This paper presents a comparative study of using the modal curvature index and the modal flexibility index for damage localization in the cable-stayed Kap Shui Mun Bridge from the bridge global modal data before and after damage. Based on a precise and validated three-dimensional finite element model of the bridge, a series of damage cases associated with the deck are introduced in the simulation study. They are the damage occurring at the members within deck segments and the damage occurring at the support and bearing system of the deck. The damage indices are applied to determine the specific deck segment that contains damaged member(s). The simulation study is conducted with the following focuses: (i) performance comparison of the two indices in the absence of noise; (ii) tolerance of the two indices to noise; (iii) influence of the number of measured modal vectors on the identification accuracy of the two indices. The analysis results show that performance of the two indices is different for different damage types. The two modal indices are complementary to each other in damage indication. In general the flexibility index performs better than the curvature index for damage indication, especially in the case of damage occurring at the bearing system. For most damage cases, the flexibility index is better in anti-noise than the curvature index, and the curvature index is more sensitive than the flexibility index to the number of the measured modal vectors (degree of the modal incompleteness).
The experiment which based on the stress performance of unbonded and bonded prestressed concrete beam, has made a systematically research on the stress and strain variation law of pretressing tendon in the aforementioned reinforcement prestressed concrete structure. When the bonded prestressed concrete beam bearing load, there is a larger variation in stress and strain of prestressing reinforcement along the length. The maxima of stress and strain of prestressing reinforcement in bonded prestressed concrete beam appears in midspan, it is achieved the yield stress and yield strain, the minima appears in bearing, the stress and strain of prestressing reinforcement in bonded prestressed concrete beam is proportional to the distortion. The stress and strain of prestressed reinforcement in unbonded prestressed concrete beam is almost the same along the length.
This paper demonstrates a new abnormal index based on frequency change for structural health monitoring (SHM) which utilizes probability and statistics method. And it was introduced to analyze a steel frame. The results show it could indicate the abnormity of corresponding test cases clearly.
Based on the statistical probability of abnormal frequency offset, this paper puts forward a new structural damage alarm index. Demonstrating the feasibility of corresponding structural damage alarming method, this article introduces the index to analize a steel frame structure in frequency domain. The results show the abnormal index defined in sense of statistics indicates the abnormity of corresponding test cases clearly.
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