Adaptation of torsional constant 

See Ref.[1], Chapter 10.1.5.,  Ref.[2],3.5 and Ref.[3],3.3.4..

When steel sheeting is used, the torsional constant It is adapted for symmetric/asymmetric I sections, channel sections, Z sections, cold formed U, C , Z sections.

The torsional constant It is adapted with the stiffness of the sheeting:

with

l

the LTB length

G

the shear modulus

vorhCq

the actual rotational stiffness of sheeting

CqM,k

the rotational stiffness of the sheeting

CqA,k

the rotational stiffness of the connection between the sheeting and the beam

CqP,k

the rotational stiffness due to the distortion of the beam

k

numerical coefficient

= 2 for single or two spans of the sheeting

= 4 for 3 or more spans of the sheeting

EIeff

bending stiffness of per unit width of the sheeting

s

spacing of the beam

ba

the width of the beam flange (in mm)

C100

rotation coefficient - see table

h

beam height

t

thickness beam flange

s

thickness beam web

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