Manuel L. Romero

An optimum retrofit strategy for moment resisting frames with nonlinear viscous dampers for seismic applications

The dynamic response of a multi-story steel moment resisting frame (MRF) equipped with fluid viscous (VS) dampers and subjected to seismic loads is investigated numerically. The structure is retrofitted with two fluid VS dampers per story in its middle bay. Its dynamic response is analyzed when retrofitted with linear and nonlinear VS dampers. Two performance indices are developed in order to evaluate by means of a simple procedure the adequacy of each retrofitting option. The different options are evaluated and an optimum design is selected. The main objective of this numerical research is to build a simple methodology leading to an optimum retrofitting option with nonlinear fluid VS dampers. A secondary objective of the study is to compare the structure response retrofitted with linear and nonlinear VS dampers and finding an optimum retrofit strategy attending to two performance indices that are developed. The seismic behavior of a six-story steel structure is analyzed and it is found that the maximum force experienced by the dampers in the nonlinear case may be reduced in more than a 35% in comparison with the linear retrofitting case with a similar structural seismic performance.

Advances in the analysis of short span railway bridges for high-speed lines

The physical model based on moving constant loads is widely used for the analysis of railway bridges. Nevertheless, the moving loads model is not well suited for the study of short bridges (L⩽20–25 m) since the results it produces (displacements and accelerations) are much greater than those obtained from more sophisticated ones. In this paper two factors are analysed which are believed to have an influence in the dynamic behaviour of short bridges. These two factors are not accounted for by the moving loads model and are the following: the distribution of the loads due to the presence of the sleepers and ballast layer, and the train–bridge interaction. In order to decide on their influence several numerical simulations have been performed. The results are presented and discussed herein.

A parallel procedure for nonlinear analysis of reinforced concrete three-dimensional frames

The paper discusses the parallelisation of complex three-dimensional software for nonlinear analysis of R/C buildings structures. It presents a comparative study for handling the nonlinear response in different parallel architectures. The nonlinear finite element model adopts a fiber decomposition approach for the cross-section of beam elements to capture nonlinear behavior of concrete. The parallelisation strategy is designed regarding three items: the numerical stability of the nonlinear procedure, the parallel sparse equation solver and the application on heterogeneous hardware: dedicated shared memory machines or clusters of networked personal computers.

Fire resistance of axially loaded slender concrete filled steel tubular columns. Development of a Three-dimensional numerical model and comparison with eurocode 4

In recent years, concrete filled tubular (CFT) columns have become popular among designers and structural engineers, due to a series of highly appreciated advantages: high load-bearing capacity, high seismic resistance, attractive appearance, reduced column footing, fast construction technology and high fire resistance without external protection. In a fire, the degradation of the material properties will cause CFT columns to become highly nonlinear and inelastic, which makes it quite difficult to predict their failure. In fact, it is still not possible for analytical methods to predict with enough accuracy the behaviour of columns of this kind when exposed to fire. Numerical models are therefore widely sought. Many numerical simulations have been carried out worldwide, without obtaining satisfactory results. This work proposes a three-dimensional numerical model for studying the actual fire behaviour of columns of this kind. This model was validated by comparing the simulation results with fire resistance tests carried out by other researchers, as well as with the predictions of the Eurocode 4 simplified calculation model.

Comparison of a Three-Dimensional Numerical Model for Fire Resistance of Axially Loaded Concrete Filled Steel Tubular Columns with Eurocode 4

In this paper, the behaviour of slender axially loaded square and circular CFT columns exposed to fire is modelled using the finite element analysis package ABAQUS. A realistic sequentially coupled nonlinear thermal-stress analysis is conducted for a series of columns available in the literature. By means of this model, a comparison between fire resistance simulations results and experimental tests found in literature is made. Similarly, simulations results are compared to the Eurocode 4 simplified calculation model predictions. Comparisons show that whereas Eurocode 4 predictions are very conservative for both circular and square section CFT columns, the results obtained from the developed numerical model are much more realistic.

Optimal design of prestressed concrete hollow core slabs taking into account its fire resistance

Abstract Prestressed hollow core slabs are a concrete element widely used as construction floor product, which manufacturing process has greatly been improved in recent years. Several research studies focused on hollow core slab performance, mainly related to its fire behavior, have provided new limit states to be assessed throughout its life cycle. Therefore, the hollow core slab design needs to be reviewed to allow for these improvements, a process which may involve changes to its geometry. In order to deal with this review, modern computational optimization techniques offer an alternative approach to traditional structural product design procedure, mainly based on the engineers prior experience. This paper proposes a hollow core slab model (including variables and constraints) to develop heuristic search algorithms, such as simulated annealing, in order to find the most economical slab design including the fire resistant constraint and taking into account all available manufacturing technologies. The optimal designs obtained by this process save up to 20% in cross-section area compared with common circular void designs from market, which is taken as a comparison pattern. The results show that traditional designs are deficient when the fire resistant constraint is considered, so that precast manufacturers and machinery designers should use optimization techniques to modify their hollow core slab geometry.

Análisis no-linear por elementos finitos de un elemento viga-columna de concreto armado

En la construccion de estructuras de concreto el Concreto de Alta Resistencia presenta enormes ventajas, sobre todo en elementos sometidos a axiales de compresion importantes, como ocurre en el caso de columnas de edificacion o de pilas de puente. Los modelos teoricos que actualmente se utilizan para el diseno de las estructuras de concreto no habrian sido posibles sin la labor investigadora de caracter experimental llevada a cabo desde su invencion. El inconveniente de realizar ensayos experimentales es que son muy costosos, por lo tanto, frecuentemente no se realizan el numero de ensayos necesarios para poder predecir el comportamiento de las estructuras reales o para desarrollar modelos simplificados de analisis. Para lograr desarrollar modelos simplificados de analisis es necesario validar un modelo numerico que sea capaz de reproducir los mas fielmente posible el comportamiento de columnas reales ensayadas experimentalmente. En este articulo se describe el procedimiento de calibracion de un modelo numerico 2D utilizando el programa ATENA , Cervenka (1998) con 44 ensayos experimentales propios, el estudio detallado de los parametros influyentes en dicho modelo y de un analisis estadistico detallado que sirve para que se concluya que la herramienta numerica se ha calibrado y es capaz de utilizarse para modelar estructuras de concreto armado con comportamiento similar y poder desarrollar modelos simplificados de analisis.

New Advances in Parallel Computing for Structural Engineering Applied to Small and Medium Size Enterprises (SMEs)

The structural nonlinear analysis is not become a wide spread tool for the practical engineer due to the high computational cost. Recent arrival of performance based design codes, ATC-40 and FEMA-273, will pull up the use of practical nonlinear analysis. The encapsulation on the new language programming (OOP) and the improvement in the network communications systems may possible to program the resolution of the nonlinear analysis system with bigger level of complexity using high performance computing. In this paper new advances in how to introduce parallel computing to the small and medium size companies in Europe are presented.