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Reinforced Concrete Chimneys Design

asked Aug 10, 2014 in Downstream-Midstream by lampanda (2,450 points)
Industrial chimneys are used as part of environmental protection. They have been used to carrying away very aggressive gases from boilers and flue gas below acid dew-point temperature.

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answered Aug 13, 2014 by lampanda (2,450 points)

The Reinforced Concrete Chimneys should be designed to the following standards:

  • ASCE 7 - Minimum Design Loads for Buildings and Other Structures
  • ACI 301 - Specifications for Structural Concrete
  • ACI 318/318R - Building Code Requirements for Structural Concrete and Commentary
  • ACI 211.1 - Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete
  • ‚ÄčACI 307/307R - Design and Construction of Reinforced Concrete Chimneys
  • ASSE/SAFE A14.3 - Safety Requirements for Fixed Ladders
  • NFPA 780 - Standard for the Installation of Lightning Protection Systems
  • CICIND - International Committee on Industrial Chimneys

The followings are general guidelines when considering the design of Reinforced Concrete Chimneys:

Cast-in-place reinforced concrete chimneys should be designed and constructed per ACI 307/307R.

Design seismic accelerations and wind speeds should be per ASCE 7.

Thermal stresses should be determined for the shell and the flue, using the largest anticipated temperature differential, including startup, shutdown, normal, and abnormal operating conditions.

Foundation design should be per ACI 318/318R.  The relevant "design overturning moment" relates to unfactored loads.  For chimneys taller than 300 ft (90 m), the entire chimney foundation must remain in compression when the completed chimney is subjected to the design overturning moment, regardless of soil type.

Foundations and elevated floors that support the flue should not be directly exposed to hot flue gases.  Sufficient insulation, vents, drains, coatings, and flashing should be provided to control concrete temperatures and minimize corrosion.

Minimum airspace width for chimneys with free-standing brickwork flues should be 8 in. (200 mm) for chimneys of heights up to 200 ft (60 m).  An additional 3 in. (75 mm) clearance should be provided for each additional 100 ft (30 m) height.  A 30 in. (750 mm) minimum clearance should be provided when inspection capability is specified.

Lightning protection should be provided per NFPA 780.

Special care should be taken to ensure the long term integrity of all items attached externally to the shell or to exposed parts of the flue.  Such items include insulation protection, rainshields, lightning conductor rods, aircraft warning lights, ladders, and platforms.  In their design and the design of their attachments, the effects of stress corrosion and fatigue damage, due to wind "flutter," should be considered.  Rainshields protecting the annular airspace should not be attached to the flue.

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