Luigi Nervi, and is celebrated as a masterpiece of the Rationalist movement. In view of this, it has been declared a work of cultural and historical interest by the Italian Ministry for Cultural Heritage and Activities, with several specific preservation restrictions on its most distinguishing structural and architectural elements. With a view to the recently planned restyling and modernization works, a diagnostic field survey and testing campaign, and a static and seismic performance assessment study of the Stadium were commissioned by the Municipality of Florence. Furthermore, a retrofit design respectful of the architectural preservation requirements was requested for its reinforced concrete structure. The contents of the diagnostic and assessment study, as well as of the retrofit design, are presented in this paper. The results of the structural analyses, carried out by means of a detailed finite element model calibrated on the field survey and testing data, show slightly unsafe static conditions in less than 10% of the beams and columns constituting the bleacher sloped frames, and diffused unsafe conditions under seismic action scaled at the Basic Design Earthquake level. The proposed retrofit solution consists in incorporating dissipative braces equipped with fluid viscous spring-dampers in several spans oriented in orthogonal direction to the bleacher frames, and installing fluid viscous pure dampers across the majority of the technical separation gaps between adjacent bleacher blocks, so as to prevent their mutual pounding. The results of the analyses in retrofitted conditions highlight a transition to safe conditions for more than half of the unsafe members, and a remarkable reduction of the demand/capacity ratios in the remaining members. Safe stress states can be reached in the latter by means of simple additional local strengthening interventions. This substantial improvement of seismic performance is achieved with a minimal visual and functional impact on the existing structures, as prescribed by the imposed preservation restrictions.

A multiscale optimization methodology for cyclic elastoplastic performance of beam-pile joint member in pile-supported wharf

A material-member-structure multiscale optimization methodology, which can be utilized for improving the elastoplastic behaviour of the beam-pile joint member in pile-supported wharf under cyclic loading, was developed on the base of the application of high-specific stiffness material. Based on the representative volume element (RVE) method, the parameterized relations between the mesoscale phases (e.g., steel fibers, interfacial transition zone, and matrix) and macroscale homogenized elastoplasticity of ultrahigh-performance concrete (UHPC) reinforced with steel fibers were obtained under periodic boundary conditions. The physical equivalence relation between material scale and member scale was established by utilizing the refined constitutive model with the macroscopic mechanical parameters and exponential decay damage evolution factors. UHPC material property tests and cyclic loading tests of small-scale beam-pile joint specimens were performed respectively, and the results were analyzed and utilized to validate the numerical model and multiscale optimization method. Using the computational platform ABAQUS, the cyclic elastoplastic performances of the novel beam-pile joint members were evaluated numerically by pseudo-static hysteretic loading. As an illustration, a multiscale modelling approach for the pile-supported wharf frame system was presented and employed to assess the seismic performance improvement through the optimization of the beam-pile joint members. The coupled solution of refined member damage and large-scale structural bearing capacity was realized by utilizing the deformation coordination condition and force balance equation, which bridges the member scale and structure scale. This study aims to provide a reference for future design and optimization of the joint members in marine frame structures, to enhance cyclic bearing capacities and reduce reinforcement consumptions.

Improvement of seismic performance of self-centering mid-rise RC frames by adding semi-rigid rocking columns

Improvement of seismic performance of self-centering mid-rise RC frames by adding semi-rigid rocking columns

Seismic Fragility Analysis of Existing RC Frame Structures Strengthened with the External Self-Centering Substructure

Based on a practical engineering case of seismic strengthening, this paper used the enlarging cross-section method and an external self-centering substructure to improve the seismic performance and seismic resilience of existing frame structures. Among them, the external self-centering substructure included setting a self-centering precast beam and diagonal braces. Utilizing the OpenSees finite element platform, a seismic fragility analysis was carried out to compare the improvements in seismic performance and seismic resilience before and after strengthening. The analysis results show that the proposed modelling method could be simulated satisfactorily. The maximum inter-story drift and the residual inter-story drift of the strengthened frame structures decreased significantly under the same peak ground acceleration. The peak ground acceleration of the strengthened frame structures significantly increased under different performance levels. Additionally, the exceedance probability of the strengthened frame structures was obviously reduced, which reflected that the seismic performance and seismic resilience of the strengthened frame structures were significantly improved.

Effects of RC ties on seismic performance improvement of confined masonry walls under combined in-plane, out-of-plane, and vertical loads

This study aimed at understanding the role of vertical RC ties in the seismic performance improvement of confined masonry walls under combined in-plane, out-of-plane, and vertical loads through nonlinear static analysis. For this purpose, finite element models were developed using simplified micro modelling method which were verified against the experimental results. Then, parametric studies were carried out to evaluate the response sensitivity of the masonry walls to the interaction of in-plane, out-of-plane, and vertical seismic demands. Two sets of wall models were considered; one without RC vertical ties (URM) and the other with these structural members (CM). Two ratios of height-to-length for the walls and five levels of vertical loads (representing resultant forces from dead, live, and vertical ground motion component loads) were considered. The loading was applied according to two protocols; (1) applying vertical loads prior to the application of in-plane displacement, and (2) applying out-of-plane uniform pressure after employing three different levels of vertical loads and then two different levels of in-plane displacements. It was found out that the in-plane strength of CM walls, in the worst case, changed –22% and 0% under 1 g of upward and downward vertical ground motion acceleration, respectively with respect to the wall under gravity loads only; whereas, this change for the corresponding URM walls is −100% and + 43%, respectively. The sensitivity of out-of-plane strength of CM walls to prior in-plane and vertical ground motion acceleration in the worst case was also found marginal; with −17% to −1% change under 1 g of upward and downward vertical ground motion acceleration, respectively. The change for the corresponding URM walls was −100% and −27%, respectively.

Steel Structures Research Update: Slotted-Hidden-Gap Connections and Intentional Eccentricity for Steel Brace Members

Research on alternatives for steel brace members and their connections is highlighted. These studies are a collaboration between Dr. Colin Rogers, Professor and Acting Chair at McGill University, and Dr. Robert Tremblay, Professor at Polytechnique Montreal. Research on braces with intentional eccentricity (BIEs) is motivated by improvements in seismic performance compared to concentrically loaded brace (CLB) members. A brief summary of the background, motivation, and research objectives is presented. Also provided are selected highlights of the experimental program and supplementary finite element study. The slotted-hidden-gap (SHG) connection may eliminate the need to reinforce HSS braces at knife-plate connections, but existing design guidance is limited. Through an extensive, integrated program of numerical parametric studies and physical tests, the research team developed SHG connection design and detailing guidelines.

Design and seismic performance of precast segmental bridge columns repaired with UHPC jacket after earthquake-induced damage

Precast Segment Bridge Columns (PSBCs), which attract more attention owing to the merits of faster construction rate and higher construction quality compared with monolithic columns, are prone to serious damage under a severe earthquake. Seismic performance improvement and rehabilitation of earthquake-damaged PSBCs are significant to promote applications in seismic-prone areas. Ultra-high performance concrete (UHPC) jackets, which are promising in the field of rapid retrofit of civil structures, were used to retrofit damaged PSBCs in this study. To investigate the seismic design method and performance of repaired PSBCs using UHPC jackets, a 1/10-scale earthquake-induced damaged PSBC was retrofitted based on a proposed reinforcement design method, and tested under vertical loading and incremental lateral cyclic loading. The failure mode, hysteresis curve, residual displacement, and energy dissipation capacity of the repaired column were compared with those of the original column. In addition, based on a verified 3D finite element model by the test, a parameter analysis was conducted to explore the effect of the height and wall thickness of the UHPC jacket on the seismic behavior of the repaired PSBCs. The results indicated that the earthquake-damaged PSBC repaired with the UHPC jacket had an equivalent initial stiffness, 18.9% higher energy dissipating ability at 4.0% drift ratio and 16.2% larger strength compared with the undamaged column. The numerical simulation showed that the height and thickness of the UHPC jacket had an influence on the failure location and strength of the repaired PSBCs. Besides, the design method for the damaged precast column reinforced with the UHPC was confirmed by the test and finite element model, and it could be applied to the retrofit design of the damaged precast segment column.

Seismic performance improvement using bolt-on isolators on interconnected slender electrical equipment

The slender electrical equipment in substations is fragile to damage during earthquakes owing to the seismically sensitive structure, low material strength, and coupling effects from interconnected equipment. To improve the seismic performance of the slender electrical equipment in the interconnected circuit system, the design and characterization of an assembled isolation system were recommended. The solution was based on a novelty combination application of bolt-on isolators and a support block by reducing the bending stiffness of slender equipment to achieve vibration isolation function. The isolation function test was performed on isolators from characteristics of stiffness variation and damping. Finally, the effectiveness of the proposed isolation system was proved in seismic performance improvement of interconnected slender electrical equipment using a comparison shaking table test, which was performed on a full-scale interconnected circuit, consisting of two ±800kV composite pillar insulators connected by a tubular busbar. Therefore, thus isolation system can provide effective seismic protection for interconnected slender equipment in proper design.