A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Level Two (Advanced FAQs)
Part III: Road Furniture
1. Why are concrete profile barriers designed with curved surface
profiles? (CBP1)
Safety fencings are designed to contain vehicles in the carriageway in
which they are traveling and prevent them from rebounding into the road
and causing hazards. For normal fencing design, when vehicles crash into
safety fencings, it will give way so as to absorb as much energy as possible,
thus reducing the impact forces on the vehicles. Moreover, it serves to
realign the vehicles along the carriageway when vehicles hit on them.
However, for concrete profile barriers they are not designed to absorb
energy during vehicle crashing, but to hold the vehicles hitting on them. In
this connection, concrete profile barriers are designed with curved profiles
so that vehicles can mount and go up partly on them, and yet they will not
cause overturning of vehicles. Reference is made to Arthur Wignall, Peter
S. Kendrick and Roy Ancil.
For shallow-angle crashing of cars, they would climb on the lower slope
face of concrete profile barriers. On the other hand, when a car hits at a
large angle to the barrier, the bumper collides with the upper sloping face of
concrete profile barrier and the car rides upwards. This provides the uplift
of the car whose wheels move up the lower sloping face of the barrier. It is
not intended to lift the car too high, otherwise it may result in rolling. Since
the friction between the wheels and barriers provide extra lifting forces, it is
undesirable to design rough finish on these faces. In essence, the kinetic
energy of the car during collision is transformed to potential energy during
its lifting up on profile barrier and finally converted back to kinetic energy
when the car returns to the road.
2. What are the advantages of having corrugation in crash barriers?
(CBP1)
The layout of corrugated beam barriers is that the beams are corrugated in
the longitudinal direction so that it provides higher lateral stiffness with a
thinner material. Moreover, the distance of beams posts and crashing
vehicles are considerably increased.
In case the beam barriers are tensioned, it is intended to create a stiff
beam erected on relatively weak posts. During vehicle collision, the posts
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