Deployment: Bridge Mount

Matt Bartos edited this page Jun 12, 2017 · 2 revisions


This section details the procedures for deploying a bridge-mounted water level sensor.

The first part of this section lists the parts needed to construct the mounting frames, and describes the process of putting the frames together.

The second part of this section outlines the procedures for deploying a bridge-mounted sensor node. The sensor node is attached to a bridge deck using four threaded rods fixed in anchoring epoxy. The procedure for deploying the node is as follows:

  • First, the site is surveyed and the locations of the mounting holes are marked.

  • Next, the mounting holes are drilled into the bridge deck using a concrete drill.

  • After drilling, the mounting holes are filled with anchoring epoxy, and the threaded rods are inserted.

  • Finally, after the epoxy has cured, the mounting frame is placed over the threaded rods and the sensor is activated.

Buying the mounting hardware

The following table gives the parts and prices needed to construct mounting frames for five nodes (all products listed are from McMaster-Carr). Note that for some parts, allowances for spares have been included.

Full part name McMaster ID Price / Unit Qt Needed per Node Qt / Unit Total Units Needed Total Price
Steel strut channel, slotted, 1-5/8″ x 1-5/8″, galvanized, 10′ length 3310T64 $54.48 0.6 1 3 $163.44
Strut channel accessory, 90 degree angle bracket, 4-hole, galvanized steel 33125T146 $4.85 3 1 15 $72.75
Strut channel accessory, U-style bracket for 1-5/8″ D Strut, galvanized steel 33125T194 $5.38 3 1 15 $80.70
Corner brace for strut channel, 2 hole, galvanized steel, 8″ long 3574T22 $10.35 1 1 5 $51.75
Strut Channel Nuts, Zinc-Plated, 1-5/8″ High Channel, 1/2-13 Thread Size 3259T44 $6.71 12 5 12 $80.52
Type 316 stainless steel hex head cap screw, 1/2″-13 thread, 1″ long, fully-threaded 93190A712 $4.99 14 5 14 $69.86
Type 316 stainless steel flat washer, 1/2″ screw size, 0.531″ID, 1.250″ OD 90107A033 $9.71 14 25 4 $38.84
Type 316 Stainless Steel Hex Nut, 1/2″-13 Thread Size, 3/4″ Wide, 7/16″ High 94804A340 $4.51 3 10 2 $9.02
Type 316 stainless steel hex head cap screw, 5/16″-18 thread, 3/4″ long, fully threaded 93190A581 $3.77 4 10 2 $7.54
Type 316 Stainless Steel Flat Washer, Oversized, 5/16″ Screw Size, 0.344″ ID, 1.250″ OD 91525A230 $5.43 4 10 2 $10.86
Type 316 Stainless Steel Hex Nut, 5/16″-18 Thread Size, 1/2″ Wide, 17/64″ High 94804A030 $5.92 4 50 1 $5.92

Creating the frames

The first step in the deployment process is to construct the mounting frames that attach the sensor nodes to the bridge deck.

These frames are constructed using galvanized steel strut channels, and are attached to the sensor nodes via screws that fit into the bottom of the sensor enclosure. Note that we use galvanized steel because it provides a good balance between strength and corrosion resistance. For outdoor applications, non-galvanized steel should not be used. Aluminum is also a valid choice, except that one must be careful to choose compatible fittings such that the screws and nuts do not corrode. A schematic for our frame is shown below (note that the rightmost vertical bar is optional, and is not used for the nodes that we deployed):

Mounting frame schematic

For each frame, you will need:

  • Strut channel, 4-slot length (x2)
  • Strut channel, 8-slot length (x2)
  • Strut channel, main section (length will depend on the size of the mounting surface)
  • Corner brace (x1)
  • 90-degree angle bracket (x2)
  • U-style bracket (x2)
  • Strut channel nuts, 1/2″-13 thread (x12)
  • Hex head cap screw, 1/2″-13 thread, 1″ long (x14)
  • Washer, 1/2″ screw size (x14)
  • Hex nut, 1/2″-13 (x2)
  • Hex head cap screw, 5/16″-18 thread, 3/4″ long (x4)
  • Washer, 5/16″ screw size (x4)
  • Hex nut, 5/16″-18 (x4)
The strut channel pieces will need to be cut to size using a band saw. The process for constructing these frames is fairly self-explanatory. Simply attach the pieces together using the appropriate fittings, nuts and bolts. Strut channel pieces are connected to each other using the 1/2″-13 thread size connectors, while strut channel pieces are connected to the sensor enclosure using the 5/16″-18 thread size connectors. The two 1/2″-13 hex nuts are used to secure the U-style connectors to the frame. You can see the finished product (excluding the U-style connectors) below: Nodes with mounting frames

Preparing the sites

The next step is to visit each site, find an appropriate location for the sensor, and mark the locations where the mounting holes will be drilled. Visiting the site

The easiest way to mark the drill hole locations is to bring the mounting frame, and place it over the bridge barrier. The four holes in the two U-style connectors can then be used as a stencil for the drill hole locations.

Marking the mounting holes

Now that the site has been inspected, we are ready to start drilling!

Drilling the mounting holes

The following tools will be needed to drill the mounting holes at the site:
  • Concrete drill
  • Portable generator
  • 1/2″ diameter 4″ length stainless steel threaded rods (x4)
  • 5/8″ concrete drill bit (9/16″ will also work)
  • Painter’s tape (for marking drill bit length)
  • 10 oz. caulking gun
  • High-strength anchoring epoxy
  • Eye protection
  • Face mask
The steps for preparing the mounting holes are as follows:
  1. First, put on your eye protection and face mask (safety first!).
  2. Insert the 5/8″ concrete drill but into the concrete drill. We will be drilling a 3″ hole in the concrete, so use painters tape to mark the drill bit 3″ from the tip of the bit. Note that the diameter of the drill bit should be 1/16"-1/8" larger than the diameter of the threaded rod (which in this case is 1/2").
  3. Drill a 3″ hole at each of the four marked locations on the concrete barrier, using the painter’s tape to judge when 3″ have been drilled.
  4. After drilling, check the alignment of the holes by placing the mounting frame over the holes and inserting the threaded rods.
Checking hole alignment

Next, we will be filling the mounting holes with epoxy and securing the threaded rods.

Securing the threaded rods and installing the frame

The following tools will be needed to secure the threaded rods:
  • High-strength anchoring epoxy
  • 10 oz. caulking gun
  • Flashlight
  • Compressed air
  • 1/2″ diameter nylon brush
  • Rag or shop towels
  • Impermeable gloves
  • 3/4″ socket wrench
  • 1/2″ diameter 4″ length stainless steel threaded rods (x4)
  • 1/2″ diameter hex nuts (x4)
  • 1/2″ diameter washers (x4)
The steps for securing the threaded rods are as follows:
  1. Ensure that you are wearing impermeable gloves (you really don’t want to get epoxy on your hands).
  2. Clean each of the mounting holes thoroughly using the compressed air and the nylon brush. We want to make sure that the amount of concrete dust inside the holes is at a minimum. Excessive dust will prevent the epoxy from binding securely to the concrete. You can use a flashlight to inspect the inside of each mounting hole.
  3. Insert the tube of anchoring epoxy into the caulking gun and remove the seal.
  4. Depress the trigger on the caulking gun and squeeze some of the anchoring epoxy into a throwaway container. Continue to squeeze out the epoxy until the epoxy is thoroughly mixed (the degree of mixing is indicated by the color of the epoxy exiting the tube).
  5. Once the epoxy is thoroughly mixed, insert the caulking gun into a mounting hole and fill the hole approximately halfway with epoxy.
  6. Insert the threaded rod into the hole while slowly rotating it clockwise. This ensures that the epoxy properly binds to the threads. If excess epoxy spills out of the hole, make sure to clean it up quickly with a rag.
  7. Keep in mind that the epoxy will become hard very quickly, meaning that you have limited time to complete this step.
  8. Repeat the process for each hole.
  9. To ensure that the threaded rods stay aligned, place washers over the threaded rods and then place the two U-style connectors over the threaded rods while the epoxy cures.  A section of strut channel can be placed through the U-style connectors to align them. The washers are used to guarantee that the U-style connector does not bind to the epoxy underneath.
  10. Wait approximately four hours for the epoxy to cure.

The result should look something like this:


Mounting rods with epoxy

After the epoxy cures, place the frame over the threaded rods and tighten the apparatus in place using a 3/4″ socket wrench.

This concludes the bridge mount deployment procedure.

Finished node - side view Finished node - top view
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