The Monroe Street Bridge, above, not only provides a major north-south link; it also serves as a symbol of the city of Spokane, Washington. Shawn Toner Photography
At the time of its completion, in 1911, the Monroe Street Bridge, in Spokane, Washington, was the longest concrete arch bridge in the United States, and it soon became a revered symbol of the city. To restore the aging and, in some cases, crumbling structure to its former glory, engineers rehabilitated the main arch ribs and piers and after removing the deck, spandrel columns, and spandrel arches replaced them with matching elements that will last another 75 years. By David C. Moyano, P.E., S.E., M.ASCE, and Stephen J. Shrope, P.E., S.E., M.ASCE
n the mid-1990s, the City of Spokane, Washington, embarked on an effort to either replace or repair the ailing Monroe Street Bridge, a critical and historically important transportation link that had been constructed in 1911 and attained a listing in the National Register of Historic Places in 1976. The city decided to rehabilitate the 94-year-old concrete arch bridge—which is also listed in the Spokane City-County Historic Preservation Department’s Spokane Register of Historic Places—by adhering as closely as possible to the original design. The investigation, design, and construction process was extensive, requiring that the engineers not only determine the complex structural requirements of the crossing but also develop a set of solutions that would be both technically and politically acceptable. The process required coordination with a host of regulatory agencies, political bodies, expert consultants, technical and funding authorities, construction contractors, and the public. But the result was the preservation of an early-20th-century landmark bridge that will serve the public well into the 21st century.
The Monroe Street Bridge serves as an important transportation link for Spokane, connecting the northern and southern portions of the city across the 136 ft (41.5 m) deep canyon carved by the Spokane River. The bridge is uniquely positioned below the river falls and, as such, has become an icon and tourist attraction. It has an overall length of 896 ft (273 m) with a 50 ft (15 m) wide roadway and 9 ft (2.7 m) wide sidewalks on either side. Its superstructure is composed of a 281 ft (85.6 m) main arch spanning the Spokane River, two flanking 120 ft (36.5) arch spans, and approach viaduct arches at each end. Together, these elements create a dramatic, open-spandrel arch structure across the gorge.
The bridge began to show signs of wear and tear by the 1970s, and as a result several limited investigations of the structural condition were performed. The investigations confirmed problematic conditions. In 1997, after years of investment in bridge maintenance, the city proceeded with a comprehensive structural condition inspection and assessment with the intent of repairing or replacing the bridge. David Evans and Associates (DEA), of Portland, Oregon, was selected to perform the work, which was initiated in May 1998 and completed in October of that year.
Four massive concrete pavilions with arched openings, above, straddle the sidewalks. Each pavilion contains a memorial plaque in tribute to the pioneer spirit of the then-young city. Shawn Toner Photography
The 1998 investigation concluded that deterioration of the deck, spandrel concrete, and reinforcing steel was significant and probably accelerating. Rehabilitation scenarios were developed and conceptual designs were prepared for three options: do nothing, rehabilitate the bridge to extend its life by 20 years, or rehabilitate the bridge to extend its life by 75 years.
Following input from the public, the 75-year rehabilitation option was selected. The concept included the full removal of the existing deck, the spandrel columns, and the spandrel arches and the repair of the existing main arch ribs and piers. The 1998 study put the construction cost at $15.2 million and the overall program at $20 million in 2002 dollars.
DEA was later selected to develop the final design and contract documents and manage the construction. The firm received notice to proceed with the final design in October 2000. Stringent compliance with local, state, and federal statutes governing the preservation of structures of historical importance was required. An extensive public outreach program was developed and implemented while the city pursued funding sources for the project.
The final design called for removal of the entire 180 ft (55 m) colonnade-style north approach viaduct and its replacement with a replica that would be constructed of cast-in-place (CIP) concrete. The spandrel columns and spandrel arches were to be rebuilt in kind with CIP concrete. The 135 ft (41 m) south approach viaduct was to receive a structural concrete deck overlay. All original concrete remaining in place—primarily on the large arches and main piers—was to be repaired and sealed.
Wildish/F.E. Ward Constructors, of Vancouver, Washington, was the successful bidder at $12,370,717. Construction began in January 2003 and was completed in September 2005. The contractor made use of a complex system of platforms that were constantly being reconfigured to catch debris and contain water runoff as well as facilitate safe access to the bridge. An early partnering effort by the contractor, the engineers, and the city helped to quickly resolve construction challenges and public concerns and eventually bring the project in under budget. As a result of a program designed to lessen any diminution of the historical stature of the crossing, the project also provided the city with a beautiful promenade nearby overlooking the river and bridge featuring interpretive panels highlighting the site, the bridge’s history, and the rehabilitation project. The project was deemed an overwhelming success by the city and the public.
The Romanesque multiple-arch design of the crossing was developed by the City of Spokane’s engineer, J.C. Ralston. Construction began in 1909 and was completed in 1911.
Family of Alfred Butler
ach of the bridge’s two main arch ribs is 130 ft (40 m) high and 16 ft (5 m) wide; the ribs are 6 ft 9 in. (2 m) deep at their crowns and flare to a width of 19 ft 9 in. (6 m) and a depth of 18 ft 6 in. (5.7 m) at their spring points (the piers). The north approach structure is an eight-span concrete arched colonnade 180 ft (55 m) long. The deck structure consists of concrete-encased, built-up riveted steel beam members. The original south approach was a 135 ft (41 m) timber trestle structure.
The Romanesque multiple-arch design of the crossing was developed by the City of Spokane’s engineer, J.C. Ralston; the architecture firm Cutter and Malmgren, of Spokane, designed the bridge’s ornamental railings and four massive concrete pavilions, one on top of each main arch pier, which straddled the sidewalks with arched throughways. Each pavilion contained memorial plaques in tribute to the pioneer spirit of the then-young city. The design and construction documents were completed and construction began in September 1909. The final cost of the project was $535,000. Approximately half the final cost was for labor and half was for materials.
In 1916 the south approach trestle was replaced with a CIP concrete colonnade similar in design to the north approach structure; however, rather than the embedded steel beam approach used for the north approach, a more conventional reinforced-concrete construction method was used for the new approach.
The Monroe Street Bridge served a fast-growing and vibrant Spokane. Constructed at the dawn of the age of the automobile, the volume and speed of the traffic it carried increased rapidly over the years, and the bridge began to enjoy a prominent place in city and tourist activities. It was featured in countless artists’ renderings, paintings, and postcards as a symbol of the city and was used for parades, for “fly-unders” by barnstormers in the 1920s, and even for a campaign in the 1930s to promote safe driving, several cars being pushed off the bridge to demonstrate what could happen to careless drivers. Only minor changes to the bridge were made over the years. In 1918 the wood deck planks were replaced with brick paving. The original bronze ornamental lighting, which had been the target of frequent vandalism, was removed in 1925 and replaced with more conventional lighting. Structural investigations of the bridge in 1976 and 1979 found serious deterioration in the bridge’s deck structure.
The 1979 report concluded that the entire deck structure had a limited remaining service life. Minor maintenance continued through the 1980s concurrently with planning and investigations aimed at adding another bridge across the gorge, but ultimately the decision was made that, because of its historical importance, only the Monroe Street Bridge should occupy that important location in the city.
s part of DEA’s 1998 assessment, experts from the firm of Burgess & Niple, Ltd., of Columbus, Ohio, examined all parts of the bridge, assessing and mapping areas of deterioration and concern. Concrete and steel surfaces were sounded with hammers and visually inspected. Section loss of steel members from corrosion was measured. Many concrete core samples were taken from the bridge in various locations for laboratory testing, which was conducted by ctl Laboratories, of Skokie, Illinois. Those tests measured strength, chemical and physical composition, and the general condition of the concrete.
Concrete powder samples were taken at various locations of the structure and tested to investigate the presence of chlorides and carbonation in the concrete. The testing indicated significant variability; the chloride content ranged from 0.3 to 40 lb/cu yd (0.18 to 23.7 kg/m³) of concrete. (The threshold beyond which corrosion of the embedded steel occurs is 1 lb/cu yd [0.59 kg/m³].) Carbonation of the concrete—a change in the concrete’s chemistry resulting in a lower pH and leading to corrosion of the steel—was discovered at depths up to 5 in. (127 mm).
The condition inspection also found that built-up steel beams encased in concrete as part of the deck structure were in very poor condition and were continuing to corrode. This corrosion resulted in the spalling of large pieces of concrete, some of which were hanging from the structure and were estimated to weigh more than 100 lb (45 kg). The steel rivets holding individual steel plates together also had corroded, and in many instances the rivets were missing or easily broken off when struck by a hammer.
The conclusion of the corrosion assessment was that the steel within the concrete would continue to corrode at a rate equal to or greater than that already experienced by the structure. This corrosion was a significant threat to the load-carrying capacity of the deck system. However, this corrosion did not appear to be a serious threat to the load-carrying capacity of other bridge components because only minimal amounts of reinforcing steel were used in the large arches and piers and because the original design was conservative.
Alkali silica reactivity (ASR) was detected in all of the concrete samples, which were taken at a variety of locations. ASR results from the use of a particular type of stone aggregate in the concrete mix that reacts with the cement paste, creating an expansive gel. This expansive gel can crack the concrete, making it weaker and less durable.
The safe load-carrying capacity of the bridge structure was determined by comparing the loads imposed by the weight of the structure and standard highway vehicles with the capacity of the bridge members to support the loads. This analysis indicated that the bridge could support standard vehicles for another five to seven years as long as key areas were regularly inspected and maintained. Portions of the bridge, however, did not meet current specifications and had deteriorated to the point of structural deficiency. The investigation revealed that these elements would not collapse all at once but would instead gradually crack and deflect. To ensure public safety and continued service, it would be necessary to regularly monitor their condition. Major repairs and rehabilitation would be necessary for the bridge to remain in service for an extended period.
The final report on the investigation generated by DEA defined the functional condition of the bridge as “poor” using the system set forth in the Manual for Condition Evaluation of Bridges, published by the American Association of State Highway and Transportation Officials (AASHTO); the bridge scored a 4 on AASHTO’s scale of 0 to 9, 0 denoting a failed condition and 9 being excellent. A Federal Highway Administration (FHWA) inventory rating, which represents the load a bridge can carry using normal design factors, was 0.6 with respect to the spandrel arches and 0.9 with respect to the floor beams. The operating rating, which represents a safe load capacity and is less conservative than the inventory rating, was determined to be 1.0 as long as regular analyses of the composite action in the floor beams and the redundancy in the arch spandrel beams were undertaken.
A structural analysis of the bridge was performed using the general analysis program GT-STRUDL, which is maintained by the Georgia Institute of Technology. The arch floor system was analyzed as a three-dimensional grid structure to account for the distribution of live loads among the various members. Although the floor system was designed to be supported by the built-up structural steel beams acting as simple spans, it actually behaved as a monolithic concrete slab stiffened by the floor beams and stringers and supported on the spandrel beams and columns. The spandrels were designed as continuous beams but acted as cantilevered column capitals to support the floor beams.
The spans of the south approach, which was constructed more recently than the rest of the bridge, were discovered to be structurally adequate for highway traffic loads. The design of the superstructure DOEs not conform to current standards, but the analysis indicated that it had adequate strength. The substructure capacity could not be determined from the design plans, but observations of the bridge indicated it was performing well.
The beam spans above the arches were structurally deficient for their design loads, although they were performing adequately for legal loads with regular inspection. The bridge deck as originally designed was structurally adequate. The reinforcing details, however, did not meet current AASHTO design specifications, and substantial deck reinforcing steel had been lost to corrosion. Since the slab was thicker than the minimum required and embedded steel stringers and beams provide restraint, the deck was able to support the wheel loads through arching action, even though it was not adequately reinforced according to AASHTO design guidelines. The report concluded that continued corrosion and delamination of the slab would reduce its capacity and that local failures could be expected in the future.
The arch ribs and piers were deemed structurally adequate for their current loads, but cracks in the south arch ribs indicated that pier or arch movements had occurred in the past. Although it was not clear when this occurred—or whether it was still happening—the report offered the opinion that these cracks occurred early in the life of the structure and that the piers and arches were no longer moving. Repair and monitoring of these cracks were recommended to determine whether there was a weakness in the foundation support of the south pier of the south arch.
The north approach spandrel arches and beam spans were deteriorating and in poor condition. In addition to the general deterioration, lateral loads placed on the structure by fill placed along the west side of the bridge had cracked the columns and were causing continued movements of the foundation. Because there were many redundant load paths in the approach structure, it had not failed, but its condition would not support its design loads with the required safety factors for more than approximately five years.
he recommended rehabilitation measures resulted from a consideration of many factors. The technical data obtained through the study were blended with significant engineering and construction judgment and experience to develop practical, realistic, and effective rehabilitation recommendations. The first option, which would be to do nothing, would have led to the closure of the structure and another sequence of decision making regarding bridge replacement; this was not acceptable. Both the 20-year and the 75-year rehabilitation option would address the structural deficiencies and meet criteria for federal funding, but since the cost savings that could be realized by undertaking the 20-year option were minimal, the 75-year option was chosen.
Because of the historical importance of the bridge, Washington State’s historic preservation officer, the Spokane City-County Historic Preservation Department, and that department’s Spokane Historic Landmarks Commission were key participants in the review process. Workshops with these agencies and organizations led to their full support of the 75-year rehabilitation option, and workshops and briefings with the city council resulted in their approval as well.
Extending the service life of the Monroe Street Bridge another 75 years would require the following:
Removing the deck, sidewalks, railings, spandrel arches, and columns of the south, main, and north arch spans down to the top of the existing arch ribs and replacing them with a visually matching concrete structure;
Removing the asphalt wearing surface on the south approach spans and installing a structural overlay;
Installing new joints and a properly functioning drainage system along the entire structure;
Constructing a new exterior concrete railing to match the existing railing;
Restoring the existing pavilions in place;
Installing a traffic barrier to separate the travel lanes from the sidewalks that would resist vehicle impacts but not detract from the historical character of the bridge;
Injecting epoxy into the concrete cracks;
Monitoring cracks in the south arch ribs for movement;
Cleaning and sealing the arch ribs and piers;
Completely replacing the north approach with a new structure that would replicate the existing multiarch viaduct and provide for a future pedestrian trail beneath;
Performing biannual inspections of the remaining original structural elements in order to check for spalling and delamination.
The engineering team believes that the service life of the bridge after being rehabilitated in this manner could well exceed 75 years with proper maintenance, although no current quantifiable measures are available to validate that assessment.
The rehabilitation strategy required the bridge to be closed to all modes of traffic during the estimated 30-month construction period; traffic was to be rerouted across other river crossings nearby. The final roadway and sidewalk widths were to be the same as on the original bridge. In addition to renovations that extended the life of the bridge, the work carried out could in no way diminish the bridge’s historical stature. The latter was a requirement of the certificate of appropriateness (COA) issued by the Spokane Historic Landmarks Commission. Additionally, DEA consulted with the Washington State Department of Transportation (WADOT), the FHWA, the Washington State Department of Ecology (DOE), the Washington State Department of Natural Resources (DNR), the Washington Department of Fish and Wildlife (WDFW), the U.S. Fish and Wildlife Service, the U.S. Army Corps of Engineers, and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service to verify permit requirements, conduct reviews, and ensure that the public was adequately involved. The city did not require any discretionary permits or actions, and no local building or development permits were needed. However, because the city was proposing the project, it acted as the principal agency under the State Environmental Protection Act.
The WDFW required a hydraulic project approval, which applies to any construction or other work that will use, divert, obstruct, or change the natural flow or bed of any body of freshwater or salt water in the state. This includes all construction in the water as well as over the ordinary high-water line (OHWL) and may include activities outside the OHWL that would directly affect fish and their habitat. After consulting with the DNR, the team determined that an aquatic resources use authorization notification would be required. The FHWA, acting through WADOT, required a local agency project approval, as it does for all transportation projects using federal funds. The DOE required a National Pollutant Discharge Elimination System (NPDES) construction storm-water permit because the project was expected to disturb more than 1 acre (0.4 ha) of ground surface.
After consulting with the Spokane Historic Landmarks Commission and Washington State’s historic preservation officer, a finding was issued stating that the work would, in fact, have an “adverse effect” on the bridge’s historical character because of the amount of original material to be removed. As a result, a formal document called a programmatic 4(f) was drawn up to establish the mitigation measures that would be taken, and a memorandum of agreement was developed. Mitigation measures included the development of interpretative kiosk panels discussing the rehabilitation project and the history of the bridge and its site and the development of documentation for the Historic American Engineering Record and of a video chronicling the project. In keeping with the COA, this proactive compliance program also included several work sessions with agencies concerned with historic preservation.
With the regulatory and historic preservation issues addressed, the final design phase was initiated with a study of bridge alternatives that evaluated various structural systems for realizing the rehabilitation. Six alternatives for the deck were evaluated, and the recommended alternative was precast, prestressed concrete slabs 12 in. (305 mm) deep and 20 ft (6 m) long with a CIP topping of concrete 5 in. (127 mm) thick. The choice was based on cost, ease of erection, and serviceability. The transverse floor beams were specified as cip, reinforced concrete.
|Although the main arch could be preserved, the bridge's deck had to be completely replaced. The contractor completed the work about the main arch first, then moved on to the side arches and approach spans.
David Evans and Associates, Inc.
Two structure types for the spandrel columns and arches were considered: precast, prestressed concrete and CIP, reinforced concrete. Both types could be designed and detailed to meet the design loads and aesthetic requirements. CIP concrete has the advantage of not requiring special connection details that might be susceptible to long-term corrosion and so was recommended for the spandrel columns and arches as well as for the sidewalks and sidewalk brackets. But a performance specification for precast, prestressed concrete was provided so that the general contractor could propose an alternative precast-concrete design if that seemed feasible.
Three structure types were evaluated for the replacement of the north approach structure. The recommendation was for a CIP elevated structure that would match the bridge’s existing side elevation. This system was recommended for its low cost of construction and its ability to accommodate the trail. Additionally, this structure type takes advantage of the low reactions of the 20 ft (6 m) deck spans so that the floor beams can span from outer column to outer column without interior pier walls.
Two alternatives were evaluated for the concrete pavilions on top of each of the four main arch piers: a complete replacement replicating the original units and the removal, repair, and reinstallation of the existing units. The former was recommended because it was the only structurally sound solution and also was the only way to provide a 2 ft (0.6 m) clearance from the curbline to the historically significant features.
The exterior railings were to be reconstructed to match the original bridge railings using CIP concrete pilasters and precast-concrete panel sections. The precast-concrete sections are designed to span horizontally to each pilaster. Connections between the precast-concrete panels and the pilasters are hidden from view. The panels are located 1 in. (25 mm) above the concrete sidewalk slab to allow for edge drainage of the sidewalks.
The interior traffic barrier will be installed on top of the raised sidewalk curb and run continuously along the curbline past the reconstructed pavilions. The agencies concerned with historic preservation requested a study to address the type of railing that would be used on the barriers. The recommended type was a CIP rail with an aesthetic treatment imparted by the concrete form liner and a decorative steel extension on top.
Slabs of precast, prestressed concrete seemed the logical choice for deck durability and ease of construction. After considering input from a value engineering study, the decision was made to use 12 in. (305 mm) thick slabs with a 20 ft (6 m) span. This resulted in a light superstructure and also made it possible to use relatively light construction equipment. It also offered an efficient use of substructure members, as well as a span arrangement similar to that of the original bridge.
The reinforced-concrete spandrel columns and arches were designed with a geometry matching the original arches and columns. Reinforced-concrete crossbeams span transversely to support the ends of the precast slabs.
iven the complex nature of the project, an internal, independent design check was performed by a separate DEA team to verify the structural adequacy of the proposed reconstruction. The structure was analyzed for the final reconstructed configuration as well as for the various stages of bridge removal and reconstruction.
The dead load of the new construction was essentially deemed equivalent to the original. Because the arch ribs had performed adequately for the original loading, analysis indicated that the dead loads arising from the new construction would not cause distress. But the existing arch ribs are very lightly reinforced and therefore have limited moment capacity. It was preferable to keep the unfactored tensile stresses in the arch ribs below the cracking stress level. The ultimate moment capacity was compared with the factored loads to determine the factor of safety against failure.
The moments arising from uniformly applied loads were relatively minor. The largest moments would be caused by unbalanced loading that might occur during removal of certain elements and reconstruction or under live loads. It was therefore necessary to develop a sequence for the bridge removal and reconstruction that would minimize the moments in the arch ribs. The engineers determined that the bridge removal for each arch needed to begin at the arch’s crown and proceed uniformly toward its ends. A similar sequence was required for the reconstruction.
The reconstruction also improved the capacity of the existing arch ribs. An expansion joint through the deck and spandrel walls over the crown of the north and south arches was eliminated, and the new spandrel walls were made continuous over the crown and properly doweled into the existing arch ribs to create a composite action. The resulting section is an inverted T with a significantly larger section modulus and ultimate moment capacity.
Most of the materials used for the rehabilitation were conventional, that is, 4,000 psi (27,580 kPa) concrete and 60 ksi (414 MPa) steel reinforcement with epoxy-coated reinforcement in the 5 in. (127 mm) thick deck. But extra attention was paid to the deck and sidewalks; here, high-performance concrete (HPC) was used. The FHWA’s Innovative Bridge Research and Construction Program funded the use and monitoring of this concrete in these areas in order to further its own research on HPC. The concrete consists of type II cement with a microsilica admixture and 1.5 in. (38 mm) polypropylene fibers.
The structural integrity of the main arch ribs and piers was deemed acceptable, but a close inspection revealed many minor cracks and spalls as well as a few significant cracks in one of the south arches and its pier. A special investigation was undertaken to determine the best approach to use in the repair process, and that process yielded specifications for a combination of epoxy injection and various types of epoxy mortar patching or dry packing of the cracks and spalls, depending on their depth, width, and severity.
During the design phase of the project considerable resources were committed to keeping the public informed about the project, obtaining input, and ultimately obtaining approval and enthusiastic support. Such consultation with the affected—and paying—public was essential because residents expressed strong concern over the historical, environmental, and economic ramifications of the project. Not only is the Monroe Street Bridge a primary access route; it is considered by many to be the city’s most distinctive symbol. The citizens of Spokane have a great attachment to the bridge and the history it represents.
From the outset, effective planning was of cardinal importance. Public meetings were scheduled and conducted to provide information on the findings of investigations and on rehabilitation options. Such evidence as photos, charts, and even samples of the deteriorating concrete was presented at public meetings. Follow-up meetings kept the community apprised of any changes and the project’s progress. Additionally, an elaborate mobile kiosk presenting the same information paid visits to city hall, libraries, and shopping malls. A project Web site was established and updated, and it included a webcam during construction. Representatives of the city, the engineering firm, and the contractor also spoke at meetings of public service groups and technical societies.
A unique element that assisted in the team’s efforts to keep the public apprised was the early construction of the promenade overlook, which enabled the public to observe the construction and the waterfall and to read about the history and rehabilitation of the bridge. The 300 ft (92 m) long, 5 ft (1.5 m) wide overlook incorporates the same type of concrete bridge railing used on the bridge, as well as colorful ceramic panels that provide information about the bridge’s history.
he construction challenges related to rehabilitation projects are markedly different from those encountered in new construction; predicting the costs and schedules can be difficult because there are so many unknowns when dealing with an existing structure, especially an older one. This was certainly the case on this project.
The contract schedule called for completion in 600 working days. To accomplish this, the bridge was closed to traffic, and construction commenced in January 2003—not the most auspicious time in the sometimes difficult winter climate of Spokane. Wildish/F.E. Ward Constructors, an experienced bridge contractor, was aware of the need to effectively use working days and did so throughout the project. Various challenges, including necessary additions or changes to the design, were quickly resolved by the team. The final result was completion of the project in September 2005, three months over schedule but $2 million less than the original estimate.
Perhaps the greatest physical challenge was the limited access to the existing bridge, which greatly affected the overall project sequence as well as many day-to-day logistical decisions. Although a large staging area was available on the north end, space was severely limited to the south. Because the contractor’s lower bid was partially predicated on using large crawler cranes for material handling, the center arch had to be completed first, using the decks of the side arches for access. After completing the center arch and the deck above it, the contractor was able to accelerate the project by working on the side arches and the approaches at the same time.
David Evans and Associates, Inc., and Seareach, Ltd.
The weakened deck of the old bridge also added to the access challenge; the contractor was required to use timber cribbing for the crane, and the cribbing had to be moved ahead of the crane for each sequence.
Exacting, often perilous efforts were required to save and restore the original arches and main piers while reconstructing the bridge superstructure. A complex system of containment and work platforms had to be constantly reconfigured beneath the bridge to comply with environmental and worker safety requirements. Sometimes the platform reconfigurations were carried out at night to facilitate daytime construction. The members of the large, primarily local labor force applied their various trades 130 ft (40 m) over the river in all weather conditions. Safety was a prime concern for the contractor, and the project was completed without serious accidents.
The contractor was also confronted with several environmental compliance challenges, the primary one being “zero discharge” of demolition material or water into the Spokane River. To accomplish this, the contractor erected platforms that were covered with steel cargo nets and heavy plastic tarps to facilitate the removal of even the smallest waste material. During the washing and sealing of the concrete elements that were to remain, plastic lining was installed on the platforms to collect and direct wash water to containers, where it was tested and then taken off-site for disposal. Air pollution was addressed by measures to reduce dust and contain sprayed-on materials. Various regulatory agencies have offices within sight of the bridge, adding to the pressure felt by the contracting firm, but the company was praised by the agencies for its environmental stewardship.
s would be expected on any rehabilitation project, a number of surprises were encountered that required special consideration and added time. Part of the problem was that there were no reliable plans from the original construction showing the details and reinforcement of the spandrel arches and piers. Additionally, even though the 1998 inspection had been quite thorough, some confined areas had been inaccessible, leading to some interesting discoveries during construction. For example, large steel elements—primarily eyebars from a steel bridge constructed at the same location in 1892—were revealed in the concrete. Apparently the early bridge builders decided that these pieces, which were probably lying on the site after the steel bridge collapsed, would be useful inside the new concrete bridge. Perhaps more disconcerting was the discovery of 90 years’ worth of pigeon droppings that had accumulated over the top of the main arches. This 23 ton (21 Mg) mass had to be dealt with by a hazardous materials specialist.
Some of the concrete elements—primarily the end piers of the side arches—were found to have little or no reinforcement. What had originally been anticipated to be crack repair on several of the piers became a complete reconstruction as the demolition activity exposed weak and crumbling concrete. Additionally, the team expected that the dimensions of such elements as the arches, beams, and railing posts would be repetitive; they were not. Constant modifications were necessary in the concrete forms and spacing to match the new elements with the old.
Among the features of historical importance that required special attention were the pedestrian railing and pavilions, the plaques—which required cleaning—and several large, 800 lb (363 Mg) concrete bison skull adornments that had to be replicated. The final results were lauded by the public and local preservation advocates.
All of the steps involved in this project—from the 1998 investigations to the development of a final alternative, the conceptual and final designs, and the construction—were animated by a desire to preserve the Monroe Street Bridge as a community icon. The owner, the engineer, the contractors, the agencies involved, the suppliers, and the public all worked hand in hand, and proudly so, to make this bridge rehabilitation a success. The bridge reopened with great fanfare in September 2005. The three-day, on-the-bridge celebration included dining, dancing, parades, flybys, speeches by dignitaries, informative and educational activities, and a spectacular fireworks display. This endeavor by the City of Spokane will ensure that this national landmark remains a key part of the city’s transportation system as well as a historical and scenic focal point for citizens and visitors alike.
David C. Moyano, P.E., S.E., M.ASCE, is a senior vice president of David Evans and Associates, Inc., which is based in Portland, Oregon. From his office in Salem, Oregon, he served as the project’s manager. Stephen J. Shrope, P.E., S.E., M.ASCE, who works out of the firm’s office in Spokane, Washington, is a vice president of the firm and was the principal in charge of the project. The historical photos are courtesy of the family of Alfred D. Butler, the city engineer for the City of Spokane from 1917 until his death, in 1941. Butler was the assistant city engineer during the construction of the Monroe Street Bridge, and he was the first person to drive a car across it.