Chpt 10 Flashcards
Because concrete is noncombustible, it is widely used in
Fire resistive construction
In almost all structural applications concrete is reinforced with
Steel
Is produced from Portland cement coarse and fine aggregates, and water
Concrete
Concrete must be ____ in order to reach its proper strength
Cured
Hardening or concrete involves a chemical process known as
Hydration
In hydration , water combines with particles of cement to form a microscopic gel. As the concrete hardens, this gel gives off heat, which is known as the
Heat of hydration
In addition to maintaining proper moisture, concrete that is curing must be maintained at the correct temperature, ideally between
50-70f
Theoretically, properly cured concrete continues to harden indefinitely at a gradual rate, however, normal design strength is reached after
28 days
Different types of concrete can be produced for specific purposes. This is accomplished by varying the ingredients or adding chemicals to the concrete mixture, these are generally known as
Admixtures
Like masonry, concrete is strong in compression but weaker in
Tension
Because concrete is weak in tension, it cannot be used where tensile forces occur in a structure. To resist tensile forces, concrete is reinforced with ______ placed within the concrete before it hardens
Steel reinforcing bars
With_____, steel bars are placed in the formwork and the wet concrete is placed in the formwork around the bars
Ordinary reinforcing
The vertical reinforcing of bars are known as _____ and are provided to resist the diagonal tension
Stir ups
Although the primary function of placing reinforcing steel concrete is to resist tensile forces, the steel can also be used to support some of the
Compressive forces
In ____ a compressive load is induced in the concrete before the load is applied
Prestressing
In_____ concrete, steel strands are stretched between anchors producing a tensile force in the steel
Pretensioned concrete
When concrete is ______, the reinforcing steel is not tensioned until after the concrete has hardened
Posttensioned
As a general rule, reinforcing steel should not be cut in the course of fire fighting operations unless it is necessary to
Rescue trapped victims
Concrete can be either
Cast in place or precast
Is placed into forms at the building site as a wet mass and hardens in forms
Cast in place concrete
Is placed in forms and cured at a precasting plant away from the job site.
Precast concrete
Permits the designer to cast the concrete in a wide variety of shapes
Cast in place concrete
This type of concrete does not develop its designed strength until after it has been placed in the location where it will be used
Cast in place concrete
Most ____ is proportioned at central bulk plants and then mixed in a mixing truck enroute to the job site
Cast in place concrete
The quality of concrete is of significance to firefighters. Concrete that is of poor structural quality will behave poorly under fire conditions by
Spalling and even breaking apart
The single most important factor in determining the ultimate strength of concrete is the
Water to cement ratio
If too much water has been used in the mix, the final product will not achieve its desired strength. The presence of excess moisture in the concrete also produces _____ in the concrete due to freezing conditions or the heat of fire
Spalling
When the concrete arrives at the job site, it’s quality is checked by administering a test known as a
Slump test
Another method of testing concrete is to make small test cylinders of a concrete batch and subject them to
Compression testing
The following are common cast in place structural systems
Flat slab
Slab and beam
Waffle construction
The _____ is a simple system that consists of a concrete slab supported by concrete columns.
Flat slab concrete frame
The slab of concrete varies in thickness from 6 to 12 inches
Flat slab concrete frame
In a building that will have heavy live loads, the area around the columns is reinforced with additional concrete in the form of
Drop panels or mushroom capitals
If the building will support light loads, this additional reinforcing is not necessary. The system then is known as a
Flat plate
A _____ consists of a concrete slab supported by concrete beams
Slab and beam frame
This framing system is extremely light weight and is best suited for buildings with light floor loads
Slab and beam frame
Slabs in this type of construction can sometimes be as thin as 2 inches
Slab and beam
Due to the thin slab, the concrete beams must be closely spaced in order to provide adequate support. This spacing often gives an appearance similar to wood joists and is sometimes referred to as
Concrete joist construction
When the concrete beams run mainly in one direction, the framing is known as a
One way reinforced slab
Slab and beam concrete framing can also feature concrete beams running in two directions. Such a system is known as a
Two way slab construction
The pattern results from the placement of square forms over which the wet concrete is placed.
Waffle construction
derives it’s name from the waffle like pattern of the bottom of the concrete slab
Waffle construction
May be produced at a precasting plant some distance from the work site
Precast concrete
A major disadvantage to using _____ is the need to transport the finished components to the job site
Precast concrete
Can be built using whole precast modular units but it is more common to assemble precast parts into a framework for a building
Precast concrete buildings
Precast concrete structures have more in common with steel framed buildings than with
Cast in place concrete buildings
A common form of construction used with precast concrete is known as
Tilt up construction
When precast beams are to be supported by columns, the beams may be supported by ____ cast into the column.
Corbels
A____, also known as a bracket, is a ledge that projects from the column and supports the beam.
Corbel
Concrete is a fundamentally _____ that performs well under fire conditions
Fire resistive material
Prestressed concrete systems may be somewhat more vulnerable to ____ than ordinary reinforced construction
Failure
The fire resistance of concrete assembly is affected by such variables as the following
Concrete density Concrete thickness Concrete quality Load supported by the concrete Depth of concrete cover over the reinforcing bars
Cast in place concrete buildings have an advantage over precast buildings because the continuity of the assembly provides an inherent restraint to movement of the intersecting members such as columns and beams
This results in a fundamentally greater structural rigidity of cast in place buildings
When openings exist in concrete slabs or walls, the ability of the concrete to act as a barrier is lost unless the opening is protected by an appropriately rated assembly such as a
Fire door or shutter
Of concrete is caused primarily by the expansion of the excess moisture within the concrete when it is either heated or when it freezes
Spalling
Newer concrete that is not completely cured is subject to more severe ____ when exposed to fire
Spalling
Because concrete has a relatively good insulating properties, it tends to retain the heat of an expose the fire and release it slowly, similar to the manner in which a masonry oven releases heat. This general effect is referred to as the
Heat sink effect
Concrete is a noncombustible building material that is strong in compression but weak in
Tension
Have greater inherent rigidity than precast structures
Cast in place
