Experimental and Analytical Study of Reinforced Concrete Column and Core Shortening in a Tall Building.
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In tall concrete buildings, columns and core walls experience axial shortening due to combined effect of heavy loading, shrinkage and creep. If the stress distribution across the floor plan is disproportionate, columns and core walls within a single storey may shorten by different amounts. This differential can introduce extra loads and moments within elements and also induce distortion of attached service elements such as claddings, pipes, partitions, that leads to serviceability problems. A number of columns and core walls in a 80-storey building (Q1 Tower, Gold Coast, Australia) were instrumented during its construction. Axial shortening data of these vertical elements were collected during 3 year construction period. Regular measurement of shortening of columns/core walls was undertaken using a manual DEMEC measuring device in a systematic manner over pre-determined time periods. Laboratory tests were also conducted on the concrete delivered to the construction site. The properties examined (using standard test methods) include strength, elastic modulus, shrinkage and creep of the concrete. A comprehensive study on the prediction models of concrete properties related to axial shortening was conducted. The performance of major code models for prediction of the tested concrete properties was evaluated. The laboratory tested concrete results were compared against predicted values yielded by each model and the most accurate and reliable model was identified. In some cases, these identified methods are modified or regression lines are derived from test data and used instead to ensure optimum prediction accuracy. An axial shortening estimation method was developed. The method which incorporates a construction sequence simulation based on actual construction history of the Q1 Tower and several material models for the estimation of time dependent properties of concrete including a varity of code material models and a combination of modified/fitted models was used in the well accepted Age Adjusted Effective Modulus Method (AEMM) formulation to produce predicted value of axial shortening. Comparisons of measured and predicted axial shortenings of the building were then made. Performance of the adopted axial shortening prediction method when incorporated with different material models was also assessed. The best model combination was then identified. Sensitivity analysis of factors affecting axial shortening prediction was also conducted.
Master of Philosophy (MPhil)
Griffith School of Engineering
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