Troubled bridges over water; maintaining the nation’s inventory

Drivers whizzing over the Mianus River on Interstate 95 in Connecticut were blissfully unaware that a pin holding the span had shifted, something a routine inspection nine months earlier had failed to discover. Three people were killed in the resulting 1983 collapse when a 100-foot section of 1-95 gave way.

And on Feb. 18, 1995, in Montgomery County, Pa., the turn-of-the-century Norristown Markley Street Bridge collapsed into Stoney Creek, causing the Norristown Times Herald to remark, “It was immediately apparent that the borough’s main artery would need some severe surgery.”

After the Norristown Markley Street Bridge collapse, an elaborate system of detours was established to redirect about 10,000 vehicles per day through heavily congested local streets. It was estimated that a replacement bridge, at a cost of about $3 million, would take two years to design and three years to build.

The bridge, owned by the borough of Norristown, is located in the heart of the central business district on heavily traveled Pennsylvania Route 202, a major fourlane divided state highway.

The bridge carried two north-bound traffic lanes and a turning lane. An adjacent, more recently constructed PennDOT two-lane bridge carried south-bound traffic. The north-bound bridge consisted of two 60-foot spans crossing Stoney Creek.

After consultation with PennDOT, a plan was developed to install a temporary “Bailey” type panel bridge financed by the County Commissioners.

The project involved a partial demolition of the existing plate girder bridge, which consisted of three traffic lanes and an outboard sidewalk.

The sidewalk was supported by a small plate girder on the outside and the main bridge plate girder on the inside. The sidewalk and its two supporting plate girders were retained.

The remaining bridge structure was to be demolished while the sidewalk was to remain in service. This design permitted erection of the panel bridge with a very limited clearance of approximately six inches on one side and approximately 24 inches on the other.

The design of a new independent structural support and protection of an active 18-inch cast iron sanitary sewer main during construction presented another challenge.

This main had been previously hung on the existing floor beams, which were to be removed during the demolition phase. Great care had to be taken to safeguard the sewer line against damage and/or failure. An emergency plan was developed to handle the sewage in the event of a pipe failure.

The design and construction services were performed by Robert H. McKinney jr. Associates, Pottstown, Pa. A Mabey two-lane Universal Bridge, manufactured by the Mabey Bridge Co. of Baltimore, was used in the project.

The installation was completed and opened to traffic on Oct. 13, 1995, two days ahead of the 45-day scheduled completion.

DANGEROUS CROSSINGS

Two years ago, a series of Ohio news articles on the nation’s unsafe bridges were published about the same time an NBC broadcast, “Dangerous Crossing,” aired. The reports sparked a controversy concerning the deterioration of U.S. bridges and what was being done to replace them.

“The reports found potentially unsafe bridges in every state and highlighted the special problems associated with fixing them,” says Ronald Poole, public information specialist with the Ohio Department of Transportation (ODOT).

More recently, national attention has been focused on the estimated one-fourth of the nation’s interstate bridges described as “structurally deficient or functionally obsolete.”

“The safety of our nation’s bridges should concern us all,” Poole says. “Bridge collapses in recent years have demonstrated that decay, due to a lack of proper funding, poses a real threat to motor safety.”

Poor or delayed maintenance also poses additional hazards. The Federal Highway Administration’s (FHWA) National Bridge Inventory shows that the number of deficient bridges more than doubled between 1982 and 1993, from 18 percent to 39 percent.

Officials now estimate that it could cost somewhere in the neighborhood of $78 billion to repair them.

State DOT data, collected by the American Association of State Highway and Transportation Officials (AASHTO) was supplied to the FHWA, who ranked bridges according to structure, function and deficiency.

The five areas with the highest percentage of deficient bridges in 1995 were: New York (63 percent), Washington, D.C. (60 percent), Massachusetts (58 percent), Hawaii (53 percent) and Rhode Island (49 percent).

Among the top 25 worst bridges in the nation (based on USA Today’s analysis of 1993 FHWA data by Barbara Hansen and Paul Overberg), New York bridges rank 1, 2, 3, 4, 7, 8, 11, 12, 19, 21 and 23 (see chart, p. 38).

Bridges carrying more than 15,000 vehicles a day make up only 9 percent of the nation’s bridge inventory, yet carry 70 percent of bridge traffic.

According to the FHWA, the northeast has the highest percentage of deficient busy bridges at 56 percent — due, in part, to older structures, corrosive de-icing salts and higher traffic.

Among structural areas of concern, the FHWA has identified six weak spots:”

* Decks. Water can seep through cracks and rust steel reinforcing bars, which then expand, cracking chunks of concrete.

* Weight. Excessive load, especially if repetitive, may cause stress and vibration that creates cracks.

* Joints. Water seepage through joints jamages supports.

* Bearings. Rust can block movement, creating pent-up stress that causes cracks and prevents bridge from expanding and contracting as it responds to temperature changes.

* Paint. Cracks and chips allow steel beams to rust, weakening them enough so that heavy loads cause additional cracks.

* Other forces. Vehicles, quakes or flood debris that strike a bridge can crack or deform parts. Normal flow also can erode soil around the foundation. Even minor damage creates an opening for rust or rot.

CABLE CORROSION

Other areas of concern include the in-service condition of cables in suspension bridges, cable-stayed bridges and other cable-supported structures that can be affected by weather, volume/weight of traffic and age.

According to “Cable Corrosion In Bridges And Other Structures,” a new report published by the American Society of Civil Engineers, New York City, and written by Frank Stahl and Christopher Gagnon, corrosion problems associated with cable-supported structures tend to be unique and must be examined on an individual basis.

Anti-corrosion methods currently employed on suspension bridge cables include galvanizing wires and covered by paint, neoprene-hypalon system of cable wrapping, glass-reinforced acrylic resin system covering and the use of corrosion inhibitors and coatings, used individually or in combination to obtain the maximum benefit.

In cable-stayed bridge construction, various anticorrosion methods — polyethylene pipe with PVC tape wrapping and filled with cement grout, grease or other corrosion-inhibiting material; inert impregnation; metalcoat; or epoxy coating — are used.

“The suspension system consisting of the main cables, cable anchorages, tower and anchor saddles and suspender ropes can attain a long service life if properly maintained,” the authors say, and inspection and maintenance programs are imperative to avoid costly collapses and repair.

The George Washington Bridge spans the Hudson River between Upper Manhattan, N.Y., and Fort Lee, N.J. Originally designed as a two-deck structure, only the upper deck was initially built. The lower deck was added to the structure and opened to traffic in 1962.

The bridge is supported from four 36-inch diameter cables by pairs of wire-rope suspenders, which pass through openings in the sidewalk and are attached l the webs of the transverse floorbeams by socket bearing connections. The addition of the lower deck provided easy access for inspection and maintenance to many structural details that previously were inaccessible and could be inspected only from painter’s scaffolds.

Once access became available from the lower deck, previously hard-to-reach areas were carefully inspected. For example, when the retainer casting was removed, it was discovered that the wire seizing had almost entirely corroded away on many of the ropes; accumulated dirt and debris had also started to corrode the exterior wires of the rope itself.

Dirt and debris had also collected in the confined spaces between rope, floorbeam web and stiffeners. Moisture from rain and snow running down along the rope and residue from snow-melting salts had accelerated destruction of the galvanized coating on the ropes and spread of corrosion damage.

Among other repair and maintenance assignments, ropes with three or more broken wires were removed for physical tests and replaced. The overall conclusion reached from the extensive testing program was that “many years of remaining service life could reasonably be expected from the suspender ropes if adequate means could be developed to arrest corrosion at the present level”, Stahl and Gagnon say.

When the Golden Gate Bridge, spanning the entrance to San Francisco Bay, was opened to traffic in 1937, its main span of 4,200 feet set a record that lasted for nearly 30 years. Its two main cables are each composed of 61 strands of galvanized wire. They were constructed by the air-spinning method and protected by galvanized wire wrapping laid over red lead paste. Suspender ropes support the structure.

In addition to be being located in a marine atmosphere, the bridge is exposed to heavy salt-laden fog for extended periods every year, making it more susceptible to corrosion.

Innovative corrosion coating repair of the Golden Gate Larkspur Ferry Terminal’s steel piles and perimeter beams recently was completed by the Golden Gate Bridge, Highway and Transportation District of San Francisco, and Tapecoat Co., Evanston, Ill.

TC Enviroshield Modular System modules were installed both in and out of the water without the need for a dry steel surface and met project requirements including proven corrosion protection, reinspection capability, aesthetic appearance, accommodation for lateral braces, environmental sensitivity, competitive pricing and easy field application and adjustment.

ENGINEERED SILOXANE COATINGS

The Peace Bridge crosses the Niagara River between Buffalo, N.Y., and Fort Erie, Ontario, Canada. Owned and operated by the Buffalo & Fort Erie Public Bridge Authority (an international entity composed of an equal number of representatives from Canada and the United States), the bridge is funded entirely through user fees.

More than 300 million vehicles have crossed the bridge since Edward, the Prince of Wales, and U.S. Vice President Charles Dawes officially opened it on Aug. 7, 1927.

Additionally, by carrying more than 11 percent of all North American trade and 14 percent of all trade between the United States and Canada, the Peace Bridge has become an international passageway. Nearly 4,000 trucks and 23,000 cars cross it each day, and traffic has continued to grow steadily.

Training classes include hands-on exercises

The National Asphalt Pavement Association has released its 1996 Training Program, with these upcoming courses: “Paving Superintendents’ Training Course” (March 11-13, St. Louis), “Materials & Mix Design” (March 24-29, Aubum, Ala.) and “Environmental & OSHA Compliance” (April 2-4, Alexandria, Va.).

The Paving Superintendents’ training course is designed for general and paving superintendents and paving foremen and covers topics such as Principles of Supervision, Project Planning & Scheduling, Human Relations, Traffic Control, Laydown Methods & Procedures and Compaction Methods & Procedures.

The Materials & Mix Design course is for public and private industry personnel who have responsibility for HMA company or commercial testing laboratory facilities, are laboratory technicians or will be working in those areas.

The course features both classroom and hands-on laboratory exercises. Topics covered included Asphalt Cement, Aggregates (blending and sampling), Marshall Mix Design and Mix Design Adjustments and Troubleshooting.

The Environmental & OSHA Compliance course is designed for HMA facility managers, environmental and safety managers and other company executives making decisions and responding to environmental and occupational safety and health laws and regulations.

The course covers Environmental Liability; Air, Water and Hazardous Materials Issues; Spills; Underground Storage Tanks; Emergency Planning; and OSHA, Community Right-to-know Reporting Requirements, Enforcement, Inspections and Audits.

Programs on the training courses offered, with details on course content and registration information, are available from the National Asphalt Pavement Association, 5100 Forbes Blvd., Lanham, Md. 20706; (301) 731-4748; fax: (301) 731,4621.

The 25 Worst Bridges In The United States

With five steel arches of varying widths and an additional truss span across the Erie Canal on the American side, the bridge still features its original reinforced concrete deck, and the structural steel framing is essentially unchanged.

Maintenance program costs had risen from approximately $2.23 per square foot in 1984, to $18.79 per square foot in 1991. Spurred by the accelerating costs, the authority decided to re-evaluate its painting program.

A maintenance survey showed that 8.2 percent of the bridge, which was covered in a lead-based paint, was rusted to an ASTM grade 7; 13 percent displayed topcoat failure.

Concerned about compliance with environmental laws and sensitivity to environmental groups, the authority met with Canadian and U.S. agencies prior to the project. And, because the bridge serves as a transporter for major telecommunications systems, which run underneath it, worker health was also a concern.

The authority outlined its project for lead-based paint removal and recoating of the entire bridge over a four-year period.

Additional challenges, such as jurisdictional problems between Ontario and New York and the complications of completing the project from the water and around traffic, helped drive up bids.

“A single-source management approach was decided on,” says Stephen Mayer, operations manager for the authority. Ameron Protective Coatings Group, Brea, Calif., was selected for all phases of surface preparation and coatings application, including removal of old coatings, lead abatement and recoating of the 3,700-foot-long structure.

The project was viewed as a demonstration, evaluating leadbased paint abatement and disposal, monitoring project costs and ensuring environmental concerns were met.

A two-coat zinc/epoxy system featuring PSX-700 siloxane-epoxy was applied as a topcoat over a zinc-rich epoxy primer.

Part of a new family of “engineered siloxane” coatings and surfacers based on a proprietary chemistry, the product greatly enhances substrate and surface resistance to corrosion, weathering, heat and a broad range of aggressive chemicals.

BRIDGE REPLACEMENT

Built in 1892, the Pine Creek Bridge, located in the village of Blackwell, Pa., was a single-lane through truss with a 13-ton weight limit. It consisted of a 191-foot single span with a 14-foot-two-inch vertical clearance and a curb-to-curb width of just 15 feet. Recurring ice jams over the years had damaged the old truss and even lifted it off its bearings on one occasion.

The stretch of creek, designated a Priority IA Scenic River by the Pennsylvania Department of Environmental Resources, is heavily used for recreation. While that fact alone would have raised environmental concerns for a new bridge that carries State Route 414 through the Pine Creek Canyon, other factors also affected the replacement of the bridge. For example:

* Closure of the existing bridge would have imposed a 55-mile detour on user traffic;

* the roadway took a 90-degree turn at its west abutment, running parallel to a rock slope and leaving the road sandwiched between the steep incline and the stream. This pronounced turn off the old bridge often brought traffic to a virtual stop;

* making a massive roadcut with retaining walls was ruled out early as the solution because of environmental impacts. The Mid-State Hiking Trail passes through the area, and the east bank of the scenic stream was flanked by an archaeological site eligible for the National Register of Historic Places; and

* a canoe access area adjoined several acres of woodlands.

Any new construction was virtually certain to affect one, if not all, of these features, especially since SR 414 was to remain open during construction.

After examining several alternatives, a site, which was selected approximately 200 feet downstream, offered several benefits. Those benefits were:

* maintenance of traffic for’ the only north/south route through Pine Creek Canyon;

* minimal impacts to the canoe access and archaeological site;

* maintenance of the Mid-state Trail; and

* avoidance of impacts on the wetlands.

Because of the curvature required on the new bridge, a 53-degree, 30-minute curve was inr-orporated into the approach. This avoided impacts to the rock incline but required a short girder as an addition to the typical fourgirder framing.

Designed as a two-span structure of weathering steel 1-girders, the bridge offers two, 10-footwide lanes with 4-foot wide shoulders. At the west end the design uses a 24-inch-deep rolled beam to provide support for the deck slab, which is on a 93-degree radius at the parapet. To gain economy in framing, the typical girders are straight.

The location downstream from the original bridge did not eliminate the possibility of ice jams created by the nearby confluence of Pine Creek and Babbs Creek when sustained low temperatures set in on the area during winter.

A higher bridge would have required retaining walls along the mountainside and resulted in significant environmental degrada, tion. To protect the center pier, engineers used an independent ice breaking nose with steel armor. The nose is supported by an independent system of piles constructed with base sockets for anchorage to resist uplift forces.

AILING BRIDGES

The nation’s system is aging quickly, and most states are finding themselves in a bit of a crunch as they dig around for the money needed to perform the necessary maintenance.

And ailing bridges, more often than not, have to suffer severe damage before they are noticed and money coughed up for repairs.

Nursing these bridges back to health has become a challenge, competing against heavy traffic loads, sait and water, freeze and thaw.

There are more than 570,000 bridges in inventory in the United States at the present time. Some were built before the automobile; most were constructed after World War II — many need costly repairs.

Though highway officials stress that no major bridges now pose a threat to safety, more than 107,000 are listed as structurally deficient.

Nearly 80,000 bridges have been declared functionally obsolete, and those termed deficient account for almost 170,000 of the nation’s bridge stockpile.

USING TECHNOLOGY

States like Ohio are rapidly assimilating technology to address challenges of inspecting and repairing deficient and decaying bridges. Some computer system now are designed to aid in the process of bridge inspection and maintenance.

The ODOT’s Bridge Management System (BMS) keeps a centralized, electronic inventory of more than 42,000 bridges in the state and has additional components that track bridge inspections and aid the department’s decision-making process. Complete histories of each bridge also are fully accessible.

The database details information on Ohio’s bridges, which can be accessed by qualified personnel to learn past analyzes and summaries of information on specific bridges. Users can update the information, creating folders with the most current information on bridge inspections and maintenance work.

“That [1993] NBC investigation brought to light what bridge inspectors across the country already knew,” Poole says. “Being able to tell when a bridge is about to fall is not an exact science.”

Even with the best training possible, he maintains, making decisions about maintenance requirements is still a great challenge.

“DOTS across the country are facing funding limitations and competing public demands to keep bridges open,” he says. “Managers need tools to help them make responsible decisions about what repairs will “be made at any given time.”

Pontis, the Latin word for bridge, is a special network-level system that allows its user to create dynamic probability models that give accurate measures of how much money is needed to maintain bridges at or improve bridges to an acceptable level. Using sub-model systems, Pontis can take information from the database and project costs of maintenance, repair, rehabilitation and improvement. It can then integrate these models into a single, long-range bridge program, setting needed priorities for repairs and projects within budget constraints over a period of time.

As a means of adding even more information to the database, ODOT bridge engineers and computer experts created a pilot program using imaging technology. Bridge Management Imaging System (BMIS), developed with the help of Burgess and Niple, Columbus, Ohio, allows a variety of documents to be stored with the rest of the data in BMS, Poole explains.

“The BMIS uses image scanners to store all kinds of paper files into an electronic folder. This means that a computer file on a bridge can now include digitat recreations from all kinds of paper sources, in addition to the standard type-faced documents,” he says. “Virtually every piece of information on a bridge can be made available at the click of a button.”

Another innovation, the digital camera, has allowed the Office of Engineering Policy to record an image in digitized form on a computer disk. The image can then be downloaded directly into the BMIS.

“Pictures of a bridge can be stored directly in the proper electronic folder without the expense or time associated with developing and processing film,” Poole says.

And some of Florida’s engineering students are able to get an early handle on the specific challenges deficient bridges pose.

“To get the most out of their education, engineering students need to get out of the classroom and into the field to see how the work is actually done,”says Joseph Lobuono, president of Lobuono, Armstrong & Associates (LAA), Tallahassee, Fla., the firm sponsoring one-day seminars and site visits to the Roosevelt Bridge replacement project now under construction in Stuart, Fla.

The bridge poses challenges such as heavily used roadway in the middle of downtown Stuart, a relatively long crossing of a shallow waterway with considerable barge traffic and a local community that is very concerned with the bridge’s impact on the appearance of their historic downtown area.

“It is important to supplement classroom training with exposure to real projects, with all the unforeseen challenges they present,” Lobuono says. “One of the great challenges for our country is ensuring that we have an adequate supply of capable engineers entering the profession, ready and able to meet the formidable task of building and properly maintaining tomorrow’s sophisticated transportation infrastructure.”