Advanced Numerical Method for Estimate Fire Resistance of Partially Encased Beams Conference Paper uri icon


  • The ultimate design goal for fire safety engineering is the conception of safe structures. To achieve this goal, advanced calculation methods may be used for the assessment of safety in structures and in particular of structural elements. In order to ensure that ultimate limit requirements are fulfilled, it is necessary to predict failure of each type of material and element during the design process of buildings. This paper deals with the numerical modelling of partially encased beams, which are composed structural elements, widely used in tall buildings, with two or more different materials and types of construction. Normally are used with reinforcement rebars and with or without structural link to slabs that may use concrete to increase fire resistance. Instability problems may occur because concrete may not have the age to resist and also because the concrete may slip over steel, crack or crush. Lateral torsional buckling (TLB) is an instability phenomenon that should be considered. This paper presents Ansys material and geometric non-linear finite element model for determining lateral torsional buckling resistance of partially encased beam with and without encasement reinforcement in fire conditions. The steel part of the composed section will be modelled by finite shell element, concrete part by three-dimensional finite solid elements, the bond slip contact with finite non-linear spring elements and the rebar reinforcement will be considered in perfect contact with concrete, using finite bar element. Elevated temperatures will be applied in both four sides of the cross section along the beam length, based on ISO834 standard fire. Beams will also be subjected to uniform bending corresponding to a specific degree of load bearing capacity. Failure of concrete will be predicted and based on smeared band approach through modification of the stress - strain fields. Fire resistance will be determined for the last time increment in which it is possible to sustain the equilibrium.

publication date

  • January 1, 2006