Tests of Residual Shear Transfer Strength of Concrete Exposed to Fire

Abstract

Reinforced concrete is one of the most widely used structural components about which much scientific research has been conducted; however, some of its characteristics still require further research. The main focus of this study is the effect of direct fire on the shear transfer strength of concrete. It was investigated under several parameters including concrete strength, number of stirrup legs (the steel area across the shear plane), and fire duration. The experimental program involved the testing of two sets (groups) of specimens (12 specimens each) with different concrete strengths. Each set contained specimens of two or four stirrup legs exposed to direct fire from one side (the fire was in an open area to simulate a real-life event) for a duration of one, two, and three hours. The results of the comparison showed the importance of using high-performance concrete (instead of increasing the number of stirrup legs) to resist shear stress for the purpose of safety. A significant reduction in shear strength occurred due to the deterioration of the concrete cover after three hours of direct fire exposure.

Behaviour of steel beam subjected to the fire

“…This means that the fire resistance R30 of unprotected steel beam will be analysed. The loading for fire resistance analysis is determined according to [8] for extraordinary loading case combination with bending moment value Mfi,d = 880 kNm.…”

“…The steel temperature was determined according to [8] and nominal temperature curve (Fig. 2) for beam flanges and beam web.…”

“…Behaviour and design of eccentrically loaded hot-rolled steel SHS and RHS stub columns at elevated temperatures was described in [6], Non-linear analysis of composite beam subjected to fire was done in [7]. Fire load modes are described in EN 1991-1-2, which shows simplified and improved models [8]. Simplified fire models are sufficient for general practice but they are limited in size of the fire sections, in size of the fire load and distribution of thermal energy.…”

“…Nominal temperature curve (Fig. 2) indicates fire section temperature dependence only on time of fire [8].…”

“…When 𝜃𝜃 𝑡𝑡 is gas temperature in relevant fire section [°C] and t is time [min]. 2 Fire loaded beam analysis According to [8], the fire resistance of a steel beam under thermal loading by nominal temperature curve can be determined by a standard calculation or a numerical model. The paper deals with chosen steel beam fire resistance determination by these two approaches and compares the results.…”