Acceleration Response Of Structure Research Articles

Global performance of multi-story stiffness-eccentric RC structures subjected to progressive seismic excitations: Shaking table investigations

Asymmetric structures have demonstrated poor seismic performance while experiencing major earthquakes in the past. Such structures exhibit complex vibration characteristics under seismic shaking as there is coupling between the lateral and torsional components of vibration. These coupled vibrations tend to cause weak locations under torsional distress, which eventually leads to the global failure of the structure. This paper presents the experimental evaluation of a plan-asymmetric structure with stiffness eccentricity. The experimental investigation was conducted by means of shake table testing on a 1/4-scaled reinforced concrete (RC) frame shear wall structure exposed to progressive seismic excitations. The structural response is monitored from a global failure perspective both in the elastic and inelastic states under increased torsional vibrations. The experimental findings indicate that: (1) irregularities in a structure can lead to significant amplification of the dynamic response due to induced torsional vibrations (2) the damage in the structure influences the dynamic properties of the structure, which eventually tend to influence the global structural response (3) structural acceleration response is more sensitive to seismic excitations and appears to have more influence on local oscillations compared with structural displacement response and (4) floor rotations excessively increase with the increasing damage state of the structure. Based on the physical inspection and extracted measurements, the shear wall sustained severe damage, whereas beams and columns at the flexible edge of the structure formed plastic hinges in critical zones.

Shaking table test study on seismic performance of RC frame structure with NES

A new type of nonlinear vibration absorber NES (Nonlinear Energy Sink) studied in this paper belongs to the structural passive control technology, which consists of a horizontal track and an additional mass block. Acting as a damper absorb and dissipate energy, the NES completes the target energy transfer by generating a horizontal nonlinear restoring force and reduces the response of the main structure. In this paper theoretical analysis of the new NES was analyzed by the expression of the restoring force of the NES and the equation of motion of the additional NES system are deduced. Shaking table test was carried out on the 1:4 scale RC frame structure model installed with the new NES shock absorber, focusing on the research on the energy dissipation and shock absorption effect of the NES shock absorber, and whether it can improve the seismic performance of the RC frame structure damaged in the earthquake. The results show that the NES installed in the RC frame structure has sufficient nonlinear displacement and energy dissipation capacity under the moderate and strong earthquakes, showing a very good energy dissipation and shock absorption effect. The NES can reduce the top story displacement and acceleration response of the main structure under the action of earthquake; the top story displacement and absolute acceleration response are related to the natural frequency of the frame and the spectral characteristics of seismic waves, so that the vibration control effect is affected by the frequency spectrum of seismic waves. In the frequency domain analysis of the frame dynamic response, the nonlinear energy well exhibits the characteristics of broadband control. This type of NES significantly reduces the seismic response of damaged structures, improves the seismic performance of damaged structures under moderate to strong earthquakes, and decreases the risk of potential collapse and construction costs during earthquake aftershocks.

Novel triple friction pendulum-tuned liquid damper for the wind-induced vibration control of airport control towers

The airport control tower has been widely constructed for rapidly expanding transportation demand, whose anti-wind performance and high-efficiency upgrading technology are attracting increasing attention. To provide an efficient liquid-incorporated solution for wind-induced vibration control of airport control towers, this study proposes a novel triple friction pendulum tuned liquid damper (TFPTLD) and establishes a control demand-oriented design framework to facilitate the design of TFPTLDs. The configuration and theoretical analysis model of the TFPTLD are introduced, based on which the TFPTLD-equipped tower-like structure is established. Stochastic response analysis is performed to obtain the responses under stochastic wind and white noise. Correspondingly, extensive parametric research is conducted to explore the optimal parameters and clarify the vibration control demand-oriented design procedure and easy-to-use fitted design formula for the TFPTLD. Furthermore, a robustness investigation is undertaken to quantify the advantages and sensitivity of the TFPTLD to the stiffness and damping components. Finally, the TFPTLD is applied to an airport tower subject to experimental wind loads to illustrate the effectiveness of the devices and proposed design method. The results show that the proposed TFPTLD yields a compact solution to the high-level performance upgrading of the airport control tower subjected to wind excitations, which significantly reduces the structural acceleration and displacement responses. Following the proposed demand-oriented design method, the TFPTLD exhibits higher effectiveness, larger frequency bandwidth, and more robust wind-induced vibration control than conventional TLDs with the same liquid mass. Benefitting from the triple friction pendulum, a small installation space is required, and the tuning effect of the liquid mass is independent of the change in liquid mass, which can be comprehensively utilized for vibration control to maintain the daily function of liquid tanks.

A benchmark shaking table test on the seismic responses of an extra‐large LNG storage tank

AbstractIn recent years, many large‐scale liquefied natural gas (LNG) storage tanks have been built all over the world. Due to their high constructional cost and important functions to the public, the academic and engineering communities are very concerned with the operational safety of these important infrastructures once subjected to potentially disastrous actions, that is, earthquakes, typhoons, tsunamis, and so forth. This work presented a benchmark test in evaluating the aseismic performance of extra‐large prestressed reinforced concrete (RC) LNG storage tanks. A 1:14 scaled model of the prototype LNG tank was designed and constructed for shaking table tests. Two recorded and two artificial earthquake ground motions with peak ground acceleration (PGA) up to 1.2g were selected successively as seismic inputs to the tank. The acceleration, displacement, shear force, and strain responses of the model structure were presented, analyzed, and discussed in detail. It was found that due to the differences in the frequency spectra, the seismic excitations have distinct influences on the responses of the tank model. In particular, the wall‐roof junction was detected as the weakest part of the outer tank, and the filling water had non‐negligible effects on the overall seismic responses of the tank. Verified finite element simulations were also presented as supplements to the experimental study. Some suggestions were made with the aim to improve the designs of LNG storage tanks.

Experimental Investigation on Vibration Control of a Suspended Particle-Tuned Liquid Damper

The particle-tuned liquid damper (PTLD) can combine the functions of baffles and energy-dissipating materials, such as highly viscous liquids, by integrating the particle dampers into a conventional tuned liquid damper (TLD). However, the particles distributed only at the bottom of the container cannot drive the motion of water in the middle layer to function effectively. Therefore, a suspended particle-tuned liquid damper (SPTLD) is proposed in this study and its effectiveness and reliability are examined compared with the conventional TLD through shaking table tests. Based on the experimental results, a parametric analysis of the SPTLD is further conducted to investigate the damping mechanism of the SPTLD, including the number of particles, the excitations with various amplitudes, and the use of suspended versus floating particles in liquid. The test results revealed that SPTLD successfully controlled the structural acceleration responses under seismic excitations with good reliability; the peak acceleration response was reduced by 67.4% and the RMS value was reduced by 75.9%. In the SPTLD, the particles filled in the container can drive more liquid to effectively participate in the sloshing motion, and the superimposed damping effects involving collisions and the energy-dissipation mechanisms of buoyancy and hydraulic resistance in the SPTLD lead to an improvement in the vibration control performance. Furthermore, the comparison of SPTLD and the floating particle-tuned liquid damper (FPTLD) demonstrates the better availability of SPTLD in practical applications, especially for some slender structures with limited plane space on the top floor.

Container Quay Crane Structural Response under Trolley Traveling

Structural response of quay crane should take more attention with the growth of worldwide logistics demand and quay crane size. This paper analyzes the response mechanism of the metallic structure of the quay crane induced by trolley traveling. An on-site test has been conducted. The time domain of crane girder acceleration signal shows that the main influence of the trolley traveling on crane structure is the high-frequency impact passing through the hinge point. The spectrum shows the main frequency of structure vertical vibration and impact vibration. Single girder model and theoretical derivation reveal that the vertical displacement response is quasistatic. A refined numerical model of the whole crane structure is established. The interaction between the trolley and the girder is realized by S-M contact method. The calculated results are basically consistent with the measured signal. The acceleration result indicates the same information as on-site test such that the structural acceleration response of in-service crane is affected by trolley in high-frequency band. The displacement results in three directions of 10 points on the girder show that the trolley traveling has significant effect on the vertical displacement. The lateral displacement shows the eccentric loading condition of girder. The displacement spectrum indicates that the trolley has little dynamic effect on displacement response of crane structure. The response can be treated as quasistatic.

Seismic performance improvement of base-isolated structures using a semi-active tuned mass damper

Base isolation can achieve a reduction in floor acceleration and inter-story drift. However, it may suffer from excessive displacements under near-fault and far-field earthquakes. To improve the aseismic performance of passive base-isolated structures, in this paper, a semi-active tuned mass damper (STMD) with variable stiffness and damping is presented. A combined control algorithm based on output signals only is developed for the STMD first. Then, the STMD is applied to an eight-story linear base-isolated structure and also a nonlinear one. As for the linear model, which represents a theoretical benchmark, an optimized passive TMD (PTMD) is used for comparison. As for the nonlinear model, lead rubber bearing (LRB) is considered and simulated using the well-known Bouc-Wen model. Eight earthquakes with different spectral characteristics and peak ground amplitudes are chosen, and two PTMDs are optimized for comparison, while one is tuned to the pre-yield period of the base-isolated model and the other is tuned to the post-yield period of the base-isolated model. Numerical results show that, generally, STMD has the best control effect in both linear and nonlinear models. For displacement responses, because STMD can vary its stiffness and damping, it can mitigate the structural first-mode response effectively, and can achieve both top story and isolated level responses reduction. As for acceleration responses of the top story, STMD achieves excellent performance in the structural second-mode acceleration response mitigation. Therefore, STMD can improve both displacement and acceleration performances of both linear and nonlinear base-isolated structures effectively.

Seismic Structure-Soil-Structure Interaction between a pair of buildings with consideration of rotational ground motions effects

During an earthquake, buildings are analysed dynamically without any consideration of their neighbouring structures and usually this also neglects the influence of surficial rotational ground motion. Population growth and increased land costs have increased the spatial density of buildings in urban areas. This closer proximity of buildings to one another leads to more complex interactions between buildings and the surficial seismic ground motion field that includes both horizontal and rotational components. To address these issues, this paper explores the Structure-Soil-Structure Interaction (SSSI) between a pair of buildings, including the surficial horizontal and rotational ground motions. A reduced-order parametric model of this complex system is proposed. Ground accelerogram data recorded from the 6-DOF sensor SINAPS@ Kefalonia (Greece) post-seismic experiment and the SMART-1 array in Taiwan were employed. This extensive parametric study analyses over six million system/ground motion cases. Results suggest that the rotational ground motion can affect the seismic response when the SSSI is considered, producing an additional amplification of acceleration responses of certain structures. The impact of the rotational ground motion depends principally on the fundamental natural period of the building, and the SSSI depends mainly on the frequency ratio (here Ωb) between the buildings.

Structural damage assessment through a new generalized autoencoder with features in the quefrency domain

Recently, the challenges in modeling complex dynamical systems, and the advancement in machine learning methodologies have indicated a new promising direction for damage assessment in civil and mechanical systems. Powerful and efficient data-driven approaches have been increasingly employed in Structural Health Monitoring (SHM) to extract Damage Sensitive Features (DSFs) from the monitored dynamic response of structures. In this study, a New Generalized Auto-Encoder (NGAE), integrated with a statistical-pattern-recognition-based approach that uses the power cepstral coefficients of structural acceleration responses as DSFs, is proposed for structural damage assessment. This NGAE is well-generalized in the components of cepstral coefficients that represent the structural properties of the entire system thanks to a newly defined encoder-decoder mapping, which largely reduces rid of the data variance attributed to different types of excitations and measurement noise. The cepstral coefficients, by virtue of a compact representation of the structural properties, can greatly simplify the structure of the NGAE, and therefore, significantly accelerate training and inference speeds with very few computational requirements. Two specific evaluation metrics that relates to the autoencoder signal reconstruction error are defined and used to assess the presence of damage. The proposed method has been validated through numerical simulations and experimental data, and shows better performance compared to a Traditional Auto-Encoder (TAE) and the Principal Component Analysis (PCA).

Identification of Wind Loads on Structures Based on Modal Kalman Filter with Unknown Inputs

Wind loads on structures are difficult to directly measure, so it is practical to identify structural wind loads based on the measurements of structural responses. However, this inversed problem is challenging compared with conventional load identification as wind loads are time-space coupled and spatially distributed dynamic loads on structures. An improved method is proposed for identifying wind loads on structures using only partial measurements of structural acceleration responses in this paper. First, the wind loads on a structure are decomposed by proper orthogonal decomposition as a series of time-space decoupled sub-distributed dynamic loads with independent basic spatial distribution functions and time history functions. Herein, structural modes are adopted as the basic spatial distribution functions and structural modes of discretized and continuous structural systems are investigated. Then, a history function of the decomposed wind load is identified in the modal domain based on modal Kalman filter with unknown inputs, which is proposed by the authors. Finally, the distributed wind loads are reconstructed for discrete or continuous structural systems. The feasibility of the proposed algorithm is verified by two numerical examples of identification of wind loads on a discrete shear frame and a wind turbine tower, respectively.

Enhancement of nonlinear signal-based control to estimate earthquake excitations from absolute acceleration responses of nonlinear structures

This study constructs an inverse method for multi-storey structures with nonlinear hysteretic characteristics commonly used in earthquake and structural engineering. Constructing the inverse methods, which accurately reconstruct an input signal from a response and structural information, has been challenging owing to the severity of the nonlinear characteristics as well as structural complexity. Nonlinear signal-based control (NSBC) can achieve the exact input estimation from a nonlinear structural response when its linear model is exactly invertible. However, its estimation accuracy decreases when the exact inversion of the linear model is impossible, and an approximation is required. This study introduces a controller design consisting of three enhancements of NSBC to realise accurate input estimation even when the inversion requires an approximation; the estimation of an earthquake excitation from acceleration in the absolute coordinates of nonlinear structures is a typical example. The first enhancement is the improvement of a differentiator used to convert an improper inverse model into a proper one. The second is the zero-stiffness design wherein the stiffness of all storeys in the linear model is intentionally set to zero. The third is the addition of inner-error feedback actions to conventional NSBC controllers. The effectiveness of these enhancements is examined via numerical simulations of the input estimations of nonlinear 2/4-degree-of-freedom (2/4DOF) systems shaken by an earthquake excitation. The enhanced NSBC successfully estimates the earthquake excitation with 100% accuracy from one known absolute acceleration response of the nonlinear 2/4DOF systems. Its potential application for estimating earthquake excitations by realising a predetermined response on nonlinear structures is also analysed.

Seismic Response Study of L-Shaped Frame Structure with Magnetorheological Dampers

To analyze the multi-dimensional seismic mitigation performance and the torsional vibration characteristic of an L-shaped frame structure with a magnetorheological damper (MRD). Firstly, the mechanical property of the MRD is experimentally studied. Then, the calculation models of the L-shaped frame structure without and with MRDs are found through theoretical analysis, and the programs of the calculation models are compiled. Finally, the time history responses of the calculation models are calculated during the excitation of bi-directional seismic wave; the responses of displacement, acceleration, story drift ratio, shear force and bending moment and torsional vibration are then compared and analyzed. The results show that by adjusting the current, the damping force provided by the MRD can be adjusted continuously in the range of 3.1 to 120 kN. The compiled calculation model programs of the L-shaped frame structure without and with MRDs can effectively simulate the multi-dimensional seismic response of the structure. Reasonable arrangement of MR dampers can effectively reduce the displacement, acceleration, shear force, bending moment, multi-dimensional vibration, and torsional vibration response of L-shaped frame structures.

Response control analysis of a new mega‐subcontrolled structural system (MSCSS) under seismic excitation

SummaryThe mega‐subcontrolled structural system (MSCSS) was proposed in the past decade as a new construction technique for high‐rise buildings because it showed an improved structural seismic response. However, research continues to focus on further increasing the response control ability, minimizing the cost, and improving the seismic performance of MSCSS. In this paper, a novel configuration named configuration 13 is proposed that incorporates an inverted V‐bracing (chevron) along the height in the center of the structure, and a mid‐story isolation system is situated under the first mega‐beam. The response control analysis and dynamic characteristics of the novel MSCSS are studied based on the structural responses to seven seismic waves. This novel configuration shows a significant improvement of at least 30.58% in the structural acceleration response with an average overall improvement of 49.7% under an El Centro wave. Moreover, nonlinear dynamic analysis is performed under the same seven waves; the proposed configuration shows the maximum pseudo‐spectral acceleration under the El Centro input at low frequencies, while under the Kobe wave, acceleration peaks also appear at higher frequencies. Furthermore, the Hilbert–Huang transform is also applied, confirming that the proposed MSCSS shows no sudden fluctuations in its structural response under seismic excitation.

Shaking table test research on shear behavior of cross-fault geosynthetics reinforced and pile-supported embankment

Severe damages are likely to occur to the cross-fault embankment under seismicity due to shear behavior caused by the fault relative displacement, which will inevitably affect the operation of the railway lines. Previous researches on seismic shear behavior of the cross-fault embankment are mainly based on numerical simulations. To study the seismic shear behavior of the cross-fault embankment experimentally, shaking table tests were performed on two types of scaled-embankment models: the first one is the through-facing-geosynthetics reinforced and pile-supported embankment (TRPE), the second one is the wrapping-facing-geosynthetics reinforced and pile-supported embankment (WRPE). In the tests, reverse seismic excitations were inputted to two adjacent shaking tables simultaneously to simulate fault movements. The test results show that the impact of strike-slip movement is greater than thrust movement, and their coupling effect aggravates the acceleration and deformation responses of embankment structure. Under seismic excitation and filing-step effect, pore water pressure increases especially in WRPE which aggravates the deformation of piles. The comparison of seismic responses of TRPE and WRPE show that the TRPE presents better seismic performance than WRPE in cross-fault zone. The WPRE is more cost-effective. To guarantee the safety of the WRPE in cross-fault zone, the length of geogrid in WRPE should be long enough.

Topology optimization of proportionally damped structures under harmonic excitations: Analysis of velocity and acceleration responses

Topology optimization of proportionally damped structures subjected to harmonic excitations within a frequency interval is a challenging task. In this work, we consider the structural velocity and acceleration responses in a frequency interval as the optimization objectives. The optimized structures will be significantly different from those with the displacement response only due to the influence of excitation frequencies. In particular, if the acceleration amplitude of structural frequency responses in a frequency interval is considered, the optimization process usually converges to a configuration that is unable to ensure engineering feasibility. An optimization model that takes the structural static response of the structure as a weighted part of the objective function is proposed, it can make the optimized configuration more applicable for engineering design. An efficient method for calculating frequency responses over a frequency interval is also introduced. The derivatives of the objective function are derived by the adjoint method and can be calculated in a manner similar to the frequency response. Two illustrative examples are given to examine the accuracy and validity of the proposed method.

Shaking table tests and parametric analysis of dynamic interaction between soft soil and structure group

Dynamic interaction between soil and structure group (SSGI) has received increasing attention due to higher requirements for urban seismic hazard prevention in recent years, especially in densely built areas. However, investigations on SSGI effects are still limited so far. To develop a better understanding on the SSGI effect, shaking table tests were conducted on a series of soil-structure and soil-structure group systems, where the influence of structure height, the number of structures, the composition of structure group and seismic records was considered. Besides, a three-dimensional numerical model was proposed to account for the SSGI effect and was verified through experimental results, based on which parametric analyses were conducted. It is found from the test results that as compared with the soil-structure interaction (SSI), the SSGI effect on accelerations at the top of the superstructures ranged from −40% to 27%. In general, the SSGI effect is significant for soft soils, and increases with larger number of structures and smaller structure spacing. In addition, the SSGI can change the response spectra of ground acceleration and significantly alter the maximum Fourier amplitude of acceleration responses of structures.

Using Two Sensors for Damage Detection of Bridge Based on Transfer Entropy of Vehicle-bridge Information

An innovative damage identification method using only two sensors for damage detection of bridge based on transfer entropy of vehicle- bridge information is proposed in this article. In this method, a test vehicle passing through the bridge surface, and structural vibration acceleration responses at two measuring points are measured from two acceleration sensors, which one set on the bridge, and the other one set on the test vehicle. A fixed moving window is defined as a definitive length calculated by the sampling frequency and the fundamental frequency of the measured acceleration responses. The windowed pair time series extracted from the two measured acceleration responses that obtained from the bridge and the moving vehicle respectively are used to calculate the transfer entropy, which is used to define the new damage index. A simply supported beam bridge subjected to a test vehicle is simulated to verify the effectiveness and feasibility of this method. Numerical simulation results show that this method can accurately detect the damages under both single damage scenarios and multiple damage scenarios using acceleration responses obtained from bridge and moving vehicle. It indicates that the method proposed in this article has a promising application prospect in the field of bridge damage detection.

A periodic seismic isolation foundation with an extremely broad low-frequency attenuation zone: Theoretical analysis and experimental verification

The attenuation zones (AZs) of periodic structures can be used for seismic isolation design. To cover the dominant frequencies of more seismic waves, this paper proposes a new type of periodic isolation foundation (PIF) with an extremely wide low-frequency AZ of 3.31 Hz–17.01 Hz composed of optimized unit A with a wide AZ and optimized unit B with a low-frequency AZ. The two kinds of optimized units are obtained by topology optimization on the smallest periodic unit with the coupled finite element-genetic algorithm (GA) methodology. The transmission spectra of shear waves and P-waves through the proposed PIF of finite size are calculated, and the results show that the AZ of the PIF is approximately the superposition of the AZs of the two kinds of optimized units. Additionally, shake tests on a scale PIF specimen are performed to verify the attenuation performance for elastic waves within the designed AZs. Furthermore, numerical simulations show that the acceleration responses of the bridge structure with the proposed PIF are attenuated significantly compared to those with a concrete foundation under the action of different seismic waves. Therefore, the newly proposed PIF is a promising option for the reduction of seismic effects in engineering structures.

Design of a pair of isolated tuned liquid dampers (ITLDs) and application in multi-degree-of-freedom structures

The tuned liquid damper (TLD) has been proven as an effective vibration mitigation device. However, it is less efficient and robust under seismic excitations. Addressing this issue, this study proposes a dual-mode-based design methodology utilizing a pair of isolated TLDs (ITLDs) for the multi-performance vibration mitigation of multi-degree-of-freedom (MDOF) structures. Oriented by the dual-mode control target, a series of 2DOF structures were considered, and a mechanical model of the considered ITLD was established. The modal analysis was performed for the primary structure, on the basis of which feasible installation methods for the ITLDs are proposed. Correspondingly, an extensive parametric analysis and a frequency response analysis were conducted, which revealed the control advantages of a pair of ITLDs, and we explored the potential optimal design for the liquid mass and added isolation layer. Inspired by the parametric analysis results, a mode-based design procedure is proposed for a pair of ITLDs by incorporating the modal characteristics of the primary structure. Finally, the ITLDs were applied in a multi-story building structure to illustrate the effectiveness of the devices and proposed design method. The obtained analysis results show that the dual-mode mitigation effect can be satisfactorily achieved using a pair of ITLDs with the proposed design approach, as well as synthetic functionality of the pair of ITLDs. The employment of a pair of ITLDs provided effective and robust mitigation of seismic responses for MDOF structures, yielding an improved multi-response reduction compared with the TLDs with the same parameters. In particular, the seismic-excited structural acceleration responses can be suppressed for different floors, which cannot be achieved by conventional TLDs.

Frequency domain analysis method of tuned liquid damper controlled multi-degree of freedoms system subject to earthquake excitation

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.