Minnesota Department of Transportation (Mn/DOT) Historic Bridge Management Plan

Transcription

1 Executive Summary Bridge Number: 4930 Bridge 4930 (Broadway Bridge) was built in 1931 to carry vehicular traffic on Trunk Highway 21 (later TH 99, also known as Broadway) over the Minnesota River between the city of St. Peter, Nicollet County, and Oshawa Township, LeSueur County. The overall structure length is feet and the out-out width is 39.6 feet, including a cantilevered sidewalk. The superstructure is a steel, riveted, two-span, Pennsylvania through-truss, aligned on an east-west axis, flanked with reinforced concrete approach spans. The substructure includes reinforced-concrete abutments and river pier. Site conditions dictated that the river pier be skewed and not parallel with the abutments, creating an unusual design challenge for the trusses. The solution was to design the east and west spans with mirror-opposite configurations, including unequal lengths for the north and south trusses in each span: one side is shorter than the other. The east span has a 195-foot north truss with ten panels and a 176-foot south truss with nine panels. The west span configuration is reversed, with a 176-foot north truss and a 195-foot south truss. Engineers noted that a visually confusing situation would occur over the river pier where the two spans and different truss lengths meet. False members were added between the east and west spans to give the appearance of a continuous-truss superstructure when viewed from the north or south. Ornamental railings, light standards, and Classical Revival detailing of concrete elements reflect the bridge s gateway location for St. Peter. Bridge 4930, including the deck, sidewalk, and truss, is in fair condition. A failed paint system and the deterioration of substructure units supporting the truss are concerns. The deck width is deficient for a structure with an ADT of 6,200. The vertical clearance over the roadway is adequate at 15.6 feet. The load capacity is marginal for extended use, with an H 18.0 inventory rating and an HS 22.5 operating rating. The recommended future use of the bridge is rehabilitation for continued vehicular use on-site. A lessdemanding use may be considered in the future if warranted by traffic demands. The bridge should be rehabilitated based on the Secretary of the Interior s Standards for Rehabilitation (Standards) [36 CFR Part 67] and Guidelines for Bridge Maintenance and Rehabilitation Based on the Secretary of the Interior s Standards (Guidelines). Until the Federal Highway Administration (FHWA), State Historic Preservation Office (SHPO) and Minnesota Department of Transportation (Mn/DOT) have signed a historic bridge Programmatic Agreement, all proposed work on this bridge (including maintenance, preservation and stabilization activities) needs to be sent to the Mn/DOT Cultural Resources Unit (CRU) for formal review.

2 Table of Contents Bridge Number: 4930 I. II. III. IV. V. VI. A. B. C. D. Executive Summary Project Introduction Bridge Data Historical Data, including Statement of Significance and Character-Defining Features Engineering Data Existing Conditions and Recommendations Projected Agency Costs, including Applicable Funding Appendices Glossary of Preservation and Engineering Terms Guidelines for Bridge Maintenance and Rehabilitation Based on the Secretary of the Interior s Standards Current Mn/DOT Structure Inventory Report Current Mn/DOT Bridge Inspection Report Past Maintenance Reports (if available) Other Reports (if available) Cost Detail

3 I - Project Introduction Bridge Number: 4930 The Minnesota Department of Transportation (Mn/DOT), in cooperation with the Minnesota State Historic Preservation Office (SHPO) and Federal Highway Administration (FHWA), has committed to preserve selected historic bridges in Minnesota that are owned by the state and managed by Mn/DOT. In consultation with SHPO and FHWA, Mn/DOT selected 24 bridges as candidates for long-term preservation. Mn/DOT s objective was to preserve the structural and historic integrity and serviceability of these bridges following the Secretary of the Interior s Standards for the Treatment of Historic Properties (Standards) [36 CFR Part 68], and their adaptation for historic bridges by the Virginia Transportation Research Council as Guidelines for Bridge Maintenance and Rehabilitation Based on the Secretary of the Interior s Standards (Guidelines). The character-defining features of each bridge received special attention. Mn/DOT also hopes to encourage other owners of historic bridges to follow its model for preservation. The Glossary in the Appendix explains historic preservation terms used in this plan, such as historic integrity and character-defining features, and engineering terms, such as serviceability and deficiency. Mn/DOT s ongoing efforts to manage historic bridges are intended to comply with Section 106 of the National Historic Preservation Act of 1966, as amended, and Section 4(f) of the U.S. Department of Transportation Act of This effort began with Robert M. Frame s 1985 study and list of significant and endangered bridges in Minnesota and incorporates Jeffrey A. Hess s 1995 survey and inventory of historic bridges in Minnesota that were built before That inventory identified the subject bridge as eligible for listing in the National Register of Historic Places. Using the results of the 1995 study, Mn/DOT selected individual historic bridges for long-term preservation. To achieve its preservation objectives, Mn/DOT retained the consultant team of Mead & Hunt and HNTB to develop management plans for 22 of the 24 selected bridges. The remaining two bridges have been addressed through separate projects. Mn/DOT requested that the team consider a full range of options for each bridge and present the option that the team judged to be best for long-term preservation with due consideration given to transportation needs and reasonable costs. For example, if two options are explored that both result in an equivalent level of preservation for the bridge (e.g., retention of historically significant features and projected life span), but one option costs significantly more than the other, the less costly option will be recommended. In cases where one option results in a significantly better level of preservation than any other reasonable options but costs more, it will be the recommended action. Preservation objectives call for conservation of as much of the existing historic fabric of the bridge as possible. However, safety, performance and practical considerations may have dictated replacement of historic fabric, especially of a minor feature, if such action improved the overall life expectancy of a bridge. Options that were considered for the 22 historic bridges, listed from most to least preferred, are: 1. Rehabilitation for continued vehicular use on-site 2. Rehabilitation for less-demanding use on-site, such as one-way vehicular or pedestrian/bicycle traffic 3. Relocation and rehabilitation for less-demanding use 4. Closure and stabilization following construction of bypass structure 5. Partial reconstruction while preserving substantial historic fabric A recommended option was selected for each bridge through consultation among the consultant team, Mn/DOT and SHPO. Within the recommended option, the plan identifies stabilization, preservation and maintenance activities. Stabilization activities address immediate needs in order to maintain a bridge s structural and historic integrity and serviceability. Preservation activities are near-term or long-term steps that need to be taken to maintain a bridge s structural and historic integrity and serviceability for the foreseeable future. Preservation activities may include rehabilitation and replacement of components, as Project Introduction I-1

4 I - Project Introduction Bridge Number: 4930 needed, and remedial activities to address a deficiency. Maintenance activities, along with regular structural inspections and anticipated bridge component replacement activities, are routine practices directed toward continued serviceability. Mn/DOT is responsible for final decisions concerning activities recommended in the plan. Recommendations are intended to be consistent with the Standards. The Standards are ten basic principles created to help preserve the distinctive character of a historic property and its site, while allowing for reasonable change to meet new needs. They recommend repairing, rather than replacing, deteriorated features when possible. The Standards were developed to apply to historic properties of all periods, styles, types, materials, and sizes. They also encompass the property's site and environment as well as attached, adjacent, or related new construction. Because the Standards cannot be easily applied to historic bridges, the Virginia Transportation Research Council prepared Guidelines, which adapted the Standards to address the special requirements of historic bridges. The Guidelines, published in the Council s 2001 Final Report: A Management Plan for Historic Bridges in Virginia, provide useful direction for undertaking historic bridge preservation and are included in the Appendix to this plan. The individual bridge management plan draws from several existing data sources including: PONTIS, a bridge management system used by the Mn/DOT Bridge Office to manage its inventory of bridges statewide; the current Mn/DOT Structure Inventory Report and Mn/DOT Bridge Inspection Report for each bridge (the complete reports are included in the Appendix); database and inventory forms resulting from the 1995 statewide historic bridge inventory; past maintenance reports (if available, copy included in the Appendix); and other information provided by Mn/DOT. Because PONTIS uses System International (metric) units, data extracted from PONTIS are displayed in metric units. The plan is based on information obtained from Mn/DOT in 2005, limited field examinations completed in 2005 for the purpose of making a qualitative assessment of the condition of the bridge, and current bridge design standards. Design exceptions are recommended where appropriate based on safety and traffic volume. The condition of a bridge and applicable design standards may change prior to plan implementation. This plan includes a maintenance implementation summary at the end. This summary can be provided as a separate, stand-alone document for use by maintenance staff responsible for the bridge. The plan for this individual bridge is part of a comprehensive effort led by Mn/DOT to manage the statewide population of historic bridges. The products of this management effort include: 1. Minnesota 2. Individual management plans for 22 bridges 3. National Register of Historic Places (NRHP) nomination forms for 2 bridges 4. Minnesota Historical Property Record (MHPR) documentation for 46 bridges The first product, the Minnesota, is a general statewide management plan for historic bridges in Minnesota that are owned by the state, local governments or private parties. It is intended to be a single-source planning tool that will help bridge owners make management and preservation decisions relating to historic bridges. Approximately 240 historic bridges owned by parties other than Mn/DOT survive in the state as of Mn/DOT is developing this product to encourage owners of historic bridges to commit to their long-term preservation and offer guidance. This individual plan represents the second product. The third and fourth products will be prepared as stand-alone documents. Project Introduction I-2

5 II - Bridge Data Bridge Number: 4930 Date of Construction 1931 SHPO Inventory Number Common Name (if any) LE-KST-002 Broadway Bridge Location Feature Carried: TH 99 Feature Crossed: Descriptive Location: UTM Zone: 15 Minnesota River in St. Peter NAD: 1927 Easting: Northing: USGS Quad Name: Town or City: County: Saint Peter Kasota Township Le Sueur Structure Data Main Span Type: 410 Steel Continuous Truss - Thru Total Length: 402 Descriptive Information (or narrative as available) Superstructure: Substructure: Floor/Deck: Other Features: Narrative: 2, steel, rigid-connected, Pennsylvania, through-truss spans with skewed configuration at the pier concrete abutments, skewed pier concrete deck carried by 13 rolled I-beam stringers upper chords: 2 channels with X-lacing; lower chords: 2 channels with X-lacing; verticals: 4 angles with V-lacing, diagonals: 4 angles with battens; portal bracing: 6-X configuration of crossed single angles with top and bottom struts consisting of 4 angles with V-lacing; overhead sway bracing: 3-X configuration of crossed single angles with top and bottom struts consisting of 4 angles with V-lacing; top-lateral bracing: crossed members consisting of 4 angles with V-lacing; intermediate horizontal bracing: 4 angles with V-lacing; bottom-lateral bracing: crossed single angles; sidewalk on south side, supported by cantilevered metal brackets; metal lattice-work railing borders sidewalk; flexible-metal guardrails on truss members border roadway on each side; ornamental metal light standards on concrete posts at each corner of bridge; steelmaker's mark: Illinois-S-USA, Carnegie USA; bridge plaques on northeast and southwest concrete endposts ("Minnesota Highway Dept Bridge No ") Roadway Function: Ownership: Custodian/Maint. Agency: Mainline State State Bridge Data II-1

6 III - Historical Data Bridge Number: 4930 Contractor Designer/Engineer Minneapolis Bridge Company, Minneapolis, Minnesota Minnesota Highway Department Significance Statement Spanning the Minnesota River on Minnesota Trunk Highway 99 (formerly TH 21), Bridge No connects the city of St. Peter in Nicollet County, on the west, with rural Oshawa Township in Le Sueur County, on the east. In the St. Peter street system, the bridge stands on Broadway, just east of the downtown district. Locally, it is known as the Broadway Bridge. The crossing is 402 feet in length, consisting of two, rigid-connected, Pennsylvania, through-truss spans on a concrete substructure. The spans display conventional, built-up detailing -- two laced channel sections with cover plate in the upper chord, two laced channel sections in the lower chord, and four laced angle sections in the vertical and diagonal members. The bridge's overall design, however, is unconventional, largely because the current of the Minnesota River twists in mid-channel at the site. This hydraulic peculiarity dictated the construction of a skewed pier, so as to offer the least resistance to the flow of the water. Because of the oblique placement of the pier, the two truss spans required a skewed configuration at the end supported by the pier. This goal was achieved by designing each span with truss webs of unequal length and slightly different profile. In the west span, the north web is a ten-panel, 195-foot truss with inclined endposts at each end, while the south web is a nine-panel, 176-foot truss with an inclined endpost at the abutment and a vertical endpost at the pier. In the east span, the situation is exactly reversed. Although the east and west spans are structurally independent of each other, they are visually integrated by an ornamental linkage that joins their top chords together over the pier. Because of the linkage, the two spans appear to be part of a single, continuous truss, when they are in fact two, simply supported trusses. The Broadway Bridge has a concrete deck with a 30-foot roadway. Outside the truss webs on the south side, there is a sidewalk supported on metal brackets cantilevered from the bridge's flooring system. An ornamental, metal, lattice-work railing borders the sidewalk on the river side. The bridge also has an ornamental lighting system, consisting of four metal light standards, positioned on concrete posts at the four corners of the crossing. The light standards are detailed in the Classical Revival Style, with fluting on the shaft and consoles at the base. In the mid-1960s, the state highway department raised the bridge's portals and overhead sway bracing to provide greater vertical clearance for traffic. The remodeling retaine the original configuration of the features and did not significantly affects the bridge's historical integrity. In August 1929, a heavily laden grain truck collided with the east end of the Broadway Bridge in St. Peter and tumbled a span of the 1883 structure into the Minnesota River. Since the crossing was part of Minnesota Trunk Highway 21, its maintenance was the responsibility of the Minnesota Highway Department, which already had the bridge's replacement under consideration. In the fall of 1929, the state highway department developed preliminary plans for a new two-span, through-truss crossing, but civic leaders in St. Peter balked at the design. The city had just invested heavily in an ornamental lighting system for the central business district, and its merchants wanted the new Broadway Bridge, which was the eastern gateway for the downtown, to be a suitably attractive structure, preferably of concrete-arch construction. The state engineers resurveyed the bridge site and reconsidered their design. But foundation conditions on the shore were not suitable for a concrete arch, and there was not sufficient vertical clearance at the site for a deck truss. In the end, the state highway department adhered to its original recommendation for a two-span, steel, through truss, and in August 1930, the St. Peter City Council gave its approval. In covering the city's bridge story, the St. Peter Herald found consolation in the fact that the new Broadway Bridge would be no ordinary steel-truss structure, but rather a "unique engineering feat" of "special design." Historical Data III-1

7 III - Historical Data Bridge Number: 4930 The state highway department did indeed face a major challenge in the design of the new Broadway Bridge. Because the current of the Minnesota River twisted in mid-channel at the bridge site, the structure's pier would have to be placed on an oblique alignment, which dictated a skewed configuration for the ends of the truss spans at the pier. In strictly engineering terms, the design of a long-span, skewed, through truss was a demanding proposition. And in aesthetic terms, it was something of a nightmare, because the structural logic tended to impose asymmetrical massing and visually contorted lines. In the case of the Broadway Bridge, the state's design called for each span to use two different truss configurations. One web would be 196 feet in length, consisting of ten panels and terminating in inclined endposts at each end; the other web would be nine panels and 176 feet, with an inclined endpost at the abutment, but a vertical endpost at the pier. Because of the different endpost configurations, the two spans would meet at the pier in a most ungainly manner -- one span ending with a diagonal line, the other with an abrupt vertical line. As a means of visually integrating the two sections of the bridge, the state engineers decided to insert a strictly ornamental member to join the upper chords of the two spans over the pier. This device not only eliminated the unsightly gap between the two dissimilar trusses, but created a flowing upper line for the entire crossing. The result was a unified, double-arched profile that made the bridge appear to be a single, continuous truss, when, in fact, it consisted of two, independent, simply supported spans. By way of further ornamentation, the state equipped the bridge with a metal lattice-work railing and Classical Revival Style street lamps, which matched the lighting system recently installed in the city's downtown. In the fall of 1930, the state highway department awarded, on a low-bid basis, a construction contract for the Broadway Bridge to the Minneapolis Bridge Company. The total cost was $99,000, which included $3,500 for building a temporary crossing during construction, and $2,500 for removing the old bridge. Favored by unusually mild weather, the contractor worked throughout the winter and completed the crossing a month ahead of schedule, in June "The new St. Peter bridge is the most elaborate and the largest in this locality," reported the St. Peter Herald. "An ornamental lighting system is now being installed that will fit in nicely with St. Peter's fine new white way.... Thus the approach to St. Peter from the east will be a model gateway." The Broadway Bridge is eligible for the National Register under Criterion C in the area of engineering, within the historic context of "Iron and Steel Bridges in Minnesota." The Multiple Property Documentation Form (MPDF) associated with this context states, in Registration Criterion 12, that a bridge may eligible under Criterion C if it "exhibits exceptional engineering skill to meet unusual site conditions." With its skewed, through-truss design, the Broadway Bridge satisfies this criterion. The Broadway Bridge is also eligible under Criterion C for its high aesthetic qualities, as provided for by the MPDF in Registration Criterion 11. Historic Context Historic Iron and Steel Bridges in Minnesota National Register Criteria References C Minnesota Department of Transportation Computerized Bridge Database; Bridge No File, in Minnesota Department of Transportation, Waters Edge Building, St. Paul; Bridge No Storage File (plans, contract, correspondence), in Minnesota Department of Transportation Records Storage Center, St. Paul; Bridge No File, in Minnesota Department of Transportation District 7 Office, Mankato, Minnesota; following articles in St. Peter Herald: "Council Approves Plans for Bridge on Highway No. 21" (15 August 1930), "Babcock to Open St. Peter Bridge Bids October 14" (26 September 1930), "New White Way," (Diamond Jubilee Supplement, 1 October 1930), "Babcock Assures Temporary Bridge Historical Data III-2

8 III - Historical Data Bridge Number: 4930 During Building" (17 October 1930), "Broadway Bridge to Be Torn Down on November 1st" (8 October 1930), "Broadway Bridge Will Be Moved by Dec. 1" (19 October 1930), "Broadway Bridge Contractor Pours Center Pier Now" (20 February 1931), "Crew Raises Arches for Rroadway [sic] Bridge" (18 March 1931), "Broadway Bridge to Be Opened to Traffic at Once" (26 June 1931), "Broadway Bridge Has Origina Sparkle" (10 November 1986), Fredric L, Quivik, "Iron and Steel Bridges in Minnesota," Multiple Property Documentation Form, 1988, Sec. F, 9, in State Historic Preservation Office, Minnesota Historical Society, St. Paul; field inspection by Shawn P. Rounds, 6 December 1996, field inspection by Jeffrey A. Hess, 25 March Historical Data III-3

9 III - Historical Data Bridge Number: 4930 Character-Defining Features Character-defining features are prominent or distinctive aspects, qualities, or characteristics of a historic property that contribute significantly to its physical character. Features may include materials, engineering design, and structural and decorative details. Feature 1. Truss design for unusual site conditions. Because the river pier is skewed while the abutments are not, the east and west spans have unequal truss lengths and panel configurations. To avoid an irregular design situation at the skewed pier, false members were added to the trusses to create an overall configuration suggesting a continuous through-truss superstructure. This feature includes the Pennsylvania through-truss superstructure with the false members. Feature 2. Ornamental elements. Because Bridge 4930 was designed as a gateway to the city of St. Peter, it received an aesthetic treatment that includes ornamental metal railings and light standards, and Classical Revival detailing on concrete railing posts and abutments. Historical Data III-4

10 IV - Engineering Data Bridge Number: 4930 Inspection Date 5/20/2002 Sufficiency Rating [1] 69.2 Operating Rating [1,2] Inventory Rating [1,2] Posted Load [1] 0 Design Load [1] 2 Deficiency Rating Status [1] A Condition Codes Deck: 6 Superstructure: 6 Substructure: 6 Channel and Prot.: 5 Culvert: N Appraisal Ratings Struct. Eval.: 6 Deck Geometery: 4 Underclearances: N Waterway Adequacy: 4 Appr. Alignment: 8 (Inspection and inventory data in this section was provided for this project by Mn/DOT in May 2005) Smart Flag Data [1] (A check indicates data items are listed on the Bridge Inspection Report) Fracture Critical [1] Last Inspection Date Waterway Data Scour Code [1]: Y Y Roadway Data ADT Total: 6200 Truck ADT Percentage: 7 Bypass Detour Length [2]: Roadway Clearances Roadway Width [2]: Vert. Clearance Over Rdwy [2]: Vert. Clearance Under Rdwy [2]: Lat. Under Clearance Right [2]: 0 Lat. Under Clearance Left [2]: 0 Geometry Characteristics Skew: 0 Structure Flared: 0 The foundations for Bridge 4930 were determined to be stable for scour. However, an O code requires a Scour Action Plan. [1] These items are defined in the glossary in Appendix A. [2] These items are provided in metric units. Engineering Data IV-1

11 IV - Engineering Data Bridge Number: 4930 Roadway Characteristics Lane Widths: 12 Number of Lanes: 2 Shoulders Width: 3 Paved or Unpaved: Paved Comments: Concrete Guardrail Length: N/A Comments: There is no guardrail in place off the ends of the bridge. A steel guardrail protects the bridge members on the north side. A plate beam guardrail protects the bridge members on the south side. There is a rail and concrete monument 18 past the bridge itself on all four corners of the bridge. Vertical Curves: Vertical curves have a 70 mph or greater design speed Horizontal Curves: N/A Sight distance: Vertical sight distance is unlimited. Horizontal sight distance is somewhat restricted by the overhead bridge members. Other information: Curb and gutter on the west side of the bridge going into town, on the east side of the bridge, 25 on the south side, 35 on the north side. There are 20 curb catch basins on the bridge. There are 7 light poles on the bridge; 1 is broken. On the west side of the bridge before the approach panel is 26 of concrete and then it is bituminous coming from town. Just before you get to the bridge heading east the road is much wider in town. On the east side of the bridge is just the 16 concrete approach panel and then blends into a 2 lane bituminous road. The shoulders in the rural part of the road are approximately 10. The single sidewalk (on the south) is 8.6 full width including the curb and gutter and the bridge members. The outside south rail is ornamental. Floodplain Data Available data indicates that Bridge 4930 will inundate during a Q50 flood event. The District states that the bridge was closed in 1993, 1997, and 2001, when the bottom chord was submerged. Accident Data The Mn/DOT Accident Database reports 17 accidents associated with this bridge for the 15-year period of Property Damage No Apparent Injury accidents 4 Injury Possible Injury accidents 1 Injury Non-incapacitating Injury accidents 1 Fatal accident Location of Plans District 7, Bridge Office Engineering Data IV-2

12 V - Existing Conditions / Recommendations Bridge Number: 4930 Existing Conditions Available information was reviewed prior to assessing the options for preservation of Bridge 4930 and visiting the bridge site. This information is cited in the Project Introduction section of this plan. A site visit was conducted to qualitatively establish the following: 1. General condition of structural members 2. Conformation to available extant plans 3. Roadway geometry and alignment 4. Bridge geometry and clearances Serviceability Observations: The traffic railings do not satisfy FHWA requirements in In isolated locations, guardrail elements and truss verticals have minor impact damage. The roadway deck width of 30 feet is deficient for a structure with an ADT of 6,200. Mn/DOT s Bridge Preservation, Improvements, and Replacements Guidelines recommend a deck width of 38 feet. Due to the limited number of accidents in the vicinity of the bridge and the 30 mph speed limit, a design exception for the deck width may be appropriate. The vertical clearance for traffic on the bridge is 15.6 feet in the inventory, indicating that the portals and sway bracing were modified in 1964 to improve the vertical clearance from the original 14.0 feet. The 15.6 feet is deficient (with respect to reconstruction where 16.0 feet is desired), but it exceeds the 14.5 foot minimum permitted for bridge improvements. According to the District, embankment erosion near the west abutment has occurred during high stream flow conditions in the past. A portion of the embankment has been stabilized with shotcrete and large rip rap. The bridge was closed due to high water in 1993, 1997, and The current load capacity is marginal for the 20-year planning period. The inventory load rating is H18.0 and the operating rating is HS The 1982 load rating examined only the composite stringers and the floorbeams. Structural Condition Observations: The red-lead paint system has failed for truss components, the floor system, and the railings, leading to exposed structural steel, minor section loss, and pack-rusted components. The deck was replaced in The rehab plans indicate that only a bottom mat of epoxy-coated reinforcement was used; consequently, it is not surprising that there are transverse deck cracks over the floor beams and at other locations. Cracking was also noted in the sidewalks by Mn/DOT inspectors. The expansion joints and pavement joints have missing gland elements and other deterioration. The abutments contain spalls and cracking in the vicinity of the truss bearings. There is evidence that past deck drainage has freely washed on the abutments. Existing Conditions / Recommendations V-1

13 V - Existing Conditions / Recommendations Bridge Number: 4930 The modified truss expansion bearings with elastomeric pads appear to be functioning as intended. Non-Structural Observations: The bridge carries many utilities, with several conduits below the sidewalk on the south side and a gas main on the north side. The remaining ornamental light standards exhibit a range of conditions from extensive corrosion (southwest corner) to poor paint condition elsewhere. Swallow nests were evident on the substructure and below deck areas. Pigeon droppings were noted on the sidewalk below top chord elements. Pavement joints over the sleeper slab (at the transition from bituminous to concrete pavement on the west approach) and the bituminous pavement joint at the end of the east abutment slab span are in poor condition. Deck drain pipes terminate at the bottom of the stringers, allowing drainage to spray on lower chord members, which accelerates deterioration. During the site visit, an Adopt a Highway sign was noted between the gas pipeline and the lower truss chord on the north side of the bridge, just east of the pier. Date of Site Visit August 5, 2005 Existing Conditions / Recommendations V-2

14 V - Existing Conditions / Recommendations Bridge Number: 4930 EXIST_COND_PICT1: Figure 1. Looking east at the bridge. The roadway width west of the bridge is significantly wider than the distance between railings on the bridge. EXIST_COND_PICT2: Figure 2. Looking east from the north curb at the middle of the bridge. The original four rail traffic railing is on the left. A new thrie-beam railing has been added on the right. EXIST_COND_PICT3: Figure 3. Looking north at the northeast corner of the bridge. The light standard is missing on the transition pier. The curb concrete on the jump span is deteriorated. EXIST_COND_PICT4: Figure 4. Looking south at the southwest corner of the bridge. The base of the light standard has extensive corrosion and should be removed or repaired. The start of the thrie-beam railing and the pedestrian railing is also visible. Existing Conditions / Recommendations V-3

15 V - Existing Conditions / Recommendations Bridge Number: 4930 Figure 5. Outer details of the pedestrian railing and fascia. Localized failure of the paint system on the railing is visible. Several utilities are carried on the bridge. Figure 6. Looking north at the south face of the west jump span. EXIST_COND_PICT7: Figure 7. Looking north along the west transition pier. Spalls on the pier wall and graffiti are present. During previous rehabilitation efforts, elastomeric bearing pads were incorporated into the bearing assemblies. Figure 8. Looking east at the floor system and the skewed river pier. Note the tight stringer spacing and the lower lateral bracing. Existing Conditions / Recommendations V-4

16 V - Existing Conditions / Recommendations Bridge Number: 4930 Overall Recommendations With few accidents over the past 15 years and with a 30-mph speed limit, option 1 (rehabilitation for continued vehicular use on-site) is feasible. Deck width remains a primary concern. The Mn/DOT Roadway Design Manual specifies a minimum roadway width of 32 feet for an undivided, low-speed, urban section with two traffic lanes. National standards provide a lesser minimum width, with only 28 feet required. Supported by FHWA, these standards recognize that structures that tolerably meet the criteria may be retained and identify historic significance as a factor to consider in the retention of existing bridges. Option 2 (rehabilitation for less-demanding use on-site, such as one-way vehicular or pedestrian/bicycle traffic) should be considered in the future if traffic demand warrants four lanes of capacity. Reconfiguring the bridge as a one-way facility is possible. Option 3 (relocation and rehabilitation for less-demanding use) is cost-prohibitive due to the size of the trusses. Option 4 (closure and stabilization following construction of bypass structure) and Option 5 (partial reconstruction while preserving substantial historic fabric) were not considered because more desirable options are feasible. Recommended Future Use: Rehabilitation for continued vehicular use on-site. Recommended Stabilization Activities: 1. Seal cracks in the deck, slab, and sidewalk. 2. Trim brush adjacent to wingwalls. 3. Remove the metal sign lodged on the gas line on the north side of the bridge. 4. Remove the light standard with the corroded base at the southwest corner of the bridge. Recommended Preservation Activities: 1. Determine recommended preparation and coating system for the truss, floor system, metal railings, and ornamental light standard components. Prep and completely repaint the steel components. 2. Determine the chloride contamination of the sidewalk, deck, slabs, and substructure elements. Identify and delimit spalled regions and deteriorated portions of concrete requiring repair. Repair concrete using standard Mn/DOT repair methods, consistent with the National Park Service's Preservation Bulletin 15 - Preservation of Historic Concrete. Consult with Mn/DOT's Office of Bridges and Structures before making final determination of the means and methods of concrete repairs. Apply Mn/DOT special surface finish to exposed concrete subsequent to the repairs. Apply anti-graffiti coating to the areas of the concrete susceptible to graffiti. 3. Repair the north curbs on the abutment slab spans. 4. Add an approach panel at the east end of the bridge. 5. Repair the sleeper-slab approach pavement joints on the west approach. Existing Conditions / Recommendations V-5

17 V - Existing Conditions / Recommendations Bridge Number: Mill and overlay the deck and abutment slab spans and the west approach slab. 7. Extend the deck drains to an elevation that matches the bottom of the lower chords. 8. Repair the original ornamental lighting components. Following the Secretary s Standards, replace components that are missing or deteriorated beyond repair. 9. Perform a load rating analysis of the truss, floor system, and abutment slab spans. Utilize a threedimensional model for the truss to capture effects associated with the skewed pier. Confirm that components have at least an HS 18 inventory capacity. If elements have adequate capacity, no further action is required. If elements are deemed to have inadequate capacity, investigate retrofit options that increase the load capacity while complying with the Secretary s Standards with minimal effect on character-defining features. Projected Inspections to Monitor Bridge Condition Routine: 1. Routine fracture-critical inspection annually, unless superseded by a more rigorous inspection. Implement resulting recommended maintenance efforts within a 12-month period. 2. Conduct in-depth, arm s length inspections on 4-year intervals. Implement resulting recommended maintenance or repair efforts within a 24-month period. Special: 1. Inspect scour countermeasures at least once every four years and after all major flows. Recommended Maintenance Activities 1. Flush truss members, sidewalk, deck, railings, and substructure units with water annually, preferably in the spring. 2. Seal cracks in the deck and sidewalk on a 5-year cycle. 3. Spot-paint the truss and railings on a 10-year cycle. 4. Completely repaint the truss and railings on a 40-year cycle. Existing Conditions / Recommendations V-6

18 VI - Projected Agency Costs Bridge Number: 4930 Qualifier Statement The opinions of probable costs provided below are in 2006 dollars. The costs were developed without benefit of preliminary plans and are based on the above identified tasks using engineering judgment and/or gross estimates of quantities and historic unit prices and are intended to provide a programming level of estimated costs. Refinement of the probable costs is recommended once preliminary plans have been developed. The estimated preservation costs include a 20% contingency and 5% mobilization allowance of the preservation activities, excluding soft costs (see Appendix D, Cost Detail, Item 5: Other). Actual costs may vary significantly from those opinions of cost provided herein. For itemized activity listing and costs, see Appendix D. Summarized Costs Maintenance costs: $24,700 annualized Stabilization activities Superstructure: $0 Substructure: $0 Railing: $0 Deck: $5,500 Other: $2,500 Total: $8,000 Preservation activities Superstructure: $425,000 Substructure: $25,000 Railing: $30,000 Deck: $260,000 Other: $258,000 Contingency: $185,000 Total: $1,183,000 Applicable Funding The majority of funding for the rehabilitation and reuse of historic bridges in the state of Minnesota is available through federal funding programs. The legislation authorizing the various federal funding programs is the Safe, Accountable, Flexible, and Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU). SAFETEA-LU programs include the Transportation Enhancement (TE) Fund, the Surface Transportation Program (STP), the Highway Bridge Replacement and Rehabilitation Program (HBRRP), National Highway System Funds, and the National Historic Covered-Bridge Preservation Program. A program not covered by SAFETEA-LU, the Save America s Treasures Program, is also available for rehabilitation and reuse of historic bridges that have national significance. Other than the Save America s Treasures Program, the federal funds listed above are passed through Mn/DOT for purposes of funding eligible activities. While the criteria for determining eligible activities are determined largely by federal guidelines, Mn/DOT has more discretion in determining eligible activities under the TE fund. The federal funding programs typically provide 80-percent federal funding and require a 20-percent state/local match. Typical eligible activities associated with these funds include replacement or rehabilitation of structurally deficient or functionally obsolete bridges for vehicular and, non-vehicular uses, painting, seismic retrofit, and preventive maintenance. If a historic bridge is relocated, the Projected Agency Costs VI-1

19 VI - Projected Agency Costs Bridge Number: 4930 estimated cost of demolition can be applied to its rehabilitation at a new site. It should be noted that the federal funds available for non-vehicular uses are limited to this estimated cost of demolition. However, TE funds can be applied to bridge rehabilitation for non-vehicular use. State or federal bridge bond funds are available for eligible rehabilitation or reconstruction work on any publicly owned bridge or culvert longer than 20 feet. State bridge bond funds are available for up to 100 percent of the abutment to abutment cost for bridges or culverts longer than 10 feet that meet eligibility criteria. A more in-depth discussion regarding funding can be found in the Minnesota Historic Bridge Management Plan. Special Funding Note N/A Projected Agency Costs VI-2

20 Appendices Bridge Number: 4930 Appendix A. Glossary of Preservation and Engineering Terms

21 Glossary Appraisal ratings Five National Bridge Inventory (NBI) inspection ratings (structural evaluation, deck geometry, under-clearances, waterway adequacy, and approach alignment, as defined below), collectively called appraisal ratings, are used to evaluate a bridge s overall structural condition and loadcarrying capacity. The evaluated bridge is compared with a new bridge built to current design standards. Ratings range from a low of 0 (closed bridge) to a high of 9 (superior). Any appraisal item not applicable to a specific bridge it is coded N. Approach alignment One of five NBI inspection ratings. This rating appraises a bridge s functionality based on the alignment of its approaches. It incorporates a typical motorist s speed reduction because of the horizontal or vertical alignment of the approach. Character-defining features Prominent or distinctive aspects, qualities, or characteristics of a historic property that contribute significantly to its physical character. Features may include structural or decorative details and materials. Condition rating Level of deterioration of bridge components and elements expressed on a numerical scale according to the NBI system. Components include the substructure, superstructure, deck, channel, and culvert. Elements are subsets of components, e.g., piers and abutments are elements of the component substructure. The evaluated bridge is compared with a new bridge built to current design standards. Component ratings range from 0 (failure) to 9 (new); element ratings range from 1 (poor) to 3 (good). In rating a bridge s condition, Mn/DOT pairs the NBI system with the newer and more sophisticated Pontis element inspection information, which quantifies bridge elements in different condition states and is the basis for subsequent economic analysis. Deck geometry One of five NBI inspection ratings. This rating appraises the functionality of a bridge s roadway width and vertical clearance, taking into account the type of roadway, number of lanes, and Average Daily Traffic (ADT). Deficiency The inadequacy of a bridge in terms of structure, serviceability, and/or function. Structural deficiency is determined through periodic inspections and is reflected in the ratings that are assigned to a bridge. Service deficiency is determined by comparing the facilities a bridge provides for vehicular, bicycle, and pedestrian traffic with those that are desired. Functional deficiency is another term for functionally obsolete (see below). Remedial activities may be needed to address any or all of these deficiencies. Deficiency rating A nonnumeric code indicating a bridge s status as structurally deficient (SD) or functionally obsolete (FO). See below for the definitions of SD and FO. The deficiency rating status may be used as a basis for establishing a bridge s eligibility and priority for replacement or rehabilitation. Glossary A-1

22 Design exception A deviation from standard bridge design practices that takes into account environmental, scenic, aesthetic, historic, and community factors that may have bearing upon a transportation project. A design exception is used for federally funded projects where federal standards are not met. Approval requires appropriate justification and documentation that concerns for safety, durability, and economy of maintenance have been met. Design load The usable live-load capacity that a bridge was designed to carry, expressed in metric tons according to the allowable stress, load factor, or load resistance factor rating methods. An additional code was recently added to assess design load by a rating factor instead of tons. This code is used to determine if a bridge has sufficient strength to accommodate traffic demands. A bridge that is posted for load restrictions may not be adequate to accommodate present or expected truck traffic. Fracture critical Classification of a bridge having primary superstructure or substructure components subject to tension stresses and which are non-redundant. A failure of one of these components could lead to collapse of a span or the bridge. Tension members of truss bridges are often fracture critical. The associated inspection date is a numerical code that includes frequency of inspection in months, followed by year, and month of last inspection. Functionally obsolete (FO) The FHWA classification of a bridge that cannot meet current or projected traffic needs because of inadequate horizontal or vertical clearance, inadequate load-carrying capacity, and/or insufficient opening to accommodate water flow under the bridge. Historic fabric The material in a bridge that was part of original construction or a subsequent alteration within the historic period (e.g., more than 50 years old) that has significance in and of itself. Historic fabric includes both character-defining and minor features. Minor features have less importance and may be replaced more readily. Historic bridge A bridge that is listed in, or eligible for listing in, the National Register of Historic Places. Historic integrity The authenticity of a bridge s historic identity, evidenced by the survival and/or restoration of physical characteristics that existed during the bridge s historic period. A bridge may have integrity of location, design, setting, materials, workmanship, feeling, and association. Inspections Periodic field assessments and subsequent consideration of the fitness of a structure and the associated approaches and amenities to continue to function safely. Inventory rating The load level a bridge can safely carry for an indefinite amount of time expressed in metric tons or by the rating factor described in design load (see above). Inventory rating values typically correspond to the original design load for a bridge without deterioration. Maintenance Work of a routine nature to prevent or control the process of deterioration of a bridge. Glossary A-2

23 Minnesota Historical Property Record (MHPR) A documentary record of an important architectural, engineering, or industrial site, maintained by the MHS as part of the state s commitment to historic preservation. MHPR typically includes large-format photographs and written history, and may also include historic photographs, drawings, and/or plans. This state-level documentation program is modeled after a federal program known as the Historic American Buildings Survey/Historic American Engineering Record (HABS/HAER). National Bridge Inventory Bridge inventory and appraisal data collected by the FHWA to fulfill the requirements of the National Bridge Inspection Standards (NBIS). Each state maintains an inventory of its bridges subject to NBIS and sends an annual update to the FHWA. National Bridge Inspection Standards Federal requirements for procedures and frequency of inspections, qualifications of personnel, inspection reports, and preparation and maintenance of state bridge inventories. NBIS applies to bridges located on public roads. National Register of Historic Places The official inventory of districts, sites, buildings, structures, and objects significant in American history, architecture, archaeology, and culture, which is maintained by the Secretary of the Interior under the authority of the National Historic Preservation Act of 1966 (as amended). Non-vehicular traffic Pedestrians, non-motorized recreational vehicles, and small motorized recreational vehicles moving along a transportation route that does not serve automobiles and trucks. Includes bicycles and snowmobiles. Operating rating Maximum permissible load level to which a bridge may be subjected based on a specific vehicle type, expressed in metric tons or by the rating factor described in design load (see above). Posted load Legal live-load capacity for a bridge usually associated with the operating or inventory ratings as determined by a state transportation agency. A bridge posted for load restrictions may be inadequate for truck traffic. Pontis Computer-based bridge management system to store inventory and inspection data and assist in other bridge data management tasks. Preservation Preservation, as used in this report, refers to historic preservation that is consistent with the Secretary of the Interior s Standards for the Treatment of Historic Properties. Historic preservation means saving from destruction or deterioration old and historic buildings, sites, structures, and objects, and providing for their continued use by means of restoration, rehabilitation, or adaptive reuse. It is the act or process of applying measures to sustain the existing form, integrity, and material of a historic building or structure, and its site and setting. Mn/DOT s Bridge Preservation, Improvement and Replacement Guidelines (BPIRG) describe preservation differently, focusing on repairing or delaying the deterioration of a bridge without significantly improving its function and without considerations for its historic integrity. Glossary A-3

24 Preventive maintenance The planned strategy of cost-effective treatments that preserve a bridge, retard future deterioration, and maintain or improve its functional condition without increasing structural capacity. Reconstruction The act or process of depicting, by means of new construction, the form, features, and detailing of a non-surviving site, landscape, building, structure, or object for the purpose of replicating its appearance at a specific period of time and in its historic location. Activities should be consistent with the Secretary of the Interior s Standards for the Treatment of Historic Properties. Rehabilitation The act or process of returning a historic property to a state of utility through repair or alteration which makes possible an efficient contemporary use, while preserving those portions or features of the property that are significant to its historical, architectural, and cultural values. Historic rehabilitation, as used in this report, refers to implementing activities that are consistent with the Secretary of the Interior s Standards for the Treatment of Historic Properties. As such, rehabilitation retains historic fabric and is different from replacement. However, Mn/DOT s Bridge Preservation, Improvement and Replacement Guidelines (BPIRG) describe rehabilitation and replacement in similar terms. Restoration The act or process of accurately depicting the form, features, and character of a property as it appeared at a particular period of time. Activities should be consistent with the Secretary of the Interior s Standards for the Treatment of Historic Properties. Scour Removal of material from a river s bed or bank by flowing water, compromising the strength, stability, and serviceability of a bridge. Scour critical rating A measure of bridge s vulnerability to scour (see above), ranging from 0 (scour critical, failed, and closed to traffic) to 9 (foundations are on dry land well above flood water elevations). This code can also be expressed as U (unknown), N (bridge is not over a waterway), or T (bridge is over tidal waters and considered low risk). Serviceability Level of facilities a bridge provides for vehicular, bicycle, and pedestrian traffic, compared with current design standards. Smart flag Special Pontis inspection element used to report the condition assessment of a deficiency that cannot be modeled, such as cracks, section loss, and steel fatigue. Stabilization The act or process of sustaining a bridge by means of making minor repairs until a more permanent repair or rehabilitation can be completed. Structurally deficient Classification indicating NBI condition rating of 4 or less for any of the following: deck condition, superstructure condition, substructure condition, or culvert condition. A structurally deficient bridge is restricted to lightweight vehicles; requires immediate rehabilitation to remain open to traffic; or requires maintenance, rehabilitation, or replacement. Glossary A-4