Ch. 7 Wood Construction Flashcards
Compressive strength of WOOD:
325-1700 psi
Allowable tensile strength of WOOD:
700 psi
As water leaves wood:
- shrinks in size
- INCREASE in strength
Causes of deterioration in wood bldgs
Insects.
Decay.
Shrinkage
Wood varies significantly with: (3)
- species
- grade
- direction of load with respect to grain
Most structural lumber has a moisture content of:
19% or less
Lengths of squared wood used for construction
Lumber
Solid lumber includes _____, _____, and _______. (BLT)
Boards - nominal thickness of 2 in. or less.
Dimensional lumber - nominal thickness of 2 to 4 in. or more
-Dimensional lumber lengths = 8-18 feet, in 2 ft increments
-rafters can be supplied in lengths up to 24 ft.
Timber - nominal thickness of 5 in. or more
Actual dimensions of wood are ________ than the nominal dimension.
Smaller
Wood disadvantages: (4)
- wood is NEVER dimensionally true
- conditions can change its size and shape
- wood does not shrink or swell uniformly
- can have defects (knots, knotholes, decay, insects, splits, warping)
Glulam.
Individual laminations:
Depths range from _____ and lengths _______.
3/4-2 in. Thickness.
3-75 in. Depth, Up to 100 ft. Length
Three types of joints to join laminated members end to end:
Butt-easy to produce, CAN’T be used for tensile along the beam.
Scarf-tensile.
Finger-tensile.
Structural Composite Lumber (SCL)
-allow outer fibers as well as inner portions
3 types:
Laminated Veneer Lumber (LVL) - outer portion, laminated in parallel, 1 3/4-3 1/2 in. thick.
Parallel Strand Lumber (PSL) - outerMOST, veneers 2-8 ft, odd-shaped, CURED under pressure, strongest.
Laminated Strand Lumber (LSL) - LONG strands (12 in.), steam-pressing, short span.
Rotary sliced. Direction of grain at right angles. Exterior veneers-grain in long dimension. Individual layers - 1/16-5/16 in. Panels 1/4-1 1/8 in., 4x8 sheets
Plywood
Long-strand like wood particles.
3-5 layers.
Oriented with each layer in same direction.
Stronger/stiffer than wafer/particle board.
Sheathing and subflooring in wood-frame buildings.
Oriented strand board
Wood particles bonded with synthetic resins.
Particles from 1 in. to very fine.
Aka flakeboard, chipboard, or shavings board.
Single or multilayer.
Sizes up to 8 x 40 ft.
Not generally used for structural applications
Flooring in manufactured/mobile homes
Particleboard
Similar to particleboard but uses wafer-like pieces of wood that are LARGER than those used in particleboard.
Largely replaced by OSB.
Waferboard
Face and back panel such as plywood or OSB bonded to central core material. Core-paper honeycomb, plastic foam. Structural insulated panel (SIP). -core is expanded polystyrene Core up to 1 ft. thick
Composite or sandwich panels
Grade stamp on back of structural panel that indicates: (2)
Intended structural application.
Suitability for exposure to water
Span rating of 32/16 means:
ROOF OVER FLOORING.
-roof sheathing on 32 in. apart or as subflooring on joists 16 in. apart
Manufacturing members away from job site permits (2)
Greater quality control.
More efficient use of materials
Trusses categorized as (3)
Light-frame-2 in. nominal members.
Heavy timber-8-10 in., steel gusset plates with through bolts.
Split-ring trusses-screws/bolts tend to concentrate load application
Verticals webs-plywood, LVL, OSB.
Flanges-LVL or solid lumber.
-frequently used for floor joists
-also used for rafters in framing of roofs
Box beams or I-beams
Voids created by _____, _____, and ______ result in many square feet of combustible surface area…
Floor, roof and wall cavities
Relative hazard posed by a combustible material such as wood is a function of several variables including: (3)
Ignition temperature.
Heat of combustion.
Ratio of surface area to mass.
Pyrolysis begins at a temp somewhere:
BELOW 392F.
Generally relates in lowered ignition temp of a material
Initial products of pyrolysis are:
Water and carbon DIOXIDE
_______ is the total amount of thermal energy that could be released if the fuel were COMPLETELY burned.
Heat of combustion of a fuel.
Measured in Btu’s per pound or kilojoules per gram
Severity of fire and fire growth rate determined by: (3) TRR
- TOTAL amount of fuel available
- RATE at which fuel is CONSUMED
- RATE at which energy is RELEASED
Two main methods of fire-retardant treatment are:
- pressure impregnation (accelerate formation of charring)
- surface coating (reduce surface burning-flame spread rating)
Disadvantages and limitations of of fire-retardant treatment (2)
Chemicals that are water-soluble (cannot be used for exterior applications).
Treatment will reduce its strength
Surface coating used primarily to:
Reduce surface burning of wood
-flame spread rating
Fire retardant chemicals that may be used:
AABBSZ
- Ammonium phosphate
- Ammonium sulfate
- Boric Acid
- Borax
- Sodium dichromate
- Zinc chloride
Most fire-retardant chemicals operate by:
Accelerating the formation of CHARRING in the wood when exposed to heat
Hygroscopic treatment of wood would:
React with moisture and make wood brittle and crumble.
-when used for roof sheathing, unevenness and sagging would occur 3-5 years after installation
Thermoplastic composite lumber is a wood-like product produced from:
Wood fiber and polyethylene or polyvinylchloride
- flame spread rating of 80.
- not intended for structural framing.
- main application = outside decks and railings.
- manufactured in sizes comparable to sawn lumber.
- MAIN ADVANTAGE is resistance to weathering
Two basic types of wood framing systems:
Timber framing.
Light-wood framing.
Other wood construction types.
- pole construction
- log construction
- prefabricated panel construction
Smaller wood frame structures, such as _____ and _____, can be constructed WITHOUT ENGINEERING ANALYSIS.
Private garages.
Single-family dwellings
_____ or ________ require engineering analysis.
Large OR
Custom-designed
Most wood frame buildings don’t exceed ____ stories
3
Engineered wood structures can be built ______ stories high.
Several
Heavy timber framing dimensions for columns and beams
Columns = 8 x 8 inches. Beams = 6 x 10 inches
Heavy timber design, beams and columns are made of _______ and exterior walls are ______ bearing panels, with an exterior siding that may be any of ______
- wooden timbers
- non-load
- several materials
- corrugated sheet metal sometimes*
The overall integrity of wood-frame systems is affected by:
The METHODS used to join the joists, beams, and columns.
Wood-frame.
Engineer must take into account factors unique to the wood (4)
Specific gravity of wood.
Shrinkage of wood.
Position of fasteners, such as bolts, relative to the grain.
Relative size of the wood and members and the fasteners
Glulam used frequently in heavy timber construction where:
Greater lengths are required
act same manner under fire conditions as solid timbers
Most popular wood framing is:
Light wood-frame construction
Light wood:
- framing:
- walls formed from vertical members, or studs, that are:
- 2x4s or 2x8s
- 2 x 4s or 2 x 6s, 12, 16 or 24 inches on center
Light wood: floors are supported by:
- solid joists
- truss joists
- wood I-joists
- Exterior wall studs continuous
- Second floor supported by ribbon boards
- advantage of minimizing effects of lumber shrinkage (greater degree in cross-sectional than length)
Balloon framing .
“Ribbon holds balloon”
Paper mache balloon doesn’t shrink
This type of construction uses shorter, more easily handled lengths of lumber
Platform
makes use of more horizontal members in frame
The shrinkage in platform framing can produce greater ______ movement at different points, causing cracking of plaster and misalignment of door and window openings.
Vertical
_____ framing is also know as Western Framing (or western frame construction).
Platform
plate at top of studs=inherent fire stop
Usual requirement for attic space subdivided is (draft-stopping):
Subdivided into areas of 3,000 sq. ft.
Draft stops also called:
Dividers hung from ceiling in large open areas that are designed to minimize mushrooming effect of heat and smoke
- curtain boards
- draft curtains
Outside of studs to provide structural stability.
OSB, plywood, particle board or exterior gypsum sheathing.
Also called decking or roof decking
Sheathing
Combustibility of siding affect fire behavior in 2 ways:
Exterior communication - through window/door openings
Ignited by exposing fire
Brick veneer adds ________ and must be tied to the wood frame at INTERVALS of _______.
Little to structural support.
16 inches
Difficult to determine brick bearing walls from brick veneer. One frequently used rule in brick bearing wall is:
EVERY 6th COURSE is header course (ends of brick facing out).
General rule because:
-masonry bearing walls may use ties
-veneer walls have half-bricks that resemble header course.
Two types of Type V construction:
V-A = 1 hr rated, 5/8 in. gypsum board or plaster. V-B = no interior finish, no rating/resistance
Impact-resistant gypsum used:
School and correctional facilities
Where truss joists used in floor construction, possible for fire to spread in _____ directions, _____ to and _____ to truss joists.
4.
Parallel AND perpendicular
Ignition-Resistant Construction (Wildland-Urban Interface)
-factors used to evaluate hazard severity in a given location: (4)
- ground slope
- clear space around property
- water supply
- climate
Ignition-Resistant construction features (2)
Fire-resistant roof coverings.
Exterior walls that is either a) noncombustible or b) 1-hr fire-resistive rating
Forces that affect ALL bldgs:
Settling.
Erosion.
Weathering.
Insulation types
Combustible-foam.
Noncombustibles-glass wool, rock wool and fiberglass.
Loose fill-granulated rock wool/cork, mineral wool, glass wool.
Deterioration from several causes unique to wood
Insects.
Decay.
Shrinkage
Bldg components give rise to possibility of fire originating within concealed spaces (5):
- heating ducts
- electrical wiring
- plumbing
- cooking exhausts
- chimneys
Post and beam framing characteristics
- posts 4x4 or 6x6 in.
- spaced 4-12 ft. apart
- more labor intensive than light frame
- must be braced (diagonally or wall panels)
- wood surface exposed = eliminates combustible voids
Fire stopping size vs draft stopping size
Fire stop = 2 in. nominal, gypsum, cement fiber, mineral wool, glass fiber (stud walls, stair stringers, behind soffits).
Draft stop = 1 in. nominal or cement fiber board (attic)
Overall integrity of wood-frame systems is affected by:
The methods used to join the joists, beams, and columns.
