Lateral Buckling Tests Research Articles

Axial and lateral buckling analysis of kevlar/epoxy fiber‐reinforced composite laminates incorporating silica nanoparticles

AbstractThe aim of this study was to experimentally determine the effect of silica nanoparticles (NS) on the buckling characteristics of Kevlar/epoxy fiber reinforced composite laminates. The composite samples with different weight fractions of NS particles, namely 0.0, 0.5, 1.0, 1.5 and 2.5 wt%, were prepared by vacuum assisted resin transfer molding (VARTM) and subjected to axial and lateral buckling tests. Additionally, the buckling tests were performed on the samples with different lengths (125, 150, 175, 200 and 225 mm) to analyze in more detail the influence of NS fractions on axial and lateral buckling performances. Morphology and failure mechanisms of the samples were analyzed using scanning electron microscopy images of critical regions of each sample. The results showed that the incorporation of NS particles led to higher critical buckling load values for both axial and lateral buckling. The highest critical buckling load values for both axial and lateral buckling events were observed for 1.5 wt% NS particle content in Kevlar/epoxy composite laminates. Further increasing of NS resulted with the decrements in critical buckling loads because of poor interfacial bonding between NS particles and epoxy resin, primarily due to onset of agglomeration. As it is expected the decreases in length of samples resulted with significant increases in both the axial and lateral buckling characteristics. The results of this research can be used to design composites with high buckling resistance, especially for applications where loading may compromise structural stability and functionality, such as tall buildings, structural bridges and roofs, rail tracks.

The gravity load simulator – Re-visited

A review of loading arrangements for lateral buckling tests on pultruded glass fibre reinforced polymer (GFRP) beams is presented. It is suggested that the Gravity Load Simulator (GLS), used for similar tests on steel beams could also be used for lateral buckling tests on GFRP beams and, moreover, it could be analysed and designed using exact calculations rather than the iterative method used more than 50 years ago. This conclusion is demonstrated by re-analysing the old iteratively designed GLS. The exact analysis is then used to analyse and design a new GLS for lateral buckling tests on pultruded GFRP beams. The new GLS was fabricated from aluminium bar and plate and details of its overall dimensions and layout and the types of bearings used in its pin joints are described. Thereafter, the test arrangement and instrumentation used to demonstrate the GLS’s accuracy, i.e. maintaining the horizontal translation of the jack’s base as the GLS sways in the lateral buckling plane, is presented. It is shown that the GLS performs extremely well and its use in laboratory testing is illustrated.

Lateral distortional buckling tests of a new hollow flange channel beam

The LiteSteel beam (LSB) is a new hollow flange channel section developed by OneSteel Australian Tube Mills using their patented dual electric resistance welding and automated continuous roll-forming process. It has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a relatively slender web. The LSBs are commonly used as flexural members in buildings. However, the LSB flexural members are subjected to lateral distortional buckling, which reduces their member moment capacities. Unlike the commonly observed lateral torsional buckling of steel beams, the lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist, and cross sectional change due to web distortion. An experimental study including more than 50 lateral buckling tests was therefore conducted to investigate the behaviour and strength of LSB flexural members. It included the available 13 LSB sections with spans ranging from 1200 to 4000 mm. Lateral buckling tests based on a quarter point loading were conducted using a special test rig designed to simulate the required simply supported and loading conditions accurately. Experimental moment capacities were compared with the predictions from the design rules in the Australian cold-formed steel structures standard. The new design rules in the standard were able to predict the moment capacities more accurately than previous design rules. This paper presents the details of lateral distortional buckling tests, in particular the features of the lateral buckling test rig, the results and the comparisons. It also includes the results of detailed studies into the mechanical properties and residual stresses of LSBs.

Lateral Buckling Tests on Cold-Formed Z-Beams

This paper is concerned with the lateral buckling capacities of cold-formed lipped Z-beams (CFZs). It is argued that design code formulations that are based on those for hot-rolled I-beams may be inappropriate for CFZs, because of the very different cross-sectional shapes and methods of manufacture, and that there is a need for test data on the lateral buckling capacities of CFZs. Described are a series of six lateral buckling tests on simply supported, unbraced CFZs, and a series of subsidiary tests, including tension tests, a torsion test, and measurements of initial crookedness and twist. The test beams failed catastrophically by local or distortional buckling of the most compressed element of the cross section. The moments at failure were lower when the beam lateral deflections increased the compression in the compression flange lip, and higher when they increased the compression in the flange-web junction. The lateral buckling test results are compared with theoretical predicitons and with capacities calculated using existing design codes AS4100 and AS/NZS4600. Agreement between the test results and theoretical predictions is reasonably good. The single design curve of AS/NZS4600 may be unduly optimistic for near-uniform bending and unnecessarily conservative for high-moment gradients in beams of intermediate slenderness. Improvements of the design method of AS4100 are suggested for future design code formulations.

Lateral Buckling Tests on Cold-Formed Channel Beams

This paper is concerned with the lateral buckling capacities of cold-formed lipped channel-section beams (CFCs). It is argued that design code formulations based on those for hot-rolled I-beams may be inappropriate for CFCs, because of the very different cross-sectional shapes and methods of manufacture, and that there is a need for test data on the lateral buckling capacities of CFCs. The paper describes a series of 10 lateral buckling tests on simply supported unbraced CFCs of two different cross sections, and a series of subsidiary tests, including tension tests, a stub-column test, section moment capacity tests, torsion tests, residual stress measurements, and measurements of initial crookedness and twist. The lateral buckling test results showed that the CFCs failed catastrophically by local or distortional buckling of the most compressed element of the cross section after quite large deformations. The failure moments were lower when a beam lateral deflection increased the compression in the compression lip, and higher when they increased the compression in the flange-web junction. The lateral buckling results showed good agreement with theoretical predictions. The lateral buckling results were also compared with design codes AS 4100 for hot-rolled sections and AS/NZS 4600 for cold-formed sections. It was found that the predictions by AS 4100 were generally closer to the test results while the predictions by AS 4600 were too high for beams with thinner wall thickness, but too low for beams with thicker wall thickness. It is suggested that the formulations of AS 4100 be used for the lateral buckling capacity design of CFCs, instead of those of AS 4600.

Effects of load position on the lateral buckling response of pultruded GRP cantilevers —Comparisons between theory and experiment

Details of a series of lateral buckling tests on a pultruded GRP I-section cantilever beam are described. The cantilever, which had spans ranging from 0.5 to 1.5 m, was subjected to point loads applied above, at and below the centroid of the free end cross-section. Vertical and horizontal deflections and the rotation of the free end cross-section were recorded as the beam was loaded and unloaded. Lateral buckling loads computed from modified simple closed form formulae and finite element eigenvalue analysis were compared with the maximum test loads. The computed buckling loads were generally significantly lower than the maximum test loads, though the differences between the loads appeared to be smallest for the longest span with the load applied just above the lower flange of the free end cross-section. The tests showed that significant vertical free end deflections develop before the cantilever buckles laterally and it is concluded that the effects of prebuckling deformations and geometric nonlinearity in addition to a more accurate evaluation of the in-plane shear modulus may have to be taken into account in order to achieve a closer correlation between the numerical analysis and the test results.

Lateral buckling tests on rectangular crosssection pultruded GRP cantilever beams

Results of a series of tests on rectangular cross-section pultruded GRP cantilever beams are presented. The beams are loaded in their stiffer plane of symmetry by means of a single point load acting through the centroid of the cross-section at the free end. Each beam was loaded well into the lateral postbuckling regime and then unloaded. Throughout the loading and unloading regimes end displacements, i.e. horizontal and vertical translations and the rotation of the cross-section, were recorded. Plots of support moment versus free end rotation are presented for all 16 beams tested and critical support moments (calculated using a modified formula for the critical moment of an isotropic cantilever) are compared with experimental maximum moments. The maximum support moments applied in the tests are also compared with theoretical critical support moments for span to depth ratios ranging from 4 to 25. It is shown that critical support moments provide reasonable lower bound estimates of the maximum support moments provided the span to depth ratio, l/d, exceeds 10.

Lateral buckling of pultruded GRP I-section cantilevers

A series of lateral buckling tests on pultruded GRP I-section cantilever beams is described. Comparisons of the theoretical critical loads, determined from approximate formulae and numerical finite element eigenvalue analysis, with the test results are presented. They reveal that linear buckling analysis does not provide an accurate estimate, for use in design, of the maximum tip load that a GRP cantilever may support. It is concluded that both initial deflections and pre-buckling deformations may need to be accounted for in order to model accurately the response of tip loaded pultruded GRP cantilevers.

Lateral Buckling Tests on Coped Steel Beams

Very little experimental data are available regarding lateral buckling of coped beams. In order to investigate and understand their behavior, six lateral buckling tests were conducted on a W12×14 section with different coping details. The results of each test are compared with a finite element computer solution and a proposed design method. Other available test results are also used in the comparison. Results of the tests indicate that the reduction in buckling load due to coping can be very significant depending upon the coping details. It is also found that the adjacent span restraint can increase the buckling load of coped beams significantly. The computer solutions agree with the test results both in buckling loads and buckled shapes. Comparison also indicates that the design method proposed is conservative.

Lateral buckling tests on monosymmetric plate girders

Abstract A series of tests on laterally unrestrained, welded, unequal flange girders is described. Attention is given to the careful design and fabrication of the test girders so as to ensure a proper representation of full-scale bridge girders, including the presence of controlled and realistic levels of imperfection. The ways in which the specially designed test apparatus met the need for clearly identifiable boundary conditions are discussed in some detail. A preliminary presentation and discussion of the test results is included; this confirms that welded, monosymmetric beams (whose larger flanges are in tension) possess lower lateral buckling strengths than either rolled sections or equal flange welded sections.

Lateral buckling behaviour of monosymmetric plate girders

Abstract The results of a series of lateral buckling tests on approximately one-third scale models of steel bridge girders are presented. All specimens, which had unequal flanges, were carefully fabricated with controlled levels of residual stress due to welding and initial crookedness. The performance under load of each of the 12 specimens is discussed in some detail and the separate and combined effects of the different imperfection levels are identified. When considered in combination with all existing test data for laterally unrestrained beams, the present results confirm the need for a lower design curve for welder sections. They also suggest that special attention is required for welded sections with unequal flanges, where such beams are loaded with the larger flange in tension (termed LFT-monosymmetric sections).

Inelastic lateral buckling of steel beam–columns

A series of investigations of the inelastic lateral buckling behaviour of steel beam–columns is described. These originate from many previous studies of the elastic lateral buckling of beams. It was found that present methods of predicting the effects of moment gradient in elastic beam–columns are unnecessarily conservative, and it was concluded that many practical continuous beam–columns will have significant warping restraints.Fourteen inelastic lateral buckling tests were carried out on 9 continuous steel beam–columns. The results of these tests were compared with predictions made by a new and improved finite element computer method of analyzing inelastic buckling, and very good agreement was found. The analytical method was then used to develop a simple approximation for predicting the inelastic buckling of isolated beam–columns with unequal end moments, and a design method was proposed. Key words: beams, buckling, columns, flexure, residual stresses, steel, structural design, structural engineering, torsion.