Page 124 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 3 BRIDGE FAILURE STUDIES AND SAFETY ENGINEERING 99

and OSHA standards. Lack of quality control for materials testing and an unrealisticly quick
construction schedule need to be avoided.
2. New foundation construction techniques: Many problems and substandard performance
of foundations observed in structures on expansive soils occur from faulty construction
practices. The construction equipment and procedures that are used depend on the founda-
tion soil characteristics and soil profi les. Construction techniques that promote a constant
moisture regime in the foundation soils should be used during and following construction.
3. Self-consolidating concrete (SCC) for use in drilled shaft applications: Whenconventional
concrete is used in congested drilled shafts, coarse aggregatesmay bridge between reinforc-
ing bars, which may lead to segregation of the concrete between the inside and outside of
thereinforcing cage. SCC is feasible for use in congested drilled shaftapplications.

3.9 VESSEL COLLISION OR FLOATING ICE AND SUGGESTED PREVENTIVE ACTIONS
3.9.1 General
Bridge piers located on navigable rivers are likely to be hit in fog or in darkness usually
from barges or ocean going ships. Damage to timber fenders which shield the piers may also be
caused by floating ice at high velocities. The EOR must assemble the following information:

1. Characteristics of the waterway including:
• A nautical chart of the waterway
• Type and geometry of the bridge
• Preliminary plan and elevation drawings depicting the number, size, and location of the
proposed piers, navigation channel, width, depth, and geometry
• Average current velocity across the waterway.
2. Characteristics of the vessels and traffi c including:
• Ship, tug, and barge sizes (length, width, and height)
• Number of passages for ships, tugs, and barges per year (prediction for 25 years)
• Vessel displacements
• Cargo displacements (deadweight tonnage)
• Draft (depth below the waterline) of ships, tugs, and barges
• The overall length and speed of tow.
3. Accident reports.
4. Bridge importance classifi cation.
Table 3.7 shows failure details for a large number of impacts from ships, which is also a
cause of concern for the shipping industry.
3.9.2 Design Vessel

The design of all bridges over navigable waters must be checked for possible vessel colli-
sion. Conduct a vessel risk analysis to determine the most economical method for protecting the
bridge. The number of vessel passages and the vessel sizes are embedded as an integral part of
the vessel collision risk analysis software.
1. The Florida DOT’s MathCAD software for conducting vessel collision risk analysis may be
used. The software computes the risk of collision for several vessel groups with every pier.
When calculating the loads and load factors probability, the overall length of each vessel
group is used instead of the length overall (LOA) of a single design vessel.
2. Widening of bridge on navigable waterway: Major widening spanning navigable waterways
must be designed for vessel collision. Minor widening spanning navigable waterways will
be considered on an individual basis for vessel collision design requirements.