Building Construction Chapter 10

Like masonry, concrete is strong in compression but weaker in tension. The ultimate compressive strength can range from ______ psi to _____ psi.

2,500psi to 6,000psi

Slab and Beam Framing. Pg. 268

A slab and beam frame consist of a concrete slab supported by concrete beams. This framing system is extremely lightweight and is best suited for buildings with light floor loads. Slabs in this type of construction can be as thin as 2 inches. The concrete beams must be closely spaced in order to provide adequate support to the thin slab. The spacing often gives an appearance similar to what Joyce and is sometimes referred to as concrete Joyce construction. Slab and beam systems are often highly susceptible to fire damage because of the finesse of the slab.

What is superplasticizer? Pg.258

Admixture use with concrete or mortar mix to make it workable, pliable, and soft while using relatively little water

What is cement? Pg. 258

Any adhesive material or variety of materials which can be made into a paste with adhesive and cohesive properties to bond inert aggregate materials into a solid mass by chemical hardening. For example Portland cement is combined with sand and or other aggregates and water to produce mortar or concrete

Precast concrete is placed in forms and cured at a plant away from the job site. Precast concrete structural members are then transported to the job. Cast in place concrete is placed into forms at the building site as a wet mask and hardens and prepared forms. Both can achieve fire resistive ratings required by building codes. which has an advantage?

Cast in place concrete buildings have a structural advantage of a precast buildings because the nature of the construction of cast in place provides an inherent continue witty and intersecting members. Discontinuing the results in a fundamentally greater structural rigidity for cast in place buildings

The fire resistance of a concrete assembly is affected by such variables as the following: Pg. 266

Concrete density Concrete thickness Concrete quality Supported load Depth of concrete cover over the reinforcing bars.

Advantages of precast concrete. Pg. 269

Higher degree of quality control possible then with cast in place concrete: -Pre-casting forms can be located under a shelter -Ingredients can be finally controlled for a quality -Mixing and pouring the concrete can be more mechanized and efficient. Work can proceed more quickly at the job site: -Construction and removal of on-site forms and frameworks is unnecessary. -Work can proceed immediately because concrete is already hardened. Precast concrete sandwich panels can be produced using polystyrene core to improve the insulating properties of the precast concrete. From a construction standpoint, precast concrete structures have more in common with steel frame buildings down with cast in place concrete buildings.

Ideal temperatures for concrete to be cured at? Pg. 264

Ideally between 50 and 70°F Concrete cured at or above 100°F will not reach its proper strength. Concrete cured near freezing temperatures will harden more slowly.

What is admixture? Pg. 258

Ingredients or chemicals added to concrete mix to produce concrete with specific characteristics

Flat-Slab Concrete Frames: Pg. 267

Is a simple system that consists of a concrete slab with concrete columns for support. The slab of concrete ranges and thickness from 6 to 12 inches. Sheer stressors develop in the concrete with a slab intersects the supporting columns.

What is aggregate? Pg. 258

Particulate material used in construction to provide a stable bedding or reinforce a composition material. Used as an extender in concrete. Can be graded into course and fine grain sizes and material types including sand gravel stone etc.

What is a flat plate floor slab

Plain floor slab about 8 inches thick that rests on columns spaced up to 22 feet apart and depends on diagonal and orthogonal patterns of reinforcing bars for structural support because the slab lacks beams; ***Simplest and most economical floor system***

What is postensioning? Pg. 262

Post tensioned reinforcement uses reinforcing steel cables that are not tensioned until after the concrete has hardened to a certain strength. The forces that are produced in the post tensioning process remain locked in the steel for the life of the assembly.

Why might prestressed concrete systems be more vulnerable to failure than ordinary reinforced concrete? Pg. 263

Prestressed concrete systems may be more vulnerable to failure than ordinary reinforced concrete. The systems use reinforcing cables and rods made of high strength steel that can yield at temperatures as low as 752°F. Therefore for the same depth of cover (insulation) a prestressed assembly will fail sooner than a conventional reinforced assembly

What is pretensioning? Pg. 262

Pretensioned reinforcement uses steel strands stretch between anchors producing a tensile force in the steel. Concrete is then placed around the steel strands in allowed to harden. After the concrete has harden sufficiently, the force applied to the steel strands is released. As the force is released, the strands exert a compressive force in the concrete. When the steel strands are released, the concrete member usually takes on a slight upward deflection. As loads are applied to the pretension member, the deflection usually disappears and the member becomes flat.

Waffle construction. Pg. 268

Slab and beam concrete framing featuring concrete beams running into different directions is known as a two way slab construction. Two-way slab construction is known as waffle construction because of the waffle like pattern on the bottom of the concrete slab. The pattern results from the placement of square forms over which the wet concrete is placed. Waffle construction is used with bands are short and floor loadings are high. This design provides a thicker slab while eliminating the weight of a necessary concrete in the bottom half of the slab. Reinforcing steel place in the bottom of the form Mark provides reinforcement and two directions.

Shapes commonly used with precast concrete include slabs and tees. Pg. 270

Slabs Hollow Core Slabs Single Tee Double Tree

What is prestressing? Pg. 261

Stress introduced to the concrete before the load is applied; accomplished by tensioning reinforcing bars before the concrete is poured This technique tightens the reinforcing steel, adding compressive stressors to surrounding concrete.

What is concrete? Pg. 258

Strong, hard building material produced for a mixture of Portland cement and an aggregate filler/binder to which water is added to form a slurry that sets into a rigid building material

In prestressing, decompressive stresses counteract the tensile stressors from the applied load. Two common methods of prestressing concrete are pretensioning and posttensioning. Regardless of any tension, reinforcing steel should not be cut during fire fighting operations unless it is necessary to rescue trapped victims. Why?

The steel strands are stretched like giant rubber bands if they are cut, they are likely to spring out of the concrete, injuring emergency responders.

How long does it take for concrete to reach designed strength? Pg. 264

Theoretically, properly cured concrete continues to harden indefinitely at a gradual rate; normal design strength is reached after 28 days

What is tilt up construction? Pg. 270

Tilt up construction is a common form of construction use with precast concrete. And tilt up construction reinforced wall panels are cast at the job site and horizontal casting beds. After the concrete has cured, a crane tilts the wall panel up into the vertical position. Temporary bracing is provided until the roof supports or other permanent horizontal bracing is provided. This type of construction requires that the roof assembly maintain structural integrity; Failure of the roof can result in failure of the wall from outward horizontal forces.

What is the single most important factor and determining the ultimate strength of concrete? Pg. 264

Water to cement ratio