Development of probability models for concrete formwork live loads
Failure of concrete structures during construction constitutes a significant percentage of construction failures. Formwork failure is among the major causes of concrete construction failures. One of the causes of slab formwork failures is overloading. The major slab formwork loads include dead, live, equipment impact and wind loads. In this study slab formwork live loads are investigated. In recent years, a trend has been developing toward placing design codes on a probabilistic bases. Developing probability-based design criteria for construction requires an extensive data bank of actual construction loads. In this study to collect sufficient data for developing probability-based live load models for multistory concrete building construction, thirty-two concrete building projects in twelve cities were visited and surveyed. In this survey, weight of objects considered as live loads were determined by the inventory method or direct weighing. In order to build a representative construction live load data-base, the survey included buildings with a wide range of characteristics. These characteristics included size, construction cycle time, number of floors, availability of storage space around the construction site, formwork system used, future intended use and slab design. The collected construction live load data were divided into two groups: Live loads on formwork before pouring the slab and live loads on newly poured slabs. Each live load group was studied and analyzed separately because of differences in the nature of these loads. The statistical moments of the collected loads for several averaging areas were calculated and appropriate probability models were fitted to the load data. A stochastic process was developed to represent the construction live loads. The parameters of the process were determined from the collected data. The developed probability model was used to determine the statistical moments and the distribution function for an equivalent uniformly distributed load that produces (statistically) the same forces in formwork members as the actual observed formwork loads.
Haitham Najib Ayoub,
"Development of probability models for concrete formwork live loads"
(January 1, 1992).
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