Retrofitting of High Flowable Reinforced Concrete One–Way Damaged Slabs Exposed to High Temperature

Abstract

Exposure of reinforced concrete (RC) buildings to an accidental fire may result in cracking and loss in the loading capacity of their major components, columns, beams, and slabs. The damage that RC slabs receive under high temperatures is expected to be more greater as compared to other components; owning to the slabs' relatively high surface to volume ratio and to their shallow depth. It is a challenge for structural engineers to develop efficient retrofitting techniques that enable RC slabs to restore their structural integrity after being exposed to intense fires for a long period of time. In this research a laboratory tests are carried out to show the effect of using the Carbon Fiber Reinforced Polymers (CFRP) retrofitting to restore the load capacity of the one-way slabs after being subjected to different fire exposures (300, 500 and 700)0C temperatures and loading till failure. Experimental investigation was carried out on twenty one slab specimens , made of high flowable concrete, eighteen are retrofitted with CFRP sheets after burning and loading till failure while three are retrofitted with CFRP sheets after loading till failure but they are not exposed to fire. All slabs were tested in a simply supported span and subjected to two-point loading while the main variables were difference in temperature levels (300ºC,500ºC and 700ºC),different concrete compressive strength (20MPa, 30MPa and 40MPa) and different cooling method (gradually and sudden cooling conditions).The structural response of each slab specimen was investigated in terms of load-deflection,ultimate load carrying capacity and mode of failure and the results are compared with that of control specimens. The experimental results, generally, indicate that slabs retrofitted using CFRP sheets are restored flexural strength values nearly equal to or lower than those of the reference slabs, the retrofitted slabs exhibited larger deflection than the control slabs at ultimate loads.Retrofitting unburned slabs after loading regained from 94% to 98% of their original load capacity.Other slabs, slabs subjected to 3000C temperature regained from 71% to 84% of the load capacity of the original control specimens ,slabs subjected to (500)0C temperature regained from 60% to 78% of the load capacity of the original control specimens, slabs subjected to (700)0C temperature regained from 42% to 62% of the load capacity of the original control specimens. Most of the tested slabs failed by concrete crushing at mid span and partial debonding of certain retrofitting systems was also observed for a few cases.