Beam-Column Design Procedure
Procedure
- Obtain required axial force and moments from a permitted structural/stability analysis, including required second-order effects.
- Determine available axial strength and available flexural strengths and from the applicable member-strength provisions.
- Select the applicable Chapter H interaction equation.
- Evaluate the interaction with second-order required moments.
- Verify bracing, connections, drift/serviceability, and seismic-system requirements separately.
Example 1: Higher Axial-Ratio H1 Interaction
A W14x90 in compression has , , , and . Assume the moments already include required second-order effects and there is no y-axis moment.
Step-by-Step Solution
0 of 3 Steps CompletedExample 2: Lower Axial-Ratio H1 Interaction
A beam-column has , , , and .
Step-by-Step Solution
0 of 3 Steps CompletedExample 3: What P-Delta Means
A story carries total vertical load while its floor level translates laterally by .
Step-by-Step Solution
0 of 2 Steps CompletedExample 4: B1 Member-Curvature Amplification
For an LRFD approximate second-order check, let , , , and first-order nontranslation moment . There is no translation moment in this isolated example.
Step-by-Step Solution
0 of 3 Steps CompletedExample 5: B2 Story-Translation Amplification
For an LRFD approximate second-order check, the story has and elastic sway buckling strength . First-order translation moment in the member is .
Step-by-Step Solution
0 of 2 Steps CompletedExample 6: Combined B1/B2 Required Moment
Use , , , and .
Step-by-Step Solution
0 of 2 Steps CompletedExample 7: Instability Boundary
Suppose an approximate B1 calculation has and .
Step-by-Step Solution
0 of 2 Steps CompletedExample 8: Direct Analysis vs. B1/B2
Two engineers analyze the same frame. Engineer A uses a rigorous second-order model with the Direct Analysis Method requirements. Engineer B uses a permitted approximate second-order B1/B2 procedure.
Step-by-Step Solution
0 of 3 Steps Completed- Use available strengths in the interaction equation and required second-order forces/moments on the demand side.
- and are distinct member/system deformation effects.
- B1/B2 is an approximate second-order procedure, not the Direct Analysis Method.
- A zero or negative amplification denominator signals instability/out-of-scope behavior.
- Bracing and connection detailing must provide the restraint assumed by the analysis.