A two-span RC slab that measures 6400mm×800mm×100mm with 3000mm spans and 200mm overhang on each end was tested to failure in the laboratory. UB sections were used as supports. The slab was designed according to the moment redistribution method with 11 N6 bars at 75mm centres for both positive and negative reinforcement. The slab was incrementally loaded at the middle of each span to different load levels to create crack damage using four-point loading. Twelve loading stages were performed with increasing maximum load level. Two load cells are used to record the static loads on left and right spans. The crack locations and lengths were monitored in addition to the displacement measurements. Four displacement transducers are located at two sides of the middle of each span to measure the deflection under the static load. Three sets of accelerometers with nine of them in each set are evenly distributed along the slab to measure the dynamic responses. The measured responses from the RC slab in different cracked damage states are analyzed using the wavelet transform (WT). The damping ratios and instantaneous frequency are extracted. The results show that the damping ratio and instantaneous frequency changes could be two good indicators of damage in the reinforced concrete structure.
In this paper, a dynamic method will be developed to identify the surrounding bedding conditions of an undersea
pipeline. The pipeline on the seabed is modeled as a simply supported beam on an elastic foundation. Two parameters
are used to describe the scour or free span of the pipeline: they are the central location of the scour or span and the width
of the scour or span. The study takes into account the dynamic interaction between the pipeline and the elastic
foundation. The parameters are determined from natural frequencies of the pipeline. The effect of the number of natural
frequencies and the measurement noise levels on the accuracy of the identification results of the pipeline bedding
conditions is studied. Numerical simulation shows that the method is effective and reliable to assess the bedding
conditions of the undersea pipeline.
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