Study On Fire Resistance Of Reinforced Concrete Beams Strengthened By External Steel Plates

The external steel plate reinforcement method has been widely used as a reliable technology for strengthing and repairing of reinforced concrete structures due to its advantages of convenient construction,low cost,space saving,and good reinforcement effect.Research results have indicated that,the epoxy resin between the steel plate and concrete will have serious deterioration of mechanical and bond properties at high temperature.The anchoring plate reinforcement method,while resisting the stripping of the steel plate and the deterioration of the bonded properties at high temperatures,has been improved.However,under the fire conditions,the reinforced steel plate still faces the risk of serious degradation of the mechanical properties of steel plate,which could result in a sudden collapse when the plate without fire protection.Therefore,a more complete understanding of the fire behaviors of reinforced concrete(RC)structures with external steel plates is required.In this paper,the fire resistance of full-scale RC beams strengthened with external steel plate exposure to fire is carried out,the effects of different reinforcement methods,anchor materials,and different fire protection measures on the fire resistance of beams strengthened with external steel plates are discussed.The main research works are included as follows:Two groups of eight full-scale RC beams strengthened with steel plate were tested under fire condition.The methods of reinforcement were bonded steel plate system,direct-shear anchorage system,and conventional anchorage system,among direct-shear anchorage system divided into organic glue(epoxy resin base anchor material)and inorganic glue(cement base anchor material)because of the anchor bolt anchor material.And there are a total of 4 specimens in each group.The fire test was carried out on the two sets of test specimens under the condition of with/without fire protection layer,and the failure mode,mid-span deformation,temperature field distribution and fire-resistant time were discussed.The results showed that:(1)In the case where the actual load ratio is not more than 0.48,the fire insulation of the strengthened beam can reach 110 minutes even without fireproof coating;(2)When no fire-proof coating is applied,different external steel plate strengthened methods have little effect on mid-span deformation and fire endurance.(3)When fire-proof coating is applied to RC beams strengthened with anchorage system,the maximum deflection at mid-span is only 40 mm after exposure to fire for 3 hours although the load ratio is 0.6;(4)The mid-span deflection of specimens strengthened with direct-shear anchorage system with fire-proof coating is smaller than that of conventional anchorage system in the pre-fire stage,but the difference gradually decreases at the later stage of the test;(5)When the difference between the anchor hole diameter and the anchor bolt diameter is 2mm,the anchor material has less influence on the deformation,fire-resistance limit and temperature field of the specimens.Innovations in this paper as follows:(1)This is the first time to study the fire-resistance performance of RC beams strengthened by external steel plate under ISO-834 standard fire-stuck panels.The methods of strengthening including bonding steel plate,conventional anchorage technique,and direct-shear anchorage technique.The strengthening method and fire-proof coating were analyzed.(2)This is the first time to study the fire-resistance performance of RC beams strengthened by direct-shear anchor plates using different kinds of anchoring material.The anchoring materials including organic anchors(epoxy-based)and inorganic anchors(cement-based)to reinforced specimens the impact of performance.