Near-field Excitations Research Articles

An inerter-enhanced bistable nonlinear energy sink for seismic response control of building structures

Structural control strategies have attracted great attention in reducing unwanted structural responses. To mitigate the vibrations of seismically excited buildings, this paper proposes a novel vibration control device: an inerter-enhanced bistable nonlinear energy sink (BNESI). A three-story building structure is selected as an example, where the BNESI is attached to the top of the structure and linked to the top second floor of the structure, to explore the control effect of the device under earthquakes. The restoring force of the BNESI and equations of motion for the BNESI-controlled system are derived first. Subsequently, a multi-objective optimization design method of the BNESI is proposed and applied in building structures. The input energy robustness of the BNESI is then accessed by various initial velocities subjected to the structures. Moreover, the seismic vibration mitigation capacity of the BNESI is systematically investigated under a group of near-field and far-field excitations. Analysis results show that the proposed design algorithm for BNESI can be an attractive alternative to effectively obtain optimal parameters of the control device. The BNESI is less sensitive to the input energy levels, and can stably capture and dissipate energy from the primary structure. Also, the BNESI system provides good control effectiveness with less sensitivity to the uncertainty of seismic excitations. In addition, with less standard deviation, the damper stroke of the BNESI is only about a quarter of that of the TMD under the same excitation. Moreover, the damage to the primary structure has a negligible effect on the control effect of the BNESI system. Meanwhile, the BNESI can decrease the energy dissipation demand on the structure, and the energy distribution mode of the BNESI system shows less sensitivity to the frequency decrease of the structure.

Investigation of torsion in asymmetric mid-rise structures on the pile-raft system considering soil-structure interaction

The adverse conditions of the soil such as soft soil can have seismic consequences that may either amplify seismic response or render the structure vulnerable. On one hand, the design and construction of asymmetric structures have become prevalent due to aesthetic considerations and structural space limitations. Studies indicate that structures with geometric irregularities are susceptible to seismic forces, leading to non-uniform distribution of floor drifts, excessive torsional behavior, and more, depending on the degree of irregularity. In this research, the main goal was to investigate the effect of soil and structure interaction on the torsion of asymmetric Mid-Rise Structures. To achieve this goal two asymmetric Steel moment frame system 15-story structures aim to address the effect of interaction between soil and structure on the seismic performance, one with a rigid base and the other with a flexible base, one with a rigid base and the other with a flexible base. To mitigate the settlement of soil-associated structures, a pile-raft system is employed, considering the softness of the soil. Additionally, to study the torsional behavior of these structures, their planes are asymmetrically designed in L-shape and C-shape configurations, subjected to four ground motion excitations in both far and near-field scenarios. Three-dimensional finite element numerical simulations are performed using Abaqus software. Various configurations of the pile-raft system for the asymmetric C-shape structure are examined to assess the effects of pile diameter and length on the torsional irregularity coefficient. The results show that the soil-structure interaction increases the maximum floor rotation angle, placing these structures in critical conditions concerning torsional irregularity under near-field and far-field seismic excitations.

A low-cost bonded scrap tire rubber isolator in rural regions: Experimental, numerical and theoretical analysis on mechanical behavior

The utilization of low-cost scrap tire pads (STP) made from recycled tires presents a promising alternative to traditional rubber isolators (i.e., fiber-reinforced elastomeric isolators) in rural construction. However, the STP was limited in application to practicing structures due to stability with a shear strain level of 100 % and the significant variability of the mechanical behavior at the same parameters. For these issues, this paper presents a bonded scrap tire rubber isolators (BSTRIs), based on earthquake demand parameters for rural area buildings. In addition, a series of vertical compression and horizontal shear tests were conducted to evaluate the dependency of mechanical behavior on surface pressure (σ0), the first and the second shape factor (S1 and S2). Then, a finite element (FE) model of BSTRIs was developed and validated. The experimental and FE results show that the σ0, S1, and S2 overwhelmingly effect on mechanical behavior (i.e., critical pressure, vertical stiffness, horizontal stiffness, and damping ratio). Moreover, the new theoretical formulations on critical pressure, vertical stiffness, and horizontal stiffness were developed to evaluate the stability of BSTRIs. Finally, based on experimental result, a nonlinear dynamic response was conducted including the BSTRIs-supported and based-fixed unreinforced masonry (URM) buildings under 22 far-field and 28 near-field seismic excitations. The results indicated that the base shear of the BSTRIs-supported URM were decreased by 66.5 % and 50.1 % in far- and near-field record, respectively, compared with the response of the fixed-base URM building.

Negative stiffness and inerter-based dampers: Novel seismic response control approach for base isolated liquid storage tanks

Liquid storage tanks (LSTs) have become indispensable to civil engineering infrastructure. LSTs are used not only for storing harmless fluids but also explosive, toxic, and hazardous substances. Thus, the ability of LSTs to withstand significant seismic activity without damage is a major worry. Strong pulse-type characteristics in near fault (NF) type of ground motions have shown significant base and sloshing displacements for a commonly adopted structural control measure: base isolation (BI). The current study introduces negative stiffness and inerter dampers (NSIDs) as supplemental response control measures to LSTs with BI (BILSTs). Conventional supplemental damping applications in the isolation system are helpful in displacement reduction at the isolator level, but the upper structure response gets severely affected. This study presents NSIDs, characterised by the damping magnification effect, as supplemental dampers to BILSTs. The continuous liquid mass within the tank is represented by discrete lumped masses referred to as sloshing, impulsive, and rigid mass. The stiffness constants of these lumped masses are derived by considering the tank wall and stored liquid physical parameters. The optimal supplemental damping parameters are deduced by developing contour plots describing the sloshing and base displacement response reduction (mitigation) ratios. Through analytical studies conducted using real earthquake records, it has been demonstrated that appropriately designed Negative Stiffness and Inerter Devices (NSIDs) yield enhanced performance for Base Isolated Liquid Storage Tanks (BILSTs). These optimised combinations of NSIDs effectively mitigate isolator displacement, base shear, lumped sloshing mass displacement, and sloshing mass height in response to both near-field (NF) and far-field (FF) base excitations.

Probabilistic Seismic Performance Assessment of Tall RC Special Moment-resisting Frame Buildings Equipped with Buckling-restrained Braces under Near-field Excitations

Many tall buildings have already been constructed near faults throughout the world, several of which have sustained casualties and economic losses during strong ground motions. This study investigates the effect of near-fault excitations on the vulnerability of tall, reinforced concrete (RC) special moment-resisting frame (SMRF) buildings equipped with buckling-restrained braces (BRBs) using seismic fragility curves. After attaining the structure’s response modification factor (R), three-dimensional (3D) models of 15-, 25- and 35-story frames were developed by the OpenSees software according to the Iranian code provisions. Thus, the seismic response of the elements was obtained. Subsequently, incremental dynamic analysis (IDA) was conducted by selecting a suitable number of compatible accelerograms in two near-field and far-field groups. Considering the maximum story drift as the demand parameter and selecting the interstory drift ratios (IDR) for the slight, moderate, extensive, and complete collapse seismic performance levels proposed by Hazus, IDA curves were plotted. Then, the seismic fragility curves were produced using the structural reliability relations. The median fragility at complete collapse damage level reduced from 0.73g, 0.62g, and 0.61g to 0.68g, 0.59, and 0.57g for the 15-, 25, and 35-story near-field and far-field earthquake models, respectively. This was attributed to increasing vulnerability and seismic fragility of the structures as a result of both height increase and distance reduction from fault. Based on the results, the most vulnerable structure, i.e., the 35-story near-fault model, experienced a 40, 17, 18, and 6% increase in median fragility at slight, moderate, extensive, and complete collapse damage levels, respectively.

The optimal configuration of negative stiffness inerter-based base isolators in multi-storey buildings

The negative stiffness inerter-based base isolators (NSIBI) are introduced in this paper. The negative stiffness device and inerters are installed inside the core of the conventional base isolators (CBI) to enhance their dynamic response reduction capacity. The novel isolators have been installed at the multi-storey building’s base to mitigate their dynamic responses during vibration. H2 optimization method applies to derive the exact closed-form expression for negative stiffness inerter-based base isolators’ optimal design parameters, such as frequency and viscous damping ratio for multi-storey buildings. Applying these H2 optimized design parameters, the optimum NSIBI for dynamic response mitigation of multi-storey buildings have been achieved. The dynamic responses of the NSIBI-controlled multi-storey buildings are compared with the dynamic responses of multi-storey buildings isolated by optimum CBI to determine the exact superior dynamic response reduction capacity of optimum NSIBI. The dynamic responses of isolated structures in the frequency domain are evaluated by forming the transfer function. Therefore, for five-storey buildings, the dynamic response reduction capacity of NSIBI is significantly 51.93% and 81.24% superior to the dynamic response reduction capacity of CBI subjected to harmonic and random-white excitations. In contrast, for ten-storey buildings, the optimum NSIBI has 77.73% and 94.02% more dynamic response reduction capacity than the optimum CBI subjected to harmonic and random-white excitations. In addition, using the Newmark beta method, a numerical study further conducts to verify the accuracy of the H2 optimized design parameters by obtaining the time history results for isolated structures subjected to near-field pulse-type earthquake base excitations. Accordingly, the optimum NSIBI have 57.591% and 55.398% more displacement and acceleration capacity than the optimum CBI for five-storey buildings. Besides, for ten-storey buildings, the displacement and acceleration capacities of optimum NSIBI are significantly around 56.42%and 55.80%, superior to the optimum CBI. Thus, the vibration reduction capacity of optimum CBI is significantly decreasing while the storey level of the multi-storey buildings increases, whereas NSIBI is still efficient in reducing the dynamic responses effectively. The paper’s outcomes are mathematically accurate and applicable to practical implementation.

Fragility analysis of containment reinforced masonry wall using equivalent frame model

A considerable percentage (over 70%) of dwellings across the globe involve masonry elements. Masonry structures are well known to be weak in resisting seismic actions. This paper presents the effectiveness of (near surface mounted) containment reinforcement as earthquake resistant feature for masonry walls. Analytical prediction of the response of unreinforced (UR) and reinforced (R) masonry structures to earthquakes are hindered by the complexity and cost of micro and macro models. Consequently, researchers have come up with simplified models of masonry walls to capture seismic responses. The Equivalent Frame Model (EFM) is one such simplified approach. The present work evaluates the performance of two-storey UR and R masonry walls subjected to In-plane seismic action through Incremental Dynamic Analysis (IDA) and Fragility Analysis (FA). EFM has been employed in commercial FEM software SAP2000.v21 to evaluate the seismic response of these walls to the ensemble of near-field and far-field excitations. Finally, the work demonstrates the superiority of Containment Reinforced (CR) masonry against seismic action.

Performance Assessment of Hybrid Steel Frames under Near-field Seismic Excitations

Assessment of the seismic performance of steel structures is topical research for a variety of earthquakes. Moment-resisting rigid steel frames are generally designed and used for high seismic zones. However, the famous Northridge in 1994 and Kobe in 1995 earthquakes exposed the shortcomings of moment frames. During these events, the beam-column connections of rigid moment frames were severely damaged. Since then, an alternative of welded connections called bolted or semi-rigid connections is considered for designing or retrofitting of steel moment frames. From the last few years, the semi-rigid connections combined with rigid connections, termed as hybrid or dual frames have become widely popular for earthquake designers and engineers due to enhanced ductility and reduced cost of construction. Earlier research work was focused on far-field (FF) earthquakes, whereas, the near-field (NF) earthquakes are crucial for civil engineering structures. In this paper, an extensive numerical study is carried on rigid and hybrid steel moment frames for NF and FF earthquakes. For this purpose, a ten-story rigid steel frame is analyzed and designed for seismic requirements as per Indian Standards. The rigid connections of frames are replaced by semi-rigid connections with a moderate degree of semi-rigidity. The six different patterns (locations of semi-rigid connections) of hybrid frames are considered here to compare the seismic performance of hybrid frames under near field earthquakes. The nonlinear response-history analyses are executed using the SAP2000 software at two scaled PGAs defined as low (i.e., 0.2g) and high (0.5g) level. An ensemble of three time-histories, each for both types of earthquakes are considered for the numerical simulation. Response quantities of interest, namely, the maximum value of base shear, story displacement, inter-story drift ratio, the total number of plastic hinges, and the square root of the sum of squares of maximum plastic hinge rotations are considered for the decision of a most appropriate pattern for hybrid frames. The results of the numerical study indicate that the response behavior for the NF earthquakes is distinctly different both in nature and magnitude. It is observed that the seismic demands under the NF earthquakes are substantially more as compared to those obtained for FF earthquakes for all cases of hybrid frames. Further, it is also found that the pattern and number of semi-rigid connections in the hybrid frame have a vital role in seismic performance.

The exact closed-form equations for optimal design parameters of enhanced inerter-based isolation systems

This paper introduces the enhanced inerter-based isolation system (EIBI) to improve broadband vibration control. Using the H2 optimization method, the exact closed-form expressions for the optimal design parameters of the EIBI, such as the frequency and viscous damping ratio, have been derived analytically. The optimal frequency and viscous damping ratios of EIBI decrease as the mass ratio of the EIBI increases. For optimal design purposes, the optimal viscous damping ratio of EIBI lies between 0.20 < ζ b < 0.30, which is practically affordable and precise to implement. The exact closed-form expressions for optimal design parameters for traditional base isolators (TBI) have also been derived using the H2 method to make a fair comparison with EIBI. When the base mass ratio of TBI increases, its optimal frequency and viscous damping ratios decrease. The response reduction capacity of each optimized novel isolator was compared to the response reduction capacity of each optimized TBI. Analysis of the frequency domain demonstrates that the response reduction capacity of the proposed EIBI is significantly 2.77% and 17.46% greater than that of the TBI subjected to harmonic and random white-noise base excitations. To verify the accuracy of the optimal closed-form expressions derived for each isolator using near-field earthquake base excitations, a numerical study employing the Newmark-beta method has been conducted. Hence, the time-history analysis reveals that the displacement and acceleration reduction capacities of EIBI are significantly superior to that of the TBI subjected to near-field earthquake base excitations by 12.86% and 24.61%, respectively. The EIBI systems are cost-effective and have greater vibration reduction capacities than TBIs.

The exact closed-form expressions for optimal design parameters of resonating base isolators

In this paper, the exact closed-form analytical expressions of the optimal design parameters for two different base isolation (BI) configurations, i.e., grounded (GR-BI) and ungrounded (UR-BI), are derived employing H2 and H∞ optimization methods. To compare the performance of resonating isolators fairly with an equivalent base isolator, an additional mass is added to the base isolator’s mass. Frequency domain and time history analysis have been conducted to obtain each isolator’s exact vibration reduction capacity. Results from frequency domain analysis show that H2 optimized ungrounded resonating base isolator has a negligible effect on the vibration mitigation compared to the equivalent base isolator having equal total mass. The response reduction capacity of the GR-BI is significantly 23.81% superior to the BI and UR-BI both while implementing H2 optimization method. On the other hand, for H∞ optimization, the response reduction capacity of the GR-BI is significantly 26.1% and 34.98% superior to the BI and UR-BI, respectively. Subsequently, numerical studies employing the Newmark-beta method have been conducted to obtain time-domain responses using near-field earthquake base excitations. Results from time history analysis depict that the response reduction capacity of H2 optimized GR-BI is significantly 47.80% and 47.51% superior to the response reduction capacity of H2 optimized BI and UR-BI. In contrast, the response reduction capacity of H∞ optimized BI is significantly 56.45% and 43.75%, superior to the response reduction capacity of H∞ optimized UR-BI and GR-BI. However, the response reduction capacity of H∞ optimized GR-BI is significantly 22.58% superior to the response reduction capacity of H∞ optimized UR-BI. The requirement of the damping ratios of all the proposed isolators are within unity; hence these are affordable. The results are mathematically accurate and feasible for practical design purposes.

An innovative methodology for hybrid vibration control (MR+TMD) of buildings under seismic excitations

In this study, the combination of magnetorheological dampers and tuned mass dampers (MR + TMD) as a hybrid control system is investigated on a 15-story shear building where MR damper is attached to the TMD to generate active control force of TMD. The seismic responses of the structure are reduced by employing MR + TMD on rooftop of the structure. The MR damper's control voltage is generated by combining IT2FLC and FOPID. The FOPID + IT2FLC, TMD, and control voltage parameters are optimized using the observer-teacher-learner-based optimization (OTLBO) algorithm to minimize the maximum displacement of the building rooftop under far-field and near-field earthquake excitations. To conduct additional research, the same method was used to mitigate structural responses for PID, FOPID, IT2FLC, and a combination of fuzzy logic type-1 (FLC) and FOPID (FOPID + FLC). All of these controllers' performances in mitigating seismic responses are compared to those of the uncontrolled system and to each other. The results indicate that FOPID + IT2FLC outperforms PID, FOPID, and FOPID + FLC controllers. Additionally, the building's rooftop displacement was reduced by an average of 35.06% using the FOPID + IT2FLC system for sixteen far-field and near-field earthquake records. Moreover, the hybrid MR + TMD system performs better than other conventional controllers. 1 The combined application of the meta-heuristic algorithm and IT2FLC controller along with FOPID controller (FOPID + IT2FLC) to mitigate structural responses. 2 Combined application of MR damper and TMD (MR + TMD) as a hybrid control device. 3 Optimizing FOPID and IT2FLC to generate the control voltage of MR + TMD. 4 Investigating PID, FOPID, FOPID + FLC controllers to compare with the proposed method. 5 Investigating the performance of the suggested method by the aim of energy consumption and 5 novel criteria such as base shear, base moment and etc.

Quantification of the Seismic Behavior of a Steel Transmission Tower Subjected to Single and Repeated Seismic Excitations Using Vulnerability Function and Collapse Margin Ratio

Transmission towers are a vital lifeline for modern living and are crucial structures that must remain operational even after a seismic event. However, the towers are largely designed to withstand the effects of wind alone and not earthquakes, and the seismic influences on tower design and construction have hitherto been ignored. The purpose of this study was to evaluate the seismic performance of a latticed steel transmission tower-line system that is subjected to a variety of seismic situations (Far-Field, Near-Field and Repeated Earthquakes) using probabilistic vulnerability functions and Collapse Margin Ratios in accordance with FEMA-P695. Nonlinear Time History Analyses were performed by incorporating an array of 36 strong ground motions to develop the Incremental Dynamic Analysis and to generate the fragility functions for three performance limit states as referenced in FEMA 356. The results showed that the single event seismic performance of the tower is better than its performance after multiple ground motions owing to aftershock impact, while near-field excitations led to greater susceptibility and fragility than far-field scenarios. Thus, near-field ground motion is more harmful to the tower and could result in its failure or collapse with only a small reduction in damage relative to the impact of the aftershock.

Comparative response assessment of different steel plate shear walls (SPSWs) under near-field ground motion

Steel plate shear walls (SPSWs) are widely used due to their high energy absorption and exceptional lateral resistance. However, the behavior of different infill panels varies, and their response under near-field seismic excitations is uncertain. To better understand how different infill panels contribute to seismic structural responses, this paper presents findings from research conducted on different types of SPSWs. The study of different types of SPSWs with infill panel aspect ratios of 1:1 and 2:1 under cyclic loading was the first part of this parametric investigation, and the second part was the study of the structural response of 3D frames with an aspect ratio of 3:4:2 and a 1:1 infill panel under near-field ground motions. The results of energy dissipation, acceleration, and drift were compared. This study's goal was to better understand how various infill panels react to near-field ground motions and cyclic loading. With a 2:1 aspect ratio, unstiffened SPSWs reduced plastic dissipation by 78% while increasing lateral stiffness by 10%. With minimal peak transient and residual interstory drifts and effectively damped floor acceleration, unstiffened SPSW demonstrated the best viscous effect and dissipated 69.42% of the total system.

Multi-objective optimal design of SC-BRB for structures subjected to different near-fault earthquake pulses

The purpose of this research is to propose a two-objective optimum design technique of self-centering buckling restrained brace (SC-BRB) characteristics based on a multi-objective cuckoo search (MOCS) optimization algorithm for structures subjected to pulse-like near-field seismic excitations. The optimal geometric specifications of shape memory alloy (SMA) and buckling-restrained brace (BRB), including the length of SMA bars, BRB core, area of SMA, and BRB core, are optimized with the aim of simultaneous reduction of the maximum displacement and acceleration of the floors of structures. The numerical analyses are then performed on 3-story and 6-story frames that have been modeled in OpenSees software under pulse-like near-fault earthquakes. The optimized SC-BRB using MOCS considerably reduces the seismic responses of both structures. The SC-BRB also performs better than BRB in severe earthquakes with a shorter fault distance and a larger moment magnitude. Furthermore, SC-BRB has a steady energy dissipation capacity due to more energy absorption in SMA. In terms of maximum top floor displacement and acceleration, the 3-story SC-BRB frame (SC-BRBF) results are reduced the values of 28.3% and 20.1% than the BRB frame (BRBF) for all considered near-fault earthquake pulses, respectively. Moreover, the optimized SC-BRB is considerably capable of reducing the hazards originating from residual drifts and deformations.

Developing a simplified method for analysis and design of isolated structures with the novel quintuple friction pendulum system under bidirectional near-field excitations

Simplified analysis methods for seismically isolated structures proposed in recent structural codes and specifications are frequently used to reduce the computational effort and to simplify the design procedure, either directly for special cases or for checking the results of nonlinear response history analysis. Of the approximate methods, the equivalent lateral force procedure using the effective stiffness and effective damping is one of the best known. In this study, the simplified method is developed by combining the equivalent lateral force procedure with the capacity spectrum method and evaluated in terms of maximum isolator displacements and base shears for isolated structures with recently invented quintuple friction pendulum isolators , with different geometrical and frictional properties, under two different response spectra with corresponding two different sets of bidirectional near-field ground motions for stiff and soft soils site classes. In order to assess the accuracy of the simplified method, the delivered results of the ELF procedure are compared to those of nonlinear response history analysis, by modelling the quintuple friction pendulum isolator 3D element in OpenSees. Eventually, comments on the accuracy of the simplified method are given to make its applications more appropriate in practical design of base isolation systems.

The effect of ground motion vertical component on the seismic response of historical masonry buildings: The case study of the Banloc Castle in Romania

The current paper aims at analysing the effect of ground motion vertical component in the case of near-field excitations on the structural response of historical masonry buildings. In this perspective, the Banloc Castle in Romania has been considered as a reference case study. This historical masonry structure was damaged by the Banat-Voiteg earthquake that occurred in December 1991 in the homonymous city. To this purpose, a FEM model of the building, set up using the DIANA FEA analysis software, has been studied in the non-linear dynamic field considering a real ground motion record based on specific source-to-site distance, moment magnitude and focal depth. The effects of the impulsive earthquake have been evaluated considering the main engineering demand parameters, such as displacements and forces, focusing on two different scenarios, namely horizontal and horizontal + vertical ground motions. The obtained results have shown that the vertical ground motion sensibly modifies the structural capacity of the building since it produces a relevant modification of the in-plane walls behaviour and the stress conditions. Important considerations about the behaviour (or seismic response modification) factor, ductility and stress in terms of axial and shear forces have been provided. Moreover, numerical damage patterns have been compared to the real cracks detected. Finally, a set of fragility curves has been derived taking into consideration the near-field effects.

Quantification study for roof truss subjected to near-fault ground motions

The effects of vertical seismic excitations have a considerable destructive potential for long-span structures, particularly for near-field earthquakes. A quantification analysis is carried out in this paper to describe the response of a 25-m long trapezoidal truss frame with a height of 9 m under Vertical Ground Motion (VGM) with the help of eight near-field seismic excitations. Linear analysis of earthquake load combinations, including VGMs, has been conducted. The VGMs are leading the design of the long-span roof truss rather than the wind load. The time history analysis is therefore performed for horizontal ground acceleration and horizontal plus vertical acceleration using SAP 2000. For this analysis, eight near-field earthquake ground motion records consisting of four with pulse and four without pulse from the PEER NGA database, consistent with the ATC-63 requirements, are selected. The response of the structure is observed in different parameters such as the axial force of the column, the vertical displacement of the ends of the roof truss and the edge of the truss, the axial load of the bottom truss, and the base moment. This work quantifies the effect of vertical seismic excitations on a long-span industrial trapezoidal truss and demonstrates the need for a time history study of the VGM component.

Interval Type-2 Fuzzy Hybrid Control of a High-Rise Building Including Soil–Structure Interaction Under Near-Field and Far-Field Ground Motions

The interval type-2 fuzzy logic controller (IT2FLC) has emerged as one of the most effective high-tech control strategies to improve the performance of structures under near-field and far-field ground motions. The present study discusses the application of this strategy in the hybrid control of the behaviour of a real high-rise shear building by considering soil–structure interaction. In this regard, a hybrid control technique, consisting of a tuned mass damper (TMD) and a magneto-rheological (MR) damper is proposed. Using an MR damper on a TMD (MR + TMD) helps to reduce the seismic responses of a high-rise building in soil–structure interaction. The utilization of this hybrid device is very useful because it does not require huge power sources. By applying the observer–teacher–learner–based optimization (OTLBO) method, the fuzzy rules of IT2FLC, the TMD parameters, and the voltage of the MR damper have been optimized for a fifteen-storey shear building under four seismic near-field and far-field excitations. Minimization of the peak displacement of the top floor by using the square root of sum of squares (SRSS) of each response to each earthquake was utilized as the optimization criterion. Then, the optimized type-2 fuzzy rules and optimized TMD parameters were examined under seven new earthquake records in the fifteen-storey building. The results obtained by comparing the proposed control and uncontrolled systems in terms of the structure interaction with soft and dense soils show that the IT2FLC- using OTLBO is an efficient control method. It is also shown that the responses of this building to the hybrid controller have been effectively improved.

Near-field earthquake performance of SC-BRBs with optimal design parameters of SMA

Self-centering buckling-restrained braces (SC-BRBs) utilizing the re-centering potential of shape memory alloy (SMA) bars are used to control the excessive residual drift response of braced frames under seismic loading. The effectiveness of SC-BRBs in controlling the seismic response of a structure largely depends on the relative strength and stiffness of SMA bars and BRB core plates. This study is focused on determining the optimum length and prestressing force levels in SMA bars to maximize the hysteretic energy dissipation and re-centering behavior of SC-BRBs and evaluating the drift response of a medium-rise braced frame under near-field earthquake excitations. The seismic performance of SC-BRBs has been numerically investigated at both component (local) and frame (global) levels using a computer software OpenSees. Both length and prestressing force in SMA rods are varied in the numerical models to evaluate the axial resistance and hysteretic energy dissipation potential of SC-BRBs. The hysteretic response of SC-BRBs is compared with that of conventional BRBs. Nonlinear dynamic analysis has been conducted on a 9-story braced frame equipped with SC-BRBs as well as BRBs under forty near-field ground motion records. The seismic drift response of braced frames equipped with SC-BRBs with different prestressing force levels is compared with that of BRBF. Based on the findings of this study, the optimum geometric parameters of SMA bars have been proposed for the design of SC-BRBs.

Seismic Control of Cable-stayed Bridge Using Negative Stiffness Device and Fluid Viscous Damper under Near-field Ground Motions

ABSTRACT Under near-field ground motions, fluid viscous dampers (FVDs) are effective in controlling deck longitudinal displacement but lead to the increase of bending moment and shear force at tower base. Negative stiffness (NS) devices are introduced in combination of FVDs for the bridge. The NS devices lengthen the fundamental vibration period of the bridge to reduce the spectrum acceleration whereas FVDs introduce extra damping to the bridge system to reduce the deck displacement. After implementing NS devices, designers have more options of designing FVDs for seismic control of the cable-stayed bridges while maintaining the design requirements under near-field seismic excitations.