CONCRETE STRUCTURES

DESIGN OF COLUMNS:
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BEAM COLUMNS:
===============
	Columns are 
	Members that carry both 
	compression force (axial load)  
	& moment
 	- pure beam action -moment governs
	- pure column - axial load governs


COLUMN TYPES BY
=================
length-to-thickness ratio:
	Short Column:
		short & stocky (h<10 Cross Sec.) 
		not based on absolute length
		high bending stiffness
		small secondary moments
  		definition short column:
		secondary moment <5% primary moment 

	Long or Slender Column:
		less stocky
		more flexible
		P-delta effect: 
		deflection of the longitudinal axis
		by primary moments create
		additional or secondary moments
		equal to the product of the
		axial force P and the
		deflection ( of the center line
		Primary moments:
		member end moments or
		moments due to transverse loads

TYPES OF COLUMNS:
==================
Tied Columns
	individual hoops 
	are used to position 
	the longitudinal steel
	rectangular cross section typical
	but can be round or L-shaped
	95% of all nonseismic columns	
 	min. 4 longitudinal bars

Spiral Columns
	closely spaced continuous spirals
	round cross section typical	
	min. 6 longitudinal bars
	pitch 1 3/8" - 3 3/8"
	for high strength
		high ductility
		high seismic forces
	Core area:
		area contained within the spiral

Design Guidelines for Columns:

	A.) 8" - 10" min. width or min.diameter
		based on clearance requirements

	B.) min. area of longitudinal
		steel to be >= 1% and < 8% of the
		cross-sectional area  

	C.) 5-6% practical to fit in column
		and maintain spacing between bars

	D.) Max. 4 bars can be bundled

	E.) Spacing between bars
		>=1.5 bar diameter >= 1.5"  

    	 F.) Min. Concrete Coverage
		p. 105 Leet Table 3.3
		1.5"	if not exposed
		2"	if exposed
		applies to:
			longitudinal rebar			
			steel ties
			spirals
		purpose of coverage:
			fire protection
			corrosion protection	

    	G.) Min 4#4 bars for square collumns
		min. 5#4 for round columns
		min. 6#4 for spiral reinforced columns