Page 149 - Bridge and Highway Structure Rehabilitation and Repair

124 SECTION 1 ADMINISTRATIVE ISSUES

• Installing spurs or bendway weirs at a bend that is migrating toward a bridge abutment.
Spurs will redirect the flow away from the abutment.

• Hydraulic countermeasures: Placement of armoring such as riprap around exposed foun-
dation
• Structural countermeasures: Underpinning of footings that were undermined by using
grout or grout bags.

3.21 REITERATING NEEDED PREVENTIVE MEASURES
3.21.1 Proposed Solutions

1. Correct diagnosis: The history of failures shows that they are not a rule, but they are not an
exception either. They may not be common, but are recurring. Failures may occur at irregular
intervals and for different reasons. Like all grim realities, every bridge which is constructed
will eventually collapse. Some will take longer than others.
Bridges are subject to displacement, movement, and sway due to the changing positions
of live load, impact, varying temperatures, and transient environmental forces such as wind,
floods, and earthquakes. It is prudent to take necessary precautions and promptly fi x any

deficiency. To avoid adverse effects resulting from failures, a diagnostic approach in design

is required.
2. Technological advances in information systems have had a great impact on data collection
and analysis.
3. There is a need for continuous inspection through structural health monitoring.
All the man-hours for bridge inspections may not be usefully spent if the bridge man-
agement system in effect has not prevented failures. It is therefore important to examine
the recurring lapses in our inspection methods, structural health monitoring, and advance
warning systems.
4. Engineering agreements may be used to perform a wide variety of safety inspection work
for bridges, culverts and other structures. Inspection related work may include:
• Routine and in-depth inspections
• While two year inspection cycles keep track of changes in structural conditions, circum-
stances may change overnight for the worse. Failure of the Minnesota I-35 bridge is a case
in point.
• Special inspections (fracture critical members, damage investigations, etc.)
• Underwater inspections
• Bridge capacity analysis and ratings
• Special studies and testing
• Providing space for bearing inspection chambers.

5. There is uncertainty about the fate of thousands of bridges classified as structurally defi cient.
Using vulnerability assessment methods, some have been assessed as more vulnerable to
failure than others. Such bridges may be located in a seismic zone or on a scour critical river
where the probability of failure is higher than in non-seismic zones or where foundations
are not subjected to erosion.

3.21.2 Design Related Actions
1. Due to in-built safety factors in design, the majority of failures occur not due to a single
cause but due to the combination of two or more extreme conditions. For example, thin
gusset plates in a steel truss are more vulnerable to failure when corroded than when they
are galvanized.
Greater vendor and construction engineer participation in revising and developing design
codes needs to be introduced and implemented.