Ricardo Hallal Fakury

Brazilian standards for steel structures fire design

The aim of this work is introduce to the international scientific community the recently released Brazilian Standards for the design of steel structures under fire situations. They are: ‘‘Steel Structures Fire Design’’ (NBR 14323/1999) and ‘‘Fire Resistance Requirements for Building Construction Elements’’ (NBR 14432/2000). The aim of structure fire design is to prevent the structure from collapsing, allowing enough time for safe evacuation of building occupants, safe fire fighting operations and reduction in damage to neighboring construction. NBR-14323 provides a simplified method for calculation of fire resistance design for steel structural elements. NBR-14432 presents prescriptive recommendations for minimum fire resistance time of construction elements. This Standard also waives fire resistance time requirements depending on building height and area, fire protection devices and occupancy. They also allow the use of alternative methods of fire safety engineering. r 2002 Elsevier Science Ltd. All rights reserved.

Finite element implementation for the analysis of 3D steel and composite frames subjected to fire

This paper presents a finite element formulation for the numerical analysis of three-dimensional framed steel, reinforced concrete or composite steel and concrete structures subjected to fire. Several specialized and commercial programs may be used for the analysis of structures in fire condition. Within this context, the purpose of this work is to present the steps taken to extend a previously developed static analysis procedure with beam elements in order to cope with the thermal and structural analysis of structures under fire action. Physical nonlinearity and material property degradation considering the temperature distribution are taken into account at the cross section level, which is divided into quadrilateral or triangular finite elements. Thermal strains are considered through the effective strain concept, and the resulting nonlinear system of equations is solved by the Newton-Raphson scheme. The accuracy and capability of the formulation to simulate the behavior of framed structures under fire action are assessed through comparison with various numerical and experimental results.

Eurocode structural fire design and its application for composite circular hollow section columns

The tabular structural fire design method for centrally loaded composite columns consisting of concrete filled steel circular hollow sections proposed in EN 1994-1-2:2005 (Eurocode 4: Design of Composite Steel and Concrete Structures - Structural Fire Design) is described here. A design procedure is then discussed, based on the determination of the temperature distribution in the cross sectional area and along the column length. A finite element based computer program is developed to implement the three-dimensional thermal analysis of different materials and geometries for given time versus temperature fire data. An example problem is shown, comparing the tabular method proposed in EN 1994-1-2:2005 and the method presented in this work.

Sobre a revisão da norma brasileira de projeto de estruturas de aço e estruturas mistas de aço e concreto, a NBR 8800

This paper starts with a historical account of the revision work being done on the Brazilian Standard for the design of steel structures and steel/concrete structures. This revision led to the September 2006 draft, here referred to as PR NBR 8800:2006. The paper then presents the basis for the development of PR NBR 8800:2006, its main guidelines and the main changes in relation to the valid Standard, released in 1986. Finally, the importance of having an up to date norm for the consistent advance of the steel construction in Brazil is highlighted.

The Challenges of Rehabilitating the Hercilio Luz Suspension Bridge

THE HERCILIO LUZ SUSPENSION BRIDGE, BUILT IN 1926, HAS BEEN OUT OF SERVICE SINCE 1991 DUE TO HIGH CORROSION LEVELS AND STRUCTURAL ELEMENT IMPAIRMENT. A COMPLETE REHABILITATION PROJECT WAS DEVELOPED. IT INCLUDES THE REPLACEMENT OF THE IMPAIRED ITEMS AND FOUNDATION STRENGTHENING. AN AUXILIARY STRUCTURE IS EMPLOYED TO SUPPORT THE CENTRAL SPAM DURING THE REHABILITATION PROCESS. A CAREFULLY STUDIED LOAD TRANSFER PROCESS, WHERE THE CENTRAL SPAN LOADING IS TRANSFERRED FROM THE EYE-BAR TOWARDS THE AUXILIARY STRUCTURE, IS PERFORMED. FOR THIS PURPOSE, A SYNCHRONIZED JACKING SEQUENCE IS EMPLOYED. THE JACKING SEQUENCE WAS PREDEFINED BY MEANS OF NUMERICAL MODEL ANALYSIS

Structural integrity assessment and rehabilitating of Hercilio Luz bridge

The Hercilio Luz suspension bridge, built in 1926, has been out of service since 1991 due to high corrosion levels and structural element impairment. A complete rehabilitation project was developed which included the replacement of the impaired items and foundation strengthening. For this, an auxiliary structure was employed to support the central span during the rehabilitation process. A carefully studied load transfer process, where the central span loading is transferred from the eye-bar towards the auxiliary structure will be performed. For this purpose, a synchronized jacking sequence will be used, which was predefined by means of numerical model analysis. All structural elements had their designs evaluated and some geometric changes were implemented. This paper presents all the methodology developed in the rehabilitation project of Hercilio Luz bridge, as well as the development stages up to the present date.

Structural Design Based on Performance Applied to Development of a Lattice Wind Tower

This paper studies the process of parametric and algorithmic design, integrating structural analysis and design for the generation of complex geometric structures. This methodology is based on the Performative Model, where the shape is generated using performance criteria. In the approach, the development of complex structures is only possible by reversing the process of thinking to generate the form with established parameters for geometry, material and loading aspects. Thus, the structural engineer no longer only participates in the evaluation phase but also appears in the early stages, creating a process of exploration and production of common knowledge among architects and engineers. To research performance-based design, the development of a conceptual lattice for a wind tower is proposed. Thus, a system is made to generate geometries using Rhinoceros software, the Grasshopper plugin, and the VB programming language, integrated with stress analysis through the Scan & Solve plugin.

A numerical model for concrete slabs under fire conditions

A numerical model for the behavior of concrete slabs in a fire is described. This model consists of a shell finite element, a damage constitutive model for concrete with steel reinforcement and the consideration of heat transfer through the thickness of the slab. An improved damage constitutive model for concrete at elevated temperatures has been implemented considering compressive and tensile behavior through an orthotropic compliance theory. The damage in compression is based on the concrete stress-strain relationships presented by the European Committee for Standardization. Several calculations have been performed to validate the improved model. The comparison with experimental tests and numerical results confirm the validity of the approach for reinforced concrete slabs subjected to large transverse displacement. Language: en

Flambagem lateral com torção em vigas com perfis de alma senoidal

A Finite Element model was developed in order to study the behavior of beams with sinusoidal webs, subjected to Lateral Torsion Buckling, taking into account residual stresses and initial imperfections. The numerical model was validated by comparison with four experimental tests. To start the analysis of the model, a linear buckling analysis is made to find the first eigenvalue and the correspondent buckling mode. The next step is to assign the buckling mode to the geometrical model and the initial imperfection to the maximum mode displacement. Then an incremental plastic analysis is done, taking into account large deflections, until the model is unable to take on any other load increments due to physical or geometrical degeneration. Comparisons between numerical and experimental results are included. Comparisons between the results of eight numerical analyses and the correspondent provisions of a procedure based on the Brazilian code NBR 8800 (1986) are also included. For these eight comparisons 6 models were chosen to reach instability in the inelastic range and 2 in the elastic range. The sinusoidal web was ignored for the calculation of the geometrical properties.

ANÁLISE EXPERIMENTAL DO COMPORTAMENTO DE BARRAS COMPOSTAS COMPRIMIDAS FORMADAS POR PERFIS TUBULARES CIRCULARES CONCÊNTRICOS LAMINADOS DE AÇO

Este trabalho apresenta um estudo teorico-experimental do comportamento de barras compostas axialmente comprimidas formadas por perfis tubulares circulares concentricos laminados de aco. O uso dessas barras e uma solucao inovadora para situacoes nas quais exista restricao de projeto quanto ao diâmetro maximo que pode ser adotado, ou que um unico perfil laminado nao atinja a forca resistente de compressao requerida. Este estudo inicia-se com a apresentacao do comportamento das barras comprimidas, abordando os aspectos da estabilidade estrutural, a influencia de imperfeicoes iniciais geometricas e de material, os procedimentos de dimensionamento normativos e o mecanismo de colapso. Foi apresentado o estudo numerico desenvolvido para os perfis tubulares circulares concentricos laminados de aco, tal como seu processo de montagem e seu procedimento de calculo. Na analise experimental, foram realizados ensaios de forca axial de compressao em barras compostas rotuladas nas duas extremidades, constituidas por dois e tres perfis tubulares concentricos, sem ligacao entre os perfis ao longo do comprimento e com ligacoes fixas e deslizantes, de modo a obter as respostas em termos de capacidade resistente e facilidade de montagem. Nessa etapa, foi desenvolvido um metodo para medir as imperfeicoes geometricas dos perfis que compoem o conjunto. A analise numerica foi realizada por meio de simulacoes via Metodo dos Elementos Finitos, utilizando o programa ABAQUS. Nessas simulacoes, para calibracao dos modelos numericos, foram consideradas as imperfeicoes iniciais geometricas e relacoes geometricas obtidas nos modelos experimentais. A formulacao proposta para o dimensionamento dos perfis tubulares circulares concentricos apresentaram valores sempre conservadores. Apos a validacao da calibracao, foi feita uma analise parametrica, variando-se as dimensoes da secao transversal dos tubos que compoem as barras compostas e sentidos das imperfeicoes geometricas iniciais desses tubos, com o intuito de investigar a influencia desses parâmetros no comportamento da barra composta e no valor da forca resistente.