§2.9 Frame Design

§2.9.1 Strength of Beams and Columns

Strong Column-Weak Beam should satisfy Equation 9-3 of the AISC 1997, Except that M*pb is based on the requirements of Section 3.2.6 in FEMA 350. Note that Cpr is always taken equal to 1.2 for this check.

§2.9.2 Lateral Bracing of Column Flanges

Lateral bracing of column flanges should be provided whenever the following equation is not satisfied:

\frac{Σ M * p c}{Σ M c} \geq 2.0

where

M*pc	=	per Section 9.6 of AISC 1997
Mc	=	as indicated in Section 3.2.6 of the FEMA 350 Requirements

§2.9.3 Panel Zone Strength

The panel zone check is per Section 3.3.3.2 of FEMA 350. In that section the thickness of the panel zone required is determined from the following equation:

t = \frac{C_{y} M_{c} \frac{h - d_{b}}{h}}{(0.9) 0.6 F_{y c} R_{y c} d_{c} (d_{b} - t_{f b})}

In RAM Frame this equation is represented by the capacity and the demand side as follows:

(0.9) 0.6 F_{y c} R_{y c} d_{c} t = Σ \frac{C_{y} M_{c} \frac{h - d_{b}}{h}}{d_{b} - t_{f b}}

This allows us to determine the panel zone demand from the beams at both sides of the column and design an appropriate web plate to carry the demand. Refer the FEMA 350 for an explanation of the parameters shown above. Note that Cpr is always taken equal to 1.2 for this check.

§2.9.4 Section Compactness Requirements

Beams should conform to the requirements of AISC Seismic Provisions. Per FEMA 350 Section 3.3.1.1 in the case of a beam with a reduced beam section the program considers the b_f/2t_f to occur at the ends of the center two-thirds of the reduced beam section (RBS). For this reason the engineer is required to input three dimensions to define the RBS, the distance face-of-column to start of RBS (a), the length of RBS (b), and the cut of the flange each side of beam (c). Refer to the v7.0 manual for more details on assigning reduced beam sections to members in the model.

For columns FEMA 350 stipulates that they should be compact unless a non-linear analysis shows that they do not yield. All of the building codes already require that the column is compact and as such no additional FEMA 350 compactness checks are performed for columns.

§2.9.5 Beam Lateral Bracing

Similar to AISC 1997 the unbraced length between supports of the beam flanges is not permitted to exceed 2500 r_y/F_y.