Eccentric Compression Loading Research Articles

Experimental Behavior of Existing RC Columns Strengthened with HPFRC Jacket under Concentric and Eccentric Compressive Load

Reinforced concrete (RC) structures built before the 1970 represent a large portion of the existing European buildings stock. Their obsolescence in terms of design criteria, materials, and functionality is becoming a critical issue for guaranteeing adequate compliance with current structural codes. Recently, a new jacketing system based on the use of high-performance fiber-reinforced concrete (HPFRC) has been introduced for strengthening existing RC building members. Despite the promising aspects of the HPFRC jacketing technique, currently, a comprehensive and systematic technical framework for its implementation is still missing. In this paper, the experimental performance of RC columns strengthened with the HPFRC jacket subjected to pure axial load and combined axial load-bending moment uncoupled from shear is investigated. The test outcomes confirmed a significant improvement of the structural performance for the strengthened columns, especially for higher values of eccentricity. Finally, a standard-based practice-oriented analytical tool for designing retrofit interventions using the HPFRC jacket is proposed. The comparison between the calculated and experimental results revealed a satisfactory prediction capability.

Behavior of strengthened concrete slab under eccentric compressive load

PurposeThe purpose of this study is experimental research of the mechanical behavior of slab reinforced by cork composite patch submitted to an eccentric progressive compressive load applied to on impact rectangle of dimensions 28 × 23 cm2. An analytical model and numerical modeling by finite elements are performed. This study is motivated by the evaluation of the effectiveness of this type of partial reinforcement to improve strength and ductility. The results are given by load-displacement curves, tensile damages cartography and ultimate strength histogram.Design/methodology/approachIn experimental protocol, the following two parameters have been considered: the dimensions of the patch and the eccentricity of the load. The sections of the patches are calculated so that the ratio (XP/YP) patch is proportional to the ratio (LD/lD), with a step of 6 cm longitudinally and 4 cm transversely. Several dimensions patches are considered: (6 × 4) cm2, (12 × 8) cm2 and (18 × 12) cm2. The eccentric punching loading test was performed with an eccentricity of the load (1/3) L’ and (2/3) L’ compared to the center of gravity of the slab. Taking into account the eccentricity of the load in estimating the rupture strength, the equations are developed. Thus, numerical simulations are carried, to extract tensile damages cartography.FindingsThe results show that the rupture begins with the appearance of cracks in the unreinforced area. For an eccentricity of 1/3L’, the best strength/section ratio is obtained for patch (12 × 8) cm2, whereas for an eccentricity de 2/3L’, the patch (6 × 4) cm2 gives a better resistance. The results highlight the influence of the composite on the ultimate load. The force-displacement relations are little modified in the elastic phase. The experimental results have been compared with the theoretical models showing a good correlation.Originality/valueThe strength and ductility are depended on the dimensions of the patch and the eccentricity of the load. The use of a patch to cover the most stressed area, in the event of an eccentric axial load is a very economical solution compared to the total reinforcement. The damage field shows that the evolution of cracks depends on dimensions and the position of the patch. Indeed, the eccentricity of the vertical load induces an additional bending moment that will influence the fracture surface. The rupture load and ultimate displacement increase with the surface of the patch.

Bolted angle members in compression –new design model including joint stiffness

AbstractPrevious research activities at Graz University of Technology, highlighted the fact that the joint stiffness has substantial influence on the compression member capacity of bolted angles.Consequently, analytical models for the estimation of appropriate spring stiffness values have been developed for several practical applications in buildings and two‐bolt connections at both member's ends. The investigated connection details comprise a fixed gusset plate (e.g. as attachment to concrete walls), a joint to the flange of an I‐shaped girder and a joint to the web of an I‐shaped girder via a gusset plate. Based on that, a design model was developed for bolted angle members with rotational spring restraints at both member's ends and an eccentric compression loading N, in order to calculate the compression member capacity Nr.This paper presents the design model in detail. In addition, the background of the model is shown, with a comprehensive calibration and validation procedure based on real tests and numerous numerical tests, respectively. Based on that, also complex failure modes, such as lateral torsional buckling, can be covered by the proposed model.

Testing and strength prediction of eccentrically-loaded circular concrete-filled double steel tubular stub-columns

Circular concrete-filled double steel tubular (CFDST) column is a high-performance composite column that has significant potential to be used in the construction of high-rise composite structures. This paper presents experimental and strength computational investigations on CFDST short columns that are subjected to eccentric compression load. A total of sixteen CFDST stub columns, two concrete-filled steel tubular (CFST) columns, and two double-skin concrete-filled steel tubular (DCFST) columns were tested to investigate their structural performance. The test behavior of the CFDST column loaded eccentrically is discussed and compared against its CFST and DCFST counterparts. The test results show that the CFDST column has improved strength and ductility under eccentric loading when compared with other composite columns. The strengths of the CFDST stub columns in this study together with the test strengths from the literature were used to assess the strength predictions by Eurocode 4 and AISC 360–16. It was found that the current predictions generally underestimate or overestimate the strengths. A new reduction factor for predicting the ultimate strengths of CFDST short columns under eccentric compression is proposed based on the test results. By adopting the newly proposed reduction factor and design method, the design predictions are found to be improved that provide reasonable estimations for circular CFDST columns loaded eccentrically.

Behaviour of cold-formed steel lipped channel sections subject to eccentric axial compression

The use of light-gauge steel framed (LSF) wall systems in low- and mid-rise buildings has increased due to the fast and clean construction and robust structural performance. Cold-formed steel studs used as the primary load-bearing component in LSF walls are often subjected to combined axial compression and bending actions caused by loading eccentricity. Research on the effects of loading eccentricity on the compression capacity has been limited while the currently used AS/NZS 4600 and AISI-S100 DSM design guidelines significantly underestimate the load bearing capacities. In this study, 35 lipped channel columns of 0.6 to 1.5 m lengths were tested under concentric and varying levels of eccentric axial compression loading and the resulting load versus axial shortening curves and failure modes were analysed. Non-linear finite element models of tested columns were developed and validated using the test results. Comparison of the ultimate capacities obtained from the tests and finite element analyses against those predicted by the DSM design guidelines showed that the current DSM design guidelines underestimate the capacities whereas a closer agreement was obtained from the improved DSM design guidelines proposed in a recent research study. This paper recommends the improved DSM design method to enable economical and safe designs.

Design model for bolted angle members in compression including joint stiffness

Knowledge of type and size of rotational restraints at the member's ends (provided by the adjacent structure) is crucial for the prediction of the compression member capacity of bolted angles. This was highlighted by means of experimental and numerical investigations in the past. Due to the eccentric connection on only one angle leg, additional bending moments are acting on the member, leading to a complex load carrying behaviour with flexural and/or lateral torsional buckling phenomena.Detailed analytical models for the estimation of appropriate spring stiffness values have been developed for several practical applications in buildings with two-bolt connections at both member's ends. The investigated connection details comprise a simply fixed gusset plate (e.g. as attachment to concrete walls), a joint to the flange of an I-shaped section and a joint to the web of an I-shaped section via a gusset plate. Based on that, a design model was developed for bolted angle members with rotational spring restraints at the member's ends and an eccentric compression loading N, in order to calculate the compression capacity NR. The thereby determined resistances NR,model are compared with the results of sophisticated 3D nonlinear finite element calculations NR,FE that consider the detailed joint configuration and the eccentric load introduction as well as equivalent geometric imperfections. It is shown that the resistances based on the proposed design procedure are slightly conservative compared to the real behaviour of the angle member. In addition, the large increase in capacity (compared to the simply supported reference case) is highlighted.

Tests of cold-formed steel built-up open section members under eccentric compressive load

An experimental study was performed on cold-formed steel built-up open section members under eccentric compressive load. The specimens with member lengths varied from 300 to 1500 mm were manufactured by composing two identical channels using self-tapping screws. The channels with longitudinal stiffeners were fabricated from the steel grades G500 and G550 zinc-coated sheets with nominal 0.2% proof stresses of 500 and 550 MPa, respectively. A total of thirty-three combined minor axis bending and compression tests were carried out under pin-ended supports to explore the buckling behaviour of the newly designed built-up section members. Six test series with a relatively wide range of axial load-to-moment ratio were included in this study to examine the interaction relationship of the built-up section beam-columns. The test loading capacities, full-history responses and failure modes were obtained for all the test specimens. Since the novel built-up open sections are not covered in the current cold-formed steel design standards, the comparisons of experimental loading capacities with nominal strengths predicted by the North American Specification, Australian/New Zealand Standard, European Code and American Specification were conducted to assess the appropriateness of the existing design rules. The applicability of axial load-moment interactive formulae specified in the aforementioned design standards with the nominal pure compressive resistance and nominal pure bending resistance determined by direct strength method was evaluated for the built-up section beam-columns. It is found that the axial load-moment interactive formulae generally underestimate the strengths of the cold-formed steel built-up open section beam-columns.

A state of the art review of fiberless and steel fiber reinforced high strength concrete columns behavior under various loadings

Efficient supplementary materials flourish the structural performance and sustainability of reinforced concrete structures. Steel fiber is one of these materials that have significant influence on enhancing tensile and flexural strengths and ductility of high strength reinforced concrete columns. This paper presents a review study on the structural performance of steel fiber reinforced concrete columns. The studied case was related to the columns that subjected to concentric or eccentric compression loads or combined compression loads and cyclic lateral loads. The current survey is divided into two branches; the first is related to fibreless HSC columns, while the other is specialized by SFRHSC ones. In addition to the prime actuator (steel fiber content), the investigated parameters were included concrete strength, transverse reinforcement properties, and axial load ratio. The results of this investigation showed that the positive influence of adding steel fiber on improving the flexural strength, fatigue life and resistance, delaying spalling failure of the exterior concrete shell and outward buckling of the longitudinal steel reinforcing bars. The optimum volume fraction of steel fiber used is 0.5% to 2% (by weight) and when 2% of steel fibers are introduced into the concrete mix, the columns’ cover didn’t spall away.

Improving the compressive behavior of RC walls reinforced with ferrocement composites under centric and eccentric loading

This study discusses the behavior of reinforced concrete (RC) walls reinforced with different types of ferrocement composites under concentric and eccentric loading. The study incorporated experimental examination and nonlinear finite element analysis of ten RC walls with dimensions of 1000 mm in height, 1500 mm in width, and 150 mm in depth with RC footing with dimensions 1900 mm X 500 mm X 200 mm. The specimens were divided into two groups, one examined under concentric load and the other examined under eccentric load with eccentricity of 50 mm. Also, the structural behavior of the tested walls was validated with numerical development of a finite element model utilizing Ansys 2019-R1 software. Expanded or glass fiber wire mesh ferrocement tested specimens under concentric and eccentric line compression loading exhibited enhanced ultimate loads compared to control specimens. Expanded steel wire mesh reinforcement increased the ductility ratio compared to glass fiber mesh reinforcement. Glass fiber wire mesh produced a higher first cracking load, serviceability load, load carrying capacity, and energy absorption compared to expanded wire mesh. Good agreement between numerical and experimental results in first cracking load, load-carrying capacity, crack pattern, and deflection was found. The agreement between the experimental load carrying capacity and non linear finite element (NLFE) ones is about 86 % with coefficient of variance equals 0.003 and standard deviation of 0.06. The finite element analysis gave suitable estimation for the structural performance of nonlinear ferrocement RC walls.

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.

Crack Resistance RC Columns Strengthened by CFRP System

This paper presents the experimental testing of eccentrically compressed reinforced concrete columns. There are experimental results of crack resistance of non-strengthened (control) and strengthened RC columns in the tension zone. The columns were strengthened by carbon fiber reinforced polymers (CFRP). As a result of experimental studies with the columns strengthened by CFRP, we obtain that the width of their crack decreased by an average of 33%. The eccentric compression load of the crack’s appearance increased from 40 kN to 60 kN for strengthened columns.

Experimental study on mechanical behavior of the skew joints of shield tunnels under large eccentric compressive loading

The existence of joints in shield tunnel lining rings contributes to various deformation problems, such as leakage, joint opening, cracking and dislocation, which will severely impair the safety and durability of tunnel structures. Laborious experiments having tried to work out the mechanical properties of joints, none have drawn attention to two special segmental joints existing in Shanghai metro shield tunnels, which are obliquely intersecting the frontal plane of the lining ring and thus appear askew compared with the rest. The study investigated segmental specimens with the K-shaped top block and its two adjacent segments, including two skew joints connected using straight bolts. Given two groups of experiments, their mechanical behaviors throughout the failure process when subject to a positive and a negative bending moment showed that the bending moment’s impact on bolt strain, joint opening and segmental rotation could be illustrated by two stages when the bending moment was positive and four when negative. Besides, the joint compression height slightly decreased under both conditions and tended to be stable after bolts yielded when subject to a negative moment. The joint opening angle was proved equal to the sum of the segmental rotation angles from both sides of the joint, indicating the individual segment could be regarded as a rigid body. Moreover, the maximum joint opening width increased linearly with the joint opening angle, so did the deflection at the joint position with the segmental rotation. Above all, the skew joints examined behaved similarly to but differently from those of straight joints as there happened strain advance of the bolt and the concrete at one side and strain lag at the other side, which would probably become more obvious as steeper the oblique angle of the skew joints grew.

Calculations of compressed rods considering experiments over last 100 years

The article presents the results of testing and FE-modelling of rods calculated for the central and eccentric compressive load. More than 600 tests have been analysed over the past 100 years, including made by author, in a wide range of slenderness made of steels with a yield strength of up to 1000 MPa. It is established that the existing Russian calculation methods allow us to accurately determine the bearing capacity of the rod for steel of any strength. Verification of calculation method was carried out not only by stresses and ultimate load-bearing capacity, but also by the deformations of the tested rods. It is established that for H-beams and thin- walled pipes, clarification of the design codes is required to be able to design cost-effective designs, since the code formulas give a margin. This is especially true for elements of low flexibility with small eccentricities. To clarify the codes, a method for modelling a three-line diagram of steel operation, verified with the test results, is proposed.

Design proposal for bolted angle members in compression

The type and size of the rotational restraints at the gusset plates near the member’s ends (provided by the adjacent structure) are crucial for the prediction of the compression member capacity of bolted angles. This was highlighted by the authors by means of experimental and numerical investigations in the past. Due to the eccentric connection on only one leg, additional bending moments are acting on the member, leading to a complex load carrying behaviour with flexural and/or lateral torsional buckling phenomena. Detailed analytical models for the estimation of appropriate spring stiffness values have been developed for several practical applications in buildings and two-bolt connections at both member’s ends. The investigated connection details comprise a simply fixed gusset plate (e.g. as attachment to concrete walls), a joint to the flange of an I-shaped section and a joint to the web of an I-shaped section via a gusset plate. Based on that, a design model was developed for bolted angle members with rotational spring restraints at both member’s ends and an eccentric compression loading N, in order to calculate the compression capacity NR. Within this paper, the proposed design procedure is presented. Moreover, the thereby determined resistances NR,model are compared with the results of sophisticated 3D finite element calculations NR,FEM that consider the actual boundary conditions and the eccentric load introduction as well as equivalent geometric imperfections. The finite element model has preliminary been calibrated on the experimental test results. The comparison indicates that the resistances based on the proposed design procedure are slightly conservative compared to the real behaviour of the angle member. In addition, the large increase in capacity (compared to the simply supported reference case) is highlighted. Therefore, it is concluded that the new design proposal is able to predict the compression member capacity of bolted angles safely and economically.

Studying the Behavior of Reinforced Concrete Columns Confined by Steel Structure Under Eccentrically Loading

Abstract
 This research paper presents an analytical study of a number of Reinforced Concrete Columns models which have rectangular cross section and confined/unconfined by steel Structure of vertical angles and horizontal plates. Columns are subjected to centric and eccentric compression load. The objective is to know how far the bracing is effective in increasing the strength of these columns. This type of strengthening is considered better than the concrete Structure, Carbon Fiber Reinforced Polymer (CFRP) and other types because it has many features, easy and fast to be constructed. The study demonstrated that the bracing by steel Structure led to increase the strength in large ratios and had been clear that once the thickness of steel Structure is increased, the strength increases. And once the eccentricity is increased, the strength decreases and also the failure load.
 Keywords: reinforced concrete columns, bracing, steel structure, centriccompression, eccentric compression, steel structure thickness, strengtheningeffectiveness, failure load.

Studying the Behavior of Reinforced Concrete Columns Confined by Steel Structure Under Eccentrically Loading

Abstract
 This research paper presents an analytical study of a number of Reinforced Concrete Columns models which have rectangular cross section and confined/unconfined by steel Structure of vertical angles and horizontal plates. Columns are subjected to centric and eccentric compression load. The objective is to know how far the bracing is effective in increasing the strength of these columns. This type of strengthening is considered better than the concrete Structure, Carbon Fiber Reinforced Polymer (CFRP) and other types because it has many features, easy and fast to be constructed. The study demonstrated that the bracing by steel Structure led to increase the strength in large ratios and had been clear that once the thickness of steel Structure is increased, the strength increases. And once the eccentricity is increased, the strength decreases and also the failure load.
 Keywords: reinforced concrete columns, bracing, steel structure, centriccompression, eccentric compression, steel structure thickness, strengtheningeffectiveness, failure load.

Experimental and numerical investigations on large angle high strength steel columns

The stability of columns made of large angle profiles in high strength steel and subjected to centric and eccentric compression loads is investigated through experimental tests, numerical simulations and normative approaches. The aim is to widen the knowledge on such columns and so to complement previous experimental studies that focusing on smaller angle profiles and lower steel grades. The experimental campaign consists of twelve tests. Accompanying numerical studies have been carried out, considering relevant geometrical imperfections as well as geometrical and material non-linearities. Finally, an assessment of the design member resistance according to Eurocodes has been performed. It is further discussed.

Effect of bolted shear connectors on the axial load-bending moment interaction capacity of CFT columns

In Concrete-Filled Tubular (CFT) columns under the influence of compressive loading, an omnilateral confinement pressure is exerted upon the concrete core which leads to increase in the strength, stiffness, and ductility of the column. This paper investigates the influence of bolted shear connectors on the behavior of circular and square CFT columns. Also, a comparison is made between the interactional axial load-bending moment (P–M) curves obtained from the numerical analyses and the P–M relationships put forth by different design standards. For this purpose, 18 circular and 9 square CFT columns, categorized into six groups, are subjected to eccentric compressive loading. The investigated parameters include concrete compressive strength, diameter of the steel tube, load eccentricity, and the presence of bolted shear connector. In most cases, the presence of bolted shear connectors in the column causes strength and ductility to increase, leading to an improvement in the axial load-bending moment (P–M) interaction. The employment of bolted shear connectors at 12.5 cm to 25 cm intervals results in a minimum of 5% and a maximum of 45% increase in the strength of the column.

Eccentric compressive behavior of steel fiber-reinforced RC columns strengthened with CFRP wraps: Experimental investigation and analytical modeling

Today, one of the most commonly used retrofitting techniques for reinforced concrete (RC) columns for enhancing their structural performance is to externally confine these columns with carbon fiber-reinforced polymers (CFRPs). From another aspect, the presence of steel fibers in the concrete mixture enhances the behavior of structural members. In this research, the eccentric compressive behavior of steel fiber-reinforced concrete columns strengthened with CFRP wraps, which has remained mainly under-researched, is explored experimentally and analytically. For that end, eighteen RC columns with plain concrete and fiber-reinforced concrete, confined and unconfined with CFRP sheets, length to width ratios (L/h) of 4.2 and 8.3, and load eccentricity ratios (e/h) of 0.29, 0.46, and 0.63 were manufactured and tested under eccentric compressive loading. The findings indicated that the CFRP sheets improved the loading capacity and ductility of the RC columns, while the presence of steel fibers in the concrete affected the loading capacity of the columns negligibly but made them more ductile. Further, the eccentricity of the applied load mitigated the effect of confinement with CFRP sheets on the reinforced concrete strength. Regarding the significance of the performance of these columns, an analytical model with the purpose of predicting the behavior of fibrous RC concrete columns strengthened with CFRP sheets under an eccentric compressive load was developed. In this model, by considering the simultaneous effects of the confinement with CFRP sheets and transverse reinforcement, the moment–curvature and the load–deflection diagrams were determined using the fiber section analysis method. Assessing the analytical findings against the experimental ones of the present work and those of others indicated that the proposed model is able to properly predict the behavior of fibrous concrete columns confined with transverse reinforcement and CFRP sheets under eccentric compressive loading.

Evaluation on the ultimate bearing capacity for laminated bamboo lumber columns under eccentric compression

Engineered bamboo is gaining widespread interests from researchers to exploit its excellent functional characteristics in practical engineering applications. Laminated bamboo lumber (LBL) is one of many engineered products that are currently available with the potential to be used in the construction sector. The size and shape of LBL can be easily controlled to suit design requirements making it competitive with other commonly used building materials. This paper presents a recent investigation on the behaviour of LBL columns under eccentric compression loading, and proposes analytical formulations for predicting the ultimate resistance of columns with special emphasis given on observed failure mode types. Closer inspection revealed three characteristic failure modes, denoted as Mode I, II and III hereafter, for LBL columns under eccentric compression. In Mode I, failure was initiated from glue or bracket but all bamboo fibers remained elastic; in Mode II the outer most compression fiber reached elastic-plastic stage and eventually triggered failure; and in Mode III outer most part of compression fiber achieved plastic capacity prior to failure. Detailed analytical models have been developed and presented herein for all observed failure modes’ and the performance of the proposed design equations are compared using test evidences reported by the authors. The proposed equations produced very good agreement with the experimentally obtained results, and may be adopted in future design codes for engineered bamboo.