Jose Turmo

Structural system identification of cable-stayed bridges with observability techniques

Cable-stayed bridges are highly statically redundant, light and flexible structures. This complexity highlights the role of the structural system identification (SSI) method in the calibration of the actual properties of the simplified models of these structures. This study proposes the first application of observability techniques to SSI of cable-stayed bridges. This method enables to define which subset of actual structural variables should be measured on site to identify mechanical properties, such as Youngs modulus, area and inertia, or stiffnesses (EA and EI) of deck, pylon and stay cables. The effects of the inclination and inertia of the stay cables and the existence of pylon and deck cracking in the observability of different cable-stayed bridges are studied. The results obtained are validated by the models of actual cable-stayed bridges.

New tool to help decision making in civil engineering

Structural collapses have indirectly produced important progress in science. The last lesson learnt from structural collapses reveals the important role of polyrational systems of equations in the Civil Engineering field, as all problems in Physics and Engineering involving scale variables lead to systems of these equations. Since no efficient methods are known to solve this type of equations, a powerful and efficient method to multivariate polyrational equations using observability techniques is presented in this paper. It is pointed out that this method can be applied to solve different Civil Engineering problems. The information obtained by this tool can be used to assist decision making and risk management processes during maintenance and service life. As an example of its use, a structural damage detection problem is solved.

Numerical damage identification of structures by observability techniques based on static loading tests

Abstract This article proposes the application of the observability techniques to deal with damage detection in bridges from their structural response under static loading tests. Unlike previous works based on a symbolic approach to this technique, this article presents its first numerical application. With this aim, a novel algorithm is presented, which reduces the unavoidable numerical errors produced by the lack of precision of computers. To achieve an adequate accuracy in estimations, this numerical algorithm is complemented with another method to define the proper geometry of the corresponding finite element model. The comparison of the observability technique with other existing methods presented in the literature shows that the number of required measurements is significantly lower. Furthermore, contrary to other analysed methods, no information from the undamaged structure is required. The accuracy in estimations provided by the proposed method is very high as the differences with actual values are lower than 1%.

Solving Some Special Cases of Monomial Ratio Equations Appearing Frequently in Physical and Engineering Problems

We first show that monomial ratio equations are not only very common in Physics and Engineering, but the natural type of equations in many practical problems. More precisely, in the case of models involving scale variables if the used formulas are not of this type they are not physically valid. The consequence is that when estimating the model parameters we are faced with systems of monomial ratio equations that are nonlinear and difficult to solve. In this paper, we provide an original algorithm to obtain the unique solutions of systems of equations made of linear combinations of monomial ratios whose coefficient matrix has a proper null space with low dimension that permits solving the problem in a simple way. Finally, we illustrate the proposed methods by their application to two practical problems from the hydraulic and structural fields.

Impact of measurement errors in inverse analysis

During the first step in the development of any structural system identification method, the method should be validated by noise-free measurements in the first place. Nevertheless, this assumption is far from reality as the measurements in these tests are always subjected to the errors of measurement devices. To fill this gap, this paper analyzes the effects of measurement errors in a parametric structural system identification method: the observability method. To illustrate the symbolic approach of this method a simply supported beam is first analyzed in detail. This simulation provides the parametric equations of the estimates. Then, the effects of errors in a particular measurement, errors in all measurements, load locations are studied in this structure. Two additional examples of increasing complexity are also analyzed to show the effect of modelling errors on the estimates. A fluctuation of the observed parameters around the real values is proved a characteristic of this method. The results of these structures illustrate how important the effects of modelling errors are especially in areas with low curvatures.

Tensioning Process Update for Cable Stayed Bridges

Construction of cable stayed bridges is very challenging. These structures are extremely redundant and the effect of tensioning one cable has the effect of changing the stresses of the already installed cables. In order to achieve a targeted service state at the end of the construction process careful calculations has to be done by the contractor in order to ensure it. However, deviations arise between the modelling of the tensioning process and the actual results obtained on site. In order to adjust the final stresses in the cables, a final restress of the stays is unusually required. This re-stressing operation is usually done for the whole cable, as the strand by strand stressing technique used for the first stressing operations, cannot be used anymore. This last operation is costly, time consuming and has less accuracy, compared with the strand by strand tensioning techniques. The paper will present a method to control the tensioning process on site and to modify it according to the stresses measured in the cables at each stressing stage. In this way, the chances of requiring a restressing operation are diminished.