Page 211 - Forensic Structural Engineering Handbook

THE ENGINEERING INVESTIGATION PROCESS 6.13

TABLE 6.6 Project-Specific Documents Used in Investigations (Continued)
Construction supervisor’s daily log
Local building inspector
Owner’s or developer’s field inspectors
Material strength reports or certification
Concrete compressive strength
Masonry prism strength
Steel mill certificates
Welding procedures (e.g., type of electrodes, required preheat)
Fastener certification
Results of special load tests
Project correspondence †
Owner/consultant
Intraconsultant
Owner/contractor
Consultant/contractor
Transmittal/records
In-house memoranda
Records of meeting notes
Records of telephone conversations
Consultant reports
Feasibility studies
Progress reports
Soils consultant reports (including boring logs)
Calculations
Primary structural engineer
Reviewing structural engineer
Specific subcontractor’s engineers (where required by contract)
Maintenance and modification records
*Assist principally in establishing dead loads.
† The scope will vary depending on the investigator’s assignment.

Environmental data should be obtained for all structural collapses as temperature, wind,
water, snow, ice, earthquakes, and other environmental conditions often play a key role in
structural performance and ultimately failure.
Structural Analysis

Failure analysis is not the same as analysis for the purpose of design. Design analysis uses
a code-prescribed set of probable loads and a typically conservative set of structural capac-
ities, to assist in developing a structural system with a consistent safety factor. This
approach has historically produced reasonably efficient structures that have generally per-
formed well. The codes are updated regularly to reflect changing thinking in loading, analy-
sis, and capacities. The basic limit design method currently employed compares factored
(increased) loads to factored (reduced) capacities to determine structural adequacy.
Failure analysis must use the actual loads imposed on the structure and the real-world
capacity of the structural elements. Neither of these is particularly well represented by the
code-prescribed values. Actual loads can vary greatly, and structural capacity at collapse is
almost never accurately predicted by code, being lower due to material, design or construction
defects, or higher due to post-limit capacity, enhanced material properties, ductility and redun-
dancy. Failure analysis should be based on demand-to-capacity ratios absent any factoring.