Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

# Drawbridge - Force and Moment vs. Elevation

## Calculate the acting forces and moments when elevating drawbridges or beams.

### Horizontal Beam/Drawbridge

For a beam supported at one end - like a typical drawbridge - the resultant force acting on the bridge can be calculated as

F = q L

= m g L              (1)

where

F = resultant force or weight (N)

q = uniform distributed load or weight (N/m)

L = length of beam or bridge (m)

m = continuous distributed mass (kg/m)

g = acceleration of gravity (9.81 m/s2)

For an uniform distributed load the resultant force F will act in distance

a = L / 2        (2)

The moment acting in A can be calculated as

M = F a              (3)

= F L / 2         (3b)

Note! The generic eq. 3 can be used for any combination of distributed or point loads.

#### Example - Moment with Horizontal Beam/Drawbridge

The total weight - or resultant force - of a 10 m HE-B 340B steel beam with continuous mass 134 kg/m can be calculated as

F = (134 kg/m) (9.81 m/s2) (10 m)

= 13145 N

The acting distance a for the resultant force or weight can be calculated as

a = (10 m) / 2

= 5 m

The moment acting in A can be calculated as

M = (13145 N) (5 m)

= 65725 Nm

### Elevated Beam/Drawbridge

For and elevated beam or drawbridge the distance between the action force F and the moment in A varies. For a lifting angle the distance can be calculated as

a = cos(α) L / 2         (4)

where

α = lifting angle (degrees)

Eq. 3 for the moment can be modified to

M = F cos(α) L / 2          (5)

#### Example - Moment for Elevated Beam/Drawbridge

The beam from the example above is lifted 30 degrees. The moment in A can be calculated

M = (13145 N) cos(30 degrees) (10 m) / 2

= 56920 Nm

### Elevation Beam/Drawbridge Calculator

Default values are from the examples above where a = L / 2 in horizontal position. The calculator is generic and can be used for any uniform or point load combination as long as the resultant force F and point of action a can be calculated.

#### Drawbridge Lifting Moment

Lifting moment (%) related to maximum start moment at elevation 0 degrees.

## Related Topics

• ### Dynamics

Motion of bodies and the action of forces in producing or changing their motion - velocity and acceleration, forces and torque.
• ### Mechanics

The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.

## Related Documents

• ### American Wide Flange Beams

American Wide Flange Beams ASTM A6 in metric units.
• ### Beam Loads - Support Force Calculator

Calculate beam load and supporting forces.

• ### Cantilever Beams - Moments and Deflections

Maximum reaction forces, deflections and moments - single and uniform loads.
• ### Continuous Beams - Moment and Reaction Support Forces

Moments and reaction support forces with distributed or point loads.
• ### Forces and Tensions in Ropes due to Angle

Reduced load capacities in ropes, cables or lines - due to acting angle.
• ### Normal Flange I-Beams

Properties of normal flange I profile steel beams.
• ### Torque or Moment of Force - Online Converter

Torque or moment - the tendency of a force to rotate an object.
• ### Trusses

Common types of trusses.
• ### W-Beams - American Wide Flange Beams

Dimensions of American Wide Flange Beams ASTM A6 (or W-Beams) - Imperial units.

## Search

Search is the most efficient way to navigate the Engineering ToolBox.

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

## Citation

• The Engineering ToolBox (2006). Drawbridge - Force and Moment vs. Elevation . [online] Available at: https://www.engineeringtoolbox.com/moment-elevation-angle-beam-drawbridge-d_516.html [Accessed Day Month Year].

Modify the access date according your visit.

7.25.9

.