Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014 Porto, Portugal, 30 June - 2 July 2014 A. Cunha, E. Caetano, P. Ribeiro, G. Müller (eds.) ISSN: 2311-9020; ISBN: 978-972-752-165-4 1095 ABSTRACT: Hollow-core slabs are very efficient structural members, since their voids allow a significant reduction of self- weight. Moreover, due to prestressing these slabs are able to be employed in large spans. With these advantages precast / prestressed hollow-core slabs are widely used in commercial and industrial buildings. However, for some combinations of span, thickness and materials properties, this structural system may be susceptible to excessive vibrations. In this paper a theoretical and numerical study on human induced vibrations in this type of structure is carried out. Initially a review of the dynamic loads induced by humans in activities such as walking is shown as well as acceptance criteria for human comfort. Then a parametric study on vibration sensitivity of typical structural configurations of hollow core slabs cores is developed through numerical simulations with the Finite Element Method. Some situations of interest including different spans, slab thickness and modulus of elasticity of concrete were evaluated and the vibration levels estimated. Finally the vibration levels were compared to applicable comfort levels suggested by international manuals and renowned authors. The vibrations levels were considered adequate based on a criterion of maximum dynamic displacements while inadequate according to existing limits for minimum frequency and peak acceleration. The contradiction between acceptance criteria and the occurrence of inadequate dynamic behavior for some of the evaluated slabs emphasize the importance of the continuity of this research. KEY WORDS: Hollow-core slabs, numerical simulations, human induced vibrations, comfort levels. 1 INTRODUCTION The increasing strength of construction materials as well as the frequent use of prestressing has enabled great advances in structural design and architecture of residential and office buildings. However, this development has also resulted in more slender structures, making them sometimes susceptible to excessive vibration. In the case of floors with hollow core slabs, the dynamic behaviour related to human activities is of special interest, once these elements may have natural frequencies close to those of human activities. Hollow-core slab, also known as voided slab, is a precast concrete flat slab with voids in its cross section (Figure 1). These slabs are widely employed in shopping malls, offices, parking garages, etc. Their design is normally focused in strength criteria rather than serviceability requirements. When the design load of the slabs is low, the slabs can be designed with a very high slenderness, and although they resist the loads, they may be inadequate from a dynamic point of view. Figure 1. Hollow-core slabs [1] The dynamic response of these structures is affected by several parameters at different degrees. Modifying their thickness, span and material properties may result in structures with different dynamic behaviours. In this paper, the influence of each of these parameters is evaluated trough a parametric study developed with the Finite Element Method. 2 BIBLIOGRAPHIC REVIEW 2.1 Hollow core slabs Hollow core slabs are the precast concrete element most used around the world, especially in North America and Western Europe. As other precast elements, hollow core slabs have some advantages, which include the reuse of forms, use of prestressed concrete, section with better use of materials, higher labour productivity, better quality control, reduction or absence of slab propping and fast assembly[2]. Specifically regarding the hollow core slabs, advantages that can be mentioned are the structural and economical efficiency as floor and roof systems. Besides this, the voids may be used for electrical or mechanical runs and distribute the heated air through the cores. Hollow core slabs also have an excellent fire resistance and sound transmission characteristics [3]. The hollow core slabs can be designed with or without the provision of topping concrete cast on site. The usual span varies from 5 m to 15 m and the cross section height goes from 150 mm to 300 mm. The relation between span/height can reach 50 [2]. In those cases, prestressing and high strength concrete are used. Figure 2 shows the development of hollow core slabs over the years. Parametric study on the vibration sensitivity of hollow-core slabs floors Lara Kawai Marcos, Ricardo Carrazedo Department of Structural Engineering, School of Engineering of São Carlos, University of São Paulo, Av. Trabalhador Sãocarlense 400, São Carlos, Brazil Email: [email protected], [email protected]
Parametric study on the vibration sensitivity of hollow-core slabs floors
Jun 26, 2023
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