Force-based Methods Research Articles

RC walls in Australia: displacement-based seismic design in accordance with AS 1170.4 and AS 3600

ABSTRACT Displacement-based methods, such as a non-linear static pushover analysis (e.g. the capacity spectrum method), have many advantages compared to traditional force-based design methods. However, implementing a non-linear analysis and design method in accordance with the Australian Standard for concrete structures (AS 3600) introduces many difficult technical issues into the design, of which the standard provides little guidance. The aim of this study is to provide a framework and general guidance for designers who wish to perform non-linear displacement-based analysis methods for RC wall buildings. The paper will present how these methods can be used in accordance with the Australian Standard for earthquake actions (AS 1170.4) to assess seismic compliance and then provide recommendations for the requirements stipulated by AS 3600, which includes an experimentally validated tension stiffening model, nonlinear stress-strain material curves, mean material properties and material strain limits. The paper is concluded with a case study example of how a displacement-based seismic assessment can be performed using a typical case study building.

Influence of Tool Runout on Force Measurement During Internal Void Monitoring for Friction Stir Welding of 6061-T6 Aluminum

Abstract The goal of this research was to examine how altering the amount of friction stir tool eccentricity while controlling the amount of slant in the tool shoulder (drivers of oscillatory process forces) effects the generation of process force transients during sub-surface void interaction. The knowledge gained will help improve the accuracy of force-based void monitoring methods that have the potential to reduce the need for post-weld inspection. Process force transients during sub-surface void formation were examined for multiple tools with varying magnitudes of kinematic runout. The eccentric motion of the tool produced oscillations in the process forces at the tools rotational frequency that became distorted when features (flats) on the tool probe interacted with voided volumes, generating an amplitude in the force signals at three times the tool rotational frequency (for three-flat tools). A larger tool eccentricity generates a larger amplitude in the force signals at the tool’s rotational frequency that holds a larger potential to create a distortion during void interaction. It was determined that once void becomes large enough to produce an interaction that generates an amplitude at the third harmonic larger than 30% of the amplitude at the rotational frequency in a weld with no interaction (amplitude solely at rotational frequency), the trailing edge of the tool shoulder cannot fully consolidate the void, i.e., it will remain in the final weld. Additionally, once the void exceeds a certain size, the amplitudes of the third harmonics saturate at 70% of the amplitude at the rotational frequency during full consolidation. The interaction between the eccentric probe and sub-surface void was isolated by ensuring any geometric imperfection in the shoulder (slant) with respect to the rotational axis was removed. The results suggest that geometric imperfections (eccentricity and slant) with respect to the tool’s rotational axis must be known when developing a void monitoring method from force transients of this nature.

Development of 6 DOF Displacement Sensor Using RUS Parallel Mechanism.

Nowadays, many types of manipulators have been developed and used in lots of production processes. Force-based control methods or additional mechanical devices called Remote Center Compliance (RCC) have increased the system’s compliance and accuracy. However, the force-based control method’s operating speed is low, and the RCC cannot measure deflection. Thus it cannot calculate the position of the end-effector accurately. For accurate force and position control, it is necessary to measure the deflection of the RCC and to perform this, a different type of device than the existing RCC is required. This paper presents the necessity and possibility of developing an RCC capable of measuring the displacement of the end-effector and showing the displacement sensor’s feasibility using a 6 DOF parallel mechanism. In particular, we suggest that it is possible to make devices cheaper and more compact by using angular displacement sensors. Finally, we show the possibility of use in actual industrial sites through peg-in-hole simulation using the device.

Seismic response of multi-span continuous irregular bridges using displacement-based and conventional force-based methods

In the recent years, the displacement-based seismic design (DBD) method of structures has been recognized as the alternative design method to the conventional force-based seismic design (FBD) method. The problems inherited in the FBD method are mostly overcome by the DBD method as it better correlates the structural damage with displacement-based quantities. In this study, the seismic response of multi-span bridges with varying number of spans and unequal pier heights was evaluated using the DBD method and compared with the conventional FBD method. Two approaches were employed in the DBD method, such as the traditional direct displacement-based seismic design (DDBD) approach and the proposed approach in this study entitled as alternative-to-direct displacement-based seismic design (ADBD). For seismic evaluation of the bridge structures with the FBD method, acceleration response spectra as suggested in the Bangladesh National Building Code were used; while in the DBD method, displacement response spectra for different damping ratios were developed keeping consistency with the above-mentioned design acceleration spectra. Five bridge models were used in the analysis to compare the seismic response in both the longitudinal and transverse directions taking into account the number of spans and height irregularity in the bridge models. Numerical analysis showed very obvious results that the base shear calculated by both approaches of the DBD method is found to be smaller than the FBD method indicating that an economic member section be attained for meeting the same design objective. More specifically, the ADBD approach provides the design professionals a more conservative design approach in compared with the DDBD approach keeping an economic design approach comparing with the FBD method.

Finite Element Modeling (FEM) vs. Simplified Force-Based Methods for Rigid Retaining Walls Under Earthquake Excitation

The performance of conventional rigid retaining wall under harmonic and transient ground motions is evaluated using three-dimensional finite element (FE) simulations. Rotation of wall about the base is found to be the predominant failure mechanism of the gravity retaining wall under seismic excitation. Earth pressure distribution corresponding to the peak ground acceleration is found to be nonlinear and unique in shape. The earth pressure distribution is strongly related to the rotational movement of the wall. Existing force-based methods for rigid retaining walls overestimated the earth pressure under seismic conditions compared to these numerical simulations.

A prospective cohort study of low-back outcomes and alternative measures of cumulative external and internal vibration load on the lumbar spine of professional drivers.

Objective:The aim of this study was to compare the performance of alternative measures of cumulative lifetime vibration dose to predict the occurrence of low-back pain (LBP) outcomes in a cohort of 537 professional drivers investigated at baseline and over a two-year follow up period.Methods:The exposure data obtained in the EU VIBRISKS project were used to calculate alternative measures of either acceleration- (external) or force- (internal) based lifetime vibration doses. Vibration was measured in representative samples of machines and vehicles used by the drivers. Internal lumbar forces were calculated by means of anatomy-, posture-, and anthropometry-based finite element models. The relations of LBP outcomes to alternative measures of lifetime vibration doses were assessed by the generalized estimating equations method.Results:Metrics of cumulative vibration exposure constructed with either acceleration- or force-based methods were significantly associated with the occurrence of LBP outcomes. A measure of model fitting suggested that force-based doses were better predictors of LBP outcomes than acceleration-based doses. Models with force root-mean-square doses provided a better fit to LBP outcomes than those with force-peak doses.Conclusions:Measures of internal lumbar forces were better predictors of LBP outcomes than measures of external vibration acceleration although the exposure metrics constructed with the acceleration-based method have the advantage of greater simplicity compared to the force-based method. The differences between the models with force-based doses suggest that the cumulative health effects on the lumbar spine might depend on the integrated resulting total force over the entire exposure time rather than primarily on the force peaks.

Efficient direct displacement-based seismic design approach for structures with viscoelastic dampers

Viscoelastic damper (VED) is one of most effective structural control techniques, because it provides both additional stiffness and damping to the structures. Current seismic standards implement force-based methods for the design of VEDs, which generally require extensive iterative calculations. It also causes inconsistent risk degree and economic efficiency because it is displacements, rather than forces, that are directly related to structural damage. In the past decades, researchers have developed a direct displacement-based design (DDBD) methodology. The DDBD approach begins with selecting a target displacement and estimating of the equivalent damping ratio, and then calculate the seismic demand of the structure using a substitutive equivalent elastic system. However, because of the strong nonlinearity of the VED devices, it is difficult to appropriately proportion the key parameters (i.e., damping, period) of the VED controlled structure system, which makes the DDBD method ineffective. To solve this problem, this paper proposed an efficient DDBD approach that is in accordance with the Chinese seismic design principles. The relationship between the equivalent damping and structure period of the VED-structure system is established, so the proposed approach requires minimum iterative calculations and the efficiency improves significantly. A step-by-step description of the approach is presented, in which the two key VED parameters, namely the strain amplitude and its additional damping ratio contribution to the structure, are determined by the target displacements. The approach is further examined and verified by a 24 story building. Nonlinear history analysis results confirm that, by using the proposed DDBD procedure, the designed target story drift is achieved with no iterative calculations and the structural responses of the VED-structure system satisfy the code requirements.

Applying forces to generate cartograms: a fast and flexible transformation framework

ABSTRACT Automatic production of contiguous area cartograms has become practical with computer algorithms, particularly applying forces to rubber-sheets and simulating diffusion processes. Reformulating the existing force-based and rubber-sheet methods, this article presents a fast and flexible force-based computational framework for general space transformation with solid physical and mathematical foundations. When being applied to cartogram production, this framework guarantees topological integrity, allows flexible force generation, achieves fast convergence, and avoids extreme shape deformation. Benchmarked against the recently published fast flow-based diffusion method using five datasets of various volume, compactness, and complexity, this force-based framework is faster, reduces more shape deformation, and can produce cartograms with distinctive slim or inflated styles. Additionally, the force-based framework is robust and can handle complicated datasets, whereas the flow-based method produces errors from them. Although the flow-based diffusion method often reduces cartogram size error more than the force-based (typical weighted mean error is below 0.1% versus 1%), both are outstanding with such low levels of error and their cartograms generally register little visual differences. Overall, the force-based transformation framework provides a fast, flexible, and robust alternative to the diffusion method for cartogram production.

Modulation of GPCR Function by Membrane Lipids and Water

G‐protein‐coupled receptors (GPCRs) are integral membrane proteins that regulate a wide range of normal and disease‐related physiological processes. Our understanding of the role of soft matter such as membrane lipids and cellular water on activation and regulation of the GPCR function remains incomplete. In the standard biochemical model, GPCRs behave as primarily agonist dependent bimodal switches, with little influence of the surrounding medium. However, using the visual receptor rhodopsin as a model GPCR, we show that water drives rhodopsin to a partially disordered, solvent‐swollen conformational ensemble upon light absorption, rendering the standard model obsolete [1], [2]. We placed rhodopsin under varying degrees of osmotic stress using polyethylene glycol solutes and investigated the activation equilibrium response using UV‐Visible spectroscopy. Our results show a flood of ~ 80 water molecules into the rhodopsin interior during photoactivation, a result supported by atomistic molecular dynamics simulations [3]. Furthermore, the osmolyte effects on rhodopsin activation are size dependent: large osmolytes back shift the equilibrium to inactive metarhodopsin‐I (MI), while small osmolytes forward‐shift the equilibrium to active metarhodopsin‐II (MII). We attribute these size effects to varying degrees of osmolyte penetration into the rhodopsin core. Large polymers behave similarly to ideal osmolytes and dehydrate rhodopsin, while smaller polymers wriggle into the rhodopsin interior and stabilize the open MII conformation of rhodopsin. Besides osmotic pressure, the application of hydrostatic pressure also back shifts the metarhodopsin equilibrium but for fundamentally different reasons. Integrating the two force‐based methods together with neutron scattering experiments indicates that the active state of rhodopsin is more hydrated yet simultaneously more structurally collapsed [4]. At the same time, the active GPCR undergoes dynamic volume fluctuations and solvent coupling, which give rise to greater thermal volume. Our results necessitate a new understanding of GPCR activation in which the surrounding soft matter is paramount in governing conformational energy landscapes.Support or Funding InformationNSF (MCB 11817862 and CHE 1904125) and US NIH (EY012049 and EY02604)

Improved seismic design method for steel moment frames

Force-based and displacement-based methods are two conventional approaches for the seismic design of structures. Recently, the advantages and disadvantages of these methods have activated the researchers to combine them and to introduce the hybrid force–displacement (HFD) seismic design methods. In this paper, a new method named “modified seismic coefficient” for steel moment frames (MRFs) is presented. For this purpose, the seismic behavior factor and response spectrum of the structure are determined based on actual structural response and also the fundamental period of the structure. For practical examples, at first, a series of three (3, 6, and 9-story) MRFs is designed based on the proposed method and a classic HFD method, and then, their seismic responses are evaluated using nonlinear time-history analyses. For satisfying life safety (LS) performance level, it is observed that the proposed method reduces structural weight as 27, 22, and 24% for 3, 6, and 9-story frames, respectively.

G-Protein-Coupled Receptors are Solvent-Swollen in the Functionally Active State

G-protein-coupled receptors (GPCRs) are transmembrane receptors that play critical roles in a number of physiological signaling processes. In the standard biochemical model, GPCRs behave as primarily agonist-dependent bimodal switches, with little influence of the surrounding medium. However, using the visual receptor rhodopsin as a model GPCR, we show that water drives rhodopsin to a partially disordered, solvent-swollen conformational ensemble upon light absorption, rendering the standard model obsolete. We placed rhodopsin under varying degrees of osmotic stress using polyethylene glycol solutes and investigated the activation equilibrium response using UV-visible spectroscopy. Our results show a flood of ∼80 water molecules into the rhodopsin interior during photoactivation, a result supported by atomistic MD simulations [1]. Furthermore, the osmolyte effects on rhodopsin activation are size-dependent: large osmolytes back shift the equilibrium to inactive metarhodopsin-I (MI), while small osmolytes forward-shift the equilibrium to active metarhodopsin-II (MII). We attribute these size effects to varying degrees of osmolyte penetration into the rhodopsin core. Large polymers behave similarly to ideal osmolytes and dehydrate rhodopsin, while smaller polymers wriggle into the rhodopsin interior and stabilize the open MII conformation of rhodopsin. Besides osmotic pressure, the application of hydrostatic pressure also back shifts the metarhodopsin equilibrium but for fundamentally different reasons. Integrating the two force-based methods together with neutron scattering experiments [2] indicates that the active state of rhodopsin is more hydrated yet more locally collapsed. At the same time, the active GPCR undergoes volume fluctuations and solvent coupling, which give rise to greater thermal volume. The combined force-based results necessitate a new understanding of GPCR activation in which the surrounding soft matter is paramount in governing conformational energy landscapes. [1] N. Leioatts et al. (2014) Biochemistry 53, 376−385. [2] S.M.D.C. Perera et al. (2018) J. Phys. Chem. Lett.9, 7064−7071.

Mevcut Betonarme Bir Binanın 2007 ve 2018 Deprem Yönetmeliklerine Göre Deprem Yükleri Altındaki Taşıyıcı Sistem Perfomansının Değerlendirilmesi

Son yıllarda, mevcut binaların deprem etkisi altındaki taşıyıcı sistem performanslarının belirlenmesi için kuvvet esaslı yöntemlerin yerine, şekildeğiştirme ve yerdeğiştirme esaslı doğrusal olmayan yöntemler kullanılmaya başlanmıştır. Türkiye Bina Deprem Yönetmeliği (TBDY-2018) ve Deprem Bölgelerinde Yapılacak Binalar Hakkında Yönetmelik’te (DBYBHY-2007) mevcut binaların performanslarının belirlenmesi için doğrusal ve doğrusal olmayan hesap yöntemlerine yer verilmiştir. TBDY-2018’de doğrusal olmayan hesap için önerilen yöntemler, Tek Modlu İtme Yöntemi, Çok Modlu İtme Yöntemi ve Zaman Tanım Alanında hesap yöntemidir. DBYBHY-2007’de doğrusal olmayan hesap için önerilen yöntemler, Artımsal Eşdeğer Deprem Yükü Yöntemi, Artımsal Mod Birleştirme Yöntemi ve Zaman Tanım Alanında hesap yöntemidir. TBDY-2018 ve DBYBHY-2007 arasındaki en büyük fark, betonarme kesitlerin etkin kesit rijitlikleri ve hasar sınırı tarifleridir. Bu çalışmada, mevcut 5 katlı betonarme konut yapısının DBYBHY-2007 ve TBDY-2018’e göre Doğrusal Olmayan Artımsal İtme Analizi yöntemiyle deprem yükleri altında bina taşıyıcı sisteminin performans analizi yapılmış ve sonuçlar karşılaştırılarak irdelenmiştir.

Highly efficient facial blendshape animation with analytical dynamic deformations

Adding physics to facial blendshape animation is an active research topic. Existing physics-based approaches of facial blendshape animation are numerical, so they require special knowledge and skills, additional preprocess, large computer capacity, and expensive calculations leading to low animation frame rates, and are not easy to learn, implement and use. To tackle these problems, we propose an analytical approach and develop a blending force-based framework for physics-based facial animation. The proposed approach introduces the equation of motion to consider inertial effects, damping effects and the resistance against deformations, combines them with source and target facial shapes to formulate the mathematical model of dynamic deformations, and develops a simple and efficient closed-form solution. The blending force-based framework incorporates the new proposed slider force-based, exponentiation force-based and random force-based methods built on the obtained closed form solution to achieve highly efficient facial animation. Compared with facial blendshape animation using geometric linear interpolation, the proposed approach is physics-based. It not only creates all the blended shapes generated by linear interpolation, but also a much larger superset of blended shapes. Unlike linear interpolation which can only generate blended shapes with a same deformation rate, the proposed approach can generate blended shapes with different deformation rates, resulting in special effects of acceleration and deceleration. Compared to existing physics-based approaches of facial blendshape animation which are numerical, the proposed approach is the first time to develop an analytical approach of physics-based facial blendshapes. It does not require any special knowledge and skills and is easy to learn, implement and use. More importantly, it can avoid the additional preprocess of numerical methods and create various physics-based facial blendshape animations highly efficiently. Moreover, it can be used to estimate physical parameters from real shapes and developed into an interactive and real-time physics-based shape manipulation tool.

Accurate configuration force evaluation via hp-adaptive discontinuous Galerkin finite element analysis

Engineers require accurate determination of the configurational force at the crack tip, and corresponding stress intensity factors, for fracture fatigue analysis and accurate crack propagation. However, obtaining highly accurate crack tip configuration force values is challenging with methods requiring knowledge of the stress field around the crack tip a priori. This paper proposes a method which aims to remove the necessity of knowing the stress field a priori whilst producing very accurate values of the configurational force at a static crack tip. The proposed method is demonstrated to be path independent and is combined with a robust a posteriori residual error estimator which is indicative of the accuracy of the configurational force calculation. This makes it possible to generate accurate values for the configurational force acting both perpendicular and parallel to the crack edges. Accuracies are achieved which are at least 104 times more accurate than other numerical methods which make no assumption about the local tip stress field. Therefore accurate benchmarks are determined in this paper for inclined, split and tree crack problems. In addition the new method is shown to obtain very similar values for the configurational force compared to results obtained using other methods which require knowledge of the stress field at the crack tip. The techniques presented in this paper open the door to configurational force-based methods being used for fatigue analysis.

Simplified force-based seismic design procedure for linked column frame system

Dual structural systems with structural fuse such as linked column frame system (LCF) have two main performances, including the resistance to lateral seismic loads and the proper function of structural fuse to control deformation of the other members to remain in elastic phase. The achievement of these two functions is necessary for appropriate seismic design of these systems. Undoubtedly, despite the practical complexity, displacement-based seismic design methods are generally the best method for this purpose. In contrast, conventional force-based methods are relatively simple, but it cannot easily guarantee the desired performance. In this paper, a simplified force-based seismic design method is presented for linked column frame system based on parametric studies on different structures, which are designed with displacement-based method. In addition to simplicity, the proposed method has an appropriate accuracy in terms of achieving the performance objectives. For the parametric study, 18 prototype structures with various relative lateral stiffness of moment frame and linked column system are designed with the displacement-based method. Based on the results of the structures designed with desirable performance, the criteria are proposed for the force-based design method. Based on evaluating results, the structures designed by the proposed simplified force-based method properly reached the performance objectives.

Cross Wind Effects on Vehicle–Track Interactions: A Methodology for Dynamic Model Construction

An efficient and accurate model for the dynamic assessment of vehicle-track behavior subjected to cross wind actions is developed in this paper, where the wind–vehicle–track interaction is regarded as a coupled vibration system. First, a vehicle–track interaction model is proposed by taking the hypotheses of wheel/rail rigid contact and displacement complementarity. Unlike explicit force-based methods, the vehicle-track systems are wholly coupled by interaction matrices and load vectors, which are computationally more efficient than most of the existing methods and fairly accurate in low frequency vibrations. Then, the fluctuating cross winds are simulated by the fast Fourier transform technique from spectral representations with the consideration of spatial correlation of multipoint wind time histories and vehicle movement. The unsteady cross wind forces are obtained by introducing weighting function. Finally, a modeling framework, with the coupled interactions between cross winds, vehicle, and the tracks included, is built effectively. Through the validated dynamic model, the cross wind effects on vehicle-track dynamic performance can be fully revealed. Besides, it is concluded that the dynamic performance of vehicle-track systems differs significantly in various excitation modes, i.e., average cross wind, fluctuating cross wind, and track irregularities.

Magnetic Force-Based Microfluidic Techniques for Cellular and Tissue Bioengineering.

Live cell manipulation is an important biotechnological tool for cellular and tissue level bioengineering applications due to its capacity for guiding cells for separation, isolation, concentration, and patterning. Magnetic force-based cell manipulation methods offer several advantages, such as low adverse effects on cell viability and low interference with the cellular environment. Furthermore, magnetic-based operations can be readily combined with microfluidic principles by precisely allowing control over the spatiotemporal distribution of physical and chemical factors for cell manipulation. In this review, we present recent applications of magnetic force-based cell manipulation in cellular and tissue bioengineering with an emphasis on applications with microfluidic components. Following an introduction of the theoretical background of magnetic manipulation, components of magnetic force-based cell manipulation systems are described. Thereafter, different applications, including separation of certain cell fractions, enrichment of rare cells, and guidance of cells into specific macro- or micro-arrangements to mimic natural cell organization and function, are explained. Finally, we discuss the current challenges and limitations of magnetic cell manipulation technologies in microfluidic devices with an outlook on future developments in the field.

ABOUT METHODS OF SEISMIC ANALYSIS OF UNDERGROUND STRUCTURES

As is known, underground facilities are an integral part of the infrastructure of modern society. These objects have some specific characteristics such as complex construction, high cost, long life cycle, etc. Once it is destroyed, the direct and indirect losses are more seriousness than the general structure in the ground. Under-ground facilities built in areas subject to earthquake activity must withstand both seismic and static loading. Therefore, it is very important to carry on the seismic design of the underground structure in a safe and economi-cal way. The distinctive paper presents a summary of the current state of seismic analysis for underground struc-tures. Classification and brief overview of methods of seismic analysis of underground structures (force-based methods, displacement-based methods, numerical methods of seismic analysis of coupled system “soil – under-ground structure”) are presented, problems of soil-structure interaction are under consideration as well. So-called static finite element method with substructure technique for seismic analysis of underground structures is de-scribed.

About Contemporary Seismic Analysis of Underground Structures

This paper is devoted to actual problems of seismic analysis of underground structures. Brief classification and overview of corresponding methods of analysis (force-based methods, displacement-based methods, numerical methods of seismic analysis of coupled system “soil – underground structure” and approaches to problems of soil-structure interaction) is presented. Special static finite element method with substructure technique for seismic analysis of underground structures is described. Dynamic soil-structure interaction system can be decomposed into three sub-structures: structure, near-field and far-field soil. The first stage of static finite element method is solving the free field shear stress, acceleration, velocity and displacement, when the moment that the relative displacement of the soil that the underground structure located in reaches the maximum. The second stage is computing of internal forces and parameters of boundary conditions. The third stage is construction of the static finite element model and imposing the loads and constrains computed at the second stage and then making a static analysis.

On a Reliability-Based Method to Improve the Seismic Performance of Midrise Steel Moment Resisting Frame Setback Buildings

A framework is proposed to improve seismic performance of special steel moment resisting frame (SMRF) setback structures based on the reliability-based approach. In this procedure, seismic design of midrise setback structures is modified to improve the confidence level of meeting the life safety performance level in these structures to a reliable level. To achieve this, based on the results of the incremental dynamic analysis, an algorithm is proposed to introduce more accurate equations to predict the maximum inelastic inter-story drift ratio of setback structures in linear force-based design methods. It is observed that by applying the proposed relations in the seismic design of setback buildings, this type of structures demonstrates more reliable seismic performance compared to the code-designed approach. The proposed method is economically effective in reducing the possible losses during the lifetime of SMRF setback buildings located in seismic prone areas.