Pure Axial Compression Research Articles

Interactive plastic buckling of cones subjected to axial compression and external pressure

The paper discusses the results of buckling tests on carefully machined steel cones subjected to combined loading. Two cones were subjected to pure axial compression, further two were loaded by lateral pressure and the remaining six were tested under different combinations of axial load and external pressure. Cones were relatively thick with the radius, r2, at the base to wall thickness, t, being r2/t≈50. The ratio of height, h, to the base radius, h/r2=1.0, and the semi-vertex angle was β=14°. All numerical predictions of buckling load were found to be higher than the values obtained in experiments. Experimental results were also checked against values recommended by two design codes. Buckling loads recommended by codes show that five out of ten cones would have developed permanent, plastic straining at the recommended load level. Consequences of this, for repeated loading, are also highlighted in the paper. The paper also shows that a large portion of the interactive diagram is affected by plastic strains with the first yield envelope having bi-linear shape while the collapse envelope being quadratic.

Combined stability of unstiffened cones – Theory, experiments and design codes

The elastic-plastic buckling of short and relatively thick unstiffened truncated conical shells subjected to axial compression and external pressure is investigated. This is done using numerical and experimental approach. For the numerical analysis, the finite element code is employed to obtain the domain of combined stability. To validate numerical predictions, thirteen nominally identical laboratory scale cones with 26.56° semi-vertex angle and 3 mm nominal wall thickness with integral top and bottom flanges were CNC machined from 252 mm diameter mild steel billet. Two of the models were subjected to axial compression, with further two subjected to pure lateral external pressure, while the remaining nine cones were subjected to combined action of axial compression and external pressure of different ratio. Experimental results compare well with numerical predictions except for pure axial compression. However, the accuracy of these results is strongly dependent on the approach to modeling of material. Experimental results were compared with predictions of failure loads obtained from ASME code case 2286–2, and with the ECCS design rules for the case of axial compression and lateral pressure.

Numerical modeling of lean duplex stainless steel hollow columns of square, L-, T-, and +-shaped cross sections under pure axial compression

In this paper, finite element (FE) studies for LDSS (Lean Duplex Stainless Steel) hollow columns with square, L-, T-, and +-shaped cross sections (i.e., SHC, LHC, THC and +HC respectively) are presented using ABAQUS, to gain an understanding of the cross sectional shape effects. The LDSS hollow columns having equal material cross-sectional areas with thickness varying from 5m to 20mm were subjected to uniform axial compression. Short/Stocky columns with lengths (∼1800mm) of about three times the outer width of square were considered for the analyses. Based on the analyses, it has been found that for all the NRHCs (i.e., LHC, THC and +HC) considered, a nearly linear variation of Pu with section thicknesses has been observed, although the increase for SHC was relatively slower in thinner sections (t<12.5mm). The % increase in Pu with 300% increase in t (from 5m to 20mm) has been found to be ∼1273%, 1252%, 1041% and 679%, respectively, for square, L-, T-, and +-shaped sections. The gain in Pu for LHC, THC and +HC sections as compared (expressed as Pu/Pu(sq)) to SHC are in the range 120%–150%, 130%–170%, 140%–230%, respectively. Ductility at ultimate load has been observed to be ∼0.1–0.6% for SHC, LHC and THC (all thicknesses), and +HC (t≤10mm).

Effect of short and long term freeze-thaw cycling on the mechanical behaviour of filament wound FRP-tubes

In this study, an experimental work was performed to investigate the short and long term effect of freeze–thaw cycles on the mechanical behaviour of the fibre–reinforced polymers (FRP) tubes. The tubes had a constant internal diameter (152 mm), and wall thickness 2.65 mm. The fibre orientations were mainly in the hoop direction (±60°). Test parameters in this investigation include the effect of the number and type of freeze–thaw cycles. A total of eighty coupon specimens were cut from the FRP tubes, seventy were conditioned to 100 and 300 freeze–thaw cycles (+30°C to –30°C), while the rest were kept at room temperature (22.5°C). Then, pure axial tension and compression tests were conducted in order to evaluate the change of mechanical properties of the test specimens due to the freeze–thaw exposure. The test results indicated that the axial tensile and compressive strength of the FRP tubes were increased after short and long term freeze–thaw cycles.

Evaluation of Ayrton–Perry formula to predict the compressive strength of batten columns

This research was performed to evaluate two analytical methods for predicting the compressive strength of batten columns. Batten columns were subjected to pure axial compression, and the compressive strength was measured. The analytical methods used included the well-known Ayrton–Perry and ultimate strength curve methods to calculate the compressive strength of imperfect solid web columns, but their validity has not yet been studied experimentally on built-up columns. The geometrical parameters considered included the batten plate spacing and dimensions and the distance between the two longitudinal chords. The results show that the analytical methods were generally valid for the prediction of the compressive strength in batten columns and solid web columns. Using the average results of the Ayrton–Perry and ultimate strength curve methods leads to the best prediction of the column compressive strength. It was also shown that the initial imperfections in the batten columns could have a more important effect than the geometrical specifications on the value of compressive strength.

The behavior of GFRP-stiffened and -unstiffened shells under cyclic axial loading and unloading

The results of an experimental study on the cyclic axial loading and unloading behaviors of thin-walled GFRP cylindrical shells are presented. Each specimen was tested first under pure axial compression until the first visible damage occurred, At that point, loading stopped and the unloading step started until the load returned to zero. Based on the results, it seems that for cyclic loading, using stiffened shells is better than using unstiffened shells. On the other hand, the damage growth in the stiffened shells is slower than in the unstiffened shells. For aerospace and aircraft structures, which have been using cyclic axial loading, it seems that composite structures with composite helical stiffeners are better than unstiffened composite structures.

Experimental investigation and design of aluminum columns with longitudinal welds

This paper presents an experimental investigation of longitudinally welded aluminum alloy I-section columns subjected to pure axial compression. The specimens were fabricated using 6061-T6 heat-treated aluminum alloy. The test program included 20 column tests which were separated into 2 test series of different types of welding sections. Each test series contained 10 columns. All the specimens were welded using the Tungsten Inert Gas welding method. The length of the specimens ranged from 442 to 2433 mm in order to obtain a column curve for each test series. The observed failure mode for the column tests includes mainly flexural buckling around the minor axis and the major axis by applying support except for one column (ZP1217-1) which buckled in the local zone and some columns which failed in the weld. The test strengths were compared with the design strengths predicted by the European Code and China Code for aluminum structures. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section columns, and to check the accuracy of the design rules in the current specifications.

Buckling of thin and moderately thick anisotropic cylinders under combined torsion and axial compression

The effects of anisotropy, transverse shear stiffness, length, and their interactions on buckling under pure torsion and under combined axial compression and torsion were investigated using a previously derived analytical model based on deep shell theory including anisotropy and transverse shear stiffness. The model was verified only for buckling under pure axial compression, hence results for buckling under torsion have now been compared with the results of previous analyses, and the comparison showed that the model has good accuracy for buckling under torsion. Investigation showed that the buckling loads of a cylindrical shell are affected not only by anisotropy and transverse shear stiffness but also by shell length. This means that the shallow shell theory (Donnell-type theory) is not appropriate and deep shell theory including anisotropy and transverse shear stiffness must be used.

Out-of-plane buckling of arches with varying curvature

A number of theoretical solutions have been reported for the elastic out-of-plane buckling of arches with open thin-walled sections. However, most of theses studies are limited to arches with constant curvatures such as circular arches. This paper investigates the out-of-plane buckling of arches with varying curvature. Buckling equations for arches with varying curvature are derived and verified by comparing with those proposed earlier by different researchers. For this, the out-of-plane buckling of circular arches under pure axial compression and pure bending is studied. For an application of the derived buckling equations to arches with varying curvature, buckling loads of parabolic arches are determined. The solutions for parabolic arches are successfully verified by comparing with results of previous researcher and finite element analyses. Finally, comparative studies of circular and parabolic arches are conducted. The results show that the difference in buckling loads of circular and parabolic arches increases as the rise to span ratio increases.

Experimental evaluation of elastic critical load in batten columns

A test program was devised for batten columns subjected to pure axial compression to determine the elastic critical load. Tests were conducted using specimens with various batten plate dimensions and also, various distance between two longitudinal chords. For obtaining the elastic critical load from the test results, modified Southwell plot was used. The resulted critical loads were compared with those obtained from the three existing theoretical methods of the equivalent slenderness, Paul approach and finally the SSRC method. It is found that the theoretical methods are generally conservative. The Paul approach is the most accurate method and the equivalent slenderness method using the Engesser equation gives the results with the least accuracy. The accuracy of the SSRC method is slightly less than the Paul method.

A failure envelope for ±60° filament wound glass fibre reinforced epoxy tubulars

Multiaxial stress tests were performed on filament wound glass fibre reinforced epoxy tubulars and the first failure modes observed and the stress and strain failure envelopes recorded. The tubes were produced by filament winding technique. Specimens were tested under various ratios of axial stress and circumferential stress in a MTS testing system modified to apply the internal pressure. Fourteen stress ratios were tested (hoop stress: axial stress) ranging from 0:1 (pure axial tension), 1:1, 2:1, constrained ends (εA = 0, ≈3.5:1), 4:1, 4.5:1, 5:1, 7:1, 12:1, 1:0 (pure internal pressure), 7:−1, 2:−1, 1:−1 (pure shear) and 0:−1 (pure axial compression). Five specific failure modes were observed: (1) axial failure along a dominant helical crack under axial tension dominated stress ratios. (2) Weepage at the stress ratio of 2:1 and constrained end condition. (3) Local leakage via fluid jets in the range of 4:1 to 5:1. (4) Burst under stress ratios dominated by hoop stress. (5) Axial collapse under compressive axial loads. The resulting failure strain failure envelope was fit using the maximum strain criteria with necessary modifications in the regions of leakage and axial compression. Both of these ranges were found to be fit by linear segments.

Instability of delaminated composite cylindrical shells under combined axial compression and bending

Abstract Composite cylindrical shells and panels are widely used in aerospace structures. These are often subjected to defects and damage from both in-service and manufacturing events. Delamination is the most important of these defects. This paper deals with the instability analysis of delaminated composite cylindrical shells subject to pure bending and also combined bending and axial compression, using the finite element method. The combined double-layer and single-layer of shell elements are employed, which in comparison with the three-dimensional finite elements requires less computing time and space for the same level of accuracy. The effect of contact in the buckling mode has been considered, by employing contact elements between the delaminated layers. The interactive buckling curves and postbuckling response of delaminated cylindrical shells have been obtained. In the analysis of post-buckled delaminations, a study using the virtual crack closure technique has been performed to find the distribution of the strain energy release rate along the delamination front. The results show that under pure bending, laminated cylindrical shells are more sensitive to the presence of delamination, than they are under pure axial compression. It was also observed that the effects of delamination are more apparent when the composite cylindrical shells are subjected to combined axial compression and bending. In this case, with a slight increase of the applied bending moment, the strain energy release rate distribution on the compressive side of the cylinder changes drastically.

Buckling and postbuckling of single-walled carbon nanotubes under combined axial compression and torsion in thermal environments

The buckling behavior of single-walled carbon nanotubes under combined axial compression and torsion is investigated by using molecular dynamics simulations, to evaluate interactive buckling loads, and to assess the effect of temperature changes on bucking and postbuckling responses. Simulation results show that both the armchair and zigzag tubes exhibit nonlinear interaction curves at different temperature considered, and the interactive buckling loads are strongly size dependent. The buckling and postbuckling behavior of single-walled carbon nanotubes depends strongly on the temperature. Rise in temperature results in decrease of interactive buckling loads and postbuckling equilibrium paths, and the effect of temperature varies with the value of load-proportional parameter. The results also reveal that the single-walled carbon nanotubes may display two kinds of typical buckling configurations under combined loads, which are characterized by notable features distinct from those presented in pure axial compression or torsion.

Problems of geometric non-linearity and stability in the mechanics of thin shells and rectilinear columns

An analysis of the current state of the geometrically non-linear theory of elasticity and of thin shells is presented in the case of small deformations but large displacements and rotations, the ratios of which are known as the ratios of the non-linear theory in the quadratic approximation. It is shown that they required specific revision and correction by virtue of the fact that, when they are used in the solution of problems, spurious bifurcation points appear. In view of this, consistent geometrically non-linear equations of the theory of thin shells of the Timoshenko type are constructed in the quadratic approximation which enable one to investigate in a correct formulation both flexural as well as previously unknown non-classical forms of loss of stability (FLS) of thin plates and shells, many of which are encountered in practice, primarily in structures made of composite materials with a low shear stiffness. In the case of rectilinear elastic whereas, which are subjected to the action of conservative external forces and are made of an orthotropic material, the three-dimensional equations of the theory of elasticity are reduced to one-dimensional equations by using the Timoshenko model. Two versions of the latter equations are derived. The first of these corresponds to the use of the consistent version of the three-dimensional, geometrically non-linear relations in an incomplete quadratic approximation and the Timoshenko model without taking account of the transverse stretching deformations, and the second corresponds to the use of the three- dimensional relations in the complete quadratic approximation and the Timoshenko model taking account of the transverse stretching deformations. A series of new non-classical problems of the stability of columns is formulated and their analytical solutions are found using the equations which have been derived with the aim of analyzing their richness of content. Among these are problems concerning the torsional, flexural and shear FLS of a column in the case of a longitudinal axial, bilateral transverse and trilateral compression, a flexural-torsional FLS in the case of pure bending and axial compression together with pure bending and, also, a flexural FLS of a column in the case of torsion and a flexural-torsional FLS under conditions of pure shear. Five FLS of a cylindrical shell under torsion are investigated using the linearized neutral equilibrium equations which have been constructed: 1) a torsional FLS where the solution corresponding to it has a zero variability of the functions in the peripheral direction, 2) a purely beam bending FLS that is possible in the case of long shells and is accompanied by the formation of a single half-wave along the length of the shell while preserving the initial circular form of the cross-section, 3) a classical bending FLS, which is accompanied by the formation of a small number of half-waves in the axial direction and a large number of half-waves in a peripheral direction which is true in the case of long shells, 4) a classical bending FLS which holds in the case of short and medium length shells (the third and fourth types of FLS have already been thoroughly studied in the case of isotropic cylindrical shells), 5) a non-classical FLS characterized by the formation of a large number of shallow depressions in the axial as well as in the peripheral directions; the critical value of the torsional moment corresponding to this FLS is practically independent of the relative thickness of the shell. It is established that the well-known equations of the geometrically non-linear theory of shells, which were formulated for the case of the mean flexure of a shell, do not enable one to reveal the first, second and fifth non-classical FLS.

Experimental investigation of aluminum alloy circular hollow section columns

This paper presents an experimental investigation of aluminum alloy circular hollow sections subjected to pure axial compression between fixed ends. The specimens were fabricated using 6063-T5 and 6061-T6 heat-treated aluminum alloy. The test program included 29 column tests which were separated into 4 test series of different type of aluminum alloy and cross-section geometry. Each test series contained at least 5 columns with both ends transversely welded to aluminum end plates using the Tungsten Inert Gas welding method, and 2 columns without welding of end plates. Hence, the effects of welding on aluminum alloy columns could be investigated. The specimen length ranged from 300 to 3000 mm in order to obtain a column curve for each test series. The observed failure modes for the column tests include yielding, overall buckling, and material yielding in the heat-affected zone. The test strengths were compared with the design strengths predicted by the American, Australian/New Zealand and European specifications for aluminum structures. The purpose of this paper is to present the test results of aluminum alloy circular hollow section columns with and without transverse welds, and to check the accuracy of the design rules in the current specifications.

RBS polymer encased concrete wall. Part II: Experimental study and theoretical provisions for combined axial compression and flexure

Royal building systems (RBS) consist of rigid polymer extruded components that slide and interlock together to create continuous formwork for monolithic concrete walls. The resulting system is highly durable, very efficient in terms of energy and acoustic performance, weather proof, highly resistant to mold growth and termites attack, and is virtually maintenance free. The polymer encasement provides crack control vertically and horizontally for the concrete, and provides vertical tension reinforcement thus increasing the structural strength of the wall. The current paper presents the results of an experimental study of these walls subjected to pure axial compression and combined axial compression and flexure. In addition, theoretical provisions which consider the contribution of the polymer to structural strength enhancement are derived based on the experimental results.

Response of drilled shafts with minor flaws to axial and lateral loads

The use of drilled shafts as foundations for bridges and other structures has greatly increased in recent years due to the advent of routine non-destructive evaluation (NDE) methods. The availability of the NDE methods has given engineers and contractors the false impression that any defects that may have been produced during construction due to problems in concreting, drilling, casing, slurry and rebar cage placement can be identified and repaired before the bridge is opened to traffic. In reality, there is a lower limit on the size of defects that can be detected by current NDE techniques, which recent studies have identified it to be roughly between 10 and 20 percent of the cross-sectional area of the shaft. In this study, eleven 1/3-scale concrete shafts with minor void flaws were tested in the lab to determine the effects of minor void flaws on the stiffness, structural capacity, mode of failure, cracking pattern and ductility of concrete shafts, without the confining soil. Three different loadings were considered for the shafts: (a) pure flexure, (b) pure axial compression, and (c) combined axial compression and flexure. The size of the void was taken equal to 15 percent of the cross-sectional area of the shaft. The shape of the void resembled a wedge with the outer arc length and length of the void along the centerline of the shaft being both variables. The results of the lab tests showed that void flaws that penetrate the concrete core of a shaft are more critical than those that are located within the concrete cover. Further, the presence of a void affects the ductility of a shaft subjected to axial compression much more than it affects the axial strength. Computational methods that are based on strain compatibility and force equilibrium can predict the strength of a defective shaft with reasonable accuracy. Ultimately, the study will be helpful in developing rationally based structural resistance factors for drilled shafts that account for possible presence of minor void flaws.

Buckling of stainless steel square hollow section compression members

Abstract This article describes a test program on cold-formed stainless steel square hollow section (SHS) subjected to pure axial compression. A series of tests was compressed between fixed ends. The specimens were cold-rolled from stainless steel sheets. The tests were performed over a range of column lengths, which involved local buckling and overall flexural buckling. Measurements of overall geometric imperfections and material properties of the specimens were conducted. The experimental column strengths were compared with the design strengths predicted by the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures. Generally, the three specifications conservatively predict the strengths of the tested fixed-ended cold-formed stainless steel SHS columns. However, the design rules in the Australian/New Zealand Standard are slightly more reliable than the design rules in the American and European specifications.

Column Tests of Cold-Formed Steel Channels with Complex Stiffeners

This paper presents an experimental investigation of cold-formed steel channels with complex stiffeners subjected to pure axial compression for fixed-ended columns. The complex stiffeners of the channel sections consist of simple lips with return lips. A total of 30 column specimens were tested. The specimens were brake pressed from high strength zinc-coated structural steel sheets. Four different cross sections with different flange slenderness were tested over a range of column lengths. Detailed measurements of material properties, geometric imperfections, and local buckling loads of the specimens were conducted. Interaction of local and overall buckling was observed in the tests. Failure modes include local buckling, distortional buckling, and flexural-torsional buckling. The test strengths of the columns are compared with the design strengths predicted by the American Specification and the Australian/New Zealand Standard for cold-formed steel structures. Design column curves are also plotted. It is shown that the design strengths predicted by the American Specification are generally unconservative for short and intermediate columns, whereas the design strengths predicted by the Australian/New Zealand Standard are generally conservative for all column lengths. This is because the Australian/New Zealand Standard has a separate check for distortional buckling of singly symmetric sections.

Biomechanical evaluation of vertebroplasty using injectable calcium phosphate cement

Biomechanical evaluation of vertebroplasty using injectable calcium phosphate cement