Analysis Of Chimneys Research Articles

Effects of blast-induced random ground motions on the stochastic behaviour of industrial masonry chimneys

This paper focuses on the stochastic response analysis of industrial masonry chimneys to surface blast-induced random ground motions by using a three dimensional finite element model. Underground blasts induce ground shocks on nearby structures. Depending on the distance between the explosion centre and the structure, masonry structures will be subjected to ground motions due to the surface explosions. Blast-induced random ground motions can be defined in terms of the power spectral density function and applied to each support point of the 3D finite element model of the industrial masonry system. In this paper, mainly a parametric study is conducted to estimate the effect of the blast-induced ground motions on the stochastic response of a chimney type masonry structure. With this purpose, different values of charge weight and distance from the charge centre are considered for the analyses of the chimney. The results of the study underline the remarkable effect of the surface blast-induced ground motions on the stochastic behaviour of industrial masonry type chimneys.

Effect of foundation flexibility on the across-wind response of reinforced concrete chimneys with free-standing liners

Chimneys with free-standing liners are often analyzed as fixed base cantilever beams, ignoring the effect of soil-structure interaction on their response. However, soil-structure interaction influences the dynamic response of chimneys in two ways: it alters the natural frequencies, damping ratios, and mode shapes, and it results in coupling of the response of the liner and the shell. In this analysis, the stack was modelled as a continuous cantilever beam with distributed stiffness and mass supported by a flexible foundation. It was found that the relative shell-liner deflection for the flexible foundation case was approximately 35% higher than that for the fixed base case. This increase in deflection may exceed design tolerances for a chimney cap and may lead to liner and (or) shell damage if combined with other adverse conditions such as aerodynamic interference effects with other chimneys. The base forces in the shell decrease significantly due to the foundation flexibility, with values as low as 50% of those of the fixed case. The base forces in the liner were approximately 35% of shell base forces for the fixed base case. These forces are not accounted for in the design of liners using the fixed base assumption. It was concluded that the effects of the foundation flexibility are significant and must be included in the analysis of chimneys with free-standing liners. This is especially true for chimneys in regions with low seismic activity, since the design of the liner would be based on minimal lateral forces.Key words: soil-structure interaction, chimneys, dynamic response, wind.

Effect of foundation flexibility on the across-wind response of reinforced concrete chimneys with free-standing liners

Chimneys with free-standing liners are often analyzed as fixed base cantilever beams, ignoring the effect of soil-structure interaction on their response. However, soil-structure interaction influences the dynamic response of chimneys in two ways: it alters the natural frequencies, damping ratios, and mode shapes, and it results in coupling of the response of the liner and the shell. In this analysis, the stack was modelled as a continuous cantilever beam with distributed stiffness and mass supported by a flexible foundation. It was found that the relative shell-liner deflection for the flexible foundation case was approximately 35% higher than that for the fixed base case. This increase in deflection may exceed design tolerances for a chimney cap and may lead to liner and (or) shell damage if combined with other adverse conditions such as aerodynamic interference effects with other chimneys. The base forces in the shell decrease significantly due to the foundation flexibility, with values as low as 50% of those of the fixed case. The base forces in the liner were approximately 35% of shell base forces for the fixed base case. These forces are not accounted for in the design of liners using the fixed base assumption. It was concluded that the effects of the foundation flexibility are significant and must be included in the analysis of chimneys with free-standing liners. This is especially true for chimneys in regions with low seismic activity, since the design of the liner would be based on minimal lateral forces.Key words: soil-structure interaction, chimneys, dynamic response, wind.

Chimneys, towers and masts

AbstractThis article describes the particular problems associated with the design and analysis of chimneys, towers and guyed masts. Procedures for the analysis under wind action are described and the treatment of aerodynamic stability outlined. Safety aspects are discussed, including how they are treated in the draft Eurocode, for both ultimate and fatigue limit states.

Approximate Fundamental Frequencies for Chimneys

Chimneys are shell structures that are used for discharging gaseous effluents from factories or power plants. When designing a chimney, obtaining the fundamental frequency or period is necessary to be able to determine: (1) lateral forces due to earthquake; and (2) the critical wind velocity that would cause resonant vibrations, due to the shedding of the Karman Vortex. Determining the natural frequencies and performing the dynamic analysis of chimneys has become easier using computers. When performing the preliminary chimney design, engineers require a rapid means for obtaining a reasonably accurate fundamental frequency of a chimney to permit necessary modifications to develop the best design. For this reason, approximate formulas for fundamental frequencies are indispensable for practicing engineers. This note considers unguyed and unlined chimneys (or chimneys with self-supported independent lining). Several commonly used approximate formulas for computed fundamental frequencies are given. Frequencies for chimneys with practical ranges of dimension variables were obtained by computer using Newmark's method. Computer results were compared with those obtained by the existing formulas. From these studies, new approximate formulas that fit the computer results better than the existing formulas are proposed.