3.1.3 Drip inducer (or drip)
A drip inducer is a recess or groove within, or a protrusion below, an underside surface.
Its purpose is to interrupt the flow of any water along that surface and cause it to drip off, a watershed.
Water running down or blown against the side face of the parapet beam of a bridge will then run or be blown along the soffit of that beam and any adjacent cantilever and down the side face of the deck itself, causing unsightly staining and reducing durability. By preventing most of the water from following this path, the presence of a drip in the underside of the parapet beam helps avoid this defacement.
Detail 3.1.3-1 Drip inducer (water-shedding)
PREFERRED
Option A tapered recess. While both A and B have been used extensively, Option A is the more recent and is considered to be the most effective.
Option C is also favoured where a downstand beam is required to mask irregularities in the deck pour and achieve a good alignment to the parapet beam. In this case, the downstand itself forms the drip.
AVOID
Right-angled recesses.
Any reduction in cover to reinforcement in the vicinity of the drip.
REMARKS.
Arright angle offers the most effective drip, but the edges are tapered slightly to allow easy removal of the timber former. The lead drip edge could be a right angle.
The dimensions shown in Detail A are considered to be the minimum to achieve the desired effect. A wider, deeper recess detail will achieve some improvement but not beyond 75 x 25 mm,
The need to provide a recessed drip in conjunction with Detail C should be considered if the width of the downstand increases beyond 200 mm.
Because of the continuity of the drip groove and its location in a very vulnerable area, open to the elements, it is important that cover to the reinforcement in the vicinity of the drip does not reduce below that required by the specification.
Consideration should be given to where the drips of water will land, so that the problem is not transferred to another critical point, eg the top of the bottom flange of an adjacent main girder.
Another way of forming a drip is to use a flat aluminium or plastic strip glued or riveted to the concrete edge face and projecting 20-25 mm below the soffit. This is more likely to be suitable where aesthetic considerations are not important and the main aim is to protect the concrete soffit and deck face, such as within abutment galleries.
Dimension D, downstand of Option C, value to be 50 mm minimum for drip inducement, but may be greater for other purposes, eg see Detail 3.1.8-1 for use with edge beams.
출처: CIRIA C543 Bridge detailing guide Michael Soubry
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