Maximum Relative Displacement Research Articles

Investigation of the Solid-State Wave Gyroscope Toroidal Resonator Design Parameters Effect on the Second Mode Frequency

This article relates to the study of the solid-state wave gyrocope sensitive element design, made as a torus. The article discusses the most common shapes of solid-state wave gyroscope resonators. The advantageous features of the toroidal shape are determined with respect to the classical sensitive elements manufactured by turning methods. The necessity of production transition into mini-SSWG resonators by blowing quartz glass is shown, since the technology eliminates vibrations of the workpiece, and increases maximum achievable accuracy. Based on the generalization of information from foreign researchers, the technology of toroidal mini-resonators production by blowing is presented. Questions are raised about the production technology that requires additional study in order to improve the tactical and technical characteristics of the mini-SSWG, with a toroidal resonator. Using the finite element method, the relation between frequency of the second mode of toroidal resonator natural oscillations and parameters determining its shape is established. The test sensor diameter varies from 1.5 mm to 10 mm. The height takes values from 0.33 mm to 3.3 mm. An inversely proportional relation of the frequency and the diameter of the toroidal resonator base is revealed. A regression equation has been compiled. The study of the second oscillation mode, which is a working one, was carried out in order to find the optimal size ratio of the toroidal sensing element. Optimal is understood as such a shape and dimensions of a resonator that provides the required mechanical strength and gives minimum operating vibration frequency, with maximum relative displacement of the sensing element edge. The general purpose of the work is to reduce the mass and dimensions of the SSWG by using toroidal resonator and thermomechanical method of its obtaining while ensuring high accuracy of the gyroscope.

Design loads and integrated performance metrics for highway bridges impacted by heavy vehicles

Current prescriptive design provisions adopt a constant impact design load to address vehicular collisions to bridge piers. This practice can account for neither the vehicle characteristics nor the pier’s structural properties, which may render the existing highway bridges vulnerable to accidental heavy vehicle collisions. To address this limitation, the first objective of this article is to develop a predictive model to efficiently link the impact design load with influential structural and vehicular parameters. An essential step to achieve this objective is to use validated finite element modelling approaches to obtain the impact force-time history response for vehicle-bridge collision events with varying structural and vehicular characteristics. Statistical techniques are employed for optimal model determination. As an alternative to the prescriptive design, the performance-based approach features the ability to explicitly define structural collision safety and deliver efficient design solutions. Two complementary performance metrics (percentage loss of axial capacity and the ratio of the maximum relative displacement at the impact location to the pier height) are proposed to characterize collision-induced damage in an objective manner. The integration of these two metrics into collision performance assessment makes it possible to quantify the capacity of a bridge to resume its normal operation after collision incidents.

Cooperative predictive set point modulation control of high‐speed trains

AbstractCooperative control of high‐speed trains can improve the safety and efficiency of high‐speed railway transportation. However, the velocity and distance overshoots in the cooperative control of multiple high‐speed trains is an undesirable behavior, which will lead to unsafe and inefficient train operation. To address this issue, a cooperative predictive set point modulation control approach for high‐speed trains is proposed. First, the cyber‐physical modeling of multiple high‐speed trains is presented. The longitudinal dynamic characteristics of high‐speed trains are established in the physical layer, and the cyber layer represents the communication topology of high‐speed trains based on graph theory. Second, a cooperative control rule is designed to achieve the velocity consensus and maintain safe distance between adjacent trains. Moreover, the set point automatic adjustment with correction enable (SPAACE) is leveraged to smoothly adjust the set‐point of high‐speed trains to suppress the overshoots of train velocities and inter‐train distance. Finally, the performance of the proposed method is verified in three different simulation scenarios: normal, acceleration and deceleration conditions. The simulation results show that the proposed method reduces the maximum relative displacement by 62% and the velocity error by 34%.

Seismic response analysis of shallowly buried subway station in inhomogeneous clay site

It is of great significance to study the seismic response of the shallowly buried subway station in the inhomogeneous site caused by the soil consolidation. The dynamic characteristics of Shanghai soft clay under different confining pressures were studied by a series of dynamic triaxial tests. The nonlinear analysis was used to investigate the influence of the inhomogeneous clay site on the seismic response of the shallowly buried subway station. The variations of dynamic shear modulus ratio and damping ratio under different buried depths were obtained. The research results indicate that the damage to subway stations is more serious in the inhomogeneous clay site under the same seismic wave. The inhomogeneity of the clay site has an amplification effect on the horizontal relative displacement between the ceiling and bottom slabs, as well as the vertical displacement of the ground surface. However, the effect of the inhomogeneous site on the acceleration of the slabs and the maximum horizontal relative displacement of the middle column is small. After the earthquake, the horizontal relative displacement of the middle column is strongly affected by the inhomogeneous site. The results can provide a reference to the earthquake prevention and disaster reduction in the soft clay area.

Seismic performance of gravity retaining walls

AbstractIn the present study, the seismic performances of gravity retaining walls having both inclined back side and inclined backfill were investigated under sinusoidal acceleration excitations using series of shaking table tests on 750 mm height physical model. The effects of input peak ground acceleration (), inclination angle of backfill material (α) and inclination angle of back of the gravity retaining wall (β) on acceleration amplification factor (), maximum peak lateral relative () and maximum residual lateral displacement () of the wall, surface settlement () of the backfill material, inertial force () and horizontal dynamic active force () were assessed. It was observed that higher values of the were obtained from the experimental results as compared the ones from current seismic design codes. Moreover, the six results of shaking table tests revealed that the phase difference was appeared between the inertial force and dynamic earth pressures. Pseudo‐static limit equilibrium methods resulted in over conservative results and could not truly reflect the seismic behavior of gravity wall due to the inertial forces and phase difference not taken into consideration.

Novel screw fixation placement configuration for the treatment of Pauwels type III femoral neck fractures: a finite element analysis.

Verticality of transcervical hip fractures in young patients is usually connected with typically high-energy fractures which are known as Pauwels type III. Artificial femoral head replacement surgery is mostly not considered for treating femoral neck fractures in such patients. The commonly used devices for the fixation of vertical femoral neck fractures are multiple screws or a sliding hip screw with or without an antirotation screw. Size, location and length of the screws are the most effective parameters in terms of the structural performance of internal fixation implants, but the optimal configuration of the screws is necessary to be investigated to direct the clinical practice. The aim of this study is to compare the biomechanical stability of the standard inverted triangle configuration with the various newly proposed x-crossed screw configurations. FEA simulations carried out in this study demonstrated that using an x-crossed-right assembly in treating Pauwels type III femoral neck fractures satisfies the biomechanical stability in terms of maximum von Mises stresses and maximum femoral head displacement. However, in terms of maximum relative neck fracture displacement, the x-crossed-right assembly would not entirely suffice the desired biomechanical stability. Therefore, using an x-crossed screw assembly in treating femoral neck fractures would provide the needed biomechanical stability.

Design and Optimization of an Index Finger Exoskeleton With Semi-Wrapped Fixtures and Series Elastic Actuators.

This paper proposes a novel index finger exoskeleton with semi-wrapped fixtures and elastomer-based clutched series elastic actuators. The semi-wrapped fixture is similar to a clip, which improves the convenience of donning/doffing and connection stability. The elastomer-based clutched series elastic actuator can limit the maximum transmission torque and improve passive safety. Second, the kinematic compatibility of the exoskeleton mechanism for the proximal interphalangeal joint is analyzed, and its kineto-statics model is built. To avoid the damage caused by the force along the phalanx, considering the individual difference in the size of the finger segment, a two-level optimization method is proposed to minimize the force along the phalanx. Finally, the performance of the proposed index finger exoskeleton is tested. Statistical results indicate that the donning/doffing time of the semi-wrapped fixture is significantly less than that of the Velcro. Compared with the Velcro, the average value of the maximum relative displacement between the fixture and the phalanx is reduced by 59.7%. Compared with the exoskeleton before optimization, the maximum force along the phalanx generated by the exoskeleton after optimization is reduced by 23.65%. The experimental results show that the proposed index finger exoskeleton can improve the convenience of donning/doffing, connection stability, comfort, and passive safety.

Experimental study on the wave-induced dynamic response and hydrodynamic characteristics of a submerged floating tunnel with elastically truncated boundary condition

Hydrodynamic load and motion response are the first considerations in the structural design of a submerged floating tunnel (SFT). Currently, most of the relevant studies have been based on a two-dimensional model test with a fixed or fully free boundary condition, which inhibits a deep investigation of the hydrodynamic characteristics with an elastic constraint. As a result, a series of difficulties exist in the structural design and analysis of an SFT. In this study, an SFT model with a one-degree-of-freedom vertical elastically truncated boundary condition was established to investigate the motion response and hydrodynamic characteristics of the tube under the wave action. The effect of several typical hydrodynamic parameters, such as the buoyancy-weight ratio, γ, the relative frequency, f/fN, the Keulegan–Carpenter (KC) number, the reduced velocity, Ur, the Reynolds number, Re, and the generalized Ursells number, on the motion characteristics of the tube, were selectively analyzed, and the reverse feedback mechanism from the tube's motion response to the hydrodynamic loads was confirmed. Finally, the critical hydrodynamic parameters corresponding to the maximum motion response at different values of γ were obtained, and a formula for calculating the hydrodynamic load parameters of the SFT in the motion state was established. The main conclusions of this study are as follows: (i) Under the wave action, the motion of the SFT shows an apparent nonlinearity, which is mainly caused by the intensive interaction between the tube and its surrounding water particles, as well as the nonlinearity of the wave. (ii) The relative displacement of the tube first increases and then decreases with increasing values of f/fN, Ur, KC number, Re, and the generalized Ursells number. (iii) γ is inversely proportional to the maximum relative displacement of the tube and the wave force on the tube in its motion direction. (iv) Under the motion boundary condition (as opposed to the fixed boundary condition), the peak frequency of the wave force on the SFT in its motion direction decreases and approaches the natural vibration frequency of the tube, whereas the wave force perpendicular to the motion direction increases. When the incident wave frequency is close to the natural vibration frequency of the tube, the tube resonates easily, leading to an increased wave force in the motion direction. (v) If the velocity in the Morison equation is substituted by the water particle velocity measured when the tube is at its equilibrium position, the inertia coefficient in the motion direction of the tube is linearly related to its displacement, whereas that in the direction perpendicular to the motion direction is logarithmically related to its displacement.

Optimized passive/semi-active vibration control using distributed-multiple tuned facade damping system in tall buildings

To reduce wind-induced vibrations, Tuned Mass Dampers (TMD) are widely used in high-rise buildings. However, traditional TMD system requires large additional damping mass and huge installation space at the top floors of the building. In this paper, a novel distributed-Multiple Tuned Facade Damping (d-MTFD) system is investigated. This system employs the outer skin mass of the Double-Skin Facade (DSF) as the damping mass. In the upper stories, the DSF's outer skin, mounted on a guide rail system, is designed to be parallel moveable. The passive/semi-active d-MTFD system, which is assumed to be installed on a 76-story benchmark building under across-wind excitation, is optimized using multi-objective Genetic Algorithms (GA) for two defined objectives: minimizing the peak top floor acceleration and controlling the maximum peak relative displacement of all the moveable DSF's outer skins. On-off groundhook control and displacement-reducing bang-bang control are used as semi-active control strategies. The rolling friction caused by the guide rail system has a considerable impact on the optimization results. These results are presented in the form of Pareto fronts. Optimized parameters can be selected to yield a good trade-off between both objectives. The optimized passive/semi-active d-MTFD systems can highly improve the structural response. Compared with the optimized passive d-MTFD system, the use of semi-active control can reduce the vibration of the DSF's outer skin significantly. Comparing the selected optimized cases with similar peak top floor acceleration, the peak top floor facade relative displacement using displacement-reducing bang-bang control decreases 58.3%, and the Root Mean Square (RMS) value decreases 61.4%.

Triangular support intramedullary nail: A new internal fixation innovation for treating intertrochanteric fracture and its finite element analysis

BackgroundProximal femoral nail anti-rotation (PFNA) and Gamma nail were recommended for intertrochanteric fracture, however, with high rate of post-operation complications. The triangular support intramedullary nail (TSIN) was designed to reduce the risk of postoperative complications related to Gamma nail and PFNA, and the aim is to compare the biomechanical characters of Gamma nail, PFNA and TSIN for fixation of intertrochanteric fracture and prove the rationality of the concept of triangle fixation in the treatment of intertrochanteric fractures. MethodsThe finite element model of proximal femur was constructed according to the CT data of femur. Intertrochanteric fracture models with Evans type Ⅰ and Ⅳ were established and fixed with Gamma nail, PFNA and TSIN by UG-NX 12.0. The finite element analysis software was used to compare the stress distribution and displacement of three implants fixation models. ResultsUnder axial loading of 600 N, the peak stress and maximum displacement of intact proximal femur was 13.78 MPa and 1.33 mm, respectively. The maximum stress of TSIN for fixation of Evans type Ⅰ and Ⅳ intertrochanteric fractures was 86.23 MPa and 160.63 MPa which was significantly lower than that of Gamma nail and PFNA. The maximum relative displacement of fracture section in Gamma nail and PFNA fixation models was 0.18 mm and 0.19 mm which has 135% and 148% higher than in TSIN fixation models for fixing Evans type Ⅰ intertrochanteric fracture, and 0.47 mm and 0.59 mm which has 91% and 140% higher than in TSIN fixation models for stabilization of Evans type Ⅳ intertrochanteric fracture. ConclusionCompared with Gamma nail and PFNA fixation, TSIN has superior advantages in stress distribution and construct stability. We believe that triangle fixation concept help to reduce the risk of post-operative complications associated with PFNA and Gamma nail and improve the clinical effect of intertrochanteric fracture.

Ultra-low wide bandwidth vibrational energy harvesting using a statically balanced compliant mechanism

Structure design of ultra-low wide bandwidth vibrational energy harvesters remains an open issue. In this research, a statically balanced compliant mechanism (SBCM) is proposed, dynamically modelled, and experimentally demonstrated to address this need. This SBCM is designed based on the concept of stiffness compensation between a linear component with positive-stiffness (two double parallelograms in parallel) and a nonlinear component with negative-stiffness (two sets of post-buckled fixed-guided compliant beams in parallel). A design guideline of the SBCM starting from using rapid-design stiffness compensation equation is provided for reasonably approximate and accurate results. Subsequently, a dynamic analytical model of the displacement response of the SBCM to harmonic base excitation has been derived based on the averaging method. The nonlinear force-displacement relationship of the system was obtained through nonlinear finite element analysis (FEA) simulations in this regard and a 5th order polynomial fit was chosen taking only odd terms into account. The accuracy of this analytical model is confirmed by numerical analysis. Next, a prototype of the SBCM was fabricated and its applicability to piezoelectric vibrational energy harvesters (PVEHs) was demonstrated by integrating piezoelectric capacitors made of PVDF films with compliant beams of the SBCM to generate electric outputs in response to the bending of the beams. Static balancing is achieved over a continuous displacement range of 2 mm around the origin. Bi-stability and mono-stability were observed with the same prototype by adjusting the length of the positive-stiffness beams. Under static-balancing condition, the SBCM is able to respond to a wide range of ultra-low frequencies with low accelerations, which has been established experimentally, analytically and numerically. In dynamic experiments, the steady-state relative displacement amplitude H is 2.9 mm under an excitation condition of 6 Hz and 0.1g (1g=9.8 m/s2), and it reaches a maximum of 9.4 mm under 12.75 Hz and 0.25 g. A 30%-Hmax frequency bandwidth is introduced to assess the nonlinear dynamic performance of the SBCM from a mechanical perspective. The maximum experimental 30%-Hmax bandwidth of the structure is 6.75 Hz (from 6 Hz to 12.75 Hz) at 0.25 g and the corresponding theoretical value is 8.73 Hz (from 3.34 Hz to 12.07 Hz). Under the same excitation condition, it is shown that the maximum relative displacement amplitude deceases as the jump-down frequency increases. In addition, super-harmonic and sub-harmonic oscillations are observed in the dynamic experiments. The SBCM can provide a practical structural solution for harvesting energy from a range of vibrational scenarios (e.g. ocean waves, human motions and bridge vibrations) with ultra-low wide bandwidth frequencies and weak accelerations. The concept of SBCM is suitable to be combined with various energy conversion principles and is not limited to piezoelectric sources alone. When miniaturized, the SBCM concept can be of particular interest to researchers active in energy harvesting for microelectromechanical systems (MEMS) technology.

Long-Term Earthquake Response Monitoring of Nineteenth-Century Timber Temple Kencho-ji, Japan

ABSTRACT In this study, we have conducted earthquake monitoring on a timber Buddhist temple constructed in 1825. Between 2008 and 2019, 75 strong motion were recorded. The maximum response acceleration was recorded during the 2011 Tohoku earthquake, Japan. From the long-time monitoring, the influence by time due to deterioration and exterior force was expected, but the natural frequency of vibration/stiffness did not show any fluctuation in our 12 years of measurement. There was a strong correlation with the natural logarithm of the maximum relative displacement, reflecting the non-linear elastic characteristics of timber structures. However, the natural frequencies of vibration were 10–20% higher in the summer than in the winter, when the climate was hot and humid. The effect of moisture content on the mechanical properties of wood was also investigated and an idealized relationship between the maximum relative displacement and the normalized natural frequency of vibration by MC was proposed.

Analysis of Longitudinal Force of Beam and Rail of Continuously Welded Rails (CWR) on Railway Bridge

To study the longitudinal force of CWR on viaduct, a track-bridge-pier finite element model is established. Taking a multi-span simply supported beam with a maximum span of 32.7m of an elevated CWR as an example, the additional expansion and contraction forces, displacement between rail and beam and the force of pier are calculated, and whether the rail stress meets the requirements when setting constant resistance fasteners is checked. The results show that: (1) For the left and right lines, the maximum additional expansion forces of single strand rail are both 211.13kN, and the maximum relative displacements between beam and rail are both 6.572mm. (2) The maximum value of the additional expansion and contraction forces and the relative displacement between beam and rail of the same line occur at the same position. The left line is at ZFZ29 pier and the right line is at ZFS31 pier. (3) The maximum force of pier in this section is 500.80kN, and the pier numbers are ZFZ27 and ZFS29. (4) The rail stress is less than the allowable stress of 352MPa, and the rail strength meets the requirements.

Experimental Study on the Force Characteristics of Superlong Pile Groups in Silty Sand

Laboratory model testing of single pile and superlong pile groups in saturated silty sand was conducted to investigate the response and bearing behavior of superlong pile groups with a high or low cap under vertical loads. The load transfer mechanism and bearing behavior of the pile shaft were discussed in detail. The load‐settlement curve of the loaded superlong pile groups belongs to the type of gradual descent in silty sand. The transferred load decreased along the pile length during loading, but the gradients differed in different positions of the superlong pile group foundation with a high or low cap. The maximum shaft friction of the superlong pile groups with a high and low cap is about 2.5 times and 1.8 times, respectively, than that of the single pile. In addition, the tip resistance of the piles in the pile group foundation is about 2–3.5 times that of the single pile. The friction resistance of the superlong pile group foundation with a low cap was slightly larger than that of the high cap in the entire pile length, and two peaks and one peak, respectively, were observed. Under the ultimate load, the pile‐soil maximum relative displacement of the friction on the pile side in the silty sand stratum was about 3% of the pile diameter. Under the ultimate load, the load sharing ratio of the pile side resistance of the two types of pile group foundations was about 60% of the total load. The load sharing ratios at the pile tip of the superlong pile groups with high and low caps are 40% and 33%. Furthermore, equations were proposed to determine the axial capacity of the superlong pile group based on the single pile bearing capacity and were applied to analyze the test pile. The calculated ultimate bearing capacity was similar to the measured value, with a maximum error of only 4.88%, thus validating the proposed method.

Seismic Finite Element Analysis of Lightning Arrester Combination by Casing and Pillar Insulator

The seismic performance of electrical equipment in substations has a great impact on the normal operation of the whole substation. The results of the modal analysis show that the fundamental frequency of the three devices is in the range of 0.9Hz∼1.1Hz. The maximum stress of the casing for the three devices is respectively 55.43MPa, 45.39MPa, 35.26MPa, when the peak acceleration 0.4g seismic action is verified. The maximum stress of insulator is respectively 47.01MPa, 62.72MPa and 30.85MPa, and the maximum relative displacement of the top for the equipment is 617.2mm.

Insights on fault reactivation during the 2019 November 11, Mw 4.9 Le Teil earthquake in southeastern France, from a joint 3-D geological model and InSAR time-series analysis

SUMMARY The 2019, Mw 4.9 Le Teil earthquake occurred in southeastern France, causing substantial damage in this slow deforming region. Field observations, remote sensing and seismological studies following the event revealed that coseismic slip concentrates at shallow depth along a ∼5 km long rupture associated with surface breaks and a thrusting mechanism. We further investigate this earthquake by combining geological field mapping, 3-D geology, InSAR time-series analysis and a coseismic slip inversion. From structural, stratigraphic and geological data collected around the epicentre, we first produce a 3-D geological model of the region surrounding the rupture using the GeoModeller software. Our model includes the geometry of the geological layers and the main faults, including the La Rouvière Fault, (LRF) the Oligocene normal fault that ruptured during the earthquake. We generate a time-series of surface displacement from Sentinel-1 SAR data ranging from early 2019 January to late 2020 January using the NSBAS processing chain. The spatio-temporal patterns of surface displacement for this time span show neither a clear pre-seismic signal nor significant post-seismic transient deformation. We extract the coseismic displacement pattern from the InSAR time-series, highlighting along-strike variations of coseismic surface slip. The maximum relative displacement along the line of sight is up to ∼16 cm and is located in the southwestern part of the rupture. We invert for the slip distribution on the fault from the InSAR coseismic surface displacement field. Constraining our fault geometry from the geological model, acceptable fault dip ranges between 55° and 60°. Our model confirms the reactivation of LRF, with reverse slip at very shallow depth and two main slip patches reaching, respectively, 30 and 24 cm of slip, both around 500 m depth. We finally discuss how the 3-D fault geometry and geological structure may have impacted the slip distribution and propagation during the earthquake. This study is a step to reassess the seismic hazard of the many faults similar to the La Rouvière one along the Cévennes fault system, in a densely populated area hosting several sensitive nuclear sites.

Improvement on optimal design of dynamic absorber for enhancing seismic performance of nuclear piping using adaptive Kriging method

For improving the seismic performance of the nuclear power plant (NPP) piping system, attempts have been made to apply a dynamic absorber (DA). However, the current piping DA design method is limited because it cannot provide the globally optimum values for the target design seismic loading. Therefore, this study proposes a seismic time history analysis-based DA optimal design method for piping. To this end, the Kriging approach is introduced to reduce the numerical cost required for seismic time history analyses. The appropriate design of the experiment method is used to increase the efficiency in securing response data. A gradient-based method is used to efficiently deal with the multi-dimensional unconstrained optimization problem of the DA optimal design. As a result, the proposed method showed an excellent response reduction effect in several responses compared to other optimal design methods. The proposed method showed that the average response reduction rate was about 9% less at the maximum acceleration, about 5% less at the maximum value of the response spectrum, about 9% less at the maximum relative displacement, and about 4% less at the maximum combined stress compared to existing optimal design methods. Therefore, the proposed method enables an effective optimal DA design method for mitigating seismic response in NPP piping in the future.

Performance comparisons of triple friction pendulum bearings with different sliding surface properties

In this study the time history analyses are carried out three dimensionally for a simple five-story concrete structure seismically isolated incorporating triple friction pendulum bearings with different sliding surface properties with the help of the ABAQUS finite element program. The altering friction surface properties are friction coefficient and radius of curvature. The performances of the various isolators are compared with each other as well as with those of a fixed based structure. For this purpose, maximum relative story displacements, story accelerations and column base shear forces are investigated as seismic reactions. According to the analysis results it can be stated that the seismic reactions of isolated structures are significantly reduced when compared to those of the fixed supported structure. Additionally, when triple friction pendulum bearing isolators with different friction coefficients and friction surface radii are compared, it can be observed that increasing the friction coefficient increases the reactions of the structure while increasing the friction surface radii decreases the reactions

Computational analysis on unbalanced tension in overhead power lines under non-uniform accreted ice

Unbalanced tension in the overhead power lines under non-uniform ice is important for the design of towers. Based on the constant conductor length and numerical iteration methods, a numerical calculation method to determine the unbalanced tension under non-uniform accreted ice in one span for both the single-span and multi-span sections has been developed. Meanwhile, the horizontal tension and sag distribution calculated by the numerical calculation method are in good agreement with the finite element analysis (FEA) model established in the ANSYS software and the field situation. The responses of the unbalance tension and the maximum relative displacement of the conductor under different parameters, including span length, ice length, ice thickness, number of spans, and elevation difference were investigated. Also, the application of a numerical calculation method to practical line situations was discussed. The results show that the non-uniform ice clearance reaches the flashover condition first compared with the static clearance and the dynamic clearance under different span lengths, ice thicknesses, and voltage levels, especially in the low voltage level power lines.

Maximum drift estimation based on only one accelerometer for damaged shear structures with unknown parameters

This paper presents a method to estimate the maximum inter-story drift and relative displacement time history of multi-degree-of-freedom (MDOF) shear structures underground-motion excitation by using only one accelerometer installed on a floor when the structures are damaged during the event and hence modal parameters change and become unavailable. First, the absolute acceleration and relative displacement are formulated in modal coordinates and a state-space expression is derived. Then, a scheme to determine the unknown natural frequencies of the damaged structure is devised with the help of the genetic algorithm (GA) and a reasonably chosen fitness function, and the mode shapes are updated by solving a set of nonlinear equations with respect to each group of frequency variables in the GA. The applicability of this method was studied in numerical simulations that examined the effect of the extent of damage to the structure and the selection of the lower bound of the GA variables. Further simulations were conducted to investigate the modal truncation error and robustness against measurement noise of the proposed approach. Finally, the method was validated in a shake table experiment. The results indicate that the time history of the relative displacement and maximum inter-story drift can be accurately estimated in the case of a significant reduction in structural stiffness and a large search range of GA variables. The results also show the method is robust against noise and performs well even when only the lower modes are included in the model.