Force-deformation Relationship Research Articles

Pseudo-dynamic response and analytical evaluation of blind bolted CFT frames with BRBs

This paper presents the experimental and analytical studies on the blind bolted end plate concrete-filled steel tube (CFT) composite frames with buckling-restrained braces (BRBs). A series of pseudo-dynamic tests (PDTs) on two 2/3-scaled two-story, one-bay blind bolted end plate CFT (BECFT) composite frames with BRBs showed that the novel dual system exhibited good hysteretic behavior and high ductility. The moment capacity, initial rotational stiffness, rotation capacity and the mathematical moment-rotation model of a BECFT composite joint were systematically analyzed and modified to some extent. Meanwhile, the shear force-deformation relation of a CFT panel zone was suggested and checked for its applicability. Furthermore, the macroscopic finite element (FE) model incorporating semi-rigid characteristic of the joint and shear response of the panel zone was developed by OpenSees program. The numerical analytical results would match better with experimental data when the FE model took the gusset plate stiffness into account in comparison with other models neglecting this case. Both experimental and FE analytical results indicated that the BRBs were in elastic state to provide great lateral stiffness and resistance under small earthquakes, and they yield first to stably dissipate energy under severe earthquakes. The combination of BECFT composite frames with BRBs will extend the feasibility of the novel dual system in high- or even super high-rise buildings.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ РАБОТЫ ЗАМКОВОГО СОЕДИНЕНИЯ СТЕНОВЫХ ПАНЕЛЕЙ НА РАСТЯЖЕНИЕ ДО ОБРАЗОВАНИЯ ТРЕЩИН

A large-panel design scheme includes floor elements, wall panel elements, and joints between them. The rigidity and strength characteristics in tension, compression and shearare required to be knownfor correct modeling of large-panel buildings. Due to the lack of universal formulas in the normative and reference literature for determining the strength and rigidity of various types of joints, it is necessary to conduct additional research. In 2014 a new type of vertical monolithic joint for large-panel buildings was developed: the fastener joint of wall panels, which has significant strength and rigidity. The fastener includes acheck clamp, which connects the loop outlets on panel ends and the steel plate, which connects the ends of the clamp. It isnecessary to correctly evaluate the strength and rigidity of the joint for its fully- functional application. The experimental research on the joint in tension discovered its bilinear force-deformation relationship (with great rigidity before cracking, and with marginal one after). To analyze the large-panel buildings under the influence of the main operational loads, it is enough to model the joint’s work on the first stage (before cracking). The aim of the research is to study the fastener joint in tension before cracking. The paper compares the results of numerical modeling with the sample testing results, and determines the rigidity and cracking load for joints with other values of the grouting concrete strength and the diameters of the loop outlets. The research was carried out using flat finite-element model in the Lira-SAPR CAD software package. The results of calculation of the joint model are generally consistent with the results of samples testing. In addition, the rigidity and cracking load were determined for joints with various parameters (concrete strength and loop outlet diameter). The results of the study can be usedfor designing large-panel buildings with this type of joint.

A High-Precision and Miniature Fiber Bragg Grating-Based Force Sensor for Tissue Palpation During Minimally Invasive Surgery.

This paper presents a novel Fiber Bragg Grating (FBG)-based palpation force sensor to explore tissue abnormalities during minimally invasive surgery. The proposed sensor design mainly consists of a miniature force-sensitive flexure, one tightly suspended optical fiber embedded with one FBG element and associated connectors and fixations. The flexure design has been prototyped through the configuration synthesis of Sarrus mechanism by using a rigid-body replacement method to achieve an excellent axial linear force-deformation relationship and a large measurement range. The mounted fiber has been configured at the flexure's central line with its two ends glued, and its tight suspension configuration can achieve improved resolution and sensitivity and avoid the FBG chirping failure compared to the commonly used direct FBG-pasting methods. Finite element method (FEM)-based simulation has been performed to investigate both static and dynamic performance to aid in structural design. Simulation-enabled structural optimization design has also been implemented to further improve the proposed design and the sensor's sensitivity has been increased. The optimized sensor design has been prototyped and calibrated to demonstrate an excellent linearity with a small linearity error of 0.97% and achieve a high resolution of 2.55 mN within a relatively large measurement range of 0-5N. Dynamic force stimulation experiments, in vitro palpation implementation on a silicone phantom embedded with simulated tumors and ex vivo indentation experiments on a porcine liver have validated the effectiveness of the presented sensor design.

Collapse-Limit Input Level of Critical Double Impulse for Damped Bilinear Hysteretic SDOF System With Negative Post-yield Stiffness

The collapse-limit input velocity level of the critical double impulse simulating the principal part of near-fault ground motions is derived for an elastic-plastic structure with viscous damping and P-delta effect. The structural system is modeled by a bilinear hysteretic SDOF system with negative post-yield stiffness reflecting the P-delta effect which plays a key role in the collapse behavior. Since the critical timing of the second impulse in the double impulse has been proven as the zero-restoring force timing after the first impulse for the elastic-plastic SDOF system with viscous damping, that property is used again in this paper. It is shown that the collapse-limit input level of the critical double impulse can be obtained as a function of the post-yield stiffness and the damping ratio by using the energy balance law and the quadratic-function approximation of the damping force-deformation relation. The applicability of the collapse-limit level to actual recorded ground motions is investigated through the time-history response analysis for the stable and collapse models under two actual earthquake ground motions.

Effects of subfreezing temperature on the seismic response of lead rubber bearing isolated bridge

Seismic isolation is one of the most effective ways to minimize structural damage during and immediately after any seismic event. The objective of base isolation is to provide enough horizontal flexibility during seismic excitation while providing adequate performance under all service load. Rubber based isolation systems, such as elastomeric bearings and Lead Rubber Bearings (LRBs), have been widely used as seismic isolators for bridges. Due to their superior performance and combined isolation and energy dissipation functions in a single compact unit, LRBs have gained much popularity in the bridge industry. However, the main constituent of LRB, rubber, is very sensitive to low temperatures and related duration of exposure. At low temperature, rubber undergoes crystallization stiffening which substantially effects the mechanical properties of LRB. The objective of this study is to evaluate the seismic performance of a base isolated bridge at subfreezing temperature. The bridge is seismically isolated using LRBs and assumed to be located in Montreal, Quebec, Canada where a temperature variation between +35 °C to -35 °C is expected. Using a detailed 3D finite element model of the bridge and considering the bridge component material properties and bearing properties at summer and winter service temperatures, the performance of the isolated bridge is evaluated in terms of isolator force-deformation relationship, force demand in the substructure, deck acceleration, and shear strain in the isolation bearing. Finally, fragility curves are developed to evaluate the effect of subfreezing temperature on the seismic response of LRB isolated bridges. Analysis results show that freezing condition may have a notable effect on the component fragility as well as the bridge system fragility.

Analytical Modeling of Moderately Ductile RC Frame Structures for Seismic Performance Evaluation Using PERFORM-3D

Performance-based vulnerability assessment of buildings requires dynamic inelastic analysis, which cannot be conducted without reliable analytical models. An important aspect of analytical building models involves hysteretic modeling of force-deformation relationships. PERFORM-3D software was used to generate fragility curves for moderately ductile buildings in Eastern Canada using hysteretic models with different features reflecting the recommendations of different North American standards. Two-story and five-story reinforced concrete (RC) frame buildings were considered for this purpose. The parameters that define rotational limits, as specified in ASCE 41-13 and ACI 369R-11 as well as the National Building Code of Canada (NBCC), were assessed. The results indicate that the variations in modeling parameters did not result in significant differences in fragility response at immediate occupancy and life safety performance levels, whereas the fragilities at the collapse performance level were affected. The probability of exceeding collapse prevention in buildings modeled as per NBCC was higher than those modeled using the ASCE 41-13 and ACI 369R-11 requirements.

Distributed plasticity model for analysis of steel structures subjected to fire using the direct stiffness method

This article develops a temperature-dependent distributed plasticity model in a direct stiffness method (DSM) based formulation for coupled nonlinear thermo-mechanical analysis of steel space frames. The developed framework considers geometric and material nonlinearities, and performs coupled thermo-mechanical analysis by a two-level spatial discretization strategy. An isotropic hardening plasticity in combination with the von Mises yield criterion is considered, where the temperature-dependent yield function is derived from the stress-strain relations of Eurocode 3. The effects permanent plastic strains, large deformations and temperature-dependent material properties are directly incorporated in to the force deformation relations derived in a DSM based setting. Such a DSM based framework in conjunction with the distributed plasticity model facilitates higher computational efficiency. To ensure full coupling between mechanical and thermal solvers, thermodynamically consistent plastic heating term is added to the energy balance of the system. Also, connection flexibility is accounted for by developing a zero-length spring element integrated with 1-D beam-column elements. Five numerical examples are presented to demonstrate the efficacy of the developed framework. Within the numerical investigation, the importance of plastic heating coupling in the context of macro modelling based structural fire analysis of steel structures is quantified and the results indicate that such a coupling can be ignored in such macro scale structural fire computations.

Measurement of contact force-deformation relation during elastic collision of two identical spheres

Measurement of contact force-deformation relation during elastic collision of two identical spheres

Measurement of contact force-deformation relation between two identical spheres during elastic-plastic impact

Measurement of contact force-deformation relation between two identical spheres during elastic-plastic impact

Dynamic modelling of elastic-plastic beams under impact

This study is aimed to investigate the dynamic response of a fully clamped beam subjected to impact loadings by a rigid mass. First, the analytical formulae are derived for predicting the quasi-static force-deformation relations of an elastic-plastic beam during loading and unloading. For a particular impact scenario in which the striker with a heavy mass impinges the mid-span of the beam at a low speed, it is assumed that the dynamic deformation mode remains identical to the quasi-static one. By employing energy method, the quasi-static characteristics are utilized to develop an elastic-plastic theoretical model of the beam under impact loadings so as to predict its dynamic behaviour during the loading, unloading and subsequent elastic vibration stages. Validation and comparison are conducted against numerical simulations using the commercial software package ABAQUS and it is shown that the proposed elastic-plastic theoretical model is capable of providing a good prediction of the overall dynamic behaviour of the beam under impact. In parallel, comparisons between the predictions of the current elastic-plastic model and those of the rigid-plastic analysis are carried out to highlight the elastic effect on the accuracy of modelling an elastic-plastic beam under impact.

Three-Dimensional Catheter Distal Force Sensing for Cardiac Ablation Based on Fiber Bragg Grating

This paper presents a high-sensitivity triaxial catheter distal force sensor for cardiac ablation through the combined use of a force-sensitive flexure and fiber Bragg grating (FBG) sensing. A miniature force-sensitive flexure has been designed as the catheter tip, and it has an elliptical hinge with a symmetric structure for two-axial transverse force sensing and employs a pair of U-type beam slots above the hinge to sense the $z$ -direction force. Five optical fibers embedded with an FBG element each have been integrated with this flexure to detect the force-induced strain on the flexure. Each fiber is configured as a tightly suspended status with its two ends fixed, ensuring to achieve an improved sensitivity. The theoretical force–deformation relationship has been derived, and the approach for decoupling force and temperature has been presented. Finite element modeling based simulations have been performed to support the parametric design and improvement of the flexure structure. Static calibration experiments demonstrate the excellent resolution values of 2.13 and 2.52 mN for both transverse directions within –1 to 1 N, and 23.12 mN for the axial direction within 0–2 N. The linearity, repeatability, and hysteresis errors have been characterized with less than 5.3%, demonstrating the stable performance. The force and temperature can be effectively decoupled and detected with a temperature less than 60 °C. Dynamic loading experiments at different spatial angles and in vitro experiments in a silicone aortic vessel phantom have been carried out to further validate the effectiveness of the proposed design.

Design, Development and Calibration of a Lightweight, Compliant Six-Axis Optical Force/Torque Sensor

This paper introduces the fabrication of a six degree-of-freedom force and torque sensor based on fiber-optic sensing technology and its novel calibration methodology. The sensor is cost effective, lightweight, and flexible with a large force and torque measurement range suitable for biomechanics and rehabilitation systems particularly when a wearable sensing system is desired. Six fiber-optic sensing elements are used to detect three main forces Fx , Fy , and Fz , and three main torques Tx , Ty , and Tz . Sensor data were collected by applying dynamic forces and torques with various magnitudes, directions, and frequencies and compared with measurements obtained from a standard force and torque reference. The proposed calibration procedure is intended to reduce errors stemmed from a nonlinear force-deformation relationship and to increase the estimation speed by splitting the calibration into two estimation models: a linear model, based on a standard least squares method ( LSM ) to estimate the linear portion, and a nonlinear decision trees’ model ( DT ) to estimate the residuals. Both the models work simultaneously as a single calibration system named least squares decision trees LSDT . Using LSDT , the estimation speed increased by 55.17%, and the root mean square errors ( RMSEs ) reduced to 0.53%. In comparison, each model separately had a RMSEs of 1.26% and 4.70% for the DT and the LSM , respectively.

Dynamic response of self-locked energy absorption system under impact loadings

The self-locked energy absorbing system can prevent lateral splash of tubes from impact loadings without any requirements for boundary constraints or inter-tube fasteners, thus breaking through the limitation of widely-used round tube systems. To reveal the mechanism of the impact response of self-locked systems, both impact experiment and FEM simulations are carried out. Based on the experimental and simulation results, a one-dimensional theoretical crushing model of the system is developed to analyze the dynamic response of the system, in which a plastic hinge model of the unit cell is proposed for the force-deformation relation. Three deformation modes of the system are predicted and observed, and moreover, the criteria to determine the deformation mode of the system are established analytically. A guideline on the design of the self-locked system is summarized, which is helpful in practical applications.

Harnessing the anisotropic multistability of stacked-origami mechanical metamaterials for effective modulus programming

This study examines a three-dimensional, anisotropic multistability of a mechanical meta material based on a stacked Miura-ori architecture, and investigates how such a unique stability property can impart stiffness and effective modulus programming functions. The unit cell of this metamaterial can be bistable due to the nonlinear relationship between rigid-folding and crease material bending. Such bistability possesses an unorthodox property: the arrangement of elastically stable and unstable equilibria are different along different principal axes of the unit cell, so that along certain axes the unit cell exhibits two force–deformation relationships concurrently within the same range of deformation. Therefore, one can achieve a notable stiffness adaptation via switching between the two stable states. As multiple unit cells are assembled into a metamaterial, the stiffness adaptation can be aggregated into an on-demand modulus programming capability. That is, via strategically switching different unit cells between stable states, one can control the overall effective modulus. This research examines the underlying principles of anisotropic multistability, experimentally validates the feasibility of stiffness adaptation, and conducts parametric analyses to reveal the correlations between the effective modulus programming and Miura-ori designs. The results can advance many adaptive systems such as morphing structures and soft robotics.

Seismic effectiveness of top-story mass dampers for inelastic two-way asymmetric-plan buildings

Self-mass dampers, which use intrinsic parts of structures as tuned mass dampers, are economically advantageous in terms of the materials and space required. Previous research proposed using the top story of a two-way asymmetric-plan building as a self-mass damper, referred to as a top-story mass damper (TSMD), for suppressing the seismic response of an elastic building. In light of the promising results of that research, this study further explores the seismic effectiveness of TSMDs when two-way asymmetric-plan buildings become inelastic under earthquake loads. Furthermore, this study explores the possibility of using a pair of elastic TSMDs to alleviate the detuning effects caused by yielding of the main structure. One TSMD of the pair is designed according to the previous research and is responsible for suppressing the vibrations of the target building in elastic states. The other TSMD is designed based on the properties of collective force–deformation relationships and is responsible for suppressing the vibrations of the target building in inelastic states. The collective force–deformation relationships are the pushover curves of the target building when subject to the collective modal inertia force vectors of the first triplet of vibration modes of the building. This study looks at one single-story building and one 20-story building, which are shaken into various damage states, as the numerical examples for evaluating the seismic effectiveness of TSMDs for inelastic two-way asymmetric-plane buildings.

Numerical Model of Cold Press-Formed Square Steel Tube Columns Considered with Degradation Behavior due to Local Buckling and/or Fracture

In steel building structures, local buckling and/or fracture of columns could occur during strong ground motions, furthermore complete collapse might be induced due to the column strength degradation. In this paper, cold press-formed square tube columns are targeted, and numerical model being able to trace precisely degradation behavior is proposed. In order to take account of both local buckling and fracture with low computational costs, multi-spring model which consists of some uni-axial springs is adopted. Axial force-deformation relationships of uni-axial springs are provided on flat area and corner area of square tube severally, and are separated into skeleton part and hysteresis part. All parameters on force-deformation relationship are identified based on finite element analysis results of short columns under monotonic or cyclic axial loading. Comparing between analysis results by multi-spring models and past cyclic loading test results or finite element analysis results, it is clarified that degradation behavior of cold press-formed square steel tube columns can be traced with high accuracy.

Effect of modelling parameters on non-linear seismic response of concrete structures

The non-linear numerical analysis of reinforced-concrete structures presents several difficulties due to the complicated behaviour of reinforced concrete under cyclic lateral loading. For practical use, design guidelines provide simplified non-linear models which are implemented in many structural analysis programs. However, restrictions and assumptions on which the models are based may influence the seismic response of existing structures. The primary aim of the work reported in this paper was to identify possible differences in structural response due to selected non-linear modelling parameters. Based on these findings, the aim was then to provide guidance for practical computer models capable of representing a realistic non-linear seismic response. A set of numerical models was constructed and then a force–deformation relationship for each model was compared with experimental results. Sensitivity of response due to changes in each member's modelled plasticity and hysteresis was further investigated on a ten-storey reinforced-concrete building under five different seismic inputs. The analyses confirmed that storey displacements and degree of plastic deformation were influenced by modelling preferences. A fibre model was found to be more reliable in reflecting non-linear behaviour.

Nonlinear analysis of reinforced concrete plane frames exposed to fire using direct stiffness method

This article presents a framework based on the direct stiffness method for nonlinear thermo-mechanical analysis of reinforced concrete plane frames subjected to fire. It accounts for geometric nonlinearity, material nonlinearity, and nonlinear thermal gradients and incorporates two-way coupling between thermal and structural analyses. Force deformation relations are derived from classical Euler–Bernoulli beam theory and are expressed in terms of temperature-dependent stability and bowing functions. This is one of the unique features of proposed framework and allows a coarser spatial discretization to be used as opposed to full finite element–based approaches (such as SAFIR [registered trademark of the software SAFIR developed at the University of Liege]). The cross sections of the structural members are discretized with two-dimensional meshes for thermal analysis while structural analysis utilizes a line element based on direct stiffness method. Equivalent bending and axial rigidities of this line element are computed using several fibers along the length of the member, passing through the nodes of the two-dimensional mesh used for thermal analysis. The total strain at each fiber is decomposed into mechanical, thermal, creep, and transient thermal components. A discrete damage parameter is introduced at fiber level to ensure irreversibility of crushing and cracking in accordance with relevant constitutive laws. Five numerical examples are presented to demonstrate the accuracy and efficacy of the developed framework with respect to theoretical solutions, experimental observations, and some of the existing macro- and micro-finite element–based approaches. It is found that the developed framework can predict the response of reinforced concrete structures very well.

3D Finite Element Modeling of GFRP-Reinforced Concrete Deep Beams without Shear Reinforcement

This paper presents the numerical investigation of nine Glass Fiber-Reinforced Polymer (GFRP) concrete deep beams through the use of numerically-efficient 20-noded hexahedral elements. Cracking is taken into account by means of the smeared crack approach and the bars are simulated as embedded rod elements. The developed numerical models are validated against published experimental results. The validation beams spanned a practical range of varying design parameters; namely, shear span-to-depth ratio, concrete specified compressive strength and flexural reinforcement ratio. The motivation for this research is to accurately yet efficiently capture the mechanical behavior of the GFRP-reinforced concrete deep beams. The presented numerical investigation demonstrated close correlations of the force–deformation relationships that are numerically predicted and their experimental counterparts. Moreover, the numerically predicted modes of failure are also found to be conformal to those observed experimentally. The proposed modeling approach that overcame previous computational limitations has further demonstrated its capability to accurately model larger and deeper beams in a computationally efficient manner. The validated modeling technique can then be efficiently used to perform extensive parametric investigations related to behavior of this type of structural members. The modeling method presented in this work paves the way for further parametric investigations of the mechanical behavior of GFRP-reinforced deep beams without shear reinforcement that will serve as the base for proposing new design guidelines. As a deeper understanding of the behavior and the effect of the design parameters is attained, more economical and safer designs will emerge.

USE OF DISC SPRINGS IN A PELLET FUEL MACHINE FOR PRESSURE REGULATION AND PREVENTION OF DAMAGE

The use of biomass fuel pellets is becoming widespread as a renewable and environment-friendly energy. Pellet fuels are produced in various pellet machine types. Pellet machines encounter problems such as pressure irregularities and choke at the initial start for different kinds of biomass feedstock. In this study, disc springs are integrated into a vertical axis pellet machine for a pressure regulation and design optimization. Force-deformation and stress-deformation relations of disc springs are investigated using analytical and finite element methods. Pelletizing pressures were calculated based on disc spring force values using the Hertzian stress formula. Utilized disc springs ensured the pressure regulation, production efficiency increase and damage prevention on the die-roller mechanism.