Flashcards in Ch. 10 Concrete Construction Deck (88):
Concrete produced from: (3)
*mortar=Portland cement, sand, lime, water*
Aggregates make up a ______ percentage of TOTAL VOLUME of concrete
Curing concrete requires: (2)
Hardening of concrete is chemical process called
*heat of hydration-cement forms gel, gel gives off heat*
Keeping concrete moist (4)
Covering with plastic film.
Sealing compounds (to slow evaporation)
Temperature for concrete curing
Ideally between 50-70F
-at or above 100F not reach proper strength
-near freezing, harden slower
*massive structures, heat of hydration adversely affects strength*
During curing, concrete will _________. Concrete hardens ______. Normal design strength reached ______.
InDEFINITELY at a gradual rate
AFTER 28 days
Density reduced _____.
Flows more freely _____
Admixture, such as shale or clinker.
Ultimate compressive strength of concrete
Techniques to reinforce concrete: (2)
Prestressing reinforcing (pretensioning and posttensioning)
Ordinary reinforcing (3)
Concrete COMPACTED around rebar
Concrete hardens and ADHERES to deformities on surface of bars
Job of design engineer to specify: (3)
Number of reinforcing bars
Their size (diameter)
Depth of concrete cover
Diameters of standard-size reinforcing bars
.375 - 2.257 inches
Fundamental tensile and compressive forces are ________ throughout a beam.
*Diagonal tension forces also must be resisted*
Vertical reinforcing bars are known as ____ and resist the ____ tension.
Concrete BEAMS are frequently cast in the shape of a _____.
*reinforcing steel placed in the bottom of the tee to resist TENSILE force*
Although the primary function of placing reinforcing steel in concrete is to resist _______ forces, the steel can also be used to support some of the _______ forces.
In ________, a _____________ is induced in the concrete before the load is applied
Preloading of the steel creates ________ stresses in the concrete that counteract the ______ stresses that result when the loads are applied.
Prestressing process requires _____ loads to be applied to the concrete along the _______ of the beam. These loads can result in the _____ of the concrete over time.
The forces that are initially applied in the prestressing process are __________ than the forces theoretically needed to support the concrete and the applied loads.
In pretensioned concrete, ______ are stretched between anchors producing a ___________ in the steel. Concrete is then placed around the steel.
Pretensioned: After the concrete has hardened sufficiently, the force applied to the steel strands ________. As the force on the strands is released, the strands exert a ___________ on the concrete.
In pretensioned concrete, when the steel strands are released, the member usually takes on a _____________ deflection.
In posttensioned, the reinforcing steel is not tensioned until ___________.
AFTER the concrete has hardened. (Post)
As a general rule, reinforcing steel ____________ in the course of firefighting operations unless it is necessary to ______.
Should not be cut
Rescue trapped victims
_____ is placed into forms at the building site as a wet mass and hardens in the forms OR
_____ is concrete that is poured into forms as liquid and assumes the shape of the form in the position and location it will be used.
Cast in place permits the designer to cast the concrete in a _____________.
Wide variety of shapes
Wet concrete is transported from the truck to formwork either by _____ or ______.
Hoisting it in large buckets
Great care must be exercised in the ____, ____, and ____ of concrete to ensure good quality.
The ______ of concrete is of significance to firefighters. Concrete that is of poor structural quality will behave poorly under fire conditions by ______ and even _________.
The single MOST IMPORTANT factor in determining the ultimate STRENGTH of concrete is the __________.
An amount of water GREATER than required for curing is added to the concrete mix to _________________ as its placed in the forms.
Increase its workability
The presence of ________ in the concrete also produces _______ due to ____________.
Spalling in the concrete
Freezing conditions OR the heat of fire
When concrete __________________, it's quality checked by ________ known as a _______.
Arrives at the job site
Administering a test
Slump test is used to ___________ by measuring the amount that a ____________ of the concrete settles or _______ after it is removed from a __________ test mold.
Check the moisture content of concrete
Small, cone-shaped sample
Concrete with ______ slump will fail the test and may be rejected by the ____________.
Another method of testing concrete is to _______________ and subject them to ___________.
Make small test cylinders of a concrete batch
Compression test: this method is ______ but has the disadvantage of requiring that the _______________ before the results are known. This test would be __________ if the concrete were ultimately found to be _________.
Concrete be permitted to harden
Large cast-in-place structures cannot be cast in _________. _________ unavoidably occur between _____________.
To provide for transfer of __________ from one placement to the next, the reinforcement steel will _________.
Loads and forces
Overlap the joints
The following are common cast in place structural systems: (3)
Slab and beam
_______ is a simple system that consists of concrete slab supported by concrete COLUMNS
Flat-slab concrete frames
*slab with columns*
_______ is a simple system that consists of concrete slab supported by concrete BEAMS
Slab and beam framing
*aka concrete joist construction*
Flat-slab concrete frames
The slab of concrete varies in thickness from _________. _______ stresses develop in the concrete where the slab intersects the supporting column.
6 to 12 in.
In a building that will have heavy live loads, the area around the columns is reinforced with additional concrete in the form of ____ or _______. If the building will support light loads, additional reinforcing _________ and this is called ________.
Drop panels or mushroom capitals
Is not necessary
Slab and beam
This framing system is ________ and is best suited for buildings with ____ floor loads. Slabs in this type of construction can sometimes be as thin as ______.
Extremely light weight
Slab and beam
Due to the thin slab, the concrete beams must be ______ in order to provide adequate support. The spacing often gives an appearance similar to ________ and is sometimes referred to as ___________.
Concrete joist construction
Slab and beam
Concrete beams run MAINLY in one direction, _____________ slab.
Concrete beams running in two directions, ______ construction.
Two-way framing where spans are ____ and _____ loadings are high.
Bldgs using ________ are often highly susceptible to fire damage due to their thin nature. Fire proofing is _________.
Slab and beam
Pattern result from placement of _______ over which ________ is placed.
This design provides a ______ slab while reducing the weight of _______ in the ____ half of the slab.
Reinforcing steel placed in the bottom of the formwork provides reinforcement in ___________. Slabs of this type, therefore, are also known as __________.
A poured concrete slab can be supported by _________ instead of _________.
Structural steel beams
*Type 1, must be provided fireproofing*
______ concrete is placed in forms and cured at a location other than the construction test.
*Poured and set according to specification in a controlled environment*
The precast structural shapes, including ____, ____, and _____ are transported to the job site and hoisted into position.
Several advantages to using precast concrete: (1 of 3)
Higher degree of quality control
-sheltered environment/not exposed to weather
-high degree of quality control
-mixing and pouring more mechanized
Major disadvantage to using precast is:
Need to transport the finished components to the job site.-Transportation increases cost and limits the size of the shapes.
Precast concrete structures have more in common with _____ than with cast-in-place concrete buildings.
Precast concrete SLABS for floor systems can be cast in standard shapes that include: (4)
Solid slabs (short spans up to approx. 30 ft)
Single tee slabs (tee slabs - spans up to 120 ft)
Double tee slabs
A common form of construction with PRECAST is known as _________. Reinforced wall panels cast in horizontal casting beds. After _________, the wall panels are tilted up into the vertical position by a crane. Temporary bracing until roofs or permanent horizontal.
Tilt-up (precast) OR
Concrete has cured
Tilt-up walls can be ______ stories in height. Tilt-up walls can support several types of roof including: (4)
Precast structural elements are usually _______ than corresponding cast-in-place components. However, the use of precast concrete results in a ___________________ that is inherent with cast-in-place concrete frames.
Loss of continuity
In a precast concrete structure, the connections between the individual components are _________ of structural engineering.
A variety of techniques, such as _____, _____ and ______ can be used to connect precast structural elements.
When precast beams are to be supported by columns, the beams may be supported by _______ cast into the column. _______ is a ledge that projects from the column and supports the beam.
Corbel (also known as a bracket)
Simple designs of this type are not inherently rigid and the slabs need to be ________ to resist _______.
Laterally tied together
Short steel beam cast into the precast column.
Precast beams are secured to the column through the use of _________ cast into the columns or though the use of ___________.
Posttensioned steel cables
Very common precast for parking garages.
The _____ and ______ make precast structural systems a practical choice.
Buildings supported by a ________ are usually enclosed by a non-bearing curtain wall.
Curtain wall/concrete frame.
The choice of material is determined by _______, ________ and ______.
Thermal insulation properties
________ concrete systems may be somewhat more vulnerable to failure than _______________ concrete.
Reinforcing cables and rods used in prestressed systems are made of high-strength steels that have lower yield points, can yield at a temp of _______.
Structural lightweight concrete has a _____ density than ordinary concrete and has a _________ thermal conductivity. Therefore, it acts as a ______________ against a heat of fire than ordinary concrete. However, it is not used for _____________.
__________ concrete buildings have an advantage over _________ buildings because of the continuity of the assembly provides an inherent restraint to movement of the ___________, such as _________.
Columns and beams
The expansion of water creates ________ forces within the concrete.
Concrete has good insulating properties and tends to retain the heat of an exposing fire and release it slowly, similar to masonry oven. This general effect is referred to as _______.
Heat sink effect
Spalling of concrete will result in ________ and __________.
Failure of the reinforcing bars
Failure of the structural assembly
Advantages of concrete (4)
Produced from RAW materials (locally available/low in cost).
Does NOT BURN.
Resists INSECTS and effects with contact of SOIL
Create a variety of architectural SHAPES
Concrete types (7)
Coloring can be added for _______________. Such as coloring concrete when _____________.
Aesthetic or safety reasons.
It is placed over buried electric cables
Steel bars support some of the compressive load and also resist ____________ in the column from sources such as ____ and _____. Compressive forces in column great enough to cause steel bars to buckle. To avoid, lateral reinforcing provided ________.
Around vertical bars
Ordinary reinforcing has inherent limitations.
Concrete beam/floor slab supports a load, concrete in the beam in tension is ___________.
Doing NO work
Cutting through reinforcing steel with saw or torch is ____________ because the steel is ____________. If they are cut, they are likely to ___________, injuring emergency responders. __________ may also lead to the failure of the concrete structural element, resulting in a collapse or partial collapse.
Particularly dangerous in POSTTENSIONED concrete
Not bonded to the concrete
Spring out of the concrete
RELEASING the posttensioned element
Several advantages of using precast (2 of 3)
Work can proceed more quickly
-no need for formwork at site
-no need to wait for concrete to harden
-no need to construct/remove forms, add'l costs
Several advantages of using precast (3 of 3)
Precast concrete sandwich panels can be produced using polystyrene core (insulating properties)
Concrete structural systems.
Fire resistance of concrete assembly is affected by such variables as: (5)
Load supported by concrete
Depth of concrete cover over reinforcing bars
**concrete = 1 to 4 hrs**
EXTENT to which concrete undergoes spalling depends on ________________. (2)
Amount of excess MOISTURE.
Length of TIME since concrete was placed