Drag plate
Drag plates are used when movements occur between two components that have to be bridged. To compensate for the transition, a drag plate is installed over a defined distance.
Towing plate for bridges
Drag plates in building construction
Towing plate at the manhole
Towing plate at the transition at the pedestrian suspension bridge
bridges
In the case of bridges, the foundation, abutment wall and bridge girder components form a fairly rigid unit. On the other hand, the immediately adjacent subsoil is to be regarded as soft. Settlements occur that are particularly pronounced in the filling area. Without an intermediate component, there would be a crack in the roadway that would be a few centimeters. In order to avoid this paragraph for the traffic, a drag plate is implemented. Depending on the bridge, this is three to six meters long and rests on the one hand on the abutment wall and on the other hand on the natural ground at a frost-free depth. The towing plate is usually made of reinforced concrete and statically calculated like a bridge girder that has two supports. After production, the drag slab is poured in and the road surface is applied.
Building construction
If structures are subjected to different loads, there is a risk that both structures will experience different subsidence. A transition between the structures must now be made with a movable drag plate in order to avoid unpleasant, constantly changing steps. For this purpose, supports and plate structures are used, which are articulated on both sides. These drag plates can be made with any building material that is also used for ceilings (wood, steel, reinforced concrete, fiber concrete, composite construction).
Manhole
If the frost protection layer is not sufficiently dimensioned when building a road, the subsoil below will freeze in winter. The entire street rises to the extent that the frozen ground expands. This is caused by the formation of ice in the pores, where the volume increases by approx. 10%, as there is a volume expansion of approx. 10% at the transition from water to ice. Simple recalculation:
When 50 cm of ground freezes, the following uplift occurs:
The soil has about 30% of the pores filled with water, these freeze over
50 cm * 0.30 * 0.1 = 1.5 cm elevation of the road in winter.
The sewer shaft is built frost-free and therefore does not rise in winter. As a result, the manhole cover is lower than the roadway in winter. In winter it "sinks" into the road by the calculated amount.
Road lifting at manhole covers
renovated sewer area
The two pictures show the usual condition, on the one hand the lifting of the carriageway in winter and on the other hand the attempt to repair the cracks around the manhole cover, which in the present case shows little success. The solution to the problem seems to be a construction with a drag plate - designed as a ring - as it is indicated in the construction drawing, but no practical systems are currently known on the market.
literature
- Requirements and behavior of drag plates on road bridges; G. Malho, S. Martin, Civil Engineer, Volume 90, Sept. 2015
- Expansion compensation system for various manhole covers in the floor area, E. Haar, Institute for Underground Infrastructure Gelsenkirchen, Newsletter 2001
