CONCRETE STRUCTURES

PRESTRESSED CONCRETE:
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Prestressing:
	A technique of introducing stress of 
	a predetermined magnitude into a
 	structural member to improve its behavior.

	Prestressing is used in concrete to
	introduce compression into regions 	where 
	tension stress will be created by applied loads.

Facts:
	1949 Walnut Lane Bridge -	
		Philadelphia first US prestressed 
	50% reduction of dead weight
	80% of prestressed members are
			precast

Materials:
	Prestressed Steel:
		1.	Stranded Cable (7 strands)
			tensile strength 250-270 kips/sqin
		2.	High strength bars
			145 - 160 kips/sqin
			3/4" - 1 3/8" (

	Concrete:
		1.	Poured in Place Concrete
			2.5 - 4 kips/sqin
			for short spans 20'-0" max
		2. 	High Strength Concrete
			4 - 10 kips/sqin
			for longer structures
			over 75'-0"
			dead weight = major load
		3..	Reduced weight

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ASSOCIATIONS