Dynamic Magnification Factor Research Articles

Enhanced hybrid active tuned mass dampers for structures

Based on the recent research by Li and Cao in 2015, now taking the stroke mitigation as a target, the enhanced hybrid active tuned mass dampers (EHATMD) have been proposed in order to attenuate undesirable oscillations of structures under the ground acceleration. In accordance with the mode generalized system in the specific vibration mode being controlled (simply referred herein to as the structure) and continuing to make use of the negative normalized acceleration feedback gain factors scheme, the dynamic magnification factor (DMF) has been formulated for the structure furnished with an EHATMD. Then, the criterion for the optimum searching can be determined as the minimization of the minimum values of the maximum DMF (min.min.max.DMF). Employing the genetic algorithm, the effects of varying the key parameters on the optimum performance of EHATMD have been scrutinized in order to capture the expected performance. Furthermore, for a comparison, the optimum results of hybrid active tuned mass dampers (HATMD) with the same initial design parameters using both the genetic algorithm and negative normalized acceleration feedback gain factor scheme are also taken into consideration. Results of analysis have demonstrated that EHATMD outperforms HATMD and thereby may be regarded as a novel extension of HATMD.

Optimum design of a novel pounding tuned mass damper under harmonic excitation

In this paper, a novel pounding tuned mass damper (PTMD) utilizing pounding damping is proposed to reduce structural vibration by increasing the damping ratio of a lightly damped structure. The pounding boundary covered by viscoelastic material is fixed right next to the tuned mass when the spring–mass system is in the equilibrium position. The dynamic properties of the proposed PTMD, including the natural frequency and the equivalent damping ratio, are derived theoretically. Moreover, the numerical simulation method by using an impact force model to study the PTMD is proposed and validated by pounding experiments. To minimize the maximum dynamic magnification factor under harmonic excitations, an optimum design of the PTMD is developed. Finally, the optimal PTMD is implemented to control a lightly damped frame structure. A comparison of experimental and simulated results reveals that the proposed impact force model can accurately model the pounding force. Furthermore, the proposed PTMD is effective to control the vibration in a wide frequency range, as demonstrated experimentally.

Dynamic Performance Characteristics of Pre-Stressed Cable RC Truss Floor System under Human-Induced Loads

Excessive floor vibrations in slender structural systems due to human activity are becoming more prevalent. This may result in serviceability problems such as discomfort to occupants and even subsequent public panic. This paper describes the experimental and analytical studies on the vibration performance of a long-span pre-stressed cable RC truss (PCT) floor system, along with an extensive comparison between the present results and the current vibration design criteria used in the USA and China. The dynamic responses of this floor system under heel-drop, falling-into-seats, and jumping loads were obtained through on-site tests. The test results show good agreement in natural frequencies of the PCT floor system with others, but there are obvious differences in peak accelerations and damping ratios. A method based on the classical plate theory was adopted to determine the fundamental frequency of the system. Dynamic magnification factors (DMFs) under different loads were calculated using the inversion technique and then compared with the results available from others. Some of the conclusions achieved may be incorporated into the structural design of the system of concern to improve safety and serviceability. They can also serve as the basis for developing the relevant design guideline.

Simplified calculation methods for all-vertical-piled wharf in offshore deep water

All-vertical-piled wharf is a kind of high-piled wharf, but it is extremely different from the traditional ones in some aspects, such as the structural property, bearing characteristics, failure mechanism, and static or dynamic calculation methods. In this paper, the finite element method (FEM) and theoretical analysis method are combined to analyze the structural property, bearing behavior and failure mode of the all-vertical-piled wharf in offshore deep water, and to establish simplified calculation methods determining the horizontal static ultimate bearing capacity and the dynamic response for the all-vertical-piled wharf. Firstly, the bearing capability and failure mechanism for all-vertical-piled wharf are studied by use of FEM, and the failure criterion is put forward for all-vertical-piled wharf based on the ‘plastic hinge’. According to the failure criterion and P–Y curve method, the simplified calculation method of the horizontal static ultimate bearing capacity for all-vertical-piled wharf is proposed, and it is verified that the simplified method is reasonable by comparison with the FEM. Secondly, the displacement dynamic magnification factor for the all-vertical-piled wharf under wave cyclic loads and ship impact loads is calculated by the FEM and the theory formula based on the single degree of freedom (SDOF) system. The results obtained by the two methods are in good agreement with each other, and the simplified calculation method of the displacement dynamic magnification factor for all-vertical-piled wharf under dynamic loads is proposed. Then the simplified calculation method determining the dynamic response for the all-vertical-piled wharf is proposed in combination with P–Y curve method. That is, the dynamic response of the structure can be obtained through the static calculation results of P–Y curve method multiplied by the displacement dynamic magnification factor. The feasibility of the simplified dynamic response method is verified by comparison with the FEM under different conditions.

Performance of tuned tandem mass dampers for structures under the ground acceleration

It is widely acknowledged that the tuned mass damper (TMD) is one of the most effective and simplest passive control devices, but its limited control performance is still a troubling problem. In order to surmount the shortage of TMD, the tuned tandem mass dampers (referred herein to as TTMD) have been proposed for mitigating the undesirable oscillation of structures under the ground acceleration. Based on the formulation of the mode-generalized system in the specific vibration mode being controlled, the analytical expression is then derived for the dynamic magnification factor of the structure furnished with a TTMD. The optimum criterion can thereby be defined as minimization of the minimum values of the maximum dynamic magnification factor with a set of optimization variables embedded so as to give full play to the control device potential. The optimization implementation of TTMD is carried out by the MATLAB-based coding and debugging. For the purpose of a mutual authentication to the optimization results, three metaheuristic algorithms, namely, genetic algorithm, particle swarm optimization, and simulated annealing, are concurrently taken into consideration. Results demonstrate that the proposed TTMD endows with the superior stroke performance with respect to TMD.

Seismic performance assessment of blind bolted steel-concrete composite joints based on pseudo-dynamic testing

This paper aims to investigate seismic behavior and dynamic responses of semi-rigid composite joints composed of steel-concrete composite beams and concrete-filled thin-walled steel tubular (CFTST) columns. A range of pseudo-dynamic tests (PDTs) was performed on two full-scale blind bolted end-plate joint specimens, including one flush and one extended end-plate typed joint. The input ground motion adopted for the PDTs was Ispara seismic acceleration record and scaled to represent various seismic hazard levels. Using Ispara earthquake record with different peak ground accelerations (PGAs), a lot of useful data about hysteresis behavior, stiffness degradation and energy dissipation capacity was obtained. The data was also estimated in detail to characterize the seismic performance of this kind of composite joints. Dynamic responses of beam-to-column joint including displacement and acceleration responses, and dynamic magnification factor were discussed. The experimental results indicated that the structural responses of the test joints under seismic actions coincided with the desired performances analyzed for varying damage levels. The study affirms that the blind bolted end-plate composite joints to CFTST columns possess good energy dissipation seismic performance, so they can provide sufficient ductility and adequate strength to satisfy the seismic design requirement.

Vibration of bi-dimensional functionally graded Timoshenko beams excited by a moving load

This paper studies the vibration of bi-dimensional functionally graded Timoshenko beams excited by a moving concentrated load. The volume fraction of constituent materials is assumed to vary in both the thickness and longitudinal directions by power-law functions. The governing equations of motion based on Timoshenko beam theory are constructed from Hamilton’s principle. A finite element formulation is derived and used in combination with the Newmark method in computing the vibration response. A parametric study is carried out to highlight the effect of the material distribution and moving load speed on the vibration characteristics of the beams. The numerical results show that the two grading indexes which govern the variation of the effective material properties have opposite effect on the natural frequencies, dynamic magnification factor and mid-span axial stress. The influence of the aspect ratio on the dynamic behavior of the beams is also examined and discussed.

Parameter sensitivity study of dynamic response for jack-ups by FEM analysis

Jack-up platforms will generally behave as highly dynamic systems because of the structure flexibility. The environmental forces acting on these jack-ups will therefore induce significant dynamic response. In this paper, based on ANSYS, the three-dimensional model of a truss leg jack-up was built. With interaction of fluid–structure–soil being considered, a series of static analysis, modal analysis, and transient analysis were performed for the model with different dimensional or load parameters; and the dynamic magnification factors were calculated. Sensitivity of these parameters on the dynamic response of jack-ups were discussed in detail.

Accurate dynamic analysis of functionally graded beams under a moving point load

ABSTRACTBased on the physical neutral surface, an N-node novel weak form quadrature beam element is proposed and the explicit formulas for computing the stiffness and mass matrices are given. The proposed element is then used to analyze the dynamic behavior of the functionally graded material (FGM) beams under a moving point load. Both elasticity modulus and mass density vary exponentially across the thickness. Investigations show that the maximum dynamic magnification factors are independent of the power-law exponent k at a fixed nondimensional parameter α. This finding may be useful in design and engineering applications.

High Response Performance of a Tuned-Mass Damper for Vibration Suppression of Offshore Platform under Earthquake Loads

Currently, tuned-mass dampers (TMDs) are widely applied to maintain the stability of offshore platforms in hostile environments; however, the stability system of offshore platforms faces considerable challenges under critical earthquake loads of the initial period. Therefore, this study concentrated on the high response performance of a simple passive TMD system, and numerical and experimental investigations were performed using a 1 : 200-scale prototype. The obtained results indicated that the displacement, acceleration, and their power spectral density all decreased significantly for the offshore platform with the TMD system. By further analyses of its high response characteristics, it was validated that the TMD reactions can commence within the first 3 s of earthquake excitation, while the fundamental natural frequency was consistently tuned for the TMD system dependent on the dynamic magnification factor. The evaluation indices also confirmed that this method is effective in reducing the overall vibration level and the maximum peak values of the offshore platform exposed to earthquake excitations, mainly because of its high response characteristics.

Optimum Parameters for Tuned Mass Damper Using Shuffled Complex Evolution (SCE) Algorithm

This study is investigated the optimum parameters for a tuned mass damper (TMD) under the seismic excitation. Shuffled complex evolution (SCE) is a meta-heuristic optimization method which is used to find the optimum damping and tuning frequency ratio for a TMD. The efficiency of the TMD is evaluated by decreasing the structural displacement dynamic magnification factor (DDMF) and acceleration dynamic magnification factor (ADMF) for a specific vibration mode of the structure. The optimum TMD parameters and the corresponding optimized DDMF and ADMF are achieved for two control levels (displacement control and acceleration control), different structural damping ratio and mass ratio of the TMD system. The optimum TMD parameters are checked for a 10-storey building under earthquake excitations. The maximum storey displacement and acceleration obtained by SCE method are compared with the results of other existing approaches. The results show that the peak building response decreased with decreases of about 20% for displacement and 30% for acceleration of the top floor. To show the efficiency of the adopted algorithm (SCE), a comparison is also made between SCE and other meta-heuristic optimization methods such as genetic algorithm (GA), particle swarm optimization (PSO) method and harmony search (HS) algorithm in terms of success rate and computational processing time. The results show that the proposed algorithm outperforms other meta-heuristic optimization methods.

Parametric Selection of Dynamic Vibration Absorbers for Resonant Suppression of Structure-Absorber Systems

The selection of absorber parameters is of utmost significance for structural vibration control by dynamic vibration absorbers. Based on the classical frequency tuning approach by Den Hartog, optimal damping ratio is derived in close form by equating the dynamic magnification factors of the structural motion at three particular frequencies of interest. In addition, by maximizing the two identical modal damping ratios through root locus in the first quadrant of complex plane, the corresponding absorber damping ratio is derived and proposed as the upper bound of the absorber damping ratio for practical applications.

Shaking Table Test on 145 kV HV Reactor Composite Bushing

As a key component of power transmission and distribution systems, HV reactor bushing made of porcelain have suffered serious damage in previous earthquakes. In order to enhance seismic ability, the new type bushing made of composite material have been used in high seismic fortify-cation intensity projects. The test requirement in this analysis included: the selection of dynamic magnification factor、the selection of excited wave、the control of tolerance between input peak acceleration and output peak acceleration. During the shaking test, the dynamic characteristics, including frequency and damping ratio, and the seismic response of the composite bushing was obtained. Based on the analysis results of the bushing, the judgment of the seismic capacity was achieved.

Hybrid active tuned mass dampers for structures under the ground acceleration

Summary The hybrid active tuned mass dampers (HATMD)—a new control system—have been proposed to attenuate undesirable oscillations of structures under the ground acceleration. Based on the authors recent exploration, the performance of the active tuned mass damper (ATMD) with the negative normalized acceleration feedback gain factors (NNAFGF) scheme is better than that with the positive NAFGF (PNAFGF) scheme; therefore, the active control forces of the HATMD are generated by combined use of both the NNAFGF and PNAFGF schemes. In the light of the mode-generalized system in the specific vibration mode being controlled (simply referred here to as the structure) and accordingly deduced formulae, the expression then is defined for the dynamic magnification factor (DMF) of the structure furnished with the HATMD. Naturally, the criterion for the optimum searching can be determined as the minimization of the minimum values of the maximum DMF. By resorting to the selected criterion and utilizing a genetic algorithm, the effects of varying the key parameters on the optimum performance of the HATMD have been scrutinized both to arrive at the parameter combinations that make it best work and to make an attempt to shed light on the particular phenomena that for it there may exist. Furthermore, for the purpose of comparison, this study simultaneously investigates the optimum performance of both the ATMD and active–passive tuned mass dampers (APTMD) employing the proposed NNAFGF scheme. It is found in terms of numerical results that the HATMD outperforms both the ATMD and APTMD. Copyright © 2014 John Wiley & Sons, Ltd.

Research of Seismic Effect for Light Steel Structure with Added Stories

Light steel structure with added stories is a economic and effective method of strengthening design for existing buildings, and it is promoted and applied widely. But it still has some problems about computing of seismic action effect. The computing is not simply in accordance with the base shear method. The value of dynamic magnification factor which was counted as ß needs further research. In this paper, the value of is 2 on the basis of theoretical analysis and calculation example. The safety factor of the value is higher, and the design with the ß is more economic and reasonable.

Impact Response Spectrum for Design of Ship-Bridge Collisions

Due to the complexity involved and limited study on the topic, the equivalent static method, adopted in the current codes for structural design of bridges under ship collisions, does not take into account the dynamic amplification effect correctly. An accurate assessment of impact force based on refined numerical simulation is time consuming and is normally too complex for ordinary design procedure. Herein, with reference to the earthquake response spectrum method, an impact response spectrum method, which considers the dynamic amplification effect and is efficient for design, is proposed. Through refined numerical simulations of ship-rigid wall collisions, 81 impact force time histories associated with 9 typical ships under 9 velocities are obtained. The dynamic magnification factor (DMF) of single-degree-of-freedom (SDOF) systems with different periods and damping ratios experiencing the 81 impact force time histories are then studied. The relationship of DMF and period under different damping ratios, i.e. the DMF spectrum, is yielded by statistical analysis, based on which the impact response spectrum is obtained. Finally, the design combination method for multi-degree-of-freedom based on the impact response spectrum of SDOF is discussed for a continuous beam bridge.

Study on the Characters of Seismic Response Spectra Based on China Financial Information Mansion

Rare study is done on floor response spectrum of super-high rise building, but it is an important condition for the seismic response analysis of floor subsidiary structure. Therefore, based on the early calculation model of China Financial Information Mansion, the floor response spectrum is calculated under different input ground motion. The floor and ground response spectrum is compared with each other from the seismic coefficient, dynamic amplification coefficient, characteristic period and the form of response spectrum. The results shows that: the floor seismic coefficient and the magnification coefficient are greater or smaller than the ground ones, the biggest difference of which is nearly 1 times; all the floor character period are greater than the ground ones, the biggest difference of which is over 60%; there are obvious differences between the floor and ground dynamic magnification factor spectra form under some conditions, of which the second peak of the former one is probably very large, even near to the peak of the first one, while the latter has no such phenomenon. Therefore, during the process of calculating the seismic response of floor subsidiary structure, it is necessary to consider the change of floor seismic coefficient, dynamic magnification factor, characteristic period and spectra form based on the main structure.

DYNAMIC MAGNIFICATION FACTOR FOR CONCRETE WIDE BEAM UNDER FREE FALL LOADING

Present endeavor is devoted to investigate the dynamic magnification factor of concrete wide beams contain different sizes of steel fibers under the effect of impact forces. Many parameters were considered in the current work namely central wide beam deformation, length of the used steel fibers and failure modes of the wide beams. Twenty two wide beams have been used to perform current impact test. A finite element model has been constructed with considering 3D solid elements to simulate the performance of the wide beam. It is observed that the computed dynamic magnification factor of the beam is decreased with introducing long steel fibers in the concrete wide beam member. Good matching with correlation more than 80% has been found between present finite element modeling results and the experimental outcomes with using four-noded solid elements in the analysis

Analyzing Loads from Ice Shedding Conductors for UHV Transmission Towers in Heavy Icing Areas

In this paper, a finite element analysis (FEA) model of seven span continuous conductors and insulators for an ultra high voltage (UHV) transmission line in a heavy icing area was established for ice shedding analysis. The parameters considered in the ice shedding simulation analysis include damping ratio, ice shedding ratio, ice shedding modes, and ice thickness. The dynamic responses including jumping heights, unbalanced tensions, and vertical loads at the end of the insulator were obtained. The effects of each of the parameters on the dynamic responses were discussed. The design values for unbalanced tensions and vertical loads were proposed for the UHV suspension tower in a heavy icing area based on the analyses results. The dynamic magnification factors of the vertical load should be between 1.06 and 1.11. For the suspension tower in 20 and 30 mm icing areas, the uplift load percentage is proposed to be 10%. For the suspension towers in 40 and 50 mm icing areas, the uplift load percentage is proposed to be 5%.

Dynamic Magnification Factor in a Box-Shape Steel Girder

The dynamic effect of moving loads on structures is treated as a dynamic magnification factor when resonant is not imminent. Studies have shown that the calculated magnification factors from field measurements could be higher than the values specified in design codes. It is the main aim of present paper to investigate the applicability and accuracy of a rule-based expression for calculation of dynamic magnification factor for lifting appliances used in marine industry. A steel box shape girder of a crane is considered and transient dynamic analysis using computer code ANSYS is implemented. Dynamic magnification factor is calculated for different loading conditions and compared with rule-based equation. The effects of lifting speeds, acceleration, damping ratio and position of cargo are examined. It is found that rule-based expression underestimate dynamic magnification factor.