Aitor Baldomir

Cable optimization of a long span cable stayed bridge in La Coruña (Spain)

This document describes an optimization problem of cable cross section of a cable stayed bridge considering constraints of cable stress and deck displacement. Since the bridge is still in the design phase, the geometry and the mechanical characteristics are subjected to changes. In order to avoid creating different structural models, a computer code was written to produce a model from geometrical and mechanical data and solve the optimization problem. At the end of the document, two examples are included to show the capabilities of the methodology presented.

Improved Optimization Formulations for Launching Nose of Incrementally Launched Prestressed Concrete Bridges

The conventional design process of a launching nose of an incrementally launched bridge is based on trial-and-error methods to reduce bending moment of prestressed concrete deck at the foremost support during launch. With this method, there is no guarantee that the obtained solution is the best among all the possible solutions, since they all depend on the experience and intuition of a designer, and they are also restricted by a limited number of possible iterations. Given that launched bridges constitute an important constructive typology, all the available capacities of design innovation should be incorporated, including numerical optimization. This research work proposes an objective and rigorous formulation to optimize the launching nose of a launched bridge under real constraints that a bridge designer can encounter in practice. Comparing the results obtained by conventional process and those obtained by optimization techniques allows us to verify that some of the assumptions considered in classical design methods of a launching nose are not based on any theoretical foundation. This fact demonstrates the utility of numerical optimization to improve a design.

Simultaneous Cross Section and Launching Nose Optimization of Incrementally Launched Bridges

The conventional design process of the launching nose of an incrementally launched bridge is usually based on parametric models with great limitations and the use of a trial and error technique to improve the design. Facing the disadvantages of traditional approaches, the use of numerical optimization techniques permits the development of objective, rigorous, and complete formulations. This work solves the design optimization problem of an incrementally launched prestressed concrete bridge during construction, searching simultaneously for the optimum cross section dimensions and the prestressing forces of the concrete deck, as well as the most adequate characteristics of the launching nose for the best economic solution. A computer code that allows the generation of a deck was developed, under real design constraints similar to those a bridge designer may encounter in practice. This code is very useful for preliminary phases of a project. The results obtained with this innovative formulation show the benefit of considering numerical optimization tools.

A methodology for identification of dynamic parameters in assembled aircraft structures

Finite Element Models (FEM) are widely used in order to study and predict the dynamic properties of structures. Comparing dynamic experimental data and analytical results, respectively, of the real and modelled structure, shows that the prediction of the dynamic response can be obtained with much more accuracy in the case of a single component than in the case of assemblies. Generally speaking, as the number of components in the assembly increases the calculation quality declines because the connection mechanisms among components are not represented sufficiently. Specifically for aircrafts, it is quite common that Frequency Response Functions (FRF) obtained via Ground Vibration Test (GVT) show a certain degree of discrepancy from the FRF calculated with the FEM, particularly across the sections where joining is discontinued. When this happens it is necessary to tune up the values of the dynamic parameters of the joints, to allow the numerical FRF to match the results of the experimental FRF. From a modelling and computational point of view, these types of joints can be seen as localized sources of stiffness and damping and can be modelled as lumped spring/damper elements. In this paper this is done by formulating an optimization problem. The approach has been applied to a FEM that mimics the rear fuselage of a commercial aircraft and the numerical results shows that the procedure is very efficient and promising.

Size optimization of shell structures considering several incomplete configurations

The need to increase the safety of structures has led to a more comprehensive studio of factors that influence it. The safety level required will depend on the responsibility associated to the structure functionality, being higher in those whose collapse could cause a large economic impact or loss of human life. Thus, this circumstance must be taken into account in the final sizing of the structure, even when the occurrence probability of the partial collapse is very low.

Survey of reliability analysis methods for design optimization of aircraft structures

Aircraft structures have to meet the requirements of safety and efficiency. Those requirements can be formulated as a mathematical optimization problem to define the most suitable configuration which minimizes the weight, satisfying the goals of performance and reliability. Design requirements are imposed as constraints, which guarantee that the optimum design fulfills these conditions. It is usual to define such constraints and also the variables as deterministic values. However, some of these values are best defined as random variables and so, an optimization procedure under uncertainty has to be considered. There are different alternatives in order to evaluate the reliability of the constraints. In this work, a survey of the performance of several reliability analysis methods applied to evaluate the constraints in an optimization procedure is presented. Two examples are selected to demonstrate the behaviour and performance of the methods when applied to different structural typologies.

An efficient approach to structural optimization of aircraft structures considering parameter variation

α = magnitude of the change in design variables β = new design variable (Vanderplaats’ formulation) e = relative error λ = buckling load factor σ = normal stress c = positive constant (Vanderplaats’ formulation) F = objective function g = design constraint i = design variable index j = active constraint index p = parameter ∆p = parameter increase r = inactive constraint index S = vector of feasible directions w = vertical displacement X = vector of design variables X = vector of optimum design variables Xaprox = vector of approximate optimum design variables

A Comparison Of Flutter Speed Of The MessinaBridge Considering Several Cable Configurations

The bridge over the Messina strait is an ambitious initiative started a few decades ago, which is likely to become reality in the near future. Several modifications have been made to the continuously changed preliminary design, so that the bridge is safe under a wide range of wind speeds. In this paper, a study of the significance of the cable configuration in terms of the number of cable planes and their location is presented discussing the relative efficiency of each of them.

Optimum Size, Position And Number Of Cables In Cable-stayed Bridges

A methodology to obtain the minimum weight of cables in cable-stayed bridges has been developed. The number of cables, anchor positions on the deck, the crosssectional areas and post-tensioning cable forces have been considered as design variables simultaneously in the optimization process. Two different strategies are proposed using both genetic and gradient-based optimization algorithms. Finally, the Rande Bridge (Vigo, Spain) has been chosen as the application example of both approaches.

Reliability-Based Optimization of the Stacking Sequence Layup in Post-Buckled Composite Stiffened Panels

This paper presents a methodology to carry out Reliability-Based Design Optimization (RBDO) in composite stiffened panels. The target is to maximize the reaction force that the panel can withstand before collapse, setting the shortening of failure as the probabilistic constraint. The design variables are the stacking sequence orientations of the composite plies while the random parameters are the elastic properties of the material. In order to predict the collapse load properly, post-buckling and progressive failure analyses are considered within the FE solver employed.