The wide application of corrugated steel web bridges has led to a rising demand on accurate tools to analyze this type of structures. Current computational models for these analyses are mainly related to those models using 2D (or 3D) beam elements, solid (shell) elements. Despite the modelling simplicity, beam models can predict the overall structural behavior but failed to provide a refined response on local areas. On the other hand, the elaborated models are better at capturing the local
response. However, they are faced with computation and convergence difficulties. To fill this gap, this paper investigates a new model to analyze the structural behavior of corrugated steel web bridges. In this model, the concrete slabs and corrugated steel webs are simulated by the grid composed of 3D beam elements. Specially, the folding effects of the webs are simulated by modifying the mechanical parameters of the longitudinal elements in the grids of beams. The performance of the model is studied by comparing the results from it and those from solid models. These comparisons include the vertical deflections in the longitudinal direction and the vertical deflections in the transverse direction at midspan and one-fourth point of the span. In addition, the
normal stresses and the shear stresses due to different loadings are investigated. The results indicate the accuracy and the applicability of this new model to analyze the corrugated steel web bridge.
The accumulation of progressive deterioration of structures might lead to the failure of structures. In order to avoid potential accidents, it is important to carry out condition assessment using structural system identification. This is based on the assumption that damage of structures can be reflected in the change of parameters. In every SSI method, measurement errors are introduced in the process of data collection and simulation errors also exist due to the inherent property of the algorithm used. The observability method has been proposed to deal with structural system identification under static loadings. Up to now, error analysis for this method has not been addressed yet. To fill this gap, this paper evaluate the effects of measurement errors and simulation errors on the observability method. The effects of measurement errors in a specific measurement and in all measurements are considered. The result indicate that the loading case and the location of the measrement is of primary importance. Also, rotations are less sensitive to errors than vertical deflections. On the
other hand, the error propogation during the identification regarding the recursive steps and the curvature of structure is also illustrated.
The rapid bloom of cable-stayed bridges has been propitiated by the development of erection techniques and improvements of construction materials. Nevertheless, the economic boom of the last decade has deflected attention from economic cost to iconic aesthetical appearance
increasing significantly designer’s freedom. This structural freedom has enabled the proliferation of a number of non-symmetric cable-stayed bridges. Despite of the number of built examples, the analysis of non-symmetrical cable-stayed bridges has not received considerable attention from the researchers. In fact, the effects of the main design parameters in the structural behavior of these bridges are not addressed in detail in the literature. To fill this gap, this paper studies the structural response of a number of non-symmetrical cable-stayed bridges. With this aim, a parametric analysis is performed to evaluate the effect of each of the main design parameters (the ratio between the main and the back span length, the pylon, the deck and backstay stiffnesses, the pylon inclination, and the stay configuration) of this kind of bridges. Furthermore, the role of the geometrical nonlinearity and the steel consumption in stays are evaluated.
One of the most important causes of the rapid progress of cable-stayed bridges in recent decades is the development of the construction techniques that made their erection possible. Cantilever method and temporary support method are the most common procedures to build such bridges. The temporary support method is the fastest way of building cable-stayed bridges because conventional construction techniques may be used. This fact simplifies the erection task and leads
to lower costs. However, when environmental factors or the requirements of the foundations or the sea or river crossing prevent the placement of temporary supports during construction, the cantilever erection method is commonly used. Focus on the research has been mainly devoted to the structural behavior of these structures under construction or service conditions, but the erection procedures and their calculations are not so studied. This paper aims to present practical tools to be used by the designer or the contractor for construction control of the tensioning process of the stays. Namely, a procedure to calculate the stress to be given to the first strand when the strand by strand tensioning technique is used and a procedure to update rationally the tensioning process of a cable stayed bridge when divergence between the foreseen stresses in the stays and the actual ones are noticeable.
This paper proposes a method for simulating the structural response of composite bridges with corrugated steel webs. Numerical modelling methods with various model dimensionalities have been widely used in
the simulation of this type of structure. Among these methods, one-dimensional finite element model can satisfactorily capture the general reponse but it fails to give the stress result in the structure, which is
necessary for refinement design. Also, the intensive computation and convergence issue of 3D solid model make this model less attractive, though it might be more capable of accurately simulating the local
response of composite bridges. The spatial grid model is proposed as a simple but accurate solution to model the general and local responses of the composite bridges with corrugated steel webs. In this model,
top slabs, bottom slabs and webs are characterized by orthogonal beam elements, wherein the stiffness of these beam elements are determined by the principle of equivalent displacements. For simplicity, the corrugated steel webs were modelled by steel plates of the same depth as the original webs. The folding effect of the corrugated steel webs was simulated by the reduction of the elastic moduli of the longitudinal element for webs. Thorough comparison was carried out between the proposed model and 3D solid model in terms of the vertical displacements, normal stresses, shear stresses under various loading cases. The shear lag effect in the concrete slabs was also investigated by the proposed model. The result verifies the applicability and precision of the proposed method in the refinement design of composite bridges with corrugated steel webs.
JUN, L.; Xu, D.; LOZANO-GALANT, J.; Nogal, M.; Turmo, J. International Association for Bridge and Structural Engineering Symposium p. 3261-3268 Data de presentació: 2017-09-09 Presentació treball a congrés
In structural system identification, measurement errors and simulation errors are closely related with the accuracy of the identification method. In this paper, the effects of these two types of errors on structural system identification by observability method(OM) are thorougly discussed. An example structure is analyzed step by step. For the very first time, the analytic expression of the flexural stiffness is given by the
observability method. Using this expression, the effects of errors in a particular measurement, random errors in all measurements are analyzed. Also, two examples are used to illustrate the effect of simulation errors of observability method. It is observed that the estimations fluctuate during the recursive process. Also, the accuracy of the estimations decreases sharply at null curvature zone. For this reason, it is highly recommended to adopt different load cases to alleviate this situation.
Lozano-Galant, J.A.; Lei, J.; Ramos, G.; Nogal, M.; Xu, D.; Turmo, J. Congreso de la Asociación Científico-Técnica del Hormigón Estructural p. 1-10 Data de presentació: 2017-06-22 Presentació treball a congrés
During the process of structural system identification, errors are unavoidable. This paper analyzes the effects of measurement and simulation errors in structural system identification based on observability techniques. To illustrate the symbolic approach of this method a simply supported beam is analyzed step-by-step. This analysis provides, for the very first time in the literature, the parametric equations of the estimated parameters. The effects of several factors, such as errors in a particular measurement or in the whole measurement set, load location, measurement location or sign of the errors, on the accuracy of the identification results are also investigated. It is found that error in a particular measurement increases the errors of individual estimations, and this effect can be significantly mitigated by introducing random errors in the whole measurement set. The propagation of simulation errors when using observability techniques is illustrated by two structures with different measurement sets and loading cases. A fluctuation of the observed parameters around the real values is proved to be a characteristic of this method. Also, it is suggested that a sufficient combination of different load cases should be utilized to avoid the inaccurate estimation at the location of low curvature zones.
This is the peer reviewed version of the following article: [Lei, J., Lozano-Galant, J. A., Nogal, M., Xu, D., and Turmo, J. (2017) Analysis of measurement and simulation errors in structural system identification by observability techniques. Struct. Control Health Monit., 24: . doi: 10.1002/stc.1923.], which has been published in final form at http://onlinelibrary.wiley.com/wol1/doi/10.1002/stc.1923/full. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Durante la construcción de los puentes de hormigón, los fenómenos
diferidos, tales como la fluencia y la retracción, pueden afectar significativamente la geometría y los esfuerzos de este tipo de estructuras. De hecho, estos fenómenos modificarán la fuerza del tesado de los tirantes en fase de servicio. Para compensar estas pérdidas pueden ser necesarias operaciones de retesado, con el consiguiente incremento del coste de explotación. En la literatura se han presentado un gran número de métodos para simular el proceso constructivo de los puentes atirantados. Todos estos métodos suelen asegurar que no se exceden los esfuerzos ni las deformaciones admisibles en los diferentes elementos. Sin embargo, algunos de estos métodos, concretamente aquellos basados en una simulación “hacia atrás”, no permiten incluir directamente los efectos de la retracción ni la fluencia. Para recrear los efectos de estos fenómenos diferidos se suele utilizar una simulación “hacia delante”. El principal problema de esta simulación es que tradicionalmente incluye complejos procesos iterativos que incrementan el coste computacional. Para resolver estos problemas, en este artículo se propone un algoritmo, Forward-Direct Algorithm, que permite simular el proceso constructivo de los puentes atirantados de hormigón incluyendo los fenómenos de retracción y fluencia. La principal ventaja de este método es que permite compensar las pérdidas de los tirantes a lo largo de la vida útil de la estructura por medio de las operaciones de tesado realizadas durante el proceso constructivo, permitiendo así evitar las operaciones de retesado en servicio. Para ilustrar la simulación de este método, se analiza una estructura basada en un puente real.
Tradicionalmente, el comportamiento de las estructuras se suele modelizar mediante modelos numéricos con propiedades mecánicas conocidas. Sin embargo, los valores reales de las estructuras construidas raramente coinciden con los teóricos y para garantizar la fiabilidad del modelo es necesaria su calibración. A este proceso se le conoce como identificación estructural. En este artículo se presenta la aplicación de la observabilidad, para estimar el valor las rigideces
de estructuras reales a partir de su respuesta estática. Este método permite resolver el sistema de ecuaciones polinomiales que aparece cuando se consideran rigideces desconocidas dentro de la matriz de rigidez de una estructura.
Even if solid circular columns are very popular, codes do not usually propose specific formulations for evaluating the shear strength of such structural types or if they do, they do so in a very simplified manner. Despite the fact that shear stresses in circular crosssections do not align with the shear reinforcement, codes do not propose any efficiency factor to take into account this misalignment. After a thorough bibliographic research on the previous studies on the matter, the shortage of work accomplished on the topic has been assessed and the unsolved problems identified. Hence, an analytical model for evaluating the contribution of the transverse reinforcement in concrete members of solid circular cross section is presented in this paper. Considering transverse reinforcement as a continuous mean, an innovative formula for evaluating the shear transferred by both circular and spiral reinforcement in solid members is presented. Such formula is simplified and some efficiency factors are proposed, which cover most of the practical cases to be faced in the design process.
Nowadays, new products are introduced in concrete mixes to reduce the effects of shrinkage, which are the main reason of most of early age cracking phenomena, especially when curing is not performed in accordance to best practices. The lack of a standardized methodology to quantify concrete cracking complicates the determination of the effectiveness of different solutions and comparison between them. This research presents an evaluation through images of the suitability of fibres and shrinkage-reducing admixtures to control early shrinkage cracking in slab-type concrete elements. The use of this technique has permitted quantifying the typical cracking parameters objectively and analyse probabilistically the average crack width. Results show a delay and reduction of cracking after adding shrinkage-reducing admixtures and fibres in concrete, especially 1kgm-3 of polymeric microfibres. The incorporation of these components directly into the mix modified the behaviour of concrete, reducing shrinkage cracking from the beginning of moisture losses.
This is the accepted version of the following article: [Ruiz-Ripoll, L., Barragán, B. E., Moro, S., and Turmo, J. (2016) Evaluation of the Techniques to Mitigate Early Shrinkage Cracking through an Image Analysis Methodology. Strain, 52: 492–502. doi: 10.1111/str.12191], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/str.12191/abstract
Observability techniques enable the structural system identification of static structures from a symbolic approach. The main advantage of this method is its deep mathematical foundation that enables the definition of parametric equations for the estimates. Nevertheless, this symbolic approach is not enough for the application of this method on actual structures. To fill this gap, this article presents the introduction into the symbolic structural system identification by observability techniques of a new numerical approach. This application includes the development of an algorithm that reduces the unavoidable numerical errors produced by the lack of precision of computers. 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.
Nogal, M.; Lozano-Galant, J.A.; Turmo, J.; Castillo, E. Structure and infrastructure engineering Vol. 12, num. 9, p. 1216-1227 DOI: 10.1080/15732479.2015.1101143 Data de publicació: 2016-09 Article en revista
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%.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Structure and Infrastructure Engineering on 2016, available online at: http://www.tandfonline.com/10.1080/15732479.2015.1101143
Diaz de Teran, J. R.; Haach, V.; Turmo, J.; Jorquera Lucerga, J. J. Advances in concrete construction Vol. 4, num. 3, p. 173-194 DOI: 10.12989/acc.2016.4.3.173 Data de publicació: 2016-09-01 Article en revista
his paper consists in a study of a new contructive sequence of road viaducts with Movable Scaffolding System (MSS) using numerical tools based on finite element method (FEM). Traditional and new sequences are being used in Spain to build viaducts with MSS. The new sequence permits an easier construction of one span per week but implies some other issues related to the need of two prestressing stages per span. In order to improve the efficiency of the new sequence by reducing the number of prestressing stages per span, two solutions are suggested in this study. Results show that the best solution is to introduce the 100% of the prestressing force at the self-supporting core in order to improve the road viaduct construction with movable scaffolding system by reducing execution time without increasing economic costs.
Diaz, J.R; Haach, V.; Turmo, J.; Jorquera, J. ASCE. Journal of bridge engineering Vol. 21, num. 9, p. 04016050-1-04016050-11 DOI: 10.1061/(ASCE)BE.1943-5592.0000831 Data de publicació: 2016-09 Article en revista
The current paper relates the state of the art of construction of viaducts with a movable scaffolding system (MSS). Two different procedures are introduced: the traditional sequence and the new sequence applied to some viaducts in Spain. The traditional sequence consists of two phases: first, concreting the bottom slab and webs, and then concreting the top slab of the deck. Once the first and second casting phases are completed, the total prestressing force is introduced. The new sequence consists of concreting a self-supporting core (i.e., the bottom slab, webs, and only a portion of the top slab). Once the self-supporting core has hardened, a partial prestressing force is introduced so that the scaffolding can be advanced to the next span; the central zone of the top slab is cast in a second phase. Both sequences are described here with their constructive peculiarities and issues.
Two different procedures of construction are introduced: the traditional sequence and the new sequence. The traditional sequence consists in a first casting phase that is formed by the lower slab and webs and a second casting phase that is formed by the top slab of the deck. Once the first and second casting phases are completed, the total prestressing force is introduced. The new sequence consists in a first casting phase or selfsupporting core that is formed by the lower slab, webs and top slab cantilevers and a second casting phase that is formed by the central zone of the top slab. Once the self-supporting core is completed, a partial prestressing force is introduced so that the scaffolding can advance to the next span. This paper studies if the new sequence is competitive in order to construct viaducts by comparing internal forces and stresses between the traditional sequence and the new sequence. The results confirm that the new sequence is competitive and some issues related to it to date can be solved or ignored.
Two different procedures of construction are introduced: the traditional sequence and the new sequence. The traditional sequence consists in a first casting phase that is formed by the lower slab and webs and a second casting phase that is formed by the top slab of the deck. Once the first and second casting phases are completed, the total prestressing force is introduced. The new sequence consists in a self-supporting core that is formed by the lower slab, webs and top slab cantilevers and a second casting phase that is formed by the central zone of the top slab. Once the self-supporting core is completed, a partial prestressing force is introduced so that the scaffolding can advance to the next span. Both sequences are described with their constructive peculiarities and issues related to the constructive easiness and cost reductions.
The stay forces in service of the cable-stayed bridges are usually defined in early stages of design, when the construction process has not even been conceived in detail yet. For this reason, the effects of the evolutionary erection of the superstructure are rarely included into the definition of these forces. Nevertheless, these effects might play an important role in the structural behavior both during construction and in service. To fill this gap, this paper studies the effects of the evolutionary erection of the superstructure into the
structural behavior of cable-stayed bridges. To this aim, a new method to include these effects into the definition of the OSS is proposed. This method is based on the minimization of the bending energy of the structure. Furthermore, to illustrate the effects of the evolutionary erection of the superstructure, this method is applied in steel cable-stayed bridges of growing complexity erected on temporary supports.
The unknown properties of a structure can be identified from different measurement sets. The selection of an adequate set is a key pretest decision in any Structural System Identification (SSI) method. Among the different SSI methods, the authors recently proposed the novel application of observability techniques to SSI. This technique can be applied regardless of the types of load as it shares the same system of equations as the stiffness matrix method. A hitch that does not allow the practical application of the observability
method is the fact that the measurement set selection needs to be carried out by a trial and error analysis, that is to say, without a systematic procedure. To fill this gap, this paper proposes an innovative tool, the observability trees, to address the selection of an adequate measurement set for adequate structural identification by observability techniques. This tool also illustrates graphically how the unknown estimates are successively calculated throughout the recursive process of the observability analysis. The trees are defined by two different elements: tree nodes (unknown variables that correspond with unknown estimates, as stiffness, areas or inertias) and tree branches (information measured in the nodes of the structure, such as rotations or deflections). The aim of the method is to define an observability flow that enables the connection of the pursued tree nodes. To illustrate the application of the observability trees, a set of beam bridges of growing complexity are analyzed in detail.
Turmo, J.; Lozano-Galant, J.A.; Mirambell, E.; Xu, D. International Association for Bridge and Structural Engineering Symposium p. 363-370 DOI: 10.2749/222137816819258717 Data de presentació: 2016-05-09 Presentació treball a congrés
Most codes assume a rigid interaction between concrete and steel in composite beams. This assumption assumes that there is no relative slip at the interface of both materials and Navier’s hypothesis is fully applicable. Nevertheless, all shear connections are flexible to some extent and therefore, full interaction is rarely achieved in practice. For this reason, partial interaction, with a relative slip at the interface, always appears in actual structures. The simulation of this relative slip is of primary importance because it affects both the deflections and the stresses in concrete and steel members. To carry out this simulation, a number of analytical and numerical models are proposed in the literature. The main problem of most of these models is that they cannot be easily applied for design work. To fill this gap, a two-dimensional finite element model is proposed. In this model, the different elements of the composite beams are simulated only by frame elements, easing its practical application. To validate the accuracy and the efficiency of the proposed model, a finite element model is verified against those results obtained by analytical equations available in the literature.
Nogal, M.; Lozano-Galant, J.A.; Turmo, J. International Association for Bridge and Structural Engineering Symposium p. 498-505 DOI: 10.2749/222137816819258933 Data de presentació: 2016-05 Presentació treball a congrés
The observability techniques have been proposed to deal with structural system identification under static loading tests. Up to now, this method has only been analyzed from a symbolical point of view. Despite the elegance of this approach, this mathematic analysis is far from being applicable in actual structures. To fill this gap, this paper presents a new observability procedure that combines both a symbolical and a numerical approach. To illustrate the potential of the proposed method, the observability technique is compared with two alternative methods presented in the literature. This comparison shows that, unlike to other analyzed methods, no information from the undamaged structure is required. Furthermore, the number of measurements required to be measured for damage detection is significantly reduced.
In this issue, the first authors, from Ireland, address the topic of decision making for infrastructure managers in a paper where the minimum level of confidence that is required in order to make a rational intervention decision is studied, and how uncertainty can affect it (Hanley and Pakrashi, 2016). The second paper (Oliveira Pedro and Reis, 2016) emphasises the importance of mastering the state of the art before starting to design, to build or to exploit a given infrastructure. Oliveira Pedro and Reis from Portugal give us a thorough list of the main landmarks on steel–concrete composite cable-stayed bridges over the last 50 years by analysing their main features (Figure 1). Furthermore, a contribution from Malaysia and Iran (Ghazvinei et al., 2016) deals with an interdisciplinary (hydrology, geotechnics and structures) threat to our bridges – abutment scour. This paper proposes a model that gives a reliable prediction of the scour of a protruding abutment for uniform sediment. Later in this issue, Pipinato (2016) shows the design steps and the outcome for an impressive 1·1-km-long multispan network arch bridge in Italy. A series of analyses of the different parameters that govern the solution has been done and the actual values of the final solution have been chosen in order to optimise the material grade, the structural shape and the structural detailing. The last paper presents a study by a team from India (Kulkarni et al., 2016). The primary aim of this paper is to see the applicability of the response reduction factor prescribed in the seismic codes for bridges with tall piers. Finally, we end this issue with a book review by Iain Gibb (2016) on the book Bridge Engineering Handbook, 2nd edition – Substructure Design (Chen and Duan, 2014).
Despite of the growing number of built examples, the analysis of non-symmetrical cable-stayed bridges has not received considerable attention from the researchers. In feet, the effects of the main design parameters in the structural behavior of these bridges are not addressed in detail in the literature. To fill this gap, this paper studies the structural response of a number of non-symmetrical cable-stayed bridges. With this aim, a parametric analysis is performed to evaluate the effect of each of the main design parameters (the ratio between the main and the back span length, the pylon, the deck and backstay stiflhesses, the pylon inclination, and the stay configuration) of this kind of bridges. Furthermore, the role of the geometrical nonlinearity and the steel consumption in stays are evaluated.
Despite of the growing number of built examples, the analysis of non-symmetrical cable-stayed bridges has not received considerable attention from the researchers. In fact, the effects of the main design parameters in the structural behavior of these bridges are not addressed in detail in the literature. To fill this gap, this paper studies the structural response of a number of non-symmetrical cable-stayed bridges. With this aim, a parametric analysis is performed to evaluate the effect of each of the main design parameters (the ratio between the main and the back span length, the pylon, the deck and backstay stiffnesses, the pylon inclination, and the stay configuration) of this kind of bridges. Furthermore, the role of the geometrical nonlinearity and the steel consumption in stays are evaluated.
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.Theconsequence 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 algorithmto 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.
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.
This paper presents a finite element model for the analysis of composite beams with partial interaction. In this model, the elements of the composite beams are modeled by six different types of frame elements. Compared with other methods presented in the literature, the main advantages of the proposed method are as follows: (1) intuitiveness, as the different elements of the model present a close and easy to understand relation with the structural behavior of the composite beam; (2) applicability as the method directly provides useful information for the design work; (3) versatility and generalization in dealing with any combination of loading and boundary conditions (Furthermore, the proposed model enables the analysis of statically indeterminate structures, tapered beams as well as structures with non-uniform shear connector distributions.); (4) easy elaboration of models; and (5) possible widespread use of the model, as the proposed method can be implemented in any structural software. To validate the accuracy and the efficiency of the proposed model, a set of FEMs are verified against those results obtained by analytical equations available in the literature for different boundary and loading conditions. Furthermore, a set of parametric studies are performed to investigate the effects of the size of the FEMs along with the influence of the connection stiffness on the behavior of composite beams with different I beams.
In a staggered erected cable-stayed bridge made of concrete, time-dependent phenomena effects might play an important role in both its geometry and its stress state. In fact, because of these phenomena stays will indeed lose force. To compensate these loses, one or two re-stressing operations are traditionally planned during the life time of long span cable- stayed bridges made of concrete. These re-stressing operations might be technologically challenging and always imply additional costs. To guarantee that allowable stresses and deflections are not exceeded during erection, a number of simulation methods are presented in the literature. Some of these methods, concretely those based on a backward simulation approach, fail addressing the effects of the time-dependent phenomena. To simulate these effects, methods based on the forward simulation approach are traditionally followed. Nevertheless, the main trade-off of these algorithms is that their computation is based on complex iterative processes that make simulation more time consuming. Furthermore, these methods are not able to avoid the need of additional re-stressing operations in service to prevent the effects of the time-dependent phenomena.
To fill all these gaps, a new simulation algorithm, the Forward-Direct Algorithm (FDA), is formally presented in this paper to simulate the construction process of cable-stayed bridges including the time-dependent phenomena effects. This algorithm takes advantage of the unstressed length of the stays concept to carry out a computationally efficient simulation based on an innovative direct simulation approach. The major advantage of this algorithm is the fact that the prestressing operations during construction can be defined to avoid the need of additional re-tensioning operations in service. To illustrate the creep and shrinkage effects, the proposed algorithm is applied to a real cable-stayed bridge.
Traditionally, the structural response of a bridge is modelled by simplistic physics-based models in which the mechanical and geometrical properties are assumed as known. Nevertheless, this is not the case in most actual structures where the values of the actual properties are unknown due to uncertainties in the materials, in the construction methods or in the stress state. In some cases, a calibration of the computer models using monitoring information of the actual structure is required to improve the accuracy of the predicted structural response. To carry out this task Structural System Identification (SSI) methods can be used.
Recently, the authors proposed a promising static SSI method based on observability techniques. This method addressed the problems appearing when unknown parameters are assumed into the stiffness matrix of a structure. The observability method was efficiently applied to deal with simple structures, such as single and multiple span beams. Nevertheless, the presented works did not address the peculiarities appearing in complex structures with different load-bearing elements, such as cable-stayed bridges.
To fill this gap, this paper proposes the first application of observability techniques to deal with the SSI of cable-stayed bridges. This work enables to define which set of deflections or rotations should be measured on site to identify a certain set of unknown mechanical properties in the deck, the pylon and the stay cables. A set of academic examples, of growing complexity, are used to explain the role that the inclination and cracking of the load-bearing elements of a cable-stayed bridge plays in the SSI by observability techniques. The results obtained in these academic structures are validated by more complex models of real cable-stayed bridges.
In last years, the traditional blackboard teaching has been supplemented by visual aids like slide projectors and videos. The phenomenal growth of the Internet has brought in new teaching media, such as E-learning. Online courses and multimedia material over the Internet open the educational experience up to distant students without schedule restrictions, making E-learning an attractive option especially for professionals. Nevertheless, the overwhelming amount of material currently available might complicate the offer selection. Furthermore, internet globalization makes that quality levels of these materials might differ significantly. Aware of these problems, IABSE created the E-Learning board to address conveniently the online learning in structural engineering. Recently, the Association has created a new platform that aims to become a leader in quality online education. As a way to promote the use of this platform, the E-learning board proposes a debate focused on how the future of structural engineering education is linked with the different kinds of E-learning in both academia and industry training.
Castillo, E.; Lozano-Galant, J.A.; Nogal, M.; Turmo, J. Journal of civil engineering and management (Spausdinta) Vol. 21, num. 6, p. 689-697 DOI: 10.3846/13923730.2014.893904 Data de publicació: 2015-08 Article en revista
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.
Ruiz-Ripoll, L.; Shah, S.; Barragán, B.E.; Turmo, J. Journal of materials in civil engineering Vol. 27, num. 7, p. 04014202-1-04014202-7 DOI: 10.1061/(ASCE)MT.1943-5533.0001163 Data de publicació: 2015-07 Article en revista
The use of self-consolidating concrete (SCC) has become more prevalent due to its economic and technological advantages over other types of concrete. Nevertheless, issues relating to casting and placement hinder its widespread use. One of the primary concerns of using SCC is related to its high formwork pressure, which affects any type of structural element, whether it is precast or cast on site. This study aimed to make correlations between different parameters obtained through slump flow and shear rheological tests in order to determine what the implication would be on the evolution of formwork pressure for five typical precast SCC mixes. The parameters were slump flow diameter, spreading rate, yield stress, plastic viscosity, and rate of structural rebuilding (stress relaxation). In addition, the advantages, from the point of view of cost and safety, of incorporating nanoclays and viscosity-modifying admixtures in SCC to reduce initial pressure and increase rate of pressure drop to optimize the formwork design were demonstrated.
One of the first steps in the design of any structure consists on carrying out a simulation of its construction process guarantying that the safety thresholds are not exceeded on site. In the case of statically redundant structures, such as stayed-structures, this simulation is subjected to a number of computational difficulties. Traditionally, the simulation of the construction process of a cable-stayed bridge might be carried out from two alternative simulation approaches: the Backward and the Forward approach. In these two methods changes in geometry, boundary conditions and applied loads throughout erection are successively added to the preceding (forward simulation) or the following (backward simulation) construction stage, by the superposition of stages principle. The application of this principle is the main inconvenience of these two simulation approaches because it increases the computation time. Furthermore, intermediate stages cannot be directly analyzed. To solve all these problems a new algorithm, the Direct Algorithm, is presented in this paper to deal with the simulation of the construction process of steel cable-stayed bridges. To speed up the computation, this algorithm takes advantage of the unstressed length concept. This assumption enables an innovative direct simulation that does not require the application of the superposition of stages. The proposed algorithm is indicated for optimization processes and simulation of changes in the tensioning process of steel cable-stayed bridges. Furthermore, this methodology is so simple that it can be implemented in any computer software. After presenting the main assumptions of the Direct Algorithm, a cable-stayed bridge is analyzed. Finally, the obtained results are compared with those provided by two different methods in the literature.
This paper proposes an innovative method for selection of measurement sets in static parameter identification of concrete or steel bridges. This method is proved as a systematic tool to address the first steps of Structural System Identification procedures by observability techniques: the selection of adequate measurement sets. The observability trees show graphically how the unknown estimates are successively calculated throughout the recursive process of the observability analysis. The observability trees can be proved as an intuitive and powerful tool for measurement selection in beam bridges that can also be applied in complex structures, such as cable-stayed bridges. Nevertheless, in these structures, the strong link among structural parameters advises to assume a set of simplifications to increase the tree intuitiveness. In addition, a set of guidelines are provided to facilitate the representation of the observability trees in this kind of structures. These guidelines are applied in bridges of growing complexity to explain how the characteristics of the geometry of the structure (e.g. deck inclination, type of pylon-deck connection, or the existence of stay cables) affect the observability trees. The importance of the observability trees is justified by a statistical analysis of measurement sets randomly selected. This study shows that, in the analyzed structure, the probability of selecting an adequate measurement set with a minimum number of measurements at random is practically negligible. Furthermore, even bigger measurement sets might not provide adequate SSI of the unknown parameters. Finally, to show the potential of the observability trees, a large-scale concrete cable-stayed bridge is also analyzed. The comparison with the number of measurements required in the literature shows again the advantages of using the proposed method.
Cable-stayed bridges can be rarely built on a single construction stage and staggered construction is commonly used. The effects of this staggered construction are not only economical as they might also play an important role in the structural behaviour in service. Despite of this importance, these effects are rarely included into the definition of the structural response in service. In order to fill this gap, this paper deals with the effects in service of the staggered erection of steel cable-stayed bridges built on temporary supports. To do so, a criterion based on the minimization of the bending energy in terms of stay forces is applied to several cable-stayed bridges. This study shows the importance of the existence of the pylon-deck connection as well as the number and location of both construction joints and temporary supports during staggered erection.
Lozano-Galant, J.A.; Ruiz-Ripoll, L.; Paya-Zaforteza, I.; Turmo, J. Baltic journal of road and bridge engineering Vol. 9, num. 4, p. 241-250 DOI: 10.3846/bjrbe.2014.30 Data de publicació: 2014-12 Article en revista
In current practice, the effects of the evolutionary erection of cable-stayed bridge superstructure are rarely included into the simulation of its tensioning process. In fact, stay forces in service are usually defined in early stages of design, when the construction process has not even been conceived in detail yet. In order to fill this gap, the effects of the evolutionary erection of cable-stayed bridge superstructure throughout the tensioning process are studied in this paper. This study is focused on steel cable-stayed bridges erected on temporary supports. For the very first time a new criterion to include the effects of the evolutionary erection of cable-stayed bridges into the definition of the stay forces in the service state is presented.
The time-dependent phenomena effects might play an important role in the structural behavior of a cable-stayed bridge during construction and in service. In fact, because of these effects the target state of stresses (Objective Service Stage, OSS) can only be achieved at a certain target time. In the literature, a number of software have been presented to study creep and shrinkage effects during cantilever erection of cable-stayed bridges. Nevertheless, the effects of these phenomena in the alternative erection technique, the temporary support erection method, have received little attention. Furthermore, none of the presented software are able to: (1) Define a determined OSS for a given time including the time-dependent phenomena effects and the evolutionary erection of the superstructure. (2) Simulate the construction process assuring the achievement of a given OSS without the need of an overall iterative process taking into account time-dependent phenomena. (3) Provide the prestressing sequence in such a way that no additional tensioning operations are required to correct creep and shrinkage effects in service. To fill all these gaps, a new algorithm, the Forward-Direct Algorithm (FDA), is formally presented in this paper to simulate the construction process of cable-stayed bridges built on temporary supports. The main innovation of this algorithm consists of introducing the time-dependent phenomena effects into the unstressed length of the stays concept to calculate the prestressing strains to be introduced during the last re-tensioning operation. The application of the unstressed length concept has major advantages both in the simulation (as the OSS can be achieved without any overall iterative process) and in service (as re-tensioning operations to correct time-dependent phenomena effects can be avoided). To illustrate the creep and shrinkage effects during the construction and in service the FDA is applied to a real cable-stayed bridge. Furthermore, an analysis to define the optimum time to achieve the OSS is presented.
In order to complete the design of any structure, an adequate simulation of its construction process is required. This simulation tries to guarantee that the structure can be built safely, that is to say that safety thresholds are not exceeded during the construction stages. In the case of cable-stayed bridges, simulation procedures must be prepared to deal with the computational difficulties derived from their statically redundancy.
Traditionally, the simulation of the construction process of a cable-stayed bridge is carried out from two alternative simulation approaches: the Backward and the Forward approach. In these two methods structural changes produced during erection are successively added to the preceding (forward simulation) or the following (backward simulation) construction stage. This superposition of stages is the main trade off of these methods because it increases the computation time. Furthermore, these approaches do not enable the direct simulation of intermediate construction stages.
To solve these problems the Direct Algorithm (DA) is presented in this work to deal with the simulation of the construction process of cable-stayed bridges built on temporary supports. To speed up the computation, this algorithm takes advantage of the unstressed length of the stays concept. This assumption enables an innovative direct simulation of the construction process that does not require the superposition of stages. The DA is indicated for optimization processes and simulation of changes in the tensioning process of cable-stayed bridges. Furthermore, the DA is so simple that it can be implemented in any computer software.
The structural response of any structure is traditionally predicted by simplistic physics-based models. In these models the mechanical and geometrical properties are assumed as known. Nevertheless, this is not the case in most actual structures where the values of the actual properties (such as axial or flexural stiffness) are unknown due to uncertainties in the materials, in the construction methods or in the stress state. In some cases, a calibration of the computer models is required to improve de accuracy of the predicted structural response. To carry out this task Structural System Identification (SSI) methods can be used.
In this paper, a new parametric method for SSI from static excitation response is proposed. This method is based on the observability of the structure, understanding as such the problem of identifying which is the subset of characteristics of the structure, such as Young's modulus, area, inertia, and/or products of them (axial or flexural stiffnesses) that may be uniquely determined when a subset of deflections and forces at nodes is provided. This method has lead to the development of a powerful mathematical tool to deal efficiently with polynomial systems of equations with a number of applications in many fields of science and engineering.
To illustrate the applicability of the proposed method, the analysis of the SSI of two structures of growing complexity is presented
The construction of both medium and long span precast concrete segmental bridges is widely spread throughout Spain. Usually, the segments have multiple-keyed epoxy joints, and are assembled by internal prestressing. Yet, there is a more recent type of bridge with dry joints and external prestressing. In these last ones, shear is transferred through physical support between keys and friction between faces of the compressed joint. This shear force is evaluated using friction coefficients from tests, where joints were subjected to service compressive stresses. However, normal stresses at ultimate limit state can reach much higher values. Hence, the friction coefficient used currently to design segmental concrete bridges is an extrapolation of the experimental values. It is assumed that the value advocated is the same for any normal stress level and any concrete type, although the roughness of their flat surfaces is different in each case.
Nowadays, the absence of friction data for both segments made out of ultra-high strength and self-consolidating concrete, and the very few tests performed on high strength concrete, complicate the innovation of precast segmental bridges. The optimization of their design and construction is also affected by the lack of standards for mix designing ultra-high strength concrete with local materials, and for quantifying formwork pressure due to self-consolidating concrete.
This doctoral thesis presents a simple experimental method for measuring friction coefficient between precast segments based on push-off tests. Flat dry joints of six concrete types (conventional, self-consolidating, high strength, high strength self-consolidating, high strength fibre reinforced, and ultra-high strength concrete) were tested under two confining pressure levels. The combination of both parameters provided friction values for conventional and high performance concrete subjected to normal stresses of around 50 and 100% of the ones registered at ultimate limit state. All concrete tested were made with local materials. For this reason, this work also provides a mix design procedure to achieve ultra-high performance concrete with compressive strength above 150 MPa at industrial production. It consisted of the modification of the mix proportions according to the results obtained after applying the trial-and-error techniques at distinct scales.
The possibility of using self-consolidating segments in this bridge type led to analyse the influence of the mix design on the evolution of formwork pressure. This doctoral thesis contributes to understand better which materials can achieve a balance between superior fresh properties of self-consolidating concrete and low lateral pressure build-up. Five typical precast self-consolidating mixes were subjected to slump flow, rheological and thixotropic tests. As a result, slump flow diameter, spreading rate, yield stress, plastic viscosity, and rate of structural rebuilding (stress relaxation) were measured. The correlations made between these different parameters allowed estimating the implication of water content, nanoclays and viscosity-modifying admixtures on the development of lateral pressure and its rate of pressure drop.
The results of each test were compared with standards and recommendations and other research for corroborating the data and information used so far, for determining their structural safety, and for improving and completing current design codes. From the points of view of cost, time and safety, all this research contributes to promote the use of high performance concrete, and to optimize the design and the construction of segmental bridges, especially precast viaducts built span-by-span.
LOZANO-GALANT, J.; Nogal, M.; Castillo, E.; Turmo, J.; Paya-Zaforteza, I. Congreso Internacional de Estructuras: Congreso de la Asociación Científico-técnica del Hormigón Estructural Data de presentació: 2014-06-03 Presentació treball a congrés
En este artículo se presenta la aplicación de un nuevo método para la detección de daños en estructuras a partir de su respuesta estática. Este método aplica las técnicas de observabilidad para resolver el sistema de ecuaciones que aparece cuando se consideran rigideces
desconocidas dentro de la matriz de rigidez de la estructura. Esta aplicación ha permitido desarrollar una potente herramienta para resolver sistemas de ecuaciones polinomiales con múltiples aplicaciones en numerosos campos de la ciencia y la ingeniería. El método de la observabilidad se ha comparado con otros métodos de detección de daños propuestos recientemente en la literatura. Esta comparación muestra las numerosas ventajas de la utilización del método de la observabilidad y recomienda el uso de esta metodología para detección de daños en estructuras.
LOZANO-GALANT, J.; Ruiz-Ripoll, L.; Paya-Zaforteza, I.; Xu, D.; Turmo, J. Congreso Internacional de Estructuras: Congreso de la Asociación Científico-técnica del Hormigón Estructural Data de presentació: 2014-06-03 Presentació treball a congrés
En este artículo se presenta el Algoritmo Directo (“Direct Algorithm”, DA) para simular el proceso constructivo de puentes atirantados sobre apoyos provisionales. Este algoritmo está basado en una innovadora simulación directa de las etapas constructivas que no requiere de la aplicación del principio de superposición. Para ello se utiliza el concepto de longitud sin tesar de los tirantes (“unstressed lenght”). Dada su eficiencia computacional, entre las aplicaciones del algoritmo
directo destaca su aplicación en procesos de optimización. Además, el DA puede implementarse fácilmente en cualquier programa de cálculo. Tras presentar las características del algoritmo, sus resultados se han comparado con los obtenidos por otros métodos presentados en la literatura en un ejemplo real.
Most of the methods presented in the literature to define the target service stresses (Objective Service Stage, OSS) of cable-stayed bridges rarely include the time-dependent phenomena effects. Nevertheless, especially in concrete structures, this assumption might be on the unsafe side because time-dependent phenomena usually modify service stresses. To fill this gap, this paper studies the time-dependent phenomena effects into service stresses of concrete cable-stayed bridges. After illustrating the important role of these phenomena in an asymmetrical cable-stayed bridge without backstay, a new method to include their effects into the OSS is presented. An important issue to be considered in this method is the target time in which the OSS is defined to be achieved. The application of this method to two different structures showed the convenience of defining the OSS to be achieved at early times because that way the envelope of service stresses is reduced.