Page 128 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 3 BRIDGE FAILURE STUDIES AND SAFETY ENGINEERING 103

3.11.2 Vehicular Accidents/Damage to Superstructures and Substructures
Vehicular accidents can cause damage to parapets and railings. Girders and piers get hit

by vehicles due to insufficient horizontal and vertical under clearance. Vehicular accidents may
also be caused by poor deck drainage and water accumulation after a heavy downpour. Some
causes include:
1. There may not be enough scuppers installed on the deck.
2. The magnitudes of cross slope (< 4 percent) and longitudinal slope (< 2 percent) may not
be adequate.
3. The local intensity of rainfall may be underestimated.
4. In winter months, ice layers forming on the concrete deck may create a slippery surface for
vehicle wheels.
5. In addition, deicing salts may cause early deterioration and cracking of a deck, making a
bumpy ride for motorists.

3.11.3 Suggested Preventive Action against Vehicle Collision

1. Ensuring adequate drainage of decks during storms.

2. Efficient de-icing after snowfall and posting warning signs for bridge deck freezing.

3. Improving traffic signs at approaches.
4. Avoiding centrifugal forces due to a sharp radius, or improving sight distance.
5. Discouraging drunk driving with severe penalties.
6. It is important that vehicles and the bridge be properly maintained.
7. Also, drivers should not be under the influence of drugs or suffering from drowsiness due

to lack of sleep.

3.12 BLAST LOAD AND PREVENTIVE ACTION
3.12.1 Introduction
1. Bridges provide vital linksfor the nation’s economy, defense, and quality of life. In addition
to natural hazards, the transportation infrastructure in the U.S. is vulnerable to physical,
biological, chemical, and radiological attacks.
To keep thesystem safe and operational under all circumstances systems and technologies
should be developed to prevent, detect, respond to, and remediate all attacks. The design of
bridges for blast and impact is important. Multiple hazards affect the stability and service
life of structures.
2. University of Missouri-Columbia (UMC) has a unique National Center for Explosion Re-
sistant Design. They are engaged in researchprojects to establish prototypical functionality
and architectural standards for blast-resistant barricade systems through applied research,
design, and test efforts.
3. To begin addressing this concern, FHWA has initiated a state pooled grant program entitled
“Validation of Numerical Modeling and Analysis of Steel Bridge Towers Subjected to Blast
Loading.” The research program includes a combination of blast testing against scaled steel
tower components and parallel numerical computations using a variety of analytical tools.
4. Inelastic dynamic progressive collapse analysis of truss structures: In a truss, dynamic ef-
fects may arise not only due to external dynamic loads, but also due to a sudden reduction
in the stiffness and load carrying capacity of a member. Resulting dynamic redistribution
of internal forces may lead toprogressive collapse of the entire truss structure.