How are Bailey bridge built?

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The first step in the Bailey bridge assembly is the installation of the rollers. One roller is special among them, the rocker roller. These rollers are tiltable as shown.

The simple-looking side panel is the genius part of the Bailey bridge. This structure is rugged, yet lightweight. Five to six people can easily lift it. Now, place two side panels above the rollers. Insert a heavy I-channel called a transom in between these side panels. This side support bar makes the transom's connection strong. One unit of the Bailey bridge is ready as shown below. The male-female portions of the side panels fit perfectly and are locked with pins. Please note, these sway braces are attached before the transom. Without sway braces the bridge structure wont be rigid.

Launching of the Bailey bridge - A game of Torque balancing

The next side panel connection is crucial. This is connected after adding an extender, and eventually the new side panel connects with the previous one at an angle. Just adding one more pair of side panels and the weight is now equal in both sections. What will happen now if we push the structure forward? Yes, the bridge will easily get tilted and it will rest symmetrically between two rollers as shown. Let's connect one more side panel. Weight is more on the left side of the bridge. The bridge gets tilted further and eventually it rests on the left side.

Balancing Weight in the Bailey Bridge Erection

Now the most crucial part of the erection of the bridge, the weight management. The rocker roller is the main roller of the Bailey bridge. If the weight balance goes wrong, the Bailey bridge will topple as shown.

The pivot point is at the main roller. For a successful Bailey bridge launching, the torque on the left side should be greater than that on the right side as shown below. Otherwise, the launching will end in a tragedy. But, in the last stage of the erection, the right-side torque should become higher.

We can now push and move back portions of the bridge. The torque on the right side is obviously smaller than that on the left side. Now, the assembly work of the main portion of the bridge starts. To support heavy load, the trusses of the Bailey bridge should be super strong. Let's use a triple-truss and double storey panel arrangement for the main portion of the bridge. There are single and double-truss panel arrangements as well with different storey options as shown.

Details of the bridge launching

The weight of the single-truss unit is around 1300 kg, while the weight of the triple-truss unit is around 4200 kg. The left side portion of the bridge is marked with white and the right side portion with red color as shown. This marking is important for torque calculation. The bridge looks a little dangerous now. Let's check the torque on both sides. The torque on the left side is much higher than the right side. The bridge is stable.

Phase 1

Phase 2

Let's assemble one unit piece of the bridge and push one unit forward as shown. The bridge's current position is stable according to torque analysis.

Phase 3

Let's assemble more pieces of the bridge and push it forward again. We have to assemble two more sections before pushing the bridge one unit forward. The bridge is hanging too much in the air as shown below. The torque is still higher in left side and bridge is stable.

Phase 4

Let's assemble three more section and push the bridge two section forward. The torque on the left and right sides are almost equal now; still, it's higher on the left side as shown. Bridge is still stable in this position.

Why Is the Bailey Bridge’s Launching Nose Angled Upward?

Currently, the bridge is supported only at one end. Due to its self-weight, the structure deflects a lot. If this upward bend were not there, the free end of the bridge would have gone below the level of the other river bank. The reason why Bailey bridge launching nose bent upward as shown might be clear to you now.

Phase 5

What you have to do now is just add one more section and push the bridge forward by exactly one unit length. Here obviously the torque produced by the left side remains the same, but the torque at the right side has increased. For the first time, the right-side torque has exceeded the left side torque as shown.

This weight increase will cause the free end of the bridge to automatically fall to the ground as shown.

The finishing work

Once the bridge free end fall to ground we can easily cross the bridge and lift the other end using a hydraulic jack as shown. As bridge free end lift up no we can install roller bearing on this end as well.

Installation of roller bearing in Bailey bridge

In the both end, we have installed roller bearing. Now, go for a long push until the entire river is covered with the triple-truss Bailey bridge. Now just remove the single-truss supporting portion of the bridge. The bridge is almost ready as shown. We have to do add some end support and after that, a bearing at the end of the bridge. We can remove the rocker rollers. A robust and durable bridge is ready for use. When the bridge carries a heavy load, it deflects a little bit. The bearings make sure that this slight deflection is allowed. If these bearings were not present, the bridge would have undergone too much internal stress.