Load Moment Research Articles

Experimental investigation on hysteretic performance and deformation patterns of single-side yielding precast concrete beam–column connection with energy dissipation bars

With the aim of achieving high construction efficiency, satisfactory seismic performance, and rapid restoration of structural functionality after an earthquake, this study proposes an innovative single-side yielding beam–column connection with replaceable energy dissipation bars (REDB-SYBC) for precast concrete moment-resisting frames (PCMF). During assembly, the concrete beam is attached to a column via the connection function of a non-slipping threaded sleeve assembly (NSTSA) and the support action of the shear keys (SKs) in the REDB-SYBC. This reduces the need for temporary supports for the precast beams on site. Five large-scale tests on precast concrete connections considering the partial flange effect of a slab subjected to quasi-static cyclic loading were conducted to investigate the mechanical behavior, deformation patterns, and energy dissipation (ED) capacity. The primary experimental variables included different loading protocols, restrainer forms, ED segment areas, and whether to replace the ED bars. This paper presents the assembly construction and load-carrying mechanism, and the analysis of the experimental results, including the observations, hysteretic performance, and deformation patterns. The single-side yielding deformation pattern of the REDB-SYBC connection minimized the deformation of the adjacent floor slabs and magnified the deformation of the ED bars at the bottom of a beam, thus facilitating deformation compatibility with the floor system and causing the damage to be focused on the ED bars. Consequently, the five specimens exhibited similar failure patterns via the fracture of the ED bars due to low-cycle fatigue failure, which was attributed to extensive yielding in both tension and compression. The REDB-SYBC connections exhibited a distinct beam end yielding mechanism, which demonstrated a failure pattern that was consistent with the desired “strong column and weak beam” design philosophy. The test results indicated that the proposed REDB-SYBC connection exhibited a dependable decoupled moment and shear load transfer mechanism, stable hysteretic behavior, negligible beam elongation, and reduced floor damage. The performance of a repaired specimen was nearly the same as its counterpart before repair, indicating that replacement was effective. The impact on the REDB-SYBC connection in response to a strong aftershock was also estimated by reloading an unrepaired specimen.

P12. Does posterior ligamentous complex disruption following lumbar pedicle screw and rod instrumentation affect the upper adjacent level?

<h3>BACKGROUND CONTEXT</h3> The lumbar level above the fusion segment is the most common level for the development of adjacent level instability. The posterior ligamentous complex (PLC), (eg, interspinous ligament, and supraspinous ligament) a posterior tension band that stabilizes the spine, is usually removed for laminectomy during lumbar fusion and decompression surgery. The removal of the posterior complex may jeopardize upper adjacent level stability. <h3>PURPOSE</h3> To compare mobility and principal disc strains at the upper adjacent level to L4-5 pedicel screw-rod fixation (PSR) between L4-5 PSR, L4-5 PSR+ bilateral laminotomy (PLC preservation), and L4-5 PSR+ conventional laminectomy, in cadaveric specimens. The disc strain was studied with a new optical technique of soft tissue strain analysis (3D digital image correlation (DIC) technique). <h3>STUDY DESIGN/SETTING</h3> Biomechanic testing in human cadaveric spine specimens. <h3>PATIENT SAMPLE</h3> Human cadaveric lumbar spine. <h3>OUTCOME MEASURES</h3> 1. Adjacent segment range of motion, 2. Disc surface strains. <h3>METHODS</h3> Seven human cadaveric L3-S1 specimens were instrumented with L4-5 PSR. All specimens were tested multi-directionally under pure moment loading (7.5Nm) following: 1) L4-5 PSR, 2) L4-5 PSR+bilateral L4 laminotomy while preserving PLC and 3) L4-5 PSR +L4 conventional laminectomy. DIC was performed with cameras positioned laterally (left side) to capture the change in disc principal strain (Pmax and Pmin) at upper adjacent level (L3-4) under peak load. Optical motion tracking was simultaneously performed on the right side. The disc region was divided into four similar sized quarters and included upper and lower endplates. Analysis of variance of upper adjacent level (L3-4) range of motion (ROM) and disc strain between the groups was performed. Statistically significant was set at p≤0.05. <h3>RESULTS</h3> ROM of the upper adjacent (L3-4) level was significantly greater with L4-5 PSR+laminectomy (6.26 degree) versus L4-5 PSR+ bilateral laminotomy (5.94 degree, p=0.006), and L4-5 PSR (5.20 degree, p<0.001) respectively, during flexion. During extension, left lateral bending, and axial rotation, upper adjacent level ROM was significantly greater with L4-5+ laminectomy and L4-5 PSR+ bilateral laminotomy versus L4-5 PSR (p≤0.046) but there were no significant differences between L4-5 PSR+ laminectomy and L4-5PSR+ bilateral laminotomy (p≥0.087). The intervertebral disc Pmax strains of the upper adjacent level were significantly greater with L4-5 PSR+laminectomy than L4-5 PSR during flexion (25,225 VS 18,007uE, p=0.031), extension (22,803 VS 19,356uE, p=0.020), left lateral bending (32,778 VS 24,100uE, p=0.027), right lateral bending (88,761 VS 62,869uE, p=0.024), and right axial rotation (24,747 VS 19,289uE, p=0.025). <h3>CONCLUSIONS</h3> The posterior ligamentous complex disruption during lumbar fusion surgery was associated with significant increases in upper adjacent level instability and principle (Pmax) intervertebral disc stress/strain. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

P11. Does the choice of spinal interbody fusion approach significantly affect adjacent segment mobility?

<h3>BACKGROUND CONTEXT</h3> Previous studies have concluded that LLIF, TLIF, and PLIF with posterior pedicle screw-rod fixation (PSR) provide equivalent stability in cadaveric specimens and are comparable in fusion rate and functional outcome. However, long-term complications, such as adjacent segment degeneration associated with each type of interbody device, are currently unclear. Little is known about the biomechanical effects of interbody fusion technique on the mobility of adjacent segments. <h3>PURPOSE</h3> To investigate the differences in adjacent segment mobility among three types of LIF: lateral lumbar interbody fusion (LLIF), transforaminal lumbar interbody fusion (TLIF) and posterior lumbar interbody fusion (PLIF). <h3>STUDY DESIGN/SETTING</h3> Biomechanical study of range of motion (ROM) at the vertebral levels adjacent to the construct of posterior pedicle screw-rod fixation with different types of lumbar interbody fusion techniques (LIF). <h3>PATIENT SAMPLE</h3> Human cadaveric lumbar spine. <h3>OUTCOME MEASURES</h3> Adjacent segment range of motion. <h3>METHODS</h3> Normalized ROM data at the levels adjacent to L3–L4 PSR fixation with 3 different types of lumbar interbody fusion approaches (LLIF, TLIF, and PLIF) were analyzed. Intact (n=21) and instrumented (n=7 per group) L2–L5 cadaveric specimens were tested multidirectionally under pure moment loading (7.5 Nm). Analysis of variance of adjacent segment ROM among the groups was performed. Statistical significance was set at p<0.05. <h3>RESULTS</h3> Normalized ROM was significantly greater with PLIF than with LLIF in all directions at both proximal and distal adjacent segments (p≤0.02) except for axial rotation at the distal adjacent segment (p=0.07). TLIF also had greater normalized ROM than LLIF during lateral bending at the proximal adjacent segment (p=0.008) and during flexion, extension, and lateral bending at the distal adjacent segment (p≤0.03). Normalized ROM was not significantly different between PLIF and TLIF. <h3>CONCLUSIONS</h3> The choice of lumbar interbody fusion approach influences adjacent segment motion in a cadaveric model. LLIF had the least adjacent segment motion. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

20. Biomechanical effect of facet joint violation on adjacent segment motion and disc strain following single level lumbar fusion with transpedicular screw and rod instrumentation

<h3>BACKGROUND CONTEXT</h3> Facet joint violation (FV) is a complication occurring while placing pedicle screws at the upper-most level using an entry point and trajectory too close to the superior facet joint. The incidence of FV has been reported up to be as high as 50%. However, little is known about how FV affects superior adjacent level spinal stability and especially intervertebral disc (IVD) strain after lumbar fusion. <h3>PURPOSE</h3> To investigate the biomechanical effects of FV in terms of mobility and disc surface strains at the upper level adjacent to L4-5 pedicle screw-rod fixation (PSR) in cadaveric specimens. The disc strain was studied with a new optical technique of soft tissue strain analysis (3D digital image correlation [DIC] technique). <h3>STUDY DESIGN/SETTING</h3> Biomechanic testing in human cadaveric spine specimens. <h3>PATIENT SAMPLE</h3> A total of 14 human cadaveric L3-S1 specimens. <h3>OUTCOME MEASURES</h3> 1. Upper adjacent segment range of motion. 2. Disc surface strain/stress. <h3>METHODS</h3> A total of 14 human cadaveric L3-S1 specimens were divided into two equal groups. L4-5 pedicle-rod fixation was performed in a different fashion in each group ie, facet joint preservation (FP) and facet joint violation (FV). The violation of the facet joint was defined by denuding the facet joint capsule and removing of the external cortical surface of the superior articular process with a 3 mm Leksell-rongeur. The entry point of these pedicle screws was located at the junction between the inferolateral aspect of the facet joint. All specimens were tested multi-directionally under pure moment loading (7.5Nm). DIC was performed with cameras positioned laterally (left side) to capture the change in principal disc strains (Pmax and Pmin) at the upper adjacent level (L3-4) under peak load. Optical motion tracking was simultaneously performed on the right side. The IVD region was divided into four similar sized quarters and included upper and lower endplates. Analysis of variance of upper adjacent level range of motion (ROM) and disc strain, normalized to intact, was performed between the groups. Statistical significant was set at P≤0.05. <h3>RESULTS</h3> Normalized ROM was significantly greater with FV than FP at upper adjacent level (L3-4) during right axial rotation (1.22 vs 0.99, 23% difference, p=0.047). Normalized IVD Pmax strains at the upper adjacent level (L3-4) were significantly greater with FV than FP in the anterior quadrant during right axial rotation (1.80 vs 0.83 (ratio to intact), 97% difference, p=0.003). However, there were no significant differences in ROM and disc Pmax or Pmin strains during flexion, extension and lateral bending. <h3>CONCLUSIONS</h3> Facet violations at the uppermost level of fusion construct during pedicle screw-rod fixation were associated with adjacent level torsional instability and the increase of IVD strain. This study suggested that the preservation of uppermost facet joint of fusion segment was helpful for alleviating adjacent segment mobility and stress concentrations of the IVD above the fusion segment. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Stress Distribution Analysis of DKDT Tubular Joint in a Minimum Offshore Structure

A marginal field defines as an oil and/or gas field that has a short production period, low proven reservoir, and could not be exploited using existing technology. As the demand for oil and gas keeps increasing, one of the solutions to tackle the issues is to build the modified platform which came to be more minimalist to conduct the oil and gas production in the marginal field. Naturally, the minimum offshore structures are cost less but low in redundancy, therefore, pose more risks. Although the study on the minimum structures is still uncommon, there are opportunities to find innovative systems that need to have a further analysis toward such invention. Therefore, this study took the modified jacket platform as a minimum structure, and local stresses analysis by using finite element method is applied for the most critical tubular joint with multiplanarity of the joint is taking into account. The analysis was carried out using the finite element program of Salome Meca with three-dimensional solid elements are used to model the multiplanar joint. Various loading types of axial force, in-plane bending moment, and out-of-plane bending moment are applied respectively to investigate the stress distribution along the brace-chord intersection line of the tubular joint. The results show that the hotspot stress occurred at a different point along each brace-chord intersection line for each loading type. Finally, as compared to the in-plane bending moment or out-of-plane bending moment loading types, the axial force loading state is thought to generate greater hotspot stress.

Stress analysis of multi-layered composite cylinders subjected to various loadings

Composite cylinders are widely used in many applications, common examples for these applications are power drive shafts, chemical storage tanks, rocket motor cases and pressure vessels used in aerospace vehicles. The structure of the composite cylinder can be represented as a cylinder composed of coaxial orthotropic layers. In this paper, an analytical method is used to calculate stresses, strains and displacements through the wall thickness of multi-layered composite cylinder made of orthotropic material. The method is based on the theory of elasticity of bodies having cylindrical anisotropy. This method permits accurate stress analysis of thin and thick-walled composite cylinders subjected to axial load, torsional load and bending moment. The analytical method is modified to incorporate internal and external pressure loads beside the prescribed load cases. A numerical example is presented for a composite cylinder subjected to internal pressure load with a tensile axial load. The resulted stresses and strains are used to validate 3-dimensional finite element model. A parametric study has been performed using the analytical method to investigate the influencing parameters on stress distribution within the cylinder thickness and the results are found to be beneficial to look into during the preliminary design phase.

A novel strain-based assessment method of compressive buckling of X80 corroded pipelines subjected to bending moment load

This work presents an investigation on the compressive strain capacity of resisting buckling on an X80 steel corroded pipeline subjected to a bending moment using nonlinear finite element analysis (FEA) validated by full-scale tests. The modelling results indicate that the existing strain-based assessment method is not suitable for pipelines with deep corrosion and has certain application limitations. Consequently, a new evaluation method based on far-field strain was developed to predict the buckling failure of corroded pipelines subjected to bending loads. The influence of the corrosion shape type, corrosion size (i.e., depth d, length L, and width w), pipe geometry, and internal pressure on the critical buckling strain capacity and critical buckling moment of the pipeline were studied using parameter sensitivity analysis to verify the proposed strain criteria. The results illustrate that the variation trends between the critical buckling strain and the critical buckling moment with each factor were consistent, indicating that the proposed novel strain-based evaluation method is effective and applicable. In addition, the buckling resistance of a pipeline with rectangular corrosion is relatively weaker than that with a semi-spherical corrosion pit or cylindrical grooved corrosion under the same defect size. Further, the critical compressive strain capacity of a corroded pipeline is primarily affected by the depth and width of the corrosion, whereas the effect of the corrosion length is relatively insignificant. Moreover, the critical length and width of the corrosion defect affecting the bending capacity of resisting buckling were determined as L/Dt=20 and w/πD=0.5, respectively.

Shear strength of steel plate shear walls considering the gravity load and in-plane bending moment effect by vertical stress distributions

Without considering the effect of the gravity load and in-plane bending may overestimate the shear strength of a steel shear wall. In this work, the gravity load and in-plane bending moment are equivalent to a trapezoidal distributed load. The effective width model, the cosine distribution and a three-segment distribution were respectively utilized to determine the vertical stress of the infilled steel panel under the gravity and in-plane bending moment. The tension field stress of each inclined tension strip of the steel panel, with considering a reduction caused by the vertical stress, is determined based on the von Mises yield criterion. The shear strength then can be obtained by integrating the shear stress with respect to the area of each strip along the width. The proposed approach was evaluated by an experimentally verified finite element model developed in the software LS-DYNA. Steel walls of different slenderness ratios under different compression and in-plane bending moment are discussed. The results show that the three-segment distribution can describe the effect of the gravity load and in-plane bending moment. The effective width model and the cosine distribution will underestimate the shear strength while that the equation in CAN/CSA-S16-01 will overestimate the shear strength.

Obtaining interaction diagram of concrete section exposed to fire by mathematical optimization

This paper proposes a novel method for obtaining the axial load–moment (P–M) interaction diagrams of reinforced concrete sections exposed to fire. The problem of obtaining the strength of a reinforced concrete section subjected to an eccentric load was converted into determining an optimum solution of a constrained nonlinear optimization problem. The proposed method does not limit the strains of both concrete and reinforcing bars. A sequential quadratic programming algorithm was used to solve the constrained nonlinear optimization. Discontinuity in the arctangent function was avoided by rotating the atan2 function. A bending moment offset from the tilted axis was introduced to solve the asymmetric section and uneven heating condition. The results of the examples confirm that the proposed method can produce the entire P–M interaction surface of an arbitrarily shaped reinforced composite section exposed to fire. The proposed method is much faster and more versatile than the incremental-iterative procedure. The proposed method can calculate equally spaced points on the Mx–My interaction curve which the incremental-iterative procedure cannot obtain. The proposed method can be applied to any combination of cross-sectional shape, material, and temperature history.

Construction Sequence Analysis and Conventional Lumped Analysis considering P-Delta Effect by Using Etabs

While analyzing a multistorey building frame, conventionally all the probable loads are applied after modeling the entire building frame. But in practice the frame is constructed in various stages. Accordingly, the stability of frame varies at every construction stage. Even during construction freshly placed concrete floor is supported by previously cast floor by formwork. Thus, the loads assumed in conventional analysis will vary in transient situation. Obviously, results obtained by the traditional analysis will be unsuitable. Therefore, the frame should be analyzed at every construction stage taking into account variation in loads. The phenomenon known as Construction Sequence Analysis considers these uncertainties precisely. Therefore, the building structure should be analysed at every stage of construction taking into account the load variations. In this project two cases have been considered. Whereas in Case 1 the multistoried building (G+22 storied) with floating columns and transfer girder will be analysed by response spectrum method and considering P-delta effect as a whole for the subjected loading and in Case 2 the multistoried building (G+22storied) with floating columns and transfer girder will be analysed by response spectrum method with reference to the construction sequence or staged construction and considering P-delta effect. In the present study a G+22 storey multistoried R.C.C building model is modelled using Etabs 2019 software. Response spectrum analysis is made by considering building situated in zone III.Building models are analyzed by Etabs 2019 software to study the effect of maximum positive moment, maximum negative moment, maximum shear forces, maximum deflection, maximum torsion moment of transfer girder beam and total axial load under transfer girder and floating column etc

The Detachment of an Inclined Micro-Pillar Adhered to a Dissimilar Substrate

Abstract We investigate the mechanics of the detachment of an inclined micro-pillar adhered to a dissimilar substrate when subjected to a combination of an axial load and end moment. When the micro-pillar has adhered to the substrate, singular stress fields exist at the bi-material corners. The order of singularity is estimated using asymptotic analysis. The first two terms in the asymptotic expansion lead to singular stress fields. The magnitude of the singularity is evaluated in terms of the elastic mismatch between the pillar and substrate and the micro-pillar inclination. The asymptotic stress due to the moment loading is more sensitive to the micro-pillar inclination when compared to that due to the axial loading. They are insensitive to the micro-pillar inclination when the micro-pillar is rigid when compared to the substrate. A short interfacial crack is further assumed to exist at the bi-material corner. This crack is embedded in the corner singularity region and is loaded by the singular fields due to axial and bending loads. A boundary layer analysis is performed on the singular zone to estimate the stress intensity factor when a short crack embedded in it is subjected to the singular fields. The stress intensity factors are also calculated for a long interfacial crack at the bi-material corner, which extends beyond the singular zone. By using the aforementioned results, we investigate the detachment of the inclined micro-pillar under the combination of an axial load and end moment.

Analysis of individual differences in pelvic and spine alignment in seated posture and impact on the seatbelt kinematics using human body model.

Analysis using human body models has been performed to reduce the impact of accidents; however, no analysis has shown a relationship between lumbar and pelvic/spine angle and seat belts in reducing human damage from accidents. Lumbar and pelvic/spine angles were measured in 75 individuals and the measurements were used to create three different angles for the Total Human Model for Safety model. In the present study, we focused on lumber lordosis (LL) and pelvic angle (PA). A normal distribution and histogram were used for analysis of PA (01, 10, and 50). The Total Human Model for Safety, including LL and PA, was corrected using finite element software. Simulations were conducted under the conditions of the Japan New Car Assessment Programme (JNCAP) 56 kph full lap frontal impact. Using the results of the FEM, the amount of lap-belt cranial sliding-up, anterior movement of the pelvis, posterior tilt of the pelvis, head injury criterion (HIC), second cervical vertebrae (C2) compressive load, C2 moment, chest deflectiou (upper, middle, and lower), left and right femur load, and shoulder belt force were measured. The lap-belt cranial sliding-up was 1.91 and 2.37 for PA10 and PA01, respectively, compared to PA50; the anterior movement of the pelvis was 1.08 and 1.12 for PA10 and PA01, respectively; and the posterior tilt of the pelvis was 1.1 and 1.18 for PA10 and PA01, respectively. HIC was 1.13 for PA10 and 1.58 for PA01; there was no difference in C2 compressive load by PA, but C2 moment increased to 1.59 for PA10 and 2.72 for PA01. It was found that as LL increases and the PA decreases, the seat belt becomes likely to catch the iliac bone, making it harder to cause injury. This study could help to reconsider the safe seat and seatbelt position in the future.

Probability density functions of the DoB in tubular KT-joints of jacket-type platforms under out-of-plane bending loads

The degree of bending (DoB) has a profound effect on the fatigue behavior of tubular joints commonly found in offshore jacket structures. Probability density functions (PDFs) of the involved random variables are necessary for the fatigue reliability analysis of jacket structures. The objective of present research was the derivation of PDF for the DoB in tubular KT-joints commonly found in jacket-type platforms. A total of 243 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB at the saddle positions of the central and outer braces in tubular KT-joints subjected to three types of OPB moment loading.

Modeling and validation of crankshaft speed fluctuations of a single-cylinder four-stroke diesel engine

In this study, a dynamic model of a single-cylinder four-stroke diesel engine has been created, and the crankshaft speed fluctuations have been simulated and validated. The dynamic model of the engine consists of the motion equations of the piston, conrod, and crankshaft. Conrod motion was modeled by two translational and one angular motion equations, by considering the kinetic energy resulted from the mass moment of inertia and conrod mass. Motion equations involve in-cylinder gas pressure forces, hydrodynamic and dry friction, mass inertia moments of moving parts, starter moment, and external load moment. The In-cylinder pressure profile used in the model was obtained experimentally to increase the accuracy of the model. Pressure profiles were expressed mathematically using the Fourier series. The motion equations were solved by using the Taylor series method. The solution of the mathematical model was performed by coding in the MATLAB interface. Cyclic speed fluctuations obtained from the model were compared with experimental results and found compitable. A validated model was used to analyze the effects of in-cylinder pressure, mass moment of inertia of crankshaft and connecting rod, friction, and piston mass. In experiments for 1500, 1800, 2400, and 2700 rpm engine speeds, crankshaft speed fluctuations were observed as 12.84%, 8.04%, 5.02%, and 4.44%, respectively. In simulations performed for the same speeds, crankshaft speed fluctuations were calculated as 10.45%, 7.56%, 4.49%, and 3.65%. Besides, it was observed that the speed fluctuations decreased as the average crankshaft speed value increased. In the simulation for 157.07, 188.49, 219.91, 251.32, and 282.74 rad/s crankshaft speeds, crankshaft speed fluctuations occurred at rates of 10.45%, 7.56%, 5.84%, 4.49%, and 3.65%, respectively. The effective engine power was achieved as 5.25 kW at an average crankshaft angular speed of 219.91 rad/s. The power of friction loss in the engine was determined as 0.68 kW.

Analytical investigation on the development of adaptive infilled gabled frames

Reinforced concrete infilled frame with brick masonry panel is becoming more common in recent days. Now a days this type structural frame is implemented mostly on the high-rise building because those buildings should be able to resist the lateral loads such as wind and seismic force hence, infilled frames are one of the most common lateral loads resisting system. In this study, two-dimensional single-bay, single-storey gabled infilled specimens were analyzed under static loading. The behavior of the reinforced concrete (RC) bare frame, RC infill frame with cement mortar interface is used and analyzed. In particular, the paper discusses the lateral stiffness of the frames and gives a comparative study between gabled frame and rectangular frame under static lateral load with varying parameters based on the obtained results such as displacement, lateral stiffness, bending moment and lateral load are carried out.

Biomechanical Motion Planning for a Wearable Robotic Forearm

Supernumerary robotic devices in the form of wearable arms enhance a user's reachable workspace and provide them with additional capabilities. However, the user may experience considerable force and moment loads on their body due to the robot's motion. In this letter, we present a simulation and trajectory planning framework that aims to minimize the load on a user's muscles while operating a Wearable Robotic Forearm (WRF). Using a high-fidelity model of the human arm, we construct a term for biomechanical costs that is subsequently added to the overall cost function for a motion planner. For evaluation, the planner is initialized with shortest paths linearly interpolated between ten start and goal state pairs in the configuration space, as well as with paths optimized for reaction moments using a local search. We find that the biomechanical planner coupled with locally-optimized initialization reduces mean human muscle fiber forces by up to 23.47% compared to the linearly interpolated trajectories.

Closed-form Solution of Prestressed Composite Beam Deformation

Eccentric load effect of prestressing in composite beam leads to nonlinear coupling oof deflection-slip. For the prestressed composite beam, considering axial force and eccentric moment of the prestressing equivalent load, variational equilibrium equations are imposed by the virtual work theorem which involves the interfacial slip condition. With relevant boundary conditions of different structural form, the closed-form solution can be derived. The model and closed-form solution are then validated by means of finite element analysis.

Explicit analysis of large transformation of a Timoshenko beam: post-buckling solution, bifurcation, and catastrophes

This paper exposes full analytical solutions of a plane, quasi-static but large transformation of a Timoshenko beam. The problem is first re-formulated in the form of a Cauchy initial value problem where load (force and moment) is prescribed at one end and kinematics (translation, rotation) at the other one. With such formalism, solutions are explicit for any load and existence, and unicity and regularity of the solution of the problem are proven. Therefore, analytical post-buckling solutions were found with different regimes driven explicitly by two invariants of the problem. The paper presents how these solutions of a Cauchy initial value problem may help tackle (i) boundary problems, where physical quantities (of load, position or section orientation) are prescribed at both ends and (ii) problems of quasi-static instabilities. In particular, several problems of bifurcation are explicitly formulated in case of buckling or catastrophe.

Behavior of highly ductile fiber–reinforced concrete columns under eccentric loading

Highly ductile fiber–reinforced concrete (HDC) is characterized by a tensile strain–hardening behavior and high compressive toughness, which is expected to alleviate the cracking and durability problems induced by the brittleness of high–strength concrete (HSC). In this study, HSC was substituted with HDC to construct columns. Six reinforced HDC (R/HDC) columns and two reinforced HSC (R/HSC) columns were constructed and tested under compressive loads with different eccentricities. The crack patterns, failure modes, lateral deflection curves, load–displacement curves, and strains of concrete and rebars were investigated. The test results revealed that the R/HDC column has a better failure mode and cracking pattern compared to the HSC column. A good synergy work performance between HDC and rebars significantly improved the utilization of the longitudinal rebars. A calculation method for the bearing capacity of the R/HDC column was proposed. The calculated results were in good agreement with the experimental results. The load–moment interaction curves (N–M curves) of the R/HDC column were calculated and plotted. Subsequently, the effects of HDC compressive strength, HDC tensile strength, the reinforcement strength, and longitudinal reinforcement ratio on the bearing capacity of the R/HDC column were studied using parametric analysis. The results indicate that a high tensile strain can guarantee the efficient utilization of the tensile strength of HDC.

Static repair of multiple cracked beam using piezoelectric patches

This paper addresses the problem of repairing multiple cracked beams subjected to static load using piezoelectric patches. First, the problem is formulated and solved analytically for the case of two cracks that results in ratio of restoring moments produced by employed piezoelectric patches. Since the ratio is dependent only on crack positions but not their depth, the result obtained for case of two cracks has been extended for the case of multiple cracks. This proposition is then validated by finite element simulation where repairing piezoelectric patches are replaced by mechanical moment load equivalent to the restoring bending moments produced by the piezoelectric patches. The excellent agreement between analytical solution and numerical simulation results in case of single and double cracks allows making a conclusion that a piezoelectric patch could productively repair a cracked beam by producing a restoring moment due to its piezoelectricity. Thus, the problem of repairing multiple cracked beam using piezoelectric patches is solved.