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Joseph A. YuraUniversity of Texas at Austin

BRACING FOR STABILITY

Todd A. HelwigUniversity of Houston

Sponsored by: Structural Stability Research Council American Institute of Steel Construction

L

o

STIFFNESS

STRENGTH

CONNECTION DETAILS CAN BE DETRIMENTAL

BRACE FORCES ARE DIRECTLY RELATED TO THE MAGNITUDE OF INITIAL OUT -OF-STRAIGHTNESS

GENERAL BRACE REQUIREMENTS

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Column

Beam

S I M P L E R U L E

USE BRACE SYSTEM STIFFNESS AT LEAST TWICE THE IDEAL VALUE

DESIGN THE BRACE AND ITS CONNECTIONS FOR 0.4 % OF THE COMPRESSIVE FORCE

RELATIVE BRACE DESIGN

service

ASDF.S. = 2.0

P

u

s4P sbrF = 0.004P

brF = 0.004P u2P u

Brace Stiffness( 2P/L )

Brace Strength( 0.004 P )

LRFDFactored P

= 0.75

L PP1 P2 3

FRAMES

FOR STIFFNESS AND STRENGTH

USE P

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GRAVITY

GRAVITY plus WIND

BRACE SYSTEM STIFFNESS

EFFECT OF CONNECTION DETAILS

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2

BRACING FUNDAMENTALS S I M P L E R U L E

L R F D A S D

RELATIVEBRACING

DISCRETEBRACING

COLUMN BRACING RECOMMENDATIONS

Factored Loads - P Service Loads - P S.F. = 2.0

u s

N 4 - ( 2 / n )i

i= N i= N

= 0.75

P P P

More braces require more stiffness ?!

IDEAL BRACE STIFFNESS REQUIREMENTS

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INEFFECTIVE TORSIONAL BRACE

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T O R S I O N A L B R A C I N G

SECTION IS FULLY BRACED AT A LOCATION

IF TWIST IS PREVENTED

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Joseph A. YuraUniversity of Texas at Austin

BRACING FOR STABILITY

Todd A. HelwigUniversity of Houston

Sponsored by: Structural Stability Research Council American Institute of Steel Construction