As the need for bandwidth continues to increase in all hard-line and wireless delivery technologies, the need for increased fiber infrastructure continues to expand, particularly in the Middle and Last Mile arenas. Traditionally, concrete or steel vaults and pedestals have been used to provide for storing slack cable. While these products have been used for fiber splicing and storage for decades, the emergence of vaults and pedestals made from High Density Polyethylene (HDPE) Thermoplastic materials provide an exciting new alternative.

HDPE-based vaults and pedestals meet or often beat the established load rating requirements -- plus they are easier and more cost-effective to ship and install. Unfortunately, the misconception remains that a plastic product offering is “cheap, flimsy and will not hold up” to all the environmental requirements that will be present. While this may have been the case with some of the earlier versions of plastic vaults and covers, the introduction of HDPE manufactured materials have addressed and/or eliminated the majority of these concerns.

Broadband service providers need to examine the advances available in HDPE, and learn how they can potentially save with alternatives compared with legacy solutions.

Getting Passed the Past
A key factor to consider when selecting a vault and cover is the placement or location of the product. Greenbelt areas have a load requirement of up to 5,000 pounds of static load while sidewalk/pedestrian and non-continuous vehicular traffic areas have load requirements up to 22,000 pounds of static load.

There are many circumstances where current vaults are located in a greenbelt area, with a 20,000-pound rated cover installed. While this scenario certainly meets the customers’ needs, they could be overpaying for a product that is rated much higher than they need. Why is this? One of the primary reasons that customers/installers share is based on history. They subscribe to the theory: “But that’s how we’ve always done it.” Few take the time to challenge and/or examine that thinking.

One new option is to install a polymer concrete cover and ring on top of an HDPE vault to meet the 22,000 pound requirements for sidewalk/pedestrian and non-continuous vehicular traffic, while still being able to take advantage of the weight and placement advantages of HDPE.

When considering load rating and placement requirements, the “But that’s how we’ve always done it” mentality should be challenged. Instead, broadband service providers looking to cost-effectively protect their fiber should look for vault and pedestal products that comply with the following standards:
• Telcordia GR902-CORE
• ASTM C857
• ANSI/SCTE 77 2010
• Applicable elements of the Western Underground Committee

All of these standards apply to the generic requirements for hand holes and other below-ground non-concrete splice vaults intended to house passive telecommunications components, terminal blocks, coaxial taps, and other fiber optic passive elements distributing broadband services. Specific areas included within these standards are strength and load capacities as well as thermal expansion/contraction.

Lightening the Load: HDPE Thermoplastic
HDPE Thermoplastic is an alternative to legacy storage solutions. It is structural foam that has been proven to provide a better strength-to-weight ratio when compared to concrete or polymer concrete material. HDPE material is both impact- and crack-resistant and will not warp or degrade when buried or immersed. Due to this consistent manufacturing process, high-volume yields and overall strength and durability, HDPE has been used for many years in products such as pallets, shipping containers, and utility carts.

Structural foam molding is a low-pressure injection molding process that is capable of producing very large structural parts with thick sections. The molten plastic material is injected into a mold after being mixed with a blowing agent or high-pressure gas. This produces bubbles in the plastic, causing it to foam. The foam retains the properties of the plastic but weighs less because of reduced density. A part produced this way results in a heavy cellular structure similar to wood products.

The key element in structural foam-molding is low pressure. Unlike conventional injection molding, which utilizes extremely high pressures to force materials into a mold’s cavity, structural foam molding takes advantage of a part’s configuration and the foaming action, to allow the molten resin to flow much further, and with far lower pressure, than the typical injection molding process would allow.

Passing the Tests
To achieve standards compliance, there are a number of tests and requirements that must be met. Let’s examine 3 of the major criteria involved in the Telcordia GR902 test procedure:
1. Vertical Cover Load
2. Vertical Sidewall Load
3.  Lateral Sidewall Load

The Vertical Cover Load test includes applying a 10” x 20” x 1” steel plate on top of the same size rubber pad and applying a load with a hydraulic press for 1 minute (see chart for specific details) directly in the center of the enclosure, with the cover on. This process is repeated 10 times and then the product is inspected for damage or deformity and results are either a pass or fail -- if any damage occurs.

The Vertical Sidewall Load test is basically the same test as the Vertical Cover Load (see table), except the load is placed on the cover, directly above the side of the vault. The after-test product is inspected for damage or deformity, and results are either pass or fail.

The Lateral Sidewall Load test includes placing the vault, with its cover on, on its side and placing a load over the entire side of the vault area, then using the hydraulic press applying the load ratings listed in the table. After test, the same pass/fail criteria are followed.

A product must have passed these and all of the other requirements in order for a manufacturer to be compliant and claim that their HDPE product meets the specifications and requirements.

To achieve these load ratings, a straight sidewall "I beam" design is imperative for higher load capacities as well as a waffle-design construction. This distributes the load over the strongest section of the vault wall. In addition, the material used needs to provide property characteristics to allow for the following:

Thermal Shock: Prevents cracking or splitting due to rapid temperature changes whether or not they are increasing or decreasing changes.

Freeze/Thaw: Ability to resist freeze/thaw cycles in OSP environments.

Handling: Adequate drop load ratings and shock/vibration associated with transportation of the product.

Salt Fog: Allows for environments that transport the corrosive characteristics of salt via moisture/water such as humidity, fog, and rain. (Obviously in Pacific or Atlantic coastal regions.)

In addition, HDPE vaults are available today with the option to install a polymer concrete cover and ring on top of their HDPE vault enabling them to meet the load requirement for non-continuous vehicle traffic, while still being able to take advantage of the weight and placement issues that are critical to network protection.

HDPE to the Rescue
In working with fiber optic designs, the need to look beyond traditional methodologies is the focus when searching out cost savings. The light weight of HDPE offers service providers a more cost-effective alternative to fiber deployment. Savings are possible in a multitude of areas:

Reduced installation and placement costs: Because the HDPE vaults are lighter in weight (typically 50% to 75% less) than concrete vaults, one person can effectively install and place these vaults. Using the traditional method of concrete vaults, it usually takes two or more installers to place and install them, effectively cutting this aspect of labor in half. Additionally there is typically a backhoe/crane or skid steer that is required to dig the holes and assist in placement of the concrete vaults. While this equipment would still be required to dig the hole, its overall utilization can be increase due to the fact that it can move from one vault location to another, preparing the holes and not sitting idle or waiting around to assist with the placement of the vaults.

Reduced shipping and handling costs: Lighter-weight HDPE vaults and covers allow for more products to be shipped on the same truck, thereby reducing the overall transportation costs of each deployment by as much as 80%. Because of the lighter weight, you can ship between 150 to 180 HDPE vaults on a truckload vs. 20 to 30 of the same/similar size polymer concrete vaults. In addition, material logistics (storage, material movement), becomes more manageable, also having an impact in reducing overall costs.

Reduced damage to products: Due to the HDPE material used to manufacture the vaults and covers, all HDPE vaults are impact- and crush-resistant, insuring that none of the product is damaged or broken during shipment or handling. Telcordia GR 9902-3.18 requires that a unit be dropped from 29.5" and then inspected for visible and functional damage. In order to pass this requirement, there can be no damage to the product. Concrete vaults are not required to meet this requirement. Contractually, if a concrete vault is damaged during shipment, the end customer incurs the cost of waiting while replacement product is delivered to the jobsite.

Overall safety and deployment of product: A lighter weight product has been shown to have a positive effect on the overall safety on a project. While operators and installers still need to be safety-conscious, moving a 50 pound HDPE vault does not take as much effort or equipment when comparing it to a 300 pound concrete vault.

Cost of vaults themselves: Because of injection molding process, the manufacturing cycle times on a larger HDPE part could range anywhere from 5 to 15 minutes per part (compared to at least a 24-hour cycle time for similar parts manufactured with polymer concrete material). As a result, you will typically find that the HDPE vaults and covers are marketed at a lower cost than their concrete counterparts. While the pricing may vary from vault to vault, typically you will see the HDPE option anywhere from 10% to 50% less than the traditional polymer concrete vault and cover. In addition, lead times are usually far shorter.

Service Providers are continually looking to ways to reduce deployment costs as they expand their networks. HDPE vaults, covers and pedestals offer a wide range of products, that when deployed in the correct locations/application, can provide substantial costs savings throughout the network.

How can you pass on evaluating a change in material that could save substantially in overall project costs?

About the Authors
Cheri Beranek is CEO and President, and Johnny Hill is Chief Operating Officer, Clearfield. Each has nearly 20 years of experience in data and telecommunications networking. For more information, email Johnny Hill at jhill@clfd.net or visit www.fiberpuzzle.com.

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