][ STEEL STRUCTURES ][

				STEEL COLUMNS
				==============
	   		   	      P&A 312
Column:
======
		compression member
			f = P/A
				f = unit stress
				P = concentrated load
				A = area
		complicated by effects of:	
			buckling
				slenderness main influence
			bending

Column Shapes
===========
		round tube   0
		square tube []
		H-shape wide flange
		heaviest W14x730
		built-up sections
			large columns
			special framing
			[ ] double C
		

Slenderness
========
		see also P&A 218 Chapter 6
		slenderness = L/r  
			L = unbraced length
			r = radius of gyration
 				        -----
				r = V I/A
				r = square root 
					moment of inertia
					dived by the area	
				P&A 167
		modifying factor = K 
			effects of end restraint
		slenderness for building columns
			L/r = 120 max. recommended
		relative slenderness = K x L / r

ALLOWABLE LOADS FOR COLUMNS
==============================
calculation method used for built-up members

A W 12 x 58 is used as a column
with an unbraced length of 16 ft.
Compute the allowable load.

W 12 x 58 
l = 16 ft
A 36 Steel


B. ASKED
Allowable Load


C. GRAPH
		|
		|
		|	
			l = 16 ft
			W 12 x 58
			A 36



D. SOLUTION
1. No end condition given
===================
	we assume an end condition 
	K = 1
	Table 10.2   P&A 314


2. W 12 x 58
=========
	Table 4.1 P&A 171
	A = 17 sq inch
	r x = 5.28 inch
	r y = 2.51 inch


3. Column is unbraced on both axis
=========================
	it is limited by the lower r value
	for the weaker axis
	r y = 2.51

4. Relative Slenderness
=================
	K l
	----
                 r

	1 (16 ft x 12)
	-----------------
		2.51

              = 76.5
	= 77
	can be rounded of to next higher
	figure in front of decimal point

5. Allowable Unit Stresses for Columns of A36
==================================
	Table 10.1 P&A 316
		for  Kl/r = 77
		Fa = 15.69 ksi


6. Allowable Load 
==============
		P = A x Fa
			A = 17.0 sq inches
				from 	Table 4.1 P&A 171
			Fa = 15.69
				from Table 10.1 P&A 316
		P = 17.0 sq inches x 15.69 k sq inches
		P = 266.7 kips
 


E. ANSWER
The allowable load for the column is
266. 7 kips
266 kips also correct
267 kips would be incorrect

	
STEEL COLUMNS RELATED SITES

Steel Columns

Columns

 
 








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Dr. Hermann Gruenwald

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©Dr. Gruenwald 1996, 1997