Effect Of Eccentric Loading Research Articles

Effect of eccentric loading on the stability and load-carrying capacity of thin-walled composite profiles with top-hat section

The paper investigates the influence of eccentric compressive load on the buckling, post-buckling and load-carrying capacity of thin-walled top-hat section composite columns. The columns were made of a CFRP composite material with a symmetrical arrangement of the layers by the autoclave technique. The scope of the presented study involved performing experimental tests on actual profiles as well as numerical calculations using the FEM analysis in ABAQUS® software. The experimental tests were carried out in the full range of loading, until the structure’s failure (post-buckling equilibrium paths and acoustic emission signals were measured). Regarding to FEM analysis, a nonlinear calculations using Newton-Raphson method were made. The damage initiation of the composite material was estimated based on Hashin’s theory, whereas damage evolution was described by the energy criterion (progressive failure analysis were used). The numerical results of eccentric compressive load on buckling and load-carrying capacity of composite columns were in good agreement with the experimental results.

Effect of Eccentric Load on the Undrained Bearing Capacity of Strip Footings above Voids

Abstract This study employed finite element limit analysis (FELA) to investigate the influence of eccentric loads on the bearing capacity of footings above single and double continuous voids. Upper...

Post-buckling and limit states of composite channel-section profiles under eccentric compression

This paper presents results of study investigating the post-buckling and limit states of compressed thin-walled composite channel-section profiles. Both experimental and numerical methods were used. The primary objective of experiments was to determine the post-buckling characteristics of real structures subjected to compression over the full range of loading until final failure. The experiments involved axial and non-axial compression of the C-profiles with different stacking sequences of plies, fabricated by autoclaving. The effects of eccentric load and ply stacking sequence on the non-linear stability and load-carrying capacity of the compressed structures were investigated. Numerical analysis was performed by the finite element method and it involved solving the problem of non-linear stability of the compressed thin-walled structures. The purpose of the analysis was to develop experimentally verified numerical models enabling the description of the structure's behaviour in the post-buckling range, including the moment of load-carrying capacity loss. A progressive damage model was used to assess the extent of damage in the composite material. The nonlinear calculations were made by the Newton-Raphson method using the commercial simulation software ABAQUS®.

Stability analysis of laminate profiles under eccentric load

The study investigates short thin-walled channel section columns made of a carbon-epoxy laminate. The tested columns were subjected to compression, including an eccentric compressive load relative to the gravity center of the cross section of the column. The boundary conditions applied in the study reflected simple support of the column. The scope of the study involved determining the effect of eccentric load on the structure’s stability and load-carrying capacity. At the same time, a numerical analysis by the finite element method was performed using the commercial simulation software Abaqus®. The non-linear numerical analysis of the compressed profiles was performed by the Newton-Raphson method. Failure of the composite material was described using a progressive damage model, wherein damage initiation in the composite material was described based on Hashin’s failure criteria while the evolution of damage was described by the energy-based progressive damage criterion. Results predicted by the numerical model were validated by experimental tests performed on real structures. The results enabled a comprehensive description of the composite material’s failure, starting from failure initiation until the total loss of load-carrying capacity of the column.

Model experiments to assess effect of eccentric loading on the ultimate bearing capacity of a strip footing near a dry sand slope

ABSTRACT The behaviour of shallow foundations on slopes is an important topic of interest in geotechnical engineering. This paper presents the results of laboratory model tests of an eccentrically loaded strip footing on a slope. Experiments were conducted with an eccentrically loaded model footing under various eccentricity ratios (±e/B) and normalized footing distances (d/B) and the results were compared with previous literature. The results confirm that the load eccentricity and normalized footing distance have considerable effects on the drained bearing capacity. The ultimate bearing capacity of a negative eccentric load is greater than that of a positive eccentric load up to a relative distance of d/B = 3. At this point, the bearing capacity becomes almost the same regardless of the eccentricity location relative to the slope face. Furthermore, the failure mechanism is not symmetrical; a greater failure surface length can develop on the slope side and this length decreases with increasing eccentricity.

Analytical modelling of spatial deformation pathways in planar and spatial shallow bistable arches.

We analyse spatial bistable arches and present an analytical model incorporating axial, two transverse bending and torsion energy components. We extend the St. Venant and Michell relationship used in flexural-torsional buckling of planar arches and use it in modelling spatial arches. We study deformation pathways in spatial arches and their effect on critical characteristics of bistability such as back and forth switching forces, and the distance travelled by a point of the arch. We show that not considering spatial deformation leads to incorrect inferences concerning the bistability of planar arches too. Thus, this model serves as a generalized framework for the existing analysis on planar arches since they belong to a subset of spatial arches. Additionally, the effects of eccentric loading on spatial deformations are explored for arches with a range of as-fabricated shapes and boundary conditions, and the results are validated with finite-element analysis.

Numerical and experimental analysis of stability of thin-walled composite structures subjected to eccentric load

The study investigates the effect of eccentric load on the stability and post-critical states of thin-walled composite top-hat cross-section columns made of CFRP under compression. The specimens were subjected to compressive load on the universal testing machine Zwick Z100 with regard to both axial and eccentric compressive loads. On the basis of the experimental studies, numerical models of thin-walled composite profiles were designed and verified by numerical analysis based on the FEM. The first stage of the conducted studies was performing a linear buckling analysis of stability of composite structures. The second stage of the analysis involved performing a nonlinear analysis of the thin-walled structures with geometric imperfections reflecting the lowest buckling modes. The obtained test results showed various effects of non-axial compressive load on the critical load values and stiffness of the construction in the post-critical state. In the case of eccentric loading in the direction parallel to the web of the top-hat profiles, the critical load values practically did not change – a drop in the force did not exceed 1.5%, as well as there was no change in the stiffness of the structure in the post-critical state. The realization of the eccentricity in the direction perpendicular to the profile web caused a drop in the critical force equal 43% and a significant decrease in the stiffness of the structure. On the other hand, implementation of the eccentricity load toward the web caused an increase in the critical force by more than 20%, despite very small eccentricity values of only 4mm were applied. This proved high sensitivity of the tested structures to the non-axial load in the direction perpendicular to the web of the profile. The FEM results and the experimental findings showed satisfactory agreement.

Fire Resistance of Eccentrically Loaded Reinforced Concrete Columns

Fire resistance of reinforced concrete (RC) columns in design codes is based on concentric loading conditions. The effect of eccentric loads on spalling and fire resistance of RC columns is a matter of investigation. The present study, therefore, broadly aims to determine the influence of relative levels of spalling under eccentric loads on fire resistance of RC columns. Experimental investigation is done on 3.15 m long column specimens. The experimental results indicate that the increase in load eccentricity (from 20 mm to 40 mm) increases the amount of spalling leading to exponential decrease in fire resistance (by 43%). Spalling is restricted by increase in longitudinal bars, particularly mid-perimeter bars, contributing to increase in fire resistance by 100% with doubling of number of longitudinal bars. Even the decrease in spacing of transverse reinforcement (from 300 mm to 150 mm) for eccentric loads leads to 123% increase in fire resistance. However, this advantage is limited by greater amount of compression face spalling (400% more) under eccentric loads, which is seen to increase with the density of reinforcement. For explosively spalled high strength columns, further reduction in fire resistance occurs on account of local softening of longitudinal reinforcement due to early (10 min) and protracted (up to 58 min) deep spalling. The chances of global column element buckling become more dominant with increase in load eccentricity around 40 mm. It is concluded that spalling levels change with relative change in reinforcement detailing with other parameters under eccentric loads. From this study, it is concluded that the feasibility of existing methods of determination of fire resistance for eccentrically loaded columns are inadequate and need to be revised to as per the results of this study.

The influence of load eccentricity on the behavior of thin-walled compressed composite structures

The study investigates the effect of eccentric load on the stability and postcritical states of thin-walled CFRP channel section columns under compression. Test specimens are subjected to compression on a testing machine provided with a fixture for applying eccentric compressive loads. Loading forces, deflection and strains of the column walls and web are measured. The experiments also involve examination of the operating performance of a structure undergoing buckling and determination of its postcritical equilibrium paths describing the relationship between load and deflection. Based on experimental results, numerical models of composite structures are designed and verified by the FEM. The scope of the numerical analysis involves performing a linear analysis of stability, which allows for determining the buckling mode depending on the amplitude of compressive load eccentricity and corresponding critical loads. The next stage of the analysis involves performing a nonlinear analysis of the structures with implemented geometric imperfections reflecting the lowest buckling modes. Based on obtained results, postcritical equilibrium paths of the developed FEM models are determined. Obtained equilibrium paths are then compared with experimental characteristics of real structures. The numerical results and experimental findings show a satisfactory agreement.

Strength of pile caps under eccentric loads: Experimental study and review of code provisions

Pile caps are rigid reinforced concrete structures that transfer column loads, generally consisting of a combination of an axial load and bending moments in one or two directions, to the piles. The design formulations of pile caps for more than two piles were derived from the results of experimental tests under a centered load. The practice of checking both punching and shear failure modes is common as described in the literature review, even though these formulations were developed for more slender elements. Currently, Codes ACI 318-14 and EC2 allow designing pile caps with strut-and-tie models or sectional approaches (shear, punching and flexural designs).In this study, 21 full-scale pile caps with different shear span-depth ratios and reinforcement layouts were studied to investigate the effect of eccentric loading on the strength and accuracy of the code formulations. The results show that in eccentrically loaded pile caps, the ultimate load is reduced but the maximum pile reaction increases and the secondary reinforcement proves effective to enhance the pile cap strength.Although the strut-and-tie models (STM) allow eccentric loads to be taken into consideration, they predict a much lower peak load than that observed at the experimental results and do not adequately reflect either the influence of slenderness or the failure mode.In general the sectional approach provided by Codes ACI-318-14, EC2 and MC-2010 (Level I of Approximation) lead to safe predictions of the peak load but do not always correctly predict the failure mode. The ultimate load predicted by EC-2 formulation comes closest to the experimental peak load, accurately reflects the influence of slenderness and the effect of secondary reinforcement, however, additional assumptions need to be made for its application. The ACI formulation complemented by the CRSI-2008 Special Investigation for deep pile caps is the safest but does not adequately capture the effect of horizontal and vertical secondary reinforcement. The MC2010 LoAI formulation is also conservative but does not detect the influence of slenderness or the contribution of secondary reinforcement.

Performance of high-modulus near-surface-mounted FRP laminates for strengthening of concrete columns

This study investigates the performance of high-modulus near-surface-mounted (NSM) fiber-reinforced polymer (FRP) laminates in strengthening of existing concrete columns. The focus of this study is on the compressive and buckling characteristics of carbon FRP (CFRP) laminates installed on short columns for strengthening to validate their sufficiency for further studies on slender columns. In this paper, an experimental study was designed to consider the effect of eccentric loading on short concrete columns (500 × 150 × 150 mm3) strengthened with four longitudinal NSM CFRP laminates (1.2 × 10 mm2). All specimens were tested symmetrically under the eccentricity to width ratios of 0, 10, 20, and 30% to give a single curvature bending combined with axial load. The experimental results showed no buckling/debonding failure of CFRP laminates, while some of the CFRP laminates reached to crushing points long after the peak load. Moreover, material coupon tests showed that the strength and elastic modulus of the CFRPs in compression were 34% and 86% of those in tension, respectively. The average compressive strain of NSM CFRP laminates for all column specimens under eccentric loading at peak load and after 15% drop from the peak load was 41% and 84% of their ultimate compressive strain obtained from compression coupon tests, respectively. Furthermore, a robust analytical model was developed considering the material and geometrical nonlinearities and it was verified against experimental results. Overall, the results indicated that strengthening short concrete columns with NSM CFRP laminates improved the capacity of the columns without any premature buckling, debonding, or crushing of CFRP laminates. The results will open new avenues in the FRP strengthening of concrete columns, especially slender columns, where the high-modulus NSM system can also enhance the lateral stiffness of the columns for buckling control.

Effect of eccentric loading on energy absorbing circular cap and open end frusta tube structures

The response of cap end (C) and open end (O) frusta tube made of aluminium alloy AA-1080 were explored against eccentric loading by carrying out numerical simulation. The thickness of both type of frusta tube was varied as 1.15, 1.2 and 1.3 mm whereas height of open end and cap end frusta tube were considered as 91.6 and 103 mm respectively. The semi-apical angle was varied as 5.71°and 7.59° which resulted base diameter 60.8 and 67.2 mm for both type of tubes respectively. The variation in eccentricity of loading from the axis of the tubes was kept as 5, 8 and 12 mm. The numerical simulations were carried out by using commercial finite element code LS-DYNA. The performance of structures was decided based on crashworthiness parameters like Peak force, Mean crushing force, Crash load efficiency and Energy absorption capability.For validating the numerical results, experiments were performed on compression testing machine wherein both cap end and open end specimens with the thickness of 1.15 mm were compressed with eccentricity 5 mm. The actual results were found close enough with predicted results. Cap end structure showed higher Crash load efficiency and energy absorption compared to the open end frusta tube.

The effect of eccentric loading in spent fuel pool criticality safety analyses

Eccentric fuel loading is one of the studies performed in a spent nuclear fuel criticality safety analysis. The study normally considers fuel assemblies placed at one side or corner in the rack cell. The purpose of this work is to study the effect of random placement of fuel assemblies on reactivity. MCNP was used to model the high density spent fuel pool and the depleted PLUS7 fuel. A total of 1400 cases with randomly displaced fuel assemblies in the rack cells, with and without neutron absorbers, were prepared. The results showed that none of the k-effective values from the random displacement cases exceed that of the base case where the fuel assemblies were centered in the rack cell. This suggests that eccentric fuel loading studies may not be needed in all criticality safety analyses with randomly displaced fuel assemblies.

The effect of eccentricity of load on the behavior of compressed composite columns in critical state

The study concerns a short thin‐walled channel section column made of carbon‐epoxy laminate. The tested column was subjected to compression, including an eccentric compression force relative to the gravity center of the cross‐section of the column toward its higher rigidity. The boundary conditions applied in the study reflected articulated, simple support of the column's ends. The scope of the study included determination of the effect of eccentric load on the structure's buckling mode and critical load. The critical load of the real structure was determined using approximation methods based on the post‐critical equilibrium paths of the structure obtained in experimental tests. At the same time, a numerical analysis by the finite element method was performed using the commercial simulation software Abaqus®. The numerical analysis involved solving an eigenproblem to determine the buckling mode of the structure and to determine the critical load of this structure under axial and eccentric load. The experimental results were used to verify the developed numerical models. The analysis enabled determination of the effect of eccentric load on the structure's buckling mode and critical load, which is of vital importance for the design of thin‐walled real structures that are coated with reinforcing thin‐walled stiffeners. Examples of such constructions include thin‐walled stressed‐skin structures such as an aircraft's main body section and wings, where the thin skin or outer covering is reinforced by a series of longitudinal profiles with open and closed sections. POLYM. COMPOS., 40:70–77, 2019. © 2017 Society of Plastics Engineers

Effects of Eccentric Load on Un-Strengthen and CFRP Strengthened RC Beams

CFRP strengthened reinforced concrete (RC) beams are usually tested under either three points or four point concentric loads; the effect of eccentricity is neglected in many studies. In this experimental program eight RC beams tested in two groups, GROUP ‘A’ & ‘B’. In group ‘A’ four RC beam tested, one control beam tested under concentric load and three under the eccentricity of 40, 60 and 80 mm respectively. The remaining four RC beams in group ’B’ strengthened using carbon fibre reinforced polymer (CFRP) strip and tested under the 60mm eccentricity. The experiment has confirmed the behaviour transformation from flexure failure to local failure due to variation in eccentricity. Therefore, the effects of eccentricity cannot be neglected and required special consideration before applying strengthening scheme on RC beam. The RC beams strengthen using CFRP have the ability to enhanced the load carrying capacity of beams tremendously, but the eccentric load effect on ductility, and failure mode of RC beams.

The manipulation of strain, when stress is controlled, modulates in vivo tendon mechanical properties but not systemic TGF-β1 levels

Modulators of loading-induced in vivo adaptations in muscle–tendon complex (MTC) mechanical properties remain unclear. Similarly contentious, is whether changes in MTC characteristics are associated with growth factor levels. Four groups were subjected to varying magnitudes of stress/strain: Group 1 trained with the MTC at a shortened position (MTCS; n = 10); Group 2 at a lengthened position (MTCL; n = 11; stress levels matched to MTCS); Group 3 over a wide range of motion (MTCX; n = 11); and Group 4 (n = 10) was the control population (no training). Patella tendon Stiffness (P < 0.001), Young's modulus, and quadriceps torque (P < 0.05) increments (only seen in the training groups), showed MTCL and MTCX groups responses to be superior to those of MTCS (P < 0.05). In addition, MTCL and MTCX better maintained adaptations compared to MTCS (P < 0.05) following detraining, with a pattern of slower loss of improvements at the early phase of detraining in all training groups. There were no significant changes (P > 0.05) in antagonist cocontraction, patella tendon dimensions or circulating transforming growth factor beta (TGF-β1) levels following training or detraining in any of the groups. We conclude that chronically loading the MTC in a relatively lengthened position (which involves greater strains) enhances its mechanical properties, more so than loading in a shortened position. This is true even after normalizing for internal stress. The underlying endocrine mechanisms do not appear to be mediated via TGF-β1, at least not at the systemic level. Our findings have implications with regard to the effectiveness of eccentric loading on improved tendon structural and mechanical properties.

Achilles Tendinopathy Modulates Force Frequency Characteristics of Eccentric Exercise

Previous research has demonstrated that ground reaction force (GRF) recorded during eccentric ankle exercise is characterized by greater power in the 8- to 12-Hz bandwidth when compared with that recorded during concentric ankle exercise. Subsequently, it was suggested that vibrations in this bandwidth may underpin the beneficial effect of eccentric loading in tendon repair. However, this observation has been made only in individuals without Achilles tendinopathy. This research compared the force frequency characteristics of eccentric and concentric exercises in individuals with and without Achilles tendinopathy. Eleven male adults with unilateral midportion Achilles tendinopathy and nine control male adults without tendinopathy participated in the research. Kinematics and GRF were recorded while the participants performed a common eccentric rehabilitation exercise protocol and a concentric equivalent. Ankle joint kinematics and the frequency power spectrum of the resultant GRF were calculated. Eccentric exercise was characterized by a significantly greater proportion of spectral power between 4.5 and 11.5 Hz when compared with concentric exercise. There were no significant differences between limbs in the force frequency characteristics of concentric exercise. Eccentric exercise, in contrast, was defined by a shift in the power spectrum of the symptomatic limb, resulting in a second spectral peak at 9 Hz, rather than 10 Hz in the control limb. Compared with healthy tendon, Achilles tendinopathy was characterized by lower frequency vibrations during eccentric rehabilitation exercises. This finding may be associated with changes in neuromuscular activation and tendon stiffness that have been shown to occur with tendinopathy and provides a possible rationale for the previous observation of a different biochemical response to eccentric exercise in healthy and injured Achilles tendons.

Behavior of RC Slab-Column Connections Strengthened with External CFRP Sheets and Subjected to Eccentric Loading

AbstractStrengthening of both aging and modern infrastructure has become necessary as a result of increased load demand and/or to restore the capacity of a member. For example, flat slabs (commonly utilized in parking garages) are subjected to an aggressive environment and increased traffic loads and additionally require strengthening and/or repair. Fiber-reinforced polymer (FRP) sheets and laminates externally bonded to concrete slabs around the slab-column joint are widely used to enhance the strength of flat slabs. Slab-column connections are most often subjected to eccentric loading; however, most reported studies have focused on retrofitted slab-column connections subjected to concentric loads. This paper aims to fill this knowledge gap and experimentally investigate the effect of eccentric loading on the behavior of slab-column connections retrofitted by externally bonded carbon fiber-reinforced polymer (CFRP) sheets. Six full-scale (2,000×1,000×150-mm) interior slab-column connections subjected to ...

Paper 20: Insertional Achilles Tendinopathy - Eccentric Loading vs. Radial Shock Wave Treatment

Nonoperative management of chronic tendinopathy of the Achilles tendon insertion is poorly studied. With demonstrated effectiveness of eccentric loading and of repetitive low-energy shock wave treatment in patients with midsubstance Achilles tendinopathy recently, this randomized controlled trial aimed at verifying effectiveness of both procedures exclusively in patients with insertional Achilles tendinopathy.

Research on Ultimate Bearing Capacity of Combo Steel Tube Tower Joint

The steel tube-angle connections have widely used in electric transmission towers. However, there is no technical information regarding the behavior of the connections, and it is lack of effective design of rational basis. Thus, a analytical parametric study was conducted to investigate the behavior of tube-angle connections.The analytical results were in good agreement with existing experimental results.The effects of eccentric loads and parameter change on the ultimate strength were considered. And the analytical results show that ultimate capacity of eccentric loads were significantly lower than that of the axis loads, and the ultimate load of tube-angle connections increases linearly with the thickness of the gusset plate. Besides this,diameter/thickness ratios have an effect on the capacity. In addition,as the distance between the angle end and the steel tube increases, the ultimate strength becomes lower.