7 Wood Construction Flashcards
Disadvantages to wood as construction material
Never dimensionally true
Weather will change its dimension from uneven shrink or swell
Defects, knots, holes, insects, decay, damage, splits or warping.
Wood is stronger in what direction
Parallel to the grain than against it.
Allowable tensile strength of wood
700 psi
Allowable Compressive strength of wood parallel to grain
325-1700 psi
Most structural limber has a moisture content of
19 percent or less
Different types of wood products
Solid lumber Laminated wood members. Structural composite lumber Panels Manufactured components
Glulam
Short for glue laminated structural lumber
Solid lumber includes
boards, dimensional lumber, and timbers.
Lumber boards have a nominal thickness of
2” or less
Dimensional lumber has a nominal thickness of
2-4 inches or more
Timbers have a nominal thickness of
5 inches or more
Laminated beams can have individual lamination layers of what size
3/4 to 2”. Because dimensions can be made not available in solid pieces from logs
Laminated members can be produced in depths of
3-75 inches
Three types of joints for laminated members
Scarf
Butt
Finger
But Joint is easy to produce but cannot be used when
Tensile forces are to b transmitted along the length of beam
Scar and finger joints can be used to transmit what type of force
Tensile
Veneer
Surface of attractive material laid over base of common material
Structural composite lumber SCL is composed of what types
Laminated veneer lumber LVL
parallel strand lumber. PSL
Laminated strand lumber LSL
Levels are used in applications for I joists and beams of what’s size
1.75 to 3.5 inches thick
Parallel strand lumber is the strongest of the three types of SCL and can be used for
Heavily loaded columns and long spans.
Laminated strand lumber LSL is used for
Short span beams and columns
Wood panels include
Plywood
Nonveneered panels
Sandwich or composite panels
Plywood panels have the grain oriented in the direction of the longest section with grain oriented how for the internal layers
At right angles to each other
Plywood in produced in standard sheets measuring
4x8 feet
Composite panels or sandwich panels
Produces with parallel external face veneers bonded to a core of reconstituted fibers. Example is structural insulated panel
Particle board can be in sizes up to
8x40 ft
Wafer board is similar to particle board but uses larger pieces of wood, largely been replaced by
Osb
Span rating indicates intended structural application a rating of 32/16 indicates
Use for sheeting over rafters 32 inch apart and subflooring over joists 16 inches apart.
Lumber
Lengths of wood cut and prepared for use in construction
Gusset plates
Metal or wooden plates used to connect and strengthen the intersections of metal or wood truss components
Light frame trusses
Made of 2 inch nominal members that are all in the same plane. Popular for roof framing, belt together by metal toothed gussets or plywood nailed.
Heavy timber trusses
Made of members 8 or 10 inches. Common before the use of steel
Split rings
Used when bolting or screwing timber or wood members to prevent force from bolt from being focused in one place.
Wood I beams are frequently used for
Roof rafters or floor joists
Ignition temp of wood is difficult to measure because of certain variables:
Density Size and form Moisture content Rate of heating Nature of heat source Air supply
Pyrolysis
Pre ignition combustion phase of burning when heat energy is absorbed by fuel, giving off flammable tar, pitch, vapor and gas. Pyrolysis of wood releases combustible gas and leaves a char
Heard combustion
Total amount of thermal energy (heat) that could be generated by the combustion reaction if a fuel were completely burned. Measured in btu per lb, or kilojoules per gram
Pyrolysis of wood typically begins around what temp
Somewhere below apps 392 degrees
Initial pyrolysis products are water and co2 that may be left inside The wood. Because they are non combustible products what would happen if ignition source was removed
Process would be reversible
Surface to mass ratio
Ratio of surface to mass of fuel
IBC allows fire retardant coating of wood for partition walls that are
Non load bearing with a required fire rating of 2 hours or less
Fire retardant
And substance other than water that is designed to reduce flammability of fuels or slow their rate of combustibility by chemical or physical rxn
Two main methods for fire retarding wood
Surface coating or pressure impregnation
Pressure impregnation
Wood place in vacuum tube that pulls out air from wood and then is pressurized with fire retardant. Creating a permanent treatment under right conditions.
Any of the following chemicals may be used in fire retardant chemicals
Ammonium phosphate Ammonium sulfate Boric acid Zinc chloride Sodium dichromate Borax
True or false fire retardant treatment of wood will not reduce its strength.
False it will reduce strength
Thermoplastic composite lumber is
Wood like product produced from wood fiber and polyethylene or polyvinyl chloride (pvc) as an alternative to preservative treated lumber. Not intended for structural use, but rather outside decks and railings.
Thermoplastic composite lumber is a combustible material with flame spread rating of
80, and will melt like plastic
Because of the cost in engineering and labor, along with limitations in building strength, wood building typically do not exceed what height
Three stories.
On heavy timber constructions what is the minimal beam and column size
Except roof beams, not less than 6x10
And columns are not less than 8x8
Mortise
Notch hole or space cut into a piece of timber to receive the projection part, tenon, of another timber
Tenon
Projecting member of a timber for insertion into a mortise Joint.
In the design for timber connections, engineers must consider what factors
Specific gravity of wood
Wood shrinkage
Position of fasteners such as bolts relative to grain of wood
Relative size of wood members and fasteners.
In relation to heavy timbers, how do Glulam beams behave under fire conditions.
The same as heavy timber beams, fire has no effect on the adhesives.
Post and beam is lighter than heavy timber but heavier than light frame the size of the members are
4x4 or 6x6 posts
Usually spaced 4 to 12 feet apart
Most popular type of framing is
Light wood frame construction
Light framed lumber is sized
Between 2x4 to 2x8
Light wood frame is composed how in regards to wall floor and roof members
Wall studs,
roof rafters or trusses,
floor joists, I beams or trusses
Two basic types of light wood frame
Balloon and platform
Balloon frame construction
Studs are continuous from foundation to roof possibly without fire stopping. Called so because they appeared fragile as a balloon compared to timber frame
Floor joists in balloon framing are supported by
Ribbon boards recessed into vertical stud
Vertical combustible space between studs in balloon frame provide a Chanel for
Rapid communication of fire from floor to floor
Balloon frame has the advantage of minimizing effects of shrinkage because
Wood shrinking is greater in cross sectional dimension than in length
Platform frame
Type of framing in which each floor is built as a separate platform and the studs a re not continuous beyond each floor. Also called western frame construction.
Platform framing is easier to build than balloon however in regard to shrinkage
It is more susceptible to the effects and may cause mis alignment of finishes or trim
Fire stop
Solid materials such as wood blocks used to prevent vertical spread of fire in hollow walls, floor or chases
Approved materials for fire stopping
2 inch nominal lumber Gypsum, Cement board Batts or blankets of mineral wool Glass fiber
A few locations where fires stops are required
Within stud walls at floor and ceiling level
At interconnections between vertical stud walls and horizontal joist spaces
Between stair stringers
Behind soffits
Building code requires draft stopping in attic spaces and is to be constructed in what manner
Areas sub divided into 3000 ft2 spaces and constructed of gypsum, cement fiber board, wood structural panels or 1 inch nominal lumber
Draft stops
Dividers hung from the ceiling in large open areas to minimize effects of mushrooming, also called draft curtains or curtain boards
Sheathing
Covering applied to building where siding is applied, first layer over rafters for roofing. May bay butted together or spaced about an inch apart. Also called decking or roof decking
Building paper
Between sheathing and siding to act as moisture barrier.
Because foam insulation is combustible and flame spreads fast building code imposes
Strict regulation on its use.
To prevent fire spread with foam insulation what is done
Foam is applied without air space
Cellulose fiber can be used as insulation and is treated how to reduce flammability
Treated with water soluble salts to reduce flammability, resulting in smoldering.
Asbestos siding was commonly used during what time periods
1930-1970s
Brick veneer must be tied to the facade of a building every
16 inch interval. Metal ties may corrode, doesn’t not add structural strength but does insulate and protect form exposure
Wood frame Buildings that are not finished inside, such as garages, are classified
Type V-B
When structural members of wood frame is sheathed with gypsum inside to achieve one hour rating it is classified as
Type V-A
Structural member fire resistance for wood frame can be omitted when
Rafters are 20 ft above floor or sprinklers are installed
When truss joists are used for floor construction, it is possible for fire to spread in four directions
Parallel and perpendicular to the joists
Ignition resistant construction is different from fire resistive. It’s intention is to
Reduce vulnerability of structures with hazardous wildland urban interface, by use of fire resistive roof materials or siding, or 1 hour rated exterior walls
