Flexural Residual Stress Research Articles

Experimental study on residual stresses of dual phase high‐strength cold‐formed steel angles

AbstractThe rapid advance in advanced high‐strength cold‐formed steel makes this material promising for the construction industry to use as structural framing, but necessitates an accurate understanding of mechanical properties, including residual stresses. An experimental study was conducted to measure the residual stress which is generated during the member manufacturing process of a press‐braked angle member composed of advanced high‐strength cold‐formed sheet steel. The amplitude and distribution of membrane and flexural residual stresses around the member cross‐section is presented and the magnitude of residual stresses relative to the yield strength for the test specimen and other previous studies are compared. Additionally, the cutoff length typically recommended for residual stress measurements is investigated by comparing the residual stress distribution around the cross‐section for a section taken from the center and near the end of the member.

On the mechanical behavior of polypropylene, steel and hybrid fiber reinforced self-consolidating concrete

This article presents the results of an experimental investigation on the mechanical behavior of a self-consolidating concrete reinforced with steel, polypropylene and hybrid fibers. Hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 0.50%, 1.00% and 2.00%. Polypropylene fibers were used as reinforcement in volume fractions of 0.33%, 0.66% and 1.10%. Hybrid composites (HyFRC) were also developed to study the synergy effects of both fibers. The hybrid fiber self-consolidating concrete was produced with the addition of 0.50% of hooked-end steel fibers and 0.66% of polypropylene fibers.Pre-notched SCC prims where tested under monotonic and cyclic three-point bending. The tests where controlled by the crack mouth opening displacement in order to have a better analysis of the post cracking regime. The addition of polypropylene, hooked-end and hybrid fibers was effective in improving the post-peak strength of the composites, even though the use of steel fibers promoted higher values of flexural residual stress due to its geometrical and material properties. The same behavior was observed for the fracture parameters results with an improvement of the crack growth resistance for the analyzed composites.Finally, the effect of the fiber reinforcement on the flexural behavior was studied through structural tests on fiber reinforced self-consolidating concrete beams. Both hooked-end steel fiber and hybrid composites enhanced the resistance at yielding and promoted a lower rate of stiffness degradation, while the polypropylene fiber reinforcement presented an improvement in the ductile behavior of the structural composite. The present work gives an important contribution on the structural and cyclic behavior of steel, PP and hybrid fiber reinforced concrete. The paper makes a comparison on the mechanics of the different composite systems aiming its application in structural elements.

A probabilistic examination of the ultimate strength of cold-formed steel elements

The statistical characteristics (mean and variance) of the ultimate strength of cold-formed steel plates in uniform compression and pure bending are calculated and compared to deterministic approximations. Three quantities: plate thickness, longitudinal flexural residual stress magnitude and first mode imperfection magnitude, are treated as random variables. Based on existing experimental data, appropriate probability distributions are determined for the three random variables. The ultimate strength calculations are performed numerically using the finite element method (FEM). The statistical characteristics are calculated using two methods: Monte Carlo simulation and Taylor series approximation. The results are compared to the deterministic design approach of the American Iron and Steel Institute (AISI) Specification for the design of cold-formed structural members.

Influence of flexural residual stresses on the stability of compressed angles

Abstract Structural steel elements that are obtained by cold forming become more and more popular in steel construction. Indeed they are lighter in weight and thus provide appreciable savings compared with the usual hot rolled sections. Because they are obtained by cold forming, two kinds of residual stresses occur: membranar and flexural stresses. The flexural residual stresses are usually larger than the membranar ones. However the ECCS (European Convention for Constructional Steelwork) column buckling curves were established on the basis of longitudinal membranar residual stresses only, in addition to geometrical imperfections. Using a non-linear computer program, the authors investigate the influence of longitudinal flexural residual stresses on the carrying capacity of cold formed angles. This kind of section is now widely used for erecting large transmission towers. Strain hardening due to cold forming is taken into account in the present study. From the numerical results obtained, conclusions are drawn on the suitability of European column buckling curves for cold formed angles.