Simple method for predicting temperatures in insulated FRP-strengthened RC members exposed to fire

Fire insulation layers are often provided to protect fiber-reinforced polymer (FRP)-strengthened RC members. For the fire resistance evaluation of these insulated members, accurate prediction of temperatures in the member under fire is a pre-requisite. Although for a given fire insulation scheme, the temperature analysis can be conducted using a finite-difference (FD) or finite element (FE) procedure, a much simpler, approximate method is highly attractive for practical design purposes. This paper presents such an approximate design-oriented method for predicting temperatures in insulated FRP-strengthened RC members under a standard fire exposure. The proposed method consists of two sets of formulae: (1) a set of formulae for predicting temperatures in un-protected RC members exposed to a standard fire; and (2) a set of formulae through which the fire insulation layer is converted into an equivalent concrete layer; the latter is expressed as a function of the thickness and the thermal properties of the insulation layer. As a result, the temperature analysis of insulated FRP-strengthened RC members becomes that of un-protected RC members with enlarged sectional dimensions. The accuracy of the proposed method is demonstrated through comparisons with results of existing standard fire tests.