The Structural Integrity of Wall Cladding of Large Panel Systems

[摘要] The thesis describes the results of non-destructive tests carried out on eleven orthogonally reinforced concrete sandwich panels, for the determination of their dynamic characteristics. The objective of the present investigation was to determine through the dynamic response, the structural integrity of the sandwich panels. The main dynamic characteristic of the panels under consideration was their natural frequency. The test specimens had nominal dimensions of 175mm by 1800mm by 2400mm, consisting of two concrete leaves, which were 100mm and 50mm thick, respectively. The two leaves were separated from each other through a 25mm thick insulation layer of expanded polystyrene. The test specimens were similar to the one's used in the construction industry for the construction of large panel system dwellings erected in the late 1960s and early 1970s. The eleven specimens were different from each other in the type of constraint and connection present between the two leaves, and varied from a complete concrete connection around the perimeter to none at all. In addition to this connection around the perimeter, the two leaves were also connected to each other through a system of reinforcement ties, which varied from a minimum of one to a maximum of eight. For all test specimens, the 100mm thick concrete leaf was simply supported along the top and bottom 1800mm edge. Dynamic loads were imparted through either a sinusoidal vibrator or through the impact of a hammer blow. In addition to these dynamic loads the specimens were also subjected to an in-plane compressive load of 500kN, distributed uniformly along the 100mm thick concrete leaf. The main objective of the research was the establishment of damage location in a panel, through changes occurring in the natural frequencies. These changes in the natural frequencies were used to distinguish between the various structural differences in the panels. A numerical analysis was performed for all panels, through the finite element package, FLASH, to predict the natural frequencies and determine the expected mode shapes for the first six modes. It is shown that it is possible to determine the natural frequencies of the sandwich panels under investigation, when subjected to dynamic excitation through the means of a hammer blow. It is further concluded that, it is possible to determine through changes in natural frequencies, any major structural changes occurring in the panels, without resorting to the more cumbersome experimental determination of the mode shapes. At the same time it was established that for distinguishing between minor structural changes occurring in the panels, the natural frequencies alone, are not a good enough measure, as they are too closely spaced for the successive modes and are extremely difficult to distinguish form each other.

[发布机构] University:University of Glasgow

[关键词] Civil engineering