Decrease In Load Carrying Capacity Research Articles

Stability of slender GFRP tube-confined UHPC-filled steel-encased column under axial compression: Experiment and mesoscale modeling

The stability of GFRP tube-confined UHPC-filled steel-encased columns (FUSCs) is critical for optimal utilization of its superior cross-sectional load-bearing capacity that guarantees overall structural safety. This study conducted an experimental investigation on 14 slender FUSC specimens under uniaxial compression for different aspect ratios and aggregate contents. The pressure-sensing films were applied to measure the contact pressure between the GFRP tube and UHPC, and a mesoscale finite element model was developed to uncover the role of randomly distributed fibers and aggregates in the UHPC during the failure process. Accordingly, the stability performance of slender FUSC was analyzed, and specific discussions were held on the mutual interaction mechanism between GFRP and UHPC during the loading process. The results showed that the stability of FUSCs decreased faster with an aspect ratio of l0/D > 8 (λ>30.77), resulting in the decrease of load-carrying capacity for up to 25 %. By including coarse aggregate, the distribution of steel fibers was densified, and Young's Modulus of UHPC was increased, considerably improving the stability of FUSCs. Moreover, the GFRP tube with a fixed winding angle of 50° remarkably enhanced the stability of the specimen due to the sharing of bending moment instead of providing confinement. This research outcome offers a basis for the stability control of slender FUSCs.

Experiment study on flexural performance of steel concrete composite beams under salt freeze-thaw cycles in negative moment sections

Bridge structures in cold climates face significant challenges due to freeze-thaw cycles and salt-induced corrosion. This study investigates the degradation mechanisms of the negative bending behavior of steel-concrete composite beams using normal concrete (NC) and ultra-high performance concrete (UHPC) under salt freeze-thaw cycles (SFTC), considering the impact of different stud arrangements. The results indicate that UHPC significantly enhances the cracking performance in the negative bending region of the composite beams and demonstrates high resistance to SFTC. Before undergoing SFTC, the cracking moment of the UHPC beams increased by an average of 210.5%, and stiffness by 37.3%, compared to the NC composite beams. After 150 SFTCs, the NC beams showed a significant decline in performance, with a 62.1% reduction in cracking moment, a 6.2% decrease in load-carrying capacity, and a 5.6% reduction in stiffness. In contrast, the flexural performance of the UHPC beams was almost unaffected, with only a 17.5% reduction in cracking load. Moreover, beams with a double-row stud configuration exhibited better negative bending resistance compared to those with a single-row stud configuration. Based on experimental results and data from reference, a reasonable formula for predicting the composite beams under the effect of SFTCs was proposed and proved to have satisfactory accuracy.

Research on the bearing capacity of foam concrete wall materials in green buildings

This study fabricated a combined wall with the help of a lightweight steel structural wall skeleton and foam concrete (FC) and designed four sets of strain experiments for walls with different FC densities and steel contents. In the displacement results, the higher the density of FC, the higher the load-bearing capacity. When the density of FC is 1000 and 1600 kg/m3, the wall will lose its load-carrying capacity after a maximum load of 80 and 90 kN, respectively. The greater the axial compression ratio of the sample, the greater the shear capacity of the combined wall. When the displacement distance is 30 mm, the maximum load is 162, 110, 94 and 85 kN when the shear span ratio is 1.0, 2.0, 3.0 and 4.0, respectively, and the load-carrying capacity decreases with the increase in the shear span ratio. Moreover, compared with the shear span ratio of 1.0, the load-carrying capacity decreases by 23, 41 and 51% successively. The maximum loads of the combined walls are 88, 79, 81 and 62 kN when the densities are 800, 1000, 1200 and 1600 kg/m3, respectively, and 75, 80, 81, 94 and 101 kN when the steel content ratios are 0.5, 1.0, 1.5, 2.0 and 2.5%, respectively.

A note on the response of elastic bodies whose material moduli depend on the density and the mechanical pressure

In this note we study the response of an inhomogeneous body, whose material moduli depend on the density and the mechanical pressure, that is described by an implicit constitutive relation between the Cauchy stress and the right Cauchy–Green tensor. Such a constitutive relation is relevant to the study of the deformation of porous elastic solids as the porous structure varies and the local density changes. The boundary value problems of a plate of such a material subject to uniaxial and bi-axial extension and compression are considered. We find that regions that are more porous, and thus of lower macroscopic density, have the propensity to fail than regions of higher density, in the sense the load carrying capacity decreases, when other measures such as the stress are comparable.

Prediction of bearing capacity of cracked asymmetrical double-arch tunnels using the artificial neural networks

Cracking in lining structures has the potential to seriously weaken the lining's carrying capacity. In this paper, the failure performance of cracked lining was firstly obtained by model tests and numerical simulations. An artificial neural network model was subsequently developed using extensive simulation data derived from the verified numerical model, to forecast the capacity loss in cracked double-arch tunnels. The results showed that: (1) The cracks caused the linings to undergo localized crushing failure, which greatly reduced the double-arch tunnels' load-bearing capacity. The cracked linings entered a stable working stage with cracks initially and then progressed directly to the destabilization stage, displaying hidden and sudden characteristics; (2) The neural network model, developed using a large number of numerical simulations, demonstrated outstanding predictive performance and accurately forecasted the load-bearing capacity of double-arch tunnels; (3) The depth of the cracks was the principal factor influencing the load carrying capacity decrease in double-arch tunnels, particularly in the vicinity of the void; (4) The structural capacity diminished swiftly when crack depth surpasses 30% of the lining's thickness, and larger voids and cracks closer to the voids amplified the lining-bearing capacity loss for equivalent crack depths.

Simulation study on flexural behaviour of perforated aluminium tubes

A numerical investigation was conducted to compare the flexural capacity of AA6063-T5 aluminum alloy tubes with perforations of different hole diameters (4, 6, 8, and 10 mm), hole spacing (13-26-39-52 mm) and tube wall thickness (0.5, 1, 1.5 and 2 mm) by the finite-element analysis (FEA). As the tube thickness increases, the load-carrying capacity decreases, while the LCC increases as the hole diameter increases. It was observed that the LCC increased as the distance between the holes increased. ANOVA test was used to analyze the influence of hole diameter, hole spacing, and tube wall thickness on tube load-carrying capacity. It is found from the statistical analyses that the most significant factor on maximum load is tube thickness (97.2 %) between parameters of hole diameter, hole spacing, and tube wall thickness. As a result of the second statistical analysis, the most significant factor on maximum load is hole diameter (73.14 %) between parameters of hole diameter and hole spacing. A second important factor is hole spacing on maximum load.

Analysis of lubricating characteristics of high-pressure radial piston pump with thermo-elastohydrodynamic coupling

The behavior of piston-cylinder interfaces takes important influences on lubricating characteristics of the high-pressure piston pump. For the sake of revealing the lubricating characteristics of radial piston pumps, a transient thermo-elastohydrodynamic lubrication model to analyze the interface between piston and cylinder is established with considering the effects of the bushing elastic deformation, viscosity-temperature-pressure, heat conduction and piston tilting, on the basis of coupling the finite element method and finite difference method. Furthermore, the influences of design parameters (camshaft speed, inlet pressure and average clearance) on the load carrying capacity, leakage, viscous friction, and temperature rise of the friction-pair interfaces are analyzed. The results indicate that the average clearance has the most significant influence on the lubrication performance. Increasing the average clearance from 2 to 6 μm resulted in a substantial decrease in load carrying capacity by approximately 50% and friction force by approximately 65%. The temperature rise showed a significant reduction of 55%, while the leakage increased by approximately 3-fold.

SEQUENCE OF VALLEY DEVELOPMENT OF ALAKNANDA AND ITS TRIBUTATIES & QUATERNARY SEDIMENTATION, GARHWAL HIMALAYA, PARTS OF CHAMOLI TEHRI UTTAKASHI & PAURI UTTAR PRADESH (UTTRARKHAND STATE ) INDIA

SEQUENCE OF VALLEY DEVELOPMENT OF ALAKNANDA AND ITS TRIBUTATIES & QUATERNARY SEDIMENTATION, GARHWAL HIMALAYA, PARTS OF CHAMOLI TEHRI UTTAKASHI & PAURI UTTAR PRADESH (UTTRARKHAND STATE ) INDIA

Seismic performance of RC columns under combined cyclic flexural and constant axial loadings

In this study, an experimental test procedure is conducted to investigate seismic performance of reinforced concrete columns under earthquake loading. Earthquake loading is simulated by combination of constant axial load and reversing cyclic load. The main variables of the experimental program are selected to be dimensionless axial load level and the ratio of shear span to effective column depth. Test results are compared with the current suggestions and approximations used for performance-based design and/or evaluation of reinforced concrete (RC) columns under seismic loads. It is observed that section curvature plays an important role to express failure damage limit state under cyclic loading as well as to sudden decrease in load carrying capacity. Besides, two new simple suggestions are made for performance-based design and/or evaluation process of RC columns. As a first step of this suggestions, a relation between damage limit states and curvature ductility ratios of RC columns is defined. This relation is validated with the experimental results of test columns through damage index model based on section curvature. The proposed damage limit states vary according to damage level definition and based on buckling parameter in terms of diameter, buckling length and yield strength of longitudinal reinforcement. The second suggestion is made to relate damage limit state to decrease in shear resistance of columns. To this purpose, a model to express concrete contribution to shear strength due to the proposed damage limits is used. With these two new proposed equations, it is both aimed to obtain a damage limit state in terms of curvature ductility ratio and to control ductile failure mode in a simple yet effective way.

Numerical investigation of the hybrid reinforced concrete beam using GFRP bars

The numerical study of the hybrid reinforced concrete beam using GFRP bars has been explored in this research. Finite element software ABAQUS had been used for numerical investigation. In the present research, the use of GFRP bars as a replacement to steel reinforcing bars for longitudinal reinforcement is attempted. Further, a RC beam by using GFRP as longitudinal reinforcement and steel rebars as transverse reinforcement is compared with the conventional steel reinforced concrete beam. The beams are tested for three-point bending using numerical simulation under displacement control. By performing the numerical modelling, load, strain and displacement data has been attained. Further, by using the output data, stress-strain curves of concrete, load versus strain variations in tension bars and load versus deflection curves are plotted. The stresses, deflections, strain developed in longitudinal bars, load carrying capacity, energy absorption are then calculated using the data and are compared. From the results it is observed that, the load carrying capacity decreases by 16% and the energy absorption increases by 29% when longitudinal steel bars are replaced by GFRP bars.

Compressive Behavior of Pultruded GFRP Boxes with Concentric Openings Strengthened by Different Composite Wrappings.

Web openings often need to be created in structural elements for the passage of utility ducts and/or pipes. Such web openings reduce the cross-sectional area of the structural element in the affected region, leading to a decrease in its load-carrying capacity and stiffness. This paper experimentally studies the effect of web openings on the response of pultruded fiber-reinforced polymer (PFRP) composite profiles under compressive loads. A number of specimens have been processed to examine the behavior of PFRP profiles strengthened with one or more web openings. The effects of the size of the web opening and the FRP-strengthening scheme on the structural performance of PFRP profiles with FRP-strengthened web openings have been thoroughly analyzed and discussed. The decrease in load-carrying capacity of un-strengthened specimens varies between 7.9% and 66.4%, depending on the diameter of the web holes. It is observed that the diameter of the hole and the type of CFRP- or GFRP-strengthening method applied are very important parameters. All CFRP- and GFRP-strengthening alternatives were successful in the PFRP profiles, with diameter-to-width (D/W) ratios between 0.29 and 0.68. In addition, the load-carrying capacity after reinforcements made with CFRP and GFRP increased by 3.1–30.2% and 1.7–19.7%, respectively. Therefore, the pultruded profiles with openings are able to compensate for the reduction in load-carrying capacity due to holes, up to a D/W ratio of 0.32. The capacity significantly drops after a D/W ratio of 0.32. Moreover, the pultruded profile with CFRP wrapping is more likely to improve the load-carrying capacity compared to other wrappings. As a result, CFRP are recommended as preferred composite materials for strengthening alternatives.

First principles and molecular dynamics simulation investigation of mechanical properties of the PTFE/graphene composites

In this study, the dynamic molecular structure changes in polytetrafluoroethylene (PTFE) and PTFE/graphene composites under compression were investigated. The critical formation and fracture lengths of the C–C bond in PTFE, graphene, and between PTFE–graphene were calculated from first principles. Then, molecular models of these materials were constructed through molecular dynamics simulations. Finally, the critical lengths of the C–C bonds were embedded into the molecular models to study the effect of the molecular structure change during compression on the mechanical properties of PTFE and its composite. Further, molecular models with different defect ratios (1–30%) were constructed to simulate fracture damage stages upon increasing the PTFE and PTFE/graphene composite service time. The results show that compression can induce fracture and formation of chemical bonds. The number of bonds broken is larger than the number of bonds formed; thus, the fracture damage increases. The molecular model stress decreases after bond formation, and the compression resistance of the composites decrease in the plastic deformation stage. With increasing defect ratio, the molecular model stress and load-carrying capacity decrease. The compression-induced bond formation decreases the compressive resistance to some extent and increases the tensile strength considerable.

Analytical Study of Geometric Parameter Effect on the Behavior of Horizontally Curved Reinforced Concrete Deep Beam

Nonlinear finite element simulation was once employed to look into the behavior of horizontally curved reinforced concrete deep beams under concentrated load at its mid-span. The study focused on the parametric impact of span length-to-depth (L/D) and span length-to-radius (L/R) ratios. In addition, the effect of longitudinal and spacing of shear reinforcement on the behavior of the beam has been investigated. The study considered sixteen beam specimens. Three of these specimens were straight beams as a control, and others were curved beams. The concrete-damaged plasticity model has been used to model the beam with C-25 grade concrete and steel reinforcements having diameters of ∅ 4 mm, ∅ 10 mm, and ∅ 12 mm with 568 MPa, 596 MPa, and 643 MPa steel grade, respectively. Reduced twenty-noded brick (C3D20 R) and two-noded (T3D2) elements have been used for modeling concrete and steel, respectively. The ultimate load capacity, the strain distribution, the load-deflection curve, and the load-twisting curve are the main outputs of the FE simulation. The study confirmed a considerable decrease in load-carrying capacity by up to 8.74% and 27.95% as the (L/R) ratio increased from 0 to 1.57 and the L/D ratio increased from 2.4 to 3, respectively. However, as the longitudinal steel ratio increased from 0.02042 to 0.02608 and the spacing of shear reinforcement decreased from 100 mm to 50 mm, the ultimate load capacity is increased up to 9.28% and 4.3%, respectively. Sensitivity evaluation was also conducted to see how much the independent variables (L/D ratio, L/R ratio, longitudinal bar ratio, and spacing transverse reinforcement) affect the dependent parameter (ultimate load capacity).

Experimental and numerical analyses of damaged-steel plate reinforced by CFRP patch in moisture and the acidic environment under tensile test

The FRP materials and their adhesively bonded joints to steel plates are vulnerable to harsh environments. So far, various researches have been studied on the effect of humid environments but the impact of acidic ones needs to be investigated. In the present paper, the strength of the damaged-steel plate strengthened with one sided CFRP patches exposed to distilled water and concentrated sulfuric acid environments is studied experimentally. Moreover, some numerical studies have been carried out in Abaqus software. The damage shape of the steel plate is considered a central hole with two narrow notches on two sides of this hole. To prepare CFRP patches for the experimental tests, vinyl ester resin resistant to humid and acidic environments was used. The simple tensile test at room temperature is studied for evaluation of the magnitude of reinforcement. The results of these specimens compared to non-patched dry specimens show noticeable strengthening with at least 40 and 50 percent increase in load-carrying capacity and displacement, respectively. Moreover, the comparison between the tensile test results of patched-specimens immersed in distilled water and concentrated sulfuric acid (for the duration of 8 weeks) with the dry patched ones show less than 4 percent decrease in load carrying-capacity. Comparison studies between the numerical and experimental results show that load–displacement diagrams and the failure modes are in good consistency with each other.

Effect of shrinkage on cracking and structural behaviour of reinforced glulam members

This paper deals with the question whether and to what extent reinforcing elements have a negative impact on the structural behavior of glulam members due to their potential of restraining the free shrinkage behavior of wood. For this purpose, experimental and numerical investigations were performed on three groups of reinforced glulam members (homogeneous arrangements, holes, notches) to quantify the restraining effect of the reinforcing elements. In experimental investigations the test specimens were first exposed to a slow drying process and analyzed regarding the parameters distribution of wood moisture, crack formation and shrinkage deformations. After climate storage destructive tests were realized on all test specimens with holes and notches to quantify the restraining effect by determining the decrease in load-carrying capacity. In case of beams with reinforced holes, the load-carrying capacity decreased to around 65 % − 79 % and to around 69 % − 83 % in case of beams with notches, the extent of the reduction depending on the type and arrangement of the reinforcement. The experimental investigations were extended by numerical investigations based on three-dimensional simulation models, considering the lamella structure of glulam as well as the cylindrical orthotropy of the wood structure. Critical differential moisture contents for an onset of cracking were determined by implementing a steady-state change of moisture content, followed by a probability-based evaluation of the stressed volume in tension perpendicular to the grain. Parameter studies on the three groups of reinforced glulam members showed, that an onset of cracking is influenced in particular by the quantity of reinforcing elements, their inclination to grain direction, the member height and the axial withdrawal stiffness of the reinforcement. All four influencing factors have a negative effect on the formation of cracks with increasing magnitude.

A numerical analysis on web crippling capacities of cold-formed steel channels with staggered web perforations

Cold-formed steel channel sections are provided with perforations to improve their thermal efficiency. Concentrated loads tend to buckle them locally when acting on these channel sections. When the perforations are made on webs, load-carrying capacity decreases. In the present study, the web crippling capacity of the perforated channel section was evaluated using finite element software ABAQUS CAE®. Interior two flange loading was adopted for the study. An extensive parametric analysis was performed to assess the web crippling capacities by varying the shape and size of perforations. Rectangular slotted perforations were numerically modelled by varying the corner radius of the perforated channel section from 1 mm to 6 mm. The load-carrying capacity was identified to have been reduced by 36.8%. The horizontal spacing of the perforation was varied from 75 mm to 25 mm, and the aspect ratio (width to height ratio) of perforations was varied from 20 to 10. Due to the presence of perforations, it was found that the web crippling capacity of the section was reduced by 84.5%.

Flexural behaviour of reinforced self compacting concrete beams subjected to elevated temperature before and after retrofitting

PurposeThe purpose of the paper is to study the effect of elevated temperature on load carrying capacity of reinforced self compacting concrete beams and the performance of deteriorated beams after retrofitting by GFRP sheets. The reinforced beams which were exposed to sustained elevated temperature and tested for flexural load-carrying capacity. Further deteriorated beams (exposed from 500°C to 800°C) were re-strengthened by adopting retrofitting with GFRP sheets.Design/methodology/approachThe investigation includes the concrete specimens, i.e. cubes of 150 mm, cylinders of size 150 mm dia with 300 mm height and beams of 150 × 150 × 1,100 mm, reinforced with minimum tension reinforcement according to IS 456–2000. The specimens were subjected to elevated temperature from 300°C to 800°C with an interval of 100°C for 2 h. The residual compressive strength, modulus of elasticity, load at first crack of beams and load-carrying capacity of beams for 5-mm deflection were measured before and after retrofitting.FindingsThe result shows that there is a gain in residual compressive strength at 300°C and beyond which it decreases. The modulus of elasticity, load at first crack and load-carrying capacity of beams reduces continuously with an increase in temperature. The decrease in load-carrying capacity of beams is observed from 27.55% and up to 38.77% between the temperature range of 500°C–800°C and after the retrofitting of distressed beams, the load carrying capacity increases up to 24.48%.Originality/valueBetter performance was observed with retrofitting by GFRP sheets when the specimens were distressed due to elevated temperatures.

Experimental and numerical investigations of steel fiber reinforced concrete dapped-end purlins

Dapped-end beams (DEBs), also known as thinned end beams, are often experienced in shear damages under the effect of vertical loads. Especially if the necessary precautions for thinned ends of reinforced concrete prefabricated purlins on the roofs having standard cross sections are not considered during the design, these purlins can be failed suddenly under the accumulated snow loads. This situation causes the roof to collapse completely. In order to mitigate this drawback, it is aimed to improve shear capacity of the purlins by using steel fiber reinforced concrete (SFRC) without changing the cross section geometry and reinforcement. Pursuant to this goal, experimental and numerical studies have been undertaken. The presence of steel fiber and the aspect ratio are selected as main parameters. The use of SFRC increased energy dissipation and shear capacities approximately 2.58 and 1.53 times, respectively. Moreover, the numerical analyses were performed in order to determine the optimum length of SFRC used in concrete from beam ends and fiber volume ratio to be used, and to investigate the effects of shear span to depth ratio (a/d). The results revealed that fiber volume ratio of 2% and the length of SFRC used up to the point where dapped-end region ends are recommended. Moreover, increasing the ratio of a/d results in a decrease in load carrying capacity.

Experimental Evaluation of the Load Carrying Capacity of SFRC Flat Slabs Varying the Rectangularity Index of Columns

This work aims to evaluate the punching shear carrying capacity of flat slabs of reinforced concrete added with different amounts of steel fibers and varying the rectangularity index of columns under symmetrical loading. The addition of steel fiber provide higher load-carrying capacity. However, the column rectangularity index tends to lower that load-carrying capacity for magnitudes beyond 1.5 for the tested slabs. Nine models were tested with dimensions of 1,800 × 1,800 mm and 130 mm height varying the amount of added fiber (0, 50 and 60 kg/m) and the index of rectangularity (1.0, 1.5 e 2.0). From the results, the load carrying capacity, the vertical displacement, and the crack patterns were obtained. In addition, the results were compared with other similar studies and analytical models for steel fiber. The addition of steel fibers showed to be effective in increasing the punching shear load carrying capacity, it leads to a higher number of cracks and higher vertical displacements. Regarding the rectangularity index, for those tested slabs which was below 1.5, the load carrying capacity of punching shear of the slabs increases. However, for slabs above 1.5, it was observed that the punching shear load carrying capacity decreases.

Reliability analysis of a reinforced concrete bridge under moving loads

This study presents a reliability analysis procedure for a reinforced concrete bridge exposed to different moving loads. Bridges are one of the important part of transportation infrastructure systems. As bridges age, structural weakening due to heavy traffic and aggressive environmental factors lead to an increase in repair frequency and decrease in load carrying capacity. Therefore, bridges require periodic maintenance and repair in order to function and be reliable throughout their lifetimes. In other words, condition and safety of the bridges must be monitored at regular time intervals to avoid the disadvantages of deterioration. Otherwise, sudden collapse of a bridge may lead to irreversible loss of life and property. Therefore, the importance of the structural assessment of bridges is rapidly increasing in developed countries. In this study, reliability analysis which is one of the structural performance prediction method is applied to a reinforced concrete bridge subjected to the different moving loads. The aim of this study is to observe the safety of the bridge for the effect of the increasing traffic factor over the years.