Effects of Fire on the Strength of Reinforced Concrete Structural Members

Lateef O. Onundi^1, , M. Ben Oumarou² and Abba M. Alkali¹

¹Department of Civil and Water Resources Engineering, University of Maiduguri, Nigeria

²Department of Mechanical Engineering, University of Maiduguri, Borno State, Nigeria

Cite this paper:
Lateef O. Onundi, M. Ben Oumarou and Abba M. Alkali. Effects of Fire on the Strength of Reinforced Concrete Structural Members. American Journal of Civil Engineering and Architecture. 2019; 7(1):1-12. doi: 10.12691/ajcea-7-1-1

Abstract

This multidisciplinary research focuses on the effect of fire on structures due to the Boko Haram insurgency in Maiduguri, Northern Nigeria. It is aimed at giving a further contribution to understand the effect of fire with respect to the local aggregates, quenching methods and proposing an assessment methodology based on a suitable analytical procedure applied to reinforced concrete subjected to sustained fire. Cement, river sand, Bama gravel and water in standard proportion in accordance to BS1881 Part 101 were mixed to produce beams, slabs and cubes of different sizes and cured for 28 days. The samples were burnt in a designed fire simulation furnace using sugarcane bagasse as fuel with varying air velocities for 2 hours. Cooling of samples was carried out using water splashing, CO₂ powder fire extinguisher and air cooling methods before the compressive strength tests using a Seidner Compressive Testing Machine and Non-destructive test with Rebound Hammer. The scanning electron microscopy tests were carried out using a Phenom ProX scanning electron microscope for imaging and analysis to physically examine and determine the elemental micro structural redistribution and influence on the tested samples. As the temperature within the experimental set-up reaches 900°C, the temperature around the vicinity of slab, beam or cube reached an average of 500°C. The results of the investigations show that different cooling methods induce varying levels of deteriorating and significant effects on the final internal micro-structures as well as physical, mechanical and thermal characteristics of concrete. Results from the destructive and non-destructive tests show that losses of strength vary from a minimum of 37.73% to a maximum of 86.67 % in the samples investigated. The local aggregates used namely the river sand and the Bama gravel surely influenced the medium grade reinforced concrete behaviour when subjected to fire.

Keywords:
reinforced concrete fire structural members Bama gravel quenching method spalling strength loss

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