Why should a road plate be more than just a piece of steel? Often we tend to take that piece of steel lying across a trench or roadway for granted, when in fact, there is a lot to consider. If you make the mistake of thinking of a road plate as just “any piece of steel will do,” you will eventually find yourself in big trouble.
Steel comes in many grades and thicknesses. Understanding the structural support ability is vital to protecting yourself and traffic from danger and avoiding damage to vehicles.
When a steel plate spans an excavation and traffic rolls over it, the center is depressed making the ends “flap” up. This is called “end-flap.” When the plate springs back or rebounds, it vibrates and can have a tendency to walk or move in the direction of the traffic flow.
The greatest deflection is always seen at the center of the span: the more deflection created, the greater the end-flap. This results in more migration or movement of the plate. The wider the span, the more likely end-flap will occur.
To reduce or eliminate this movement, it is important to control the end-flap at all times. Spikes and pinning is not always the best answer. Coatings that increase the friction between the road and the plate are more effective than spikes because of the amount of contact surface area. Spikes can even be ejected and become a new road hazard when the end-flap is not carefully taken into consideration. Temporary asphalt patch material or pipe joint mastic is a better solution than steel spikes.
Best of all, maintain the correct thickness for the appropriate span. When you know what the maximum span can be, offset the length of the plate toward the oncoming traffic rather than centering the plate over the hole. This way, if a plate is moved, there is less chance that it will fall into the excavation. Always mark the beginning offset of your plates to monitor any movement that might occur.
Peak traffic patterns are predictable. Reposition plates after each period of heavy traffic if necessary.
To reduce end-flap, use only steel plates of a known chemistry so the behavior is predictable. Be sure an engineer has designed the unsupported length of span to withstand H-20 loadings. When traffic will be present, never use a plate less than 1” thick, made of certified A36 steel.
Always be sure to get a copy of the tabulated data for the plate from your supplier.
If the plates you are using are not rated by an engineer for the larger spans you need, it might be time to consider temporary bridge panels.•