Structural Evaluation Report. Johnson Street Bridge Rehabilitation. Victoria, British Columbia

Transcription

1 Structural Evaluation Report Johnson Street Bridge Rehabilitation Victoria, British Columbia Prepared for MMM Group Limited Vancouver, BC May 2010

2 Table of Contents Page 1.0 Introduction Seismic Evaluation and Retrofit Background Seismic Design Criteria Soil Site Class Definition D Finite Element Analysis Analysis Results Lower Level Evaluation Upper Level Evaluation Structural Modifications for Mechanical Updates Foundation Strengthening Seismic Base Isolation Quantity Estimate Structural Condition Evaluation Background Structural Condition of Existing Bridges Paint System Condition Substructure and Underwater Condition Fatigue Evaluation Quantity Estimate Pedestrian/Cyclist Walkway Evaluation Background Alternative 1 New Pedestrian/Cyclist Bascule Bridge Alternative 2 Convert Existing Railway Bridge to Pedestrian/Cyclist Bascule Bridge Alternative 3 Upgrade Existing Highway Bascule Span Deck for Cyclist Use Quantity Estimate Conclusion References Appendix 36 Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page ii

3 List of Figures Figure 1 Design Earthquake and Large Earthquake Response Spectra Figure 2 3D Finite Element Model with Proposed Underpinning Figure 3 Steel Members Requiring Strengthening for Seismic Retrofit Figure 4 Steel Members Requiring Strengthening for Seismic Retrofit Figure 5 New Pedestrian/Cyclist Bascule Bridge Layout Figure 6 New Pedestrian/Cyclist Bascule Bridge Elevation Figure 7 New Pedestrian/Cyclist Bridge Approach Span Cross Section with Bascule Truss in the background Figure 8 New Pedestrian/Cyclist Bridge Bascule Span Cross Section Figure 9 New Pedestrian/Cyclist Bascule Bridge Cross Section at Counterweight Pit List of Tables Table 1 Reactions for Preliminary Column and Drilled Shaft Design Table 2 Steel Members Requiring Strengthening for Seismic Retrofit Table 3 Pay Items and Quantity Estimate for the Seismic Evaluations Table 4 Fatigue Evaluation for Tension Members Table 5 Pay Items and Quantity Estimate for Condition Rehabilitation Table 6 Pay Items and Quantity Estimate for Pedestrian/Cyclist Walkway Alternatives Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page ii

4 1.0 Introduction The existing vehicular and railroad Johnson Street bascule bridges were built in 1924 and are currently owned and operated by the City of Victoria, British Columbia. The City intends to move forward on the Johnson Street Bridge Project by performing a cost comparison between rehabilitating the existing bridges and replacement options. Our work includes the structural analysis and preliminary conceptual engineering related to three specific tasks. The first is the seismic analysis of the existing vehicular and railroad bascule bridges and developing a conceptual seismic retrofit scheme. The second is to perform a fatigue evaluation of the existing vehicular bridges superstructure components and evaluate if deterioration repairs need to be made to either bridge to extend their service lives. The third is to prepare conceptual designs for two (2) new pedestrian/cyclist walkway alternatives, and to evaluate replacing the highway bascule span steel grid decking to better accommodate cyclist. 2.0 Seismic Evaluation and Retrofit 2.1 Background The existing highway bridge was designed in accordance with the Engineering Institute of Canada 1918 Specifications for Highway Bridges. The existing railway bridge was designed in accordance with the Canadian Pacific Railway Company Bridge Specifications and the Engineering Institute of Canada 1918 Specifications for Machinery. The Strauss type trunnion bascule bridge was designed by the Strauss Bascule Bridge Company of Chicago, Illinois. The steel plate girder approach spans and all foundations were designed by the City of Victoria Engineering staff. (Ref. 1, 2, 3, 4 & 5) The existing highway and railway bascule bridges are supported on shared Main Pinion and Counterweight Piers. These concrete wall type piers are connected at the top with three concrete tie beams. Both foundations are supported by a grid of timber piles driven to bedrock (or practical refusal). A concrete wall type Rest Pier was founded directly on bedrock, as are the east and west abutments. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 1

5 Delcan previously analyzed the condition of the existing structures and presented their findings to the City in February 2009 (Ref. 6). As a starting point for the current study, the seismic alternatives studied, the seismic retrofit strategies proposed and the conclusions reached were reviewed. Some of those strategies that were deemed applicable were assessed further in developing our retrofit strategy. This seismic evaluation was based on the best available information. No additional geotechnical soil drilling, field inspections of the structural members or material testing were performed. 2.2 Seismic Design Criteria The Province of British Columbia has the highest earthquake activity in Canada particularly in the southwest region. Specifically the seismic hazard risk in Victoria is the highest in Canada. The risk comes not only from crustal and subcrustal earthquake activity but also from the Cascadia Subduction Zone which creates the potential for what is sometimes known as a Megathrust Earthquake. Site specific soil properties must be considered when evaluating structure behavior because soft soils can greatly amplify the ground shaking. The Seismic Design provisions of the Canadian Highway Bridge Design Code CAN/CSA-S6-06 (Ref. 7) and the British Columbia Bridge Standard and Procedures Manual (Ref. 8) are based primarily on the 1994 AASHTO LRFD Bridge Design Specifications (Ref. 9). It is based on a single-level seismic design procedure using peak horizontal ground accelerations having a 10% probability of being exceeded in 50 years. This correlates to a 475 year expected return period. Three Importance categories are identified based on social/survival and security/defense requirements. An elastic seismic response coefficient is calculated that includes an Importance Factor. This coefficient is used together with element specific response modification factors to calculate the member load effects. The performance requirements for the different Importance Categories is implied in the procedure rather than verified. Seismic standards are constantly evolving as new knowledge and understanding of the seismic hazard becomes available. Since the proposed replacement bridge option would be designed Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 2

6 for a 100 year lifetime and the retrofit option would be designed for a 40 year bridge life extension, it was deemed to be very important to follow the most current industry seismic design state of practice. The most current industry standard for bridge design in North America is the 2007 AASHTO LRFD Bridge Design Specifications 4 th Edition with the 2008 Interim Revisions Sections 3.10, and Section 10 Appendix A10 (Ref. 10). This code has evolved considerable since the 1 st Edition in 1994 and incorporates recent experience, best practices and research results. As requested, two seismic evaluations were carried out for the bridge structure, including a lower level Essential Bridge Importance Category, and an upper level Critical Bridge Importance Category. In the AASHTO LRFD Bridge Design Specification the Design Earthquake has a 7% probability of exceedance in 75 years which corresponds to approximately a 1000 year expected return period. The design earthquake motions and forces specified are based on a low probability of their being exceeded during the normal life expectancy of a bridge. The design response spectra were based on the AASHTO LRFD Bridge Design Specification, which considered the location specific, ground-motion mapping of the peak ground acceleration coefficient, the short-period (0.2 second) acceleration coefficient, and the long-period (1.0 second) acceleration coefficient. The Design Response Spectrum is developed from these coefficients, each modified by its corresponding Site Factor. The requirements of the Essential Bridge Importance Category allows moderate damage but still provides access to Emergency Vehicles and for security/defense purposes almost immediately after the Design Earthquake, and meets the general criteria of having a low probability of collapse. The performance requirement of the Critical bridge category is for the bridge to remain open to all traffic after the Design Earthquake. In addition, a Critical bridge is to be accessible to Emergency Vehicles and for security/defense purposes almost immediately after a Large Earthquake, defined as having approximately a 2500 year expected return period (3% probability of exceedance in 75 years). The AASHTO Specifications do not currently specify or give specific guidance on vertical ground accelerations values or percentages. The Canadian Highway Bridge Design Code Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 3

7 considers the load factors to indirectly account for vertical accelerations. Our analysis is based on applying two-thirds of the horizontal ground acceleration as an approximation of the vertical ground motion. This is consistent with general engineering practice and is in keeping with the general guidance given in the Canadian Highway Bridge Design Code Commentary for approximating vertical accelerations. 2.3 Soil Site Class Definition The Seismic Site Classes are assigned based on the average soil shear wave velocity in the 30 m of soil and/or rock directly beneath the foundations (Vs 30 ). Each soil and rock unit has a specific shear velocity (Vs), which is weighted proportional to the thickness of the unit in the 30 m of interest to calculate the Vs 30. The east and west abutments are founded on bedrock and are identified as Site Class A. The Rest Pier is assumed to bear on or near to bedrock and is identified as Site Class B. The Main Trunnion and Counterweight Piers are supported on timber piles through primarily soft silty clay to dense till or bedrock and are identified as Site Class D. Since the bascule trusses, counterweight towers and counterweights are supported on these two piers the seismic evaluation is based on spectral acceleration values for Site Class D. The Design Earthquake and Large Earthquake response spectra used for the seismic analysis are shown in Figure 1. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 4

8 Figure 1 Design Earthquake and Large Earthquake Response Spectra for Johnson Street Bridge, Victoria, BC, latitude = deg. and longitude = deg. with 5% damping and Site Class D D Finite Element Analysis The existing structures were evaluated under the AASHTO LRFD Seismic Design Criteria. The MIDAS structural analysis computer program (Ref. 11) was used to make this evaluation. The MIDAS input files developed by Delcan were used for this evaluation. The model only included the highway and railroad bascule spans of the bridge. The geometry of the actual trusses was considered in the model. All members were modeled with beam elements having 6-degrees of freedom at each node. The beam elements were placed along the centerlines of the actual bridge members between joints. Most truss member joints were modeled as a moment-resisting joint, except where it was necessary to release certain forces to model support conditions The analysis only considered the bascule spans in the closed position. Member mass centroid and support elevations were placed at elevations similar to the actual condition on the existing Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 5

9 bridge spans. Structural strengthening, Option 3, proposed by Delcan was reviewed and adopted in this analysis. The strengthening included transverse bracing members between the trusses and between the highway and railroad spans. Energy dissipating eccentric bracing was also included in the model. The 3D finite element model used for the seismic analysis is shown in Figure 2. The steel bracings proposed by Delcan are highlighted in red. As shown in the figure, a revised substructure underpinning design was used for this retrofit analysis. Figure 2 3D Finite Element Model with Proposed Underpinning. Multimodal spectral method was used for the seismic analysis. Sixty (60) mode shapes were considered and the member forces were estimated by combining the respective response from the individual modes using the Complete Quadratic Combination (CQC) method. Two levels of seismic analysis were considered, including the design response spectra for 7% probability of exceedance in 75 years (1000-year EQ) and for 3% probability of exceedance in 75 years (2500-year EQ). The bridge was classified as essential in the 1000-year EQ analysis and as critical in the 2500-year EQ analysis Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 6

10 Three (3) orthogonal directions of seismic excitation were applied to the model, i.e. longitudinal, transverse, and vertical directions. Each direction corresponded to the bridge axes. The vertical seismic excitation was a two-third of the horizontal seismic excitation. Load combination cases were generated based on the AASHTO LRFD specification using the 100%-30%-30% rule and the square-root of the sum of the squares (SRSS) method. In addition to the masses and dead loads included in the Delcan model, reactions from the east approach girder spans were added at the support elevation to simulate the actual loading on the counterweight pier. Eight (8) circular columns supported by larger-diameter drilled shafts anchored into bedrock were used for the underpinning of the main trunnion and counterweight piers. The tip elevation of the drilled shafts used in the Delcan model was carried on for the analysis. The elevation for the change from drilled shaft to concrete column was estimated to be approximately at the mudline. Each north and south pair of column and drilled shaft elements supports a concrete cross beam for a total of 4 cross beams. These reinforced cross beams will be cast directly against each face of the existing piers and then post-tensioned transversely together to form a sandwich with the existing concrete. The cross beams will then be post-tensioned longitudinally. The cross beams were sized by assuming that the reactions from the bascule spans are entirely transferred to the substructure underpinning during an earthquake event. After post-tensioning the cross beams, the existing concrete stem walls can be horizontally saw-cut through, leaving a small gap (approximately 150 mm) just below the cap beams to isolate the underpinning from the existing pier foundations. Longitudinal concrete struts were included between the piers similar to the existing. 2.5 Analysis Results Lower Level Evaluation Structural evaluation results for the Essential Bridge Importance Category indicate that a number of steel members need to be either replaced or strengthened and the main pinion and counterweight piers need to be underpinned to withstand the design seismic earthquake which has a 7% Probability of Exceedance in 75 years and approximately a 1000 year expected return period. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 7

11

12 From these seismic analyses, the fundamental period of the underpinned structures equaled 2.0 seconds. A response modification factor of 2.0 was used in the column-drilled shaft preliminary design based on the AASHTO LRFD specification. Load factors were also based on the AASHTO LRFD specification. The controlling reactions and factors are shown in Table 1. Table 1 Reactions for Preliminary Column and Drilled Shaft Design. Lower Level Upper Level Shear Moment Vertical Torsion V M + P T kn kn m kn kn m Column Drilled shaft Column Drilled shaft Deadload factor = 1.25 EQ load factor = 1 Overstrength factor = 1.3 for drilled shaft design Based on these seismic analysis results, the underpinning requires 1.8-m diameter columns supported by 2.4-m diameter drilled shafts. The column-drilled shaft lengths used in the analysis was agreed to by the Geotechnical Engineer. The vertical steel reinforcing rebars were about 3.7% of the gross section area of the column and were about 2% of the gross section area of the drilled shaft, respectively. The steel reinforcing amount was estimated to provide adequate strength and ductility with a flexural failure mode. The seismic analyses also showed that a number of truss members and counterweight tower members required strengthening to keep stresses below the expected stress limits. The tensile yield strength was estimated to be 205 MPa and the compression stress limit was approximately 135 MPa. Cover plates were proposed for the identified members. The steel members requiring strengthening are highlighted in red and green as shown in Figures 3 and 4. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 8

13 Figure 3 Steel Members Requiring Strengthening for Seismic Retrofit. Figure 4 Steel Members Requiring Strengthening for Seismic Retrofit. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 9

14 2.5.2 Upper Level Evaluation Structural evaluation results for this higher level earthquake for a Critical Bridge Importance Category indicate that a number of additional steel members need to be either replaced or strengthened. The additional steel members are highlighted in yellow as shown in Figures 3 and 4. The size of the main pinion and counterweight pier underpinning columns and drilled shafts also needs to be increased. This evaluation included limited damage from the Large Earthquake, defined as a 2,500 year expected return period event. From these seismic analyses, the fundamental period of the underpinned structures equaled 1.6 seconds. A response modification factor of 1.5 was used in the column-drilled shaft preliminary design based on the AASHTO LRFD specification. Load factors were also based on the AASHTO LRFD specification. Based on these seismic analysis results as shown in Table 1, the underpinning requires 2.1-m diameter columns supported by 2.7-m diameter drilled shafts. The vertical steel reinforcing rebars were about 6% of the gross section area of the column and were about 4% of the gross section area of the drilled shaft, respectively. The steel members required strengthening for seismic retrofit are summarized in Table 2. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 10

15 Table 2 Steel Members Requiring Strengthening for Seismic Retrofit. Highway Structure Railroad Structure South Truss South Truss Floorbeam/truss Joints 0, 4, 8 Floorbeam/truss Joints 14, 18 Floorbeam/truss Joints 2, 6, 12 Bracing Floorbeam/truss Joints 10 Bracing Floorbeam/truss Joints 14, 18 Bracing 16 20a Floorbeam/truss Joints 16 Bottom chord truss Bracing Bottom chord truss Bracing Bottom chord truss 8 10 Bracing 16 20a Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss 8 10 Bottom chord truss Bottom chord truss Bottom chord truss North Truss North Truss Floorbeam/truss Joints 14, 18 Floorbeam/truss Joints 14, 18 Bracing Bracing Bracing Bracing Bracing 16 20a Bracing 16 20a Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss 8 10 Bottom chord truss 8 10 Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Bottom chord truss Highway Floor Railroad Floor Floor beams Floor beam FB7 lower lateral bracing Floor beam 4 FB6, FB5, FB2 Floor beam FB4 Floor beam FB3, FB1 lower lateral bracing Tower over Main Trunnion and CT WT Piers Tower over Main Trunnion and CT WT Piers Diagonal Tower Leg Diagonal Tower Leg Vertical Tower Leg 19 20a Vertical Tower Leg 19 20a Operating Link 9 20 Operating Link 9 20 Ct Wt Truss Ct Wt Truss Ct Wt Truss Vert Ct Wt Truss Vert Ct Wt Truss Ct Wt Truss Ct Wt Truss Ct Wt Truss Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 11

16 2.6 Structural Modifications for Mechanical Updates Recommended mechanical element replacement includes the span drive machinery including the open gearing; the span support machinery including bascule span heel trunnions, counterweight trunnions and the link pins; and the span lock machinery. In discussion with the mechanical engineer it was indicated that none of these mechanical repairs would require structural modifications to the existing bridge for installation. Through the use of stronger modern materials and because of the conservatism of the original design the trunnions size and fit can be replicated without any structural modifications required. The Rest Pier span-lock mechanisms are subjected to uplift forces under seismic ground motions. Although the codes do not currently provide any specific recommendations or guidelines on vertical acceleration effects, a two-thirds ratio of vertical to horizontal is commonly used in practice. Our analysis is based on applying a vertical response spectrum that is twothirds of the horizontal response spectrum ground motion. The three orthogonal ground motion results are then combined to obtain the maximum design response. Under the calculated maximum factored design uplift force (approximately 1100 kn for the highway bridge and 850 kn for the railway bridge) the lock bar and guide wheel pin would fail. By replacing these span lock assemblies the designer will have the flexibility to integrate the new span lock design with modifications to the pier to handle seismic loads in the other directions as well. 2.7 Foundation Strengthening In 1978 repairs were completed at the north end of the Rest Pier per the Graeme & Murray plan requirements (Ref 12). The plans call for cracks and voids to be pressure grouted during the repair. The plans also require that the repaired wall area be reinforced with a 12 inch thick reinforced concrete layer attached to the wall face. A note on these plans indicate that the weep holes shown on original plans to drain the formed pier voids have not been found and the void existence is not confirmed. These formed internal cavities are shown on the 1920 plans for the Rest Pier, Main Trunnion Pier and the Counterweight Trunnion Pier. A 1990 Ocean Marine Report (Ref. 13) indicates concrete erosion and voids up to 305 mm deep at the Main Trunnion and Counterweight Trunnion Piers. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 12

17 The underwater concrete forming the pier footings is identified in a technical paper from 1924 (Ref. 5) as being a 1:2:3 concrete mix design. This would correspond to approximately a 14 MPa (2000psi) concrete compressive strength. Since the original design concrete strength is not known, the existing pier and abutment concrete should be visually inspected and concrete cores should be taken and tested for strength at the start of final retrofit design to verify capacity. The presence or absence of the formed cavities shown on the original design plans should also be investigated at that time. Roadway approach global stability analysis by the Geotechnical Engineer indicated a need for abutment stabilization. Abutment seismic retrofitting will consist of rock anchors drilled on an inclined angle through the deck, installed and anchored to the bridge seat to counter overturning seismic forces. Rock anchors will also be used to provide lateral stability for the Rest Pier. This can consist of two rows of vertical anchors supplemented with high angle anchors drilled through the base of the stem to counter any potential base sliding. 2.8 Seismic Base Isolation Due to the massive load being supported at the four bearings for each bascule span and counterweight system it is impractical to install isolation bearings of sufficient size. Any isolation system would have to provide adequate flexibility during a seismic event, but provide sufficient stiffness to withstand vehicular breaking and wind forces during normal operations. The bascule span is also subjected to higher wind loads when in the raised position. The mechanical system operational tolerances, which cannot accommodate displacements caused by wind or other loads, also preclude the use of a typical bridge isolation system. Seismic base isolation was not considered any further. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 13

18 2.9 Quantity Estimate Quantity estimates for the lower level and upper level seismic evaluations are shown in Table 3 As shown in the table, a comparison of quantities between the two retrofit levels are made. Table 3 Pay Items and Quantity Estimate for the Seismic Evaluations. Lower Level Upper Level Pay Items Description Unit Quantity Quantity % Diff. Items to be removed Concrete tie beams between the piers m Items to be installed Structural steel for strengthening tons Rock anchors (#57 Dywidag bar) West abutment 6 m socket m Rest pier 7.5 m socket m East abutment 7 m socket m Concrete cap beams Concrete 35 MPa m Reinforcing steel weight 400 MPa kg Post tensioning steel weight 1860 MPa kg Concreted columns Concrete column length m Concrete 35 MPa m Reinforcing steel weight 400 MPa kg Drilled shafts Rock socket length m Overburden shaft length m Drilled shaft length m Concrete 35 MPa m Reinforcing steel weight 400 MPa kg Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 14

19 3.0 Structural Condition Evaluation 3.1 Background The existing Johnson Street Bridges were opened to traffic over 86 years ago in January In 1966, the wooden decking of the bascule spans was removed and replaced with open steel grating. It is believed that the wooden deck of the highway counterweight span was replaced with the current concrete deck at the same time. In 1979 (Ref. 14) the railway bridge floorbeams, stringers and floor system lateral bracing were replaced. Also in 1979 (Ref. 12), concrete repairs were made to the eroded areas, between the low and high water lines, on both the east and west faces near the north end of the rest pier, and to a mud line cavity at the northeast corner. Repair plans called for additional strengthening of the repaired area with a 305 mm thick reinforced concrete, full height facing. The bridge was also painted the current blue color at that time instead of the historic black color. In the summer of 1990, Graeme & Murray conducted a structural inspection of the highway bridge; B. H. Levelton & Associates inspected the paint condition on both bridges; and Ocean Marine conducted an underwater inspection (Ref. 15). In early 1998, Graeme & Murray conducted a structural inspection of the highway bridge and Levelton Engineering performed a bridge painting assessment. Structural repair plans for the highway bridge were prepared in 1999 (Ref. 16) replacing the approach span concrete decks and making some minor structural steel revisions. In June 2008, Delcan Corporation performed a comprehensive visual structural inspection of the bridge and Stafford Bandlow Engineering performed a visual inspection of the mechanical and electrical systems. A study was then conducted to establish the scope and costs associated with either rehabilitating the bridge, including any strengthening that would be required to withstand a seismic event, or replacing the bridge. The study s findings and recommendations are contained in the Bridge Condition Assessment Report, dated February Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 15

20 3.2 Structural Condition of Existing Bridges Three available reports (Ref. 6, 13 & 15) document the physical condition of the highway and railway bridge structural components. The most recent repairs more than a decade ago in 1999 (Ref. 16) replaced the concrete decks of the highway approach spans to address some of the major concerns from the 1990 and 1999 highway bridge condition reports. The most recent repairs to the railway bridge (Ref. 14) were more than three decades ago in 1978, when the floor beams, stringers, and floor system lateral bracing were replaced. The 2009 Delcan report documented the condition of steel member corrosion, providing comments and photos. The highway bridge has experienced extensive member corrosion especially in the floor beams and stringers along the top and bottom flanges that has resulted in section loss. Built-up truss members have localized areas of pack rust between the elements. Local areas of heavy section loss occurs at some gusset plates, bracing connections, and rivets. Horizontal gusset plates have extensive corrosion. Significant corrosion was also observed on the bridge bearing plates. The railway bridge has moderate to severe corrosion along the bottom flanges of the stringers and floorbeams with local areas of section loss. Section losses including holes though components and connection plates were also observed at a number of locations in the bottom chord of the lift span. One angle leg of the south truss vertical at the east end of panel 3, (Node 6 on original drawings), has a reduction groove with an approximately 50% section loss and a through hole. Detailed field inspection should be carried out as one of the early tasks during final design to identify the amount and location of member section loss due to corrosion. Details to restore structural capacity should be developed for each type of section loss identified. During the rehabilitation construction, after all rust is removed, the remaining section properties in the identified areas should be field determined to confirm the adequacy of the rehabilitation repair design assumptions. Rivets should also be inspected to determine if they are tight and in good condition. Any questionable rivets should be removed and replaced with ASTM F1852 Tension Control Structural Bolt/Nut/Washer Assemblies with the round (button) heads placed on the most visible side of the structural member. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 16

21 Structural steel repairs will include hands-on inspection, rivet removal, replacement steel, match-drilling holes to attach new material in the field, and installing new bolts. Since the full extent of the needed repairs will only be known after a detailed field inspection, and since the work is labor intensive, it is being estimated as part of this study, on a lump sum basis. 3.3 Paint System Condition Original 1921 structural steel shop drawings (Ref. 3) indicate a linseed oil based paint system consisted of one shop coat of red lead primer, one field intermediate coat of brown graphite and a field top coat of black graphite. The 1990 B.H. Levelton Paint Evaluation Johnson Street/Bay Street Bridges Report (Ref. 13) indicates that the bridge was painted its current blue-colored alkyd paint in The paint system used was a red lead primer followed by a light blue alkyd topcoat. The report notes areas beneath the deck that needed attention. It also noted paint failure and rusting on edges of lattice work and inside of the girders. The report recommended a maintenance painting program with special precautions regarding treating the existing lead paint as hazardous waste. The 1998 Levelton Engineering Johnson Street Bascule Bridge and Side Span Maintenance Painting Report (Ref. 15) indicates that city crews had been maintaining the bridge paint. The report discussed environmental restrictions including containment for cleaning and painting, worker safety requirements and disposal of hazardous waste. Various options for cleaning and the materials available for coating, were discussed. Comparative cost data were provided but no specific painting recommendations were given. The 2009 Delcan Johnson Street Bridge Condition Assessment Report indicates that the paint coating system had failed at the time of their inspection. As requested, the Termarust paint overcoat system (Ref. 17) was evaluated as part of this study. Promotional literature pitches this is an overcoat system that requires less expensive surface preparation while stopping any further corrosion with an active corrosion inhibitor that penetrates into crevice corroded and pact rusted areas that are typical of built-up members. The Termarust paint system has a 5-year warranty and claims an average expected 25-year Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 17

22 service life depending on dry film thickness. The testing performed by the manufacturer has indicated a coating erosion rate of approximately 1 mil every 6 years. The "Single Coat" Termarust system has the following 7 steps: 1. SSPC-SP1 Solvent Cleaning to remove oil and grease 2. SSPC-SP12-WJ4 High Pressure Water Cleaning 3. Chlor*rid soluble salt remover 4. Apply Termarust TR2200 Penetrant/Sealer at connections 5. Apply a calk coat of TR2100 Self-Priming Topcoat to all edges at connections 6. Spot prime bare steel areas with TR2100 Self-Priming Topcoat 7. Fully overcoat with Termarust TR2100 Self-Priming Topcoat The term Single Coat is used by the manufacturer since product coats can be applied wet-onwet. Surface preparation with pressure water spray still requires a full containment enclosure, worker health safety measures, and provisions for hazardous waste disposal since some lead based paint will likely be removed. Full enclosure would also be required for the paint system application for overspray and VOC containment. One of the biggest differences of the Termarust system is specifying limited cleaning with pressure water spray instead of SSPC- SP10 Near-White abrasive blast cleaning. The abrasive blast cleaning is labor intensive and creates additional hazardous waste that must be contained, collected, and disposed of. In the product case histories, they have one truss bridge (used for pedestrians only) that still looks good 10 years after painting. It should be noted that the owner required preparation to include sandblasting to a 'near-white' surface condition prior to painting. This is the most costly part of conventional three-coat zinc-based bridge painting systems. Their self appraisal of other Case Histories with rust staining (after as short a time period as 19 months) is that the product has chemically stopped further corrosion. The staining is explained as either areas where the wash water was not completely removed before painting, or areas that were "very difficult (if not impossible) to clean and paint". Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 18

23 The biggest disadvantage to the system is the long drying time and the soft nature of the coating. This coating would be inappropriate on those members that can be directly accessed by pedestrians and cyclist that are crossing the bridges. In order to extend the bridges service life another forty years, we recommend that the existing structure be SSPC-SP10 Near-White abrasive blast cleaned to remove all existing paint and as much of the rust as is accessible. Full containment of the work area should be provided with all blast debris properly disposed of. Cleaning should be followed by careful inspection to identify corroded areas that need to be repaired. A conventional three-coat zinc-based bridge painting system should then be applied with special attention given to those areas that tend to trap moisture and debris. It should be noted that the cleaning and painting of the bascule spans needs to be undertaken with the span in an open upright position to allow uninterrupted marine traffic 3.4 Substructure and Underwater Condition Original design plans by the city (Ref. 1) indicate that the Rest Pier, Main Trunnion Pier and Counterweight Pier were constructed using timber caissons. A 1924 paper (Ref. 5) prepared by the City Engineer, provides further information on the construction methods. After the timber caissons were sunk into position, the inside was excavated to foundation level using dredging techniques. The rest pier sheet piles were driven around the timber caisson down to the very uneven rock surface - up to a 12 foot height difference between the north and south ends. Excavation down to the rock surface was completed using a high pressure water jet operated by a diver. After the cleaned bedrock surface was inspected by a diver, underwater concrete was placed to form the foundation and seal the bottom of the caisson. At the main trunnion and counterweight piers, timber piles were driven before placing underwater concrete for the footings. The underwater concrete used was a 1:2:3 mix proportion which typically would result in around a 2,000 psi (14 MPa) 28-day compressive strength. After the underwater concrete gained sufficient strength, the caissons were dewatered to allow the pier stems to be formed in the dry. The concrete mix for the pier stems is not indicated in the original plans or in the 1924 paper. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 19

24 Since the piers are primarily a gravity section design with little to no reinforcing, the concrete strength is not likely to be much higher than 14 MPa. Repairs at the north end of the rest pier were completed in 1979 including pressure grouting of cracks and voids. The 1978 plan (Ref. 12) also required that the repaired wall areas on both the east and west faces be reinforced with a 305 mm thick reinforced concrete layer attached to the wall face. Photos of the west face show this reinforcing in place to some distance above the waterline. Later inspection reports do not indicate any further issues in this area. The 1990 underwater inspection report by Ocean Marine (Ref. 13) indicates several areas of voids or concrete erosion at the three piers. At the counterweight pier there are a number of areas of concrete erosion up to 305 mm deep at the south end on both the east and west faces 0.6 m to 2.4 m below the waterline. The main trunnion support pier has areas of concrete erosion up to 200 mm deep and the counterweight pier has undermining at the mudline. The Delcan report (Ref. 6) indicates considerable concrete erosion at the main trunnion support pier just at and below the waterline. The report also notes minor cracking and efflorescence throughout the substructures but limited spalling. During final design for rehabilitation, it is recommended that concrete samples be taken in the areas of maximum erosion and laboratory tested for strength and durability performed on these samples. Depending on the results of the testing, consideration should be given to reinforcing the pier faces against additional erosion between the mudline and high waterline by the use of a concrete facing similar to what was previously done in Fatigue Evaluation The seismic 3D finite element model was also used for fatigue evaluation. Only the highway structure was evaluated. Live-load-induced fatigue was evaluated in the highway bascule bridge in accordance with Section of the Canadian Highway Bridge Design Code CAN/CSA- S6-06 (Ref. 7). The fatigue vehicle is the BCL-625 Truck in accordance with the British Columbia Ministry of Transportation Bridge Standards and Procedures Manual Volume 1 Clause (Ref. 8). The truck wheel loads were applied to the FE model as moving loads Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 20

25 across the structure. Both forward and backward directions were considered. One of the truck wheel lines was positioned at 0.6 m from the edge of the roadway. Average Daily Traffic (ADT) is over 30,000 vehicles. The Average Daily Truck Traffic (ADTT) is not known so a truck percentage of 10 percent was used which is consistent with an urban roadway. In the early years of the bridge s life, it was subjected to a mix of railway, streetcar and truck loads. The original 1921 plans indicate it was designed for three design live loads. The first was a Cooper E50 railway loading, (down the center of the bridge); the second for 45 ton streetcars, (a track on either side of the rail track); and the third was a 25 ton highway truck. The tracks for the railway and streetcar were likely removed at the time the open steel grating was installed in The Canadian Highway Bridge Design Code specifies a design life of 75 years for the fatigue evaluation of new bridges. Since the bridge has already seen 86 years of service and this study is evaluating extending the life another 40 years, a fatigue design life of 126 years was used in estimating the number of live load stress cycles. This may be conservative since the current truck volume is likely much higher than when the bridge first opened. However, it should be noted, that the mass of a Cooper E50 railway loading, (two locomotives without the trailing cars), of 3,160 kn is considerably higher than the current BCL- 625 design truck which is only 625 kn. The calculated fatigue stress ranges for the members under tension from the BCL-625 truck loading were calibrated. Stress ranges from stress reversal were also considered. These were compared to the fatigue stress range resistance for Detail Category D, base metal at the net section for riveted connections. The fatigue resistance was adequate for all members analyzed as shown in Table 4. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 21

26 Table 4 Fatigue Evaluation for Tension Members. Steel Member Max. Stress Min. Stress Range 0.52fsr Resistance <Fsr? MPa MPa MPa MPa MPa Bottom Chord OK Bottom Chord OK Bottom Chord OK Bottom Chord OK Bottom Chord OK Bottom Chord OK Vertical Element OK Vertical Element OK Vertical Element OK Diagonal Element OK Diagonal Element OK Diagonal Element OK Diagonal Element OK Since the fatigue resistance can be compromised by member deterioration, it is recommended that all fatigue prone details be monitored by regularly scheduled inspections. This analysis only considered live-load-induced fatigue. Regularly scheduled detailed hands-on inspection of connections should be carried out to check for displacement-induced stress cracking. 3.6 Quantity Estimate Quantiy estimate and pay items for this condition rehabilitation is shown in Table 5. Table 5 Pay Items and Quantity Estimate for Condition Rehabilitation. Pay Items Description Unit Quantity Steel repairs LS 1 Blast clean and paint steel LS 1 Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 22

27 4.0 Pedestrian/Cyclist Walkway Evaluation 4.1 Background The Regional Growth Strategy includes a desire to develop transportation alternatives. The Galloping Goose Trail is an existing multi-use trail that leads up to the Johnson Street Railway Bridge on the western approach. A study was performed by Graeme & Murray in 2000 to evaluate the feasibility of various alternatives to extend this existing multi-use trail with a multiuse trail across the Johnson Street Bridge. The city requested that the feasibility for this connection be reevaluated. As a starting point for the current study, we reviewed the alternatives studied and the conclusions reached in this 2000 study. Only the previous alternatives that were considered viable and practical were considered further in this study. The three alternatives considered in this study are: Providing a new pedestrian/cyclist bascule bridge Converting the existing railway bridge to pedestrian/cyclist bridge Upgrading the existing highway bascule span deck surface for cyclist use 4.2 Alternative 1 New Pedestrian/Cyclist Bascule Bridge The 2000 Graeme & Murray study (Ref. 18) examined the feasibility of providing a 5 m wide multi-use trail across the Johnson Street Railway Bridge. One of the options considered was to cantilever the walkway off the north side of the existing railway structure in order to provide for the multi-use trail while still maintaining passenger train service. This previous study concluded that cantilevering the 5 m multi-use trail off the north side of the moveable the Railway Bascule Span was not viable. As a result, a new completely separate Pedestrian/Cyclist Bascule Bridge Span Concept was developed as an alternative. The concept consists of a 3-dimensional truss frame, triangular in cross section, with truss panel lengths matching the existing railway bascule truss as shown in the Cycling and Pedestrian Walkway Feasibility Study Plans (Ref. 19). The separate bascule bridge span was then connected back to walkways cantilevered off from the east and west fixed approach spans. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 23

28 The currently proposed seismic rehabilitation underpinning at the existing Main Trunnion and Counterweight Piers requires drilled shafts to the north of the existing pier footings, (see Section 2.0). The close proximity of the previously proposed separate bascule bridge concept to the existing railway bridge would conflict with this proposed seismic rehabilitation underpinning. Adequate separation between the old and new structure foundations is needed both for constructability and to keep them from adversely interacting during a seismic event. To provide adequate separation, a trail alignment to the north was selected that provides a 12.5 m horizontal clearance between the structures. Wilkinson Eyre Architects developed a new Pedestrian/Cyclist Bascule Bridge layout and concept based on the previously developed truss scheme presented in the Graeme & Murray report (see Figures 5 thru 9). Figure 5 New Pedestrian/Cyclist Bascule Bridge Layout Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 24

29 Figure 6 New Pedestrian/Cyclist Bascule Bridge Elevation Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 25

30 Figure 7 New Pedestrian/Cyclist Bridge Approach Span Cross Section with Bascule Truss in the background Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 26

31 Figure 8 New Pedestrian/Cyclist Bridge Bascule Span Cross Section Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 27

32 Figure 9 New Pedestrian/Cyclist Bascule Bridge Cross Section at Counterweight Pit The development of the layout included an evaluation of how best to meet existing grades and sections on the approaches. The on-grade approaches and modifications to tie-in to the existing multi-use trail are not included in this structural evaluation, (refer to the separate Architectural Report). The New Pedestrian/Cyclist Bridge will have a width of 5.0 m. The 45 m long heel trunnion truss bascule span will cross over the shipping channel in its current location. The truss members will consist of structural steel tubing sections. Floorbeams will be W410x85 rolled steel sections supporting W200x27 stringers. Both the east and west approach spans will consist of 46 m steel deck girder spans consisting of three lines of W1090x883 girders and W200x27 edge stringers. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 28

33 A concrete trunnion support pier with a counterweight pit will be located on the east side of the channel. The pit is necessary since the counterweight dips below the high water level when the span is in the open position. The concrete trunnion support pier will also include a chamber to accommodate mechanical and electrical equipment for the span operation. The rest pier on the west side of the channel will consist of two concrete columns supporting a concrete cap beam. Wilkinson Eyre Architects developed aesthetic concepts for both of these piers, (see Figure 6). The existing fenders will be extended past the new piers to provide protection again vessel collision. Fender design was not evaluated and is beyond the scope of this study. The structural weight and centroid of the bascule span were calculated and provided to the mechanical and electrical engineers for conceptual development of the span operating equipment. With the current geometry of the structural members and counterweight, the span is out of balance. Based on preliminary structural sizes the span centroid is located 1.4 m horizontally toward the channel from the trunnion and vertically 1.6 m above the trunnion. Further analysis and cross-discipline coordination will be required to determine the modifications required and what the visual and mechanical impacts will be. Mechanical and electrical components are not included in this structural evaluation, (see the separate Machinery Rehabilitation Feasibility Study). The member sizes used in this analysis, were taken from the previous Graeme & Murray study and not verified for structural adequacy. Conceptual fixed approach span member sizes were developed to determine the preliminary foundation loadings. These were provided to the geotechnical engineer for coordination in selecting foundation types. Foundation types were selected in part based on the data from soil borings that were recently performed along the same alignment (Ref. 20). The western approach is anticipated to be supported by MSE walls. The rest pier will be supported on two 0.9 m diameter drilled shafts socketed into bedrock. The concrete trunnion support pier and counterweight pit will be supported on four 0.9 m diameter drilled shafts socketed into bedrock. The eastern abutment will be supported on four 0.9 m diameter drilled shafts socketed into bedrock. The deck surface will be a lightweight fiberglass pedestrian grating with a slip resistant surface finish. The grating main bearing bars will span perpendicular to the walkway direction. Fiberglass has the advantage of reducing the dead load and therefore the demand on the Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 29

34 mechanical and electrical operating equipment. It also has the benefits of high strength, is corrosion resistant - well suited to a salt air environment, is low maintenance, and is nonconductive. A 1.4 m high steel bicycle barrier railing will be provided on either side of the walkway for public safety. 4.3 Alternative 2 Convert Existing Railway Bridge to Pedestrian/Cyclist Bascule Bridge This alternative will replace the existing railway bridge with a pedestrian/cyclist walkway bridge thereby eliminating the Commuter Rail form of alternative transportation. The existing railway bascule bridge and fixed east and west approach spans will be converted into a pedestrian and cyclist - friendly multi-use trail. The existing railway rails, guardrails, tie-plates and other track support hardware will be removed and salvaged. The timber ties will be removed and properly disposed of. The existing open steel grating and steel channel support joists will also be removed and salvaged. The conversion will retain the existing trusses, floorbeams and stringers. Seismic strengthening and condition related repairs are covered under separate sections of this study, (see Sections 2.0 and 3.0). New steel channel joists, spanning the full width of the railway bridge will be installed to support a 5.0 m wide lightweight fiberglass pedestrian grating with a slip resistant surface finish. Because of the existing structural support configuration, the grating main bearing bars will span parallel to the stringers. The grating selected will be a close-mesh grating that is pedestrian and cyclist friendly. A 1.4 m high steel bicycle barrier railing will be provided on either side of the walkway for public safety. The at-grade approach modifications and tie-in to the existing multi-use trail are not included in this structural evaluation, (refer to the separate Architectural Report). 4.4 Aternative 3 Upgrade Existing Highway Bascule Span Deck for Cyclist Use Cyclists have reported that the existing highway bascule span surface is slippery when wet. This dangerous condition is exacerbated when cyclists are forced to share the vehicular travel lanes because of the limited roadway width between the trusses. A structural evaluation was made of how to replace the existing open steel grid roadway deck (installed around 1966) with a new cyclist-friendly surface. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 30

35 This study evaluated how to replace the deck to provide a riding surface that produces better wet weather traction for cyclists. The existing highway bascule span deck consists of a heavyduty steel open grid deck supported on steel channels. The grating main bearing bars run parallel to traffic with reticulating secondary bars riveted in between. The existing steel support channels will be removed along with the existing steel grating and salvaged. New steel support channels will be placed with a slight increase in spacing as a result of providing stiffer grating. A heavy duty close-meshed steel roadway grating with a slip resistant surface should be specified. The grating needs to remain an open grating to minimize load increases on the bascule span operating machinery and to minimize wind pressure on the span when in the fully open position. The size of the clear opening between main bearing bars should be reduced to a maximum of 13 mm. The existing structural steel tube traffic railing, although substandard, is not part of this study. If the deck is to be replaced, the traffic railing should also be upgraded to provide adequate protection for the truss and tower members as well as meeting standards for vehicle and cyclist protection. Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 31

36 4.5 Quantity Estimate Quantiy estimate and pay items for all three alternatives for pedestrian/cyclist walkway are shown in Table 6. Table 6 Pay Items and Quantity Estimate for Pedestrian/Cyclist Walkway Alternatives. Alternative Pay Items Description Unit Quantity Quantity Quantity Items to be removed Steel railing m 233 Timber curb (6" x 6") m 71 Items to be installed Timber plank (3" thick) m Steel grid m Timber joist (4" x 12") m 524 Timber ties (8" x 12") m 1058 Steel rails (80 lbs) m 233 Concrete curb (6" x 6") and gutter m 89 Open steel riveted grating m Steel joist (channel) m Structural steel kg Concrete (30 MPa) volume m Structural steel weight kg Fibergrate decking m Cyclist railing (1.4 m high) m Column (0.9 m diameter) m 60 Drilled shaft in soil (0.9 m diameter) m 116 Drilled shaft rock socket (0.9 m diameter) m 52 MSE Wall exposed surface area m Steel channels (C310) m 799 Concrete curb (6" x 6") and gutter m 89 Open steel close meshed grating m Steel channels (C230) m 688 Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 32

37

38 6.0 References 1) 1920 & 1921 Original Design Drawings Approach Spans and all Foundations by City of Victoria 2) 1920 & 1921 Original Design Drawings Bascule Bridge Design by The Strauss Bascule Bridge Co. 3) 1921 & 1922 select structural steel shop drawings by The Canadian Bridge Co., Limited 4) Superstructure of Johnson Street Bridge, Victoria Article by Resident Engineer published in The Canadian Engineer December 12, ) Details of Construction Methods and Comparative Cost of the Johnson Street Bridge in Victoria, B.C. Paper by City Engineer presented to The Engineering Institute of Canada February 27 th, ) Johnson Street Bridge Condition Assessment Report by Delcan February ) Canadian Highway Bridge Design Code and Commentary CAN/CSA-S6-06 published by the Canadian Standards Association 8) British Columbia, Ministry of Transportation, Bridge Standard and Procedures Manual Volume 1 Supplement to CHBDC S6-06 9) AASHTO LRFD Bridge Design Specifications, First Edition 1994, published by the American Association of State Highway and Transportation Officials 10) AASHTO LRFD Bridge Design Specifications, Fourth Edition 2007, with the 2008 Interim Revisions published by the American Association of State Highway and Transportation Officials 11) MIDAS/Civil Total Integrated Solution System for Civil Structural Engineers from Imbsen Software Systems 12) 1978 Johnson Street Bridge Rest Pier Concrete Repair Plans by Graeme & Murray 13) City of Victoria Johnson Street Bridge Structural Condition Report by Graeme & Murray Consultants Ltd. August Contains Paint Evaluation Johnson Street/Bay Street Bridges Report by B. H. Levelton & Associates Ltd. May 17, 1990 and an Underwater Inspection Report by Ocean Marine undated. 14) 1979 Railroad Bridge Deck System Repair Replaced floorbeams, stringers, diagonal and lateral bracing; Plans by Buckland and Taylor Ltd. 15) Johnson Street Bridge Condition Report Prepared for City of Victoria by Graeme & Murray Consultants Ltd. April 9, Contains City of Victoria Johnson Street Bascule Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 34

39 Bridge and Side Spans Maintenance Painting Report by Levelton Engineering Ltd. February 10, 1998 and a table of Ultrasound Testing Results 16) 1999 Roadway Bridge Repair Approach Span Concrete Deck Replacement; New Sidewalk Support Brackets; Misc Steel Repairs Plans by Graeme & Murray 17) Termarust Technologies, Montreal, Quebec 18) Johnson Street Railway Bridge New Cycling and Pedestrian Walkway Feasibility Report by Graeme & Murray January 20, 2000; Revised April 20, ) Johnson Street Bridge - Cycling and Pedestrian Walkway Feasibility Study Plans by Graeme & Murray January ) 21) City of Victoria Johnson Street Bridge Electrical/Mechanical Condition Report by Robert Freundlich & Associates Ltd. March ) Heritage Assessment of the Johnson Street Bridge, Victoria by Commonwealth Historic Resource Management Limited April ) Johnson Street Bridge Replacement Project Geotechnical Investigation Report by Stantec October 19, 2009 Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 35

40 7.0 Appendix Rendering of Proposed Seismic Retrofit Underpinning Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 36

41 Existing Johnson Street Bridge Assessment Structural Condition Evaluation Page 37