Page 391 - Forensic Structural Engineering Handbook

11.22 MATERIAL-SPECIFIC FORENSIC ANALYSES

specifies design rules, materials and their properties, welding and other fabrication proce-
dures, and inspection methodology. Even this code cross-references ASTM, AISI, and
AWS codes and standards.
While the proceeding discussion focuses on U.S. codes and standards it should be
remembered that the design and fabrication of steel structures has taken on a significant
international flavor. An example of this is the export of U.S. steel structures and design pro-
cedures to other parts of the world by manufactures such as Caterpillar while at the same
time foreign manufactured earth moving equipment is purchased and imported into the
U.S. markets. This international flow of design and fabricated steel structures require that
engineers today are conversant with not just their own national codes and standards but
with most international codes, such as the ISO Standards or Eurocodes. In fact many local
jurisdictions in the United States have adopted and allowed the use of international codes
and standards, as well as local and national codes and standards. The large ship container
cranes used in U.S. ports are examples of this. As a result, when assessing the integrity of
a structure, it is often necessary to follow an extended trail of information and certification
to determine what codes and standards are or were applicable to the structure when it was
constructed. Since these codes and standards change over time, it is often necessary to pur-
sue the trail through historic standards, not current ones. This process may lead to the con-
clusion that the structure in question meets the standards of the time of its construction but
not those of today. Such a finding may be particularly important if the structure is to be
retrofitted or repaired so it can be returned to service. It may have to be retrofitted exten-
sively if it is to be upgraded to current standards.

METHODS OF ANALYSIS

Many issues affect the design and analysis of steel structures. It is critical for the design
team to determine early on the structure’s anticipated design life and the loads that the
structure must sustain during its life. Additionally, it is important for the designer to con-
sider in the initial design stages the fabrication, inspection, maintenance, and repair of the
structure. If the structure is difficult to fabricate due to the designer not considering its fab-
rication, the structure may be rendered useless. Furthermore, if the structure is difficult to
maintain due to maintenance issues such that it cannot be adequately inspected and
repaired, the cost of using the structure safely over its intended life may prove to be pro-
hibitive. While the design issues of maintenance, inspection, and repair are not dealt with
in any detail in these discussions of steel structures, it is very important that the designer
gets these correct. In the remaining discussions provided here on methods of analysis, the
applied loads the structure must sustain are considered. Sometimes these loads are set forth
in regional, national, or international building or design codes. Many times the structures
intended owner or local regulators set additional load requirements over and above the
design load requirements.
Many structures and their components can be evaluated by using simple equilibrium
models and basic principles of mechanics to determine stress resultants acting on the mem-
ber. Loads and load combinations are specified in the AISC LRFD specifications for struc-
tural steel buildings with the recommended minimum loads given in Ref. 27 (ASCE 7,
Minimum Design Loads for Buildings and Other Structures). These loads are sometimes
modified by the applicable building code (e.g., Ref. 28). The availability of a larger num-
ber of structural analysis and design computer programs provide tools that are readily avail-
able to model and analyze the structure under a variety of loading conditions. Where there
is no evidence of significant plasticity, an elastic analysis will provide reasonable estimates
of the failure load. Where obvious plasticity has occurred such that large deformations are