Influence of Shear Deformation on Buckling of Pultruded Fiber Reinforced Plastic Profiles

Theoretical studies of the influence of shear deformation on the flexural, torsional, and lateral buckling of pultruded fiber reinforced plastic (FRP)-I-profiles are presented. Theoretical developments are based on the governing energy equations and full section member properties. The solution for flexural buckling is consistent with the established solution based on the governing differential equation. The new solutions for torsional and lateral buckling incorporate a reduction factor similar to that for flexural buckling. The solution for lateral buckling also incorporates the influence of prebuckling displacements. Closed form solutions for a series of simply supported, pultruded FRP I-profiles, based on experimentally determined full section flexural and torsional properties, indicate the following conclusions. For members subjected to axial compression, shear deformation can reduce the elastic flexural and torsional buckling loads by up to approximately 15% and 10%, respectively. For members subjected to bending, prebuckling displacements can increase the buckling moments by over 20% while shear deformation decreases the buckling moments by less than 5%.     

Novel Technique for Inhibiting Buckling of Thin-Walled Steel Structures Using Pultruded Glass FRP Sections

The use of composite materials for strengthening the ailing infrastructure has been steadily gaining acceptance and market share. It can even be stated that this strengthening technique has become main stream in some applications such as strengthening concrete structures. The same cannot be said about steel structures; for which research on composite material strengthening is relatively new. Several challenges face strengthening steel structures using composite materials such as the need for high-modulus composites to improve the effectiveness of the strengthening system. This paper explores a new approach for strengthening steel structures by introducing additional stiffness to buckling-prone regions. The proposed technique relies on improving the out-of-plane stiffness of buckling-prone members by bonding pultruded fiber-reinforced polymer (FRP) sections as opposed to the commonly used approach that relies on in-plane FRP contribution. The paper presents results from an experimental investigation where shear-controlled beam specimens were tested to explore the feasibility of the proposed technique. Bar specimens were also tested in tension to compare between in-plane and out-of-plane contributions of FRP to the behavior and strength of thin steel plates. Based on the results, it can be concluded that this strengthening technique has great potential for altering failure modes by delaying the initiation of undesirable local buckling of thin steel plates. Recommendations for future research efforts are made to expand the knowledge base about this unexplored strengthening technique.     

Slender Steel Columns Strengthened Using High-Modulus CFRP Plates for Buckling Control

This paper presents the results of an experimental investigation into the behavior of slender steel columns strengthened using high-modulus (313?GPa), carbon fiber-reinforced polymer (CFRP) plates. Eighteen slender hollow structural section square column specimens, 44×44×3.2?mm, were concentrically loaded to failure. The effectiveness of CFRP was evaluated for different slenderness ratios (kL/r), namely, 46, 70, and 93. The maximum increases in ultimate load ranged from 6 to 71% and axial stiffness ranged from 10 to 17%, respectively, depending on kL/r. As kL/r reduced, the effectiveness of CFRP plates also reduced, and failure mode changed from CFRP plate crushing after occurrence of overall buckling, to debonding prior to, or just at, buckling. A simplified analytical model is proposed to predict the ultimate axial load of FRP-strengthened slender steel columns, based on the ANSI/AISC 360-05 provisions, which were modified to account for the transformed section properties and a failure criteria of FRP derived from the experimental results. It was shown that for a given FRP reinforcement ratio, there is a critical kL/r at the low end, below which FRP may not enhance the strength of the column.     

Local Delamination Buckling of Laminated Composite Beams Using Novel Joint Deformation Models

Local delamination buckling formulas for laminated composite beams are derived based on the rigid, semirigid, and flexible joint models with respect to three bilayer beam (i.e., conventional composite, shear-deformable bilayer, and interface-deformable bilayer, respectively) theories. Two local delamination buckling modes (i.e., sublayer delamination buckling and symmetrical delamination buckling) are analyzed and their critical buckling loads based on the three joint models are obtained. A numerical finite-element simulation is carried out to validate the accuracy of the formulas, and parametric studies of delamination length ratio, the transverse shear effect, and the influence of interface compliance are conducted to demonstrate the improvement of the flexible joint model compared to the rigid and semirigid joint models. The explicit local delamination buckling solutions developed in this study facilitate the design analysis and optimization of laminated composite structures and provide simplified and improved practical design equations and guidelines for buckling analyses.     

Experiments on the Buckling Behavior of Ring-Stiffened Pipelines under Hydrostatic Pressure

Submarine pipelines are deemed as thin-walled structures in which relative external pressure may be created in some cases of fluid transmission. The certain effect of this type of loading is local buckling and its propagation along the considerable length of the line. In this study, an experimental program has been performed, in which the influence of ring stiffeners on the buckling strength of pipelines is investigated. In the tests, only hydrostatic pressure is considered as the major loading case, and the effect of further loads is neglected. The modes of initial buckling, buckling propagation, postbuckling, and development of yield lines and the final collapse of the pipeline have been closely appraised. It is verified that the buckling threshold highly hikes up by attaching some light ring stiffeners. By decreasing the ring spacing, the difference between buckling and failure loads is diminished and torsion-type yield lines at failure mode occur on the pipe skin.     

Dynamic Axial-Moment Buckling of Linear Beam Systems by Power Series Stiffness

The paper applies the power series method to find the dynamic stiffness for the dynamics axial-moment buckling analyses of linear framed structures. Since the formulation is exact in classical sense, one element is good enough for the entire beam. The dynamic stiffness thus obtained can be decomposed into the stiffness, mass and initial stress matrices at a particular frequency, a particular axial force and a particular initial moment. The given axial force and moment can be nonuniformly distributed. The interaction diagrams in classical loading conditions of uniform moment, moment due to concentrated and distributed lateral force are given explicitly. The effects of warping rigidity, torsion rigidity, axial tension and compression are investigated in detail. The static and dynamic interaction buckling of a two-section I-beam structure is studied. Finally, we conclude that the three dimensional interaction diagram of the dynamic biaxial moment buckling can be obtained simply by rotating the three dimensional interaction diagram of the dynamic mono-axial moment buckling about the frequency axis if the bimoments are appropriately scaled. It is shown that application for non-uniform section is not suitable due to convergent problem. The method is very efficient that many interaction diagrams are produced for the first time.     

Lateral–Torsional Buckling of Singly Symmetric Tapered Beams: Theory and Applications

A general variational formulation to analyze the elastic lateral–torsional buckling (LTB) behavior of singly symmetric thin-walled tapered beams is presented, numerically implemented, validated and illustrated. It (1) begins with a precise geometrical definition of a tapered beam; (2) extends the kinematical assumptions traditionally adopted to study the LTB of prismatic beams; (3) includes a careful derivation of the beam total potential energy; and (4) employs Trefftz’s criterion to ensure the beam adjacent equilibrium. In order to validate and illustrate the application and capabilities of the proposed formulation, several numerical results are presented, discussed and, when possible, also compared with values reported by other authors. These results (1) are obtained by means of the Rayleigh–Ritz method, using trigonometric functions to approximate the beam critical buckling mode, and (2) concern the critical moments of doubly and singly symmetric web-tapered I-section simply supported beams and cantilevers acted by point loads. In particular, one shows that modeling a tapered beam as an assembly of prismatic beam segments is conceptually inconsistent and may lead to rather inaccurate (safe or unsafe) results. Finally, it is worth mentioning that the paper includes a state-of-the-art review concerning one-dimensional analytical formulations for the LTB behavior of tapered beams.     

Local Buckling of Elastically Restrained Fiber-Reinforced Plastic Plates and its Application to Box Sections

An analytical study of local buckling of rectangular composite plates rotationally restrained elastically along unloaded edges and subjected to nonuniform in-plane axial action at simply supported loaded edges is presented. A variational formulation of the Ritz method is used to establish an eigenvalue problem, and by using combined harmonic and polynomial buckling deformation functions, which satisfy all the restrained boundary conditions, the explicit solution of plate local buckling coefficients is obtained. The explicit formulas for local buckling strength of orthotropic plates are simplified to the cases of isotropic plates, which are consistent with classical solutions. The elastically rotationally restrained plates are further treated as discrete plates or panels of fiber-reinforced plastic (FRP) box shapes, and by considering the effect of elastic restraints at the joint connections of flanges and webs, the local buckling strength of FRP box shapes is predicted. The theoretical predictions are in good agreement with transcendental solutions and finite-element eigenvalue analyses for local buckling of FRP box columns. The present explicit formulation can be applied to determine local buckling capacities of composite plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes.     

Fiber-Reinforced Polymer-Confined Circular Concrete Columns: Investigation of Size and Slenderness Effects

Laboratory investigations of the compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns have generally been carried out using relatively small-scale specimens, and the majority of theoretical models that have been developed so far are based on test data from such specimens. However, the use of small specimens may conceal possible scale effects. In this study, the influence of slenderness ratio and specimen size on axially loaded FRP-confined concrete columns was investigated experimentally, and the results have been compared to theoretical models and experimental results gathered from the published literature. The investigation aims to validate past results obtained from concrete cylinders and to verify existing empirical models as well. Three different specimen diameters and two slenderness (length-to-diameter) ratios, combined with two FRP-confinement materials, were varied as parameters. According to the statistical analysis of the results, it is shown that conventional FRP-confined concrete cylinders can effectively be used to model the axial behavior of short columns. Size effects, however, are clearly evident in very small ( ≈ 50?mm diameter) specimens. The usefulness of published results involving such small-scale specimens is therefore questionable, as is the validity of theoretical models and strength predictions based on test data from small-diameter specimens.     

Bounds on Flexural Properties and Buckling Response for Symmetrically Laminated Composite Plates

Nondimensional parameters and equations governing the buckling behavior of rectangular symmetrically laminated plates are presented that can be used to represent the buckling resistance, for plates made of all known structural materials, in a very general, insightful, and encompassing manner. In addition, these parameters can be used to assess the degree of plate orthotropy, to assess the importance of anisotropy that couples bending and twisting deformations, and to characterize quasi-isotropic laminates quantitatively. Bounds for these nondimensional parameters are also presented that are based on thermodynamics and practical laminate construction considerations. These bounds provide insight into potential gains in buckling resistance through laminate tailoring and composite-material development. As an illustration of this point, upper bounds on the buckling resistance of long rectangular orthotropic plates with simply supported or clamped edges and subjected to uniform axial compression, uniform shear, or pure in-plane bending loads are presented. The results indicate that the maximum gain in buckling resistance for tailored orthotropic laminates, with respect to the corresponding isotropic plate, is in the range of 26–36% for plates with simply supported edges, irrespective of the loading conditions. For the plates with clamped edges, the corresponding gains in buckling resistance are in the range of 9–12% for plates subjected to compression or pure in-plane bending loads and potentially up to 30% for plates subjected to shear loads.     

Effects of the Loading History on the Local Buckling Behavior and Failure Mode of Welded Beam-to-Column Joints in Moment-Resisting Steel Frames

The cyclic behavior of welded beam-to-column joints for moment-resisting steel frames was assessed by constant amplitude cyclic quasi-static tests. Reanalysis of the results showed that the failure mode of the joints strongly depends on cycle amplitudes. A premature brittle failure of the welds may occur if the cycle amplitude is not large enough to cause local buckling of beam flanges. Influence of both flange and web slenderness ratios on local buckling behavior, investigated through an experimental parametric study, is discussed. Four tests, carried out adopting different variable amplitude displacement histories, confirmed that isolated large amplitude cycles have beneficial effects on the joint response, extending its life; on the contrary, many large cycles clustered together endanger the seismic performance of beam-to-column joints. Numerical analyses allowed interpretation of the experimental data in terms of local stresses and strains. For “large amplitude” cycles numerical results indicate a local state of strain causing a progressive collapse for low-cycle fatigue while, in case of “small amplitude” cycles, brittle failure mode is due to the ratcheting of material.     

Composite Action and Adhesive Bond between Fiber-Reinforced Polymer Bridge Decks and Main Girders

This paper describes the behavior of hybrid girders consisting of fiber-reinforced polymer (FRP) bridge decks adhesively connected to steel main girders. Two large-scale girders were experimentally investigated at the serviceability and ultimate limit state as well as at failure. One of the girders was additionally fatigue loaded to 10 million cycles. Compared to the behavior of a reference steel girder, deflections of the two girders at the SLS were decreased by 30% and failure loads increased by 56% due to full composite action in the adhesive layer. A ductile failure mode occurred: Deck compression failure during yielding of the steel girder. The adhesive connections were able to prevent buckling of the yielding top steel flanges. Thus, compared to the reference steel girder, the maximum deflections at failure could be increased up to 130%. No deterioration due to fatigue loading was observed. Based on the experimental results, a conceptual design method for bonded FRP/steel girders was developed. The proposed method is based on the well-established design method for hybrid girders with concrete decks and shear stud connections. The necessary modifications are proposed.     

Interaction between Steel Stirrups and Shear-Strengthening FRP Strips in RC Beams

RC beams shear strengthened with either fiber-reinforced polymer (FRP) U-jackets/U-strips or side strips commonly fail due to debonding of the bonded FRP shear reinforcement. As such debonding occurs in a brittle manner at relatively small shear crack widths, some of the internal steel stirrups may not have reached yielding. Consequently, the yield strength of internal steel stirrups in such a strengthened RC beam cannot be fully used. In this paper, a computational model for shear interaction between FRP strips and steel stirrups is first presented, in which a general parabolic crack shape function is employed to represent the widening process of a single major shear crack in an RC beam. In addition, appropriate bond-slip relationships are adopted to accurately depict the bond behavior of FRP strips and steel stirrups. Numerical results obtained using this computational model show that a substantial adverse effect of shear interaction generally exists between steel stirrups and FRP strips for RC beams shear strengthened with FRP side strips. For RC beams shear strengthened with FRP U-strips, shear interaction can still have a significant adverse effect when FRP strips with a high axial stiffness are used. Therefore, for accurate evaluation of the shear resistance of RC beams shear strengthened with FRP strips, this adverse effect of shear interaction should be properly considered in design.     

冷轧带钢整体和局部屈曲及后屈曲的有限元分析

采用通用的有限元分析软件ANSYS,建立了冷轧宽薄板二维有限元模型,分析计算在不同应力形式下,不同宽厚比的带村屈曲失稳特性及后屈曲变形路径.基于该计算结果建立的板形控制目标已在现场调试通过,实践证明它的效果良好.     

Absence of an Interaction Between Navigational Strategies Based on Local and Distal Landmarks.

In 3 experiments, rats were required to escape from a Morris pool by swimming to a submerged platform that was located at the apex of a notional, equilateral triangle with 2 different landmarks occupying the corners at the base. Training for 1 group was always conducted in view of the landmarks surrounding the pool and with the triangular array in a fixed orientation. Subjects could therefore identify the direction of the platform from a single landmark within the pool by reference to cues outside the pool or to the other landmark within the pool. Both strategies were used, and the results from additional groups revealed that the first of these strategies did not affect the acquisition of the second one. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies on the Interaction between Yttrium and Human Erythrocyte Membrane

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Study on Interaction between Lanthanum and Phosphor in Purity Steel

Using SEM and EDS some particles containing La and P were discovered in low oxygen and sulfur purity steel with lanthanum. In these particles low melting point elements such as As and Sb also were detected. According to the result of simulative calculation of segregation, it is shown that La and P enrich so strongly in the process of solidification that their concentrations can satisfy thermodynamic condition to forme LaP compound or meet the requirements to forme eutectic phase in the last stage of solidification. Therefore, the particles are concluded as LaP compound or eutectics, which exist on grain boundary mainly.     

微气泡与钢中非金属夹杂物相互作用机理的研究

介绍了微气泡与夹杂物之间的相互作用原理和几种气泡去除非金属夹杂物的方法,并计算了气泡与夹杂物之间相互作用的主要参数。在此基础上提出了利用超细固体粉末诱发微小气泡去除钢液中细小夹杂物的方法,并进行了大生产试验,结果表明,与传统工艺相比,利用此方法处理后的铸坯中氧化物夹杂数量明显减少,夹杂物数量减少近40%,铸坯中全氧含量降低到0.000 6%～0.000 8%。     

Fundamental Study on Interaction between Top Blown Jet and Liquid Bath

It is important to understand the physical interaction between top‐blown oxygen jets and liquid steel in basic oxygen steelmaking furnaces (BOF). In the present study, cold model experiments and CFD simulations were carried out with single‐ and multi‐hole nozzles and the velocity profiles of jets were successfully simulated. Water model experiments were also performed to study the cavity formation and the spitting phenomena by the impinging jets. The cavity shapes and the spitting behavior were correlated to the top‐blowing conditions by considering the characteristics of multi‐hole nozzle jets.