BRIDGE 4930 – SCOPING STUDY Bridge 4930 Final... · Petros Xanthakos in his text, Bridge Strengthening and Rehabilitation (Prentice Hall PTR, 1996), reports on a handful of studies

Bridge 4930 Scoping Study Phase 2 – Final Report

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BRIDGE 4930 – SCOPING STUDY Trunk Highway 99 over the Minnesota River at St. Peter, Minnesota FINAL – PHASE 2 REPORT Evaluation of Rehabilitation Options October 14, 2010 Prepared by Olson & Nesvold Engineers, P.S.C. Mead & Hunt, Inc. A.A. Sehlin Consultants Genesis Structures, Inc.


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TABLE OF CONTENTS 1. Executive Summary ................................................................................ 3

2. Purpose of Phase 2 .................................................................................. 3

3. Design Criteria ........................................................................................ 4

4. Description of Bridge 4930 ....................................................................... 7

5. Discussion of Options ............................................................................. 12

i. Option 1 – Minimal Rehabilitation ....................................................... 14

ii. Option 2 – Major Rehabilitation ......................................................... 23

iii. Option 3 – Major Rehabilitation and the Addition of Jump Spans ............. 36

6. Conclusion ........................................................................................... 48

7. Appendices .......................................................................................... 51


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1. Executive Summary The feasibility of rehabilitating the historic Broadway Bridge (Bridge 4930) at its current location is described in this report. This is the second phase of a scoping study for Bridge 4930. Phase 1 of the study collected data from technical experts and stakeholders and determined the constraints for the project. This report, Phase 2, describes three alternatives that were considered: Option 1 (Minimal Rehabilitation), Option 2 (Major Rehabilitation), and Option 3 (Major Rehabilitation and the Addition of Jump Spans). Graphics and narrative describe the details of each option along with their associated costs. Each rehabilitation option was evaluated with a 20-year planning window. This was chosen to match the planning window used for the individual historic bridge management plan assembled for Bridge 4930 in 2006. Each option was also evaluated for compliance with the Secretary of the Interior’s Standards for the Treatment of Historic Properties, Standards for Rehabilitation (Appendix B). Lastly, the options were compared and contrasted with each other. Based on meeting the Secretary Standards and having a lower cost, Option 2 emerged as the preferred alternative for preserving the bridge in place on the Trunk Highway System.

2. Purpose of Phase 2

The Broadway Bridge (Bridge 4930) is one of 24 historic bridges owned by Mn/DOT that are listed in the National Register of Historic Places and that have been identified for preservation as part of a 2008 Programmatic Agreement (PA) between Mn/DOT and other stakeholders. The PA requires Mn/DOT to preserve and maintain Bridge 4930 according to the maintenance specified in the structure’s Historic Bridge Management Plan (2006). The PA also requires that the Secretary of the Interior’s Standards for the Treatment of Historic Properties will be used to determine whether work on the bridge would constitute what is termed an “adverse effect” to the historic property in the Section 106 process. The historic significance of Bridge 4930 is exemplified in the bridge’s character-defining features (skewed pier truss design, ornamental railing, light standards, and abutments, and continuous lower chord truss configuration over the pier). All rehabilitation work on the bridge is subject to review under the Section 106 process for compliance with the Secretary’s Standards. This is the second phase of a scoping study for Bridge 4930. The constraints for the project were identified by Mn/DOT District 7, Mn/DOT’s Cultural Resources Unit, the Mn/DOT Bridge Office and other stakeholders (State Historic Preservation Office [SHPO] and the City of St. Peter) and documented in the Phase 1 Report. Phase 2 examines preservation options for keeping the bridge in-service on Trunk Highway 99. If authorized, Phase 3 of the project would examine a preservation option that would relocate the


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truss spans upstream from their current location to a park and convert them to pedestrian use.

This report describes and evaluates the continued feasibility and merits of three on-system options for rehabilitating Bridge 4930. The evaluation considers how each option:

Impacts the bridge’s character-defining features and historic fabric

Impacts the serviceability of the bridge (geometrics and load capacity)

Impacts the reach of the Minnesota River in the vicinity of the bridge

Impacts the serviceability of the Trunk Highway 99 in the vicinity of the bridge (see Rehabilitation Option/Work Task Matrix in Appendix A)

Impacts the development of a regional trail system as identified by the City of St. Peter in their master plan (see Rehabilitation Option/Work Task Matrix in Appendix A)

3. Design Criteria

Bridge rehabilitation projects must comply with many criteria. These criteria range from policy documents (Mn/DOT’s Bridge Preservation Improvement, and Replacement Guidelines, and Bridge 4930 Historic Bridge Management Plan) to constraints associated with different funding sources (e.g. FHWA Sufficiency Rating values). Fundamentally, the investment in the rehabilitation project needs to be prudent and it needs to balance the following Mn/DOT goals:

Improving the load capacity of the bridge Improving the shoulder widths on the bridge Improving the hydraulic operations during high water at the

bridge Managing increasing ongoing maintenance associated with the

bridge Strategically using limited resources and capitalizing on the

current availability of Chapter 152 Bridge Funding Partnering with the City of St. Peter and Le Sueur County on

their plans for regional trails Complying with updates to Chapter 152 of Minnesota State

Statutes (requirements for load path redundancy in highway bridges). Refer to Phase 1 report for discussion on seeking a Chapter 152 exemption for Bridge 4930.

Ensuring that rehabilitation details are technically sound and are durable

Maintaining the bridge’s condition within state guidelines Complying with the historic bridge PA including preserving and


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maintaining Bridge 4930 in accordance with the 2006 Historic Bridge Management Plan and application of The Secretary of the Interior’s Standards for the Treatment of Historic Properties to evaluate whether work on the bridge would constitute an adverse effect to the historic property.

Complying with Section 106 of the National Historic Preservation Act

Bridge Deterioration Rates One of the primary parameters in the life cycle cost analyses that follow is the service life of the bridge after a rehabilitation option has been performed. Both functional criteria (geometrics and load capacity) and condition criteria (NBI inspection condition codes) are used to estimate the remaining service life of the bridge. The geometrics of the bridge and its load carrying capacity (assuming good maintenance practices) vary little with time. The condition of components such as the superstructure, substructure, and deck continue to degrade with time (even with good maintenance practices.) Relatively little information has been published related to general highway bridge deterioration rates. Petros Xanthakos in his text, Bridge Strengthening and Rehabilitation (Prentice Hall PTR, 1996), reports on a handful of studies pertaining to bridge deterioration models. He reports that in general it can be assumed that bridges deteriorate on average one tenth of one National Bridge Inventory (NBI) condition rating per year. This implies that a bridge with a superstructure in NBI Condition 8 would take 10 years to drop to a NBI condition 7. Bridge 4930 has 2010 NBI condition codes of: Deck - 5 Superstructure – 5 Substructure –5 This implies that within 10 years these components of Bridge 4930 will drop from 5s (fair condition) to 4s (poor condition). Any one of these components dropping to a 4 will classify the bridge as structurally deficient. After any of the rehabilitation options are executed, the NBI condition codes would increase. They would most likely increase to an NBI condition 7 or 8 for the superstructure and substructure. Though recently rehabilitated, these components will not be returned to a new state. Chlorides will still be contained in substructure components and pack rust will be embedded in some of the superstructure connections.


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This implies that a rehabilitated bridge has a service life of approximately 30 to 40 years before it degrades back to a condition 4 which is structurally deficient and eligible for replacement. It should also be noted that Xanthakos reports that County owned bridges have a longer service life compared to State Highway Agency owned bridges. State owned bridges are typically subjected to larger traffic volumes, heavier truck traffic, and more aggressive salting and sanding operations. Based on Figure 2-37 in Xanthakos’ book, the increase in service life of a County owned bridge is on the order of 35 to 40 percent above that of a State Highway Agency owned bridge. A bridge taken off of the highway system and converted to pedestrian use would be expected to have an even longer service life than one on the local road system. Pedestrian bridges are typically not subjected to heavy truck loads and are much less likely to be damaged as a result of vehicle impacts.

The NBI Condition Codes for Bridge 4930 over the past 27 years for the Deck Superstructure and Substructure are presented in Graph 1. The bridge had substantial rehabilitation work performed in 1982. In general, the NBI Condition Codes have dropped roughly 1/10th of a point per year.

Graph 1 – NBI Condition Code History

012345678

9

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Deck

Superstructure

Substructure

BRIDGE 4930 ‐ NBI INSPECTION CONDITION CODES

INSPECTION YEAR


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Chapter 152 Funding It should be noted that in response to the I-35W bridge collapse the 2008 Minnesota State Legislature authorized additional funding for Mn/DOT to rehabilitate and replace structurally deficient and fracture critical bridges throughout the state. These Chapter 152 funds give Districts significant monies above what they have historically received in the past to work with bridges. As enacted by the Legislature, the Chapter 152 funding is a 10 year funding program. It is anticipated that in 2018, bridge funding levels will return to their pre 2008 level.

4. Description of Bridge 4930

The Broadway Bridge carries Trunk Highway 99 over the Minnesota River at St. Peter. Constructed in 1931, the primary spans for the bridge are two Pennsylvania through-truss spans. Each of the truss spans is unique in that one end of the span is square and the other end (which rests on the river pier) is skewed. The pier is skewed to align it with the flow of the Minnesota River and improve its hydraulic characteristics. Short concrete slab spans are integrated into the abutments. The bridge has an overall length of 402 feet. The primary geometric characteristics of Bridge 4930 are presented in two figures. Figure 1 contains the General Plan and General Elevation views. Figure 2 contains the transverse sections of the bridge. The Phase 1 Report provides additional details on Bridge 4930 and its history. Please refer to this report for more information.


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Figure 1


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Figure 2


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Gusset Plate Capacity – Current and Expected Background In 2008, LHB Engineers prepared a load rating analysis of the gusset plates on Bridge 4930. Because the bridge has similar gusset plates in each quarter section, they analyzed only the southwest quarter section which has the largest loads. Each gusset plate was rated in eight different areas: tension, flexure, shear, block shear, buckling, edge buckling, and bearing and shear of the rivets. In accordance with standard Bridge Office policy the load rating was reported assuming 5% and 15% section loss in the plates. Table 1 provides the controlling load ratings for the upper gusset plates assuming 5% section loss and the lower gusset plates assuming 15% section loss.

Truss Joint

Controlling Inventory L.R.

Controlling Operating L.R.

L4 HS 34 HS 58 L8 HS 34 HS 57 L10 HS 21 HS 38 U4 HS 16 HS 30 U6 HS 16 HS 31

Table 1 – Controlling Load Ratings of Gusset Plates in 2008 Also in 2008, Mn/DOT preformed the bi-annual fracture critical inspection of Bridge 4930. During this inspection, the controlling gusset plates were inspected for section loss, distortion and loose or distressed rivets. Two of the gussets plates were on the upper chord (U4 and U6) and three of the gusset plates (L4, L10, and L11 which is similar to L8)were on the lower chord. No section loss, loose/distressed rivets or distortions were found in the upper chord gusset plates. For the lower chord, no loose or distressed rivets were found. However, two of the three gusset plates had section loss: 14.5% in one (L4) and 3% to 22% in the other (L11, which is similar to L8). Also, one gusset plate (L10) had a minor bow in the edge due to fit up at construction, but no section loss. Because the bow was due to fit up, there was little concern that the bow would grow and reduce the capacity of the gusset plate in the future. Assessment and Rehabilitation Options The load rating capacity, of the bridge was considered when determining whether or not to replace or strengthen the existing gusset plates as part of the rehabilitation options. Currently the capacity of the bridge is controlled by elements other than gusset plates (interior floor beams). To determine if the gusset plates become controlling elements for the load capacity of the bridge in years 20, 30, and 40, past section loss rates were extrapolated forward. A description of the extrapolation process and its results follow.


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It should be noted that at the completion of a rehabilitation project, a bridge should have minimum inventory load rating of HS 18 (HS 20 is preferred). Similarly, the critical operating load rating is typically HS 30 at the completion of a rehabilitation project (Year 0). Components with capacities below these values should be strengthened or replaced as part of the rehabilitation project. In 2008, the upper gusset plates had the lowest load rating and those inspected had no section loss. In Year 0 for this report, all of the upper gusset plates are assumed to have a section loss of 0%. For future years 20, 30, and 40, they are assumed to have section losses of 1%, 2%, and 3% respectively. These gusset plates are assumed to have little section loss based on past history and because they are not exposed to the chlorides and flood damage like the lower gusset plates. In 2008, two of the lower gusset plates had an average section loss of 14% across the plate. L10 had no section loss. Information on the other gusset plates is not available, but is assumed to be no worse than the section loss found on L4 and L11. In Year 0 for this report, all gusset plates, except L10 and L11, are assumed to have a section loss of 15%. L10 is assumed to have the same section losses as the upper gusset plates because it had no section loss in 2008. L11 (L8) is assumed to have a section loss of 25% in Year 0 since it had a maximum of 22% in 2008. Year 0 in this report is when the bridge is approximately 80 years old. Knowing the assumed section loss over the last 80 years, the assumed section loss was extrapolated to Year 20, 30, and 40 for each of the gusset plates. Table 2 provides the assumed section loss in Years 0, 20, 30, and 40.

Gusset Plate Location

Assumed Section Loss Year 0 Year 20 Year 30 Year 40

U4, U6, and L10 0% 1% 2% 3% L4 15% 19% 21% 23%

L11 (L8) 25% 31% 34% 37% Table 2 – Assumed Section Loss for Gusset Plates

Load ratings were revised based on the assumed section loss. Table 3 provides the controlling load ratings for the upper and lower gusset plates in Years 0, 20, 30, and 40.


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Jt.

Year 0 Year 20 Year 30 Year 40 Critical

Inv. L.R.

Critical Oper. L.R.

Critical Inv. L.R.

Critical Oper. L.R.

Critical Inv. L.R.

Critical Oper. L.R.

Critical Inv. L.R.

Critical Oper. L.R.

L4 HS 34 HS 58 HS 32 HS 55 HS 31 HS 53 HS 30 HS 51 L8 HS 28 HS 48 HS 25 HS 43 HS 23 HS 40 HS 21 HS 37 L10 HS 25 HS 45 HS 25 HS 44 HS 24 HS 44 HS 24 HS 44 U4 HS 18 HS 35 HS 18 HS 34 HS 17 HS 33 HS 17 HS 33 U6 HS 19 HS 36 HS 19 HS 35 HS 18 HS 34 HS 18 HS 34

Table 3 – Controlling Load Ratings of Gusset Plates in Years 0, 20, 30, and 40

As shown in Table 3, the lower gusset plate inventory load ratings are not expected to drop below HS 20. For this reason, all of the options included in this report do not recommend replacing or strengthening the lower gusset plates. As also shown in Table 3, the gusset plates U4 and U6 have an inventory load rating of HS 18 in Year 0 when assuming 0% section loss. Since the upper gusset plates have little contact with chlorides and are not directly impacted by flood events, they have a relatively slow deterioration rate. Consequently, this report does not recommend replacing or strengthening the upper gusset plates as part of the rehabilitation options.

5. Discussion of Options

At the start of Phase 2, four options were considered. During consultation with the State Historic Preservation Office (SHPO) on January 28, 2010, it was decided that one of the four options would not be pursued further. It became clear the option titled “Major Rehabilitation and Raising the Trusses” would likely not comply with the Secretary of the Interior’s Standards for Rehabilitation as compared to the other three options. In addition, this option was found to provide minimal benefits in other areas. A work task matrix describing all four of the initial rehabilitation options that were considered is provided in Appendix A. This section of the report details the characteristics of each of the three remaining rehabilitation options. Each option is discussed in a brief narrative in the following topic areas:

Description of the Rehabilitation, a general overview of the rehabilitation strategy

Life Cycle Narrative, a narrative describing the life-cycle

characteristics of bridge components


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Construction Issues, a narrative describing the construction

steps necessary to execute the rehabilitation

Serviceability, a narrative describing the serviceability of the bridge after the rehabilitation strategy is executed

Cost, a narrative describing the construction cost associated

with executing the rehabilitation strategy

Compliance with Secretary of the Interior’s Standards, a narrative describing the effects on the historic property associated with the rehabilitation strategy and their degree of compliance with the Secretary’s Standards.


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i. Option 1 – Minimal Rehabilitation

a. Description of the Rehabilitation

Option 1 is a basic rehabilitation strategy to keep Bridge 4930 as is and in service without improving the load carrying capacity of the bridge or improving its hydraulic operations performance. Figures 3 and 4 graphically summarize the work tasks associated with this option. Major work tasks associated with this option include a complete painting of the truss and floor system. In addition, gusset plate connections would be sealed to retard future section loss. No bridge deck replacement is scheduled as part of this option. Instead, cracks in the deck are periodically sealed to slow the intrusion of chlorides into the deck. This option includes repair of the abutments and pier. In recent years, the abutment bearing seats or pedestals and backwalls have periodically been repaired by District 7. Both types of substructure units (pier and abutments) are in a condition that warrants major rehabilitation based on criteria in the Mn/DOT Preservation Improvement and Replacement Guidelines. No change would be made to the hydraulic performance as part of this project. The District would continue to remove debris and close and detour the bridge on Trunk Highway 99 during high water events. The ornamental metal railing would be prepped and painted. It is assumed that sidewalk railing painting activities would be executed concurrently with the truss painting project. Special handling and containment practices would need to be used to repaint these items with the existing lead-based paint system. The sidewalk pavement would be periodically sealed to limit the intrusion of chlorides. Ornamental light fixtures would be rehabilitated and painted or replaced. The light fixture at the northeast corner of the bridge is missing and would be replaced in-kind. During the design phase of the rehabilitation project, all of the remaining light standards would be evaluated for rehabilitation or replacement.


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Figure 3


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Figure 4


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b. Life cycle narrative Eleven activities were considered as part of the life cycle cost analysis for this option. The activities, the year(s) in which the activities take place, the cost per occurrence, and the present value of the all occurrences are presented in Table 4. In addition to the rehabilitation project costs, the ongoing expenses incurred by the District are also considered. These expenses include annual maintenance items, such as flushing the bridge with water. Also included is an estimated annualized cost to cover the expenses associated with bridge inspection activities. Based on current guidance provided by Mn/DOT’s Office of Investment Management, the discount rate of money has been assumed to be 2.9% for this analysis. Within the table, cells that are shaded gray are used to identify the year(s) in which specific activities take place. For example, Activity 3 (Seal Cracks in the Deck) is assumed to take place on a five-year cycle (in Year 0, Year 5, Year 10, and Year 15). As an example, the present worth of the cost of sealing the cracks in the concrete deck four times is $59,000. Each occurrence of sealing the cracks in the deck is assumed to cost $18,000 in the year the sealing occurs. Due to the discount rate of money, Year 5, Year 10, and Year 15 costs for sealing the deck cracks are reduced when they are brought back to Year 0. Respectively these costs are: Year 5 - $15,602.60, Year 10 - $13,524.40, and Year 15 - $11,723.10. Summing the four values results in a cost of $58,850.10 which rounds to $59,000.

$18,000 Present Value at Year X =

(1+2.9%)year A short description of the basis for each item presented in the Option 1 life cycle cost table follows: Item 1 – Complete Truss and Floor System Repainting The cost is based on a painting contractor’s estimate. It assumes the 50,000 square feet of paint area presented in the Structure Inventory Report is accurate. The Contractor’s number was split between Item 1 and Item 5. This value includes the cost to seal the gusset plates, but does not include traffic control costs. It is assumed that bridge will be closed to traffic for a few weeks during the rehabilitation of the bridge.


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Item 2 – Spot Painting of Truss and Floor System Spot painting assumed to be 10% of Item 1 Item 3 – Seal Cracks in the Deck Based on three full-width transverse cracks in each truss panel (1800 linear feet) Item 4 – Abutment and Pier Rehabilitation Rehabilitation assumes 50 percent of the existing substructure units’ concrete will be added to both abutments and the river pier. Assumes 285 cubic yards of concrete at $655 per yard and 38,500 lbs of epoxy coated reinforcement at $1.30 per pound. Also assumes a lump sum cost of $500,000 is needed for river access to pier, cofferdams and excavation and backfill work at abutments. Item 5 – Complete Ornamental Railing Repainting The cost is based on a painting contractor’s estimate (based on the 50,000 square foot of paint area presented in the Structure Inventory Report). The Contractor’s number was split between Item 5 and Item 1. Item 6 – Spot Painting of the Ornamental Railing Spot painting assumed to be 10% of Item 5. Item 7 – Rehabilitate Light Standards For estimating cost, conservatively assumed that all 7 of the existing light standards may need to be replaced. Cost of replacement light standards secured from a historic lighting supplier. Also includes an assumed cost for an electrical subcontractor to install the standards. Item 8 – Seal Cracks in the Sidewalk Pavement Assumes two full width sidewalk cracks in each truss panel (250 linear feet) Item 9 – Flush Bridge Annually and Other District Maintenance Assumed value to cover flushing of the bridge with water to remove debris and chlorides. Item 10 – Annualized Costs of Inspections Assumed value to represent the annualized costs associated with routine, fracture critical, and underwater bridge inspection activities. Item 11 – Remaining Capital Value of Bridge at Year 20 The remaining capital value of the bridge is an economic


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estimate of the remaining value of the bridge to the owner. This value is based on the serviceability of the bridge for the Trunk Highway system and does not attempt to place an economic value on the historic value of the bridge. The bridge currently has marginal load carrying capacity. It is assumed that load capacity requirements for bridges on the Trunk Highway System will continue to increase over the next 20 years. Without improvement to the load carrying capacity of the bridge, the bridge is assumed to have no value for the Trunk Highway System in Year 20. For this item, we have assumed that the demolition cost of the bridge is equal to the scrap value of the steel.


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Table 4


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c. Construction Issues This option is the minimal rehabilitation option and consequently has the fewest number of construction issues. Construction issues presented below are keyed to the activities listed in Table 4. Item 1-Complete Truss and Floor System Repainting Due to the size of the bridge, containment of the superstructure to prevent lead-based paint debris from reaching the Minnesota River and its banks will be costly. Item 4-Abutment and Pier Rehabilitation Rehabilitation of the abutments may require supporting the truss on temporary supports. Transferring reactions to the temporary supports while the abutments are rehabilitated will be complicated.

d. Serviceability

This option has the fewest serviceability improvements. No improvement is made to the horizontal clearance on the bridge. No improvement is made to the load capacity of the bridge. No improvement is made to the hydraulic opening or Minnesota River channel in the vicinity of the bridge. A modest improvement in lighting is expected as the light standard at the northeast corner of the bridge is replaced.

e. Cost The cost of this rehabilitation option over the next 20 years is estimated to be $1,488,000 in 2010 dollars. In Year 0 (2010) dollars, the expenditures total $1,488,000. The Remaining Capital Value of the bridge in Year 20 is $0. The Year 0 Remaining Capital Value is also $0.

f. Compliance with Secretary of the Interior’s Standards

Option 1 as presented is in compliance with the Secretary’s Standards and would not constitute an adverse effect under Section 106. Option 1 involves a small number of specific work areas to be reviewed for compliance with the Secretary’s Standards when preparing plans and special provisions. These elements will be evaluated under Standards for Rehabilitation 2-7 (see Table 7 and the text in Appendix B):

a. Paint color. Investigate the paint color(s) used for the bridge historically when selecting the color for painting the truss and floor system as well as the ornamental


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railing. There may be additional concerns if it is determined that the railing needs structural modifications.

b. Repair of concrete abutments and pier. The abutments and pier are included in the character-defining features. In particular, any concrete repairs will need to match the existing historic concrete in color, texture, and surface detail, particularly historic architectural or aesthetic treatments. In addition, any work on the pier should be reviewed for more substantial changes to the overall appearance, form, shape, and design of this important feature.

c. Ornamental light fixtures. The ornamental light fixtures are significant architectural and functional elements and part of a character-defining feature. The fixtures will need to be inspected to determine if they will be repaired or replaced, with rehabilitation being a priority. If replaced, they would be replaced in kind.

d. Option 1 – Minimal Rehabilitation, as proposed, complies with the Secretary’s Standards. This option does not meet the roadway standards. See Table 7, Analysis of Bridge 4930 Options Under Section 106 for further information.


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ii. Option 2 – Major Rehabilitation

a. Description of the Rehabilitation Option 2 is more extensive than Option 1. This option improves the load carrying capacity of the bridge by strengthening the floor beams. No improvement is provided to the hydraulic operations performance. Figures 5 through 9 graphically summarize the work tasks associated with this option. Figures 5 and 6 describe the rehabilitation tasks in a general fashion. Figure 7 describes the strengthening of the floor beams. Figure 8 describes the replacement of the concrete deck. The deck replacement will replicate the existing deck thickness instead of using the minimum 8” deck thickness used today. An increase in deck thickness would increase the dead load on the bridge and adversely affect the load rating of the bridge. Figure 9 describes the replacement of the sidewalk concrete. The sealing of cracks in the concrete deck and the sealing of cracks in the concrete sidewalk is delayed five years in this option. New concrete is assumed to be installed for both of these components in Year 0. With a substantial investment made in the superstructure (strengthening of the floor beams) as part of this option, a more extensive rehabilitation of the abutments and pier is required. Consequently, the construction cost for this activity is much larger than for Option 1. No change would be made to the hydraulic performance as part of this project. The District would continue to remove debris and close and detour the bridge on Trunk Highway 99 during high water events. The ornamental railing and ornamental light fixtures would be rehabilitated and/or replaced in-kind in the same manner as they would be in Option 1.


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Figure 5


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Figure 6


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Figure 7


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Figure 8


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Figure 9


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b. Life Cycle narrative Fourteen activities were considered as part of the life cycle cost analysis for this option. The activities, the year(s) in which the activities take place, the cost per occurrence, and the present value of all occurrences are presented in Table 5. Most of the activities listed in Table 5 were included in Option 1. Additional activities include: strengthening of the floor beams, more extensive abutment rehabilitation, a new concrete bridge deck, and new concrete sidewalk pavement. In addition to the rehabilitation project costs the ongoing expenses incurred by the District are also considered. These expenses include annual maintenance items, such as flushing the bridge with water. Also included is an estimated annualized cost to cover the expenses associated with bridge inspection activities. Within the table, cells that are shaded gray are used to identify the year(s) in which different activities take place. For example, Activity 5 (Seal Cracks in the Deck) is assumed to take place on a five-year cycle (in Year 5, Year 10, and Year 15). Based on current guidance provided by Mn/DOT’s Office of Investment Management, the discount rate of money has been assumed to be 2.9% for this analysis. A short description of the basis for each item presented in the Option 2 life cycle cost table follows: Item 1 – Complete Truss and Floor System Repainting The cost is based on a painting contractor’s estimate. It assumes the 50,000 square feet of paint area presented in the Structure Inventory Report is accurate. The Contractor’s number was split between Item 1 and Item 7. This value includes the cost to seal the gusset plates, but does not include traffic control costs. It is assumed that traffic will need to be detoured during rehabilitation efforts in Year 0 for a period of three to four months. Item 2 – Spot Painting of Truss and Floor System Spot painting assumed to be 10% of Item 1. Item 3 – Strengthening of Truss Floor Beams This cost covers the material, equipment, and labor costs associated with strengthening the floor beams. It assumes that work is performed while the concrete deck is removed.


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Item 4 – New Concrete Bridge Deck This cost covers removal of the existing deck and the material, equipment, and labor costs associated with casting a new concrete deck on the truss spans. Item 5 – Seal Cracks in the Deck Based on three full-width transverse cracks in each truss panel (1800 linear feet). Item 6 – Abutment and Pier Rehabilitation Rehabilitation assumes 70 percent of the existing substructure units’ concrete will be added to both abutments and the river pier. Also assumes a lump sum cost of $500,000 is needed for river access to pier, cofferdams and excavation and backfill work at abutments. Item 7 – Complete Ornamental Railing Repainting The cost is based on a painting contractor’s estimate (based on the 50,000 square foot of paint area presented in the Structure Inventory Report). The Contractor’s number was split between Item 7 and Item 1. Item 8 – Spot Painting of the Ornamental Railing Spot painting assumed to be 10% of Item 7. Item 9 – Rehabilitate Light Standards For estimating cost, conservatively assumed that all 7 of the existing light standards may need to be replaced. Cost of replacement light standards secured from a historic lighting supplier. Also includes an assumed cost for an electrical subcontractor to install the standards. Item 10 – New Concrete Sidewalk Pavement This cost covers removal of the existing sidewalk and the material, equipment, and labor costs associated with casting a new concrete sidewalk on the truss spans. Item 11 – Seal Cracks in the Sidewalk Pavement Assumes two full width sidewalk cracks in each truss panel (250 linear feet). Item 12 – Flush Bridge Annually and Other District Maintenance Assumed value to cover flushing of the bridge with water to remove debris and chlorides. Item 13 – Annualized Costs of Inspections Assumed value to represent the annualized costs associated with routine, fracture critical, and underwater bridge inspection


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activities. Item 14 – Remaining Capital Value of Bridge at Year 20 With an improved load capacity the bridge is assumed to have a service life of 30 years. This service life extends beyond the 20 year planning window. To account for the value of the bridge for service life years 21 through 30 the remaining capital value is computed. It should be noted that this is not the salvage value of the bridge. If taken out of service in year 20, the bridge is likely to have negligible salvage value because little if anything could be utilized as part of a replacement structure. The remaining capital value is simply the cost of a replacement bridge multiplied by a coefficient. The coefficient is based on three parameters; the real discount rate, the service life of the asset, and the year of evaluation within the service life of the asset. At year 0, the coefficient is 1.00. At the end of the service life the coefficient is 0.0. Graph 2 shows the impact of the discount rate on the remaining capital value coefficient for an asset with a 30 year service life. A very small discount rate approximates a straight line (Green 0.5% line). As the discount rate increases, the asset has a more nonlinear curve (Blue 5% line).

Graph 2 – Remaining Capital Value Coefficients for a 30 Year Service Life Asset (three different discount rates)

With a discount rate of 2.9%, at year 20, a 30-year service life asset has a Remaining Capital Value Coefficient (RCVC) of 0.43.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20 25 30

RCVC

Year Within Asset Service Life

5%

2.90%

0.5%

Discount Rate


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A replacement bridge cost was used to arrive at the Remaining Capital Value (RCV) for the bridge. A replacement bridge cost of $5,250,000 was used for this item. The replacement bridge was assumed to be 60 feet wide, 500 feet long, and to have a unit cost of $175 per square foot. (The replacement bridge length of 500 feet was used to provide better hydraulic performance at this location.) Multiplying the RCVC by the replacement bridge cost produces the Year 20 RCV value of $2,257,500. The value of the RCV at Year 0 is $1,274,000.

$2,257,500 Present Worth of RCV at Year 0 =

(1+2.9%)20


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Table 5


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c. Construction Issues This option has more construction issues than Option 1 and fewer than Option 3. Construction issues below are keyed to the activities in Table 5. Item 1-Complete Truss and Floor System Repainting Due to the size of the bridge, containment of the superstructure to prevent lead-based paint debris from reaching the Minnesota River and its banks will be costly. Item 3-Strengthening of Truss Floor Beams Strengthening of the floor beams should be performed when the bridge deck is removed. This will simplify access to the work area and will improve the efficiency of the cover plate by applying both deck dead loads and live loads to the strengthened section. If the cover plates were installed while the deck was in place, only the live loads would be carried by the cover plate reinforced section. At each end of the floor beams, the new cover plates will be terminated prior to the connection plates for the lateral bracing. Item 6-Abutment and Pier Rehabilitation Rehabilitation of the abutments may require supporting the truss on temporary supports. Transferring reactions to the temporary supports while the abutments are rehabilitated will be complicated. Rehabilitating the substructure units while the deck is removed will minimize dead loads and reduce the size of temporary supports.

d. Serviceability

This option has more serviceability improvements than Option 1 and fewer improvements than Option 3. No improvement is made to the horizontal clearance on the bridge. An improvement is made to the load capacity of the bridge. It will have an inventory rating greater than HS18. No improvement is made to the hydraulic opening or Minnesota River channel in the vicinity of the bridge. A modest improvement in lighting is expected as the light standard at the northeast corner of the bridge is replaced. During this rehabilitation, this may be an opportunity to explore improving light output from each standard. The replacement of the deck and sidewalk concrete should reduce crack sealing requirements over the remaining years of the planning window.

e. Cost

The present worth of all costs of this rehabilitation option over the next 20 years is estimated to be $740,000 in 2010 dollars. In Year 0 (2010) dollars, the expenditures total $1,878,000.


October 14, 2010 35

The Remaining Capital Value of the bridge in Year 20 is $2,257,500. Moving this value back to Year 0 produces a Remaining Capital Value of $1,274,000 in 2010.

f. Compliance with the Secretary of the Interior’s Standards

Option 2 as presented is in compliance with the Secretary’s Standards and would not constitute an adverse effect under Section 106. Option 2 involves all work areas to be reviewed for compliance with the Secretary’s Standards in Option 1, plus the additional areas noted below. These elements will be evaluated under Standards for Rehabilitation 2-7 (see Table 7 and the text in Appendix B):

a. Truss floor beams. Each truss floor beam will be strengthened by attaching a steel cover plate to the beam’s bottom flange with hex-head bolts. While attaching a cover plate to the top flange would be preferred under the Secretary’s Standards because it would be less visible, it would also create an additional problem with the design of the replacement concrete deck and potentially add dead load to the truss. In addition, plating the bottom flange adds strength where it is most needed—at the bottom instead of the top. The use of hex-head bolts, in the head-down position, is acceptable to distinguish the work as new, in compliance with the Secretary’s Standards. The cover plate can be removed in the future and the bolt holes filled, making the change reversible. The use of a cover plate for floor beam strengthening as described would not constitute an adverse effect.

b. Repair of abutments and pier. Because the repairs to abutments and the pier are expected to be more extensive under Option 2 than Option 1 (but not yet detailed in this report), the Secretary’s Standards review of any proposed plans will need to be more detailed because of the significance of the architectural details and the historic design of the pier.

c. Option 2 – Major Rehabilitation, as presented, complies with the Secretary’s Standards. See Table 7, Analysis of Bridge 4930 Options Under Section 106 for further information.


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iii. Option 3 – Major Rehabilitation and the Addition of Jump Spans

a. Description of the rehabilitation and the figures

The Option 3 rehabilitation project is more extensive than either Option 1 or Option 2. This option improves the load carrying capacity of the bridge by strengthening the floor beams and improves the hydraulic opening of the bridge by adding jump spans east of the existing bridge. Figures 10 through 13 graphically summarize the work tasks associated with this option. Figures 10 and 11 describe the rehabilitation tasks in a general fashion. Figures 12 and 13 describe the appearance of the jump spans in the vicinity of the east end of the truss and over the jump span pier. Sealing cracks in the concrete deck and the concrete sidewalk is delayed five years in this option. New concrete is assumed to be installed for both of these components in Year 0. With a substantial investment made in the superstructure (strengthening of the floor beams) as part of this option, a more extensive rehabilitation of the abutment and pier is required. Consequently, the construction cost for this activity is much larger than for Option 1. The addition of jump spans and adding additional flood plain capacity in the vicinity of the bridge increases the hydraulic opening below the bridge. This results in lowering headwater elevations during flood events which provides two primary benefits. First, the potential for debris striking the historic truss during a flood event is reduced. Secondly, there will be some hydraulic benefit to the Trunk Highway 22 crossing located approximately 1 mile upstream of Trunk Highway 99. The ornamental railing and ornamental light fixtures would be rehabilitated and replaced in-kind in the same manner as they would be in Options 1 and 2.


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Figure 10


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Figure 11


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Figure 12


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Figure 13


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b. Life cycle Sixteen activities were considered as part of the life cycle cost analysis for this option. The activities, the year(s) in which the activities take place, the cost per occurrence, and the present value of the all occurrences are presented in Table 6. Table 6 includes all of the activities in Option 2 and the construction of two jump spans, channel excavation, and east embankment restoration activities. In addition to the rehabilitation project costs, the ongoing expenses incurred by the District are also considered. These expenses include annual maintenance items, such as flushing the bridge with water. Also included is an estimated annualized cost to cover the expenses associated with bridge inspection activities. Within the table, cells that are shaded gray are used to identify the year(s) in which different activities take place. For example, Activity 5 (Seal Cracks in the Deck) is assumed to take place on a five-year cycle (in Year 5, Year 10, and Year 15). Based on current guidance provided by Mn/DOT’s Office of Investment Management, the discount rate of money has been assumed to be 2.9% for this analysis. A short description of the basis for each item presented in the Option 3 life cycle cost table follows: Item 1 – Complete Truss and Floor System Repainting The cost is based on a painting contractor’s estimate. It assumes the 50,000 square feet of paint area presented in the Structure Inventory Report is accurate. The Contractor’s number was split between Item 1 and Item 7. This value includes the cost to seal the gusset plates, but does not include traffic control costs. It is assumed that traffic will need to be detoured for three to six months during rehabilitation and construction efforts in Year 0. Item 2 – Spot Painting of Truss and Floor System Spot painting assumed to be 10% of Item 1. Item 3 – Strengthening of Truss Floor Beams This cost covers the material, equipment, and labor costs associated with strengthening the floor beams. It assumes that work is performed while the concrete deck is removed. Item 4 – New Concrete Bridge Deck


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This cost covers removal of the existing deck and the material, equipment, and labor costs associated with casting a new concrete deck on the truss spans. Item 5 – Seal Cracks in the Deck Based on three full-width transverse cracks in each truss panel (1800 linear feet). Item 6 – Abutment and Pier Rehabilitation Rehabilitation assumes 70 percent of the existing substructure units’ concrete will be added to both abutments and the river pier. This cost assumes that piling will be added to the east abutment as it is converted to a pier and that it will be supported on a substantial temporary support. Also assumes a lump sum cost of $500,000 is needed for river access to pier, cofferdams and excavation and backfill work at abutments. Item 7 – Complete Ornamental Railing Repainting The cost is based on a painting contractor’s estimate (based on the 50,000 square foot of paint area presented in the Structure Inventory Report). The Contractor’s number was split between Item 7 and Item 1. Item 8 – Spot Painting of the Ornamental Railing Spot painting assumed to be 10% of Item 7. Item 9 – Rehabilitate Light Standards For estimating cost, conservatively assumed that all 7 of the existing light standards may need to be replaced. Cost of replacement light standards secured from a historic lighting supplier. Also includes an assumed cost for an electrical subcontractor to install the standards. This item includes the cost of three additional light standards for the jump spans. Item 10 – New Concrete Sidewalk Pavement This cost covers removal of the existing sidewalk and the material, equipment, and labor costs associated with casting a new concrete sidewalk on the truss spans. Item 11 – Seal Cracks in the Sidewalk Pavement Assumes two full width sidewalk cracks in each truss panel (250 linear feet). Item 12 – New Approach Jump Spans This item considers the cost of material, labor, and equipment to install piling, foundations, substructure units, steel beams, reinforced concrete deck and sidewalk, and railings on two 75 foot jump spans.


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Item 13 – Channel Excavation and East Bank Restoration This item covers the cost associated with excavating 180,000 cubic yards of material on the east bank of the river above the ordinary high water level in the vicinity of the jump spans. It also includes costs for reconstructing the levee on the east bank of the river. Item 14 – Flush Bridge Annually and Other District Maintenance This is an assumed value to cover flushing of the bridge with water to remove debris and chlorides. Item 15 – Annualized Costs of Inspections Assumed value to represent the annualized costs associated with routine, fracture critical, and underwater bridge inspection activities. Item 16 – Remaining Capital Value of Bridge at Year 20 With an improved load capacity and improved hydraulic characteristics the bridge is assumed to have a service life of 40 years. With a discount rate of 2.9%, at year 20, a 40-year service life asset has a Remaining Capital Value Coefficient (RCVC) of 0.64. A replacement bridge cost was used to arrive at the Remaining Capital Value (RCV) for the bridge. A replacement bridge cost of $4,750,000 was used for this item. Similar to Option 2, the replacement bridge was assumed to be 60 feet wide, 500 feet long, and to have a unit cost of $175 per square foot. Although, since Option 3 requires excavation of the channel to build the jump spans, the replacement bridge cost used for Option 2 was reduced by $500,000 to account for excavation that would not need to occur with the bridge replacement. The excavation of the channel associated with this Option was assumed to provide a $500,000 cost reduction to the cost of the replacement bridge. Multiplying the RCVC by the replacement bridge cost produces the Year 20 RCV value of $3,040,000. The value of the RCV at Year 0 is $1,716,000.


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Table 6


October 14, 2010 45

c. Construction Issues This option is the most extensive rehabilitation option and consequently has more construction issues than either Option 1 or Option 2. Construction issues presented below are keyed to the activities listed in Table 6. Item 1-Complete Truss and Floor System Repainting Due to the size of the bridge, containment of the superstructure to prevent lead-based paint debris from reaching the Minnesota River and its banks will be costly. Item 3-Strengthening of Truss Floor Beams Strengthening of the floor beams should be performed when the bridge deck is removed. This will simplify access to the work area and will improve the efficiency of the cover plate by applying both deck dead loads and live loads to the strengthened section. If the cover plates were installed while the deck was in place, only the live loads would be carried by the cover plate reinforced section. Item 6-Abutment and Pier Rehabilitation Rehabilitation of the abutments may require supporting the truss on temporary supports. Transferring reactions to the temporary supports while the abutments are rehabilitated will be complicated. Rehabilitating the substructure units while the deck is removed will minimize dead loads and reduce the size of temporary supports. Modifying the east abutment to carry both truss reaction and jump span reactions will be complicated. Item 12-New Jump Spans The new jump spans are uncomplicated steel beam spans. However construction of a bridge seat at the current east abutment will require creativity to avoid conflicts with existing components. Item 13-Channel and East Embankment Restoration A significant amount of channel excavation is required as part of this option. In addition, the east bank of the river will need to be reworked to tie into existing topographic features.

d. Serviceability

This option has more serviceability improvements than either Option 1 or Option 2. No improvement is made to the horizontal clearance on the bridge. An improvement is made to the load capacity of the bridge. It will have an inventory rating greater than HS18. An improvement is made to the hydraulic opening for the Minnesota River channel in the vicinity of the


October 14, 2010 46

bridge. The improvement in hydraulics should reduce the potential for debris strikes on the historic truss and also allow Trunk Highway 99 to remain in service during a larger flood event. However, the improvement in hydraulics is modest and it is likely that the bridge will need to be closed prior to Trunk Highway 99 during certain high water events. A modest improvement in lighting is expected as the light standard at the northeast corner of the bridge is replaced. During this rehabilitation, this may be an opportunity to explore improving light output from each standard. The replacement of the deck and sidewalk concrete should reduce crack sealing requirements over the remaining years of the planning window.

e. Cost

The present worth of all costs of this rehabilitation option over the next 20 years is estimated to be $2,921,000 in 2010 dollars. In Year 0 (2010) dollars, the expenditures total $4,637,000. The Remaining Capital Value of the bridge in Year 20 is $3,040,000. Moving this value back to Year 0 produces a Remaining Capital Value of $1,716,000 in 2010.

f. Compliance with the Secretary of the Interior’s Standards Option 3 as presented is in compliance with the Secretary’s Standards and would not constitute an adverse effect under Section 106. Option 3 involves all work areas to be reviewed for compliance with the Secretary’s Standards in Option 1 and Option 2, plus the additional areas noted below. The additional elements will be evaluated under Standards for Rehabilitation and particularly Standards 8 and 9, which apply to new additions and related new construction (see text in Appendix B). In general, Standards 8 and 9 state that the historic property—particularly the character-defining features—should not be destroyed or harmed by new construction. The new construction should be done so that there is the least possible loss of historic materials and so that character-defining features are not obscured, damaged, or destroyed. The new construction should make clear what is historic and what is new. The design of the new work may be contemporary or it may reference design motifs from the historic bridge. It should be compatible in terms of mass, materials, relationship of solids to voids, and color. The size and scale of the addition should be limited in relationship to the historic bridge.


October 14, 2010 47

a. Added jump spans. Option 3 includes the addition of two new spans to the east end of the historic truss. This option is proposed instead of a previously considered alternative of raising the historic superstructure by almost four feet, a change that was likely to result in a determination of adverse effect. Adding two spans of 75 feet each will result in no changes to any character-defining features, with the exception of the east abutment. The two spans, considered in this report in general form, massing, alignment, and materials, are compatible with the historic truss spans. They are tentatively designed in steel, are minimal in profile, and do not overshadow the historic structure. Their alignment is almost identical to the deck alignment of the historic bridge and their combined length of 150 feet is 25 feet less than the length of one historic span. The new pier and abutment, and the reworked existing east abutment, constitute minimal additions and alterations to the historic bridge. The new spans and east bank excavation constitute a significant change to the setting on the east side of the river, which is not part of the downtown or gateway approach and is not related to a character-defining feature. Because the historic truss is not being moved or raised, changes to spatial relationships are minimal. The conceptual design and the recommended material (steel) of the jump spans are compatible with the historic bridge. The new spans are aligned with the historic superstructure, but their size is minimal, so the relationship between the two is proportional and appropriate in size and scale. The new spans do not impact any character-defining features on the historic bridge superstructure or center pier and have minimal impact on the architectural elements of the east abutment. The new spans will have a contemporary design that will clearly differentiate them from the historic truss design. With details of design, including railings, lighting, and concrete surface treatment to be determined and reviewed, the additional spans as described in this report can be considered to be in compliance with the Secretary’s Standards and do not constitute an adverse effect.


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Option 3 – Major Rehabilitation with the Addition of Jump Spans, as presented, complies with the Secretary’s Standards. See Table 7, Analysis of Bridge 4930 Options Under Section 106 for further information.

6. Conclusion The feasibility of rehabilitating the historic Broadway Bridge (Bridge 4930) at its current location is described in this report. This report describes three alternatives that were considered: Option 1 (Minimal Rehabilitation), Option 2 (Major Rehabilitation), and Option 3 (Major Rehabilitation and the addition of Jump Spans). Each rehabilitation alternative was evaluated with a 20-year planning window to match guidance in the 2006 Historic Bridge Management Plan. It has been shown, as one would expect, that as the magnitude of the rehabilitation project increases, the serviceability of the bridge improves. It should be noted that Options 2 and 3 have costs that approach the cost of a total replacement bridge while only partially satisfying current Mn/DOT standards for a Trunk Highway. Options 2 and 3 would improve the load capacity of the bridge to current standards but would leave substandard conditions for the roadway width and the hydraulic clearance to the low steel. From a cost perspective, Option 2 (Major Rehabilitation) is the most attractive. This is largely due to the premise that the increase in load capacity will permit the bridge to have a 30 year service life moving forward. Option 1 (Minor Rehabilitation) is the second most attractive option from a cost perspective. This is largely due to the premise that without an increase in load capacity, the bridge will have only a 20 year service life moving forward. Option 3 (Major Rehabilitation with the Addition of Jump Spans) is the least attractive option from a cost perspective. After rehabilitation, the bridge is assumed to have a 40 year service life moving forward. Improvements to the channel and a slightly reduced risk of debris hits during flood events account for the service life of Option 3 being 5 years longer than Option 2. As presented in this report, each option would comply with The Secretary of the Interior’s Standards for the Treatment of Historic Properties and would not constitute an adverse effect under Section 106 (see Table 7, Analysis of Options under Section 106). As indicated in the comments for each option, additional details would require ongoing review for compliance as they are developed during a design phase, particularly for Option 3, which is not detailed at this point. The recommended option for keeping the bridge in-service on Trunk Highway 99 is Option 2. The additional costs associated with the additional Jump Spans, and corresponding excavation, in Option 3 do not offer a matching benefit in many respects. The hydraulic benefit reduces the high water elevation during flood events, but only lowers the water surface elevation by 0.30 feet. This small increment is insignificant for less than the standard


October 14, 2010 49

design frequency and will reduce the risk of debris impact only slightly. The service life is expected to be extended by a modest 10 years and the load carrying capacity is the same as that presented in Option 2. Option 1, when compared to Option 2, does little to extend the bridge’s life by only performing the minimal maintenance. The load capacity and many of the other concerns addressed by the District and Bridge Office are not addressed.


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Table 7. Analysis of Bridge 4930 Options under Section 106

Option 1 Minimal

Rehabilitation

Option 2 Major

Rehabilitation

Option 3 Major

Rehabilitation and the

Addition of Jump Spans

Character-defining features

Unusual truss design (superstructure)

Unaltered Unaltered Unaltered

Ornamental elements Unaltered Unaltered Unaltered

Other features

Substructure Unaltered Unaltered

East abutment altered to accommodate new spans

Setting Unaltered Unaltered East approach altered with added spans

New construction N/A N/A Two spans

added to east

Compliance with Secretary’s Standards

Concept is compliant

Concept is compliant. Details of repairs to abutments and pier will require review.

Concept is compliant with additional spans. Details of new construction will require review

Section 106 No adverse effect

No adverse effect

No adverse effect


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7. Appendices

Appendix A -St. Peter – Bridge 4930 – Broadway Bridge – Rehabilitation Option / Work Task Matrix (January 28, 2010)

Option Summary of

Rehabilitation Strategy

Chapter 152 Requirements

Structural Steel Deck Abutments/Pier

Minnesota River

Hydraulics Railings Sidewalk Lights Proposed

City Trail Dike / River Designation

Section 106

Review Issues

1

Preventative Maintenance and Minimal

Rehabilitation w/o Raising the Trusses

Basic rehabilitation

project to keep the bridge in

service on Trunk Highway 99

Exemption to be pursued for

historic bridge

Complete painting of truss and floor

system and sealing of

connections to protect gusset

plates

Spot repair and sealing

Pier and abutments rehabilitated

No improvement to river hydraulics.

Current river debris impact

risk maintained.

Existing sidewalk railing painted

Spot repair and sealing

of the sidewalk concrete

Ornamental light fixtures

would be rehabilitated

/ utilized

Current sidewalk and railing deficient

according to Mn/DOT

Standards

Not impacted / Navigable Waters

Light fixtures. Paint color. Concrete

Treatment. Railing

Rehabilitation

2

Major Rehabilitation w/o Raising the Trusses

More extensive rehabilitation to keep the bridge

in service on Trunk Highway

99


historic bridge

Option 1 work plus interior floor

beams and other substandard components

strengthened to provide at least HS18 Inventory

live load capacity

Current deck would be replaced

Pier and abutments rehabilitated

No improvement to river hydraulics.

Current river debris impact

risk maintained.

Existing sidewalk railing

rehabbed

Replace sidewalk concrete

when deck is replaced



/ utilized

Rehabilitated sidewalk and

railing to meet MN/DOT minimum

characteristics for a mixed use trail. Possibility

of adding a north sidewalk.



treatment. Railing

Rehabilitation. Steel details. New sidewalk.

3

Major Rehabilitation & Add Jump

Spans

Option 2 work plus the addition of jump spans to

improve Minnesota River

Hydraulics

Exemption to be pursued for the

truss spans. The jump spans

would be load path redundant


beams and other sub-standard components

strengthened to provide at least HS 18 Inventory

live load capacity. Two 75 foot jump spans (<54” tall) and designed for

HL-93 loading added on the east.

Current deck would

be replaced,

jump spans would have a normal thickness

deck

East abutment reconfigured,

existing substructures

rehabilitated. Jump span substructures

designed for 75 year service life.

River hydraulics improved.

River debris impact risk

slightly reduced.


rehabbed

Replace the sidewalk concrete when the deck is

replaced



/ utilized. Lights on the jump span would be

coordinated with those on

the truss spans.




of adding a north sidewalk

Would require reconfiguration

of the dike / Navigable Waters


treatment. Railing

rehabilitation. Steel details. New sidewalk. Design of new

spans.

4

Major Rehabilitation & Raise the Truss Spans (Pursued no

further)

Option 2 work plus raising the bridge 3.9 feet

to improve Minnesota River

Hydraulics


historic bridge


beams and other substandard components

strengthened to provide at least HS18 Inventory

live load capacity

Current deck would be replaced

Pier and abutments reconfigured and

rehabilitated

River hydraulics improved.

River debris impact risk reduced.


rehabbed

Replace the sidewalk concrete when the deck is

replaced



/ utilized




of adding a north sidewalk


Light fixtures. Paint color.

Railing rehabilitation. Steel details. New sidewalk.

Pier & new abutments may trigger

adverse affect.

TABLE 8


October 14, 2010 52

Appendix B Secretary of the Interior’s Standards for the Treatment of Historic Properties

Secretary of the Interior’s Standards for Rehabilitation As provided by the National Park Service at: http://www.nps.gov/history/hps/tps/standguide/rehab/rehab_standards.htm 1. A property will be used as it was historically or be given a new use that requires minimal change to its distinctive materials, features, spaces, and spatial relationships. 2. The historic character of a property will be retained and preserved. The removal of distinctive materials or alteration of features, spaces, and spatial relationships that characterize a property will be avoided. 3. Each property will be recognized as a physical record of its time, place, and use. Changes that create a false sense of historical development, such as adding conjectural features or elements from other historic properties, will not be undertaken. 4. Changes to a property that have acquired historic significance in their own right will be retained and preserved. 5. Distinctive materials, features, finishes, and construction techniques or examples of craftsmanship that characterize a property will be preserved. 6. Deteriorated historic features will be repaired rather than replaced. Where the severity of deterioration requires replacement of a distinctive feature, the new feature will match the old in design, color, texture, and, where possible, materials. Replacement of missing features will be substantiated by documentary and physical evidence. 7. Chemical or physical treatments, if appropriate, will be undertaken using the gentlest means possible. Treatments that cause damage to historic materials will not be used. 8. Archeological resources will be protected and preserved in place. If such resources must be disturbed, mitigation measures will be undertaken. 9. New additions, exterior alterations, or related new construction will not destroy historic materials, features, and spatial relationships that characterize the property. The new work shall be differentiated from the old and will be compatible with the historic materials, features, size, scale and proportion, and massing to protect the integrity of the property and its environment. 10. New additions and adjacent or related new construction will be undertaken in a such a manner that, if removed in the future, the essential form and integrity of the historic property and its environment would be unimpaired.

Documents

BRIDGE 4930 – SCOPING STUDY Bridge 4930 Final... · Petros Xanthakos in his text, Bridge Strengthening and Rehabilitation (Prentice Hall PTR, 1996), reports on a handful of studies