Pre-Engineered, code-compliant post foundation integrates fence at the face of retaining walls.
DHL Distribution Facility, Allentown, Pa.
Wall design and construction firms
Security is a top priority in the shipping industry. So when plans for DHL’s new 290,000-square-foot distribution facility in Allentown, Pa., called for 3,450 linear feet of retaining wall along the perimeter of this 72-acre site, the chain link fencing above the walls quickly became a topic of concern for the wall contractor and construction manager.
"It is rarely understood by the client that fencing cannot be installed on top of perimeter walls without careful design considerations," said Andre De Carville, vice president of Pickering Valley Landscape, Inc. "The grading plan noted a fence above every wall but did not provide a structural detail showing how to integrate our work with that of the fence contractor."
Segmental retaining walls’ (SRW) most appealing quality is how the dry-stacked block face and geosynthetic reinforcement (geogrid) combine to form a retention system capable of holding back steep slopes and handle heavy loads. A limitation, however, is that the dry-stacked wall face has minimal resistance to overturning in the upper two or three courses when a point load is applied to the block. This is precisely what happens when a load is placed on a fence post in close proximity to the wall face. That, along with tearing through the embedded soil reinforcement behind the wall with an auger, can greatly affect both the integrity of the wall and fence structures.
Sleeve-It units were placed at the desired spacing then capped during wall construction. Once the wall is backfilled, the weight of the overlying soil provides support for the fence system.
The construction team contacted Strata Systems, manufacturer of a pre-engineered, code-compliant product called Sleeve-It 1224R. Strata provided test reports and additional calculations to the project engineer of record explaining how the Sleeve-It approach meets or exceeds the building code requirements for railings along the sides of elevated walking surfaces. A Strata technical representative also was available for on-site consultation.
With only 10 days from the bid award date to provide a final wall design, and 120 days from ground breaking for the new facility to be fully operational, there was no time to waste. "We recommended the use of the pre-engineered Sleeve-It system to the construction manager, Opus Corporation, for integrating the chain link fence with the SRWs." said Wall Design Engineer Bart Shippee, P.E. "The Sleeve-It product test data translates exceptionally well for a 6-foot-tall chain link fence with 10-foot post spacing addressing the [International Building Code] load criteria for railings in commercial applications."
In all, more than 350 Sleeve-It units were installed during wall construction. Sleeve-It 1224R is typically pre-assembled at the material staging area for the wall, then set in place with desired post spacing when wall construction has reached approximately 24 inches from the final top of the wall. "I was not only amazed with how the Sleeve-It product works, but that I was able to fit two pallets in the back of my pickup truck rather than pulling a trailer with 12-foot sections of pipe tied down", commented Pickering Field Supervisor Ron Buchanan. "This was our first project with Sleeve-It, and since there was virtually no learning curve required, our wall production rate was not slowed at all."
When wall construction was completed, the fence installer arrived to complete the perimeter fencing. "We showed up ready to auger holes and much to our surprise the holes were already there," said Scott Risbon with Earthcare Landscaping Inc. "There was even a lid on every one that kept the topsoil from filling the holes during several rain storms after the wall was built."
Strata’s Sleeve-It design negated the need for a 36-inch offset of the fence on top of the wall. This 3-foot real estate savings translated into a total area savings of 10,000 square feet for the entire project. Traditional methods of integrating a railing at the wall face would have added two to three times greater cost to this portion of the project. The result was a well-secured facility completed on time and within budget.
Contributed by Strata Systems, Inc.
Building code requirements
The 2006 International Building Code, Section 1013.1 and 1013.2 requires a minimum 42-inch railing near the open sides of elevated walking surfaces that exceed 30 inches in height. Section 1607.7.1 states that handrail assemblies and guards shall be designed to resist either a 200-pound concentrated load or a 50-pound-per-linear-foot load, application dependent. This load is required to be safely transferred through the supports of the fencing or guard system and into the structure (foundation). Most municipalities in the United States have adopted these building codes.