Flexural Stiffness of Normal and Sandwich Reinforced Concrete Beam Exposed to Fire Under Fixed Loading

Abstract

This study focuses on the experimental investigation of normal and sandwich reinforced concrete beam exposed to fire in order to evaluate their flexural stiffness. Two beams specimen of 200×300×4000 mm have been cast and tested under flexural loading. The first one has been a normal concrete beam (N) and the second one has been a sandwich concrete beam (SW) with 50 mm skin thickness and 200 mm core thickness. The skin compressive strength of 25 MPa and the core compressive strength of 15 MPa have been considered. The skin strength has been also applied to the N beam. The beams have been reinforced with a plain bar of 3ϕ12 as a tensile reinforcement and 2ϕ10 as compression reinforcement. Both the tensile and the compression reinforcement have yield strength of 300 MPa. The beams have been tested in a full-size furnace under standard fire testing. Nine thermocouples for measuring temperature have been mounted. An LVDT, which has been protected by fire-resistant material, has been placed at the center of the beam to measure the deflection. The 8.63 kN load has been employed at 1/3 span of the beam. Test results have showed that the flexural stiffness of the beam strongly affected by the accumulative temperature representing temperature and firing time. The strength of the N beam drops significantly after 15 minutes of firing and the beam strength has been totally lost. The firing of 45 minutes has needed to decrease the strength of the SW beam then has decreased gradually until 120 minutes of firing.
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