Force Transfer Research Articles

Mechanical Behaviour Assessment and Optimization of Construction Sequence for an HSS Vierendeel Truss

Long-span Vierendeel trusses in construction are challenged by smooth force transfer and critical stress control concerns. In this article, construction sequences characterized by loading/unloading due to various assemblies of the branches and/or temporary lattice column supports are focused on to reproduce their related mechanical behaviours in finite element modelling. Typical bending moment and shear force diagrams for hollow structure section (HSS) chords are analysed first, and then combined with a corrected assessment index in the development of an optimized construction scheme through effective discussion. It is observed that the branch assembly sequence has significant but reversed influences on either the bending moments or the shear forces of the interior support and the midspan of the HSS chords. The influence of the branch assembly sequence on the bending moment and shear force are compromised with the introduction of a temporary support. The corrected assessment index superimposed by the internal force and the deflection is demonstrated properly to represent the strength and the serviceability requirements, especially for characterizing the removal of a temporary support after the completed construction of a twelve-panel Vierendeel truss for the roof of an assembly hall.

Wetland restoration, household income, and livelihood structure of farmers

BackgroundWetland restoration is an important measure for restoring wetland ecosystems and their ecological benefits, with the goal of restoring their ecological functions and resources. However, wetland restoration affects farmers' incomes and livelihoods. Although existing research has contributed to a deeper understanding of the relationship between wetland restoration and farmers' household incomes, some issues require further consideration. Therefore, here, we aimed to analyse the impact of wetland restoration on farmers' incomes and provide empirical evidence for the coordination mechanism of protection and development in the Poyang Lake Wetland in Jiangxi Province.MethodsBased on 2 years of balanced panel data of 365 households around the Poyang Lake wetland, this study analysed the influence of policies related to wetland restoration and how variables such as the cultivated land area, labour force transfer, and location of nature reserves impact farmers' income. To this end, we used a two-way fixed-effect model to test the robustness by using propensity score matching, and the influence mechanisms of wetland protection policies, such as wetland restoration, wetland ecological compensation, and the Yangtze River fishing ban, on farmers' income interactions were explored.Results and discussionThe results showed that, due to the policy of wetland restoration was implemented a long time ago, the negative impact of the policy on reducing farmers' household income is not significant now. Further, farmers' family livelihood strategies have changed, and choosing other types of agricultural production and off farm employment are currently the main choices for farmers. Wetland restoration has changed their income structures. Additionally, the two wetland restoration policies and banning of fishing have had synergistic effects. The findings of this study are helpful in understanding how wetland restoration around nature reserves influences farmers' household incomes. Further, they can provide policy insights for promoting an increase in income and the optimization of the income structure of communities around lake wetland nature reserves.

Effectiveness of shear key on torsional resistance of precast beam: An experimental and numerical investigations

The present study evaluates the behaviour of wet precast beam-to-beam connection under pure torsion through experimental and numerical studies. A wet connection is provided at the central region of the precast beam. Two precast beam elements are connected by welding the overlapped portion of reinforcement bars projecting from each beam element. Furthermore, inward and outward shear keys are provided within the connection region to examine the efficacy of shear keys on the torsional resistance of the precast beam. Also, the behaviour of precast beams with and without shear keys is compared with monolithic beams. Experiments are conducted using a loading frame, designed and fabricated to create a pure torsion effect on the beam specimen under the application of monotonic vertical load. The response of test specimens is evaluated through various parameters such as torque and corresponding twist at different phases of loading, torsional ductility index, crack formation and failure propagation. Experimental studies show that shear keys provided within the connection region effectively contribute to force transfer and enhance torsional resistance of the precast beam by 16 %−24 % as compared to monolithic beam and precast beam without the shear key. A numerical analysis of the precast beam is carried out, and the behaviour of test specimens obtained from experimental studies is compared. The damage pattern and torque-twist behaviour obtained from numerical studies adequately simulate the response of test specimens observed during the experimental study.

Mathematical and Buongiorno nanofluid modelling to predict the thermal and solutal performance of magneto-bioconvective Casson nanofluid flowing in a rotatory disk

Abstract This study aims to improve how heat and mass move in systems that use viscoelastic nanofluids under magnetic fields. These systems are commonly used in industries like biotechnology, energy, and medical devices. The significance of this work lies in exploring the steady flow of magnetohydrodynamic (MHD) Casson nanofluids, incorporating the Buongiorno nanofluid model and swimming microorganisms. This research seeks to deepen the understanding of complex fluid behaviors by examining the effects of thermal radiation and chemical diffusion under thermal and solutal convective boundary conditions. The governing equations, which are inherently nonlinear due to the presence of multiple physical effects, are converted from two-dimensional partial differential equations (PDEs) to ordinary differential equations (ODEs) using a similarity transformation. A semi-analytical solution is derived using the collocation pseudo-spectral method within the MAPLE computational software. The study investigates how factors like Casson and magnetic parameters, Eckert number, Brownian motion, and thermophoresis affect the flow rate, temperature distribution, species concentration, and microorganism motility. These results are validated by comparing them with established benchmarks. The key findings reveal a pronounced oscillatory behavior in the temperature profile at higher Eckert number values, while increased Brownian motion and thermophoresis lead to greater nanoparticle dispersion near the disk surface. Higher Lewis and Peclet numbers lead to increased microorganism concentration, demonstrating stronger convective and advective effects. These insights are vital for optimizing drag force, thermal gradients, and mass transfer in engineering applications that involve rotating disks and magnetic fields.

Sub-modelling based fatigue evaluation of welded details in composite trapezoidal corrugated web girders under coupled thermal-structural loading

Exploring the long-term performance of welded details in composite trapezoidal corrugated web (TCW) girders is a significant focus for the service life of these structures exposed to atmospheric environment and traffic flow. The majority of the present studies have been conducted without accounting for thermal stresses induced by temperature differences and accurately reflecting internal force transfers for the composite girders in flexural bending. The fatigue behaviour of the welded details in these girders under coupled thermal-structural loading is investigated herein through experimental and numerical methods. The results indicated three stages for the structural degradation from the test performance and justified a proper allowance of the cross-sectional stress in coordination with the flexural curvature in the derivation of S-N relations comparable to similar details in related design codes. A sub-modelling procedure is implemented to capture the thermal gradient, the local stress concentration, and the crack distribution in global modelling while replicate the semi-elliptical surface crack at the external side of the fillet weld toe in local modelling. The fatigue lives predicted from the proposed analytical model match reasonably well with experimental and numerical results, indicating its good applicability incorporating characteristic geometric correction factors into classical theoretical calculation for fatigue evaluation.

Thermal and mechanical analysis of thermal break structure in balcony with basalt fiber reinforced polymer

Thermal break structure is an effective design to reduce building energy consumption in balcony. The traditional stainless-steel bars or other FRP components reinforced thermal break structures can't enable both mechanical performance and thermal insulation concurrently because these materials are difficult to have low thermal conductivity and high mechanical properties at the same time. This paper proposes to use basalt fiber reinforced polymer (BFRP) to construct the thermal break structure due to the high load-bearing capacity and thermal insultation of BFRP. The thermal performance of the structure is systematically verified through three-dimensional simulation. Influence of thermal break widths, loading point positions, shear reinforcement forms and reinforcement types on the mechanical properties of the structure is investigated. The results show that BFRP can significantly reduce the linear heat transfer transmittance while ensuring structural mechanical properties. A larger thermal break width leads to the low load-bearing capacity of the structure. Lower BFRP compressive reinforcements need enough diameter to provide compressive strength and shear reinforcement forms can significantly increase the mechanical properties of the thermal break. Upper tensile reinforcements can be selected depending on the stiffness and insulation requirements in practical engineering. Based on experimental results, force transfer mechanism is analyzed and the rationality of the structural design is identified. The maximum length of the cantilever slab without shear reinforcement forms is approximately 2.94 m when meets the serviceability limit state. The results suggest that newly designed BFRP thermal break structure can effectively solve thermal bridge problems in balcony.

Basic Analysis for Evaluation of Tennis Volley Skill Using Body Propagated Vibration Sensing

In sports that use tools, it is necessary to master tool manipulation with a high degree of accuracy because proficiency in tool manipulation leads to victory or defeat in a competition. The purpose of this study was to clarify the force transfer of the body, including the racket, from the perspective of vibration analysis to realize training to efficiently improve tennis skills. In this study, we measured the propagating vibration, surface electromyography of finger flexors and extensors, and racket movement under two conditions of strong- and weak-volleying in tennis and aimed to explain the meaning of the measured propagating vibration in terms of muscle control and racket kinematics. Based on the experimental results, it was confirmed that it is feasible to measure the change in stiffness from the racket to the wrist due to the muscle co-contraction owing to the propagating vibration signal intensity. These results indicate the possibility of evaluating tennis shot skill by analyzing the propagating vibrations measured using a wearable vibration measurement system.

Abdominal wall muscle ultrasound assessment and level of experience in Pilates - an exploratory study

The core refers to a group of muscles that allow optimal force transfer along the body’s kinetic chain and is critical for movement. The goal of this quasi-experimental study was to investigate the relationship between the experience level of Pilates participants and abdominal wall thickness. For this, we compared the thickness of four abdominal muscles—transversus abdominis (TrA), internal oblique (IO), external oblique (EO), and rectus abdominis (RA)—as measured before and after 8 weeks of Pilates training in three conditions, namely, relaxation, abdominal hollowing, and plank exercise. Eighteen participants were distributed into three groups with different levels of Pilates practice—experienced (EG; n=6), inexperienced (IG; n=7), and control (CG; n=5) groups. The RA showed a tendency to increase post-intervention in the EG (all conditions: p=0,002, p=0,006, and p=0,002, respectively for relaxation condition, abdominal hollowing and standing plank). Additionally, significant differences were found in relaxation (p=0.003, d=−0.744) and plank (p=0.009, d=−0.630) conditions in the IG. Significant differences were also registered in the EO muscle in the IG (all conditions: p=0.046, p=0.013, and p=0.008, respectively; d=0.464, d=−0.596, and d=−0.637, respectively). IO muscle thickness tended to increase in the CG in all conditions (p=0.044, p=0.006, and p<0.001, respectively) and the EG in relaxation and plank conditions (p=0.009 and p=0.007, respectively). Within groups, the effects of Pilates practice were more significant post-intervention, with the exceptions being under the contraction condition in the deepest muscles (IO: p=0.109, d=0.083; TrA: p=0.194, d=0.062). Our hypothesis was partially confirmed because 8 weeks of Pilates practice have improved significantly the thickness of the RA and EO muscles in the IG.

Сompression and Shear of an Ideal-plastic Wedge with a Rough Stamp (Frictional Contact Model)

The transfer of shear force through frictional contact on rough surfaces of precompressed plastic bodies is studied. As a contact model, we consider the problem of plastic compression of a wedge by a rough flat stamp with the condition of Prandtl friction on the contact surface. A technique is proposed for determining the maximum shear load perceived by frictional contact.

Numerical Study on Seismic Performance of a New Prefabricated Reinforced Concrete Structural System Integrated with Recoverable Energy-Dissipating RC Walls

To enhance the performance of infill walls and reduce seismic damage, this paper proposes a novel prefabricated reinforced concrete (PRC) energy-dissipating wall, forming a new recoverable energy-dissipating PRC (ED-PRC) structural system. The system features pre-set gaps on both sides and the top of the PRC wall, with flexible materials filling the gaps on the sides. The top of the PRC wall is connected to the beam through several double-conical mild steel dampers to ensure the efficient transfer of horizontal shear forces between the main frame and the PRC wall. A numerical study was employed to investigate the seismic performance and the staged yield capacity. The results show that this design achieves a yielding sequence of dampers → wall → main frame. Furthermore, during the early to mid-phases of the cyclic loading simulations, the double-conical mild steel dampers with the low yield point utilized in the ED-PRC structural system exhibited exceptional energy dissipation capabilities. Notably, the LY100 dampers accounted for up to 61.84% of the total energy dissipation, with the LY160 and LY225 dampers contributing 55.35% and 50.25%, respectively. It indicates that the proposed ED-PRC structural system significantly enhances the ductility and the energy dissipation capacity under seismic loading while substantially reducing damage to the primary structure. The use of prefabricated components facilitates modular construction, allowing for quick dismantling and replacement after an earthquake, thereby rapidly restoring the structural seismic resilience.

Light and scanning electron microscope characterization of mandibular symphysis tissue as a functional adaptation in the mandible development of human fetuses.

When developing, the mandible presents great plasticity and contains condensed mesenchymal cells that develops into Meckel's cartilage, of which the anterior part forms the mandibular symphysis. Mandible human development studies focus on investigating whether the beginning of mandibular fusion in fetal period is related to symphysis ossification and the tensions imposed on it, considering that tongue movements, mouth opening, and closing can be seen in fetuses. This research analyses tissue modifications during human mandibular symphysis growth using light and scanning electron microscopy to relate them to its functional structure. The study sample consisted of 12 human fetuses distributed into two groups: Group I (GI) of 10-14 weeks old and Group II (GII) of 20-24 weeks old. Fragments of mandibular symphysis were removed en bloc together with the surrounding tissues to preserve the relation with adjacent structures. Decalcified specimens were prepared in semi-serial coronal sections 5-μm-thick and stained with hematoxylin and eosin, Masson՚s trichrome, Verhoeff, and Sirius red for histological analysis with light microscopy. Collagen fibers Type I or III and elastic fibers were quantified by volume fraction (Vv). Coronal sections of the GI and GII symphyseal region were submitted to scanning electron microscopy. Comparison between groups used independent t-test. Our study presents the different endochondral ossification stages in the anterior part of Meckel's cartilage in GI. Both groups showed abundantly vascularized mesenchymal tissue with intense cellular activity forming the mandibular symphysis, such as a source of new osteoblasts adjacent to the newly deposited bone matrix. Scanning electron microscopy analysis revealed an invasion of the bony trabecula in the transverse direction from the hemimandible, rectilinear in GI and sinuous in GII due to interdigitating bone process, promoting its ossification. In collagen Vv analysis was verified a prevalence of type I in GII and type III in GI, indicating a proportional relation between maturation and tissue arrangement. Functionally, the collagen and elastic fibers in the mandibular symphysis were arranged in a pantographic network, and the fibrillar interconnectivity clearly contributes to resilience capacity and efficiency of the force transfer. This study inferred the functional significance of the knowledge about the tissue composition of mandibular symphysis, and the importance of this tissue for surrounding structures. The mesenchymal tissue of mandibular symphysis participates in bone growth process, revealing an adaptation mechanism of mandibular symphysis in the fetal period investigated.

Significance of mixed convection and heat transfer flow past a vertical Riga plate in the presence of alumina nanoparticles: Analysis of streamlines for oblique stagnation point

AbstractThe aim of the current study to inspect the magnetic flow properties and heat transport features near an oblique stagnation point of a nanofluid with mixed convection through a vertical Riga plate are examined. The Riga plate is a familiar actuator made out of permanently fixed electrodes and magnets that moved away from the plate due to an exponential decline in the Lorentz force. Nanofluid is taken into consideration due to its peculiar properties, such as remarkable thermal conductivity is the significance of the study. These properties are important in heat exchangers, electronics, advanced nanotechnology, and material sciences. Using usual similarity transformations, the group of leading partial differential equations is distorted into a group of nonlinear ordinary differential equations. Then, a very proficient procedure namely bvp4c is utilized to discover the solution. For particular values of the different influential fluid parameters, the characteristics of the dimensionless temperature and velocity along with drag force and heat transfer are investigated graphically. In addition, the symmetrical results were initiated for both cases of the slip and without slip parameters. It is demonstrated that for greater influence of the volume fraction of nanoparticles, the normal and tangential velocity profile drops down for the instances of aiding and opposing flows due to fluctuations in the presence of slip factor, and absence of slip factor. In contrast, the temperature profile intensifies in both the cases of slip parameters and without the slip parameter owing to the phenomenon of assisting flow and opposing flow subject to superior impressions of the nanoparticle volume fractions. It is also observed that depending on the equilibrium between buoyancy effects, obliqueness, velocity slip parameters, and straining motion, the location of the point of zero shear stress (friction factor on the surface of the wall) is displaced to the right or the left of the origin.

Understanding the interaction forces between shield-triggered autoinjectors and skin: an in-depth noninvasive study

ABSTRACT Objective This noninvasive study aimed to understand the interaction between shield-triggered autoinjectors (AI) and skin at the point of activation, hypothesizing that the AI’s housing absorbs a significant amount of the user-applied force depending on shield design and skin characteristics. Methods Twenty-seven volunteers used a test device measuring applied force versus shield force and indentation depth relative to shield length (2,4,6,8 mm) in standing and sitting positions. Results Significant differences were found between applied and shield force for the different shield lengths. Shorter shields resulted in significantly lower force transfer coefficients, with means ranging from 0.72 for the 2 mm shield to 0.94 for the 8 mm shield. ANOVA revealed statistically significant factors (p < .05), including position and gender, with females generally having lower coefficient values. Indentation depth increased with higher forces and varied significantly between positions without significant shield length impact. Conclusion The findings confirm that an increase in shield length at the point of activation reduces skin friction with the housing, resulting in less force loss and a lower device activation force perceived by the user. Force loss can be further reduced by standing up. Understanding device-tissue interactions will support development of better AIs with fewer user failures.

A Study on the Mechanical Behavior of a Wind Turbine Foundation with a Constrained Structural Shear Connector

Aiming to solve the problems that a wind turbine foundation with a foundation pipe may suffer from grouting, where the concrete around the interface collapses and the interface disintegrates under a long-term wind load, a kind of wind turbine foundation with a constrained structural shear connector is proposed. In this article, the scaling model tests and a finite element simulation of a traditional stud foundation pipe, perforated steel shear connector foundation pipe, and three groups of constrained structural shear connector foundation pipes with different anchored depths are presented. The force transmission mechanism and damage mechanism of constrained structural shear connector wind turbine foundations are revealed, and the shear resistance of a constrained structural shear connector is analyzed. The influences of buried depth and other parameters on the mechanical properties of the shear connector are also investigated. The results show that the constrained structural shear connector has the advantages of stronger interfacial stiffness and significant force transfer and diffusion, and can more effectively connect the foundation pipe and concrete foundation to work together. It can give full play to the material advantages of concrete and reinforcements, and effectively improve the embedded stiffness and durability of concrete foundations. It can solve the problem of cracks in concrete caused by local pressure. At the same time, it is suggested that the diameter of the surrounding concrete should be in the range of 3 to 4 D, and the embedment depth of the stud should not be less than 0.4 D to give full play to the performance of the constrained structural shear connector.

The effect of enzymatic GAG degradation on transverse shear properties of porcine cornea

The structural integrity of cornea depends on properties of its extracellular matrix, mainly a mixture of collagen fibers and soluble proteoglycans (PGs). PGs are macromolecules of negatively charged sulphated glycosaminoglycans (GAGs) covalently attached to a protein core. GAGs appear as bridges between adjacent collagen fibers and could facilitate force transfer between them. Furthermore, GAGs are responsible for corneal hydration by attracting and maintaining water molecules into the extracellular matrix. Based on these observations, GAGs are expected to be essential for biomechanical properties of cornea. The primary objective of the present study was to determine the effects of GAGs on shear properties of cornea. For this purpose, GAGs were enzymatically removed from porcine corneal disks by keratanase II enzyme. After confirming the successful removal of GAGs by histochemical methods, torsional rheometry was performed to characterize the shear stiffness of GAG-depleted samples as a function of axial strain. It was found that the shear modulus of all samples was a function of applied shear strain and compressive strain. Beyond the range of linear viscoelastic response, the average complex shear modulus decreased with increasing the shear strain. Increasing the axial strain from 0% to 40% significantly increased the average complex shear modulus of corneal disks in all groups. Finally, the enzyme treatment with keratanase II enzyme significantly decreased the shear stiffness. The experimental measurements were discussed in terms of microstructural and compositional properties of corneal extracellular matrix and it was concluded that GAGs play a significant role in defining shear properties of cornea.

Performance of nodal regions of reinforced concrete frame corners subjected to opening bending moments

Design of frame corners in presence of opening moments is a task that has concentrated many research and engineering efforts in the past. It deals with the response of discontinuity regions, where beam theory does not hold valid and the use of equilibrium-based models (such as strut-and-tie models or stress fields) could be a suitable manner to understand the transfer of forces and to lead to consistent reinforcement detailing. However, the assessment of efficiency factors for equilibrium-based models is not straightforward for such details as their response has been observed to be governed in many cases by the tensile resistance of concrete and crack propagation. Furthermore, most efforts so far have been devoted to determining only the resistance of the region as a function of its reinforcement detailing, but limited works have been dedicated to their post-peak response. The post-peak response is nevertheless instrumental for redundant structures, as it governs the level of potential redistributions of internal forces in order to develop the full structural resistance of the system. Such aspect has become even more significant in present days, where the assessment of existing structures with potentially poor nodal detailing has become a need to avoid unnecessary retrofitting or replacement, in an effort to reduce carbon footprint of construction. In this paper, comprehensive research on this topic is presented. It is based on the results of a large database compiled by the authors comprising 126 tests. After filtering of the database, conclusions on the expected response of several details are obtained. Also, a general procedure grounded on an equilibrium-based model is proposed, providing tailored efficiency factors as a function of the mechanical reinforcement ratio and detailing type, but also providing a complete description of the post-peak response. This latter model is based on a kinematically-compatible displacement field for the post-peak phase, allowing to evaluate the opening of the cracks in the nodal region and the associated softening of resistance.

Experimental study on seismic behavior of a novel RC slab- SC wall joint based on UHPC and rebar – steel plate lap splices

Steel plate concrete shear walls (SC walls) have been widely used in practical projects because of great mechanical properties. For the application in nuclear power plant containment, the joint of specially shaped reinforced concrete slab and SC walls is difficult to design and construct. By using ultra-high performance concrete (UHPC), a new type of joint with the non-contact lapping method is proposed in this paper, which has advantages of simple construction, superior performance, suitable cost, and wide application range. Five RC-UHPC slab-shear wall joints were designed and tested under reciprocating load to study the effects of structures of lapping steel plate, shear-resisting methods, and interfacial reinforcing methods on the mechanical properties of the joints. The test results showed that the joints adopting the new structures were damaged for the flexural failure of the concrete area, with no damage to the joint zone, while the other specimens failed in the shear failure of the joint zone. It can be demonstrated that the ribs formed by bars and studs on the lapping steel plates are effective measures for non-contact force transferring, and interfacial reinforcing bars can improve the strength of the interface between concrete and UHPC. The force transferring efficiency of the new joints was close to or more than 90%, which indicates that the proposed joint structures can effectively realize the non-contact lapping force transferring. The design formulas and suggestions are proposed based on the analysis of the mechanism of new structures.

An analytical model for predicting fatigue crack arrest and growth behavior in metal plates strengthened with unbonded prestressed reinforcing strips

Fatigue crack arrest and life extension of metallic structures can be achieved by using prestressed strips for fatigue strengthening. However, the popularization of prestressed strengthening techniques has been limited by lack of versatile analytical methods. In this paper, an analytical method is developed for predicting the fatigue behavior of centrally cracked metal plates after being anchored with prestressed reinforcing strips, based on linear elastic fracture mechanics and the superposition method of stress intensity factors. The force transfer between reinforcing strips and metal cracked plates is modeled using the displacement compatibility principle. The finite-width correction factor for centrally cracked metal plates subjected to four-point concentrated forces is derived, allowing the model to analyze the effect of different anchorage locations on the effectiveness of strengthening. The analytical model is validated through experimental data and finite element analysis. The results show that the model is highly accurate and can be used to analyze how different anchorage locations affect fatigue reinforcement.

Axial behavior variation of 72-story concrete-filled steel tubes with different joint connections due to interface debonding considering long-term deformation of concrete core

Long-term concrete deformation including shrinkage and creep occurring seriously threats the longevity, safety and serviceability of concrete-filled steel tube (CFST) structures. In this study, numerical simulation on the variation of axial behavior of 72-story CFST structures with different joint connection details due to interface debonding considering shrinkage and creep of concrete core is carried out. Three connection details including connections with inner horizonal diaphragms only, two-direction through-beams only, and inner horizontal diaphragms combined with two-direction through-beam, are considered, respectively. Vertical loading from floors is treated as centralized vertical force applied on steel tube directly. The shrinkage of concrete core is simulated by decreasing concrete temperature. A cohesive constitutive law and a Coulomb friction model are employed to describe the interface behavior in tangential direction before and after debonding, respectively. The interaction between concrete core and steel tube in normal direction is treated as a hard contact. The concrete plastic-damage (CPD) constitutive model is used for concrete core and a plastic constitutive law is employed for the steel tube. The initiation of the interface debonding between steel tube, H-shaped steel beam flanges, inner diaphragms and concrete, the variation of the force transfer path, stress redistribution, steel tube yielding and the final failure are described in detail. Results show that the axial load-carrying capacity of each CFST structure has a decrease of 26-28% when compared with that determined by the current design code where the confinement effect is considered, and a decrease of 9-10% when compared with that determined by the current design code where the confinement effect of steel tube is not considered. Moreover, the axial stiffness decreases to 76-78% of their theoretical values when debonding is not considered. Numerical results show that the interface debonding negatively affects the long-term axial load-carrying capacity and stiffness obviously, which has not been considered in current design codes. Some comments on the design of CFST members are proposed based on the numerical simulation results.

Development of a Novel Beam-Based Finite-Element Approach for the Computationally Efficient Prediction of Residual Stresses and Displacements in Large 3D-Printed Polymer Parts

Recently, 3D printing of large, structural polymer parts has received increasing interest, especially for the creation of recyclable structural parts and tooling. However, the complexity of large-scale 3D polymeric printing often dictates resource-intensive trial and error processes to achieve acceptable parts. Existing computational models used to assess the impact of fabrication conditions typically treat the 3D-printed part as a continuum, incorporate oversimplified boundary conditions and take hours to days to run, making design space exploration infeasible. The purpose of this study is to create a structural model that is computationally efficient compared with traditional continuum models yet retains sufficient accuracy to enable exploration of the design space and prediction of part residual stresses and deformations. To this end, a beam-based finite element methodology was created where beads are represented as beams, vertical springs represent inter-bead transverse force transfer and multi-point, linear constraints enforce strain compatibility between adjacent beads. To test this framework, the fabrication of a large Polyethylene terephthalate glycol (PETG) wall was simulated. The PETG was modeled as linearly elastic with an experimentally derived temperature-dependent coefficient of thermal expansion and elastic modulus using temperature history imported from an ABAQUS thermal model. The results of the simulation were compared to those from a continuum model with an identical material definition, showing reasonable agreement of stresses and displacements. Further, the beam-based model required an order of magnitude less run time. Subsequently, the beam-based model was extended to allow separation of the part from the printing bed and the inclusion of part self-weight during fabrication to assess the significance of these effects that pose challenges for existing continuum models.