Code Sections and Analysis - The Analysis of Irregular Shaped Structures - page 3

set the criteria and requirements for diaphragms, chords, collectors, and their design.
Comparing the IBC, ASCE 7, and the SDPWS reveals that the definitions for a dia-
phragm and its components under both wind and seismic loading are nearly identical.
In practical terms, all diaphragms must have boundary members consisting of drag
struts, chords, collectors, or other vertical lateral-force-resisting elements. Collectors are
required at all offsets and areas of discontinuity within the diaphragm, including at
openings. These requirements also apply to shear walls. Forces at all discontinuities
and openings must be dissipated into the diaphragm or shear wall without exceeding
its design capacity. The codes and standards specify that the sheathing shall not be used
to splice boundary elements or collectors. Furthermore, all diaphragms and shear walls
shall contain continuous load paths along all boundaries and lines of lateral force resis-
tance and across all discontinuities.
The following sections are presented to show agreement between the codes and
standards with regard to lateral-force-resisting systems that resist wind and seismic
forces. These sections have been selected for their relevance to this topic. These sections
should be reviewed in their entirety when reading each chapter of the topic.

1.2 IBC 2009 Code Sections Referencing Wind and Seismic 1

Chapter 16
1602.1 Definitions
Diaphragm : A horizontal or sloped system acting to transmit lateral forces to the
vertical-resisting elements. When the term “diaphragm” is used, it shall include
horizontal bracing systems.
Diaphragm Boundary : In light framed construction, a location where shear is trans-
ferred into or out of the diaphragm sheathing. Transfer is to either a boundary
element or to another force-resisting element.
Diaphragm Chord : A diaphragm boundary element perpendicular to the applied
load that is assumed to take axial stress due to the diaphragm movement.
1604.4 Analysis [partial quote]
Load effects on structural members and their connections shall be determined by
methods of structural analysis that take into account equilibrium, general stabil-
ity, geometric compatibility, and both short- and long-term material properties.
Any system or method of construction to be used shall be based on a rational
analysis in accordance with well-established principles of mechanics. Such analy-
sis shall result in a system that provides a complete load path capable of transfer-
ring loads from their point of origin to the load-resisting elements.
The total lateral force shall be distributed to the various vertical elements of
the lateral-force-resisting system in proportion to their rigidities, considering the
rigidity of the horizontal bracing system or diaphragm. Except where diaphragms
are flexible, or are permitted to be analyzed as flexible, provisions shall be made
for the increased forces induced on resisting elements of the structural system
resulting from torsion due to eccentricity between the center of application of the
lateral forces and the center of rigidity of the lateral-force-resisting system.
Every structure shall be designed to resist the overturning effects of the appli-
cation of the lateral forces specified in this chapter. See Section 1609 for wind
loads, Section 1610 for lateral soil loads, and Section 1613 for earthquake loads.