FERRO EMENT ROOFS AND FLOORS WITH LOST FORMWORK

Abstract

Various types of precast roofing and flooring units have been developed for construction of residential and industrial buildings all over the world. These have not proved to be popular in India, because of the low volume of their production and high self weight of components necessitating costly equipment for transportation and erection. Prefabricated ferrocement panels offers a variety of possibilities for use in many locations where economy, ease of construction and aesthetics are of prime importance. Most of the ferrocement housing applications have so far been directed towards low cost mass housing solutions particularly in Cuba. The floor and roof elements commonly used in various forms are channel section, Box shape, L-section, I-section etc. In the present work, a new type of roofing and flooring element in the form of a channel section with double protuding flanges on both sides, not requiring formwork has been investigated. This :bare element can be used straight way as roofing element. Alternatively an insitu concrete topping can be provided over these elements after filling the troughs with any light weight inert material to act as a flooring element. The -bare ferrocement element act as formwork for insitu concrete and it acts integrally with the insitu concrete In load resistance. The experimental investigation has been carried out by testing near prototype size ferrocement roof and floor elements. Three ferrocement roof elements were tested under uniformly distributed load (udl) placed over the entire top flange. Also three ferrocement floor elements were Joined at the level of the top flange and a thin cement concrete topping placed over the flanges and cured. •This composite section was tested under udl over the entire top flange and full span. The application of load was stopped when the load corresponding to the limit state of serviciability was achieved. The composite element was subjected to loading and unloading cycles reloaded and subjected to sustained loads upto service loads of short durations. The experimental investigation shows that the limit state of serviceability for ferrocement roof/floor element is governed by the maxmimum crack width. At the recommended crack width of 0.1 mm the span/deflection ratio is higher than the value of 250 permitted by I.S. Code 456-1978. Further the yielding of the reinforcement does not occur even at the load corresponding to a limiting span/deflection ratio of 250 for the specimen. The triple ferrocement floor elements under loading, unloading and reloading behaved as one single unit by undergoing downward deflection along the entire width at any cross-section. The span/deflection ratio was 473, which is above the value of 250. Placing the cement concrete on the top flanges results In lowering the deflection. The failure of the element is characterised by well distributed flexural cracks over the bottom flange and side webs. The sustained loading also leads to an increase in the width of cracks and the region of crack formation.