BRIDGE INSTALLATION GUIDE
This document has been prepared to provide Links Bridges’ customers with assistance and advice on the most cost-effective options for Bridge Installation.
If you are installing a bridge for the first time, it can seem like a daunting task and expensive mistakes can be made.
A quick read of this document will educate you on some of the key considerations and options. Then, detailed discussions with Links Bridges will help you select the path forward that makes the most sense for your specific situation.
The details included in this document are specific to Links Bridges designs.
PART 1: THE MOST COMMON MISTAKE
The most common mistake that adds cost to a bridge project is sizing the bridge such that the ends are at or very close to the edge of whatever is being spanned.
This is a problem for a few reasons:
- It limits foundation options to what is usually the most expensive type of foundation – a concrete abutment that is required to act as a retaining wall to prevent erosion. This type of foundation requires maximum excavation as it is designed with a base that extends back from the bridge path.
- In many jurisdictions, disturbing a waterway in this manner will attract the interest of regulatory authorities who will insist that the installation be done in a manner which prevents disturbance of the body of water. This then requires the installation of temporary coffer dams to re-route the water while the foundation is being excavated, formed, and poured.
- In summary, it can make the process for preparation of bridge foundations expensive, time consuming and messy due to the extent of excavation required.
The solution in most cases is to size the bridge 2 to 3 feet longer at each end (a total of 4’ to 6’) to allow sufficient easement from the edge of the body of water that it will be completely undisturbed during the bridge installation.
PART 2: FOUNDATION OPTIONS
This section provides a brief description of the options for foundations. There is always the potential for site-specific or bridge-specific variables that can exclude some of these options.
1. RE-USING EXISTING FOUNDATIONS:
Re-using existing foundations is the most cost-effective foundation option. Links Bridges makes re-using foundations possible with our custom manufacturing process.
2. CONCRETE FOUNDATIONS
Everyone is familiar with concrete foundations. This is by far the most commonly used material to anchor bridges historically.
There are numerous design options for concrete foundations:
- Spread Footings: These involve large blocks of concrete formed and poured to a depth dictated by frost lines and soil characteristics. A wall of concrete is formed on top of the block of concrete, and this is what the Bridge beams will bear on and are anchored to. These are rarely used for our bridges and would only be required in situations where extreme lateral loads (hurricane winds) or extreme uplift loads (intense flow flooding) were involved.
- Drilled Piers: The involve cylindrical concrete forms poured to a depth dictated by frost lines and soil characteristics. Each bridge end generally requires 2 or more such piers and these are typically joined by a formed and poured block of concrete on the top. This block is what Bridge beams bear on and are anchored to.
- Concrete Slab: This option is appropriate for areas where ground frost is not a consideration. Slabs are formed and poured at each bridge end to an appropriate size and depth and bridge beams are anchored to these.
- Pre-cast Concrete: This is an option that can be appropriate for relatively small residential bridges for the DIY approach. It involves creating a trough to an appropriate depth, stabilizing/leveling that with landscape cloth and crushed stone and putting heavy pre-cast concrete (like cinder blocks) on these to serve as a platform for the bridge beams. These offer minimal resistance to uplift forces so should be buried to an appropriate depth.
Where concrete is the preferred option for foundations, the specific design of the foundation should be done by a Professional Engineer. The amount, size, and layout of the rebar – which give concrete foundations their strength – needs to be designed based on the soils, frost lines, loads and other considerations.
3. HELICAL PILE FOUNDATIONS
This is Links Bridges preferred option for most of our bridge installations. Over 80% of Links Bridges installations to date have been installed using Helical Pile Foundations.
The key benefits of Helical Piles as a foundation option for our Bridges include the following:
- Less expensive than concrete for most situations. In our experience the costs for concrete foundations can be highly variable and even unpredictable. But they are almost always more and sometimes considerably more than Helical Piles.
- Faster bridge installation. A typical Bridge installation for one of our
Bridges using Helical Piles is completed in less than one day – including the Piles. With concrete, there is time for excavation, forming, pouring, curing. This is a minimum of 2 days and in most cases 3 to 4 days. In both cases, the time required to place and anchor the actual Bridge is less than 2 hours once the foundations are ready.
- Less collateral damage. This is true in at least a couple of ways:
1. With Helical Piles there is minimal excavation (usually 1’ to 2’ depth at each pile location) and all of that is returned to its place prior to completion. With Concrete there is a requirement to remove several cubic yards of materials.
2. With Helical Piles the biggest piece of equipment used for the foundation is a Mini-Excavator (with an auger attachment). With Concrete, a full truck delivering the Concrete can weigh up to 35 tons or more.
No Geotechnical Report costs. When a Professional Engineer is asked to design foundations, they generally will insist on a ‘Soils Report’ so that the foundation design can be tailored to site conditions. When using Helical Piles, the operator gets ‘back pressure’ readings as a Pile is being placed. These readings are translatable to ‘load-bearing’ capacities.
If after placing a (7’ long) Pile, the readings indicate insufficient bearing capacity, an extension is connected to the Pile and the process resumed to the depth required to achieve load bearing capacities required.
PART 3: BRIDGE INSTALLATION
This section of the document is a step-by-step guide on how to install a Links Bridges fiberglass bridge using Helical Piles. (Disclaimer: These steps may vary depending on the situation)
The typical Installation for one of our bridges uses the following:
- One Pile per Beam for each end of the Bridge. (e.g. – 6 foot Wide Bridge with 2 Beams requires 4 Piles, 8 foot Wide Bridge with 3 Beams requires
6 Piles, 10 foot Wide Bridge with 4 Beams requires 8 Piles.
- Typical Pile Sizes are 7 feet Long X 3 inches in Diameter. Soil conditions or unusual loading requirements could dictate thicker Piles.
- Each Pile requires a Pile Cap – 12 inches X 12 inches with four 3/8-inch holes predrilled 2 inches in from the corners.
STEP 1. INSTALL HELICAL PILES
When installing a Helical Pile foundation a few steps are required:
- Find the correct location for each pile: You can locate each pile location using the measurements in our Technical Package. Helical Piles are to be centered directly under the bridge beams, 6 inches in from the end of the beam.
- Install the Helical Piles: When installing Helical Piles the “Top of Pile” elevation will dictate the height of the bridge.
- Install and level Pile Caps: Level the Helical Piles then place Pile Caps atop the Helical Piles.
STEP 2. PLACE THE BRIDGE
- Transport the Bridge: After Helical Piles are installed and Pile Caps have been placed the Bridge will need to be rigged with straps rated to handle the Bridge weight with a safety margin. Rigging should be done by tucking straps under the ‘curbs’ in the space provided by the ‘blocking’ that is part of the side rail. The Bridge’s weight is symmetric so Rigging should be positioned to ensure a balanced load.
- Place the Bridge: Set the Bridge on top of Pile Caps. There is a couple of inches ‘margin of error’, but the target is to have the last 1 foot of the Bridge Beams at each end bearing on the Pile Caps.
STEP 3. SECURE THE BRIDGE
- Drill into the Beams: Once the Bridge is placed atop the Pile Caps you will need to clear enough space beneath each of the Pile Caps to allow you to drill from underneath the Pile Cap. Use the pre-drilled 3/8-inch holes in the Pile Caps as a guide to drill holes in the bottom of the Bridge Beams.
- Secure the Beams to the Pile Caps: Place 3/8-inch Bolts with a washer and nut inside the drilled holes and tighten.Attach the Fiberglass Plate: After all Bolts are installed, attach the supplied Fiberglass Plate to cover the voids in the Beams and between the Beams. You will use the small flanges at the ends of the beams for attachment and put 4 screws per Beam – 2 on each side. Pre-drill holes for the screws and use 1/8-inch Tapcons (or 2 inches) for screws.
- Attach the Fiberglass Plate:After all Bolts are installed, attach the supplied Fiberglass Plate to cover the voids in the Beams and between the Beams. You will use the small flanges at the ends of the beams for attachment and put 4 screws per Beam – 2 on each side. Pre-drill holes for the screws and use 1/8-inch Tapcons (or 2 inches) for screws.
STEP 4. COMPLETION
Now that the Bridge is installed the remaining steps involve backfilling, landscaping, cart paths, etc. all of which are outside the purview of this document.