X - HKU Libraries

V.4 .2.7Amendment No. V-l/91 (Jan.)4.2.7 Collision Loads4.2.7.1 Highway overbridgesUnited Kingdom, Department of Transport hasproposed amendments to BD 37/88 Appendix A (BS 5400 : Part2) clauses 6.8 and 7.2 resulting from the incorporation ofHeavy Goods Vehicle collision forces for highway structures.The collision loads on supports of bridges and bridgesuperstructures over highways have now been substantiallyincreased. The proposed amendments as given in Appendix4.2.4 shall be used for the design of highway structures.Supports exposed to possible vehicle collisionsshould be protected by metal or concrete barrier fences.Gantry supports should be designed to resist anominal load of 50 kN acting in the worst possible directionand at the worst height up to 3000 mm above the adjacentcarriageway.4.2.7.2 Railway overbridgesThe potential collision loading on a bridge overa railway track is many times any of the loadings given in4.2.7.1. Effective protection of supports against derailmentcollisions is accordingly difficult. Clause 4.13.5 containsrecommendations concerning not only the collision loadingsfor which allowance should be made but also other means bywhich the severity of collision effects may be ameliorated.4.2.7.3 Bridges over navigation channelsBridge piers situated in navigation channels maybe subjected to ship collision loadings . The magnitude andform of such collision loadings depend so much on thelocation of the bridge and the nature of the shipping usingthe navigation channel that specific guidance cannot begiven, but the possibility of ship collisions should alwaysbe considered at the design stage and appropriate protectionprovided. Clauses 4.18.4 and 4.13.6.5 also deal with shipcollisions.4.2.8Parapet loadingLoads transmitted by vehicle collisions withparapets to structural elements supporting parapets shouldbe dealt with as described in section 6.7 of BS 5400Part 2.Vehicle parapets and vehicle pedestrian parapetsshould be designed in accordance with the requirements ofsection 4.15 of this chapter.Railway overbridge parapets should be designed toresist the loads described in clause 4.15.13 of this chapter.Pedestrian parapets should be designed to resistthe loads described in clause 7.1.2 of BS 5400 : Part 2.