Post-ultimate Behavior Research Articles

Buckling strength and post-ultimate behaviour of lipped channel section short columns under eccentric compression

The paper presents the results of a large experimental testing campaign and of a numerical parametric study on the influence of the load eccentricity on the buckling behaviour and the ultimate strength of thin-walled cold-formed steel columns with lipped channel cross-section subjected to eccentric compression around the major axis. The numerical study was carried out using the finite element method (code Ansys) and the finite strip method (code CUFSM). The selected numerical results were compared with the experimental test results. Some conclusions concerning sensitivity of buckling strength and redundancy of load-carrying capacity in the post-buckling (either elastic–plastic or plastic) range to the magnitude of eccentricity, depending on the eccentricity position according to major axis and column dimensions are derived.

Ultimate and post-ultimate behaviour of thin-walled cold-formed steel open-section members under eccentric compression. Part II: Experimental study

Part II of the paper presents the results of the experimental program into the post-failure behaviour of thin-walled cold-formed steel lipped channel members subjected to eccentric compression about the minor axis. The tested samples are subjected to compression with a wide range of positive and negative eccentricities. Thus, the evolution of plastic mechanisms and the use of them to characterize the ultimate strength is examined, both by experimental tests and by FE simulations. Comparative diagrams of equilibrium paths obtained experimentally and from FE simulations together with post-ultimate curves obtained via yield line analysis are shown based on developed mechanisms models. Some conclusions are drawn regarding the applicability of the plastic mechanisms developed to determine the load-carrying capacity of the members under investigation. Finally, further research perspectives are presented.

Behavior of concrete masonry infills bounded by masonry frames subjected to in-plane lateral loading – Experimental study

This paper presents an experimental study on the in-plane behavior of a masonry infilled frame system, referred to as all-masonry infilled frames. This infilled frame system is one where both the infill and the bounding frame are built with one material, i.e., masonry units. In this study, masonry columns and beams were constructed from custom-made masonry boundary element units and fully grouted and reinforced, whereas the infill panel was constructed with half-scale standard 200 mm concrete masonry units and was ungrouted. The objective of the study is to investigate the effects of several design parameters on the behavior of this type of infilled frame and assess its performance against its infilled RC frame counterparts. A total of fifteen specimens was tested in this study, including 11 all-masonry infilled frame specimens and four RC framed specimens. The results showed that all-masonry infilled frame and its RC frame counterpart exhibited similar behavior in terms of stiffness and strength. While the RC framed infill showed pronounced corner crushing at failure, the masonry framed infill failed by severe diagonal cracking extending into the boundary columns. The all-masonry infilled frames also showed a better ability to sustain the ultimate load as displacement increased and the post-ultimate behavior was more ductile than their RC frame counterparts.

Ultimate and post-ultimate behaviour of thin-walled cold-formed steel open-section members under eccentric compression. Part I: Collapse mechanisms database (theoretical study)

The paper investigates the possibility to use the local plastic mechanisms to characterize the ultimate strength of short thin-walled cold-formed steel members subjected to eccentric compression and presents a database of local plastic mechanisms of failure for lipped channel section columns subjected to eccentric compression about minor axis. The background of yield line analysis related to thin-walled steel members is presented. Also, the buckling behaviour of examined members is briefly discussed. The geometries of the theoretical models of local plastic mechanisms for those members, for a wide range of applied eccentricities, are presented in detail. Comparative diagrams of equilibrium paths obtained from FE simulations together with post-ultimate curves derived via yield line analysis are shown based on developed mechanisms models. At the end, some conclusions concerning the applicability of presented mechanisms models for determination of load-carrying capacity of structures under investigation are derived.

Ultimate shear resistance and post-ultimate behavior of double-corrugated-plate shear walls

ABSTRACT The double-corrugated-plate shear wall (DCPSW) is composed of two identical corrugated plates that are assembled using connecting bolts. The DCPSW can exhibit much greater shear resistance than the ordinary steel corrugated plate shear wall (SCPSW) since the former forms a series of closed-sections while the latter is with open sections. In this paper, the shear resistant behavior of the DCPSWs is investigated. By using a validated FE modeling scheme, a parametric study of aspect ratio, bolt column number, corrugated plate thickness and yield stress of the DCPSWs is performed to investigate their effects on the shear resistant behavior. By analyzing the FE results, the ultimate shear resistance factor φ and the residual strength factor φr which corresponds to a final state with a drift angle of 2.0% of the DCPSW are obtained. It is found that both factors are negatively related to the normalized slenderness ratio λn. The φ-λn and φr-λn relationships obtained in this study are capable of providing conservative predictions of the ultimate shear resistance and post-ultimate residual strength for the DCPSWs. Finally, the shear resistant curves between shear load and drift angle of the DCPSWs with the variable of the normalized slenderness ratio λn are established. These shear resistant curves are regarded as simplified constitutive models when performing the required push-over elastoplastic analysis of the DCPSWs under severe earthquake excitation.

Generalised component model for structural steel joints

This paper presents a generalised component model for structural steel joints that extends the Component Method to the post-ultimate and post-fracture ranges. In this approach, a tri-linear spring model was developed for each individual component to include their post-ultimate behaviour, and a new concept of the instantaneous centre of rotation was introduced to track the changing load condition of each series of springs in a multi-spring system. The proposed generalised component model can predict the full-rangeM − θ curves of multi-spring models containing any number of deformable springs, and does not pose numerical difficulties in the post-ultimate range where some springs unload. The method is potentially applicable to all types of steel joints. The paper presents the application of the method to recent experimental tests on bolted moment end plate connections, showing good agreement over the full range of behaviour including fracture. The paper also demonstrates the application of the method to produce the backbone curve for a hysteretic model for the bolted moment end-plate connection.

Bond behaviour of steel plate reinforced concrete beams

This technical note presents an experimental study on the bond behaviour of chequer steel plate reinforcements in concrete members based on the beam-end method. The effects of lozenges of the chequer steel plate, the use of steel bolts, and the thickness of the concrete cover on the bond behaviour are investigated. The experimental program includes five specimens designed as beam-end pullout members. Each specimen is 225 mm wide, 300 mm high and 600 mm long. Stirrups with 80 mm centre-to-centre spacing are used as confinement for all specimens. The first specimen is reinforced with a deformed steel bar whereas the remaining specimens are reinforced with steel plates. All specimens except for the one reinforced with a smooth steel plate failed by pullout accompanied by splitting crack. The lozenges of chequer steel plate increased the ultimate pullout failure load by 80% compared to that of the specimen reinforced with a smooth steel plate. It has also been found that the pullout failure load of a steel plate reinforced concrete member can be significantly affected by the thickness of the concrete cover. Two other significant findings are that the pre-ultimate slippage of a steel plate reinforced concrete member is much less than that of a deformed steel bar reinforced one, and that the post-ultimate behaviour of the former is much more ductile than the latter. Comparisons between the present test results and the earlier test results involving reinforced concrete beams subjected to four-point bending tests suggest that the beam-end method may not be an appropriate method for comparing the bond strength of a chequer steel plate against that of a reinforcing bar.

Determination of the patch loading resistance of girders with corrugated webs using nonlinear finite element analysis

The corrugated steel plate is a widely used structural element in many fields because of its many favourable properties. This structural layout has spread in the field of bridges, too, especially for steel and composite bridges. Against of the numerous applications there are no standard design formulas for the patch loading resistance of girders with trapezoidally corrugated steel webs. The focus of the current paper is the determination of its design value with nonlinear finite element analysis. Experimental research is conducted on 12 test specimens. Failure mode, load carrying capacity and post ultimate behaviour are analysed. Based on the executed experiments numerical model is developed, and the patch loading resistance is determined by nonlinear analysis using geometrical and material nonlinear analysis and imperfections. The applied imperfection shape and scaling factor used for the nonlinear analysis are investigated and its influence on the structural behaviour is determined. Based on the experiments and numerical investigations, recommendations are formulated for possible equivalent geometric imperfection shape and scaling factor for girders with corrugated webs.

True Stress-True Strain Models for Structural Steel Elements

A standard uniaxial tensile test, which establishes the engineering stress-strain relationship, in general, provides the basic mechanical properties of steel required by a structural designer. Modern numerical analysis techniques used for analysis of large strain problems such as failure analysis of steel structures and elements metal forming, metal cutting, and so forth, will require implementation and use of true stress-true strain material characterization. This paper establishes a five stage true stress-strain model for A992 and 350W steel grades, which can capture the behavior of structural steel, including the postultimate behavior of steel, until fracture. The proposed model uses a power law in strain hardening range and a weighted power law in the postultimate range. The true stress-true strain model parameters were established through matching of numerical analysis results with the corresponding standard uniaxial tensile test experimental results. The material constitutive relationship so derived was then applied to predict the load-deformation behavior of coupons with a hole in the middle region subjected to direct tension loading. The predicted load-deformation behavior of perforated tension coupons agreed well with the corresponding test results validating the proposed characterization of the true stress-true strain relationship for structural steel.

Degradation of the compressive strength of unstiffened/stiffened steel plates due to both-sides randomly distributed corrosion wastage

The paper addresses the problem of the influence of randomly distributed corrosion wastage on the collapse strength and behaviour of unstiffened/stiffened steel plates in longitudinal compression. A series of elastic-plastic large deflection finite element analyses is performed on both-sides randomly corroded steel plates and stiffened plates. The effects of general corrosion are introduced into the finite element models using a novel random thickness surface model. Buckling strength, post-buckling behaviour, ultimate strength and post-ultimate behaviour of the models are investigated as results of both-sides random corrosion.

Design of Retrofitting for Damaged Rectangular Hollow Sectioned Struts

This paper is an investigation into retrofitting rectangular hollow sectioned (RHS) struts, the axis of which was damaged during loading. Retrofitting is achieved by welding stiffening plates onto the webs of damaged struts along a portion of their spans. A model for the analysis of pinned crooked retrofitted RHS struts in compression considering geometric nonlinearity and partial yielding about the midspan is described and compared with test results showing good agreement. The model is applied to the design of stiffeners for damaged struts in order to recover their compressive strengths. Stiffener sizes are evaluated for different strut axis crookedness. It is shown that a maximum efficient second-moment of area of the stiffening plates exists independently of the aspect ratios of the RHS cross sections and of the stiffening plates. A relationship between the length of the stiffener and the magnitude of allowable midspan crookedness of the damaged strut is determined. The effects of retrofitting on the secant stiffness of the strut and their postultimate behavior are discussed.

The flexural behaviour of fixed-ended channel section columns

The paper presents a study of the behaviour of thin-walled channel sections compressed between fixed ends. The paper emphasises the differences between the behaviour of fixed-ended and pin-ended channel sections, arising mainly from the fact that the local buckling induces bending of pin-ended channel sections but not of fixed-ended channel sections. As a result of the different effects of local buckling, the strength of a fixed-ended channel section column exceeds that of a pin-ended column of the same effective length. The increase in strength is quantified for a particular channel section, and is studied through the transition from pinned to fixed-end support by analysing columns which are elastically restrained against rotations at the ends. The paper also investigates the imperfection sensitivity and post-ultimate behaviour of fixed-ended channel section columns. It is shown that fixed-ended columns are less sensitive to local imperfections and that they exhibit greater post-ultimate ductility than pin-ended columns. The study is confined to columns whose overall buckling mode is the flexural mode.

Effect of testing techniques on the post-ultimate behaviour of concrete in compression

The paper is concerned with an investigation into the effect of testing techniques on the behaviour of plain concrete specimens under increasing uniaxial compressive load. It is found that for load increasing to the maximum level that can be sustained by the specimen, specimen behaviour is essentially independent of testing technique effects. However, for load levels beyond this peak level, the testing technique effects are found to be significant such that, if they can be completely eliminated, a more realistic description of post-peak specimen behaviour may be a complete and immediate loss of load-carrying capacity as soon as the peak load is exceeded.

A review of explosive characteristics of prestressed secondary containments near the ultimate load

The principles of load-structure interaction as they pertain to secondary containment structures are reviewed. These principles are illustrated by simple computations for a 1:14 scale model test structure. It is demonstrated that the pre-ultimate behavior should be identical for both pneumatic and hydraulic loading systems but that the post-ultimate behavior will differ substantially. However, in each case the post-ultimate behavior may be explosive. Implications with respect to complete and local failures of real containments are also briefly examined.