Análise dinâmica de uma passarela sujeita ao carregamento de pedestres

Abstract

Nowadays, with the development of engineering, mainly civil engineering, buildings are more slimmer and along. With that, comes the vibrating problems on the structures, caused by low frequencies of it that could cause the resonance effect, amplifying the vibrations. In particular case of footbridges, the resonance effect happens when the vibrating frequency of the structure reaches the walking frequency or the frequency from another activity the pedestrian may do. The footbridges cause physical discomfort when they get to the resonant state by the big vibrations that could, sometimes, make the cross impracticable or even collapse the structure. Many international institutes created their technical standards to regulate the construction of footbridges, proposing some evaluating parameters for users comfort. The mainly parameter of the standards is based on the calculation of the structure’s acceleration, as it is at AISC’s practical guide. Where the limit value of the acceptable acceleration vary according structure’s frequency and the structure’s usefulness, for example, hospitals or offices the tolerance to vibration is very low due the minimum vibration be very uncomfortable. With this, many mathematical models have been made to try to qualify the force generated by the human load on the structure. The most known is Murray’s model that is compound for harmonic series. The object of this work is make the analysis of vibration of a footbridge, bi-supported with crossbeams and longitudinal beams of steel and board of concrete, by national standard, the NBR 6118(ABNT, 2003), whose discretion the removal of 20% of natural frequency of the structure of the critical frequency. And the vibration analysis using as criteria the Practical Guide to AISC (American Institute of Steel Construction) whose criterion acceleration. The calculation of the acceleration is made with the structure submitted a forced vibration of the load indicated by AISC. The analysis of free and forced vibration are made through software SAP2000 (CSI, 2008), which uses finite element method.