Minnesota Department of Transportation (MnDOT) Local Historic Bridge Report

Transcription

1 Executive Summary Bridge L4005, constructed in 1905, carries pedestrians and a single lane of vehicular traffic on Township Road 124 over Riceford Creek in Houston County. The bridge is owned by Black Hammer Township. Bridge L4005 is significant as the earliest and longest surviving half-hip Pratt pony truss built by the Joliet Bridge and Iron Company in Minnesota. Bridge L4005 is a riveted/bolted steel Pratt pony truss with timber deck. The bridge has been significantly altered presumably due to deterioration concerns regarding the steel truss members. The three-panel truss originally spanned 41 feet and the W18 steel stringers now span approximately 53 feet. Due to the W18 stringers relatively long span combined with their connection to the truss floorbeams, when heavily loaded, the resulting structure spans as a combination of the truss and stringers. A load rating for the structure indicates a posted load of 4 tons. The steel truss was found to be in fair to poor condition with lower chord deformations and areas of significant section loss within the lower chord noted as primary deficiencies. Bridge L4005 is significantly compromised in terms of load carrying capacity and has also been altered from its original form. Preservation of the structure including restoring load capacity and original geometry can be reasonably accomplished and a process is outlined herein. Any work on Bridge L4005 should proceed according to the Secretary of the Interior s Standards for the Treatment of Historic Properties (Standards) [36 CFR part 67] and The Secretary s Standards with Regard to Repair, Rehabilitation, and Replacement Situations, as adapted by the Virginia Transportation Research Council (Guidelines). SEPTEMBER 2013

2 Bridge Location SEPTEMBER 2013 Bridge Location - i

3 Table of Contents Executive Summary Bridge Location I. Project Introduction II. Historic Data III. Bridge Data IV. Existing Conditions/Recommendations V. Projected Costs Appendices A. Glossary B. Guidelines for Bridge Maintenance and Rehabilitation based on the Secretary of the Interior s Standards C. Documents SEPTEMBER 2013 Table of Contents - ii

4 I Project Introduction This Bridge Report is a product of a comprehensive study performed for approximately 140 historic bridges owned by county, city, township, private and other state agencies besides MnDOT. The study is the second phase of a multi-phased process developed and executed in partnership with representatives from the Federal Highway Administration (FHWA); State Historic Preservation Office (SHPO); MnDOT State Aid; MnDOT Cultural Resources Unit (CRU); the US Army Corps of Engineers (USACE); local public works and county highway departments; county and township boards and city councils; the preservation community and the general public. To perform the study, MnDOT retained the consultant team of LHB Inc., Mead & Hunt Inc., and The 106 Group. The general goals of the study include: Gathering and compiling the existing historic and bridge condition data and other relevant information on the bridges in the study group into bridge reports. National Register nominations for a select number of bridges within the study group which the bridge owner may request a nomination to be prepared. Updating MnDOT s Management Plan for Historic Bridges in Minnesota based on the study s findings. Producing a narrative for the MnDOT Historic Bridge Website to disseminate information regarding locally owned historic bridges in Minnesota. Investigating and preparing a summary regarding how other states have funded historic bridge programs and structured Programmatic Agreements when multiple non-state entities are the owners of historic bridges. The Bridge Reports compile and summarize the historic and engineering information concerning the structures. The reports also document the existing use and condition of the bridges along with assessments of the maintenance, stabilization and preservation needs of each structure, including cost estimates. The maintenance activities, along with regular structural inspections and anticipated bridge component replacement activities are routine practices directed toward continued structure serviceability. Stabilization activities address immediate needs identified as necessary 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 preserve and in some cases restore a bridge s structural and historic integrity and serviceability. In assessing preservation activities, a design life of 20 years or longer is typically considered. In addition to general restoration activities and dependent on the severity of deterioration, preservation activities may include spot repair, disassembly and reassembly or replacement of specific bridge components. Recommendations within the Bridge Reports are consistent with the Secretary of the Interior s Standards for the Treatment of Historic Properties (Standards). The Standards are basic principles created to help preserve the distinct character of a historic property and its site, while allowing for reasonable change to meet new engineering standards and codes. The Standards recommend repairing, rather than replacing deteriorated features whenever possible. The Standards apply to historic properties of all periods, styles, types, materials and sizes and encompass the property s location and surrounding environment. SEPTEMBER 2013 Project Introduction I - 1

5 I Project Introduction The Standards were developed with historic buildings in mind and cannot be easily applied to historic bridges. The Virginia Transportation Research Council (Council) adapted the Standards to address the special requirements of historic bridges. They were published in the Council s 2001 Final Report: A Management Plan for Historic Bridges in Virginia, The Secretary s Standards with Regard to Repair, Rehabilitation, and Replacement Situations, provide useful direction for undertaking maintenance, repair, rehabilitation, and replacement of historic bridges and are included in the Appendix to this report. Existing bridge data sources typically available for Minnesota bridges were gathered for the study. These sources include: PONTIS, a bridge management system formerly used by MnDOT to manage its inventory of bridges statewide, and its replacement system, SIMS (Structure Information Management System) The current MnDOT Structure Inventory Report and MnDOT Bridge Inspection Report. Reports are available for the majority of the bridges (not available for bridges in private ownership) Database and inventory forms resulting from the 2012 Minnesota Local Historic Bridge Study and other prior historic bridge studies as incorporated into the database Existing Minnesota historic contexts studies for bridges in Minnesota, including Reinforced- Concrete Highway Bridges in Minnesota, , Minnesota Masonry-Arch Highway Bridges, , Iron and Steel Bridges in Minnesota, and Minnesota Bridges Field investigations documenting the general structural condition and determining characterdefining features Additional data sources researched and gathered for some of the bridges as available also included: Files and records at MnDOT offices Original bridge construction plans, rehabilitation plans, and maintenance records of local owners Files and documents available at the SHPO office, including previous inventory forms, determinations of eligibility, studies, and compliance documents Existing historic and documentary material related to the National Register-eligible bridges The Appendix contains the following: a Glossary explaining structural and historic preservation terms used in the report, the Guidelines for Bridge Maintenance and Rehabilitation based on the Secretary of the Interior s Standards, a list of engineering and historic documents available for this bridge, and copies of the MnDOT Structure Inventory and Bridge Inspection Reports current at the time of the report preparation. The Bridge Report will provide the bridge owner and other interested parties with a comprehensive summary of the bridge condition and detailed information related to the historic nature of the bridge. This information will enable historic bridge owners to make informed decisions when planning for their historic properties. SEPTEMBER 2013 Project Introduction I - 2

6 II Historic Data This narrative is drawn from previous documents, as available for the subject bridge, which may include determination of eligibility (also known as Phase II evaluation), Minnesota Architecture/History Inventory Form, National Register nomination, Multiple Property Documentation Form, and/or applicable historic contexts. See Sources for details on which documents were used in compiling this Historic Data section. Contractor Designer/Engineer Joliet Bridge and Iron Company Joliet Bridge and Iron Company Description Located in rural Black Hammer Township in southwestern Houston County, Bridge L4005 carries a dirt, township-owned, road across Riceford Creek about 3 miles north and west of Spring Grove. The 41-foot span is a rigid-connected, steel, three-panel, half-hip, Pratt pony truss on steel H-piling abutments with timber plank backwalls and flared timber plank wingwalls. The two truss webs are identically detailed. Two channel sections with cover plate and battens form the top chord, while two angle sections with battens comprise the lower chord. Vertical members consist of four angle sections with V-lacing; diagonal members are paired angle sections with battens. The wood deck rests on eight rolled stringers (six I-beams and two outer channel sections) bolted to the top flanges of rolled I-beam floorbeams, which, in turn, are bolted to the superstructure. A portion of a metal plaque remains on the bridge's northeast endpost, bearing the following inscription: "... IE... E & IR... IET " The plaque reveals that the bridge was the work of the Joliet Bridge and Iron Company of Joliet, Illinois. Bottom-lateral bracing consists of crossed rods. The bridge's H-piling abutments indicate that the original substructure has been rebuilt, possibly because the superstructure was moved to its present site from another location. Significance Research in state and county archives failed to uncover information concerning the construction of Bridge L4005. As evidenced by inspection reports on file with the Houston County Highway Department, the structure has been on its present site at least since the early 1970s. The bridge's northeast endpost bears a fragment of a metal builder's plaque, inscribed as follows: "... IE... E & IR... IET " This inscription indicates that the bridge was originally designed and constructed in 1905 by the Joliet Bridge and Iron Company of Joliet, Illinois. Operating in the Midwest since at least the late 1890s, Joliet Bridge and Iron was responsible for building a number of steel pony trusses in southern Minnesota during the first two decades of the twentieth century. In addition to five bridges in Houston County, six other examples of the firm's work have been identified in Brown, Cottonwood, Faribault, Nobles, and Watonwan Counties. In its design of Bridge L4005, Joliet Bridge and Iron employed a Pratt pony truss variant known as the "half hip" configuration, so-called because the truss webs omitted the customary vertical member at the hip position. Because the half-hip design used less steel than the conventional Pratt pony truss, it was cheaper to produce, which made it popular with economy-conscious township and county governments. Like other surviving Minnesota examples of Pratt pony trusses designed by Joliet Bridge and Iron, Bridge L4005 has rigid connections, which were preferred over pin connections by many "Good Roads Movement" advocates because the resulting truss web appeared to be sturdier under live load. However, SEPTEMBER 2013 Historic Data II - 3

7 II Historic Data even rigid-connected, half-hip, Pratt pony truss were unsuitable for the increasingly heavier traffic loads of the twentieth century. When the Minnesota Highway Commission published its first bridge specifications, it prohibited the use of the Pratt design by requiring that all future pony-truss construction employ a rigidconnected Warren configuration. In 1913, the Minnesota Legislature approved a series of measures that gave the Minnesota Highway Commission control of almost all bridge designs in the state. A proponent of standardized bridge construction, the commission prepared a comprehensive set of plans and specifications that mandated the use of specific bridge types for specific span lengths, defined acceptable and unacceptable detailing practices, and prescribed construction procedures for both steel and concrete structures. Periodically updated, until superseded in the late 1920s by similar guidelines issued by the American Association of Highway Officials, the Minnesota Highway Commission's regulations for bridge construction ushered in an era of design uniformity that lasted for the remainder of the twentieth century. Before 1913, Minnesota bridge construction was largely in the hands of municipal, township, and county governments. Although a few counties and cities had professional engineers on staff to prepare bridge plans and superintend construction, most local governments acquired bridges through a process of competitive bidding by private bridge-building firms, which tailored their designs and construction practices to suit the expectations and finances of their clients, as much as to satisfy the physical demands of the site and the functional requirements of traffic. The result was a wide variety of bridge designs, some well-engineered and some not. Over the years, the vast majority of these "non-standard" bridges were eventually replaced by state-designed structures, but a few still survive. Bridge L4005 is among the survivors. Bridge L4005 has experienced minor modifications over time, the most significant of which was its relocation sometime in the 1970s. As such it has diminished integrity of location and setting. However, the bridge continues to provide a water crossing and thereby retains integrity of feeling and association. Since early-twentieth-century trusses were designed to be relocated if necessary, this circumstance does not drastically affect Bridge L4005's historic integrity. No other modifications to the structure are known. As such, the bridge continues to retain integrity of workmanship, materials, and design. The period of significance is 1905 to correspond with the date of construction. Extant half-hip pony trusses are uncommon in the state. This bridge represents the longest and oldest surviving half-hip Pratt pony trusses built by the Joliet Bridge and Iron Company in Minnesota. Bridge L4005 is the state's best example of the firm's work with this particular bridge type. It is eligible for the National Register under Criterion C in the area of Engineering, within the Multiple Property Documentation Form (MPDF) of "Iron and Steel Bridges in Minnesota." The MPDF associated with this context states, under Registration Criterion 5, that a bridge may be eligible for the National Register if it was built by a company that was "very important to the construction of bridges in Minnesota." As an excellent example of the work of Joliet Bridge and Iron Company, Bridge L4005 satisfies this criterion. SEPTEMBER 2013 Historic Data II - 4

8 II Historic Data Historic Context Iron and Steel Bridges in Minnesota, National Register Status Criterion A Significance Criterion C Significance Historic District SHPO Inventory Number Eligible (Individually) N/A Engineering: Important type; Work of a master N/A HU-BLH-011 Sources Used to Compile Section II Historic Data Bridge L4005 File in Houston County Highway Department, Caledonia, Minnesota; "An Act Relating to Public Highways" (Chapter 235), General Laws of the State of Minnesota (St. Paul: The Pioneer Company, 1913), Bridge L4005 File in Minnesota Department of Transportation, Waters Edge Building, Roseville. Frame, Robert M., "Historic Bridge Project: A Report," prepared for the State Historic Preservation Office of the Minnesota Historical Society, and the Minnesota Department of Transportation, 1985, 81. Minnesota Department of Transportation Bridge Database. Minnesota Highway Commission, Report, , Minnesota Highway Commission, Standard Specifications for Steel and Concrete Highway Bridges, 1912; Houston County Board of Commissioners, Proceedings, 1905, in Houston County Courthouse, Caledonia. Quivik, Fredric L., "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 Damian Hess, 26 October Field investigation by LHB, Inc. and Mead & Hunt, 24 May SEPTEMBER 2013 Historic Data II - 5

9 II Historic Data 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. Often, the character-defining features include important historic fabric. However, historic fabric can also be found on other elements of a bridge that have not been noted as character-defining. For this reason, it is important to consider both characterdefining features and the bridge s historic fabric when planning any work. Feature 1: Design and construction of a rigid-connected, half-hip, Pratt pony truss as designed by the Joliet Bridge and Iron Company, an important Minnesota bridge building company. This feature includes the half-hip configuration as well as the riveted panel connections common to this era of bridge building. SEPTEMBER 2013 Historic Data II - 6

10 III Bridge Data Date of Construction (remodel) 1905 Common Name (if any) Location Feature Carried: TWP 124 Feature Crossed: Riceford Creek County: Houston Ownership: Black Hammer Township MnDOT Structure Data *Data Current (as of): Sep 2013 Main Span Type: 301 STEEL BM SPAN Main Span detail: Substructure Type - Foundation Type: Abutment: 1-Concrete - 1-Spread/Soil Piers: 3-Steel - 4-Pile Bent Total Length: 53 ft Main Span Length: 41 ft Total Number of Span(s): 3 Skew (degrees): 0 Structure Flared: No Flare Roadway Function: Rural, Local Custodian/Maintenance Type: Township Reported Owner Inspection Date 09/18/2012 Sufficiency Rating 30.9 Operating Rating HS 5.4 Inventory Rating HS 4.4 Structure Status P Load Posted Posting VEH: 4 SEMI: DBL: Design Load UNKN Current Condition Code Roadway Clearances Deck: 5 Roadway Width: 15.9 ft Superstructure: 5 Vert. Clearance Over Rdwy: N/A Substructure: 6 Vert. Clearance Under Rdwy: N/A Channel and Protection: 6 Lat. Clearance Right: 0 ft Culvert: N Lat. Clearance Left: 0 ft Current Appraisal Rating Roadway Data Structural Evaluation: 2 ADT Total: 4 (1986) Deck Geometry: 8 Truck ADT Percentage: Not given Underclearances: N Bypass Detour length: 99 miles Waterway Adequacy: 6 Number of Lanes: 1 Approach Alignment: 3 Fracture Critical No Waterway Data Deficient Status S.D. Scour Code: K-LIMITED RISK Non-MnDOT Data Approach Roadway Characteristics **Number of Crashes reported Lane Widths: 8 ft in MnMCAT within 500 feet Shoulder Width: N/A of Bridge Site 0 Shoulders Paved or Unpaved: N/A Roadway Surfacing: Aggregate Location of Plans Plans Available N/A No Plans Available * Non-MnDOT data collected during field survey. All other fields of data collected from MnDOT September of See Appendix C for MnDOT inventory and inspection report data. ** Unless a significant number of crashes are noted on or near a bridge, the accident data is not detailed in this report. SEPTEMBER 2013 Bridge Data III - 7

11 IV Existing Conditions/Recommendations Existing Conditions Available information, as detailed in the Project Introduction section, concerning Bridge L4005 was reviewed prior to visiting the bridge site. The site visit was conducted to establish the following: 1. General condition of structure 2. Conformation to available extant plans 3. Current use of structure 4. Roadway/pedestrian trail geometry and alignment (as applicable) 5. Bridge geometry, clearances and notable site issues General Bridge Description Bridge L4005 is a riveted/bolted steel Pratt pony truss that has been significantly altered presumably due to deterioration concerns regarding the steel truss members. The alteration to the structure reportedly occurred in In 1999 new concrete abutments consisting of 12-inch-thick concrete sills cast directly on grade were placed approximately 5 feet behind each of the original abutments and the truss stringers were replaced with six, W18 beams that now span over the truss floorbeams and bear on the newly placed abutments. The three panel Pratt truss originally spanned 41 feet and the W18 steel stringers now span approximately 53 feet. The W18 stringers are connected to the two interior panel point floorbeams, however, the stringers do not bear at the truss ends where the truss ends bear on a steel channel assembly, which is sandwiched on driven steel piling to comprise the original bridge abutment. Transverse timber deck planks span across the stringers thus creating the driving surface for the bridge. Since the truss is still supported at its ends on the channel/piling assembly and yet it also bears on the steel stringers which span between the new abutments two load carrying scenarios can be considered for the structure. The first scenario is to presume the stringers spanning between the new abutments is the complete bridge structure and that they also carry the dead weight of the two center panels of the truss since the two interior floorbeams are connected to/hung from the stringers. The second scenario is to consider the truss remains a load carrying element and it thus carries the self-weight dead load of itself along with the live load imparted to the two interior floorbeams. The steel stringers in this scenario then carry the load from truss end panels to the stringer ends where they bear on the new abutments. A load capacity rating for the structure, completed in 2008 determined a load posting requirement of 4 tons for the structure. The load rating for the structure indicated that for posting loads in excess of approximately 4 tons the deflection in the stringers becomes large enough that the stringers load the truss resulting in combined structure behavior. Due to this combined effect and present deterioration to the truss members the structure is currently posted to 4 tons. At this loading level the truss is relied upon to carry little to no live load and the stringers in effect comprise the bridge and serve to support the truss. The bridge is currently open to traffic with load posting signs indicating 4 tons in place. Minimum maintenance signs are also present along the roadway segment leading to the bridge. Serviceability Observations The bridge is currently open to vehicular traffic and load posted to 4 tons as detailed above. The roadway is signed as a minimum maintenance road and combined with the bridges location it is not anticipated the bridge sees very frequent traffic. The Structure Inventory sheet for the bridge lists an ADT of 4 for SEPTEMBER 2013 Existing Conditions/Recommendations IV - 8

12 IV Existing Conditions/Recommendations Condition Observations Superstructure The steel truss is in fair to poor condition. The majority of the truss elements exhibit minor section loss rust deterioration however isolated regions of significant loss/deterioration are present. More notable section loss includes from 50 percent to 80 percent section loss in the bottom chord inboard angle horizontal leg at a number of locations and a completely deteriorated splice plate connecting the horizontal lower chord angle legs at panel L1 of the north truss. The bottom chord of the south truss (upstream truss) is also bent/twisted approximately 2 inches out of plane from L0 to L2 presumably from flood debris impact. The truss deck plane diagonal tension rod bracing appears to have been removed from the center truss panel and is significantly deformed and non-functioning in the truss end panels. The steel floorbeams could not be directly accessed however appeared to exhibit moderate section loss and failed paint. The W18 steel stringers appeared in good condition overall, exhibiting minor section loss (up to 20 percent bottom flange loss) due to rust/corrosion. The W18 steel stringers have butt welded splices, which should be further investigated at the time of any detailed inspection for restoration purposes. The paint system for the truss, stringers and floorbeams is primarily failed. The transverse timber plank deck is in good condition overall. Bridge Railings The bridge railings consist of two horizontal steel angles running along the inside face of each truss. The angles comprising the rail are in fair condition overall. There is no railing in the section of bridge extending from end of truss to end of bridge at each of the four bridge corners. Bearings The truss bears through bearing plates onto two steel channels sandwiched around a driven steel pile (vertical railroad rail) at each of the four corners. It is unlikely any expansion movement occurs at these locations; thus, all four truss corners should be considered fixed. The W18 steel stringers are also secured to the concrete sills thus fixing the bridge at those locations as well. Substructures The original abutment supports the ends of the steel truss. It is comprised of driven steel piling (railroad track iron) with steel channels sandwiched one per side, bolted to the vertical pilings and creating a cap for the truss ends to bear on. Timber planks are stacked on the back sides of the rail piling to retain the approach backfill. The steel piling appears in fair condition overall, though it is apparent the interior piling are rotating into the stream at their tops, presumably due to the backwall surcharge. The channels comprising the caps appeared in fair condition though they have limited function as the truss corners appear to bear through them directly above the corner piling and the W18 steel stringers do not bear but instead cross over the top of the abutment cap with a gap present. The bolting of the cap to the piling is suspect in terms of load capacity and the channels appear bolted to the corner piles only, however present structural geometry imparts little load to the bolting. The timber backwall planks are in fair to poor condition with some of the planks unattached/settled and no longer properly retaining the backwall fill. The W18 steel stringers are supported on concrete sills behind the truss abutments. The 12-inch-deep concrete sills are perched in the fill behind the abutments and are in good condition overall, with the SEPTEMBER 2013 Existing Conditions/Recommendations IV - 9

13 IV Existing Conditions/Recommendations exception of their being undermined. It appears stream flow and soil settlement through the truss abutment backwall timbers is leading to scour beneath the concrete sills. The most severe scour was noted beneath the east sill at its north end where the sill was found to be undermined up to 6 inches deep over most of its leading edge, extending up to 2 feet inward in the 3-foot width of the sill. Approach/Waterway Observations The bridge approaches appear suitable for the current bridge function with no deficiencies noted other than a fair amount of overgrowth due the lack of travel/use. No significant waterway/channel deficiencies were noted with the exception of the noted flow behind the truss abutments which appears to be washing out the backwall/concrete sill fill slope. Date of Engineering Site Visit by LHB May 24, 2013 SEPTEMBER 2013 Existing Conditions/Recommendations IV - 10

14 IV Existing Conditions/Recommendations Condition 1: North elevation Condition 2: Bridge approach, looking west SEPTEMBER 2013 Existing Conditions/Recommendations IV - 11

15 IV Existing Conditions/Recommendations Condition 3: Treefall on south truss Condition 4: Bottom chord deformations, presumably from flood debris damage, south truss SEPTEMBER 2013 Existing Conditions/Recommendations IV - 12

16 IV Existing Conditions/Recommendations Condition 5: Underside view, truss, floorbeams and stringers - south truss in foreground, east abutment ahead (note truss bottom chord deformations) Condition 6: South truss, east end (note deterioration in bottom chord angles, gusset plate, connection bolts and bearing plate) SEPTEMBER 2013 Existing Conditions/Recommendations IV - 13

17 IV Existing Conditions/Recommendations Condition 7: Deterioration in lower chord splice plate for lower chord angles (note photo is taken looking downward (stream below) at the east interior panel point of north truss) SEPTEMBER 2013 Existing Conditions/Recommendations IV - 14

18 IV Existing Conditions/Recommendations Condition 8: Bowing and inward rotation of abutment piling tops at west truss abutment (note corner piling maintains a more plumb alignment due to connection to truss at truss bearing points) SEPTEMBER 2013 Existing Conditions/Recommendations IV - 15

19 IV Existing Conditions/Recommendations Condition 9: Stringer spanning over truss channel support abutment and bearing on concrete sill abutment, northeast corner SEPTEMBER 2013 Existing Conditions/Recommendations IV - 16

20 IV Existing Conditions/Recommendations Condition 10: Undermining at concrete sill abutment, northeast corner Condition 11: Undermining at concrete sill abutment, northeast corner SEPTEMBER 2013 Existing Conditions/Recommendations IV - 17

21 IV Existing Conditions/Recommendations Condition 12: Timber bridge deck, deck is in fair condition (note height of deck in relation to horizontal rail angles; deck height was likely raised when deeper 18-inch stringers went in over floorbeams) SEPTEMBER 2013 Existing Conditions/Recommendations IV - 18

22 IV Existing Conditions/Recommendations Overall Recommendations The bridge is currently open to vehicular traffic as a minimum maintenance road and for recommendation purposes the future use for the structure is presumed to remain the same. The preservation recommendations which follow initially assume the W18 steel stringers and their concrete abutment sills will remain in place. However, to complete a more historically correct preservation replacement of the steel stringers with stringers matching original stringer geometry along with removal of the concrete sill abutments would be required. The preservation recommendations which follow conclude with the additional work scope required to accommodate stringer replacement. Recommended Stabilization Activities 1. Restore full bearing beneath the W18 stringer concrete sills. This may require grout packing or grout injection beneath the sills. 2. Make sufficient repairs to truss abutment timber backwall planks, including anchoring to piling to allow for backfill to be restored. Restore backfill and consider capping with appropriate sized riprap. 3. Place appropriate sized riprap on upstream bank to guard against scour behind truss abutment backwalls. Recommended Preservation Activities Superstructure Steel Truss Perform detailed assessment of degree of section loss to lower chord members, lower chord gussets, and vertical and diagonal members connecting at lower chord. Perform similar assessment to other truss members, though anticipated degree of section loss is less for those members. It is anticipated a number of the lower chord angles will require in-kind replacement due to the extent of deterioration, possibly due to flood debris damage, although straightening of most flood damaged members should be feasible. It is presumed work to verticals and diagonals, gusset plate and upper chord members will be limited based on level of deterioration noted at time of assessment. The underdeck truss panel tension cross-bracing rods will require complete replacement. At the time of the assessment it was noted that some truss members were connected with rivets at both ends while others were connected with a combination of rivets and dome headed bolts depending on member end/location point. It is believed this is due either to the truss having been previously relocated or quite possibly was done to facilitate transportation and assembly of the original truss thereby not requiring the use of rivets in the field. In any case it is likely component replacement can be facilitated through the use of dome headed bolts. The abutment piling were noted to be rotating inward from embankment loading. This is due to the lateral load imparted and the interior piling are free to rotate at their tops. The four corner piling beneath the truss corners, however, are secured at their tops to the cap channels and truss corners thereby prohibiting their rotation. The top attachment of the four corner piling transfers the embankment loading into the truss lower chord, which is detrimental to the chord. This scenario could be alleviated by securing the piling/pile cap laterally to the W18 steel stringers at each end of the bridge. In this fashion SEPTEMBER 2013 Existing Conditions/Recommendations IV - 19

23 IV Existing Conditions/Recommendations the steel stringers would share the backwall load, inhibit the piling from rotating inward and minimizing the imparted load to the truss lower chord. Superstructure Paint System The current paint system on the trusses and remaining bridge superstructure is failed and the system should be replaced. It is recommended the in-place paint system be entirely removed to bare metal through abrasive blasting (which through testing is determined will not degrade portions of the steel structure which are to remain). Following removal the structure should be painted with a zinc-rich primer and a protective overcoat system with color and sheen to be selected based on the historic requirements of the structure. The in-place system will require testing to determine for the presence of lead. Due to the toxicity of lead the removal of lead paint systems requires an intensive encapsulation process. For purposes of cost estimating a lead based system has been presumed. Bearings The truss corner bearing plates should be further assessed for deterioration and rehabilitated/replaced as warranted. Rehabilitation should include restoring expansion capabilities to one end of the truss. If replacement of components is determined to be necessary replacement with components of like material and geometry should be considered to the extent possible as they are a visual element of the structure. For purposes of the preservation cost estimate replacement has been assumed. Substructures Rehabilitative repairs to the W18 stringer concrete sill abutments, truss abutment backwall timbers, backwall fill and embankment slope is discussed in the Stabilization section of this report. To affect a more permanent repair the truss abutment piling should be aligned, the backwall timbers replaced, backfill restored and the steel cap beam channels replaced. A replacement study should be undertaken to determine the most appropriate cap beam replacement material/material geometry for the bridge. The replacement cap beam should be secured to all piling and should be secured to the W18 steel stringers to prevent lateral inward rotation of the steel piling tops. For purposes of the preservation cost estimate the above defined repairs are included and presumed not to have been performed under stabilization. Railings The steel angle railing along the truss, while not meeting current code provisions, is customary for trusses of this type and age. Due to the roadway s low use, lack of reported accidents at the bridge site, and minimum maintenance status it is likely it could be provisioned to remain and would require only minor repair, blasting, repainting, and re-securing at attachment locations. Incorporation of bridge railing through the W18 stringer spans off each corner of the truss should also be investigated and studied to determine a suitable railing type that could be incorporated to increase safety while meeting the historic needs of the structure. For purposes of the base preservation estimate, repair of the in place railing and an allowance for added railing at the four bridge corners has been included. SEPTEMBER 2013 Existing Conditions/Recommendations IV - 20

24 IV Existing Conditions/Recommendations Concrete Sill Abutment Removal and Stringer Replacement In addition to the preservation measures discussed above, proper preservation of the structure would require removal of the concrete sill abutments and replacement of the existing steel stringers with shorter stringers matching the truss span length (as originally existed). This additional work would also require replacement of the abutment channel cap beam, limited re-plumbing of the abutment piling, removal and replacement of the timber deck and associated embankment slope work. An added work scope has been included within the base preservation cost estimate to account for these additional work items. Recommended Annual Maintenance Activities 1. Maintain areas around truss ends and bearings free of debris, soil, etc. to minimize further rusting/ corrosion. 2. Monitor bridge closely during flood periods to remove flood debris and respond to potential flood debris damage. 3. Maintain truss abutment backwall fill, fill beneath W18 stringer concrete sills and upstream embankment behind truss abutments. SEPTEMBER 2013 Existing Conditions/Recommendations IV - 21

25 V Projected Agency Costs Summarized Maintenance, Stabilization and Preservation Construction Cost Estimates It is important to recognize that the work scope and cost estimates presented herein are based on a limited level assessment of the existing structure. In moving forward with future project planning, it will be essential to undertake a detailed structure assessment addressing the proposed work for the structure. It is also important that any future preservation work follow applicable preservation standards with emphasis to rehabilitate and repair in-place structure elements in lieu of replacement. This includes elements which are preliminarily estimated for replacement within the work scope of this report. Only through a thorough review of rehabilitation and repair options and comprehensive structural and historic assessment can a definitive conclusion for replacement of historic fabric be formed. The opinions of probable construction and administrative costs provided below are presented in 2013 dollars. These costs were developed without benefit of a detailed, thorough bridge inspection, bridge survey or completion of preliminary design for the estimated improvements. The estimated costs represent an opinion based on background knowledge of historic unit prices and comparable work performed on other structures. The opinions of cost are intended to provide a programming level of estimated cost. These costs will require refinement and may require significant adjustments as further analysis is completed in determining the course of action for future structure improvements. A 20 percent contingency and 7 percent mobilization allowance has been included in the construction cost estimates. Administrative and engineering costs are also presented below. Engineering and administrative costs are also to be interpreted as programming level only. Costs can be highly variable and are dependent on structure condition, intended work scope, project size and level of investigative, testing and documentation work necessary. Additional studies, evaluation, and historic consultation costs not exclusively called out may also be incurred on a case-by-case basis. Maintenance, Stabilization and Preservation Costs (refer to the work item breakdown on the next page) Opinion of Annual Cost- Maintenance Activities: $ 3,400 Opinion of Construction Cost- Stabilization Activities: $ 14,080 Opinion of Construction Cost- Preservation Activities: $ 240,460 Estimated Preliminary Design, Final Design, Construction Administration Costs Preliminary Design and Assessment $ 5,000 Final Design and Plans $ 25,000 Construction Administration $ 30,000 SEPTEMBER 2013 Projected Agency Cost V - 22

26 V Projected Agency Costs ITEM NO. MAINTENANCE, STABILIZATION & PRESERVATION COST ESTIMATE (2013 DOLLARS) Bridge No. L4005 June 28, 2013 MAINTENANCE COSTS ITEM 1 CLEAN TRUSS ENDS AND BEARINGS LUMP SUM 1 $ $ MONITOR AND REMOVE DEBRIS DURING FLOODING LUMP SUM 1 $1, $1, (annualized estimate) 3 MAINTAIN FILL AT TRUSS ABUTMENT & STRINGER SILLS LUMP SUM 1 $1, $1, (annualized estimate) 20% CONTINGENCY LUMP SUM 1 $ $ UNIT ESTIMATED QUANTITIES AND COST QUANTITY UNIT COST TOTAL ESTIMATE STABILIZATION COSTS ESTIMATED MAINTENANCE COSTS $3, % LUMP SUM 1 $ $ RESTORE BEARING OF STRINGER SILLS (GROUT INJECTION) CU YD 4 $ $3, A REPAIR TRUSS ABUT TIMBER PLANKS & RESTORE BACKFILL SQ FT 180 $16.00 $2, B BACKFILL WITH RIPRAP AT "PIERS" CU YD 15 $ $2, PLACE RIPRAP ON UPSTREAM BANK CU YD 30 $90.00 $2, % CONTINGENCY LUMP SUM 1 $2, $2, PRESERVATION COSTS ESTIMATED STABILIZATION COSTS $14, % LUMP SUM 1 $13, $13, TEMPORARILY SHORE TRUSS TO COMPLETE REPAIRS LUMP SUM 1 $20, $20, REPLACE LOWER CHORD ANGLES (2 OF 6 ASSUMED) LIN FT 28 $ $4, STRAIGHTEN LOWER CHORD ANGLES (4 OF 6 ASSUMED) LIN FT 56 $80.00 $4, MISC REPAIRS TO UPPER TRUSS AND GUSSET PLATES LUMP SUM 1 $15, $15, TRUSS PANEL TENSION ROD REPLACEMENT (21' EACH) EACH 6 $1, $7, LONGITUDINALLY SECURE PILE CAPS TO W18 STRINGERS EACH 12 $ $9, LEAD ABATEMENT AND REPAINTING (TRUSS AND RAILING) LUMP SUM 1 $80, $80, REPLACE BEARING PLATES EACH 4 $1, $4, REPLACE BACKWALL TIMBERS (EST. 22' LONG 12" TALL) EACH 16 $ $6, REATTACH AND REPAIR EXISTING RAILING LUMP SUM 1 $2, $2, EXTEND RAILING AT ENDS OVER STRINGER SPANS LIN FT 24 $ $4, OPTIONAL ITEMS TO RESTORE ORIGINAL STRUCTURE: 12 REMOVE CONCRETE SILL ABUTMENT EACH 2 $ $1, ALIGN TRUSS ABUTMENT PILING EACH 10 $ $5, REPLACE TRUSS ABUTMENT CAP BEAM (24' LONG) EACH 4 $2, $8, REMOVE AND REPLACE STRINGERS TO MATCH ORIGINAL LIN FT 252 $35.00 $8, REMOVE AND REINSTALL DECK TIMBERS SQ FT 700 $8.00 $5, % CONTINGENCY LUMP SUM 1 $40, $40, ESTIMATED PRESERVATION COSTS $240, SEPTEMBER 2013 Projected Agency Cost V - 23

27 Appendices Appendix A. Glossary SEPTEMBER 2013 Appendices - 24

28 Glossary Abutment Component of bridge substructure at either end of bridge that transfers load from superstructure to foundation and provides lateral support for the approach roadway embankment. Appraisal ratings Five National Bridge Inventory (NBI) appraisal 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 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, fair A bridge or bridge component of which all primary structural elements are sound, but may have minor deterioration, section loss, cracking, spalling, or scour. Condition, good A bridge or bridge component which may have some minor deficiencies, but all primary structural elements are sound. Condition, poor A bridge or bridge component that displays advanced section loss, deterioration, cracking, spalling, or scour. 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) or N for (not applicable); elements are rated on a scale of 1-3, 1-4 or 1-5 (depending on the element type and material). In all cases condition state 1 is the best condition with condition state 3, 4 or 5 being the worst condition. In rating a bridge s condition, MnDOT 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. Corrosion The general disentegration of metal through oxidation. Cutwater The wedge-shaped end of a bridge pier, designed to divide the current and break up ice. Decay Deterioration of wood as a result of fungi feeding on its cell walls.

29 Delamination Surface separation of concrete, steel, glue laminated timber plies etc. into layers. Deck geometry One of five NBI appraisal 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 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. Design exception A deviation from federal design and geometric standards 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 tons according to the AASHTO 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 load demands. A bridge that is posted for load restrictions is not adequate to accommodate present or expected legal truck traffic. Deterioration Decline in condition of surfaces or structure over a period of time due to chemical or physical degradation. Efflorescence A deposit on concrete or brick caused by crystallization of carbonates brought to the surface by moisture in the masonry or concrete. Extant Currently or actually existing. Extrados The upper or outer surfaces of the voussoirs which compose the arch ring. Often contrasted with intrados. Footing The enlarged, lower portion of a substructure which distributes the structure load either to the earth or to supporting piles.

30 Fracture Critical Members Tension members or tension components of bending members (including those subject to reversal of stress) whose failure would be expected to result in collapse of the bridge. Functionally obsolete The Federal Highway Administration (FHWA) classification of a bridge that does not 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. An appraisal rating of 3 or less for deck geometry, underclearance, approach alignment, structural evaluation or waterway adequacy will designate a bridge as functionally obsolete. Gusset plate A plate that connects the horizontal and vertical members of a truss structure and holds them in correct position at a joint. Helicoidal Arranged in or having the approximate shape of a flattened coil or spiral. Historic fabric The material in a bridge that was part of original construction or a subsequent alteration within the historic period of the bridge (i.e., more than 50 years old). Historic fabric is an important part of the character of the historic bridge and the removal, concealment, or alteration of any historic material or distinctive engineering or architectural feature should be avoided if possible. Often, the characterdefining features include important historic fabric. However, historic fabric can also be found on other elements of a bridge that have not been noted as character-defining. 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. Intrados The innner or lower surface of an arch. Often contrasted with extrados. Inventory rating The load level a bridge can safely carry for an indefinite amount of time expressed in 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. Keystone Wedge-shaped stone, or voussoir, at the crown of an arch. Load Rating The determination of the live load carrying capacity of a bridge using bridge plans and supplemented by field inspection. Maintenance Work of a routine nature to prevent or control the process of deterioration of a bridge.