Civil Engineering Reference
In-Depth Information
CHAPTER
1
Code Sections and Analysis
1.1
Introduction
For centuries, building codes have been developed to define the standards for the
design and construction of structures. Opinions are often expressed that code require-
ments have become too complex; however, from the earliest of codes to our current
standards, codes have changed in response to our increased understanding of materials
and methods as well as our knowledge of the forces that are imposed on structures,
particularly wind and seismic forces. This understanding has been greatly increased by
past structural failures and from current state-of-the-art testing and research. In addi-
tion, changes to the code have been brought about by the reality that structures have
become increasingly complex compared to structures previously built.
The most widely used and accepted code for building design standards is the Inter-
national Building Code (IBC), published by the International Code Council (ICC).
1
The
document references a compilation of design standards that have been developed
through an open and transparent consensus process that represents all interested par-
ties and stakeholders. ASCE/SEI 7-05,
Minimum Design Loads for Buildings and Other
Structures
, is published by the American Society of Civil Engineers and the Structural
Engineering Institute
2
and is referenced from within the 2009 IBC. Wood lateral-force-
resisting systems are addressed in the National Design Specification for Wood Con-
struction (NDS-05) and
Special Design Provisions for Wind and Seismic
3
(SDPWS-08),
which are published by the American Forest & Paper Association and the American
Wood Council. The 2009 IBC, ASCE 7-05, NDS-05, and SDPWS-08 are codes and stan-
dards that are discussed in the chapters that follow.
Most of the texts and publications today only address simple rectangular diaphragms,
the analysis of which does not easily adapt to complex diaphragm and shear wall
layouts. The layout of the lateral-force-resisting system shown in Fig. 1.1 demonstrates
this problem. The vertical and horizontal offsets shown in the figure create disconti-
nuities in the diaphragm, which require special collector and drag elements to establish
complete load paths. Collectors and drag elements in diaphragms and in shear walls
are a critical part of complex lateral-force-resisting systems. The analysis and design
requirements for diaphragms under wind vs. seismic loading are topics that are often
misunderstood. Some of the confusion has been brought about by the presentation of
lateral-force-resisting systems and their elements within ASCE 7-05. Chapters 11 and 12
of that standard, which address seismic design, provide a complete and organized cover-
age of lateral-force-resisting systems and their components under seismic loading
conditions. Chapter 6 addresses the analysis and application of wind loads and pressures
on structures with regard to the main-force-resisting system (MFRS) and on components
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