Force-deformation Relationship Research Articles

Experiment Study of BFRP Bars’ Mechanical Properties

The testing rule of mechanical properties of material can be established and the mechanical performance can be found by studying the basic mechanical properties of BFRP bars. Using the opressive sleeve anchor developed by the researchers,tensile tests of BFRP bars are carried out according to the national standards of “GFRP bar tensile test methods”.The BFRP bar’s force-deformation curve is linear before the force-deformation relationship is destroyed,therefore,referring to steel wire or steel cable,the BFRP bar’s reliable strength is suggested to be approximately 80% of its ultimate tensile strength. The BFRP bar’s tensile elastic modulus is related to the content of basalt fiber.The tensile elastic modulus increases with the increase of the basalt fiber’s content and the content increases when the BFRP bar’s diameter becomes longer, so the tensile elastic modulus increases with the increase of its diameter. Compared with steel, the BFRP bar is obviously superior in the aspects of tensile strength, corrosion resistance ,etc,therefore to use the BFRP bar in reinforced concrete structures insead of steel is feasible.

Series Viscoelastic Actuators Can Match Human Force Perception

Series elastic actuators (SEAs) are frequently used for force control in haptic interaction, because they decouple actuator inertia from the end effector by a compliant element. This element is usually a metal spring or beam, where the static force-deformation relationship offers a cheap force sensor. For high-precision force control, however, the remaining small inertia of this elastic element and of the end effector still limit the sensing performance and rendering transparency. Here, we extend the concept to deformable end effectors manufactured of viscoelastic materials. These materials offer the advantage of extremely low mass at high maximum deformation and applicable load. However, force and deformation are no longer statically related, and history of force and deformation has to be accounted for. We describe an observer-based solution, which allows drift-free force measurement with high accuracy and precision. Although the description of the viscoelastic behavior involves higher-order derivatives, the proposed observer does not require any numerical differentiation. This new integrated concept of sensing and actuation, called series viscoelastic actuator (SVA), is applied to our high-precision haptic device OSVALD, which is targeted at perception experiments that require sensing and rendering of forces in the range of the human tactile threshold. User-device interaction force is controlled using state-of-the-art control strategies of SEAs. Force estimation and force control performance are evaluated experimentally and prove to be compatible with the intended applications, showing that SVAs open up new possibilities for the use of series compliance and damping in high-precision haptic interfaces.

Numerical study of dynamic behavior of concrete by meso-scale particle element modeling

Based on the Particle Element Method, a meso-scale dynamic model is developed for numerical study of the dynamic failure behavior of three-phase concrete i.e., aggregate, mortar, and interface, under different strain rates. First, a pre-processing approach based on the background grid search method proposed in our previous work is applied to generate the three-phase concrete specimen in meso-scale; second, the meso-mechanical parameters of three phases of concrete are determined by inverse method; and third, using the meso-scale dynamic model, the complete force-deformation relationship and the corresponding dynamic increase factors (DIF) at different strain rates are obtained for dynamic splitting tensile and uniaxial compression tests of concrete. The results match satisfactorily with the preceding experiments in related literatures. Different fracture patterns, consumed energy curves and force chain distributions are discussed under different strain rates, explaining the mechanism of strain rate effects in concrete. The numerical simulations show that the higher the strain rates, the more reticular meso-cracks occur, the kinetic and frictional energies become more important, and the force chains in the specimen exhibit more bifurcation, implying that the fracture process at high strain rates requires more energy demand to reach failure.

Strength reduction factors for seismic analyses of buildings exposed to near-fault ground motions

To estimate the near-fault inelastic response spectra, the accuracy of six existing strength reduction factors (R) proposed by different investigators were evaluated by using a suite of near-fault earthquake records with directivity-induced pulses. In the evaluation, the force-deformation relationship is modelled by elastic-perfectly plastic, bilinear and stiffness degrading models, and two site conditions, rock and soil, are considered. The R-value ratio (ratio of the R value obtained from the existing R-expressions (or the R-µ-T relationships) to that from inelastic analyses) is used as a measurement parameter. Results show that the R-expressions proposed by Ordaz & Perez-Rocha are the most suitable for near-fault ground motions, followed by the Newmark & Hall and the Berrill et al. relationships. Based on an analysis using the near-fault ground motion dataset, new expressions of R that consider the effects of site conditions are presented and verified.

Seismic Behavior of a Partially Infilled RC Frame Retrofitted Using GFRP Laminates

Masonry-infilled panels are normally used as partitions or as architectural elements in reinforced concrete (RC) structures. The need for incorporating openings to the walls of a building in order to provide natural lighting and ventilation leads to partial lateral confinement along the height of the column by rigid elements, such as internal partitions and facades. This situation introduces large shear stresses, when the structure is subjected to seismic forces and the columns can be seriously damaged due to captive-column effect. This paper presents the results of analytical and experimental investigations of one-third scaled two-bay two-story RC frames with partial infill in the bottom story and subjected to lateral cyclic loads. A local retrofitting strategy of strengthening RC structural elements with glass fiber reinforced polymer (GFRP) composites was adopted. Test results indicated that the retrofitted frame exhibited significantly higher ultimate strength and stiffness than the control frame (frame without retrofit). Force–deformation relationships, damage patterns, and other characteristics of the frames were also demonstrated. The aim of the GFRP retrofit was to enhance the global performance of the partially infilled structure under seismic action, by preventing the development of captive-column conditions.

Dynamic analysis methodology for progressive failure of truss structures considering inelastic postbuckling cyclic member behavior

Over the years, several catastrophic collapses of truss structures have been reported. Sudden failure or reduction in member capacity of a single member in a truss structure gives rise to dynamic force redistribution in the remaining members and may lead to progressive collapse of the entire structure. During failure, truss members can undergo inelastic cyclic behavior (including postbuckling in compression and yielding in tension) that may not have existed in the intact structure. This paper presents a methodology to incorporate the inelastic cyclic member force–deformation behavior in the dynamic analysis of truss structures and at the same time incorporates the possible dynamic effects arising from the sudden change in load carrying capacity of a member due to failure or buckling/postbuckling. The method tracks and generates the force–deformation characteristics of every member of the truss at each incremental time step. The continuous change in the load-carrying capacity and the stiffness of members during the nonlinear force–deformation history has been incorporated in the analysis scheme using the Pseudo-force approach. The solution methodology for obtaining the dynamic response of the structure is based on the finite element technique and considers elasto-plastic material and large deformation geometric nonlinearities. The methodology is applied to a two-dimensional three-member toggle redundant truss subjected to external static, quasi-static, and dynamic (sinusoidal and ramp) loads. Results delineating the effects of the inelastic cyclic axial force–deformation relation of each member and the time variation of joint displacements and member forces are presented for each loading condition. The results show that there exist cases where modeling a compression member with its actual postbuckling behavior, which although has some reserve load carrying capacity, are more critical than the case where the same member is considered to suddenly lose its full load carrying capacity at its buckling load.

Change in response of bridges isolated with LRBs due to lead core heating

This study focuses on the response of seismic isolated bridges subjected to near-field ground motions with distinct pulse type behavior in terms of maximum isolator displacements (MIDs) and maximum isolator forces (MIFs) transferred to the substructure. The employed isolation systems are composed of lead rubber bearings (LRBs) with bi-linear force-deformation relations that consider cycle-to-cycle deterioration in the yield strength of the LRBs due to heating of the lead core. MIDs and MIFs with due consideration of cycle-to-cycle deterioration are compared with that of non-deteriorating ones. Bounding analyses are also performed for comparison purposes. Nonlinear response history analyses are conducted with two bins of ground motions recorded at different soil conditions to investigate the effect of ground motion characteristics. Results indicate that MIDs are overestimated by lower bound analyses when seismic isolated bridges are subjected to near-field motions with high velocity pulses especially for the bearings with higher Q/ W ratios.

Relationships of Barge Bow Force–Deformation for Bridge Design

Loads generated during vessel collisions with bridges are inherently dependent on force–deformation characteristics of the impacting vessel. Currently in the United States, barge impact forces used in bridge design are computed with a force–deformation (crush–curve) model proposed by AASHTO. A recent study uncovered important limitations in the AASHTO barge-crushing model, and a revised procedure for developing barge force–deformation relationships was developed. However, relationships developed in this previous study were based on the assumption that impact occurred directly head on to the impacted pier; the scenario was unlikely. Impact more likely occurs at some oblique angle. This paper shows that barge impact forces on flat-faced pier surfaces (i.e., rectangular columns or waterline pile caps) are typically less severe when collisions occur at even small oblique angles. Thus, the current study focused on updating the prior crushing model to account probabilistically for reduced forces associated with oblique impact. In this paper, oblique impact forces were quantified by means of a series of high-resolution simulations of finite element barge bow crushing. Results obtained from these simulations were used in a probabilistic study to develop a force prediction model that implicitly accounted for the relative likelihood of impact occurring at particular angles. Findings from the current study were then integrated into the previously developed barge-crushing model to produce a design-oriented calculation framework that would permit bridge designers to account easily for force reductions that arise in oblique impact scenarios.

Fiber Element Based Elastic-Plastic Analysis Procedure and Engineering Application

Elastic-plastic time history analysis of super high-rise building is accomplished by the program PERFORM-3D to evaluate the global response and component deformation of structure based on fiber element theory. Direct modeling of a tall building in PERFORM-3D is complicated; hence a pre-process program ETP is established for a more effective and accurate modeling. Analysis improves that fiber element-based nonlinear analysis of the overall structure reveals the macro properties of the structure as well as the force-deformation relationship for the component and stress-strain relationship for the fiber in the micro scope. Finally, the global response, component deformation and energy dissipation of the complicated tall building designed by the current codes subjected to severe ground motions are studied in one engineering practices.

604 非線形特性による地震応答の低減と吸収エネルギの関係:(履歴復元力特性と摩擦特性がある場合)(機械力学・計測制御I)

604 非線形特性による地震応答の低減と吸収エネルギの関係:(履歴復元力特性と摩擦特性がある場合)(機械力学・計測制御I)

Geometrically Nonlinear Analysis of Plane Frames Subjected to Temperature Changes

Procedure for large displacement and stability analysis of elastic plane frames subjected to temperature changes is presented. The method of analysis is based on an Eulerian (corotational) formulation, which was developed initially for static loads, and is extended herein to include thermal effects. Local element force-deformation relationships are derived using the theory taking into consideration the effect of curvature due to temperature gradient across the element cross section. The changes in element chord lengths due to thermal axial strain, and bowing due to temperature gradient, are taken into account. This beam-column approach, using stability and bowing functions, requires significantly fewer elements per member (i.e., a beam or a column) for the analysis of a framed structure than the finite-element approach. A computational technique, using Newton-Raphson iteration, is developed to determine the nonlinear responses of structures. Numerical solutions are presented for a number of benchmark structures to demonstrate the feasibility of the proposed method of analysis.

Out-of-Plane Flexural Performance of GFRP-Reinforced Masonry Walls

The objective of this paper is to assess the out-of-plane flexural performance of masonry walls that are reinforced with glass fiber-reinforced polymers (GFRPs) rods, as an alternative for steel rebars. Eight 1 m×3 m full-scale walls were constructed using hollow concrete masonry units and tested in four-point bending with an effective span of 2.4 m between the supports. The walls were tested when subjected to increasing monotonic loads up to failure. The applied loads would represent out-of-plane loads arising from wind, soil pressure, or inertia force during earthquakes. One wall is unreinforced; another wall is reinforced with customary steel rebars; and the other six walls are reinforced with different amounts of GFRP reinforcement. Two of the GFRP-reinforced walls were grouted only in the cells where the rods were placed to investigate the effect of grouting the empty cells. The force-deformation relationship of the walls and the associated strains in the reinforcement were monitored throughout the t...

Mechanical Characterization of Human Red Blood Cells Under Different Osmotic Conditions by Robotic Manipulation With Optical Tweezers

The physiological functions of human red blood cells (RBCs) play a crucial role to human health and are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. The osmotic condition is an important factor to the physiological environment, but its effect on RBCs has been little studied. To investigate this effect, robotic manipulation technology with optical tweezers is utilized in this paper to characterize the mechanical properties of RBCs in different osmotic conditions. The effectiveness of this technology is demonstrated first in the manipulation of microbeads. Then the optical tweezers are used to stretch RBCs to acquire the force-deformation relationships. To extract cell properties from the experimental data, a mechanical model is developed for RBCs in hypotonic conditions by extending our previous work , and the finite element model is utilized for RBCs in isotonic and hypertonic conditions. Through comparing the modeling results to the experimental data, the shear moduli of RBCs in different osmotic solutions are characterized, which shows that the cell stiffness increases with elevated osmolality. Furthermore, the property variation and potential biomedical significance of this study are discussed. In conclusion, this study indicates that the osmotic stress has a significant effect on the cell properties of human RBCs, which may provide insight into the pathology analysis and therapy of some human diseases.

Dynamic Amplification of Pier Column Internal Forces Due to Barge–Bridge Collision

In the United States, bridge design provisions for waterway vessel collision typically involve static application of code-prescribed impact loads. However, results from full-scale experimental impact tests have revealed that significant mass-related inertial forces can develop in affected piers because of the overlying superstructure. In part on the basis of these findings, a dynamic (time history) analysis technique was previously developed; it predicts both impact load and structural response. In the current research, the dynamic analysis technique is combined with recently developed barge force–deformation relationships and a simplified bridge modeling technique to conduct a detailed investigation of collision-induced dynamic amplification phenomena. Design forces are quantified for a wide range of bridge types by using dynamic and static analyses. For each bridge considered, dynamic amplifications are numerically quantified by comparing dynamic to static predictions of pier column demand. Significant amplification effects are consistently found among the barge–bridge collision simulations conducted, indicating that dynamic phenomena should be accounted for in bridge design.

Series solutions for spatially coupled buckling anlaysis of thin-walled Timoshenko curved beam on elastic foundation

The spatially coupled buckling, in-plane, and lateral bucking analyses of thin-walled Timoshenko curved beam with non-symmetric, double-, and mono-symmetric cross-sections resting on elastic foundation are performed based on series solutions. The stiffness matrices are derived rigorously using the homogeneous form of the simultaneous ordinary differential equations. The present beam formulation includes the mechanical characteristics such as the non-symmetric cross-section, the thickness-curvature effect, the shear effects due to bending and restrained warping, the second-order terms of semitangential rotation, the Wagner effect, and the foundation effects. The equilibrium equations and force-deformation relationships are derived from the energy principle and expressions for displacement parameters are derived based on power series expansions of displacement components. Finally the element stiffness matrix is determined using force-deformation relationships. In order to verify the accuracy and validity of this study, the numerical solutions by the proposed method are presented and compared with the finite element solutions using the classical isoparametric curved beam elements and other researchers` analytical solutions.

Coupling Behavior of Wire Ropes Subjected to Tensile Impulses

To determine the stress state of a wire rope is tedious although analytical solution of a simple rope subjected to static load is available. While facing the problems involving complex ropes, it is usual practice to take approximations based upon the concepts of an average stress state for the constitutive ropes or for every wire. For a statically loaded cable superimposed with a tensile impulse, practically in sudden lifting of a heavy weight, the coupled axial-shearing strain waves in the cable has rarely been studied and explored through analytical approaches. Based on Costello’s force-deformation relationship and elastic wave propagation theory, analysis procedures and results are presented in this paper. Time-dependent coupled axial-torsional displacements and axial-shearing strain waves in a simple straight wire rope, due to a longitudinal impact at one end, are obtained. At the instance of the strike, a pair of coupled primary axial-torsional waves is created and begins to travel in the cable indep...

Tsunami bore forces on a compliant residential building model

The forces exerted on light-frame wood buildings as a result of surge and waves are not fully understood. With a better understanding of these types of forces, it may eventually be possible to build coastal structures to better withstand the loads. In this paper, a recent two part experimental study that focused on determining the forces induced in a structurally compliant model of a typical Gulf Coast residential building is summarized. The one-sixth scale building was designed to approximately behave as the full scale building would under wave loading using rules of energy-based similitude. The compliant model was subjected to solitary wave loading in the Network for Earthquake Engineering Simulation (NEES) tsunami wave basin (TWB) at Oregon State University with wave heights ranging from 0.1 m to 0.6 m. Then, at Colorado State University, lateral force–deformation tests on a nominally identical model were performed in order to determine the force–deformation relationship for the building. The structural deformation produced by solitary waves in the wave basin was combined with the experimentally measured deformation in the structural laboratory to determine the force induced by the waves between 0.2m and 0.6 m. Finally, a simplified force equation constant similar to the existing design code formats was found to be 0.31.

Structural modeling of SMA fiber hybrid active thin-walled composite beams

Abstract The constitutive equations relating cross-sectional loads (forces and moments) to cross-sectional displacements (stretching, bending, twisting) of thin-walled laminated beams with integral shape memory alloy (SMA) active fibers is presented. The variational asymptotic method is used to formulate the force-deformation relationships equations accounting for the presence of active SMA fibers distributed along the cross-section of the beam. The constitutive relationships for evaluation of the properties of a hybrid SMA composite ply are obtained following the rule of mixtures. The analytical expressions of the actuation components for the active beam are derived based on Tanaka’s constitutive equation and Lin’s linear phase transformation kinetics for SMA fiber. The general form of constitutive relation is applied to the cases of extension-twist coupling, corresponding to Circumferentially Uniform (CUS) and bending-twist coupling, corresponding to Circumferentially Anti-Symmetric (CAS). The present analysis extends the previous work done for modeling generic passive thin-walled laminated beams. Numerical results show that significant extension, bending and twisting deflection occur during the phase transformation due to SMA actuation. The effects of temperature on structural response behavior during phase transformation from martensite to austenite are significant. The effects of the volume fraction of the SMA fiber, the martensitic residual strain and ply angle are also addressed.

Rigid‐plastic models for the seismic design and assessment of steel framed structures

AbstractThis paper demonstrates the applicability of response history analysis based on rigid‐plastic models for the seismic assessment and design of steel buildings. The rigid‐plastic force–deformation relationship as applied in steel moment‐resisting frames (MRF) is re‐examined and new rigid‐plastic models are developed for concentrically‐braced frames and dual structural systems consisting of MRF coupled with braced systems. This paper demonstrates that such rigid‐plastic models are able to predict global seismic demands with reasonable accuracy. It is also shown that, the direct relationship that exists between peak displacement and the plastic capacity of rigid‐plastic oscillators can be used to define the level of seismic demand for a given performance target. Copyright© 2009 John Wiley & Sons, Ltd.

Torsional analysis of thin-walled composite beams with single- and double-celled sections

The exact solutions for twist angle and fiber stresses of thin-walled composite box beams with single- and double-celled sections subjected to torsional moment are presented by introducing fourteen displacement parameters. For this, a general thin-walled composite box-beam theory including the effects of elastic couplings and restrained warping is developed based on the Vlasov’s assumptions. The equilibrium equations and the force–deformation relations are derived from the energy principle. A system of linear algebraic equations with non-symmetric matrices is constructed by introducing fourteen displacement parameters and by transforming the higher order simultaneous differential equations into first-order ones. This numerical technique determines eigenmodes corresponding to multiple zero and non-zero eigenvalues and derives exact displacement functions for displacement parameters based on the undetermined parameter method. Finally, the exact stiffness matrix is determined using the member force–deformation relations. The theory developed by this study is validated by comparing several torsional responses from the present approach with those from the finite element beam model that uses third-order Hermitian polynomials and detailed two-dimensional analysis results using the shell elements of ABAQUS for coupled composite beams with single- and double-celled sections.