When placed in the sidewalk at regular jointing intervals, the diamond-shaped TripStop forms a double-keyed joint, allowing the sidewalk to articulate around the product. The joints can be cut onsite using a fine handsaw or with a combination saw with a fine-tooth blade. The product is secured with steel pegs driven through pre-drilled holes prior to the concrete pour. Photo: Jonathan Gano
When placed in the sidewalk at regular jointing intervals, the diamond-shaped TripStop forms a double-keyed joint, allowing the sidewalk to articulate around the product. The joints can be cut onsite using a fine handsaw or with a combination saw with a fine-tooth blade. The product is secured with steel pegs driven through pre-drilled holes prior to the concrete pour. Photo: Jonathan Gano

As the nation's infrastructure ages, the liability associated with sidewalk trip hazards caused largely by tree roots is mounting. Although they're prevalent in every city, those hazards pose a major legal challenge to the Americans with Disabilities Act (ADA), which defines a trip hazard as a vertical change of more than ¼ inch at a joint.

Scott Hall, public works team leader with the city of Springfield, Mo., is well aware of trip hazard implications on the ADA: “We've been sued several times over trip hazards, but in a big city you can't see every inch of the sidewalks,” he says. “Still, if the gap is more than ¼ inch you're probably going to lose [a lawsuit].” Since 2005 the city has been sued for more than $1 million in trip hazard claims and has paid out $80,000 in settlements.

Compounding the trouble caused by trip hazards is the unsuitability of repair options — including costly root pruning (which typically costs the city a pricey $500/tree) and rubber sidewalks (which the city has decided against, citing an inferior structural capacity compared to that of concrete).

But since 2007, Springfield sidewalk crews have installed a new product on more than 1,000 feet of the city's 425 miles of sidewalks. Introduced at the World of Concrete in 2005, the TripStop Articulating Sidewalk Joint is a new approach to preventing joint faults. More than 60 miles of the product have been installed in 80 cities across Australia, Canada, and the United States.

DO IT RIGHT THE FIRST TIME

“It's a one-time fix,” Hall explains. “It creates a hinge, so instead of cracking the sidewalk it lifts the whole slab. It's a really quick installation.”

As tree roots recover from the root pruning in subsequent years and resume their upward push on the sidewalk panel, the keyed joints allow the sidewalk panels to move without faulting at the joints. The joint can move up to 4 inches while remaining ADA-compliant, according to David Murray, vice president of sales and marketing for Access Products Inc. The company manufactures and distributes TripStop.

Access Products ships directly to some of its 25 municipal customers in the United States, including Long Beach, Calif., where about 2,500 feet are being installed. The company also works through 75 distributors nationwide.

The TripStop extrusion is matched to the depth of the sidewalk and is easily installed with supplied stakes. As the extrusion comes to the surface of the sidewalk, it also eliminates the need to tool the joint.

Since the product eliminates the joint faulting that often requires a premature replacement (sometimes as soon as five years after a new sidewalk is poured), its projected life span is about 50 years, Murray explains. The TripStop ranges from $5/foot for 3-inch sizes to $8/foot for 6-inch sizes.

Springfield crews modified the idea to create an alternative to TripStop — a square PVC rod rotated 45 degrees creates a similar shape to the keyed joint created by the commercial product.

That method does, however, still require tooling the joint into the surface of the newly poured concrete directly on top of the buried PVC rod.

In both cases — the TripStop installation or the in-house square PVC installation — the repaired sidewalk sections simply butt against the unrepaired existing sidewalk. That creates a cold joint between the new slab and old slab, setting the stage for future faulting.

IN-HOUSE INNOVATION

The tree roots usually continue to grow and destroy the aggregate interlock at the cold joint, lifting the entire repaired section.

Springfield's sidewalk crews found a way to transfer the load from one panel to the next across the cold joint using PVC by suspending a half-round rod between the forms before the concrete is poured. By drilling pilot holes and attaching the PVC rod with concrete anchors, it forms the same keyway at the cold joint and is mechanically anchored to the original, unrepaired section.

With the half-round PVC rod, the sidewalk has a much greater ability to accommodate movement and resist faulting.

Although the in-house jointing method adds to the installation cost of the sidewalk, it also offers cost savings resulting from eliminating the need for unnecessary future repairs.

A typical sidewalk repair lasts nearly an hour, and prices of PVC vary, particularly for the generic PVC round and square rods produced locally or regionally. Still, managers should expect to spend $3.50 to $7/joint. On a typical joint spacing of 5 feet, that amounts to an additional 75 cents to $1.50 per linear foot for the cost of the sidewalk.

“Considering that joints installed with TripStop are expected to last up to 10 times longer than those installed traditionally, the impact on Springfield's maintenance budget will be big,” Hall says. “It'll take a few years to actually see the payoff, but so far every installation is working.”

— Jonathan Gano is the superintendent of streets for the city of Springfield, Mo.