Structures Design Guidelines | Jan 2008
8 - Movable Bridges |

## 8.4 Speed Control for Leaf-driving Motors [LRFD-MHBD 5.4]

A. Design a drive system that is capable of operating the leaf in no more than 70 seconds (See Figure 8-1) under normal conditions.

B. Clearly indicate on the plans the following required torques:

1.) T A - the maximum torque required to accelerate the leaf to meet the required time of operation.

2.) T S - the maximum torque required for starting the leaf.

3.) T CV - the maximum torque required for constant velocity.

### 8.4.1 Requirements for Mechanical Drive Systems [LRFD-MHBD 5.4](01/08) Jan 2008 - Revised B. to require that drive meet 20 psf wind load in full open position.

A. Specify a drive capable of developing the torques stated above and operating the leaf (at full speed) in the 70 seconds time limit.

B. Compute the acceleration torque for the inertia and the loading specified for the maximum constant velocity torque [LRFD-MHBD 5.4.2]. In addition the drive must be capable of meeting the maximum starting torque requirements, and the machinery must be capable of holding the leaf against 20 psf wind load in full open leaf position [LRFD-MHBD 5.4.2].

### 8.4.2 Requirements for Hydraulic Drive Systems [LRFD-MHBD 7](01/08) Jan 2008 - Added “A. Use hydraulic drive systems only if approved by the SDO.”

A. Use hydraulic drive systems only if approved by the SDO.

B. Design a drive capable of developing the acceleration torque required for the inertia and the loading specified for the maximum constant velocity torque [LRFD-MHBD 5.4.2] and operating the leaf at full speed in the 70 seconds time limit stated above.

C. Longer operating times are allowed for operation under abnormal conditions. Do not exceed 130 seconds under any condition.