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Building Design and Construction Handbook - Merritt - Ventech!

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7.74 SECTION SEVEN<br />

of lateral-torsional buckling <strong>and</strong> flange local buckling. The limit state of local buckling<br />

of web does not apply.<br />

F � F � � � (7.36)<br />

cr yƒ p<br />

� � ��<br />

1 � � �p<br />

Fcr � CF b yƒ 1 � � Fyƒ �p � � � � r (7.37)<br />

2 � � �<br />

r p<br />

2<br />

Fcr � C PG/� � � � r<br />

(7.38)<br />

where F yƒ � specified minimum flange yield stress, ksi<br />

C b � bending coefficient dependent on moment gradient<br />

� 1.75 � 1.05(M 1/M 2) � 0.3(M 1/M 2) 2 for lateral-torsional buckling<br />

� 1 for flange local buckling<br />

C PG � 286,000/C b for lateral torsional buckling<br />

� 11,200 for flange local buckling<br />

� � L b/r T for lateral-torsional buckling<br />

� b ƒ/2t ƒ for flange local buckling<br />

L b � laterally unbraced length of girder, in<br />

r T � radius of gyration, in, of compression flange plus one-sixth the web<br />

b ƒ � flange width, in<br />

t ƒ � flange thickness, in<br />

�p � 300/ �Fyƒ for lateral-torsional buckling<br />

� 65/ �Fyƒ for flange local buckling<br />

�r � 756/ �Fyƒ for lateral-torsional buckling<br />

� 150/ �Fyƒ for flange local buckling<br />

<strong>Design</strong> Shear Strength. This is given by � vV n, where � v � 0.90. With tensionfield<br />

action, in which the web is permitted to buckle due to diagonal compression<br />

<strong>and</strong> the web carries stresses in diagonal tension in the panels between vertical<br />

stiffeners, the design shear strength is larger than when such action is not permitted.<br />

Tension-field action is not allowed for end panels in nonhybrid plate girders, for<br />

all panels in hybrid girders <strong>and</strong> plate girders with tapered webs, <strong>and</strong> for panels in<br />

which the ratio of panel width to depth a/h exceeds 3.0 or [260(h/t)] 2 , where t is<br />

the web thickness. For these conditions, the design shear strength is given by<br />

� V � 0.90 � 0.6A F C � 0.54A F C (7.39)<br />

n n w yw v w yw v<br />

where A w � web area, in 2<br />

F yw � specified web yield stress, ksi<br />

C v � ratio of critical web stress, in the linear buckling theory, to the shear<br />

yield stress of the web steel<br />

For tension-field action, the design shear strength depends on the ratio of panel<br />

width to depth a/h. Forh/t � 187�k/F ,<br />

yw<br />

For h/t � 187�k/F ,<br />

yw<br />

� V � 0.54A F (7.40)<br />

v n w yw

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