Local Effects Induced by Longitudinal Forces in Composite Girders

Local effects on the shear connection of composite girders induced by longitudinal actions such as the anchorages of prestressing cables, concrete shrinkage, or a uniform thermal action on the slab are analyzed. Closed-form solutions are obtained by using the simple model of a composite beam with a linearly elastic shear connection. Successively, by considering the limit scheme of an infinitely long beam, very simple formulas are derived permitting evaluation of the peak value and extension of the interface shear force distribution induced by the longitudinal actions. Numerical applications are carried out to show the effectiveness of the proposed formulas for a wide range of the shear connection stiffness and for longitudinal forces applied both along the beam axis and at the beam end.     

Asymptotic Matching Analysis of Scaling of Structural Failure Due to Softening Hinges. II: Implications

The asymptotic matching analysis in the preceding Part I has established a new kind of size effect, caused by postpeak softening of inelastic hinges in beams and frames. The present Part II analyzes various implications, particularly the size effects on the maximum loads under load control or displacement control, the design loads, and the energy absorption of the structure.     

Interactive Failure of Two Impacting Beams

A complete analysis of an inelastic beam-to-beam impact is presented. Both beams are of solid, rectangular cross-sections. The problem is formulated based on the momentum conservation and the kinematic and dynamic continuity conditions at the moving wavefront. Closed-form solutions are obtained for transient transverse velocities, deflection profiles, and tensile strains based on the moderately large deflection theory of the beam. Three different regimes of the solution are distinguished, depending on relative values of mass ratios and wave speed ratios. Critical impact velocities to break either of the beams are determined for both the striking and struck beams by assuming both beams fail by tensile necking. However, location of the fracture point depends on relative values of various parameters. It can be right in the contact zone or away from it. It is also shown that after one beam breaks, the other beam will deform further without breaking.     

Reliability of maintained ship hull girders subjected to corrosion and fatigue

A formulation is presented to account for the effect of corrosion and fatigue on the reliability of ship hulls. A time variant formulation is presented in which the effect of these degradation phenomena on the hull section modulus is quantified. The effect of maintenance actions is accounted for by considering that the repaired elements are restored to a state as new. Different repair policies can be studied and the approach can be used as a tool to plan the maintenance actions based on reliability results.     

Generic Impedance-Based Model for Structure-Piezoceramic Interacting System

This paper describes a generic impedance-based model for predicting the electromechanical (EM) impedance of one-dimensional (1D) and two-dimensional (2D) structure-piezoceramic (PZT) interacting systems. The vibration of a PZT patch is first analyzed. The effect of the host structure is then represented by its force impedance, which is obtained by a semianalytical method. Finally, experiments are carried out on beams and plates to simulate 1D and 2D problems, respectively. It is found that the predicted EM impedance of the structure-PZT interacting system coincides very well with the experimentally measured data. The results show that the predicted peaks match the natural frequencies of the host structure. The very small shift of the peaks from the natural frequencies caused by the interaction between the host structure and the PZT patch indicates that the small size PZT patch can be permanently bonded to the structure for on-line health monitoring without changing the mechanical properties of the structure too much. It is concluded that the proposed impedance-based model for general structure-PZT interacting systems can be potentially used in structural health monitoring.     

Assessment of the flexural capacity of RC beam/column elements allowing for 3d effects

The paper describes an experimental investigation of the deformational response and the stress conditions developing in the compressive zone of reinforced concrete beam-like structural elements in bending and bending combined with axial force. The results obtained confirm the findings of earlier work and demonstrate that the compressive zone at its ultimate-limit state is characterised by the development of triaxial rather than uniaxial-as widely considered-stress conditions. These findings form the basis for introducing a simple modification in the method currently used for calculating flexural capacity and it is shown that, by complementing the proposed method with an approach that takes into account the effect of yielding of the compression reinforcement on structural behaviour, it is possible to achieve predictions of flexural capacity which are considerably closer to experimentally established values than the values obtained through the use of currently adopted methods.     

Equivalent representations of beams with periodically variable cross-sections

This paper examines representations of a beam with periodically variable cross-sections. First, the rotational equivalence of a beam with two periodical steps to a uniform beam is considered when a constant bending moment is applied along the lengths of the two beams. The representation is then extended to a beam with several different steps and then to a beam with a variable cross-section. Variable bending moments are also taken into account in the equivalent representation. Equivalent representations based upon the same maximum deflection and fundamental natural frequency are derived. If a beam consists of several periodically variable units and the bending moment in each unit is considered to be constant, the various equivalent criteria can be unified. Detailed finite element analysis (FEA) shows that the plane-deformation assumptions no longer hold in the transition regions between adjacent steps. The transition area is defined using a straight line with an angle determined by curve-fitting and the results are provided in a tabular form considering all related parameters. A comparison of the maximum displacement and fundamental natural frequency shows good agreement for a number of beams with periodically variable cross-sections and their equivalent uniform beams. The study demonstrates that the equivalent representation of a beam with periodical variable cross-sections is accurate and simple to apply to engineering practice.     

Influence of fibers on flexural behavior and ductility of concrete beams reinforced with GFRP rebars

This research studies the influence of fibers on flexural behavior and ductility of concrete beams reinforced with GFRP bars. The experimental program included seven beams. The tested beams were divided into four groups. Each of the first three groups consisted of two beams one of normal strength and the other of high strength while the fourth group consisted of one normal strength beam. The first group is the reference group which had no internal fibers. The second group studied the effect of using internal polypropylene fibers in the concrete mix. The third group studied the effect of using internal glass fibers in the concrete mix while the fourth group studied the effect of using internal steel fibers in the concrete mix. The experimental results of tests showed that using GFRP as the main reinforcement for the concrete beams achieves reasonable flexural strength. Also the theoretical results calculated using ACI 440 code showed good agreement with the experimental results with an error of about 20%. The results of the current research indicated that all types of the fibers used improved the ductility of FRP- reinforced concrete beams. It was found that the span-to-experimental service load deflection ratio is relatively high when compared to the usually accepted ratio of about span/250.     

Distortional buckling of thin-walled inclined lipped channel beams bending about the minor axis

Based on the Generalised Beam Theory (GBT), two computing models are presented to analyse the distortional critical stress of cold-formed thin-walled inclined lipped channel beams bending about the minor axis. The computing model of rigid-body motion ignores the transverse bending deformation of the flange. However, the bending deformation of the flange is accounted for in the transverse bending computing model. Based on the transverse bending computing model, this paper puts up a simple method to take into account the in-plane bending of the flange. The results given by the rigid-body motion computing model does not correlate as well as those given by the transverse bending computing model with the results available in the literature. The accuracy of the transverse bending computing model is verified through comparison of its results with the known results. The comparisons demonstrate the importance of the bending deformation of the flange on the distortional buckling of cold-formed thin-walled channel beams bending about the minor axis.     

Genetic programming based formulation of rotation capacity of wide flange beams

This study is a pioneer work that proposes genetic programming (GP) as a new approach for the explicit formulation of available rotation capacity of wide-flange beams which is an important phenomenon that determines the plastic behaviour of steel structures. The database for the GP formulation is based on extensive experimental results from literature. The results of the GP-based formulation are compared with numerical results obtained by a specialized computer program and existing analytical equations. The results indicate that the proposed GP formulation performs quite well compared to numerical results and existing analytical equations and is quite practical for use.