Diaphragm Design Forces Fpx per ASCE 7-22 §12.10

Summary: Calculate diaphragm design force Fpx at each level for collector and chord design per ASCE 7-22 §12.10.1.1. Free structural design software: minimum…

Overview

Calculate diaphragm design force Fpx at each level for collector and chord design per ASCE 7-22 §12.10.1.1. Free structural design software: minimum 0.2×SDS×wpx and force from vertical distribution.

Problem statement

A two-story wood building with F1=8 kip, F2=12 kip (roof), story weights w1=40 kip, w2=40 kip. SDS=1.0. Determine Fpx at each level for diaphragm design. Collectors and chords designed for Fpx.

Workflow in StructSuite

StructSuite Step 1: enter story weights wx and heights hx. Steps 2–5: site, risk, structural system, period. Step 8: Diaphragm design forces. Fpx = (ΣFi from i=x to n)×wpx/(Σwi from i=x to n) per ASCE 7-22 Eq 12.10-1. Minimum Fpx = 0.2×SDS×wpx. StructSuite computes Fpx for each level. Critical for collectors in openings, chord reinforcement, and drag struts.

Design considerations (excerpt)

Two-story wood building: enter Level 1–2, wx (lb) and hx (ft). w1=40 kip, w2=40 kip; F1=8 kip, F2=12 kip from vertical distribution. hn drives period Ta; story weights drive Fpx formula.

SDS drives minimum Fpx: Fpx ≥ 0.2×SDS×wpx. For SDS=1.0, floor with 40 kip weight has Fpx_min = 8 kip. Minimum often governs for low-rise (1–3 stories); force distribution may govern for taller. Site Class affects SDS—soft soil raises it.

Ie from ASCE 7-22 Table 1.5-2. Residential = Risk II, Ie=1.0. Fpx minimum 0.2×SDS×wpx does not include Ie; full base shear V and Fx do.

Wood light-frame R=6.5 typical for residential. Table 12.2-1 id 16. R affects base shear V and thus Fx distribution.

Approximate Ta =…

Related terms

• StructSuite
• structural engineering
• design example
• seismic
• ASCE 7-22
• diaphragm forces

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