João Negrão

Optimization of cable-stayed bridges with box-girder decks

Abstract Box-girder decks are very effective solutions for long span cable-stayed bridges, due to their high torsional stiffness and streamlined profile, which usually lead to a good aerodynamic behaviour. A study on the optimization of such structural system is presented in this paper. The deck is modelled through the assembly of planes of plate-membrane elements. A multicriteria approach is considered for the optimization itself, with constraints on maximum stresses, minimum stresses in stays and deflections under dead load condition. Two illustrative examples are shown.

OPTIMIZATION OF CABLE-STAYED BRIDGES WITH THREE-DIMENSIONAL MODELLING

Abstract This paper describes an analytical sensitivity analysis and optimization implementation for cable-stayed bridge design. The finite element software is based on the Vax/VMS version of the Modulef code [1 MODULEF Reference Guide. INRIA (1992).] and was adapted to an IBM-PC compatible. The main focus of this research concerns the analytical sensitivity analysis developed on this platform. The cable-stayed bridge optimization is posed as a multiobjective optimization with goals of minimum cost of material, stresses and displacements. Cable anchor positions on the main girder and pylon and cross-sectional sizes of the structural members are dealt with as design variables. By using the maximum entropy formalism it is shown that a Pareto solution may be found indirectly by the unconstrained optimization of a scalar function. The validity and effectiveness of the proposed technique is examined by means of a three-span steel cable-stayed bridge.

Sizing and Geometry Optimization of Cable-stayed bridges

This paper describes a method which sets steel cable-stayed bridge design in a multi-objective optimization context with goals of minimum cost and stress. The cable anchor positions on the main girder and pylon and the cross-sectional sizes of the structural members are dealt with as design variables. A Pareto solution is found by means of an entropy-based optimization algorithm. Illustrative examples for both the fixed and variable geometry problems show the significance of dealing with cable anchor positions as design variables. The influence of the stresses arising during the erection procedure on the optimum solutions is also emphasized.

OPTIMIZATION OF CABLE-STAYED BRIDGES SUBJECTED TO EARTHQUAKES WITH NON-LINEAR BEHAVIOUR

Earthquake-resistant provisions are essential features of the design of cable-stayed bridges built on seismic prone areas. Optimization can be employed to reduce cost and enhance geometrical and/or mechanical properties of the structure, The structural analysis programme developed here allows for a three-dimensional representation of cable-stayed bridges. Sensitivity analysis is carried out by analytic means both for the combined modal analysis/response spectra and the time-history methods. This enables the prediction of the variation of the structural response to earthquakes with respect to changes in the design variables. The optimization consists of a problem of multiple goals seeking to improve objectives such as cost, stresses, code of practice and erection requirements. This optimization problem turns out to be equivalent to the minimization of an unconstrained convex scalar function, which can be done by conventional quasi-Newton methods. Illustrative examples are given describing the features and ...

Glued Composite Timber-Concrete Beams. I: Interlayer Connection Specimen Tests

The composite interaction in timber-concrete beams is usually achieved with mechanical devices, such as shear connectors or plates driven into the materials. However, this connecting system shows some inherent inconveniences, such as the need for drillings and the limited mechanical improvement owing to interface slip. Using adhesives instead of mechanical connectors might attenuate these drawbacks. However, engineers are hesitant to apply adhesives for structural purposes, mostly because of the different thermohygrometric behavior of the adhesive and the connected material(s). This is particularly concerning timber because its hysteretic response to moisture may cause interface delamination. Therefore, as a preliminary stage for the test of composite beams, an extensive experimental campaign on small-size specimens was performed. The study focused on the shear strength at the interface and the role of some factors. Several series were considered by changing those parameters, and the results were compared. Both prefabricated and cast-on-site concrete specimens were considered. The results show that this system looks suitable for structural application, at least under steady dry conditions.

Glued Composite Timber-Concrete Beams.II: Analysis and Tests of Beam Specimens

This paper reports an experimental program on composite timber-concrete beams with glued interface. The test results are compared to those provided by an analytical model based on the assumption of a fully composite behavior. Both cast-on-site and prefabricated composite timber-concrete beams were produced, aimed at simulating rehabilitation situations or the possibility of a partial or of a full prefabrication of the composite element. Timber-concrete beams with dowel-type shear connectors were also produced and tested for comparison. The results show that the strength is similar, but the glued beams displayed a larger stiffness and, consequently, smaller deflections, which may be of relevance in design. The results also show that, at least under stabilized and dry room conditions, the prevailing mode of failure is tension in timber and, when shear failure occurs, it is mostly conditioned by the shear strength of the concrete or the timber, not by that of the adhesive. As the system depends on the shear strength of the interface, a preceding program consisting in tests on small-size composite specimens was undertaken and is reported in a companion paper.

Assessment of Timber–Concrete Connections Made with Glued Notches: Test Set‐Up and Numerical Modeling

The aim of this study is to analyze the mechanical behavior of timber—concrete connections established through glued notches, as well as the parameters that may affect it, specifically in the experimental shear test procedure. With these objectives in mind, a database based on a literature survey was created, identifying different shear test set-ups. In addition, a numerical approach was also adopted, based on experimental results. A numerical finite element method model was developed in order to describe the behavior of this type of connection. To validate the model, three sets of experimental tests were used, differing according to the notch material, the concrete class and the set-up’s geometry. Using this model, parametric studies were developed to analyze the effects of the material and geometrical parameters and support conditions. The database showed that double-shear tests were the most common experimental test set-up. The numerical modeling allowed a good approximation to a connection’s linear-elastic behavior. Parametric studies showed that the parameter with the greatest effect on a connection’s stiffness was the modulus of elasticity of timber, in contrast with the support conditions. The locations chosen to measure displacements on timber and concrete elements were also shown to affect the calculated connection stiffness.

Optimum design of concrete cable-stayed bridges

The design of cable-stayed bridges involves a significant number of design variables and design objectives. The concrete cable-stayed bridge optimization is formulated here as a multi-objective optimization problem with objectives of minimum cost, minimum deflections and minimum stresses. A numerical method is developed to obtain the optimum design of such structures. This numerical method includes: structural analysis, sensitivity analysis and optimization. The structural analysis accounts for all the relevant effects (concrete time-dependent effects, construction stages and geometrical nonlinear effects). The structural response to changes in the design variables is achieved by a discrete direct sensitivity analysis procedure, and an entropy-based approach was used for structural optimization. The features and applicability of the proposed method are demonstrated by numerical examples concerning the optimization of a real-sized concrete cable-stayed bridge.

Structural Connections for Small-Diameter Poles

AbstractIn Portugal, given the large proportions of natural regeneration pine stands, a large amount of young trees must be removed from the forest, to assure the quality of mature trees and to decrease the risk of fire. With this problem in mind, a national study was launched to investigate the use of maritime pine small-diameter poles in structural applications. The study had two different tasks. The first task comprised the determination of mechanical properties and the establishment of visual and mechanical strength grading procedures and is already completed. The second task concerns the development of connections. This paper presents results within the second task. Three types of connections, regarding failure load and stiffness, were studied: connections using central plates; glued-in rods; and dowel nuts. The glued-in rods showed the highest mean failure load and, especially, stiffness. Indeed, the glued-in rods showed a mean stiffness around six times higher than the one obtained for the other st...

Optimum design of concrete cable-stayed bridges with prestressed decks

ABSTRACT This article presents an optimization-based numerical method for the design of concrete cable-stayed bridges with prestressed decks. This method includes a structural analysis module and a sensitivity analysis and optimization module. The structural analysis considers concrete time-dependent effects, construction stages and geometrical nonlinearities. The discrete direct method is used for sensitivity analysis and an entropy-based approach is used for structural optimization. The design is formulated as a multi-objective optimization problem with objectives of minimum cost, minimum deflections and stresses. Numerical examples concerning the optimization of a real sized cable-stayed bridge are presented to illustrate the applicability of the proposed method.