Seismic solutions for bridges were a major focal point of the mostly table-top exhibition at the 21st International Bridge Conference.

Seismic Energy Products offered dynamic solutions to bridges in danger of earthquake damage with the use of base isolation. This method lets a bridge or other structure remain fully operational after a major earthquake by using isolation bearings and bearing pads to maintain vertical loads while allowing horizontal movement.

Typical base isolation technology uses lead-and-rubber-layered isolators. These provide the greatest safety factor on displacement among SEP’s systems. They don’t corrode, stick-slip, or show wear, making them maintenance free.

In both new and retrofit projects, use of the isolators can lead to smaller, lighter structural members, more than offsetting their costs.

Montana, California, New Mexico, and Oregon have used or retrofitted bridges with SEP isolators. The Golden Gate Bridge, for example, was retrofitted with lead-rubber isolators and Teflon slide bearings.

R. J. Watson Incorporated featured its EradiQuake isolation bearing system. The technology minimizes forces and displacements during an earthquake using a sliding multirotational bearing assembly with damping and a maintenance-free mass energy regulator.

The system was developed using research from the Multidisciplinary Center for Earthquake Engineering Research conducted at the State University of New York.

Shake table testing shows that the system significantly reduces forces and displacements caused by strong ground motion accelerations, the company reports.

The EQS transfers bridge deck energy during a quake into heat and spring energy via the mass energy regulator. It can be adjusted to various displacement levels.

Some of the bridges using the EradiQuake isolation bearings include Chicago’s Damen Avenue Arch Bridge; Missoula, Montana’s I-90 Clark Fork River Bridge; and New York’s Kingston Rhinecliff Bridge over the Hudson River.

The company provides a no-obligation design service to examine feasibility of using EQS once an agency gives a bridge plan and elevation including live loads, dead loads, thermal and creep data, number of bearings per bent, and ground acceleration data. You can also download their Isoslide interactive software design program at www.rjwatson.com.

Earthquake Protection Systems Incorporated featured their Friction Pendulum seismic isolation bearings. The system uses characteristics of a pendulum to lengthen the period of the isolated structure, once placed between the structure and its foundation.

During an earthquake, the isolation bearing’s articulated slider within the bearing slides across a stainless-steel concave surface. This makes the bridge move with small pendulum motions. Lateral loads and shaking movements mostly remain with the bearing with minimal transfer to the bridge.

The radius of the curvature of the concave surface determines the period of the movement on the bearing, from one to five seconds. Dynamic friction ranges from 2 to 12% and effective damping from 10 to 40%.

By allowing lighter structural members, use of the Friction Pendulum Bearings cut construction costs of California’s Benecia-Martinez reports by $30 million, the manufacturer reports.

Williams Form Engineering focused on its seismic restraints. Their 150-ksi post-tension bars are used in single- or multiple-bar systems to add thousands of kips’ passive reserve tension and shear capacity to existing concrete bridges.

Bars are protected from corrosion by hot-dip galvanizing or epoxy coating.

Sika offered several products for seismic control. SikaWrap is a composite fabric used for structural and seismic strengthening. The carbon and glass-fiber fabrics can be bonded to piles, beams, or slabs.

Sika CarboDur Strips use a pultruded carbon fiber laminate with very high-tensile strength capabilities.

Construction Technology Laboratories offered its structural monitoring system to check bridge conditions, including during and after seismic activity. Sensors, instrumentation, load cells, strain-gauge-based sensors, and multi-depth deflectometers were included.

The company also had its free hand-held testing device for attendees. The NDT Select-A-Test lets you pick a problem such as delaminations and it then tells you what test to use to find an answer. Along with this device, a crack size comparing device was included. Better Roads’ readers can obtain these free. See the Briefing Box at the end of this article.

Hydraulic positioning

Enerpac focused its exhibit on its hydraulic lifting and positioning systems. The key is looking at the techniques early in the design phase, says Paul Hohensee, construction market leader for the Americas.

The company’s hydraulic systems can be used to develop segmental bridge launching and traveling-form systems; control systems for initial moving, turning, positioning, braking; and precision lifting and positioning of extremely heavy structures.

The company’s synchronous lift system runs in a PC environment or on an industrial PLC system. It can provide data recording, force measuring, and up to 72 lift points.

Two Enerpac SLC-810 synchronous lift systems lifted the north approach seismic retrofit project on the Golden Gate Bridge.

In Spain, a custom-synchronized lift system accurately positioned segments on the Piedrafita Bridge project.

A custom Enerpac integrated hydraulic system was used for bridge launching in the environmentally deep-valley Millau, France viaduct project. The system pushed the 90-foot-wide deck from both sides of the valley onto seven concrete piers. The deck is 800-feet high and 1.5-miles long.

Use of the computer-controlled hydraulic technology can reduce an eight- to- 10-year project to three years or less, Hohensee says.

Corrosion control

Advanced Pile Encapsulation is a Degussa process that protects or repairs bridge piles.

First, the surface is prepared by removing marine growth and previously applied coatings.

A custom-molded, glass-fiber-reinforced translucent jacket is placed around the pile and aggregate-filled epoxy grout is pumped into the jacket from the bottom up providing a secure bond.

A bottom-seal gasket further prevents the intrusion of corrosion-inducing elements, says Vince Kazakavich, a bridge products consultant for Degussa.

In New Orleans, 10-foot-tall APE encapsulations sealed 54-inch-diameter cylinder piles on the Lake Pontchartrain Causeway to control cracks, fill spalls, and provide future corrosion protection.

Royston’s products include Rosphalt 50, a super polymeric asphalt additive to give a superior waterproof wearing course for new composite bridge deck overlays, replacement for old bridge deck overlays, replacement of waterproofing membranes, and replacement of epoxy, latex-modified, silica fume, or high-performance concrete used for bridge deck overlays.

Royston’s Flex-Flo Expansion Joint Compound was featured, too. This two-component, primerless, solventless, flexible adhesive/compound is a true rubber. It forms an expansion joint that handles a wide variety of expansion, contraction, shear, compression, and vibration stresses.

Corrpro’s Corrpsray is a galvanic anode cathodic protection system to halt concrete bridge corrosion.

The alumunium-zink alloy is applied as a coating. The concrete serves as an electrolyte, connecting corroded steel rebar to the anode. An electrical current flows naturally from the coating to the rebar-protecting the steel. No external power supply is needed.

Materials

High-performance, lightweight aggregates created via thermal expansion of high-quality slate in rotary kilns offer better-draining, lower-load-retaining walls and fills.

Stalite’s 0.75-inch aggregate has a dry, loose density of 45 pounds per cubic foot. It can be used to produce very high strength at concrete unit weights up to 30% less than normal concrete weights.

The Northeast Solite Corporation offered facts about using structural lightweight aggregate concrete for bridge building. For example, the Benicia-Martinez Bridge in California is a five-lane balanced, pre-stressed cast-in-place segmental cantilever and lightweight concrete box girder with room for light rail on one side. The structural lightweight concrete reached 6,500 psi at 28 days.

An early use of SLC was in Utah’s Silver Creek Overpass in 1968. When replaced with a wider structure 33 years later, the SLC showed little or no deterioration.

The durability of shale materials means SLC is resistant to freeze-thaw cycles.

Transpo’s T-18 Bridge Overlay System uses lightweight waterproof methyl methacrylate polymer concrete which comes as a pre-packaged three-component system.

The package has graded aggregates bound in a slurry with a polymer binder and is broadcast with an aggregate wearing coarse.

The system has an application temperature range of 14 to 90 degrees F. It is freeze-thaw cycle resistant, gives high early strength, and cures quickly — one hour for an 0.375-inch deck layer.

Degussa featured its Degadeck Crack Sealer to repair and restore concrete bridge decks. The two-component material repairs cracks from 0125 inch to hairline. Curing time is 35 to 45 minutes.

Degussa also offers Degrades polymer concrete for larger, deeper deck repairs. Cure time is about an hour.

Other systems

Martin Marietta Composites featured its DuraSpan fiber-reinforced polymer bridge deck system. This uses fiber-reinforced polymer for a lower-weight deck — 20% of the weight of a conventional concrete deck.

The material is resistant to corrosion and freeze-thaw cycles, can be installed quickly, comes in 8- and 10-foot-wide panels, and can achieve composite action.

DuraSpan decks have been installed on steel, concrete, timber, and fiber-reinforced polymer girders.

Acrow’s Panel Bridges use modular components for quick assembly. They can be permanently installed or used as temporary bridges.

Components and galvanized zinc provide long life and low maintenance.

Where's the Money?

You’ve got to admire Pete Ruane, president and CEO of the American Road & Transportation Builders Association, who always dares to speak out.

Ruane was one of three speakers at a well-attended, if frustrating, Tuesday morning Reauthorization Session. Chaired by Gannett Fleming Incorporated’s Thomas G. Leech, P.E., S.E. (right), speakers presented their views of the badly stalled reauthorization of the Federal Surface Transportation Bill.

Declaring that the minimum acceptable figure is the $318 billion in the Senate’s recently passed version of the bill, Ruane also predicted more temporary extensions of the current bill rather than passage of the new bill. He also foresees general foot dragging on the part of our Republican-led Congress who want to pass the Bill and even have the votes to override a veto, but don’t want to embarrass the President during election year by sending him a bill he’s said he won’t sign.

While politics — even more than usual — hold up desperately needed increased funding for bridges, roads, and other transit programs, Ruane compared the recently passed House and Senate Bill versions (which must now somehow be combined) from the bridge engineer’s point of view:

Pork projects, genteelly called [House or Senate] member projects by an engineer asking questions from the audience, are currently slated to eat up $11 billion and could continue to rise. But, Ruane says, at least most of these projects are transportation related, unlike some projects from earlier years.

John Horsley, executive director of the American Association of State Highway and Transportation Officials, looked at the issue of how many states get back much less than they pay (via gasoline taxes) into the Highway Trust Fund.

The 1998 reauthorization raised the guaranteed return to 90.5%. Some want a 95% guaranteed state return equity this time.

That’s unlikely to happen, says the ever-practical Ruane, but the percentage will probably increase — because 67% of the House-Senate Bill Reconciliation Committee comes from donor states.

Bud Wright, executive director of the Federal Highway Administration, presented the Bush Administration’s goals for the reauthorization bill, focusing heavily on safety improvements to reduce the numbers killed on the highways each year. While this idea is well intentioned, stricter enforcement of anti-drunk driving laws would do more to achieve this goal than concentrating on new road access designs. About 40% of road deaths involve alcohol.

One positive Administration goal for the bill is to limit environmental comment and reaction times on projects to 180 days, rather than to allow endless delays common now, Wright said.

Ruane closed the presentation with a call to put our bridge expertise and needs in front of our Representatives and Senators or their aides on a one-to-one basis. Letters won’t do much, especially with the threat of anthrax almost ensuring no government official will actually read your letter, he said.

Ruane cited a tour which took about 30 general media reporters onto the Woodrow Wilson Bridge. The 18-wheelers rushed by them, the bridge shook, their faces paled.

A similar visit to one of your own less-than-good condition bridges could have a similar effect on your  Congressperson or aide, Ruane suggested with a smile.

Like the reporters, they might walk off the bridge, their knees weak, saying, “We need to fix this — now!”

Reprinted from Better Roads Magazine
August 2004

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