Eccentric Compression Tests Research Articles

Local buckling and capacity of press-braked ferritic stainless steel channel sections under minor-axis combined loading

This paper presents experimental and numerical studies of the local buckling behaviour and cross-section resistances of press-braked ferritic stainless steel channel sections under combined compression and minor-axis bending. An experimental programme was firstly conducted and included material testing, initial local geometric imperfection measurements and ten eccentric compression tests. Following the experimental programme, a numerical modelling programme was conducted, where finite element models were developed to replicate the test observations and then used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. The obtained test and numerical data were then used to assess the relevant design interaction curves for press-braked ferritic stainless steel channel sections under minor-axis combined loading, as set out in the European code and American specification. The assessment results revealed that the codified design interaction curves result in conservative and scattered resistance predictions, mainly owing to the conservative bending end point and inefficient linear shape. Finally, new design interaction curves were developed and shown to provide a higher level of design accuracy and consistency than the codified design interaction curves.

Mechanical Properties of L-Shaped Column Composed of RAC-Filled Steel Tubes under Eccentric Compression

In this paper, the eccentric compression test of seven specimens was conducted to explore the application possibility of recycled aggregate concrete (RAC) in L-shaped columns composed of concrete-filled steel tubes (CFST). The main parameter is the replacement ratio of recycled coarse aggregates (RCA), and an L-shaped column of composed hollow steel tubes was set as a control. The test results indicated that the bearing capacity and stiffness of the L-shaped column composed of RAC-filled steel tubes (RACFSTs) are better than those of the L-shaped column composed of hollow steel tubes. The compressive strength of concrete is reduced by 73.1% as the replacement ratio of RCA increases from 0 to 100%, while that of the column is merely reduced by 23.9%. The strength disadvantage of RAC is compensated by the confinement of steel tubes. Besides, the result of the eccentric compression test (80 mm eccentricity) was compared with the axial compression test (0 mm eccentricity). The increase in eccentricity reduced the bearing capacity and ductility due to additional bending moments. The finite element model (FEM) was established by software ANSYS to compare with the experimental results. The bearing capacity deviation of FEM is 4.23~6.56%. The parametric analysis was carried out to summarize the influence of parameters such as eccentricity, material strength, and steel tube thickness. With the increase of eccentricity, the bearing capacity of the RACFST decreases gradually. In engineering design, the bearing capacity of the RACFST can be improved by increasing the strength and thickness of the steel.

Experimental and numerical investigation of S700 high strength steel CHS beam–columns after exposure to fire

This paper presents an experimental and numerical investigation into the post-fire behaviour and residual capacity of S700 high strength steel circular hollow section (CHS) beam–columns. The experimental investigation was performed on ten S700 high strength steel CHS beam–columns and included heating and cooling of the specimens as well as post-fire material testing, initial global geometric imperfection measurements and pin-ended eccentric compression tests. A subsequent numerical investigation was conducted, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. In view of the fact that there are no specific provisions for the design of steel structures after exposure to fire, the relevant room temperature design interaction curves were evaluated, using post-fire material properties, to assess their applicability to S700 high strength steel CHS beam–columns after exposure to fire, based on the test and numerical data. The evaluation results revealed that the interaction curves provided in the American Specification and Australian Standard result in a high level of design accuracy and consistency, while the Eurocode interaction curve leads to more conservative and scattered failure load predictions. Finally, a revised Eurocode interaction curve, with more accurate end points, was proposed and shown to offer improved failure load predictions for S700 high strength steel CHS beam–columns after exposure to fire.

Mechanical behavior of steel transmission tower legs reinforced with innovative clamp under eccentric compression

Most steel lattice towers have been in service for over 20 years in China. Many existing towers are now required to carry higher loads than those for which they were originally designed because of new heavier devices and revised wind design codes. An effective way of increasing the carrying capacity of a tower is to reinforce its core leg members by attaching additional elements with bolted connections. However, the reinforcing methods proposed in previous studies require drilling into the core leg members, which results in considerable construction inconvenience. Therefore, an innovative clamp-type (IC) method is proposed herein. To evaluate the effectiveness of the proposed IC method, this paper presents results from 90 new cases comprising 10 eccentric compression tests and 80 finite element (FE) analyses of the load capacity of starred compound members, by varying the interconnector arrangement, form, spacing and bolt row, and slenderness ratio of the compound members. The experimental results show that the compound members with the IC interconnector mainly exhibit buckling failure in the core member. However, in the case of instability about the imaginary axis, the bearing capacity of the compound members with the IC interconnector is approximately 41%–62% higher than that of the single angle member. A nonlinear FE model is developed, which considers the material, contact non-linearity, and geometric imperfections. The FE model is validated against the experimental test results, which show good agreement, both in terms of failure mode and load–displacement curve. The validated FE model is used to conduct a parametric analysis to investigate the effect of slenderness ratio on the bearing capacity of the compound member. Four width–thickness ratios of connected angles and five IC interconnector spacings are considered in the parametric study. The bearing capacity values obtained from the experimental tests and FE analyses are used to assess the performance of current design guidelines. The results show that the current DL/T 5154-2012 code is too conservative by an average value of 30%. Therefore, a kd coefficient method is proposed to improve the prediction accuracy of the bearing capacity, and the method is verified against the FE and test results of the compound member with the IC interconnector under eccentric compression tests.

Post-fire behaviour and capacity of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending

The post-fire behaviour and capacity of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending have been investigated through testing and numerical modelling and reported in this paper. Eccentric compression tests were conducted on eight square HCFHST stub column specimens after exposure to the ISO-834 standard fire for 15 min, 30 min, 45 min and 80 min and two reference specimens at ambient temperature. The test results, including the load–deformation response at each load stage as well as the confinement effect, the ductility index, the evolution of the neutral axis, the effect of heating duration and the effect of initial loading eccentricity, were discussed. Numerical simulations were then carried out, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no established design codes for composite structures after exposure to fire, the relevant ambient temperature design rules were evaluated, using post-fire material properties, for their applicability to post-fire HCFHST stub columns under combined compression and bending, based on the test and numerical data. The evaluation results revealed that the European code, American specification and Australian/New Zealand standard result in relatively accurate and consistent post-fire residual resistance predictions.

Testing, modelling and design of hot-rolled stainless steel channel sections under combined compression and minor-axis bending moment

Experimental and numerical studies on hot-rolled stainless steel channel sections subjected to combined compression and minor-axis bending moment have been conducted and are fully reported in the present paper. The testing programme included initial local geometric imperfection measurements and ten minor-axis eccentric compression (combined loading) tests. The numerical modelling programme comprised a validation study, where finite element models were developed and validated against the test results, and a series of parametric studies, where the developed finite element models were adopted to generate further numerical data over a wide range of cross-section dimensions and loading combinations. The experimentally and numerically obtained data were used to assess the accuracy of the design interaction curves for hot-rolled stainless steel channel sections under minor-axis combined loading, as given in the European code and American specification. The assessment results generally reveal that the design interaction curves provided in the main body of the two design codes lead to unduly conservative and scattered failure load predictions, mainly owing to the conservative end points (i.e. the cross-section compression and bending resistances), which are calculated without considering material strain hardening. The appendix of each design code also provides an alternative method that uses the continuous strength method to account for material strain hardening in calculating the end points of the design interaction curve, and is shown to result in much more accurate and consistent predictions of failure load for hot-rolled stainless steel channel sections under combined compression and minor-axis bending moment.

Slenderness Ratio Effect on the Eccentric Compression Performance of Chamfered Laminated Bamboo Lumber Columns

Eccentric compression tests on 15 chamfered laminated bamboo lumber (LBL) columns with a height ranging from 600 to 3000 mm were conducted in order to study the eccentric mechanical performance. The failure of all specimens was caused by the crack of bamboo fiber in the tensile region. When the ultimate strength was reached, except specimens with a height of 600 mm, all other specimens could bear large deformation, showing good ductility. The lateral displacements of the specimens under eccentric compression were approximately parabolic in the direction of column height. The ultimate bending moment of LBL columns with different slenderness ratios under compression with the same initial eccentricity was a fixed value. The relationship between ultimate capacity, axial displacement, lateral displacement, and slenderness ratio was analyzed based on test results. It was found that the plane section assumption could be used to express the stress and strain distribution of chamfered LBL columns under eccentric compression. A method for calculating the ultimate bearing capacity was proposed using a constitutive model based on the Ramberg-Osgood relation and the empirical formula for calculating the ultimate capacity was given on the basis of the former research as well as the test results in this paper.

RETRACTED: An Investigation of Bearing Capacity of High-Strength SRC Columns under Eccentric Axial Load

This paper investigates the eccentric compression performance of high-strength steel reinforced concrete (SRC) columns. In addition, the feasibility of the calculation codes used for the load-carrying capacity of these columns is verified by eccentric compression tests on 10 high-strength SRC columns with Q460 and Q690 steels and two normal SRC columns with Q235 steel. Moreover, the influence of the steel strength, relative eccentricity, steel ratio, and stirrup spacing on the bearing capacity and ductility of the specimens is analyzed. It was found that the bearing capacity and ductility of the specimens significantly increases when the steel strength increases from 276.5 MPa to 774.2 MPa; the bearing capacity of the Q690 SRC column is slightly higher than that of the Q460 SRC column. In addition, the ductility coefficient of the Q690 SRC columns is significantly higher than that of the Q460 SRC columns. It was also found that increasing the eccentricity and steel ratio can improve the ductility of the specimens and the smaller stirrup spacing can enlarge the contribution of Q690 steel under the ultimate bearing capacity. It is demonstrated that Eurocode 4-2004 and AISC360-16 codes significantly underestimate the test results. In contrast, JGJ138-2016 slightly underestimates the test results when the relative eccentricity is 0.2 but overestimates the test results when the relative eccentricity is 0.6. Furthermore, in order to maximize the contribution of Q690 steel under ultimate bearing capacity, the expanded parameter analysis is carried out using a finite element model. Following the analysis results, the suggestions for designing high-strength SRC columns under eccentric load are provided.

Experimental and numerical study on eccentric compression properties of laminated bamboo columns with a chamfered section

The eccentric compression behavior of laminated bamboo lumber (LBL) columns with a chamfered section was investigated using eccentricity of 30 mm, 60 mm, 90 mm and 120 mm. The effect of eccentricity ratio on the ultimate bearing capacity, ultimate strain and failure mode was analyzed through eccentric compression tests. The failure modes of LBL columns with different eccentricities were basically same, which belonged to brittle tension failure. With the increase in eccentricity ratio, the ultimate bearing capacity and ultimate strain gradually decreased. The cross-section strain of the specimen was linearly distributed along the height direction, which conformed to the plane section assumption. The lateral deflection curves had similar characteristics under different load levels and could be expressed by sine half-wave curves. Based on the Hill failure criterion, a 3D finite element model was developed to calculate the ultimate bearing capacity of LBL columns with different dimensions under eccentric compression. According to the simulation results and test results, a general empirical formula was proposed considering both the influence of slenderness ratio and eccentricity ratio. The reliability of the proposed formula was verified by comparing the calculated results with the results in the existing literature.

Structural performance of concrete-filled square steel tubular columns encased with I-shaped CFRP under eccentric compression

This study investigated behavior of concrete filled square steel tubular (CFSST) columns encased with I-shaped CFPR under eccentric compression. Full-scale eccentric compression tests were conducted on eighteen column specimens consisting of square steel tube, concrete, and an I-shaped CFRP profile. The test program considered effects of load eccentricity ratio and column slenderness ratio. The eccentrically loaded column behavior was investigated with respect to the mid-height deflection, load, and failure modes. The development and distribution of longitudinal strain and neural axis for the column were also studied. Finite element models were developed and validated against tested results to further analyze the load-transferring mechanism of the composite column and perform detailed parametric studies. The results indicated that the CFSST column encased with I-shaped CFRP behaved in a ductile manner with the improved capacity and increased stability. Finally, design equations were developed using tested and simulated data to estimate ultimate bearing capacity of the CFSST column encased with I-shaped CFRP when subjected to eccentric compression. The predicted column capacities using the design equations matched well with the tested and simulated capacities.

Press-braked stainless steel channel sections under major-axis combined loading: Tests, simulations and design

This paper reports an experimental and numerical investigation into the cross-section behaviour and resistances of press-braked stainless steel channel sections under combined compression and major-axis bending moment. A testing programme was firstly conducted, including initial local geometric imperfection measurements and major-axis eccentric compression tests on ten press-braked stainless steel channel section stub column specimens. Following the testing programme, a numerical modelling programme was performed, where finite element models were developed and validated against the test results and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and initial loading eccentricities. Based on the obtained test and numerical data, the existing design interaction curves, as given in the European code, American specification and Australian/New Zealand standard, were assessed and shown to result in conservative cross-section resistance predictions for press-braked stainless steel channel sections under major-axis combined loading. The conservatism of the codified design interaction curves stems from the conservative end points (i.e. cross-section resistances under pure compression and pure bending), which are determined without considering the effect of material strain hardening, and the inefficient linear shape, which ignores the effect of stress redistribution. Improved design interaction curves were proposed through the adoption of (i) more accurate end points, which are calculated with a rational exploitation of material strain hardening by continuous strength method and (ii) more efficient nonlinear shape, which allows for the stress redistribution. The proposed design interaction curves were shown to result in substantially more accurate resistance predictions for press-braked stainless steel channel sections under major-axis combined loading than their codified counterparts. The reliability of the proposed design interaction curves was confirmed by means of statistical analyses.

Post-fire behaviour and residual resistances of S700 high strength steel tubular section stub columns under combined loading

This paper reports experimental and numerical studies on the post-fire behaviour and residual resistances of S700 high strength steel tubular section stub columns under combined compression and bending. A testing programme was firstly performed, including heating and cooling of specimens as well as post-fire material testing, initial local geometric imperfection measurements and eccentric compression tests. The testing programme was followed by a numerical modelling programme, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no design standards for high strength steel structures after exposure to fire, the design interaction curves for high strength steel tubular section stub columns under combined loading at ambient temperature, as given in the European code, American specification and Australian standard, were evaluated, using post-fire material properties, for their applicability to S700 high strength steel tubular section stub columns under combined loading after exposure to fire. The evaluation results revealed that all the three sets of codified design interaction curves yield overall accurate post-fire residual resistance predictions for S700 high strength steel tubular section stub columns under combined loading, with the highest level of design accuracy offered by the American specification.

Study on mechanical behavior and damage process of concrete with initial damage under eccentric load

In order to analyze the influence of eccentric load on mechanical properties and damage process of concrete with initial damage, the eccentric load compression tests of concrete under different confining pressures were carried out with the help of PFC particle flow program. The results show that: the eccentric load does not change the relationship between peak stress, crack initiation stress and confining pressure of concrete under uniform load, but decrease the value of them. The peak stress increasing coefficient under uniform load is higher than that under eccentric load, and the peak stress increasing coefficient increases in a linear function with the confining pressure, and the increasing rate is approximately the same. Under uniaxial compression of eccentric load, a type I shear crack approximately parallel to the loading direction is formed, while under biaxial compression, a bending type shear crack with the lower tip of the initial crack as the inflection point is formed. The number of microcracks in concrete under uniform load and eccentric load can be divided into three stages: the calm period at the initial loading stage, the pre-peak expansion period from crack initiation point to peak point, and the rapid increase period after the peak.

Experimental and numerical studies of S960 ultra-high strength steel welded I-sections under combined compression and minor-axis bending

The present paper reports comprehensive experimental and numerical investigations into the cross-section behaviour and resistances of S960 ultra-high strength steel welded I-sections under combined compression and minor-axis bending moment. An experimental programme, adopting two slender welded I-sections – I-120 × 120 × 6 and I-150 × 75 × 6, was firstly conducted and included initial local geometric imperfection measurements and ten minor-axis eccentric compression tests. A numerical modelling programme was then performed, where finite element models were firstly developed and validated against the test results and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. On the basis of the test and numerical data, the applicability of the design interaction curves for S700 (or S690) high strength steel welded I-sections under minor-axis combined loading, as set out in the European code, American specification and Australian standard, to their S960 ultra-high strength steel counterparts was evaluated. The evaluation results generally revealed that all the codified design interaction curves lead to unduly conservative and scattered cross-section resistance predictions, mainly owing to the adoption of conservative bending end points (i.e. cross-section bending capacities).

Testing, numerical modelling and design of stainless steel welded I-sections under minor-axis combined loading

This paper reports a comprehensive experimental and numerical investigation into the cross-section behaviour and resistances of stainless steel welded I-sections under combined compression and minor-axis bending moment. A testing programme was firstly conducted, including initial local geometric imperfection measurements and minor-axis eccentric compression tests on ten stainless steel welded I-section stub column specimens. Following the testing programme, a numerical modelling programme was performed, where finite element models were developed to simulate the test observations and then used to conduct parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Based on the obtained test and numerical data, the accuracy of the design interaction curves, as given in the current European code and American design guide, for stainless steel welded I-sections under minor-axis combined loading was evaluated. The evaluation results generally indicated that the codified design interaction curves lead to unduly conservative cross-section resistance predictions, mainly owing to the conservative end points, which are calculated without considering material strain hardening. Finally, improved design interaction curves were proposed through adopting (i) more accurate end points, which are calculated with rational exploitation of material strain hardening by continuous strength method and (ii) more proper shapes, which allow for better representation of the interaction. The proposed design interaction curves were shown to result in substantially more accurate and consistent resistance predictions for stainless steel welded I-sections under compression and minor-axis bending moment than their codified counterparts. The reliability of the new design interaction curves was confirmed by means of statistical analyses.

Prestressed CFRP-reinforced steel columns under axial and eccentric compression

Buckling limits the slenderness of steel columns in applications. This highly efficient technology, using prestressed (PS) carbon fiber reinforced polymer (CFRP) strips to reinforce steel columns against overall buckling, can be applied in new structures or to strengthen existing structures, and is easy to construct. The buckling behavior of PS CFRP-reinforced steel columns is studied with axial and eccentric compression tests. Axial compression tests are conducted on 8 specimens with three different slenderness values (105, 140, and 200); eccentric compression tests are conducted on PS specimens of slenderness 105 with four different eccentric ratios (0, 1, 2, and 3). The buckling capacity and failure modes are obtained. The obvious reinforcing efficiency is achieved by PS CFRP; the buckling capacity of PS specimens can be increased by 19%–150%. The whole loading procedure is analyzed in detail to further explain the mechanism of PS CFRP reinforcing. Four possible critical states are determined, whose order depends on the reinforcing conditions and influences the cause of buckling, which is either material yielding or slacking of the concave side CFRP. Finally, a simplified model of reinforcing efficiency is preliminarily built based on the test results.

Residual behaviour of corroded welded hollow spherical joints subjected to eccentric loads

The evaluation of corroded welded hollow spherical joints (WHSJs) under eccentric loads is necessary to ensure the safety of space structures. In this study, the corrosion characteristics and mechanical properties of standard specimens under different corrosion times were investigated through surface measurements and tensile tests. Next, eccentric compressive tests were performed on four WHSJs subjected to different degrees of corrosion to evaluate the mechanical properties. The test results showed that the logarithmic normal distribution and generalized extremum value distribution could be used to describe the pitting depth distribution precisely. Uniform corrosion was the main index that influenced the corrosion and bearing characteristics under the test conditions; the eccentric compressive ultimate load decreased by 3.8%, 9.9% and 11.8% at 100, 131, and 157 days of acetic acid mist corrosion, respectively, which corresponded to approximately 20, 30, and 40 years of environmental corrosion in Qingdao. In addition, a refined corrosion simulation method, based on corrosion morphology, and two simplified simulation methods were developed. Based on one of the simplified methods, the effects of various corrosion and size parameters on the eccentric performance of the joint were evaluated. The analysis results showed that the corrosion depth and wall thickness were the main factors that influenced the degradation of the joint bearing capacity. A simplified method for designing the eccentric performance of corroded WHSJs was developed and validated.

Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading

This paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

Behavior and design of concentric and eccentrically loaded pultruded GFRP angle columns

This paper reports results of experimental and analytical investigations on the structural behavior of pGFRP angles subjected to concentric and eccentric compression. Members with pin- and fixed-ends were tested under concentric loading. In eccentric compression tests, angles were loaded through one leg by single- and double-bolt end connections. Equations available in design manuals and analytical methods from the literature were evaluated. Failure modes for members subjected to concentric loading agreed well with analytical predictions, except pin-ended columns of lengths near the region of transition from flexural–torsional to flexural buckling mode. Angles connected by the leg were sensitive to flexural–torsional mode and exhibited a different load-deflection behavior in function of the number of bolts in the connection. Results from current design guidelines for concentric compression revealed limitations on the predicted failure load. A new design approach based on the Direct Strength Method provided suitable results. Moreover, it was found that equations based on the Equivalent Buckling Length Method can be an option for the design of pGFRP angles with bolted connections.

Eccentric compression tests and design of welded steel tube strengthened RC stub columns with high-strength grout

The post-welded steel tube and high-strength grouting material reinforcing method is a novel rehabilitation approach developed for RC structures with insufficient strength. It could significantly improve the strength without enlarging the original cross-section area. To figure out the mechanical performance of post-welded outer-wrapped steel tube and high-strength grouting material (HGM) strengthened RC (PSGS-RC) stub columns, this paper first reports on an experimental investigation. The influence of critical parameters such as the loading eccentricity and original core concrete area ratio on the behavior of this type of composite was analyzed in detail. The typical failure modes, vertical force versus axial displacement relationship, strain response, and ductility index of several crucial points are presented to better understand the mechanical performance of eccentrically loaded PSGS-PC short columns. Moreover, a detailed discussion on the strength enhancement index and concrete contribution ratio was conducted to figure out the typical feature of the novel rehabilitation method. Finally, for evaluating the resistance of eccentrically loaded PSGS-PC short columns, a design method based on the ultimate equilibrium theory was proposed. The result demonstrated that the typical failure modes of PSGS-PC short columns generally comprised the local buckling of outer-wrapped steel tube, tearing of weld, crushing of HGM and core concrete, shear failure of columns, and buckling of longitudinal rebar. The strength of eccentrically loaded PSGS-PC stub columns was enhanced with a decrease of the load eccentricity and the intrinsically core concrete column area ratio. The ductility property was significantly improved with an increase of the load eccentricity and the core concrete area ratio. This research is expected to provide a reliable design method for repairing structures that possess inadequate strength in engineering practice.