Plate Strengthening Research Articles

FRP strengthened aluminium tubular sections subjected to web crippling

This paper presents a test programme on aluminium tubular structural members that have experienced web crippling failure due to localized concentrated loads or reactions. A series of tests was performed on fibre-reinforced polymer (FRP) strengthening of aluminium tubular structural members subjected to End-Two-Flange and Interior-Two-Flange loading conditions. A total of 58 web crippling tests was conducted. The investigation was mainly focused on the effects of different adhesive and FRP for strengthening of aluminium tubular sections against web crippling. The influence of different widths of FRP plate strengthening against web crippling has been also investigated in this study. The test specimens consisted of 6061-T6 heat-treated aluminium alloy square and rectangular hollow sections. Six different adhesives and six different FRPs were considered in this study. The properties of adhesive and FRP have significant influence on the effectiveness of the strengthening. Most of the strengthened specimens were failed by debonding of FRP plates from the aluminium tubes. There are mainly four different failure modes observed in the tests, namely the adhesion, cohesion, combination of adhesion and cohesion, and interlaminar failure of FRP plate. The failure loads, failure modes, and the load-web deformation behaviour of the aluminium sections are presented in this study. It was found that the web crippling capacity of aluminium tubular sections is significantly increased due to FRP strengthening, especially for those sections with large value of web slenderness ratio.

Seismic Behaviour on Composite Strengthening for Existing Reinforced Concrete Short Columns

In order to develop an effective seismic shear strengthening method for improving the earthquake behavior of existing R/C short columns, experimental studies are conducted by using four beam-column sub assemblage specimens with a short column. Three short columns of these specimens are strengthening by steel plates and concrete, while other one is without any steel plate strengthening. All the specimens are tested under a constant gravity load and alternately repeated lateral forces. Test results demonstrate that, if the short column is strengthened by a welded square tube and concrete, then brittle shear failure does not occur and the column can develop its ultimate flexural moment capacity. It is also shown by tests that the proposed strengthening method using steel plates and concrete is applicable to repair and rehabilitate the damaged short columns failed in the brittle shear mode.

Strengthening of perforated plates under uniaxial compression: Buckling analysis

This paper focuses on the cutout-strengthening of perforated steel plates subjected to uniaxial compressive loads. The square plates considered each has a centrally placed circular hole and four simply supported edges in the out-of-plane direction. Four types of stiffeners named ringed stiffener ( RS), flat stiffener ( FS), longitudinal stiffener ( LS) and transverse stiffener ( TS) are mainly discussed. The finite element method (FEM) has been employed to analyse the elastic and elasto-plastic buckling behaviors of strengthened and unstrengthened perforated plates. The results show that the strengthened perforated plates have higher buckling strengths than those of the unstrengthened ones, while the elevations in elastic buckling stress and elasto-plastic ultimate strength are closely related to stiffener types (i.e., RS, FS, LS and TS) as well as plate geometric parameters (i.e., a plate slenderness ratio and a hole diameter ratio). Furthermore, comparisons of strengthening efficiency considering the variations of buckling stress with stiffener weight are carried out, and recommendations on the most efficient cutout-strengthening methods for the uniaxially compressed perforated square plates with centric circular holes are proposed.

Interfacial Stresses in Plated Beams with Exponentially-Varying Properties

This paper presents a method for determining the elastic shear and peel stresses in an adhesive joint between a strengthening plate and a functionally graded beam (FGB). The beam is assumed to be isotropic with a constant Poisson's ratio and exponentially-varying elastic modulus through the beam thickness. Stress distributions, depending on an inhomogeneity constant, were calculated and presented in the form of graphs. It is shown that the inhomogeneities play an important role in the distribution of interfacial stresses. This research is helpful in understanding the mechanical behaviour of the interface and design of hybrid structures. The results presented in the paper can serve as a benchmark for future analyses of functionally graded beams strengthened by fibre reinforced polymer plates.

Surface strengthening using a self-protective diffusion paste and its application for ballistic protection of steel plates

This paper deals with surface strengthening of steel plates using a self-protective diffusion paste. During the surface strengthening process, a paste containing carbon, boron or similar is applied on the steel surface. In addition to serving as a source for the various diffusion ingredients, the paste protects the steel against contact with the environment, so no packing or gas protection is necessary. Thus, the handling is in general very simple, and the surface strengthening process can be performed in a conventional air furnace. The method provides the same type of surface strengthening that is obtained by more conventional methods. In this work, the main focus will be surface strengthening by carburizing, but also boronizing and boronizing followed by carburizing have been tested out. The methods have been applied to increase the ballistic resistance of the low-strength carbon steel NVE36 (with nominal yield stress of 355 MPa) against impacts from small-arms bullets. An empirical model combining diffusion depth, heat-treatment temperature and soaking time was established on the basis of a series of experimental data. By means of this equation, the various heat-treatment parameters can be predicted when others are chosen. Ballistic perforation tests using 7.62 mm APM2 bullets showed that the low-strength carbon steel after surface strengthening obtained a ballistic limit higher than that of Hardox 400, which is a wear steel with a yield stress of about 1200 MPa.

An improved adhesively bonded bi-material beam model for plated beams

An improved bi-material beam theory with adhesive interface is presented to study the interface behavior in a conventional material (e.g., wood or concrete) beam reinforced by an externally bonded (e.g., steel or FRP) plate. Both the adherend normal and tangential deformations induced by interface stresses are considered by introducing two interface compliances, from which an improved solution of interface stress distributions is obtained. In addition, an unrealistic restriction of the same curvatures in both the adherends commonly used in most of the existing studies is released in the present theoretical formulation. Closed-form solutions of interface stresses are derived, and favorable agreements between the present solutions and those of the literature are achieved, thus demonstrating the validity of the solutions. The effects of the adherend normal and tangential deformations on the interface stress distributions are studied, and the improved accuracy of the present flexible interface over the rigid interface is illustrated. The present improved bi-material beam theory provides a better prediction of the interface stress distributions, especially for adherend materials (i.e., beam and bonded plate) made of relatively low stiffness properties (e.g., wood material as the originally strengthened beam and thin FRP composite as the strengthening plate), and it can be used to analyze the interface debonding in the beams with externally adhesive bonded plates.

The rise and fall of axial highs during ridge jumps

We simulate jumps of ocean spreading centers with axial high topography using elastoplastic thin plate flexure models. Processes considered include ridge abandonment, the breaking of a stressed plate on the ridge flank, and renewed spreading at the site of this break. We compare model results to topography at the East Pacific Rise between 15°25′N and 16°N, where there is strong evidence of a recent ridge jump. At an apparently abandoned ridge, gravity data do not suggest buoyant support of topography. Model deflections during cooling and melt solidification stages of ridge abandonment are of small vertical amplitude because of plate strengthening, resulting in the preservation of a “frozen” fossil high. The present‐day high is bounded by slopes with up to a 40% grade, a scenario very difficult to achieve flexurally given generally accepted constraints on lithospheric strength. We model these slopes by assuming that the height at which magma is accreted increases rapidly after the ridge jumps. This increase is attributed to high overburden pressure on melt that resided in an initially deep magma chamber, followed by a rapid increase in temperature and melt supply to the region shortly after spreading began. The high is widest at the segment center, suggesting that magmatic activity began near the center of the segment, propagated south and then north. The mantle Bouguer anomaly exhibits a “bull's‐eye” pattern centered at the widest part of the high, but the depth of the axis is nearly constant along the length of the segment. We reconcile these observations by assigning different cross‐axis widths to a low‐density zone within the crust.

Interfacial stresses in curved members bonded with a thin plate

The use of steel plates or externally bonded fibre-reinforced polymer laminates for flexural strengthening of concrete, masonry, timber or metallic structures is a technique that has become very popular. The effectiveness of this technique hinges heavily on the performance of the bond between the strengthening plate and the substrate, which has been the subject of many existing studies. In particular, the interfacial stresses between a beam and a soffit plate within the linear elastic range have been addressed by numerous analytical investigations. Surprisingly, none of these investigations has examined interfacial stresses in members with a curved soffit, despite that such members are often found in practice. This paper presents an analytical model for the interfacial stresses between a curved member of uniform section size and a thin plate bonded to its soffit. The governing differential equations for the interfacial shear and normal stresses are formulated and then solved with appropriate simplifying assumptions. Two numerical examples are presented to illustrate the effect of the curvature of the member on the interfacial stress distributions in a simply supported curved beam for the two cases of a point load and a uniformly distributed load. The analytical solution is verified by comparing its predictions with those from a finite element model.

Elastic analysis of adhesion stresses for the design of a strengthening plate bonded to a beam

This paper presents methods for determining the elastic shear and peel stresses in an adhesive joint between a strengthening plate and a beam. Both closed-form and finite-difference solutions are given, allowing loading, temperature effects and plate prestrain to be considered in design. The method can be used to design strengthened beams with section properties that change along the beam (such as tapered plates), and can also be used to determine the sensitivity of an adhesive joint to bond defects. The results of some typical load cases and geometries are presented to illustrate the significance of adhesive stresses.

Role of Bond in RC Beams Strengthened with Steel and FRP Plates

This paper looks at the problem of predicting the stiffness, load capacity, and failure modes of RC members strengthened in bending with bonded steel or carbon-fiber--reinforced plastic thin plates. A critical issue of this strengthening technique is that, when the plate debonds, the load capacity suddenly drops and the failure mode is typically brittle. Because of the concrete cracking diffusion and the yielding of the steel rebars, a significant amplification of the bond stresses takes place at the beam-plate interface. Delamination occurs when the bond strength is reached locally. To properly describe and adequately predict the behavior of the strengthened beams, a displacement-based fiber beam model is used. Bond slip between the beam and the plate is included by assuming separate displacement fields in the beam and in the strengthening plate. The proposed model is used to confirm and investigate distinct failure modes observed in experimental investigations. The discussion is limited to shallow beams, where shear deformations are neglected.

Buckling of Shear Loading Plates with Strengthenings

AbstractThe paper treats the influence of either weakening or strengthening of rectangular plates on the critical external buckling load. The plate geometry was chosen so that the buckling process takes place in the elastic range. The simply supported plate is loaded with shear forces per unit length which act on its edges. The results present the buckling coefficient as a junction of the ratio between the thickness of the weakening or strengthening and the initial plate. The buckling coefficient is analyzed as a function of the ratio between the weight of the weakened or strengthened plate and the initial plate weight without weakening or strengthening too.

Strengthening of Beams by Plate Bonding

At Lulea University of Technology, Sweden, research has been carried out in the area of plate bonding, i.e., the problems that can arise when concrete members need to be strengthened using epoxy-bonded plates. Both comprehensive experimental and theoretical work have been done. In this paper a derivation of the shear and peeling stresses in the adhesive layer of a beam with a strengthening plate bonded to its soffit and loaded with an arbitrary point load are presented. The results from both theory and finite-element analysis show that the stresses are very large at the end of the plate, but they quickly diminish as we move nearer the center of the beam. The magnitude of the stresses is influenced not only by the geometrical and material parameters of the beam, but also by the adhesive and the strengthening material.

Strengthening of reinforced concrete beams with composite materials: theoretical study

This paper deals with the flexural strengthening of reinforced concrete beams by means of composite thin plates. It presents a theoretical model which was developed to study the effects of various parameters on the flexural behavior of strengthened beams. From a parametric study carried out with the model, it was found that the most significant parameters affecting the ultimate flexural resistance are the concrete compressive strength, the percentage of reinforcing steel, the modulus of elasticity of the composite material and the thickness of the strengthening plate. To avoid brittle flexural failure of strengthened beams, limiting quantities of strengthening material are specified as a function of a strengthening index.

Strengthening of wide-flange columns under load

The present work deals with formulation of theoretical and analytical methods leading to the development of column strength curves. The formulations were developed for both elastic and inelastic behaviour. Two types of reinforcement have been developed for strengthening the W-shape columns under load. Since the column strength curves are based in part on the magnitude and distribution of residual stresses, it is extremely important to consider the new pattern of residual stresses due to welding process. Also, the welding sequence will affect the magnitude and distribution of residual stresses. Theoretical formulations leading to a closed-form solution for the prediction of critical load were developed for two types of strengthening using the superposition of original residual, new welding, and initial loading stresses. A nonlinear finite element analysis based on the large deformation theory of stability was used to predict the strengthened column critical load. It takes into consideration the effect of cooling residual stresses and new welding residual stresses. The formulations were incorporated with gradual penetration of yielding, the spreading of inelastic zones along the member length, the presence of residual stresses, and strain hardening of the material. Experiments were carried out to determine the actual capacity of strengthened columns. Seven specimens were tested using two and four strengthening plates. The welding stresses were measured through a series of experiments, and it was found that the parabolic distribution is a very close approximation to the actual new welding stress distribution. Key words: reinforcement of steel columns, welding stresses, welding sequence, strengthening of existing structures, buckling, steel plating, finite element.

Strengthening of Cast Iron Circular Plates by Annular Ribs

Strengthening of Cast Iron Circular Plates by Annular Ribs

Study of the stressed-deformation state of a copper-molybdenum composite using the michrohardness method

1. Using the microhardness method we constructed standards for the stress and deformation intensities of a composite material, facilitating a prediction of the mechanical behavior of the material. In particular it is possible to determine the nature of the destruction taking place in the plastic matrix. 2. Destruction of the strengthening agent creates a rectangular concentrator with the formation of approximate Lyuders-type bands. According to the distribution of the intensities it is possible to evaluate the macroscopic mechanism of deformation: at the moment of crushing of the strengthening agent, “wedging” of the adjacent material of the matrix occurs in the resulting slot, as a result of which a redistribution of the stresses takes place, accompanied by strengthening of the weakened section with an increase in the deformation of the composite. 3. The use of the fields of stress and deformation intensities makes it possible to assess the degree of effectiveness of the load of the plates, and in particular to determine the critical length of the strengthening plate, and also the dimensions of the adjacent (to the strengthener) regions of the matrix, deformed to the minimum degree.

Strengthening of plates of steel 10G2FR

Strengthening of plates of steel 10G2FR

Circular plate under a uniformly distributed impulse

Experiments are described in which simply supported circular plates are subjected to uniformly distributed impulses and the permanent deformations obtained are compared with those predicted by the bending theory of rigid-plastic plates. As opposed to the behavior of beams it is found that agreement between theory and experiment deteriorates as the impulse increases beyond a certain value especially when the predicted permanent central deflection is greater than about one-quarter of the plate radius. This illustrates the appreciable strengthening of plates due to membrane forces not taken into account in the theory.