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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.

Este artigo propõe um modelo semiempírico para estimar a resistência de conectores Crestbond (CR) contínuos e descontínuos, quando o cisalhamento do concreto governa o colapso da conexão. Esse modelo segue a tendência de padronizar as expressões para o dimensionamento de conectores constituídos por chapas de aço com recortes regulares, conhecidos no âmbito internacional como composite dowels, visto que esses dispositivos apresentam comportamentos semelhantes. A capacidade do concreto que preenche a abertura do conector em resistir ao cisalhamento é estimada, sob a perspectiva do uso de diferentes geometrias do conector, considerando fatores de ajuste nas equações já conhecidas e atualmente em uso. Para tal, o estudo teórico foi conduzido a partir de análises de ensaios de cisalhamento reduzidos por meio de simulações via elementos finitos. Por fim, o modelo proposto foi comparado com resultados de ensaios disponíveis na literatura, mostrando-se eficaz.

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This work presents the experimental evaluation of the dynamic behavior of Steel and concrete composite floors, from a human comfort point of view, when submitted to human walking. The structural model investigated was a real composite floor system under construction, with a total area of approximately 1300 m2. A preliminary numerical model was developed in order to guide the ideal positioning of excitation and instrumentation to be adopted in the experimental “in situ” evaluation. Next, free vibration tests were carried out to obtain the modal parameters of the structure. More than 180 forced vibration tests with excitation caused by a person walking at different step frequencies and directions were performed to determine de maximum structure’s response. The results found were compared with human comfort criteria recommended by national and international standards and design guides. Subsequently, a people quantity influence analysis on the dynamic response of the floor was carried out, where it was noticed that the increase in the number of users walking on the floor also increased the peak acceleration value. This fact emphasizes the need to carry out experimental evaluations considering the variation of people quantity on floor activity in order to evaluate the real scenario of human vibrations induced in the structure under service.

ResumoApresentam-se os procedimentos para dimensionamento de pilares mistos de aço e concreto do projeto de revisão da norma brasileira ABNT NBR 8800:1986, quando da atuação conjunta de força axial de compressão e momentos fletores. São, também, apresentadas as bases teóricas dos procedimentos, que têm como referências principais a norma européia EN 1994-1-1:2004 e a americana ANSI/AISC 360-05. Mostra-se, ainda, que os resultados fornecidos pelos procedimentos do projeto de revisão têm boa concordância com resultados mais precisos obtidos por uma análise pelo método dos elementos finitos. Palavras-chave:Estruturas mistas, pilares mistos, dimensionamento estrutural.

The maximum stress values determined for the circular and square sections were similar among specimens with the same interface area. At the bond interface, the highest stress values were observed in hourglass-shaped specimens.