Parapets and railings are barriers installed on highway bridges to prevent users and vehicles from falling off. There are various types of parapets such as plain, embattled, perforated, and panelled, which can be made of materials like structural steel, aluminum, and reinforced concrete. When a vehicle collides with a parapet, the outcome depends on factors like impact speed and angle. The vehicle may be retained, penetrate the barrier, or roll over it. Proper parapet design aims to safely retain vehicles and control post-impact movement to avoid secondary accidents while minimizing occupant risk.

1. Parapets And Railings For
Highway Bridges
By-
Sandeep Kumar

2. Contents-
• Introduction
• Types Of Parapet
• Importance
• Material Used
• What Happens When Vehicle Collides With Parapet
• Result Of Collision
• Design Objective
• References

3. Introduction-
• A parapet is a barrier which is an extension of the wall at the edge of
a roof, terrace, balcony, walkway. Highway or other structure.
• The word comes ultimately from the Italian parapetto.
The German equivalent Brustwehr has the same meaning. In European
standards, parapets are defined as a sub-category of "vehicle restraint
systems" or "pedestrian restraint systems"
• In śilpaśāstra, the ancient Indian science of sculpture, a parapet is known
as hāra. It is optionally added while constructing a temple. The hāra can be
decorated with various miniature pavilions, according to the Kāmikāgama

4. Types Of Parapet
• Parapets may be plain, embattled, perforated or panelled, which are
not mutually exclusive terms.
• Embattled parapets may be panelled, but are pierced, if not purely as
stylistic device, for the discharge of defensive projectiles.
• Perforated parapets are pierced in various designs such
as circles, trefoils, or quatrefoils.
• Panelled parapets are ornamented by a series of panels,
either oblong or square, and more or less enriched, but not
perforated. These are common in
the Decorated and Perpendicular periods.

5. Importance Of Parapet
• Parapets on bridges and other highway structures (such as retaining
walls) prevent users from falling off where there is a drop.
• It may also be meant to restrict views, to prevent rubbish passing
below, and to act as noise barriers.
• Parapets are structures that are designed to reduce the severity of an
accident when an errant vehicle leaves the roadway. They provide a
passive line of defence. As such, they cannot be the cause of, or a
contributory factor in, an accident.

6. Material Use For Parapet Design
• Bridge parapets may be made from any material, but structural
steel, aluminum, and reinforced concrete are common. They may be
of solid or framed construction.

7. What Happens When Vehicle Collides With Parapet
• When a vehicle collides with a parapet, there are several possible
outcomes that depend on a number of factors, including the strength
and rigidity of the parapet, the speed of the collision, the angle of
incidence, vehicle weight and the centre of gravity of the vehicle
relative to parapet’s height.

8. Result Of Collision Of Vehicle.
• the vehicle is retained and may either be stopped by, or rebound
from, the parapet.
• The vehicle may penetrate the barrier if it is not strong enough to
withstand the impact.
• The vehicle may roll over the parapet if the parapet is not high
enough.

9. Collision Phase
• Where parapet retains the vehicle, the collision process may be
broken down into four phases, which are-
• collision of vehicle’s front corner.
• Lateral scrapping against the parapet;.
• Collision of vehicle’s rear corner.
• Re-entry of vehicle onto the carriageway.

11. Design Objective Of Bridge Parapet
• The design objectives of all vehicular parapets are similar. The three
main requirements are structural adequacy, reduction of occupant
risk, and controlled post-impact vehicular response to avoid
secondary accidents and to minimize undue risk to the errant vehicle
and other road users.
• Structural adequacy is a measure of the ability of the parapet being
able to stop an errant vehicle from penetrating, under-riding or
overriding the parapet, or to redirect the vehicle in a controlled
manner. The parapet may undergo an acceptable sideway deflection.

12. Design Objective Of Bridge Parapet Conti…
• Risk to occupant is based on the acceleration and deceleration
experienced by the occupant during impact, and the hazard posed by
detached elements. Consideration should be given to the risks posed
to other road users by the detached fragments of the parapet after
impact.
• The third design objective is to control the exit angle and the post-
impact vehicle direction to reduce the likelihood of subsequent multi-
vehicle accidents involving the crash vehicle re-entering traffic after
‘bouncing’ off the parapet.

13. References-
• https://en.wikipedia.org/wiki/Parapet
• http://www.thb.gov.hk/eng/policy/transport/issues/rehs/e_chp9.pdf
• http://www.bridgedesign.org.uk/parts/parapet.html
• https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&c
d=18&cad=rja&uact=8&ved=0ahUKEwi086bErMrXAhVFQY8KHbdyA-
QQFgh0MBE&url=http%3A%2F%2Fwww.saferoad.co.uk%2Fproducts
%2Fbridge-parapets%2F&usg=AOvVaw26zWx7_qNCqmrW_12l_5eV

14. Thank You