Code Sections and Analysis - The Analysis of Irregular Shaped Structures - page 17

not required by code, the author's personal preference is to separate the gravity system
from the lateral system. In some cases it can cause additional work and potentially
increase the number of drawing sheets; however, the results are well worth the effort
because it ensures that a part of the lateral system will not be overlooked. For the engi-
neer, the clutter and confusion are reduced because only one system is being concen-
trated on at a time, thereby ensuring that a complete lateral system has been provided.
This also simplifies the plan review process and improves the quality control for the
project. For the code official, it significantly reduces the time required for a plan review.
The contractor can give a framer the lateral system sheets to complete that portion of
the structure, which reduces the chance for missed details and critical framing or con-
nections. The benefits for the building inspector are the same as for the engineer. The
lateral drawings should include a simple key plan to show the diaphragm boundaries
and required nailing. The framing plan should also call out all drag struts, collectors,
splice connections, special nailing requirements, shear walls, frames, and structural sec-
tions. All strut and collector forces should be called out on the plans. Grid lines should
be used for ease of communication over the phone or in written forms to identify spe-
cific locations. Wall elevations should be provided when walls contain openings that
require special force transfer connections or anchoring information. Inclusion of a lat-
eral system narrative and design criteria in the calculations is useful for the plan review
process, especially when the system contains complicated load paths.

1.6 Methods of Analysis

The examples in this topic provide methods of analyzing complex diaphragms and
shear walls. Each chapter contains one or two examples that demonstrate the method
or methods being discussed in the chapter. Problems, located at the end of each chapter,
are variations of the examples, each of which has a special lesson or point of interest. As
shown in those examples, the relocation of a single shear wall can significantly change
the distribution of forces through a structure. The lateral loads used in the examples are
generalized and can represent wind, seismic, or soil loads at either an allowable stress
design (ASD) or ultimate strength (LRFD) design level. The applied loads are assumed
to be the results of the individual's generation of forces to the structure, which are
appropriately factored up or down to fit the load combination and design method being
used. The number of decimal places typically used for most calculations varies from
one to two significant figures. Some of the examples are carried out using more signifi-
cant figures than would be normally be used in common practice. The intent is to pro-
vide better closure of the diaphragm chord and collector force diagrams.
The typical sign convention used in this topic is shown Fig. 1.9. One-foot by one-
foot square sheathing elements are used to show the direction of the shears acting on
the sheathing or collectors and chords. The figure shows typical positive and negative
sheathing elements when loaded in the transverse and longitudinal directions. The
figure also shows representative portions of force diagrams for collectors, struts, and
chords. For transverse loading, a positive force is drawn above the line representing
tension. A negative force is drawn below the line representing compression. In reality, it
does not make a difference on which side of the line the forces are drawn as long as the
construction of these diagrams is consistent throughout the analysis. This is so because
the force in a member will change from tension to compression upon the reversal of
the direction of the loads.