A slip base plate system is a roadside breakaway device typically for signposts or light poles that consists of two plates connected by a central bolt and nuts through slotted holes, When a vehicle hits the post from the front, the plates separate, allowing the upper post to slide away from the base plate, Key components include an anchor base plate a slip plate, a keeper plate, anchor bolts with leveling nuts, washers and high strength clamping bolts, which are intentionally not over tighten to allow breakaway.
Components and Function
Slip Base Pole: A system designed to detach in a collision, reducing impact forces.
Anchor Base Plate: Fix the bottom plate to the concrete foundation.
Slip Plate: The upper plate, attached to the pole, that slides during a collision.
Keeper Plate: A plate with slots that helps hold the anchor and slip plates together but allows them to separate during a breakaway.
Clamping Bolts: High-strength bolts that go through the anchor plate, keeper plate, and slip plate to hold them together.
Anchor Bolts: Bolts that attach the base assembly to the concrete foundation.
Leveling Nuts and Washers: Used to ensure the base plate is level and to maintain the correct configuration during assembly.
Grout: A non-shrinking material often used between the base plate and the concrete foundation to fill gaps and ensure proper load transfer.
Mechanism of Breakaway
1. Impact from the Front:When a vehicle strikes the pole from the front (the sign face side), the force pushes the two plates apart.
2. Slotted Holes:The clamping bolts position in slotted holes on the keeper plate.
3. Sliding Action:As the impact occurs, the upper slip plate slides away from the fixed anchor plate, disengaging the bolts from the slots.
4. Dislodgement:The entire pole then dislodges and falls to the ground, minimizing the force of impact on the vehicle and its occupants.
Key Benefits
Enhanced Road Safety:Slip base poles are crucial for protecting people by preventing severe secondary impacts that can result from a rigid pole becoming a hazard during a crash.
Mitigated Damage:The controlled breakaway also minimizes damage to the pole itself and other roadside elements, potentially lowering repair costs and disruption.
Designed for High-Speed Areas:Their use is especially beneficial in locations with high-speed traffic, where the risk of serious injury from an impact with a static pole is higher.
Important Considerations
Bolt Tightening: Clamping bolts must not overtighten. Over tightening will prevent the breakaway system from working as intended during a collision.
Orientation:Slip bases are designed to break away when struck from the front, they will not work if hit from the side.
Inspection: inspector must be present to ensure proper assembly and torqueing of the bolts.
Placement:Slip base poles are used on larger signs with multi posts spaced apart or on light poles where the likelihood of collateral damage from a falling pole is low.
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