A Self-Learning Manual - Institution of Engineers Mauritius

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A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU would be separated from the beams and there would be lesser deceleration experienced by the vehicles [48]. Fig. Beam barrier. 3. Why is concrete crash barriers normally used in central divider? (CPB2) Concrete crash barriers are not considered as the best barrier design because of the following reasons when compared with flexible barriers: (i) Concrete barriers possess rough surface which, when impacted by moving vehicles, tend to cause considerable damage to the vehicles. (ii) Since concrete is a rigid material and the deceleration of collided vehicles is comparatively large when compared with flexible barriers. However, concrete crash barriers have particular application in locations where the deflection of barriers is not allowed. For instance, in the central divider of a carriageway, if flexible barriers are adopted and vehicles crush into the barriers, the deformation resulting from the hitting of vehicles would result in an intrusion to the adjacent carriageway. This is undesirable because this may trigger further collisions in the adjacent carriageway and hence rigid barriers like concrete crash barriers should be adopted in this scenario. 4. What is the difference between safety fence and safety barrier? (BT1) 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. 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. 282
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU 5. What are the differences between tensioned corrugated beam and untensioned corrugated beam? (BT2) 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. 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. 6. When are the conditions which warrant the installation of safety barriers along roads? (BT1) 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. (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. 7. Can vehicular parapets withstand the collision of double-decked bus? (VP1) 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 283
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A Self-Learning Manual - Institution of Engineers Mauritius

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