Absolute Displacement Research Articles

Absolute displacement measurement using an inertial reference generated by linearised electromagnetic levitation

This paper proposes a novel passive absolute displacement measurement system (ADMS) utilising the electromagnetic levitation approach, instead of any mechanical spring. The most distinctive feature of the proposed ADMS is its measuring amplitude range of 30μm–1.2 mm with a lower frequency limit of 2 Hz. Consequently, a wider measuring bandwidth and higher measurement accuracy for absolute displacement signals can be realised without feedback/serve-type inertia sensors, which are usually expensive and vulnerable. Both features make the proposed system promising for of low-frequency measurement applications, such as precision vibration isolation of optical platforms in vibrational environments, anti-shake UAV platforms, monitoring of seismic wave signals, ship equipment protection and safety inspection of long-span bridges. First, the principles of the proposed ADMS are introduced. Subsequently, the measuring performance of the proposed ADMS is simulated and analysed. Finally, a prototype of the ADMS is constructed and tested. The experimental results confirm the validity of the proposed ADMS design and demonstrate its capability to measure the absolute displacement with a low-frequency and wider amplitude range.

Contactless Deformation Monitoring of Bridges with Spatio-Temporal Resolution: Profile Scanning and Microwave Interferometry

Against the background of an aging infrastructure, the condition assessment process of existing bridges is becoming an ever more challenging task for structural engineers. Short-term measurements and structural monitoring are valuable tools that can lead to a more accurate assessment of the remaining service life of structures. In this context, contactless sensors have great potential, as a wide range of applications can already be covered with relatively little effort and without having to interrupt traffic. In particular, profile scanning and microwave interferometry, have become increasingly important in the research field of bridge measurement and monitoring in recent years. In contrast to other contactless displacement sensors, both technologies enable a spatially distributed detection of absolute structural displacements. In addition, their high sampling rate enables the detection of the dynamic structural behaviour. This paper analyses the two sensor types in detail and discusses their advantages and disadvantages for the deformation monitoring of bridges. It focuses on a conceptual comparison between the two technologies and then discusses the main challenges related to their application in real-world structures in operation, highlighting the respective limitations of both sensors. The findings are illustrated with measurement results at a railway bridge in operation.

Wind vibration responses of structure with generalized Maxwell model viscoelastic dampers

A new method for analysis of wind vibration response of structures with viscoelastic dampers is presented. Most existing studies focused on the numerical solution, and in this paper, an analytical method based on quadratic orthogonalized power spectral density function (QO-PSDF) was applied to obtain the closed-form solution of the structural dynamic responses with generalized Maxwell model (GMM) viscoelastic damper under Davenport spectral wind excitation. Firstly, the equations in motion of GMM viscoelastic dampers were coupled with the structural dynamic equation, which was decoupled into a linear combination of first-order vibration equations through complex mode method (CMM). Secondly, the frequency response eigenvalue function (FREF) was quadratic orthogonalized, which was combined with power spectral density function (PSDF) of Davenport spectral to obtain a QO-PSDF of the structural dynamic responses, and the exact closed-form solutions of the spectral moments and variances of the dynamic response were successfully acquired using the QO-PSDF. Finally, a 16-storey reinforced concrete building structure equipped with GMM viscoelastic dampers is taken as an example to validate the accuracy and applicability of the closed-form solution through a series of structural responses, including absolute displacements, inter-storey displacements, absolute velocities, inter-storey velocities.

Influence of Abutment Stiffness and Strength on the Seismic Response of Horizontally Curved RC Bridges in Comparison with Equivalent Straight Bridges at Different Seismic Intensity Levels

Seismic design codes have imposed some limitations on the maximum subtended angle of curved bridges and allow engineers to analyze and design them using an equivalent straight bridge. This paper investigates these limitations and evaluates the AASHTO code recommendations regarding the prediction of the seismic responses of curved bridges using an equivalent straight bridge for bridges with different abutment properties at different seismic hazard levels. In this regard, the seismic responses of 21 horizontally curved and straight RC four-span bridges with different abutment types are investigated. In 7 bridge models, soil-abutment-bridge interaction is neglected, while in the rest of the bridge models, the seat-type abutments with the participation of the nonlinear backfill soil, gap, and abutment piles are used in structural modeling. First, nonlinear static (pushover) analyses are carried out to evaluate the overall behavior of the bridges with different abutment configurations in the two perpendicular principal directions. Subsequently, nonlinear time history analyses are performed to predict the seismic response of bridge elements, including column drifts and deck displacements at the place of the abutments in the radial and tangential directions at different seismic intensity levels, including the design basis earthquake (DBE) and maximum credible earthquake (MCE) excitation levels. In addition, the actual maximum displacements of the components of the bridges (i.e., the total absolute displacements) were also predicted and evaluated for different cases. It was found that the abutment properties and boundary conditions had a significant effect on the seismic response assessment of curved bridges compared to straight bridges, while such parameters are not currently considered by the design codes. The results also indicated that by increasing the seismic intensity level, more limitations should be imposed on the use of the equivalent straight bridges.

Correlation between non-spectral and cumulative-based ground motion intensity measures and demands of structures under mainshock-aftershock seismic sequences considering the effects of incident angles

One of the pivotal steps in seismic assessment of structures is the definition of functional relationships between an Engineering Demand Parameter (EDP) and a ground motion Intensity Measure (IM). This paper investigates the correlation between widely used non-spectral and cumulative-based ground motion intensity measures and corresponding engineering demand parameters for regular and irregular structures as bidirectional single-degree-of-freedom (2D-SDOF) systems. The correlation is investigated under sequential earthquakes in terms of efficiency and sufficiency, considering various seismic incident angles. Structural performance is expressed as maximum inelastic displacement, MD, maximum inelastic absolute acceleration, MA, residual displacement, RD, and hysteretic energy, EH. The results of extensive parametric analyses show that if the MD, MA, EH and RD of regular systems are considered as demand parameters, the optimal IMs in terms of efficiency and sufficiency are vsq, arms, vrs and vsq, respectively.

Structural monitoring method for RC column with distributed self-sensing BFRP bars

Reinforced concrete (RC) columns may be damaged under earthquakes or wind loads, which will severely affect their bearing capacity. Current damage evaluation methods are mainly based on displacement measurement, which makes evaluating local structural damage difficult. Therefore, this study proposes an RC column structural monitoring and evaluation method based on a distributed self-sensing basalt fiber reinforced polymer (BFRP) bar with optical fiber sensors inside. First, the self-sensing BFRP bar is introduced, including the sensing principle, inner structure, and basic sensing performance. It is found that the strain sensing coefficient of the proposed self-sensing BFRP bar presents only 2.2 % difference from that of the bare optical fiber sensor, meaning the BFRP package take no negative effect on the strain sensitivity. Second, the analytical methods of curvature and displacement are established based on the strain distribution measurement, in which the influence of bond-slip on parameter calculations is mainly considered. Finally, the proposed method was well verified by the loading tests of one RC column with self-sensing BFRP bars. Among the results, the absolute displacement measurement error increase with the development of structure damage, which can be even up to several mm after the steel yielding. However, the relative displacement measurement error can be still controlled within 20 % until the structure failure of the RC column. Considering the additional long-term performance of the proposed self-sensing BFRP bar, the proposed method is expected to implement long-term monitoring of RC columns.

Validating Clinical Distal Radioulnar Joint Examination With Radiographic Parameters.

The purpose of this study was to quantify the in vivo displacement of bilateral distal radioulnar joints (DRUJs) in resisted pronosupination. We hypothesize that this will demonstrate no appreciable difference between the left and right DRUJ, thus validating the concept of using the uninjured wrist as a control for physical examination as well as dynamic imaging studies. Thirty-two participants without a history of wrist pathology underwent a dynamic computed tomography (CT) protocol evaluating bilateral forearm rotation in neutral forearm rotation, 60° pronation, and 60° supination, including maximal isometric muscle loading. The DRUJ alignment, specifically the absolute degree and direction of subluxation of the ulna relative to the sigmoid notch, was then assessed using a modification of the radioulnar line method. There was no significant difference in the mean displacement when comparing the right and left sides in neutral, pronation, or supination. The mean displacement was also compared between male and female patients, and there was no statistically significant difference in absolute displacement in neutral (male 0.99 mm vs female 1.38 mm) or supination (male -0.57 mm vs female -0.23 mm). However, the difference in pronation was statistically significant (male 2.69 mm vs female 3.26 mm). Of the 192 sequences, the measurements of displacement of the authors were within 1 mm 86% of the time (166 of 192). Dynamic CT of bilateral DRUJs in resisted pronation, supination, and neutral demonstrated symmetry between the right and left DRUJ, supporting the concept of using the contralateral side as a control to identify instability in an injured wrist.

Ultrasound Imaging and Prevalence of Intrasheath Peroneal Tendon Subluxation in Asymptomatic Volunteers

Category: Ankle; Other Introduction/Purpose: Intrasheath peroneal tendon subluxation is typically an incidental finding in athletes with sports-related injuries and is characterized by a temporary reversal in the anteroposterior positions of the peroneus longus (pL) and peroneus brevis (pB) tendons within their common tendon sheath. It is currently unclear whether intrasheath subluxation represents normal physiologic or pathologic tendon motion. This study aims to determine the normal variation in motion of supramalleolar pB and pL tendons in multiple ankle positions and to determine the overall prevalence of intrasheath tendon subluxation in asymptomatic volunteers. Methods: Static sonographic images of the peroneal tendons in 22 asymptomatic volunteers were collected in the neutral position, in eight fixed ankle positions (active and passive pronation, dorsiflexion, supination, and plantarflexion), and during dynamic ankle circumduction. The center of each tendon in relation to the lateral fibular cortex and in relation to each other was measured in each position and used to calculate absolute and percentage displacement. Two-way ANOVA was used to determine the significance of passive versus active motion and two-tailed paired sample t-test was used to compare the mean displacement of pL and pB in active and passive positions. Results: Intrasheath subluxation was not visualized in any static position but was visualized in 33% of patients during active ankle circumduction, regardless of direction or laterality. Percent displacement was greatest in active ankle plantarflexion (55%) for pB and in active pronation (34%) for pL. A statistically significant difference in the tendon positions in relation to each other was found in the anteroposterior direction (p=0.026), but there were no statistically significant differences between active and passive motions or with ankle positioning. A non-painful ankle 'snap' was palpated by the sonographer in all cases of intrasheath subluxation. Conclusion: Intrasheath subluxation is a fairly common occurrence seen in one third of our volunteers. Our results suggest that a snapping ankle in otherwise asymptomatic patients is highly suggestive of intrasheath peroneal tendon subluxation and can be well-documented with dynamic ultrasound. Establishing the normal ranges of motion of supramalleolar peroneal tendons may assist in the evaluation of patients with lateral ankle pain.

Equivalent linearization method for seismic analysis and design of self-centering structures

Although seismic response of engineering structures can be obtained through dynamic nonlinear analysis, approximate linear elastic analysis method is often adopted to reduce the computational effort and simplify the design procedure. Due to the excellent seismic performance, self-centering (SC) concrete structures are receiving more and more attention, but there is no such an equivalent linearization method especially suitable for SC concrete structures. In this study, the influence of hysteretic behavior on maximum inelastic displacement is described conceptually, and the estimation accuracy of four classic equivalent linearization methods are explored for SC models, the results show that the absolute mean displacement errors from classic methods mostly appear in the range of 20% to 30%, and most of the mean displacement errors is negative, which is unsafe for the performance-based seismic analysis and design. Then, an empirical equivalent linearization method is proposed for SC systems by a series of dynamic nonlinear analysis and regression analysis, it is found that the estimation accuracy of the proposed method is better than classic methods, and the standard deviation of the proposed method is basically at the same level as that of the classic methods. Finally, the proposed method is applied to the displacement-based design approach, the nonlinear analysis shows that the design targets can be well meet, and the designed SC concrete structure shows superior self-centering and energy dissipation capacity.

Exploring the impact of urogenital organ displacement after abdominoperineal resection on urinary and sexual function

PurposeThis study aimed to establish the functional impact of displacement of urogenital organs after abdominoperineal resection (APR) using validated questionnaires.MethodsPatients who underwent APR for primary or recurrent rectal cancer (2001–2018) with evaluable pre- and postoperative radiological imaging and completed urinary (UDI-6, IIQ-7) and sexual questionnaires (male, IIEF; female, FSFI, FSDS-R) were included from 16 centers. Absolute displacement of the internal urethral orifice, posterior bladder wall, distal end of the prostatic urethra, and cervix were correlated to urogenital function by calculating Spearman’s Rho (ρ). Median function scores were compared between minimal or substantial displacement using median split.ResultsThere were 89 male and 36 female patients included, of whom 45 and 19 were sexually active after surgery. Absolute displacement of the internal urethral orifice and posterior bladder wall was not correlated with UDI-6 in men (ρ = 0.119 and ρ = 0.022) nor in women (ρ = − 0.098 and ρ = − 0.154). In men with minimal and substantial displacement of the internal urethral orifice, median UDI-6 scores were 10 (IQR 0–22) and 17 (IQR 5–21), respectively, with corresponding scores of 25 (IQR 10–46) and 21 (IQR 16–36) in women. Displacement of the cervix and FSDS-R were correlated (ρ = 0.433) in sexually active patients.ConclusionThis first analysis on functional impact of urogenital organ displacement after APR suggests that more displacement of the cervix might be associated with worse sexual function, while the data does not indicate any potential functional impact of bladder displacement. Studies are needed to further explore this underexposed topic.

Reproducibility of chestwall and heart position using surface-guided versus RPM-guided DIBH radiotherapy for left breast cancer.

This study compared the reproducibility of chestwall and heart position using surface-guided versus RPM (real-time position management)-guided deep inspiration breath hold (DIBH) radiotherapy for left sided breast cancer. Forty DIBH patients under either surface-guided radiotherapy (SGRT) or RPM guidance were studied. For patients treated with tangential fields, reproducibility was measured as the displacements in central lung distance (CLD) and heart shadow to field edge distance (HFD) between pretreatment MV (megavoltage) images and planning DRRs (digitally reconstructed radiographs). For patients treated with volumetric modulated arc therapy (VMAT), sternum to isocenter (ISO) distance (StID), spine to rib edge distance (SpRD), and heart shadow to central axis (CAX) distance (HCD) between pretreatment kV images and planning DRRs were measured. These displacements were compared between SGRT and RPM-guided DIBH. In tangential patients, the mean absolute displacements of SGRT versus RPM guidance were 0.19 versus 0.23 cm in CLD, and 0.33 versus 0.62 cm in HFD. With respect to planning DRR, heart appeared closer to the field edge by 0.04 cm with surface imaging versus 0.62 cm with RPM. In VMAT patients, the displacements of surface imaging versus RPM guidance were 0.21 versus 0.15 cm in StID, 0.24 versus 0.19 cm in SpRD, and 0.72 versus 0.41 cm in HCD. Heart appeared 0.41 cm further away from CAX with surface imaging, whereas 0.10 cm closer to field CAX with RPM. None of the differences between surface imaging and RPM guidance was statistically significant. In conclusion, the displacements of chestwall were small and were comparable with SGRT- or RPM-guided DIBH. The position deviations of heart were larger than those of chestwall with SGRT or RPM. Although none of the differences between SGRT and RPM guidance were statistically significant, there was a trend that the position deviations of heart were smaller and more favorable with SGRT than with RPM guidance in tangential patients.

Effective range of base isolation design parameters to improve structural performance under far and near-fault earthquakes

Triple Friction Pendulum Isolators (TFPIs) have been widely used to enhance the seismic capacity of structures in the recent decade. This study intends to measure the effect of different Ground Motion (GM) sets, including Far-Fault (FF) and Near-Fault (NF) records, on the seismic response of the Triple Friction Pendulum (TFP) isolated structures. For this aim, different Engineering Demand Parameters (EDP), including Inter-story Drift Ratio (IDR), absolute floor acceleration, base shear, residual displacement, and damage energy are measured using numerous Nonlinear Time History (NTH) analyses. A three-dimensional mid-rise special moment resisting frames (SMFs) steel building isolated with TFPIs has been designed as per ASCE 7-16. In addition, the separate and simultaneous effect of raising the damping ([Formula: see text]) and the period ([Formula: see text]) of the base isolation system on the seismic responses of the superstructure are measured to assess the structural performance and estimate the damage energy. The [Formula: see text] and the [Formula: see text] are amplified up to 30% and 4.5 times of the superstructure period in incremental steps, respectively. The results show that the damage energy of the superstructure in the Initial Design Parameters' Values (IDPVs) of the isolator under NF records with Forward-Directivity pulses (NF-FD-GMs) is more significant than damping energy, while an inverse trend has occurred for other GM sets. Increasing the IDPVs up to a certain level reduces most EDPs and consequently causes an improvement in the seismic performance of the superstructure. The novel developed empirical relationships can be utilized as useful tools to predict IDRs and the damage states of the superstructure. The variations of the EDPs with respect to simultaneous or separate increasing the IDPVs are also reported for different GM sets.

Suspension Control and Characterization of a Variable Damping Magneto-Rheological Mount for a Micro Autonomous Railway Inspection Car

This paper aims to present a suspension control strategy for a semi-active mount with variable damping utilizing a smart magneto-rheological fluid (MRF), which will be applied in a micro autonomous railway inspection car as a primary suspension to protect the inspection equipment from the large suspension vibration on rails. We proposed a new multi-pole structure design for a semi-active magneto-rheological mount (MR mount) that can provide both a high damping force and a wide damping force band. Firstly, the mathematical model of MR mount dynamics was derived; secondly, a skyhook control strategy was developed for the MR mount; and finally, a dynamic simulation problem using Matlab software was constructed to evaluate the performance of the MR mount. The dynamic simulation results showed that the proposed MR mount using a skyhook control strategy showed greater vibration isolation performance compared to conventional passive mounts. In particular, the absolute displacement, velocity, and acceleration of the detector device were reduced by 83.33%, 77%, and 70%, respectively. The suspension vibration transmitted to the inspection device also decreased significantly, compared to input oscillation (i.e., un-sprung mass oscillation). Specifically, the suspension vibration reduced by a half at the excitation frequency of 2-fold the natural frequency and by greater magnitudes at higher excitation frequencies.

Are measured InSAR displacements a function of the chosen processing method?

The benefits of InSAR to the civil engineering industry have been demonstrated on many occasions, however there is still a limited uptake by end-users, due to perceived differences between data providers and uncertainty around how to interpret results. This paper critically compares three datasets for London: Radarsat-2 (RS2) from 2011 to 2015, TerraSAR-X (TSX) from 2011 to 2017, and Sentinel-1 (STL1) from 2015 to 2017. Two of the datasets (TSX & RS2) were processed by commercial data providers, while the STL1 data were processed using ENVI ® SARscape ® by the authors. The results show an inverse relationship between the Pearson Correlation Coefficient and absolute total displacement of Persistent Scatterers (PS). There is a strong correlation between datasets for total displacement greater than 5 mm, but a weak or no correlation in the 0–3 mm range. Consequently, standard commercial InSAR datasets, processed with no a priori knowledge of the area of interest, have error margins below 3–5 mm but correctly detect all deformation phenomena exceeding this threshold. RS2-TSX both capture the spatial extent of the investigated area of dewatering induced subsidence, however STL1 measures a much broader, less pronounced zone of heave than TSX. Thematic collection: This article is part of the Remote sensing for site investigations on Earth and other planets collection available at: https://www.lyellcollection.org/cc/remote-sensing-for-site-investigations-on-earth-and-other-planets

Experimental and numerical evaluation of simulated dental arch expansion during orthodontic therapy

Abstract In this publication, methods are presented to improve predictions of perioral soft-tissue changes following the expansion of the dental arches during orthodontic therapy. Acrylic veneers with different thicknesses were reversibly attached to the buccal surfaces of the upper and lower incisors to simulate their protrusion. The resulting morphological changes of the perioral soft-tissue surface were determined by 3D face scans. Experimentally-determined 3D soft-tissue changes are compared to numerical predictions using detailed finite-element (FE) models of the face of two individuals differing in the body mass index (BMI). The results suggest that common estimates of material constants used by the detailed and individualized FE models might be sufficient to explain absolute soft-tissue displacements although differences occurred between experimental and modeling results regarding the directions of displacements. The aim of this investigation is to create predictions of post-treatment appearance that are helpful for therapy planning.

Evaluation of novel 3D-printed and conventional thermoplastic stereotactic high-precision patient fixation masks for radiotherapy

PurposeFor stereotactic radiation therapy of intracranial malignancies, a patient’s head needs to be immobilized with high accuracy. Fixation devices such as invasive stereotactic head frames or non-invasive thermoplastic mask systems are often used. However, especially stereotactic high-precision masks often cause discomfort for patients due to a long manufacturing time during which the patient is required to lie still and because the face is covered, including the mouth, nose, eyes, and ears. To avoid these issues, the target was to develop a non-invasive 3D-printable mask system with at least the accuracy of the high-precision masks, for producing masks which can be manufactured in the absence of patients and which allow the eyes, mouth, and nose to be uncovered during therapy.MethodsFor four volunteers, a personalized 3D-printed mask based on magnetic resonance imaging (MRI) data was designed and manufactured using fused filament fabrication (FFF). Additionally, for each of the volunteers, a conventional thermoplastic stereotactic high-precision mask from Brainlab AG (Munich, Germany) was fabricated. The intra-fractional fixation accuracy for each mask and volunteer was evaluated using the motion-correction algorithm of functional MRI measurements with and without guided motion.ResultsThe average values for the translations and rotations of the volunteers’ heads lie in the range between ±1 mm and ±1° for both masks. Interestingly, the standard deviations and the relative and absolute 3D displacements are lower for the 3D-printed masks compared to the Brainlab masks.ConclusionIt could be shown that the intra-fractional fixation accuracy of the 3D-printed masks was higher than for the conventional stereotactic high-precision masks.

Mechanical properties of rock bolt and analysis for the full-process of sliding failure based on rock mass absolute displacement

Previous studies rarely involved the mechanical properties of anchorage system under the condition of internal absolute displacement of surrounding rock and the solution of important parameters of anchorage system. In this paper, the absolute displacement law of rock mass under the anchorage system is analyzed by the fiber grating (FBG) multi-point displacement meter and multidirectional displacement conversion formula. Based on the coordinated deformation principle for rock bolt and rock mass, the mechanical analysis model for rock bolt-rock mass system is established, and the influence rules of rock bolt length, rock bolt diameter and rock bolt preload on the internal force distribution of rock bolt is studied based on the stress analysis of full-length rock bolt in a tunnel engineering. The results show that: (1) with the increase of rock bolt length, the anchoring effect gradually enhances, but the improvement degree decreases gradually; (2) with the increase of rock bolt diameter, the anchoring effect is enhanced; at the same time, however, the shear stress of rock bolt is larger, and the possibility of rock bolt sliding also increases; and (3) with the increase of preload, the increase of “anchor length” makes the anti-sliding ability of rock bolt increase correspondingly, and the supporting effect of rock bolt increases gradually. Then the full-process analysis for the mechanical mechanism of rock bolt sliding failure and the iterative calculation method for rock bolt displacement are studied. At last, the numerical simulation for pull-out test is carried out through the finite element analysis to verify the calculation results of mechanical model, and according to the iterative operation, the two important parameters such as the interface shear stiffness K and the interface peak shear strength τ P are solved. The analysis show that the numerical simulation results are in good agreement with the mechanical model calculation. This study can provide a theoretical basis for rock bolt support technology and support structure design. • The testing and calculation methods of absolute displacement law of rock mass are analyzed by the FBG. • The analytical expressions for the axial force and shear stress of full-length rock bolt are obtained. • The full-process analysis for the mechanical mechanism of rock bolt sliding failure is studied. • The iterative calculation method for rock bolt displacement is proposed.

A blending control for broadband vibration isolation considering zero-infinite stiffness and damping

Active vibration isolation system (AVIS) using the traditional vibration isolation technology, such as reducing suspending stiffness and adding absolute damping, has performance defects due to the residual low-frequency disturbances which still severely restrict the precision machine accuracy. This paper proposes a novel vibration control method combining inertial absolute sensor feedback (ASF) and positive relative sensor feedback (RSF), which can highly improve the low-frequency vibration isolation performance, and the blending control method is analyzed according to the vibration transmission. The results show that ASF strengthens the connection between the payload and the absolute space, while positive RSF weakens the connection between the payload and the base. By introducing ASF and positive RSF blended, the stiffness and damping between the payload and the absolute space can be increased to near infinity, while the stiffness and damping between the payload and the base can be attenuated to near zero. The blending control method includes absolute displacement feedback (ADF), positive relative displacement feedback (RDF), absolute velocity feedback (AVF), and positive relative velocity feedback (RVF). ADF combined with RDF improves the vibration isolation performance at low-frequency, while AVF combined with RVF improves the performance around the inherent frequency and high-frequency. In this way, the payload is hard to be affected by disturbances in a broad frequency region. Finally, the proposed method is verified by experiments and compared with the commonly used sky-hook damping method. It shows that the initial frequency of vibration isolation is reduced from 5.6 Hz (sky-hook damping method) to 1 Hz (the proposed method), the magnitude of vibration transmission starts with −11.1 dB (at 1 HZ), and the maximum magnitude is always below 0 dB from 1 Hz to 50 Hz.

Optimum vertical location and design of multiple tuned mass dampers under seismic excitations

An efficient optimum vertical location and design method of multiple tuned mass dampers (MTMDs) is proposed in order to reduce the response of building structures under seismic excitation. Governing equations are derived in frequency domain in terms of random vibration theory and probabilistic critical excitation method. In order to determine the location and optimum parameters of each tuned mass damper (TMD) which are mass, stiffness and damping coefficient, both top storey mean square absolute acceleration and displacement of shear building are chosen as the objective functions to be minimized via Differential Evolution (DE) optimization method. It is assumed that there is one TMD on each storey at the initial stage of the method. During the optimization, if the mass or stiffness parameters convergence to zero on a specific storey, then TMD is eliminated, so that optimum placement can be achieved. The sum of the critical effects corresponding to the selected bandwidths in the first, second and third frequency peak regions of the structure is taken into account, thus the high mode behaviors are also controlled. In order to understand the performance of proposed method, shear building model with multiple TMD is tested using different earthquake acceleration records and the findings are compared with some other studies available in the literature. The results show that the optimal MTMD design obtained from proposed method is very effective in reducing the dynamic response of building structure.

Evaluation and Updates for the USGS San Francisco Bay Region 3D Seismic Velocity Model in the East and North Bay Portions

ABSTRACTWe update the eastern and the northern portions of the detailed domain of the U.S. Geological Survey San Francisco Bay region 3D seismic velocity model (SFVM) based on comparisons of recorded and synthetic ground motions from 20 moderate (Mw 3.7–4.6) earthquakes. We modify the current SFVM (v.08.3.0) by assigning alternate property-versus-depth relations to the existing 3D geologic model. In some places, changes correspond to reassigning correct relations in which geologic units appear to be mislabeled, and in other places we subdivide geologic units where mapped geologic boundaries are missing from the 3D models so that we can implement a velocity contrast across a boundary. We also make ad hoc adjustments to velocity rules near the surface in some areas to better fit arrival times (specifically, in the Livermore basin). The updates reduce misfits in waveform correlation, travel time, cumulative absolute displacement, and peak ground velocity and are included in v.21.1 of the model. The selected earthquakes are small enough so that we neglect finite-source effects and model them as point sources. This allows us to assume that observed waveform characteristics are the result of path effects, and discrepancies between synthetic and recorded motions arise from misrepresentation of the elastic properties. Our analysis suggests refining the 3D geologic model, and adjusting the rules assigning properties to the geologic units will further improve the accuracy of the SFVM for simulating earthquake ground motions.