Time History Response Research Articles

Comparative Study on Seismic Performance of Existing Building with and without Retrofitting Using Lateral Load Resisting Systems

Due to the lack of awareness and practice of implementing earthquake resistant structures in the past, a huge number of buildings today do not comply with the existing/updated seismic codes in India. This issue is predominant in existing residential buildings which involves a high probability of loss of lives. The increase in population and clustered city areas make code non-compliance dangerous and risky especially in the Northern and North Eastern regions which come under seismic zones IV and V. Retrofitting strategies are thus an important aspect of building and life safety. This study involved the seismic performance of an adapted existing residential building taken in the North-East region. The seismic response analysis of the RC building was studied in terms of peak responses (deflection). The performance of the building was based on response spectrum and time history analysis. The main objective of this study is to provide a comparison between the most commonly used retrofit strategies – shear wall, bracings and viscous dampers. The responses of the building with the mentioned strategies and their varied configurations were modelled and analysed through ETABS software. This study outlined the feasibility of each retrofit strategy based on the optimum configuration for deflection control and basic cost estimate.

Nonlinear Seismic Analysis of RC Elevated Liquid Storage Tanks

Liquid storage tanks are strategically important due to their essential requirement of service in the post-earthquake situation. Numerical modeling of the liquid storage tank needs special attention and cannot be done in the same manner as that of the conventional buildings. In the present paper, a numerical simulation of the RC elevated liquid storage tank is presented. The staging of the tank is modeled as a multi-degree freedom system, and the container with contained liquid is modeled as a two-mass system. Free vibration analysis of the tank is carried out, and mode shapes are extracted. Further, to study the seismic response of the tank, nonlinear time history analysis is carried out. The tank is subjected to time histories of real earthquake ground motions. The varying level of the liquid in the container is another characteristic feature of tanks. The filled condition of the tank is taken into account by considering the aspect ratio (S), defined as the ratio of height of the liquid to the radius of the container. The response of the tanks with two different aspect ratios viz. 0.5 (broad) and 2.0 (slender) is studied. The linear modal analysis also carried out to understand the significance of nonlinear analysis, particularly in liquid storage tanks. Displacement, velocity, and acceleration response at the bracing levels, as well as at container levels, are obtained. Additionally, the base shear response is also obtained. The effect of aspect ratio on the free vibration analysis and the seismic response of the tanks are presented. Liquid storage tanks are special structures that have typically low fundamental natural frequencies. The nonlinear time history response of the tank showed that the higher displacement and velocity response occurs at the convective level. It is found that the linear modal analysis significantly underestimates the response of the liquid storage tank.

Study on Seismic Response of Staggered Story Isolated Structure Under Long-period Earthquake

The staggered story isolated structure is a new type of isolated structure developed from the base isolated structure. It has great isolation performance under ordinary earthquakes. However, the problem of long-period earthquakes exists in many areas. The prolongation of the natural vibration period of the structure and the resonance caused by the low-frequency part of the long-period earthquakes should not be ignored. The research on the response of the staggered story isolated structure under the long-period earthquake is not perfect. Two finite element models of staggered story isolated structure were established and non-linear time-history response analysis were carried out under ordinary earthquakes and long-period earthquakes, which including near-fault pulse-type long-period earthquakes and far-field harmonic-like long-period earthquakes. Results show that the natural vibration period of the staggered story isolated structure is prolonged, the seismic response is reduced. Under long-period earthquakes, the story drift angle, bearing displacement, story shear, plastic hinges and stress damage of staggered story isolated structure are partly larger than those of ordinary earthquakes. Under the far-field harmonic-like earthquakes, isolation performance is significantly different from those under the near-fault pulse-type earthquakes. And there are significant differences between the two models. The structure has the characteristics of vertically irregular structures and the weak position of the structure is located near the isolation layer, so more attention should be paid to the project.

Closed-form solutions of dynamic vibration equations of seismically excited structures

Novel closed-form solutions of the dynamic vibration equations of seismically excited structures are derived by using the Laplace transform. Structures with single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) are considered and modelled as lumped mass systems. Several earthquake records with different peak ground accelerations (PGAs) are used to excite such systems. To be compared, time-history responses are obtained numerically by using Newmark’s step-by-step iteration method and analytically by the proposed approach. After conducting such comparisons, the proposed approach successfully computes the exact responses of seismically excited structures.

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

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

Dynamic analysis of monopile OWTs with viscoelastic dampers based on pole-residue method

The dynamic behaviour of monopile offshore wind turbines (OWTs) equipped with viscoelastic dampers (VE dampers) modelled by a fractional Kelvin–Voigt model is governed by a fractional differential equation. Most available methods to solve this kind of equation are limited to single-degree-of-freedom systems or simple deterministic loadings. Considering an OWT under either complex deterministic or random loadings, this work develops an efficient pole-residue method to evaluate its vibration. The key of the proposed method is to express the impulse response function with fractional derivatives into a pole-residue form. Then, the dynamic response time history and the response evolutionary power spectrum (EPS) are transformed into explicit solutions. In numerical studies, a monopile OWT with a VE damper subjected to irregular wind-wave loadings and nonstationary random earthquakes is investigated. Direct Duhamel integral and Monte Carlo simulations are utilized to verify their accuracy. After adding the VE damper, the deterministic response and the random EPS are significantly reduced. By conducting sensitivity analysis, we find that the growth of the fractional order of VE dampers leads to larger damping ratios of the OWT. Increasing the damping coefficient of the VE damper results in larger natural frequencies.

Vibration control of beams under moving loads using tuned mass inerter systems

Traditional tuned mass dampers (TMDs) have been proven efficient for the moving-load-induced vibration control of beams. However, a large tuned mass is required in TMDs to adjust the structural dynamic characteristics and achieve the demanded performance targets, which leads to additional dynamic effects and inconvenience of installation. The tuned mass inerter system (TMIS) is an ungrounded lightweight passive control device, which contains a suspended mass, a parallel-connected tuned spring and an inerter-based subsystem. In this study, the application and optimization of TMISs on vibration suppression of multi-span beam models under moving load series are investigated. Using the Bubnov-Galerkin integration method, the modal-superposition generalized system for specified modes of a beam with TMIS under successive moving load series is established. Then, a design strategy for TMISs is proposed to achieve the structural target performance demand by decreasing the moving load-induced resonant responses and attached tuned mass. In the optimization algorithm, the tuned mass ratio is taken as the optimal objective, and the limited dynamic response amplitude under different speed parameters is the constraint condition. A single-span simply supported beam with the TMIS under a moving load series is analyzed. The designed TMISs are tuned to the dominating mode with the maximum mass participate factor of the main structures. TMISs show good vibration mitigation compared to TMDs with equal tuned mass. Meanwhile, under the premise of identical structural performance demands, TMISs require less tuned mass than TMDs and achieve a lightweight control effect. The corresponding dynamic amplitude vs speed curves and time history response curves of beams with TMISs and TMDs are also depicted through comparative analyses. The vertical deflection and acceleration responses apparently decrease, and the resonance is mitigated due to the designed TMISs. The sensitivity analysis results indicate that TMISs attached to beams are insensitive to the perturbance of their parameters and the input moving load excitations; thus, TMIS proves to be a robust tuning system.

Quantitative Modeling of Pulse-Like Ground Motions Using Imperialist Competitive Optimization Algorithm

Increasing attention in quantitative and qualitative models has been paid to the dominant velocity pulse of the pulse-like ground motions. Manual trial and error approach for fitting of time history and response spectrum of the actual record and simulated pulse has been employed to obtain pulse parameters of these models. In this study, a mathematical model and the imperialist competitive algorithm (ICA) are used to overcome the limitations of the previous studies. For this purpose, an objective function is defined as the norm deviation of the time history and response spectrum of the actual record and simulated pulse. The proposed approach is capable of identifying and extracting the dominant pulse of any pulse-like record, and consists of 91 pulse-like records used in this study. In all of 91 records, the highest accordance with time history and elastic response spectrum of actual records and extracted pulses is achieved. As a case study, the extracted pulses of the 1999 Chi-Chi earthquake are used to generate artificial pulse-like records. The dynamic responses of the 3-story moment frame in SAC project subjected to generated records are investigated. The results show that the proposed approach can be used in parametric studies of pulse-like ground motions.

Influence of impact velocity on dynamic performance of reinforced concrete beams strengthened with CFRP

In order to study the impact resistance and dynamic damage rule of reinforced concrete (RC) beams strengthened with carbon fiber reinforced plastics (CFRP) under different impact velocities, four CFRP strengthened RC beams were tested by using a drop-hammer impact device. The analysis results of the failure pattern, crack propagation rule, dynamic time history response and energy dissipation of the strengthened beams show that with increase of the impact velocity, the width of the main bending crack in the mid-span of CFRP strengthened beam increases first and then decreases, and the width of the main oblique crack in the mid-span increases continuously. It can also be identified that overall crack distribution converges to the mid-span area. Furthermore, the peak impact force and the mid-span peak displacement are linearly dependent to the impact velocity. The energy dissipation capacity of strengthened beams increases nonlinearly with the increase of impact velocity. The greater the impact velocity is, the less the increase rate of the energy dissipation capacity of the strengthened beam is. In addition, four stages can be divided in the test based on development of mid-span displacement, which are linear growing, nonlinear growing, rebounding and stable stages, respectively. The study can provide reference for optimal design of RC beams strengthened with CFRP.

木造平面混構造のコア配置を考慮した設計用地震力の研究

Time history response analyses of horizontal hybrid wooden structures with RC core on one or both sides are conducted considering the elasto-plasticity of the wooden part with Wayne-Stewart model as hysteretic characteristics. Then, by comparing the results with the static elasto-plasticity analyses, the effects of amplification of wooden part and eccentricity are verified, and the consistency with the horizontal load-carrying capacity calculation, such as the setting of the structural characteristics factor DS, is confirmed to form a concrete background for the design of horizontal wooden structures.

The effect of cable corrosion on dynamic response of Stonecutters Cable-Stayed Bridge model

Cable corrosion is among one of the most common damage mechanisms in cable-stayed bridges. A finite element model of the long-span Stonecutters Cable-Stayed Bridge was built, and its dynamic behaviour was investigated considering localized groups of corroded cables. The reduction in cable cross-sectional area was used to simulate corrosion levels from 25% to 75% cross-sectional loss. The corroded cables were divided into two groups of four cables, arranged in symmetric and asymmetric distributions along both decks. Natural frequencies and mode shapes were compared with a reference case with no corrosion-damaged cables. A recorded wind load was applied on the deck to investigate the time-history response of the mid-span in lateral, vertical, and torsional directions. Frequency analysis was performed on the time-history response, and coupled motions at certain frequencies were observed for certain corrosion cases and were discussed.

Dynamic Response Identification of a Triple-Single Bailey Bridge Based on Vehicle Traffic-Induced Vibration Analysis

Even though prefabricated steel Bailey bridges have been used for more than 80 years, limited studies of their structural features have been conducted, most of which do not consider their response in operational conditions. This study aimed at determining the modal parameters of a 30.48 m length Triple-Single (TS) Bailey bridge based on traffic-induced vibrations and comparing them with numerical results. Low-cost improvised accelerometers recorded and logged the actual response time histories, while a three-dimensional (3D) numerical model was developed to carry out the relevant dynamic analyses. The identification of modal parameters was based on the Operational Modal Analysis (OMA) process and the Frequency Domain Decomposition (FDD) method. Numerical analysis results are in accordance with the operational dynamic response of the Triple -Single Bailey bridge, confirming that the numerical model can effectively be used for extended dynamic analysis. In addition, the analysis of raw time histories through the OMA process indicates that the response is affected by the connections’ condition, in particular, the eventual looseness of bolts and pins. At least five eigenfrequencies were estimated and matched with relevant mode shapes.

Field Measurement on Translational and Torsional Wind-Induced Response of a High-Rise Building during Typhoon Khanun

Full measurements for the wind field atop a 32-storey building (supported by four huge columns) and for the dynamic responses of different floors were conducted on 15 October 2017 to obtain the translational and torsional responses of the high-rise building during the Typhoon Khanun. The time histories of the torsional angular acceleration responses on the 24th and 32nd floors of the high-rise building were obtained using RA013 rotational accelerometer, and those of the translational acceleration responses on the 6th, 12th, 18th, 24th, 30th and 32nd floors along axial direction were recorded by the translational accelerometer. The variation rules of the translational and torsional acceleration responses with floor height and mean wind speed were disclosed, and the response ratios between the torsional and translational acceleration were analyzed when basic time intervals were 10 min. Based on the target probability method, the value range of the acceleration peak factor with different target reliability under Typhoon Khanun was proposed. The results show that the translational and torsional acceleration peak values and root mean squares are the power functions of mean wind speed. The values of acceleration peak factors are recommended to be 3.0 and 5.0 if target reliabilities are determined as 99.38% and 100%, respectively. Research on torsional response measurements can accumulate valuable scientific data and lay solid foundations for the subsequent studies on the torsional wind-resistant design of high-rise buildings.

Instability analysis of fluid-filled angle-ply laminated circular cylindrical shells subjected to harmonic axial loading

This paper presents the dynamic instability and nonlinear vibration analysis of fluid-filled laminated composite circular cylindrical shells subjected to harmonic axial loading. The shells are assumed to be simply supported and filled with still fluid. The mathematical model is prepared by using higher-order shear deformation theory (HSDT) which considers skew modes for accurate results in the analysis of angle-ply laminated composite cylindrical shells. The contained fluid is assumed to be non-viscous and incompressible. The nonlinear governing partial differential equations (PDEs) are obtained using Hamilton's principle, and these equations are discretised into ordinary differential equations (ODEs) by employing Galerkin's method. The pseudo-arclength continuation method along with the incremental harmonic balance (IHB) method is used in order to compute the nonlinear responses, which are plotted in the frequency domain. The regions of instability are determined by adopting Bolotin's method. The time history responses and phase portraits are also studied for empty and fluid-filled laminated cylindrical shells using the Newmark-beta method. A complete set of results that examine the effect of fluid filling, static load factor, dynamic load factor and lamination scheme are obtained.

Aeroelastic Experimental Investigation of Hyperbolic Paraboloid Membrane Structures in Normal and Typhoon Winds

The lightweight and flexible membrane structure of roofs are susceptible to wind loads with the risk of damage and failure. Compared with uniform and low-level turbulence flow cases (i.e., normal winds) that have been well investigated, the wind-induced vibration problem of membrane structures in high-level turbulence flows such as typhoons has been paid little attention. To address the gap, this paper aimed at investigating the aerodynamic behavior of hyperbolic paraboloid membrane structures in normal and typhoon winds by a series of wind tunnel tests. Some distinct wind characteristics of upcoming normal and typhoon flows in terms of vertical profiles of wind velocity, turbulence intensity, and power spectrum density of fluctuating winds were well simulated in an automatically controlled wind tunnel. The aeroelastic behavior of a scaled model was analyzed and discussed in terms of displacement time-history responses, probability distribution characteristics, and dynamic characteristics including the natural frequency, mode shape, and damping ratio. Results show that the increasing suction in a typhoon leads to significant growth in maximum deformations and more risks to suffer from aeroelastic instability. Non-Gaussian characteristics appear more remarkable with skewness and kurtosis increasing almost two-fold in typhoons. Structural modal parameters are influenced by both turbulence intensity and wind velocity. This study provides basic insights into the deficiency of dynamic response of membrane structures in typhoons, and promotes the applications of membrane structures in green buildings.

Measurement of flow fluctuations induced by a dielectric-barrier-discharge plasma actuator using hot-film sensors

Hot-film sensors have been used to measure the boundary-layer fluctuations and subsequently to determine the boundary-layer states. In this paper, it is proposed to use hot-film sensors as a tool to measure the effects of plasma-induced ionic wind on the boundary-layer fluctuations which can be used to find the influence of the plasma actuator far downstream of the actuator. Time history and frequency response of the hot-film output voltage are investigated to explore the effects of plasma-induced wind downstream of the actuator. Also, the effects of the peak-to-peak voltage of a DBD plasma actuator on the fluctuations of the hot-film output voltages are discussed. It is showed that as far as the effects of ionic wind can be sensed by the hot-films, the control authority of the actuator is higher. It is concluded that induced velocity in the vicinity of the plasma actuator alone does not indicate the control authority of the plasma actuator.

Interface debonding detection of grouted connection based on Lamb wave energy leakage

Grouted connections (GCs) are transitional elements that have been extensively employed in offshore wind turbine support structure to transfer loads from superstructure to foundation. However, interface debonding defects between steel tube and grout layer have an adverse effect on the durability and fatigue resistance of the GC. An effective interface debonding defects detection approach for GC is necessary. In this study, interface debonding defects detection approach based on Lamb wave energy leakage was proposed and validated numerically and experimentally. Numerical studies on Lamb wave energy leakage models and the GC models were performed to study mechanism of detection approach. Lamb wave is excited on the surface, and stress wave fields and time-history response of models were extracted and compared. Experimental investigations were carried out to verify the applicability of the proposed approach in practice. A scaled GC specimen was constructed and Lamb wave was excited by the PZT patches mounted on the surface of GC specimen. The output voltage of surface-mounted PZT sensors under different axial loads were compared. Both numerical and experimental results show that the proposed approach is effective to the detection of interface debonding defects. The damage evolution index (DEI) based on wavelet packet energy is defined and it can be adopted to qualitatively determine the initiation and evolution of the damage.

An efficient analytical approach to assess root cause of nonlinear electric vehicle gear whine

Noise, vibration, and harshness (NVH) issues pose considerable challenges for electric vehicle powertrain engineers. Gear vibrations generate an intrusive gear whine noise, with significant impact on the sound quality of electric powertrains. Dynamic transmission error (DTE) is the most quantitative indicator for gear NVH. Backlash, time variable meshing stiffness and damping contribute to DTE. Hence, a better understanding of these excitation sources is essential. A gear tribodynamics model is developed using potential energy method to estimate time variable meshing stiffness (TVMS). A fully analytical time-efficient model is proposed for lubricated contact stiffness based on transitions in the regimes of lubrication. The model accounts for the combined effects of surface elasticity and lubricant stiffness. Film thickness and damping coefficients are transiently updated at each instant during meshing cycle. The predictions from this model are compared with measured results from the literature and predicted results from Hertz contact model. The lubricated contact model successfully shows the contribution of the lubricant stiffness to TVMS and its variations with elasticity and viscosity parameters during meshing cycle. Gear harmonic and super-harmonic resonances are accurately estimated in terms of amplitude, frequencies and stiffness softening nonlinearities. Time history responses and phase-displacement diagrams show good agreement with the gear dynamics response at the main harmonic and second super-harmonic frequencies. The proposed model has a reasonable accuracy, significantly better than those from Hertzian contact models, and is considerably time efficient in comparison to numerical EHL solvers.

Theoretical and computational investigation of the fracturing behavior of anisotropic geomaterials

The fracturing process in geomaterials is studied to characterize a potential host rock for radioactive waste, such as the kaolinite-rich Opalinus Clay formation. Because of its sedimentary genesis, this rock can be considered as a transversely isotropic geomaterial. A semi-circular bending test is here modeled based on the eXtended Finite Element Method (XFEM), to check for the formation and propagation of cracks in the rock, with a particular focus on the effect of notch dimensions and scale effects on the fracturing response of the specimen in terms of peak load. Starting with the XFEM-based results, a novel analytical formulation is also proposed to approximate the response of the material in terms of load-crack mouth opening displacement. The proposed formulation is also capable to provide a reliable estimate of the peak value and time history response, compared to some experimental predictions from literature, starting from a predefined value of initial notch depth, which could represent a useful theoretical tool for design purposes.

Acceleration Based Condition Monitoring of Steel Bridges

This paper presents a frequency domain-based method for continuous health monitoring of steel truss bridge, based on the power spectral density and frequency analysis of the recorded acceleration response time histories at the selected node points of a bridge under regular operational conditions. This method is also implemented on a railway steel truss bridge connecting the mainland India to Rameswaram, named the Pamban bridge. The measured acceleration response time histories at some selected nodes on the bridge were parameterized into 4 power spectral density and frequency-based parameters. Also, the frequency analysis of the acceleration response time histories was done. The continuous variation of these parameters with measurement points was observed for about a year to investigate the suitability of these parameters to detect, locate damages in a railway steel truss bridge, and find their severity. Then, the consistency of damages detected by the variation of these parameters and the damages expected based on strain measurements and visual inspections made on the bridge was examined to evaluate the suitability of these parameters for the level 3 damage detection. The same is documented and performance of the parameters discussed.