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 distribution and time history of the concrete‐placement loads and the resulting formwork response depend on the equipment used for placing the concrete. The impact loads associated with the crane‐and‐bucket method of concrete placement are investigated. A number of factors affect the magnitude of the concrete load when emptying a bucket. These factors include 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 factors. The concrete‐flow rate from a bucket is modeled as a lognormal white‐noise random process. To verify the validity of the developed model, several lab experiments were performed using a $2.4m\times 2.4m(8\mathrm{ft}\times 8\mathrm{ft})$ formwork deck. The lab's overhead crane was used to lift the concrete‐filled buckets to various heights above the deck before discharging the concrete. Pressure and displacement transducers were attached to the formwork deck for measuring the load intensity and deck displacements.