X - HKU Libraries

4*11*5(Mbvember f 1983)Unsealed joint© enable stormwater topenetrate into the superstructures! "bearings t piersand abutments of highway structures and railway"bridges* Although stormwater penetration in Hong Kongis not so serious as in temperate climates f wherestoirawater carries snow-dispersing chemicals intostructures with highly deleterious effects, suchpenetration is undesirable as it causes corrosionof ferrous bearing components and produces anundesirable appearance.Stormwater penetration through expansionjoints may be dealt with in three ways(i)(ii)(iii)a proprietary expansion jointdesigned so that the completedinstallation is watertight maybe chosen (although in practicesuch joints are always liableto leak, and some means of drainageshould accordingly always be provided)}a proprietary expansion joint whichallows the passage of stormwater maybe used in conjunction with a drainagelayer or channel added to catchstormwater aid divert it to thedrainage system; orthe structure may be designed sothat stormwater can pass freelythrough the expansion joint to becollected on the piers and abutmentsand diverted to the drainage systemwithout accumulating round bearingsor staining visible surfaces*A conscious decision should be made at the design stageas to which of these possibilities is to be followed.Stormwater draining through track ballast ontorailway underb ridges must be collected and led away*Hot only should joints be carefully sealed, but inaddition a substantial heavy duty waterproof membraneshould be applied to the bridge deck* The waterproofmerabrance should be continued across the deck endsand taken down behind the ballast walls, with drainsto collect and remove water running down the membrane*The membrane should be suitably protected againstdamage by track ballast*