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Video Lectures for Video Lectures for B.Tech B.Tech By: By: video.edhole.com
Video Lectures for B.TechVideo Lectures for B.Tech
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Chapter 5Heavy Timber Frame Construction
5.1 INTRODUCTION TO BUILDING FRAMES
Wood beams have been used to span roofs and floors of buildings from the beginning of civilization
Earlier roof timbers were combined with load bearing masonry walls to build houses and public buildings
British and European carpenters built buildings exclusively with hand-hewn timbers with wood-to-wood connections. This was brought over to North America
Present day heavy timber construction, with exterior walls of masonry or concrete, is listed in building codes as Type 4 construction.
Progression of European timber frame construction Construction of exclusively heavy timber construction Form of an exclusively heavy timber construction
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Timber Construction History
Till the Late 1800s most – Construction was Timber (and/or masonry) with– Wood to Wood Connections
WHY?
Timer (Trees) Plentiful Craftsman Available Nails & Fasteners Rare & Expensive Few Alternatives
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Timber Construction Today
Why so Little Timber Construction Today? Alternate Structural Systems Available For Both Residential & Commercial Commercial Alternatives Concrete & Steel (late 1800s) Advantages over Timber
– Greater spans
– Lighter structures
– Increased fire resistance
– Increased versatility
– More economical
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Commercial Alternatives
Concrete & Steel (late 1800s)
Advantages over Timber
– Greater spans
– Lighter structures
– Increased fire resistance
– Increased versatility
– More economical
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Residential Alternatives
Light Wood Framing (mid 1800s)
Fasteners available @ reasonable price
Advantages* Lighter structure * Used less material * Quicker to erect
* More economical
Where/when is timber construction typically used today?
Aesthetics, appearance, feel important
– Uniqueness of Timber Construction Common Uses
– * High end residential * Restaurants, lodges, etc.
– * Public areas requiring aesthetics
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With masonry all around, the building catches fire very slowly Supports the load even after heavy charring Code recognizes the fire resistance properties of heavy timber
construction - Type 4 construction in Table 1.1 - Type 5 - Light Type 5 - Light Wood Framing Wood Framing
While unprotected steel beam collapses much earlier during a fire, a heavy timber beam can be sandblasted after a fire and left in service (after normal fire damage)
Minimum timber sizes are specified in building codes for heavy timber frame constructions
Edges must be chamfered for better fire resistance
5.2 HEAVY TIMBER FRAME CONSTRUCTION - ADVANTAGES
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5.3 PRECAUTIONS TO BE TAKEN IN HEAVY TIMBER CONSTRUCTION
Wood shrinkage: Wood is subjected to large amounts of expansion and contraction caused by seasonal changes in moisture content, particularly in the direction perpendicular to the direction of its grain fiber. These effects must be minimized by proper detailing. Beams and girders must be allowed to shrink without causing the floors and roof to sag
Anchorage of heavy timber beams to masonry walls: First the beam must be protected from decay due to moisture seepage through the masonry walls - Achieved by leaving a ventilating airspace of at least 1/2” between masonry and all sides of beam; this can be eliminated if the beam was chemically treated to prevent decay. The beam must be securely anchored to the wall so that it does not pull away from the the wall during normal services; but it must be able to rotate freely, without prying the wall apart, as it burns during a heavy fire - Methods of attachment must allow rotation of the support after the beam falls apart due to fire damage
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Mode of covering the floors and roofs with proper decking: Floor decking to be covered with a finish floor consisting of nominal 1” thick tongue-and-grooved boards laid at right angles or diagonal to the structural decking, or with plywood or particle boards
Lateral bracing of buildings: Building is normally braced against wind and seismic forces by the shear resistance of its walls, working together with the diaphragm action of its roof and floor decks
In areas of high seismic risk, the walls must be reinforced both vertically and horizontally, and the decks may have to be specially nailed, or overlaid with plywood to increase its shear resistance. In buildings with framed exterior walls, diagonal bracing or shear panels must be provided. The roof must be properly anchored to the building
5.3 PRECAUTION TO BE TAKEN IN HEAVY TIMBER CONSTRUCTION (Cont’d)
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5.4 Additional Considerations
Lack of concealed cavities for:
– MPE rough-in
– Building Insulation Span length limitations (typically limited to 20’)
Alternatives
– Large Beams – often laminated
– Heavy timber trusses
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