Page 184 - Forensic Structural Engineering Handbook

THE FIRST STEPS AFTER A FAILURE 5.17

• Include an item in the photograph that provides a sense of scale, such as a tape measure,
a coin, or a person.
• If using film, assign each photographer an identifier for his or her rolls of film. A simple
method is to use the person’s initials with a sequential suffix. For example, Roll “JFK-1,”
“JFK-2,” and so on. Also, when starting a new roll, it is helpful if the first photograph is of the
roll number. This will provide a permanent record, on the negatives, of the roll’s identity.

Video
Video can also be a valuable documentation tool. It is best suited for the following:
• An activity or process. Examples include removing and weighing a snow sample, demo-
lition operations, and other event that cannot be adequately captured with a series of still
photographs.
• Providing a “walk-through tour.”
• Low light conditions. In situations where the items of interest are so far from the pho-
tographer that a camera flash is ineffective, a video camera may be better able to capture
the conditions.
• In conditions where written note-taking is not practical, a camcorder may be used to
record verbal notes.
However, video is not suitable for all tasks, and a considerable degree of skill is needed
to make a high-quality video recording. Amateur videos often include excessive shaking,
disorientation due to panning too quickly, leaving the subject too soon, and distracting
background noise. A prime disadvantage is the need for special equipment to view the
recording.
If the situation truly warrants the use of video, consideration should be given to having
it done professionally.

New Technology
Rapid technological advances in the past few years have resulted in new techniques that
may be useful in engineering investigations.

3D Laser Scanning. 3D laser scanning is a powerful technology. Whereas traditional
surveying instruments measure distances one point at a time, and may require the use of
reflecting prisms, laser scanners are capable of scanning thousands of points per second,
without the need for reflectors. They have a range of nearly 1000 feet, and an accuracy of
1
approximately / 4 inches. The field of view is 360 degrees horizontally, and some units can
measure 270 degrees vertically. To cover large areas, or areas that are otherwise obstructed,
multiple scans can be joined using post-processing software. Laser scanning equipment,
and the associated post-processing software, is offered by a growing number of manufac-
turers, such as Leica, Trimble, and Optech.
On April 29, 2007, a tanker truck carrying 8600 gallons of gasoline overturned on an
interstate ramp on the east side of the San Francisco Bay in Oakland, California and burst
into flames. The intense heat melted the steel beams of a ramp directly above the truck, caus-
ing a 165-foot-long section to collapse. Fortunately, there were no deaths, and the injured
truck driver managed to walk away. 3D laser scanning was used by various agencies to doc-
ument the extent of damage, to provide information needed to assist with shoring and demo-
lition operations, and assist with reconstruction. Figures 5.12 and 5.13 are of this incident.