Compressed Columns Research Articles

Influence of boundary conditions on the critical and failure load in the GFPR channel cross-section columns subjected to compression

The paper deals with experimental investigation and numerical analysis on influence of boundary conditions on critical load, post-buckling behaviour and failure load of compressed composite channel-section columns. The columns were made of 8-ply glass–epoxy laminate. The six different layers arrangement were considered.Tests were conducted using two test stands. In the first of them, special self-aligning grips with spherical bearings were used. In the second stand contains a stiff plate and a table. The stiff plate was mounted to the upper jaw and has only one degree of freedom (vertical movement). The table with spherical bearing which is mounted in the bottom jaw has 3 DOF (rotations about three perpendicular axes). The strain-gauges technique has been used for all tested specimens. Additionally the second stand has been equipped with the ARAMIS system for non-contact 3D displacement measurements.Numerical analysis was conducted using ANSYS software. Two models were prepared with boundary conditions corresponding to test stands.The critical load values were determined using following methods: the load vs. square of strain difference P−(ε1−ε2)2, the load vs. strain difference P−(ε1−ε2) curve inflection point method. To the failure load estimation the Tsai-Wu criterion and maximum stress criterion have been applied.

Experimental investigation of failure process in compressed channel-section GFRP laminate columns assisted with the acoustic emission method

The experimental investigations of thin-walled channel section columns subjected to static compression are described. The columns under consideration were made of eight layers of a glass/epoxy unidirectional prepreg tape, with the autoclaving technique. Six different symmetrical layer arrangements were taken into account. The tests were performed on a Zwick Z100/SN3A universal testing machine with special self-aligning grips. The columns under investigation were loaded with the force values from zero to the maximal load destroying the profile, which allowed one to observe the column behaviour till its collapse. The strain gauges measurement technique was employed to determine the equilibrium paths, the buckling loads and the post-buckling behaviour. During all the tests, AMSY-5 AE equipment made by the Vallen company was applied to detect acoustic emission phenomena. The acoustic emission method allowed to investigate the behaviour of composite structures in the phase prior to their collapse. The results of the experimental investigations were employed to validate the proposed FE model in order to analyse the post-buckling behaviour and to determine the failure load with the well-known failure criteria.

Experimental study and theoretical analysis of carbon fibre-reinforced polymer strengthening timber pier column

Timber structure is a mainstream form of ancient Chinese architecture. However, owing to factors such as weathering and long-time duration, most of the wooden structures have been damaged badly. Using iron hoops to enhance the original structures is the traditional method for pier reinforcement, which produces limited effects. In this paper, the new reinforcement materials carbon fibre-reinforced polymer used for strengthening short pier column have been studied. We designed nine timber columns, among which eight applied the carbon fibre-reinforced polymer for reinforcement. With the maximum bearing capacity of the hoop reinforcement columns increased by 20·7%, the research proved that hoop carbon fibre-reinforced polymer has reinforcement effect on axial compression columns. Finally, this paper analysed the short pier column strengthen by carbon fibre-reinforced polymer in theory and derived the calculation formula. In compression with test results from experiments and combining the theoretical analysis, the paper concludes the feasibility of using carbon fibre-reinforced polymer for timber structure reinforcement.

Evaluation of behavior of the secondary columns in semi-supported steel shear walls

Semi-supported steel shear walls (SSSW), whose steel plate is connected to secondary columns rather than main columns of the frame, have been considered as an alternative steel shear walls to the traditional type. Many investigations have been made for proportionate designing of components of SSSW system. One of the important issues in this regard is the out of plane buckling of the secondary columns. In this paper, the plastic theory of structures is utilized to find out the axial force distribution, along the compressive column. Then, using energy method, for an assumed shear wall with specific geometry and material and a given shear force, the maximum overturning moment that makes the compressive secondary column buckles, can be determined. Repeating this method, for various shear forces, makes it possible to draw some interaction curves between overturning moments and shear forces. These curves can be used to analyze and design of semi-supported steel shear walls.

Collision Capacity Evaluation of RC Columns by Impact Simulation and Probabilistic Evaluation

Recently, increasing traffic in urban areas has led to a dramatic increase in collisions between speeding vehicles and structural columns. An impact applies a greater force to a column than its regular static or dynamic load because of the mass acceleration effect of the vehicle. Vehicle impact can cause catastrophic damage to structural columns and ultimately cause them to collapse; therefore, an in-depth study of their structural resistance to vehicle impact is needed. This paper reports the behavior of a reinforced concrete (RC) compression member or column under a lateral impact load. The study quantitatively assessed the columns' resistance capacity and developed an impact-resistance capacity evaluation procedure. Because it is extremely difficult and costly to experimentally perform a parametric study for column impact scenarios, this analytical study was carried out using LS-DYNA, a commercial explicit finite element (FE) analysis program that simulates the effects of a high strain rate from impact or blast loading on structural and material behavior. The parameters used for this case study were cross-section shape variation, impact load angle, axial load magnitude ratio, concrete compressive strength, longitudinal and lateral reinforcement ratios, and slenderness ratio. Using the analysis results, an impact resistance capacity evaluation procedure using a probabilistic approach is proposed.

Simulation Analysis on Hysteretic Performance of Cross-type Rigid Node for Steel Frame Based on Abaqus

In order to study the cross-type rigid steel frame node hysteretic behavior of components, the axial compression ratio, H type steel column web thickness, girder section and stiffener as design parameters, 8 steel frame cross-type rigid joints and a T-type rigid joint are designed. Based on simplified mechanical model and constitutive relations of material, using ABAQUS software the corresponding finite element model is established and the hysteretic performance analysis is carried out. Through comparison between given T-type node test results and analysis results, both are in good agreement, thus the rationality of the finite element model established in this paper is verified. Simulation analysis of cross-type node is developed in further, load -displacement hysteretic curve of nodes, skeleton curve, envelope figure and the stress nephogram are extracted and comparative analysis is conducted, influence regularity of four parameters on the seismic behavior of the joints is obtained. The corresponding design suggestion for the axial compression ratio and column web and flange thickness ratio is proposed, design limit value of axial compression ratio of column should be taken as 0.5 and limit value of column web and flange thickness ratio is taken as 0.75,and these can provide reference for actual engineering design.

An analytical model for the face wrinkling failure prediction of metallic corrugated core sandwich columns in dynamic compression

This work was motivated by a necessity of simple and efficient models approximating the responses associated with all the possible failure modes of corrugated core sandwich columns in dynamic compression. In this study, an analytical model was proposed for the prediction of face wrinkling behavior of corrugated core sandwich columns under dynamic compressive loading perpendicular-to-corrugations. The proposed analytical model has been based on the calculation of transverse motion of face ligaments near the front and back ends of a sandwich column. The governing equation for the face ligaments has been a dynamic version of Euler–Bernoulli beam–column equation, and the motions were obtained by employing the Galerkin method to solve the equation. For validation of the proposed model, FE simulations were performed to compare several metrics such as reaction force and the transverse deflection of face ligaments. It was revealed that the dynamic face wrinkling response was also affected by overall column length and the rate of loading unlike the face wrinkling strength of corrugated core sandwich columns in quasi-static compression. Finally, the model׳s limitation and efficiency were discussed.

Minimal compliance topologies for maximal buckling load of columns

This paper presents a new approach to the topology optimization of columns exposed to a loss of stability. The idea is to replace a conventional maximization of a buckling load by a locally formulated topology optimization problem based on compliance minimization. In order to do this, the standard instability analysis of a compressed column is performed first and the buckling mode is determined. Then the compressive loading is replaced by a transverse one which is selected so as to generate a bending moment, the distribution of which coincides with the one representing the considered buckling mode. Minimization of compliance is performed for the bent structure and optimal topology is generated. Finally, the critical load for the optimal column is calculated. The selected numerical results obtained with the use of the above technique, under the assumption that the buckling load is unimodal, are presented. The above approach allows generating optimal topologies using Cellular Automata (CA) method, which by nature requires local formulation of the design problem.

Coronal shear fractures of distal humerus: Diagnostic and treatment protocols.

Coronal shear fractures of distal humerus involving the capitellum and the trochlea are rare injuries with articular complexity, and are technically challenging for management. With better understanding of the anatomy and imaging advancements, the complex nature of these fractures is well appreciated now. These fractures involve metaphysealcomminution of lateral column and associated intraarticular injuries are common. Previously, closed reduction and excision were the accepted treatment but now preference is for open reduction and internal fixation with an aim to provide stable and congruent joint with early range of motion of joint. Various approaches including extensile lateral, anterolateral and posterior approaches have been described depending on the fracture pattern and complexity. Good to excellent outcome have been reported with internal fixations and poor results are noted in articular comminution with associated articular injuries. Various implants including headleass compression screws, minifragment screws, bioabsorbable implants and column plating are advocated for reconstruction of these complex fractures. Inspite of articular fragments being free of soft tissue attachments the rate of osteonecrosis and osteoarthritis is reported very less after internal fixation. This article summarizes the diagnostic and treatment strategies for these rare fractures and recommendations for management.

The Finite Element Analysis of Waste Fiber Recycled Concrete Column Compression Performance

Through the ABAQUS software to simulate the compression performance of waste fiber recycled concrete column of the different fiber length and amount of fiber volume under the monotonic load, the ultimate carrying capacity and load - concrete strain curve of waste fiber recycled concrete eccentric compression column are concluded, and compare them with experimental results. The results show that the finite element analysis results and experimental results are basically in agreement with, which proves the feasibility and correctness of the finite element analysis.

Computational Analysis of Cold-formed Steel Columns with Initial Imperfections

Cold-formed steel (CFS) structures experience very complicated buckling and post-buckling performance. The presence of any kind of uncertainties complicates the calculation of such structures. Thin-walled CFS members are known to be particularly vulnerable to the influence of initial geometric imperfections. These imperfections may be the outcome of the manufacturing process, shipping and storage or the construction process. The article provides the results of nonlinear buckling analyses of CFS C-shaped compressed columns and evaluates the influence of imperfections on the load-bearing capacity of the tested members.

Reliability assessment of compression columns in seismic EBFs

In recent years, eccentrically braced frames (EBFs) have widely been used in steel structures in different countries. These systems are known to provide relatively high ductility, strength, and stiffness against seismic loads and to offer architectural flexibility by giving large openings. Seismic performance of EBFs is subjected to statistical uncertainties of both input excitations and performance of the system. This study aims at examining the current seismic design provisions and the reliability level of compression columns in EBFs with short shear links. An analytical model of minimally designed EBFs has been developed which is based on the LRFD design approach. For reliability analysis, analytical equations have been derived. The studies show that the current seismic provisions result in a less safe design relative to the target values for a wide range of the EBF columns. To cover this, an empirical equation is proposed for resistance factor of such columns. The study also includes a sensitivity analysis for five stochastic parameters that are presented and discussed.

Comparative behavior under compression of concrete columns repaired by fiber reinforced polymer (FRP) jacketing and ultra high-performance fiber reinforced concrete (UHPFRC)

This paper summarizes the experimental results from a comprehensive research program to study the fundamental stress–strain behavior of damaged concrete repaired by two techniques: increased concrete section and bonding fiber reinforced polymer (FRP). In this work, two types of FRP composite jackets were used, carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer, and two types of concretes were used to repair the damaged concrete by increased concrete section: ordinary concrete and ultra high-performance fiber reinforced concrete (UHPFRC). Fifteen circular columns of concrete (110 × 220) cm3 were initially pre-damaged up to intense cracking, repaired by increased concrete section and by bonding FRP, and tested under uni-axial compression by loading up the damage. The impact of different design parameters, including plain concrete strength, types of composites, and type of concrete used for increasing section, was considered in this study. The strength enhancement and ductility improvement of specimens are discussed. A simple model is presented to predict the compressive strength of repaired damaged concrete columns. A significant strength and an increase in ductility were achieved, particularly when the columns were repaired by increasing section with UHPFRC and by bonding CFRP. These preliminary tests indicate that the use of UHPFRC is an effective technique for rehabilitating damaged concrete columns, highly competitive with the repaired concrete by wrapping specimens with FRP composite jackets.

On buckling collapse and failure analysis of thin-walled composite lipped-channel columns subjected to uniaxial compression

The paper deals with buckling of short thin-walled lipped-channel columns, simply supported on both ends and subjected to uniformly distributed compressive load. The main objective of the study was to investigate the structure׳s work in far post-buckling state and at collapse corresponding to the moment of the column׳s stiffness loss. The following measuring devices and methods were applied: electrical strain gauges for strain measurements, a laser sensor to measure the displacements, and the Acoustic Emission method. Along with running the experimental tests, the non-linear stability of compressed composite columns was analyzed with the Finite Element Method. The numerical and experimental results showed good agreement.

Numerical and experimental studies of compressed composite columns with complex open cross-sections

The article presents results of experimental investigations of thin-walled beams made with carbon fiber composite. Experimental studies were conducted to confirm results obtained from numerical calculations, which was performed using two different software based on finite element method and analytical–numerical method based on Koiter’s asymptotic stability theory of conservative systems modified by Byskov and Hutchinson. The studies consisted of axially compressed thin-walled columns with channel and top-hat cross section.The specimen for the tests were made of unidirectional composite – epoxy resin matrix with carbon fibers reinforcement. The specimen was manufactured using autoclave technique. Thin-walled channel columns with dimensions of 80×40×1.048mm and length of 300mm and with four different symmetrical ply arrangements were prepared.The resulting axial force, longitudinal shortening and lateral displacement were recorded during experimental tests. Additionally in chosen points the strain were registered using strain gauges measurement technique.The experimental critical loads using the different method were determined. The experimental results was compared with these obtained from finite element method (ANSYS and ABAQUS) and analytical–numerical method. The postbuckling equilibrium paths obtained from experimental tests and numerical calculation for all considered columns were compared.

Applicability of over-coring technique to loaded RC columns

Stress determination is a very important step in the assessment of the safety of existing reinforced concrete structures. In rock mechanic this goal is achieved with the over-coring technique. The main idea behind such a technique is to isolate a material sample from the stress field in the surrounding mass and monitor its re-equilibrium deformation response. If the materials remains elastic, and elastic properties are known, stresses may be obtained from the corresponding measured strains. The goal of this paper is to evaluate if the over-coring technique is applicable to reinforced concrete members. The results of an experimental investigation on the behaviour of compressed concrete columns subjected to the over-coring technique are presented. Considerations about the range of applicability of the technique are made by comparing the measured and the theoretical stresses. After that, results of failure tests on drilled specimens are presented and discussed. Furthermore, the response is compared with that of columns core-bored before the compressive test. Finally, comparisons with numerical analysis are shown.

Biaxially loaded high-strength concrete-filled steel tubular slender beam-columns, part II: Parametric study

Biaxially loaded high strength rectangular concrete-filled steel tubular (CFST) slender beam-columns with large depth-to-thickness ratios, which may undergo local and global interaction buckling, have received very little attention. This paper presents the verification of a multiscale numerical model described in a companion paper and an extensive parametric study on the performance of high strength thin-walled rectangular CFST slender beam-columns under biaxial loads. Comparisons of computer solutions with existing experimental results are made to examine the accuracy of the multiscale numerical model developed. The effects of the concrete compressive strength, loading eccentricity, depth-to-thickness ratio and columns slenderness on the ultimate axial strength, steel contribution ratio, concrete contribution ratio and strength reduction factor of CFST slender beam-columns under biaxial bending are investigated by using the numerical model. Comparative results demonstrate that the multiscale numerical model is capable of accurately predicting the ultimate strength and deflection behavior of CFST slender beam-columns under biaxial loads. Benchmark numerical results presented in this paper provide a better understanding of the local and global interaction buckling behavior of high strength thin-walled CFST slender beam-columns and are useful for the development of composite design codes.

Finite Element Analysis on Concrete-Filled Square Steel Tube Short Columns with Inner CFRP Profiles under Axial Compression

The new composite structure concrete-filled square steel tube (CFST) column with inner CFRP profiles is proposed. A finite element model is presented to investigate the mechanical behavior of CFST short columns with internal CFRP profiles subjected to axial compression using ABAQUS based on reasonable constitutive models of materials. In a addition, the content of CFRP profiles and width thickness ratio of steel tube’ effect are considered on mechanical properties of the column. Based on the model, the whole stage of axial compression of the short columns, failure mode and the stress mechanism of the ultimate bearing capacity state are calculated and analyzed.

Numerical analysis of compressed concrete columns confined with CFRP: Microplane-based approach

This paper presents the results of numerical studies carried out on concrete columns confined by Carbon Fiber Reinforced Polymer (CFRP) and loaded in uni-axial compression. A numerical simulation of confined columns experimentally tested by [1] is performed for relatively small concrete specimens of constant size but with different cross-section corner radius. The experimental results, reported in terms of axial stress–strain relationships and failure modes, constitute a useful database for the calibration of numerical models. These results clearly demonstrate that CFRP confinement is much less effective in square than in circular cross-sections. Therefore, the influence of the corner radius on the non-uniform stress distribution due to confinement, is numerically investigated using the proposed microplane-based model that takes into account the effect of multi-axial stress states in concrete. The experimental results are used to calibrate and verify the prediction capability of a three-dimensional finite element code (3D FE) that is based on the microplane constitutive law for concrete [2]. In the finite element model carbon fibers are modelled using nonlinear truss elements, while epoxy resin as well as concrete are modelled using microplane-based constitutive law and 3D finite elements. Given that experimental results for unconfined and confined configuration are available for each specimen, the 3D FE concrete model has been preliminarily calibrated on unconfined concrete specimens and then used in the analysis of a confined specimen. It is demonstrated that numerical models can predict behavior of confined concrete columns from the experimental investigations, confirming the predictability of the numerical microplane-based approach used.

An efficient geometrically exact beam element for composite columns and its application to concrete encased steel I-sections

In this paper, a computationally efficient geometrically exact and materially non-linear 2D Euler–Bernoulli beam finite element is proposed, which is capable of accurately capturing the buckling behaviour of steel–concrete composite columns and complies with the principles of the general method of Eurocode 4 (EC4) (EN 1994-1-1:2004, 2004). The element is easy to implement and, due to the Euler–Bernoulli constraint, only requires uniaxial material laws for both steel and concrete. The element is subsequently employed to investigate the buckling behaviour of partially and fully concrete encased steel I-section uniformly compressed columns. In particular, the results of a parametric study are presented and discussed, aiming at assessing the influence of the equivalent member imperfections and the concrete material law, in order to provide recommendations concerning their use in non-linear analysis according to the general method of EC4.