Thermal effects in design of reinforced concrete structures

Reinforced concrete structures are usually exposed to different environmentally or operationally imposed thermal effects which are preferably treated as idealized-steady-flow condition in case of persistent design. In contrast, having an accidental design situation like fire, an idealized-transient-flow condition could be assumed to interact with the structure boundaries. The current work, mainly, deals with some critical thermal considerations in design of three types of structures which are cooling towers and concrete chimneys for the case of steady flow governing the boundaries and tunnel structures exposed to fire as a transient action. This paper is mainly based on the results of two research projects, one dealing with design of reinforced concrete cooling towers and circular chimneys [1] other one covering a fire design of tunnel structures [2]. In case of design of cooling towers, thermal effects should be considered in both circumferential and meridional directions by assuming the reduced stiffness of the cross section whereas regarding the concrete chimneys, the thermal gradient causing bending moment around the vertical cross section is of a permanent nature and is the only dominant action to limit the crack bending moment. In design of tunnel structures exposed to fire, the complexity of structural response and the high degree of different parameters involved affect the results of nonlinear analysis. The latter requires to take into account the thermally-induced-direct and-indirect effects as well as the reduced material properties spontaneously. The existing simplified methods for fire design, therefore, might result in conservative considerations which could be modified for some restricted similar cases.

Keywords:

thermal , reinforced concrete , design , structures