Formulas: Torsional Bracing

Equation C-A-6-9

The torsional brace requirements are based on the buckling strength of a beam with a continuous torsional brace along its length, as presented in Taylor and Ojalvo (1966) and modified for cross-section distortion in Yura (2001):

Formula 2

$\overline{\beta_{T}}=n \beta_{T} / L$ is the continuous torsional brace stiffness per unit length or its equivalent when $n$ point braces, each with a stiffness $\beta_{T}$, are used along the span, $L$, and the factor 2 accounts for initial out-of-straightness (the continuous torsional ideal bracing stiffness is thus taken as

Equation C-A-6-10

Formula 4

The strength requirement for beam torsional bracing is developed based upon the critical initial twist imperfection of $\theta_{o}=0.002 L_{b r} / h_{o}$, where $h_{o}$ is equal to the depth of the beam (Wang and Helwig,

Formula 5

Based on the use of an effective bracing stiffness equal to 3 times the ideal torsional bracing stiffness, the torsional bracing required moment resistance may be estimated as $M_{r b}=\beta_{T} \theta_{o}$.

Formula 6

Equation C-A-6-12

lateral bracing on the flange subjected to flexural compression, the required torsional and lateral brace stiffnesses can be reduced relative to the base values specified in Sections 6.3.1 and 6.3.2, but should satisfy the following interaction equation:

where

$\beta_{L b r}=$ actual or provided lateral brace stiffness, kip/in. (N/mm)

$\beta_{L b r o}=$ required lateral brace stiffness given by Equation A-6-6 for panel bracing or Equation A-6-8 for point bracing acting alone, kip/in. (N/mm)

$\beta_{T b r}=$ actual or provided torsional brace stiffness, kip-in./rad (N-mm/rad)

Found in

• BEAM BRACING