Load Deflection Research Articles

Biomechanical Analysis of Camellia oleifera Branches for Optimized Vibratory Harvesting

To investigate the biomechanical properties of Camellia oleifera branches under two loading speeds within a specific diameter range, three-point bending tests were conducted using a universal material–testing machine. The tests were performed at loading speeds of 10 mm/min and 20 mm/min on branches with diameters ranging from 5 mm to 40 mm. This study aims to provide insights into the design of a manipulator gripper used in a vibrating harvester for Camellia oleifera fruit. Four main varieties of Camellia oleifera were tested to determine their elastic modulus. The nonlinear least squares method, based on the hyperbolic tangent function, was employed to fit the bending load–deflection curves of the branches. This process constructed multi-parameter transcendental equations involving elastic modulus, diameter, and loading speed. Results indicated that the branches of four Camellia oleifera varieties exhibited significant differences in their biomechanical properties, with their modulus of elasticity ranging from 459.01 MPa to 983.33 MPa. This suggests variability in the bending performance among different varieties. For instance, Huaxin branches demonstrated the highest rigidity, while Huashuo branches were softer in general. For the proposed empirical fitting equations, when the fitting parameter k is 168 ± 20 and the parameter c is 3.102 ± 0.421, the bending load–deflection relationship of the branches can be predicted more accurately. This study provides a theoretical basis for enhancing the efficiency of mechanized vibratory picking of Camellia oleifera and optimising the design of the gripper.

Mechanical Behavior Research on IHB-CFRP Anchorage Scheme to Reinforce the Flexural Performance of Concrete Beams

This article investigates the use of Carbon Fiber Reinforced Polymer (CFRP) plates with additional anchors to enhance reinforced concrete slab beam structure. A test proposes an improved additional anchorage measure to solve the debonding problem during anchoring. Three point bending load test are carried out to analyze the influence of different anchoring positions on the reinforcement effect. An optimized Improved Hybrid Bonding CFRP (IHB-CFRP) additional anchoring measure is given. The shear friction model proposed in the IHB-CFRP anchoring scheme can simulate the additional adhesion resistance well. The article investigates the concrete crack extension, load–deflection relation, the strain distribution of CFRP plate, CFRP and concrete interface shear stress. It can be seen that the IHB-CFRP anchoring scheme improves the interface bonding ability and bearing capacity of the reinforced specimen.

A flexibility approach for geometric nonlinear static analysis of guyed masts

The present study proposes a novel flexibility-based approach for the large displacement analysis of guyed masts. The guyed mast is modeled as an equivalent beam–column supported by catenary cables, and the exact force–displacement relations of sagging cables and slender beam–column are accounted for with sufficient rigor. The proposed method starts with formulating two mutually exclusive sets of second-order force–displacement equations, one for the mast and the other for the cables. Flexibility matrices are derived in an incremental form for an Euler–Bernoulli beam–column using the well-known Variational Iteration Method (VIM). Since an exact Lagrangian multiplier is used in the correction functional, the displacements obtained from this numerical method are also exact. The cable behavior is studied using Irvine’s model, which is the most accurate and realistic one since it represents the equilibrium configuration of the cable using a catenary curve. But, the model is non-algebraic and is unsuitable for complex structures. Hence, Irvine’s equations are recast into an incremental form to obtain exact incremental flexibility matrices. Then, displacement compatibility is re-established between the mast and the cables at their interfaces. This method can effectively address the eccentric compression on the mast shaft from the supporting guy cables, stay slackening, postbuckling of the mast, and trace the mast’s nonlinear response for large displacements. A multi-level guyed mast is analyzed to demonstrate the practical application of the proposed method. Classic examples of single-level guyed towers are used to illustrate the behavior in the postbuckling and post-slackening region. The sensitivity of a guyed mast to cable prestress levels, as well as mast shaft imperfections, are also discussed. The solved examples are also analyzed using commercial finite element software packages, and comparisons are drawn regarding their accuracy in capturing the load–deflection response under large displacements.

Application of an Instability‐Based Fracture Model for Prediction of Crack Initiation in Modified 9Cr–1Mo Steel

ABSTRACTDuctile fracture of modified 9Cr–1Mo steel was investigated using smooth and notched bar tension tests. Round and flat notched specimens with varying notch acuity ratio were used to investigate the influence of stress state on the fracture strain. Simulations of the experiments were performed using the extended finite element method, together with an instability‐based crack initiation criterion based on the micromechanics of void coalescence. The parameters in the plasticity model were determined using smooth bar tension tests, whereas the void nucleation parameters were calibrated from experiments on a shallow‐notched specimen. Subsequently, the load–deflection responses and strain to crack initiation have been predicted for round and flat notched specimens with various notch acuities, and central notched specimens with notches oriented at various angles to the loading axis. Using a single set of parameters, the model was able to quantitatively predict fracture in different specimen geometries encompassing a range of stress states.

Bending Test of Rectangular High-Strength Steel Fiber-Reinforced Concrete-Filled Steel Tubular Beams with Stiffeners

To better understand the bending performance of rectangular high-strength steel fiber-reinforced concrete (HSFRC)-filled steel tubular (HSFRCFST) beams with internal stiffeners, ten beams were subjected to a four-point bending test. The primary considerations were the strength grade of the HSFRC, the steel fiber content, the internal stiffener type, and the circular hole spacing of the perfobond stiffener. The moment–curvature and flexural load–deflection curves were calculated. The mode of failure and the distribution of cracks of the infill HSFRC were observed. The presence of steel fibers greatly improved the bending stiffness and moment capacity of HSFRCFST beams, with the optimal effect happening at a steel fiber content of 1.2% by volume, according to the experimental findings. The type of stiffener influenced the failure modes of the exterior rectangular steel tube, which were unaffected by the compressive strength of the infill HSFRC. On the tension surface of HSFRCFST beams, the crack spacing of the infill HSFRC was virtually identical to the circular hole spacing of perfobond stiffeners. When the circular hole spacing was between two and three times the diameter, the perfobond stiffener worked best with the infill HSFRC. The test beams’ ductility index was greater than 1.16, indicating good ductility. The test beams’ rotational capacities ranged from 6.26 to 13.20, which were greater than 3.0 and met the requirements of the specification. The experimental results demonstrate that a reasonable design of the steel fiber content and the spacing between circular holes of perfobond stiffeners can significantly improve the bending resistance of rectangular HSFRCFST beams. This provides relevant parameter design suggestions for improving the ductility and bearing capacity of steel fiber-reinforced concrete beams in practical construction. Finally, a design formula for the moment capacity of rectangular HSFRCFST beams with stiffeners is presented, which corresponds well with the experimental findings.

Hybrid Reinforced Concrete Frames with Engineering Cementitious Composites: Experimental and Numerical Investigations

Reinforced concrete (RC) structures are vulnerable to damage under dynamic loads such as earthquakes, necessitating innovative solutions that enhance both performance and sustainability. This study investigates the integration of Engineered Cementitious Composites (ECC) in RC frames to improve ductility, durability, and energy dissipation while considering cost-effectiveness. To achieve this, the partial replacement of concrete with ECC at key structural locations, such as beam–column joints, was explored through experimental testing and numerical simulations. Small-scale beams with varying ECC replacements were tested for failure modes, load–deflection responses, and crack propagation patterns. Additionally, nonlinear quasi-static cyclic and modal analyses were performed on full RC frames, ECC-reinforced frames, and hybrid frames with ECC at the joints. The results demonstrate that ECC reduces the need for shear reinforcement due to its crack-bridging ability, enhances ductility by up to 25% in cyclic loading scenarios, and lowers the formation of plastic hinges, thereby contributing to improved structural resilience. These findings suggest that ECC is a viable, sustainable solution for achieving resilient infrastructure in seismic regions, with an optimal balance between performance and cost.

Experimental investigation on shear performance of RC T-beams strengthened with hybrid bonded CFRP strips

This study presents an experimental investigation on shear performance of strengthened reinforced concrete (RC) beams with hybrid bonded carbon fiber-reinforced polymer (CFRP) strips. Six RC T-beams were prepared including a reference beam, a beam strengthened with externally bonding (EB) method, and four beams strengthened with hybrid bonding (HB) method. Different spacings between steel plate and initial damage of beam were also considered in the test. Failure modes, cracking process, load–deflection curves, and strain development of beam components were discussed in detail. Test results showed that ultimate shear capacity and ductility of RC beams are both improved by HB method and fasteners effectively prevent the FRP debonding failure before shear failure of RC beams. Fasteners changed the propagation path of the critical diagonal cracks which extended towards the steel plate instead of hinge support. Maximum strain of CFRP strip using HB method, which is over 45% of its ultimate tensile strain, is more than twice that using EB method. Modified theoretical models were finally employed to evaluate the shear strength of RC beams increased by HB method. The comparison of theoretical and test results showed that predicted range of load increment agrees well with the test results.

Model scale tests on the behaviour of single piles in cohesive soils under combined loads

ABSTRACT Model scale tests were conducted to study the influence of combined loads (uplift + compressive, uplift + lateral, lateral + compressive and lateral + uplift) on stress distribution, ultimate capacities and deformations of single piles in Indian black cotton soils, in comparison to pure uplift and lateral loads. Numerical analysis was performed in Plaxis 3D to examine the effect of pile slenderness ratio (L p /d = 15, 20 and 25) on ultimate capacity and pile head displacements. The test results showed that uplift capacity and pile head displacements increased by 35–49% and 30–50% with an increase in staged compressive loads, respectively. Therefore, piles subjected to combined uplift and compressive loads should be designed for pile head displacements rather than uplift capacity. The compressive loads did not affect the stress distribution along the pile–soil interface. However, lateral loads altered stress distribution, resulting in a curved failure plane and a substantial increase of 80–150% in the uplift capacity of piles under combined uplift + lateral loads. The lateral load–deflection curve for 60% and 80% of staged uplift loads showed an elastic response, indicating that the pile and surrounding soil did not yield under the applied lateral loads.

Bench-scale thermomechanical assessment of carbon fibre reinforced polymer C-channels

This study investigates the thermomechanical response of carbon fibre reinforced polymer (CFRP) C-channels using a bench-scale apparatus that combines mechanical loading and radiant thermal exposure. The study aims to assess the behaviour of pre-loaded CFRP C-channels, representative of aircraft sub-structures when subjected to fire conditions. Woven prepreg CFRP C-channels were tested under cantilever point load deflection while exposed to varying heat fluxes. Key aspects examined during the study include failure times, displacement, temperature distribution, and failure modes. The findings reveal that heated, pre-loaded C-channels experience distinct phases of physico-chemical decomposition and mechanical degradation. The mechanical degradation includes upward shear buckling of the horizontal flanges and vertical web, along with outward buckling of the vertical web towards the heat source. The study shows that thermal decomposition and mechanical degradation occur simultaneously, influenced by heat flux intensity. Higher heat fluxes accelerate decomposition and reduce load-bearing capacity, while lower fluxes slow degradation. Displacement data indicates that heat flux intensity significantly affects structural response. Temperature measurements show higher fluxes lead to elevated temperatures and steeper gradients, impacting failure times and modes. Increased temperatures correlate with shorter failure times, and variability in failure times decreases as heat flux rises. These insights are significant for understanding the thermomechanical response of C-channels in aircraft sub-structures. The knowledge obtained can contribute to developing more robust and safer aircraft designs, particularly for components exposed to fire conditions, enabling engineers to establish more precise safety margins for CFRP structures, potentially preventing catastrophic failures and thereby enhancing overall aircraft safety.

Flexural behavior of bonded post-tensioned concrete beams with steel or GFRP bars

Post-tensioned concrete beams with GFRP reinforcement have gained attention in recent years due to their unique flexural behavior and potential cost benefits. Because of the absence of comprehensive guidelines in international codes and limited application in constructions, this hybrid system is adopted in the current paper as a pioneering solution for sustainable and eco-friendly construction practices. Particularly noteworthy is the corrosion resistance of GFRP bars, which significantly enhances the durability of structures. The influence of using GFRP with bonded post-tension concrete beam is experimentally investigated compared to concrete beams with prestressing and non-prestressing reinforcement. Eight concrete beams with different reinforcement types and ratios were cast and tested under three-point load. Flexural resistance, crack pattern, deflections, and strains of the beams were compared with a reference beam with prestressing and non-prestressing reinforcement. Experimental load capacities of the tested beams were compared to those obtained from various international codes. The experimental results revealed that the beams with GFRP bars had smaller failure load and larger deflection compared to those with non-prestressing steel by up to 25 % and 37 %, respectively. A 3D finite element model (FEM) was developed and validated by comparing the numerical results with those obtained from the experiments. A sensitivity analysis was performed, using the validated FEM, by changing the concrete strength, steel yield stress, and GFRP ultimate strength by ± 20 %. The sensitivity analysis included seventy-two beams which had the same dimensions, loading, and boundary conditions of the tested beams. Changing the concrete strength only led to varying the beam capacities by −7 % ∼ + 4 %. Changing the steel yield stress only led to changing of the beam capacities by −13 % ∼ + 11 %. No change was observed when the GFRP ultimate stress was varied by 20 %.

Various configurations of externally bonded strain-hardening cementitious composite reducing shear failure risk of defected RC beams

This study delves into the efficacy of external strengthening methods in improving the shear behavior of defected reinforced concrete (RC) beams that lack shear stirrups, utilizing both experimental and numerical methodologies. Failure risk of such beams is a potential threat which is mitigated carefully to increase building safety and sustainability to avoid risk of construction failure. Ten RC beams underwent three-point experimental testing to assess the influence of the strengthening scheme and the presence of mechanical anchors. Two beams were designated as control specimens, while eight beams were strengthened with the application of additional strain-hardening cementitious composite (SHCC) layer in various configurations. These configurations encompassed single-sided, two-sided, and strip applications, with the inclusion of mechanical anchors. The study found that employing a single-sided SHCC, incorporating vertically bent bars into the RC beam, is recognized for its efficient alleviation of degradation in shear reinforcement. The incorporation of three SHCC strips to partially reinforce the compromised beams demonstrated a modest impact on the initial stiffness. Nevertheless, noteworthy enhancements of 46% and 42% were observed in both cracking and ultimate loads, respectively. Furthermore, increasing the number of the SHCC strips to four resulted in a more significant improvement in the load–deflection responses. Enhancing the compromised beams by applying four SHCC strips to the beams using bolts offers a feasible alternative to the configuration where SHCC was uniformly attached along the entire defected zone. Moreover, a numerical model was created to simulate the tested beams. The model effectively anticipated the progression of cracks, ultimate capacity, and deflection, indicating excellent agreement with the experimental observations.

Study on bending performance of prefabricated glulam-cross laminated timber composite floor

Abstract The glulam-cross laminated timber (CLT) composite floor is a type of prefabricated composite floor that integrates glulam beams and CLT slab into a unified structure using shear connectors. To investigate the bending performance of the glulam-CLT composite floor, the bending test was conducted on a full-scale composite floor under static load. The study comprehensively analyzed the failure mechanism, load–deflection behavior, interface slip and strain distribution of the glulam-CLT composite floor. The test results of the composite floor indicated that the failure mode was tensile fracture of the wood beam at the bottom. As the load increased, the deflection deformation of the mid-span beam exceeded that of the edge beam. When the load reached its ultimate limit, the deflection deformation of the mid-span beam increased by 14.4% compared to the edge beam. In the early loading phase, the strain distribution of the composite section satisfied the assumption of a plane section. However, the strain distribution deviated from this assumption with the increased load due to the relative slips between the glulam beam and CLT flange. To calculate the bending performance of the composite floor, the M-shaped section of the glulam-CLT composite floor was simplified as T-section composite beams. The linear-elastic method for determining the flexural rigidity and ultimate bearing capacity of the glulam-CLT composite floors was proved to be accurate and reliable. The findings provided valuable insights into the bending behavior of the CLT flange under load and emphasized the non-uniform stress distribution caused by shear lag effects.

Annular sector plates made of FG graphene origami-enabled auxetic metamaterial under bending and buckling loading: A VDQ-based approach

The behaviors of annular sector plates made of functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAMs) under the action of buckling and bending loads are investigated herein using a numerical approach. Multiple GOEAM layers with graphene origami (GOri) content are considered for the plate which changes in layer-wise patterns. Moreover, the material properties of the plate are calculated using novel genetic programming-assisted micromechanical models. In order to derive the governing equations, the Mindlin plate theory in conjunction with Hamilton’s principle is utilized within the framework of the variational differential quadrature (VDQ) method. The vector-matrix representation of the presented formulation can be beneficial from the viewpoint of implementing numerical approaches. The governing equations are then discretized and solved based on VDQ matrix differential and integral operators so as to obtain the critical buckling load and maximum lateral deflection of plates with different edge conditions. The effects of GOri content, folding degree and distribution pattern on the results are studied. It is revealed that increasing the GOri content leads to the negative Poisson’s ratio (NPR) effect which respectively reduces and increases the lateral deflection and the critical buckling load.

Structural Design Considerations for a Large Single Span Reinforced Concrete Monolithic Beam-Column Structures

Large-span reinforced concrete structures present unique design challenges that necessitate meticulous consideration of load-bearing capacity, deflection control, reinforcement, and material choices. For spans exceeding 10 meters, structural engineers must carefully apply the principles and recommendations of Eurocode 2 to ensure that the structure is safe, functional, and durable. This paper explores the critical aspects of designing large single spans in reinforced concrete beam- column systems using Eurocode, with a focus on load distribution, reinforcement detailing, deflection limits, and material properties. Practical insights into the implementation of these guidelines are provided through examples, offering structural engineers in Nigeria a comprehensive approach to achieving safe and cost- effective long-span structures.

Evaluation of the Flexural Behavior of One-Way Slabs by the Amount of Carbon Grid Manufactured by Adhesive Bonding

Fiber-reinforced polymers (FRPs), which are resistant to corrosion, are used as reinforcement material for concrete. However, the flexural behavior of concrete members reinforced with FRPs can vary depending on the properties of FRPs. In this study, the flexural behavior of one-way concrete slab specimens reinforced with a new grid-type carbon-fiber-reinforced polymer (CFRP) (carbon grid) manufactured by bonding pultruded CFRP strands to an adhesive was investigated. The experimental results indicated differences in the load–deflection relationships of the specimens depending on the carbon grid reinforcement amount. Specimens in which the carbon grids were over-reinforced or reinforced close to the balanced reinforcement ratio reached the maximum load due to concrete crushing and exhibited ductile failure. The specimen under-reinforced with the carbon grid exhibited brittle failure. Specimens with carbon grid reinforcement close to a balanced reinforcement ratio exhibited maximum loads ranging from 0.43 to 0.61 times the calculated flexural strength, which resulted in becoming 0.86–1.00 lower in the specimens with a wider width of the CFRP strands. This study proposes coefficients to estimate the stiffness of carbon-grid-reinforced concrete flexural members after cracking. Applying these coefficients resulted in stiffness calculations that reasonably simulated the behavior of the specimens reinforced with carbon grids after crack formation.

Comparison of the flexural and flexural-bond behaviour of beams reinforced with CFRP rods with different surfaces

Carbon-fibre-reinforced polymer (CFRP) bars are available with diverse surfaces and with a wide range of tensile strengths compared with traditional rebars. However, CFRP rods in beams require a larger cross-section than steel rebars in order to meet the required anchorage length in current design standards. The goal of this work was to compare the flexural and flexural-bond behaviours of CFRP-reinforced beams and steel-reinforced beams using four-point flexural tests. CFRP rods with thread-wrapped and sand-coated surfaces, each with distinct characteristics, were used. Additionally, two shear span/depth ratios were considered (2.5 and 3.5). The results indicated pseudo-plastic behaviour in the load–deflection curves of the CFRP-reinforced beams. This behaviour was attributed to the slip due to the reduced bond strength between the concrete and reinforcement, leading to the final failure. Based on the surface type of the CFRP rods, a cross-sectional design with the maximum load exceeding the design load was realised, even when the CFRP-reinforced beam failed to satisfy the required anchorage length. These findings suggest that the current anchorage length equations may be overly conservative, indicating the need for appropriate adjustments to the design approach.

Enhancing structural damage evaluation of PC girder bridges through digital twinning Bayesian model updating

Developing a unified analytical framework to assess the structural performance of deteriorated prestressed concrete (PC) girder bridges is important for their maintenance. This study aims to construct a physics-based digital twin framework for PC girder bridges incorporating Bayesian model selection and updating, a high-fidelity three-dimensional (3D) finite element (FE) model, and a method for simulating prestressed tendon damage. In this study, three PC girder specimens were designed and tested to evaluate the effects of tendon rupture near the anchorage region on structural performance. Bayesian model selection was used to determine the most plausible model class based on the estimated model evidence. The most probable values (MPVs) of the model parameters, derived from the estimated posterior probability density functions (PDFs), were then used to calibrate the FE model, which reflects a healthy state of the PC girder bridge. This updated FE model serves as the baseline for conducting what-if scenario simulations. Subsequently, nonlinear segments of the constitutive model, obtained from coupon tests, and a simulation method for tendon rupture were incorporated into the updated FE model. Nonlinear static simulation results obtained through the updated model were found to be consistent with both the observed crack pattern and the load–deflection curve. The reliability of the digital twinning FE model for assessing tendon damage and for predicting the residual load-bearing capacity was verified through comparison with measured data. Therefore, the digital twinning Bayesian model updating approach shows potential applications in continuous structural health monitoring (SHM) of PC bridges.

Global buckling behaviour and design of cold-formed steel octagonal hollow section columns under compression

This paper experimentally and numerically investigated the global buckling behaviour of cold-formed steel octagonal hollow section columns. A test programme was first conducted on 10 OctHS steel columns made of Q460 and Q690 high strength steels. Each steel grade comprised five specimens with distinct geometric dimensions. Material properties and initial global imperfection were measured and are reported herein. Axial load versus mid-height lateral deflection curves, axial load versus axial strain curves, and failure modes of OctHS specimens are presented and discussed. In conjunction with laboratory works, finite element models were subsequently developed to replicate the load-deformation responses and failure modes of OctHS columns against the experimental results. Following the validation of proposed numerical modelling technique, extensive parametric studies were performed to evaluate the effects of steel grade, cross-section slenderness, member slenderness, and initial global imperfection. Furthermore, results from 10 test specimens and 608 numerical models were used to comprehensively assess the applicability of current codes of practice on the design of OctHS long columns. Modifications and design recommendations were proposed based on the assessment results. Corresponding reliability analyses were also performed for each design method.

Numerical Investigation of Cold Formed Z Purlins with Lap Bolted Connection

Abstract The main aim of this paper is to investigate the flexural rigidity of lapped cold-formed steel (CFS) purlin connections under monotonic loading, using a numerical model developed with finite element software ABAQUS. The purlins are made up of CFS Z-section, while high strength bolts of diameter 12 mm and grade 8.8 have been used. The test setup consists of simply supported two Z-section that are connected together using overlap connection, where load is being applied at mid span. Furthermore, a parametric study has been conducted to investigate various parameters including, length of lapped connections, thickness, and depth of CFS section and arrangement of bolts, to end up with a total of 15 case specimens. All case specimens were examined in detail in terms of load carrying capacity and deflection characteristics. The results showed that overlap connection is capable of transmitting moment and acts as semi-rigid connection. Moreover, results proved that increasing the ratio of overlap length to beam span resulted in an increase in connection moment capacity. Additionally, decreasing the ratio of lap length to section thickness increases the flexural capacity. Finally, the specimens with bolts in both flange and web at the position of overlap connection were found to have the highest moment capacity.

Enhancing Conveyor Belt Performance: Evaluating the Impact of In-creased Capacity Using Belt Analyst Software

This study investigates the effects of increasing conveyor belt capacity from 148.5 tons per hour (t/h) to 180 t/h on the overall system performance, employing both manual measurements and simulations using Belt Analyst software. The research aims to evaluate critical parameters such as effective pulling force, motor power requirements, structural load, and belt deflection, which are essential for determining the feasibility and impact of such an upgrade. The analysis reveals that with the capacity increase, the effective pulling force required rises to 14,072 N, while the motor power usage escalates to 15 kW. Concurrently, the structural load experiences a significant increase from 46.144 kg/m to 56.238 kg/m, and belt deflection intensifies from 22 mm to 27 mm. These findings suggest that increasing the conveyor belt capacity to 180 t/h, may lead to increased stress on the structure and belt, which could potentially affect the lifespan and performance of the conveyor system. Furthermore, while the conveyor system's performance enhances at the higher capacity, it also places additional stress on the system's components. The study further examines the implications of these changes, emphasizing the potential risks to the conveyor belt’s structural integrity and the possible reduction in its lifespan due to the increased mechanical stress. It is highlighted that careful consideration and precise engineering adjustments are necessary when planning capacity enhancements to avoid adverse effects on the system's longevity and reliability.