Ch 07 Heavy Timber and Mill Construction


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Ch 07 Heavy Timber and Mill Construction

  1. 1. 7 Heavy Timber and Mill Construction
  2. 2. Objectives (1 of 2) <ul><li>Identify and describe the similarities and differences between mill and heavy timber (Type IV construction) </li></ul><ul><li>Identify the dimensions of heavy timber members </li></ul><ul><li>Describe why the misnomer “slow burning” is inappropriate for heavy timber buildings </li></ul>7
  3. 3. Objectives (2 of 2) <ul><li>Identify the hazards of conflagration breeders </li></ul><ul><li>Describe the hazards of vacant heavy timber buildings and structures under demolition </li></ul><ul><li>Identify new structures that incorporate heavy timber construction </li></ul>7
  4. 4. A History of Mill and Heavy Timber Construction <ul><li>Heavy timber construction descendent of true mill construction </li></ul><ul><li>Developed in New England </li></ul><ul><li>Building design that eliminated serious faults of mill construction </li></ul>7
  5. 5. Mill Features (1 of 3) <ul><li>Exterior bearing and nonbearing walls are masonry </li></ul><ul><li>Columns and beams are of heavy timber with cast iron connectors </li></ul><ul><li>Floors are of thick grooved, splined, or laminated planks </li></ul>7
  6. 6. Mill Features (2 of 3) <ul><li>Roofs supported by beams or timber arches and trusses </li></ul><ul><li>Adequate fire barriers </li></ul><ul><li>Ends of girders are fire cut </li></ul><ul><li>Cast iron box </li></ul><ul><li>Corbelled beams </li></ul><ul><li>Scuppers </li></ul>7
  7. 7. Mill Features (3 of 3) <ul><li>Concealed spaces are eliminated </li></ul><ul><li>Vertical openings are protected </li></ul><ul><li>Automatic sprinkler system </li></ul><ul><li>Special hazards put in detached buildings </li></ul>7
  8. 8. Conversion, Modification, and Preservation (1 of 2) <ul><li>Remodeling </li></ul><ul><ul><li>Often detracts from the original fire characteristics </li></ul></ul><ul><ul><li>Columns may have been removed </li></ul></ul><ul><ul><li>New trusses do not have the inherent resistance of the old columns and beams </li></ul></ul>7
  9. 9. Conversion, Modification, and Preservation (2 of 2) <ul><li>Changes in Use </li></ul><ul><ul><li>Conversions to tenant factories, storage, discount stores, and apartments </li></ul></ul><ul><ul><li>Fire loads are often beyond capacity of the installed sprinklers </li></ul></ul><ul><ul><li>Unsprinklered areas are created </li></ul></ul>7
  10. 10. Heavy Timber Building <ul><li>Requires careful maintenance </li></ul><ul><li>Deficiencies should be clearly noted </li></ul><ul><li>Realistic prefire scenarios are required </li></ul>7
  11. 11. Code-Classified Heavy Timber Construction <ul><li>Type IV construction </li></ul><ul><li>Often lacks at least one feature vital for fire safety </li></ul><ul><ul><li>Unprotected steel columns, part-steel trusses, unsprinklered void spaces, or no sprinkler protection </li></ul></ul>7
  12. 12. Heavy Timber Construction Contractors <ul><li>Be wary of those who claim to be erecting a heavy timber structure </li></ul><ul><li>Many do not know the actual dimensions required </li></ul>7
  13. 13. Heavy Timber Theory <ul><li>Heavy timbers are difficult to ignite </li></ul><ul><li>Will char on the surface only </li></ul><ul><li>Over the years the floors may have been soaked with flammable and combustible fluids </li></ul>7
  14. 14. Slow Burning? <ul><li>Proponents of heavy timber construction </li></ul><ul><ul><li>Believe “slow burning” means “collapse resistance” </li></ul></ul><ul><ul><li>Statement true only if fire department can maintain interior offensive operations </li></ul></ul>7
  15. 15. Definition of Conflagration Breeder <ul><li>A structure that presents severe exposure problems that are capable of initiating a large, multiple building fire which is not easily contained </li></ul>7
  16. 16. Characteristics of a Conflagration Breeder  <ul><li>Radiant heat and fire brands </li></ul><ul><li>Large collapse zones </li></ul><ul><li>Fire spread </li></ul><ul><li>Shut-off sprinkler systems, open equipment shafts, and uncompartmented areas </li></ul>7
  17. 17. Fighting a Conflagration Breeder <ul><li>Expect the fight of your life </li></ul><ul><li>You need: </li></ul><ul><ul><li>Large water supply </li></ul></ul><ul><ul><li>Numerous heavy caliber streams </li></ul></ul><ul><ul><li>Large collapse zone </li></ul></ul><ul><ul><li>Extensive brand patrol downwind </li></ul></ul><ul><ul><ul><li>Luck </li></ul></ul></ul>7
  18. 18. Use of Unprotected Steel <ul><li>Unprotected steel can fail early and trap fire fighters </li></ul><ul><li>Alteration permits give clues to real composition </li></ul>7
  19. 19. Beams <ul><li>Penetrated for conduits or pipes </li></ul><ul><li>Long bolts and nuts are used </li></ul><ul><li>Metal can provide a path for heat to reach the interior </li></ul><ul><li>Watch for spliced timbers with overlapping joints and metal connectors </li></ul>7
  20. 20. Full Sprinkler Protection <ul><li>Needs to be adequately maintained </li></ul><ul><li>Only fire protection measure to prevent a disaster in a heavy timber building </li></ul>7
  21. 21. Rehabilitation and Demolition Hazard <ul><li>Fire sprinkler systems </li></ul><ul><ul><li>Must be adequately maintained </li></ul></ul><ul><ul><li>Expense may be seen as road block to construction project </li></ul></ul>7
  22. 22. Problems with Rehabilitation <ul><li>Abandoned buildings </li></ul><ul><li>Conversions to multiple occupancy </li></ul><ul><li>Rehabilitations into apartment or office occupancies </li></ul>7
  23. 23. Vacant Buildings <ul><li>Cities with recent massive downtown fires </li></ul><ul><ul><li>Baltimore </li></ul></ul><ul><ul><li>Philadelphia </li></ul></ul><ul><ul><li>Lynn (Massachusetts) </li></ul></ul><ul><ul><li>Minneapolis </li></ul></ul><ul><ul><li>Indianapolis </li></ul></ul><ul><ul><li>Montreal </li></ul></ul>7
  24. 24. Characteristics of Massive Downtown Fires <ul><li>Old combustible interior masonry buildings </li></ul><ul><li>Fire barriers removed or inoperable </li></ul><ul><li>Sprinkler systems removed or disabled </li></ul><ul><li>Only fuel was the interior structure of the building </li></ul>7
  25. 25. Vacant Structures <ul><li>Sprinklers are often turned off </li></ul><ul><li>Open invitation to arson </li></ul>7
  26. 26. Modern Heavy Timber Buildings <ul><li>Not being built in record numbers </li></ul><ul><li>A niche for certain types of occupancies </li></ul><ul><li>Most common use is the modern heavy timber church </li></ul>7
  27. 27. Summary <ul><li>Heavy timber construction is a descendent of true mill construction </li></ul><ul><li>Remodeling has detracted from original fire characteristics </li></ul><ul><li>Proponents often advance the term slow burning </li></ul><ul><li>Full sprinkler protection is the only adequate fire protection measure </li></ul>7