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Should vehicular parapets be designed to be strong?

Parapets are designed to satisfy different containment levels. The containment level represents the magnitude of impact that the parapet is supposed to uphold.

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A parapet designed as low containment level can hardly withstand the impact by large vehicles which may even damage the parapet. On the other hand a parapet designed as high containment level can effectively contain safety large vehicle. However, when it is collided by light vehicles, it is expected that it would cause considerable damage to the light vehicles and its passengers on board. Therefore, strong parapets may not necessarily mean a good parapet.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Can vehicular parapets withstand the collision of double-decked bus?

Basically the major problem associated with the collision of double-decked bus lies on the possible overturning of the bus upon collision. The overturning moment is the product of impact force and the difference in the centre of gravity of bus and the height of vehicular parapet. The restoring moment is the product of bus weight and 0.5 times the width of bus.

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In fact, owing to the elastic deformation of both the parapet and bus, it is expected that the impact force, and hence the overturning moment may not be larger than the restoring moment for 1.1m high vehicular parapet. Computer simulations have to be conducted to verify if a double-decked bus traveling at a certain speed would roll over the parapet when impacted at a certain angle.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

When are the conditions which warrant the installation of safety barriers along roads?

In general there are several main conditions which warrant the installation of safety barriers along roads:

(i) It protects vehicles from hitting a roadside object (e.g. bridge pier, sign post, walls etc). Conversely, it protects the roadside object from damage by collision of vehicles.

(ii) It avoids the crossing over of vehicles over central median.

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(iii) It protects the vehicle from falling down a steep slope (more than 3m high)

(iv) A poor record of accidents involving run-off vehicles.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What are the differences between tensioned corrugated beam and untensioned corrugated beam?

Tensioned corrugated beam is mainly used in high speed road while untensioned corrugated beam is mainly used in low speed road.

Tensioned corrugated beam is designed mainly for use on central reservation. When a vehicle crashes into tensioned corrugated beam, the beam remains in tension while the post gives way to allow for deformation.
Tensioned corrugated beam absorbs impact energy by deflecting as a whole and helps the vehicle decelerate, and at the same time guide it back towards the carriageway in a gradual and controlled manner. Tensioned corrugated beam is normally not used on curves with radius less than 120m.

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Untensioned corrugated beam is commonly used for road bends where radius of curvature is small as the use of untensioned beam does not require tensioning device. It is designed to deform in beams and to re-direct impacting vehicles on a course as close as possible parallel to the barrier.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the difference between safety fence and safety barrier?

A safety fence is intended to absorb some energy caused by hitting vehicles and to realign the vehicles to move parallel to the safety fence.

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A safety barrier is intended to provide containment instead of energy absorption upon hit by vehicles. Hence, it is anticipated to have little deflection and deformation only. After crashing, it serves to re-direct the vehicles along the line of barrier.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.