Parapets and railings for highway bridges

A brief introduction of parapets

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.

10. 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.

11. 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.

12. 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&cd=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

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