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ABSTRACT: The effect of Soil-Structure Interaction (SSI) was studied for tall industrial Reinforced Concrete (RC) chimneys with annular raft and piled raft under along-wind load. Effects of SSI were evaluated using three different soil types and three different thickness of the annular raft. The along-wind load was computed according to IS:4998 (Part 1)-1992. The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic behaviour. FE analysis was carried out for two cases of SSI; (I) chimney with annular raft and (II) chimney with piled raft. The responses in chimney and raft were evaluated for both the cases and compared to that from conventional method. It is found that due to the addition of piles, the radial bending moment and settlement of raft are significantly reduced by more than 40%, especially for very tall chimney resting on loose sand.
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1 INTRODUCTION
1.1 General
Tall chimneys of height more than 100m are very common in many countries. The demand of increasing the height of chimney is more as it directly related to social and economic aspects of the country. Along wind loads are the predominant forces for tall slender chimneys.
1.2 Background of the problem
It is very difficult to analyse the chimneys with transient wind loads precisely by available analytical procedures because of uncertain variability of wind and therefore a designer is forced to use approximate design techniques [Manohar (1985)]. Studies by Pour & Chowdhury (2008) proved that base moment of tall chimney founded on soft soil increase up to 10% due to along-wind load and decrease up to 50% due to across-wind load that may affect the design forces. Considerable reduction in the bending moments in the annular raft foundation of tall chimneys due to the effect of flexibility of supporting soil under alongwind load is reported by Jayalekshmi et al. (2011). The above studies neglect the three dimensional semiinfinite medium of an unbounded domain of soil stratum. There are hardly any studies on SSI effect on tall chimneys especially considering the 3D integrated chimney-foundation-soil continuum system. More realistic and accurate computational models and methods are required to assess the effect of SSI. Limited studies focused on the response...