DYNAMIC MODELING OF SLAB FORMWORK DURING CONCRETE PLACEMENT

The static and dynamic loads applied to hand-set slab formworks during the pouring of a concrete slab are investigated. The spatial distribu tion and time history of the concrete-placement loads and the resultin g formwork response depend on the equipment used for placing the concr ete. The impact loads associated with the crane-and-bucket method of c oncrete placement are investigated. A number of factors affect the mag nitude of the concrete load when emptying a bucket. These factors incl ude the height of fall, concrete slump, bucket-discharge rate, and the dynamic properties of the slab formwork. A single-degree-of-freedom, variable mass, dynamic model is developed for calculating the concrete -placement loads by taking into consideration the above-mentioned fact ors. The concrete-flow rate from a bucket is modeled as a lognormal wh ite-noise random process. To verify the validity of the developed mode l, several lab experiments were performed using a 2.4 m x 2.4 m (8 ft x 8 ft) formwork deck. The lab's overhead crane was used to lift the c oncrete-filled buckets to various heights above the deck before discha rging the concrete. Pressure and displacement transducers were attache d to the formwork deck for measuring the load intensity and deck displ acements.