Book 29 Building Construction Flashcards
Book 29 Building Construction
Now, let’s focus on the first portion of size-up, “analyzing the situation.” When this portion of a size-up is applied to a structure fire, one of the first considerations should be the
type and construction of the building. These two factors will indicate:
Rate of burning.
Possible avenues of fire spread. (false ceilings, multiple attics, facades, etc.)
Problems that will have a direct impact on efforts to confine a fire.
Structural integrity.
Time necessary to conduct safe fireground operations.
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Book 29 Building Construction
Conventional construction utilizes structural members that depend on size for strength.
SIZE = STRENGTH
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Book 29 Building Construction
lightweight truss construction does not derive strength from size. Strength is obtained from multiple members that are in compression and tension.
Unfortunately, new construction methods are usually NOT designed to assist fire suppression operations.
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Book 29 Building Construction
The amount of time that a structure can be considered structurally strong is dependent on the following factors:
Type of Construction.
How long the fire has been burning.
Fire Intensity
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Book 29 Building Construction
GABLE ROOF
A frame configuration of conventional or ordinary construction that consists of a ridge board and rafters that cross the outside walls. Rafters are usually 2 x 6 inches or larger and are usually 16 inches to 24 inches “on-center.”
Additional support is provided by collar beams and ceiling joists. This roof is found in semi-flat to steep pitch configurations.
2 x 6 inch rafters (spaced up to 36 inches “oncenter” for steep pitched roofs) were commonly utilized for roof structural members.
1 x 6 inch ridge board or the lack of a ridge board which resulted in the 2 x 6 inch rafters butted together.
Lightweight construction utilizes 2 x 3 or 2 x 4 inch wood trusses held together by metal gusset plate connectors.
Common “on-center” spacing for truss rafters is 24 inches.
The strong areas of this roof are the ridge and the area where the rafters cross the outside walls.
When metal connector plates and surrounding wood are exposed to fire, the connector plates will quickly fail by pulling out of the wood.
Newer roofs use 3/8 or 1⁄2 inch plywood as a decking instead of 1 x 4 inch or 1 x 6 inch space sheathing.
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Book 29 Building Construction
Metal gusset place connectors
The most common are ___ gauge steel plates with prongs that produce ___ inch penetration.
18
3/8
Book 29 Building Construction
Eighteen-gauge “roof truss clips” may be found nailed to the bottom chord (every ___ to ___ trusses) and top plate of interior walls.
three to five
Book 29 Building Construction
HIP ROOF
lack of the A-frame configuration
The ridge board and rafters are usually 2 x 6 inches or larger. Rafters are usually 16 to 24 inches “on center,” similar to the gable roof. “Rough cut” 2 x 3 or 2 x 4 inch rafters 36 inches “on-center” were also utilized in older wood frame structures with steep pitched roofs.
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Book 29 Building Construction
HIP ROOF
lack of the A-frame configuration
The ridge board and rafters are usually 2 x 6 inches or larger. Rafters are usually 16 to 24 inches “on center,” similar to the gable roof. “Rough cut” 2 x 3 or 2 x 4 inch rafters 36 inches “on-center” were also utilized in older wood frame structures with steep pitched roofs.
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Book 29 Building Construction
BOWSTRING ARCH ROOFS - 1930’s, 1940’s, and 1950’s
2 x 12 or 2 x 14 inch of lumber comprises the arch trusses
Rafters are 2 x 6 inches or larger and covered by 1 x 6 inch sheathing (diagonal or straight) and composition roofing material.
Plywood decking (on top of the sheathing) is utilized, if modified for the Earthquake Ordinance.
fails in sections
The underside of the roof is usually common to the interior of commercial warehouse type structures or the arch trusses can be modified to allow storage in the attic area or ceilings
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Book 29 Building Construction
LAMELLA ARCH ROOF
An egg crate, geometric or diamond-patterned roof. Constructed from 2 x 12 inch wood framing with steel plates and bolts at junctions of framing.
decking is 1 x 6 inch
This type of an arch roof is supported by exterior buttresses or internal tie rods with turnbuckles, and is common on gymnasiums, large buildings used for recreational activities, large supermarkets, etc.
total roof collapse may occur if fire removes more than ___% of the roof structure. Total roof collapse of the roof
can result from “the domino effect.”
20
Book 29 Building Construction
TIED TRUSS ARCH ROOFS
Uses metal tie rods to offer lateral support for the walls of the building.
Tie rods (usually ___ inch in diameter) with turnbuckles are used below each arch member to ensure the arches do not push the exterior walls outward. Tie rods may pass through exterior walls outside plates, which facilitate identification of this style of roof. Proper tie rod tension is maintained by turnbuckles. Top chords of arch member may utilize laminated 2 x 12’s or large members. Rafters are 2 x 10 inches or larger and covered by 1 x 6 inch sheathing
The primary hazard of this roof is early failure of the metal tie rods and turnbuckles.
Will fail in section or total collapse
5/8
Book 29 Building Construction
SAWTOOTH ROOF
rafters of 2 x 8 inches or larger
The sloping portion is covered with 1 x 6 inch sheathing (or 1⁄2 inch plywood in newer roofs)
this type of roof is easy to ventilate; utilize the hinged panes of glass.
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Book 29 Building Construction
CONVENTIONAL FLAT ROOF
Rafters 2 x 6 or larger
1 x 6 decking or plywood
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Book 29 Building Construction
Plywood which may be found in ___ inch to ___ inch thickness’ offer minimal structural integrity under fire conditions.
3/8” to 5/8”
Also says lightweight plywood decking is 3/8 to 1/2
Book 29 Building Construction
WOODEN I BEAM ROOF
top and bottom parallel wooden chords that are connected by a wooden stem.
Two-by-fours are used as chords, but 2 x 3 inch chords are common.
Stem - ____ inch plywood or “chip-board”
The common on-center spacing is 24 inches.
Nailing blocks are spaced ___ feet apart.
Prior to nailing, the plywood sheets are placed so the 8-foot dimension crosses the roof structural members and the 4-foot dimension parallels the roof structural member.
3/8
four
Book 29 Building Construction
OPEN WEB ROOF
top and bottom parallel wooden chords that are cross-connected by steel tube web members.
The steel tube web members are prefabricated from ___ to ___ inch cold rolled steel tubing with the ends pressed flat into a semicircular shape with a hole punched through the end.
These flattened ends are inserted into slots in the chords and steel pins (up to ___ inch)
Spans to ___-feet are possible
The common on-center spacing is 24 inches.
one to two
one
70
Book 29 Building Construction
METAL GUSSET PLATE ROOF
Wood trusses predominantly composed of 2 x 4’s that are held together by metal gusset plate connectors. Trusses for roofs are constructed in a wide variety of shapes (flat, gable, hip, etc.) all shapes share common features.
Eighteen-gauge steel plates with prongs that produce 3/8 inch penetration are common and used in a wide variety of applications.
Utilization of 2” x 4”s in a span of up to ___ feet may be found in flat metal gusset plate roofs. Decking material is usually 1⁄2 inch plywood. Dwellings will use 3/8 inch or 1⁄2 inch plywood.
80
Book 29 Building Construction
PANELIZED ROOF
Laminated beams - ___ x ____ inches
Beams are spaced ___ x ____ feet apart and can be in excess of ___ feet
6” x 36”
12 to 40 feet
100’
Book 29 Building Construction
PANELIZED ROOF
purlin is ___ x ____ inches and spaced ___ feet apart
Metal gusset plate trusses are beginning to be substituted for conventional purlins, resulting in substantial cost savings as well as an additional collapse hazard.
4 x 12
8’
Book 29 Building Construction
PANELIZED ROOF
Joists measuring 2 x 4 inches by eight feet are installed with metal hangers on 24 inch centers between the purlins, parallel to the beams. Sheets of 4 x 8 feet x 1⁄2 inch plywood are nailed over this framework. The plywood decking is then covered with composition roofing material.
The strengths of this roof are:
Beams
Purlins
Building Perimeter
When the insulation (kraft paper) is subjected to fire or sufficient heat, the foil covering will peel away from the middle layer of tar impregnated paper. The paper will give off flammable gases that rise and build up between the insulation paper and plywood decking. When the ignition temperature of the gases is reached, the gases will flash, resulting in heavy char to the surrounding wood and burning insulation paper dropping to the floor below (which contributes to rapid spread of the fire).
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