Page 117 - Bridge and Highway Structure Rehabilitation and Repair

92 SECTION 1 ADMINISTRATIVE ISSUES

• The available flow width may be reduced due to construction of cofferdams.
• Velocities through the remaining opening will increase, thereby increasing scour in the
channel and around the structure.
• Any river pollution from construction material needs to be monitored. Regular cleaning
of the channel may be required.
• Approvals for stream encroachment permits will be necessary.
• The effect of driving sheeting or bed armoring on existing utility needs evaluation.
• Countermeasures may extend into adjacent property limits. Any construction easement
needs to be carefully evaluated and permits obtained.
• Tidal conditions will affect working methods and working hours for construction.
• The health and safety of construction personnel will be a concern due to water depth.

3.6 DESIGN DEFICIENCY AND PREVENTIVE ACTIONS

3.6.1 Incorrect Design Assumptions or Modeling Errors
Table 3.5 shows reasons for failures from assumptions which are usually made in analysis.
Failures result when assumptions do not truly represent the behavior of the superstructure in the
field. Figure 3.11 shows a newspaper cartoon published in Karachi, Pakistan after the 2007 col-

lapse of a bridge.

3.6.2 General Preventive Measures
1. Provide space for bearing inspection chambers.
2. Apply load and resistance factors based on LRFD methods.
3. Ensure seismic retrofit against minor and recurring earthquakes.

4. Provide scour countermeasures.
5. Effectively monitor through remote sensors.
6. Study failure mechanisms of different types of structural systems.
7. Maintain quality control and personnel safety during construction.
8. Develop and make available codes for rehabilitation of mixed structural systems should be
developed and made available.

Figure 3.11 The impact of engineering decision on bridge users: A cartoon shows a family in Karachi offering
prayers before crossing a bridge. The public is cautiously aware of bridge safety conditions.