Fundamentals of Building Construction, Materials & Methods, 5 th Edition Copyright © 2009 J. Iano....

Fundamentals of Building Construction, Materials & Methods, 5 th EditionCopyright © 2009 J. Iano. All rights reserved.

History

• Simple timber-framed structures appear with the oldest known civilizations.

• The traditional braced frame structure first appears in the middle ages.

4 HEAVY TIMBER FRAME CONSTRUCTION


Contemporary

• Contemporary timber frame construction may be used for both residential and nonresidential structures.

HISTORY



FIRE-RESISTIVE HEAVY TIMBER CONSTRUCTION


Resistance to Fire of Large Timbers

• Large wood members have greater resistance to fire than unprotected steel.

• Steel, due to its high thermal conductivity, quickly heats up and loses strength during fires.



Resistance to Fire of Large Timbers• Large timbers are

slow to absorb heat, slow to catch fire, and slow to burn.

• The charred outer layer of a partially-burned timber insulates and protects the inner undamaged portion of the timber which retains the capacity to carry some load.



Heavy Timber Construction

• Fire-resistive, traditional Mill Construction consists of heavy timber framing within brick masonry exterior walls.

• In the contemporary building code, Type IV Heavy Timber construction requires heavy timber framing within noncombustible—masonry, steel, or concrete—exterior walls.




• Timbers must meet minimum size requirements to qualify as Type IV-HT construction in the building code.

• Members with lesser dimensions are classified as wood light frame (Type V) construction.

Supporting Floor Loads Supporting Roof and Ceiling Loads Only

Columns 8 x 8 (184 x 184 mm) 6 x 8 (140 x 184 mm)

Beams and Girders

6 x 10 (140 x 235 mm) 4 x 6 (89 x 140 mm)

Trusses 8 x 8 (184 x 184 mm) 4 x 6 (89 x 140 mm)

Decking 3 decking plus 1" finish (64 mm decking plus 19 mm finish)

2" decking, or 1 1/8" plywood (38 mm decking, or 29 mm plywood)




In IBC, note how allowable heights and areas of Heavy Timber (Type IV-HT) buildings exceed those for unprotected steel (Type III-B).




Allowable heights and areas of Heavy Timber buildings also exceed those of light wood frame (Type V) structures.



Wood Shrinkage

• Wood column/beam connections are designed to minimize the effects of cross-grain shrinkage that can lead to differential settling between interior framing and exterior walls made of materials that are not prone to shrinkage.

• Right: Traditional cast iron pintle column base.



Wood Shrinkage

• Right: Contemporary beam/column connection with bearing blocks, split rings, steel straps.

• Note how beam ends are not supported on cross-grain material.



Beam Anchorage

• Fire cut beam ends (right): Collapse of beam must not topple supporting wall.



Beam Anchorage

• A ventilating air space around the beam end prevents moisture in the masonry wall from seeping into the beam.



Beam Anchorage

• Upper clip restrains beam from side-to-side movement while allowing rotation due to structural deflection or beam collapse in a fire.



Floor and Roof Decks

• Decking comes in depths of 2" to 8", capable of spanning roughly from 5' to more than 20'.

• To achieve the required fire-resistance, floor decking must be covered with tongue-and-groove boards or plywood.



Floor and Roof Decks

• Fire-resistive heavy timber floors and roofs must be constructed without concealed cavities where fire could develop undetected.

HEAVY TIMBER CONSTRUCTION


Bracing Heavy Timber Structures

• HT structures may be braced against lateral forces with diagonal framing members, shear walls of masonry or concrete, or rigid panels attached to the building frame.

LATERAL BRACING



• To meet contemporary standards, historical structures may require insertion of new steel or reinforced concrete bracing elements.

LATERAL BRACING



• Floor and roof diaphragms must also be securely tied to the supporting structure.

• Right: New OSB, metal straps, and structural angles tie the floor structure of an historic mill building to its masonry walls.

LATERAL BRACING


Building Services

• When floor and roof systems cannot have concealed spaces, services such as lighting, ductwork, sprinkler piping, electrical wiring must be routed in the open.

HEAVY TIMBER CONSTRUCTION



CONNECTIONS


• Knee bracing with traditional, pegged mortise and tenon joinery

CONNECTIONS


• Proprietary fastening system with self-drilling steel dowels and concealed steel plates

CONNECTIONS


CONNECTIONS

• Fabricated steel seat, concealed plates, and exposed through-bolts


CONNECTIONS

• Steel plate gusset with tie rod and through-bolts


CONNECTIONS

• Copper sheet metal flashing to protect against moisture absorption at vulnerable ends of large timbers exposed to the weather



LONGER SPANS IN HEAVY TIMBER


Large Beams

• Glulam beams can span over 80', and arches even further.

LONGGER SPANS IN HEAVY TIMBER


Trusses

• Heavy timber trusses can span beyond 200'.



Domes

• The Washington State Tacoma Dome spans 530'.


Fundamentals of Building Construction, Materials & Methods, 5 th Edition Copyright © 2009 J. Iano....

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