Bridges

Those of us who live in the Portland metropolitan area are familiar with the many bridges over the Willamette and Columbia Rivers, and we can certainly appreciate their importance during the morning and afternoon commutes. But of course, those aren't the only bridges that have an impact on our lives-in fact, according to the Oregon Department of Transportation (ODOT), there are nearly 6,600 bridges in Oregon alone, and these bridges carry not only people and their vehicles but nearly all the goods and services that we find essential in today's life.

So it's with some level of concern that we note the frequent news stories about the deteriorating state of our nation's infrastructure, including its bridges. A testament to this problem, and a financial commitment to help solve it, is reflected in the recent passage of a transportation funding package in Oregon, known as OTIA III (Oregon Transportation Investment Act), which, through increased DMV and trucking-related fees, finances $2.5 billion in transportation construction projects. Of this, $1.3 billion is earmarked for repairing and/or replacing state bridges.

We mentioned in our last newsletter that we'd been awarded a three-year contract with the Bridge Engineering Section of ODOT to provide professional services for the evaluation of state highway bridges. Under this contract, we'll provide services to ODOT on a project-to-project basis in the areas of failure analysis, materials evaluation, nondestructive testing, and performance testing via strain gage/data acquisition.

While our contract with ODOT may be new, the work we'll be performing isn't--we've been working on projects involving Oregon's bridges for several decades now and as such, already have an "up close and personal" relationship with a number of them. With this in mind, we thought it would be interesting and timely to share a few of our past bridge projects with our readers.

Fremont Bridge

In October 1971, during the construction of the Fremont Bridge in Portland, a 15-foot long crack occurred in one of the four girder-truss joints where the arch ribs intersect the longitudinal girder. (More simply put, the crack was in one of the major structural components of the bridge!) MEI-C was retained to conduct a comprehensive failure analysis.

Our analysis revealed that the crack was due to a complex interaction of over two dozen contributory factors, including ones related to design, material, fabrication, and ambient environment (temperature, in this case).

As a result of our findings, the failed section was redesigned and replaced, along with the other three girder-truss joint sections on the bridge. Our work led directly to upgrading of official highway bridge standards, including design practices, material specification, and fabrication procedures. Oh, and just to put the magnitude of the problem into perspective, the repairs delayed the bridge opening over a year and cost about $5 million!

Fremont Bridge Facts

• The Fremont Bridge has the longest main span of any bridge in Oregon, and it is the longest tied-arch bridge in the world.
• To minimize the impact on navigation during construction, the 6,000-ton, 902-foot long center span was built off site on Swan Island, then floated into position and hoisted to its present location, 175 feet above the river.

Broadway Bridge

In 1978, during routine maintenance of the 1913 vintage Broadway Bridge in Portland, several foot-long cracks were found visually in the face of the north roller (or, more correctly, the "Rall wheel") on the west span. MEI-C was retained to inspect all the rollers to determine if additional cracks were present and to remove samples from the cracked area and conduct a metallurgical analysis to establish the cause for the cracks.

Our analysis revealed the cracks were brittle in nature, of relatively recent origin, and had originated from as-cast, nonmetallic inclusion stringers, which acted as a plane of weakness. Our analysis also revealed that the cast steel of the rollers was a nonstandard nickel-chromium steel requiring special welding procedures.

With this information, we established an appropriate welding procedure for the material, allowing the rollers to be repaired in place, thereby avoiding the expense of replacing them, while at the same time, restoring their structural integrity.

Broadway Bridge Facts

• The Broadway Bridge is one of three bascule bridges in Portland (the Morrison and Burnside being the other two), and is an example of a Rall-type bascule bridge.
• Bascule bridges have "leaves" that rotate upward and away from each other, providing clear passage for river traffic. In a Rall-type bascule bridge, the counterweights are located above the roadway, as is much of the operating mechanism.
• When the Broadway Bridge was built in 1913, it was the longest double-leaf bascule bridge in the world. Now, 90 years later, the Broadway Bridge is still the world's largest Rall-type bascule bridge and is one of the few surviving ones.
• In 1910, the year before construction began on the Broadway Bridge, there were 2,500 licensed vehicles in Oregon. By 1913, when the bridge opened, there were 14,000. By 1996, there were 2,851,000!

Bull Run Watershed Bridges

KPFF Consulting Engineers was retained by the City of Portland Bureau of Water Works to conduct a seismic study of two bridges that support the pipelines supplying potable water to Portland from the Bull Run Watershed. MEI-C was retained to conduct an inspection of the structural support pins in the bridges.

Both bridges had been designed and built in the late 1890's, and had already withstood the test of time for over 100 years, but were they suitable for continued service to provide an uninterrupted water supply to the city?

Our inspection was by longitudinal wave (straight beam) ultrasonics from the ends of the pins. Although the inspection indicated the presence of variations in acoustic properties, no significant flaws were found.

Bull Run Watershed Bridges

• Although old in their own right, these two bridges aren't quite the oldest active ones in Oregon. That honor goes to the nearby Bull Run River and Sandy River Bridges.
• These two bridges were initially part of the original Burnside Bridge in Portland, built in 1894. When the current Burnside Bridge was built in 1926, the two spans from the original bridge were relocated to their current sites in the Bull Run Reservoir area.

I-5 Vancouver Interstate Bridge

The next time you're stuck in traffic on I-5 trying to get across the interstate bridge to Vancouver, think back to what it must have been like prior to 1917 when the bridge was built. For the previous 47 years, folks had to cross the river on a ferry, which began regular service way back in 1870.

A joint venture by Clark and Multnomah Counties, the bridge was a milestone in transportation between Portland and Vancouver. Its opening was greeted with great fanfare at an opening ceremony attended by a crowd estimated at almost 50,000.

In 1960, as part of a project to refurbish the 1917 vintage lift span, the forged steel trunnions were modified to accept tapered roller bearings in place of the plain sleeve bearings that had been originally installed. In 1987, the trunnions were inspected ultrasonically, and a small flaw indication was found in one of them. MEI-C was retained to remove three coupons from one of the trunnions and conduct a laboratory analysis to establish the chemical, physical, and metallurgical properties of the material.

In 1997, ODOT replaced the counterweight sheaves and steel ropes on one of the towers and repaired a crack in one of the trunnions.

I-5 Vancouver Interstate Bridge Facts

• When the I-5 Interstate Bridge opened in 1917 -on Valentine's Day- there weren't any interstate "freeways" anywhere in the country, and the speed limit on the bridge was 15 miles per hour. Portland's population was already almost a quarter of a million, while Vancouver's was only about 10,000.
• Originally, the bridge consisted of only one, four-lane span, and it wasn't until 1958 that a second span was built, just west of the original span. Today, the bridge carries over 120,000 vehicles daily.

St. Johns Bridge

The St. Johns Bridge over the Willamette River in Portland is often considered the most elegant of Portland's bridges. Completed in 1931 at a cost of $4,000,000 the bridge contained the longest main span of any suspension bridge west of Detroit. Now, 72 years later, weather, traffic and the passage of time have taken their toll on the bridge, resulting in a rutted and worn bridge deck, crumbling sidewalks, broken utility conduits, and worn suspension cables at some locations. In 2002,

ODOT awarded a $33- million contract to Max J. Kuney Construction of Spokane Washington to rehabilitate the bridge.

The project will include complete removal and replacement of the concrete bridge deck and sidewalks, upgrades to the drainage and lighting systems, improvements to the Bridge Avenue ramps on the west side of the Willamette River, and a complete paint job -after removal of the old, lead-based paint.

MEI-C has been providing materials analysis and testing services to Kuney Construction, establishing the compositions of the old materials, writing welding procedures for joining new materials to the old, and tensile testing samples of some of the new bolts that will be installed to secure the cables.

St. Johns Bridge Facts

• The St. Johns Bridge was named after the community of St. Johns, which had been named after James Johns, a settler in the Oregon Territory. The bridge replaced the last ferry in Portland, a system which, appropriately enough, had been started by Mr. Johns in 1852 with a single rowboat.
• Construction on the bridge began in September 1929, just one month before the stock market crash that triggered the Great Depression.
• The main towers are 408 feet above the water, and the clearance under the deck is 205 feet.
• At the time of its construction, the bridge had the world's largest and longest prestressed twisted rope strand cables. Each 2,645-foot long cable weighs well over one million pounds and is subject to a tension of about 17 million pounds!

Van Buren Street Bridge

The Van Buren Street Bridge, which crosses the Willamette River in downtown Corvallis, was built in 1913. ODOT, as part of its state-wide ongoing program of infrastructure review, initiated a study in 1995 to evaluate the bridge's suitability for continued service.

OBEC Consulting Engineers in Eugene was retained as the lead consultant and tasked with performing a fatigue and fracture assessment of the bridge. As part of their analysis, OBEC's engineers needed data on the actual range of stresses imposed by the service loading. MEI-C was retained by OBEC to perform an empirical stress analysis on the bridge.

To accomplish this, we mounted strain gages on five members near mid-span and monitored the dynamic loading via a computerized data acquisition system during midweek workday traffic, thereby sampling a large variety of typical commercial and industrial traffic. Additionally, ODOT provided a dump truck of known weight, which was driven over the bridge at specific speeds so we could measure the bridge's response under controlled conditions.

Van Buren Street Bridge Facts

• When the Van Buren Street Bridge was built in 1913, the Model T was still in production, having just entered its fifth year of what would be a 19-year production run.
• The bridge now has just a single travel lane, and it still has a wooden deck and walkway.
• During its early years of operation, the bridge carried a $25 fine for "riding or driving faster than a walk" or for "driving at one time more than 25 cattle or horses."

Bridge Droppings

Although we've been "up close and personal" to a number of bridges in Portland and elsewhere, the one we're closest to is the Vista Avenue Viaduct, a concrete arch bridge built in 1926 and now listed on the National Register of Historic Places. How close are we? It's only a stones throw -or a pumpkin drop- away from our building . . . Quite literally. Over the years we've been witness to many "bridge droppings" on the street in front of our building, and occasionally some of the items even end up on our roof. What do people throw off the bridge? Well, you name it, they've probably tossed it... Pumpkins of course around Halloween, but also television sets, radios, shopping carts, sacks of flour, buckets of paint, bowling balls, manhole covers. . . the list goes on and on. Most recently, it was two five-gallon buckets of stucco material, which splattered all the way to our front door. Several years ago, the Oregon Lottery Commission even filmed a television commercial here, featuring a bungee jumper leaping from the bridge. And yes, now that you mention it, it was rather distracting to be working on a project at the same time someone was whizzing up and down on a bungee cord outside our office windows!

 

wooden trestle preceding current concrete tructure circa 1917

current concrete structure 2003

For those of you who are interested in additional information about Portland's bridges, a great source of information is "The Portland Bridge Book," written by Sharon Wood Wortman, illustrated by Jay Dee Alley, and published by the Oregon Historical Society Press.