Movable Bridge

Movable bridges represent a critical application where brakes function as the ultimate safety and control mechanism, responsible for mastering immense inertia and unpredictable external forces.

On a movable bridge—whether it’s a bascule (drawbridge), vertical lift, or swing bridge—the brakes are not merely for stopping; they are fundamental to the operational safety and structural integrity of the entire system. Their roles are multifaceted:

1. Static Holding in Position: This is arguably the most critical function. Once the bridge span is in the fully open or fully closed position, brakes are engaged to lock it rigidly in place. They must be powerful enough to resist immense and fluctuating wind loads, which can exert tons of force on the large surface area of the bridge deck. They also prevent any “creep” or drift from the drive machinery, ensuring the span remains perfectly aligned for road traffic or clear for marine traffic.
2. Emergency Stopping (E-Stop): In the event of a control malfunction or an impending collision, the emergency stop system relies on the brakes to arrest the motion of the massive bridge span as quickly as is safely possible. This requires brakes with extremely high torque capacity to overcome the moving span’s enormous kinetic energy.
3. Service Stopping Assistance: While the primary drive system (often a variable frequency drive, or VFD) typically handles the smooth deceleration of the bridge during normal operation, the brakes provide the final, precise stop and hold at the end of the travel sequence. This prevents shock loads on the gearboxes and drive motors.

The design of these braking systems is always centered on a fail-safe principle. Typically, large-caliber, spring-applied, hydraulically or electrically released disc or drum brakes are used. This means that if electrical power or hydraulic pressure is lost for any reason, powerful springs automatically engage the brake, securing the bridge span in its current position. This inherent safety feature prevents a potentially catastrophic uncontrolled movement of the bridge.

For a movable bridge, the braking system is a non-negotiable safety component that provides precise positioning, emergency stopping power, and, most importantly, the ability to securely hold the structure against powerful and unpredictable environmental forces.