Flexural design of elevated slabs made of FRC according fib model code 2010: a case study

L Facconi, A Conforti, F Minelli, G A Plizzari (Universita degli Studi di Brescia)

Elevated concrete slabs are typically used as columns/piles supported floors in multi-story buildings or industrial facilities. The need to reduce construction time and costs has favoured the use of ever more advanced materials, like Steel Fiber Reinforced Concrete, as an alternative to conventional reinforced concrete. Many research studies and on-site applications have proven that steel fibers can be successfully used to totally substitute the main flexural reinforcement generally placed in conventional reinforced concrete slabs. 

However, in order to ensure the required minimum structural performance both at ultimate and serviceability loading conditions, the total removal of rebars requires the use of very high steel fiber contents (>70 kg/m3). However, the use of a proper combination of fibers and conventional rebars, generally known as Hybrid Reinforced Concrete (HRC), may represent a feasible solution to get the required structural performance by minimizing, at the same time, the total amount of reinforcement (fibers+rebars). 

This paper focuses on the design of HRC elevated slabs according to the design provisions for FRC structures reported by the fib Model Code 2010 and recently introduced also by the Italian structural design code (NTC 2018). A simplified design procedure based on a consolidated design practice is proposed.  Emphasis is given to the use of HRC for optimizing the slab reinforcement. A case study of an elevated slab made with synthetic Fiber Reinforced Concrete is used to show the effectiveness of the design procedure.

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