Compressed Columns Research Articles

Flexural performance of reinforced beams made with composite ferronickel slag concrete

Concrete containing ferronickel slag with blast furnace slag, namely composite ferronickel slag concrete or F-S concrete, is featured by low bond strength with horizontally-placed rebar compared with normal concrete of equal strength. This feature may affect the flexural capacity and deformational characteristic of F-S concrete beams, which needs to be investigated. Four under-reinforced beams were prepared and tested, including one normal concrete beam and three F-S concrete beams. The variable was the percentages of F-S powder content, i.e., 0%, 20%, 30%, and 40%. The experimental results showed that as F-S powder content increased, both the flexural capacity and ductility of RC beams decreased. For the flexural capacity analysis, directly increasing F-S powder content lowers concrete strength, thus reducing the flexural capacity. Regarding the deformational characteristic analysis, the RC beam is ideally simplified to the combination of the compressive concrete column model plus the tie bar model, and the influence of tensile rigidity effect with different bond level on the tie bar deformation is mainly studied. It is found that the lower bond stress just increases the flexural crack spacing, and changes the stress and strain distribution of rebar and concrete, but does not change the stress-mean strain relation of the rebar in the tie bar per unit length. The incorporation of F-S powder has no effect on the deformation of RC beams. Unexpectedly, the concrete strength is another important factor affecting the plastic rotation ability of RC beams. Whether increasing/decreasing the concrete strength will increase or decrease the ductility of RC beams, it is much determined by the given ratio of the longitudinal tensile reinforcement. In other words, while F-S concrete strength equals that of normal concrete, the ductility of the F-S concrete beam resembles that of normal concrete beam. F-S concrete can be applied in engineering structures, as long as it meets the design strength requirement as normal concrete does, irrespective of any F-S powder content.

Research on Hysteretic Models for Prestressed and Non-Prestressed Steel Reinforced Concrete Frames

The beam-column fibre model is used to simulate the entire hysteretic process of the prestressed and non-prestressed steel reinforced concrete frame, and the results are compared with the test results. Based on the analysis of a large number of parameters, the hysteretic curve characteristics of this kind of composite frame are discussed, and the load-displacement hysteretic models of single-storey and single-span composite frame are established. The models can comprehensively consider the influence of axial compression ratio and column slenderness ratio and can predict the hysteretic behaviour of this kind of composite frame under horizontal loads. The load-displacement hysteretic models are consistent with the numerical simulation results. Relevant research can provide reference for simplifying the elastic-plastic dynamic analysis of structures.

Compression behavior of FRP bars/coral concrete columns under axial compression loading

The axially loaded bearing capacity tests on 8 fiber reinforced polymer (FRP) bar/coral concrete columns and 1 steel bar/coral concrete column were carried out. Parameters such as reinforcement ratio, stirrup spacing, slenderness ratio and reinforcement type were discussed. The results show that the failure mechanism of FRP reinforced coral concrete column and steel bar/coral concrete column is different, but the mechanical performance is still good. Increasing the diameter of longitudinal reinforcement leads to the decrease of bonding performance between longitudinal reinforcement and concrete protective layer. Reducing the spacing of stirrups is beneficial to improve the ductility of the members, and the higher the aspect ratio, the lower the bearing capacity of the members. Then, based on the data analysis of the compression performance experiment and the comparison of references, it is suggested that the nominal yield strength of carbon fiber reinforced polymer (CFRP) reinforcement should be 0.34fy (fy is the ultimate compressive strength of the reinforcement), and the corresponding theoretical value is similar to the experimental results. Finally, the theoretical calculation formula for bearing capacity of CFRP/coral concrete axial compression column is put forward, which provides a reference for engineering practice.

Effect of progressive collapse of central column on the push-down response of two-span beam-column substructures

In this paper, a simplified model is proposed for hand calculation of the push-down curve of reinforced two-span beam-column substructures with the mid-span column subjected to a vertical load inducing progressive collapse response. The model takes into account the flexural, arch and catenary strength mechanisms and the axial stiffness of RC compressed columns. The model was validated against experimental data available in the literature. The expressions derived, in a closed form, were useful for hand calculation of push-down responses and robustness evaluation of RC framed structures. The derived explicit expressions can be applied in a step-by-step manner for tracing nonlinear behavior up to failure and to give design rules for the robustness of RC framed structures.

Mechanical properties of eccentrically compressed columns strengthened with textile-reinforced concrete under the coupled action of chloride salt corrosion and loading

Building structures located in tidal areas are more vulnerable to damage due to the coupled effect of the chloride exposure during dry/wet cycling and loading during their service life; thus, such structures need to be repaired and strengthened. In this study, to examine the mechanical properties of textile-reinforced concrete (TRC)-strengthened eccentrically loaded columns under the coupled action of chloride corrosion and loading, eccentric compression testing of 10 TRC-strengthened rectangular reinforced concrete (RC) columns is conducted, and the influence of parameters such as the eccentricity and previous load level on the effect of TRC strengthening is considered. The results show that TRC strengthening can effectively inhibit the development and extension of cracks in eccentrically compressed specimens placed in a corrosive environment (due to chloride salt) while exhibiting a satisfactory crack control. With increasing eccentricity, the utilization rate of the tensile strength of the textile increases, and the contribution of the TRC strengthening layer to the specimen strength increases. With the increase in the previous load level, the strengthening effect of the TRC becomes more notable. Finally, the changes in the microstructure in the TRC strengthening layer under different previous load levels are analysed through scanning electron microscopy (SEM), and the damage degradation mechanism of the TRC strengthening effect is explored from a microscopic viewpoint.

Comparing Fire Behaviour of Restrained Cold‐Formed Steel Columns with Stiffened and Unstiffened Sections

AbstractAlthough, some experimental investigations have already been conducted and reported in the literature on cold‐formed steel columns under fire conditions, tests on the structural response of CFS columns in compression with intermediate and edge stiffeners and with restrained thermal elongation are rarely found in the literature, hence the relevance of the current investigation. In the present study, the effect of i) cross‐section shape (including single and built‐up sections), ii) web and edge stiffener configurations (webs with and without intermediate stiffeners and flanges with single edge fold stiffeners and double edge fold stiffeners), iii) slenderness (columns with different boundary conditions: pinned and fixed ends), and iv) stiffness of the surrounding structure to the thermal elongation of such columns have been investigated using an experimental campaign. Based on the research results it is clear that the overlapping regions, composite action, number of stiffeners, section geometry and load level take a crucial role in the fire structural behavior of CFS columns.

Numerical investigation on the buckling behavior of damaged steel members constrained by outer tubes

Recently, the collapse of space truss structures has been a public concern, often triggered by local damages of key components. The enhancement effects of buckling-controlled methods on the damaged members of space truss structures are systematically investigated by the detailed numerical analysis. Different local damages are introduced to the members to discuss the influence of damage positions and levels on the bearing capacity and displacement ductility. The sensitivity analysis is also performed to select representative damage modes. Compressive sleeve columns are designed and simulated for the damaged tubes, and the simulation method is verified by the reference tests. Moreover, parametric analysis is carried out to analyze the influence of the protrusion length, stiffness ratio and gap on the post-buckling behavior of members, including the failure mode, bearing capacity, enhancement effect and displacement ductility. Different designs of the outer tubes are proposed for the inner tubes with various damages. The principle in this work can effectively guide the reinforcement of the damaged members.

Load-Carrying Capacity of Compressed Wall-Like RC Columns Strengthened with FRP

The analytical prediction of the effectiveness of fiber-reinforced polymer (FRP) in the confinement of a rectangular reinforced concrete (RC) column with a high aspect ratio (wall-like) still has an uncertain solution. In this paper, a numerical investigation of the axial response of RC wall-like columns strengthened with FRP systems was developed. Analytical solutions proposed in the literature for the assessment of the axial load capacity were presented and compared with each other and with the available experimental results. Moreover, non-linear finite element analysis was carried out, and the results were discussed, providing a simple model for the assessment of the axial compressive strength of wall-like RC columns strengthened with FRP.

Eigenproblem Versus the Load-Carrying Capacity of Hybrid Thin-Walled Columns with Open Cross-Sections in the Elastic Range.

The phenomena that occur during compression of hybrid thin-walled columns with open cross-sections in the elastic range are discussed. Nonlinear buckling problems were solved within Koiter’s approximation theory. A multimodal approach was assumed to investigate an effect of symmetrical and anti-symmetrical buckling modes on the ultimate load-carrying capacity. Detailed simulations were carried out for freely supported columns with a C-section and a top-hat type section of medium lengths. The columns under analysis were made of two layers of isotropic materials characterized by various mechanical properties. The results attained were verified with the finite element method (FEM). The boundary conditions applied in the FEM allowed us to confirm the eigensolutions obtained within Koiter’s theory with very high accuracy. Nonlinear solutions comply within these two approaches for low and medium overloads. To trace the correctness of the solutions, the Riks algorithm, which allows for investigating unsteady paths, was used in the FEM. The results for the ultimate load-carrying capacity obtained within the FEM are higher than those attained with Koiter’s approximation method, but the leap takes place on the identical equilibrium path as the one determined from Koiter’s theory.

Determination of Load-Carrying Capacity of C-Profile Glued Ti-Al Column under Temperature Environment.

The paper deals with an examination of the behaviour of glued Ti-Al column under compression at elevated temperature. The tests of compressed columns with initial load were performed at different temperatures to obtain their characteristics and the load-carrying capacity. The deformations of columns during tests were registered by employing non-contact Digital Image Correlation Aramis® System. The numerical computations based on finite element method by using two different discrete models were carried out to validate the empirical results. To solve the problems, true stress-logarithmic strain curves of one-directional tensile tests dependent on temperature both for considered metals and glue were implemented to software. Numerical estimations based on Green–Lagrange equations for large deflections and strains were conducted. The paper reveals the influence of temperature on the behaviour of compressed C-profile Ti-Al columns. It was verified how the load-carrying capacity of glued bi-metal column decreases with an increase in the temperature increment. The achieved maximum loads at temperature 200 °C dropped by 2.5 times related to maximum loads at ambient temperature.

Experimental investigation into the buckling behaviour of cable-stiffened steel columns

In this study, cable-stiffened steel columns (CSSCs), which primarily aim to enhance compression behaviour, were experimentally investigated. In contrast to other stiffened column types, the cable-stiffened steel columns investigated in this work were equipped with a three-branch crossarm system. A series of tests were performed on 2.4 m CSSCs with two different crossarm–main column connection types (i.e., rigid and scissor types). In addition to the connection types, the effects of crossarm length and initial pretension on the load carrying capacities of CSSCs were also studied experimentally. The experimental results indicate that the three-branch crossarm system is effective in improving the buckling load of ordinary compression columns. The findings prove that the scissor-type connections between the crossarms and the main column could also be used in practical applications. Moreover, a unique, asymmetric post-buckling mode for a CSSC with a three-branch crossarm system was observed. The effects of crossarm length and pretension in cables are also demonstrated. This results presented in this work could be of assistance in the further design of CSSCs.

Accurate analytical approximation to post-buckling of column with Ramberg−Osgood constitutive law

The post-buckling of a clamped column made of nonlinear elastic material and subject to axial compression is investigated in this paper. The Ramberg−Osgood type constitutive relation is adopted and it is expanded by using Taylor series. Based on Euler−Bernoulli beam theory, the exact governing equations are expressed in terms of rotation angle. Because the equations contain strongly nonlinear terms that are functions of the rotation angle, analytical solutions are virtually impossible. In this respect, this paper is focused on presenting an alternative method to construct concise yet accurate analytical approximate solutions for post-buckling of the Ramberg−Osgood column that is related to large rotation amplitude. The improved harmonic balance method is used to solve the nonlinear governing equations which are simplified via the Maclaurin series expansion and orthogonal Chebyshev polynomials. In addition, numerical solutions by applying the shooting method on the governing equations are obtained for comparison. The second-order analytical approximate solutions presented in this paper show excellent accuracy by comparing with numerical solutions. The analytical approximate method and numerical result presented in this paper can be applied as design guidelines for designing engineering structures that sustain large deformation, such as slender nonlinear compression of aluminum alloy columns, rods or braces.

Experimental Research on Reinforced Concrete Columns Strengthened with Steel Jacket and Concrete Infill

Experimental research on axially compressed columns made from reinforced concrete (RC) and RC columns strengthened with a steel jacket and additional fill concrete is presented in this paper. A premade squared cross-section RC column was placed inside a steel tube, and then the space between the column and the tube was filled with additional concrete. A total of fourteen stub axially compressed columns, including nine strengthened specimens and five plain reinforced concrete specimens, were experimentally tested. The main parameter that was varied in the experiment was the compressive strength of the filler concrete. Three different concrete compression strength classes were used. Test results showed that all three cross-section parts (the core column, the fill, and the steel jacket) worked together in the force-carrying process through all load levels, even if only the basic RC column was loaded. The strengthened columns exhibited pronounced ductile behavior compared to the plain RC columns. The influence of the test parameters on the axial compressive strength was investigated. In addition, the specimen failure modes, strain development, and load vs. deformation relations were registered. The applicability of three different design codes to predict the axial bearing capacity of the strengthened columns was also investigated.

Evaluation of the mechanical response of calcarenite specimens confined with fiber reinforced polymers after high temperature exposure

Although the confinement of compressed columns with composite materials has been extensively studied during the last decades, scarce research has been conducted in the particular case of reinforcement of stone or masonry elements subjected to high temperatures. This work reports an experimental study on the mechanical behavior of cylindrical stone specimens exposed to temperatures of 600 °C and subsequently cooled with two different methods: slow air cooling or rapid water immersion. The effect of confinement by means of carbon or glass fiber reinforced polymers (FRP) is studied. The mechanical properties of the rock are also analyzed by non-destructive tests, which constitute very appropriate techniques when working on heritage buildings. In general terms, it was found that the effect of temperature significantly reduced the strength and elastic modulus of the rock. On the other hand, FRP confinement provided large increases in strength and ultimate strain, compared to unreinforced samples. An important finding of this work is that the response of the confined specimens seems to depend basically on the properties of the FRP laminate, and not on the damage that the stone core may have suffered. Finally, the experimental results are compared with the predictions of analytical confinement models included in the most relevant international design guides. It has been proven that these models seem to provide accurate results in the case of unheated and unaltered stone, although they show larger deviations in the case of high temperature exposed specimens.

Comparison among major codes for the stability design of steel compression members in steel bridges with the partial factors taken into consideration

Provisions aimed at stability design have been drawn up by various countries according to many previous researches and their own practice. However, calculated results based on different codes greatly differ. Stability design for the steel compression members of steel bridges in four codes adopting the partial factor design method were outlined and comparatively analysed in this study. Calculation methods following the codes of four countries were detailed in the case of the steel box section column. The nominal strengths related to the normalized slenderness and width-thickness ratios were discussed and compared with FEA results. It is found that results following EC3 correspond with the FEA results better than other codes. The safety factors were calculated and compared with each other. In addition, the design strength and allowable strength among these codes were discussed. The results indicate that EC3 and AASHTO provide relatively high allowable strength for the compressive steel box section columns in general while JTG D64 and JRA give conservative results.

A novel strategy for the crossarm length optimization of PSSCs based on multi-dimensional global optimization algorithms

Prestressed stayed steel columns (PSSCs) offer a lightweight alternative for the design of slender compression columns. The stability of compression columns can be significantly enhanced by introducing crossarms. Previous research on this subject has primarily focused on load-carrying capacity estimation or analyses of the influencing factors of PSSCs. Thus, investigations of the design optimization of PSSCs remain scant. This work proposes a novel strategy for crossarm length optimization of PSSCs based on multi-dimensional global optimization algorithms. A multi-population genetic algorithm is introduced in the optimization process. The proposed optimization algorithm was demonstrated to be efficient and accurate in terms of determining the optimal crossarm length of PSSCs.

Experimental response of hot-rolled stainless steel angle columns

This paper reports on experiments addressing the buckling and collapse behaviour of pin-ended hot-rolled stainless steel equal-leg angle columns under pure axial compression, aiming to provide reliable experimental data needed to develop explicit design guidelines for hot-rolled stainless steel angle columns currently absent in European standard. The systematic experimental programme included two test groups of specimens with nominal dimensions of 60 ×60× 6 mm and 100 ×100× 10 mm produced from austenitic grade EN 1.4301, and involved tensile material tests, geometric imperfection measurements, residual stress measurements, 6 stub column tests and 20 global compression tests. A wide range of column slenderness ratios was carefully selected to account for both elastic and inelastic failure characteristics including flexural and flexural–torsional modes and the influence of the legs’ width-to-thickness ratios. The test setup and procedure together with the key experimental results and characterised failure modes, were fully reported and discussed. The test results were compared with those predicted using the design methods for compressed stainless steel angle columns provided in European and North American standards. It was observed that the specifications offer conservative strength predictions of the tested columns, primarily due to the lower distribution of initial geometric imperfections of tested columns in comparison with the permissible fabrication tolerances that are usually used as the basis of stability checks in codified design.

Experimental-Numerical Failure Analysis of Thin-Walled Composite Columns Using Advanced Damage Models.

The paper analyzes the stability and failure phenomenon of compressed thin-walled composite columns. Thin-walled columns (top-hat and channel section columns) were made of carbon fiber reinforced polymer (CFRP) composite material (using the autoclave technique). An experimental study on actual structures and numerical calculations on computational models using the finite element method was performed. During the experimental study, post-critical equilibrium paths were registered with acoustic emission signals, in order to register the damage phenomenon. Simultaneously to the experimental tests, numerical simulations were performed using progressive failure analysis (PFA) and cohesive zone model (CZM). A measurable effect of the conducted experimental-numerical research was the analysis of the failure phenomenon, both for the top-hat and channel section columns (including delamination phenomenon). The main objective of this study was to be able to evaluate the delamination phenomenon, with further analysis of this phenomenon. The results of the numerical tests showed a compatibility with experimental tests.

Experimental Optical Testing and Numerical Verification by CuFSM of Compression Columns with Modified Channel Sections.

Thin-walled channel columns with non-standard cross-section shapes loaded with gradually increasing compressive force applied at the geometric centre of gravity of the cross-section were the subject of the investigations presented in this paper. The aim of the research was to determine which of the columns has the most favourable geometrical characteristics in terms of the applied load. The main investigation was an experimental study carried out using two methods: strain gauging and the optical method. Based on strain gauging, the critical forces were determined using the strain averaging method and the linear regression tangent to compression plot method. In addition, modern optical tests were performed using the ARAMIS system. The buckling forces at which the first signs of buckling appear and the buckling modes of columns were determined. The results obtained from the experimental tests were used to validate the results of numerical tests carried out using the Finite Strip Method (CuFSM). Based on this method, the values of critical forces and the percentage contribution of individual buckling forms to the loss of stability of the compressed columns were determined.

Designing of Steel CHS Columns Showing Maximum Compression Resistance

The paper deals with a shape optimisation procedure of steel, compressed bars. Circular hollow sections (CHS) of variable cross sections and variable wall thickness are taken into account. The proposed procedure for designing of steel rods exhibiting maximum compression resistance is effective and possible to use in engineering practice. The advantage of the proposed shape of the bar is that it allows to increase the value of its load carrying capacity, i.e. it ensures the transfer of a higher value of compressive force than similar, solid struts of the same mass and length. The extent of the increase in the load capacity relative to the load capacity of the reference solid, cylindrical bar depends on the slenderness of the reference bar and ranges from 60% to 170%. Due to this very beneficial fact, it can be used wherever it is required to maintain a certain stiffness and an increased value of compressive force is desired, as well as in constructions where it is necessary to reduce weight while maintaining the adopted mechanical parameters, e.g. values of load bearing capacity. Final results achieved in the research were presented in the form of the flow chart allowing to design the compressed columns of optimum shape.