BURGOYNE BRIDGE A STATE-OF-THE-ART ANALYSIS AND DESIGN OF A THREE DIMENSIONAL-PRESTRESSED STEEL ARCH BRIDGE

10th International Conference on Short andMedium Span Bridges Quebec City, Quebec, Canada, July 31 – August 3, 2018 BURGOYNE BRIDGE: A STATE-OF-THE-ART ANALYSIS AND DESIGN OF A THREE DIM

10th International Conference on Short and

Medium Span Bridges Quebec City, Quebec, Canada, July 31 – August 3, 2018

BURGOYNE BRIDGE: A STATE-OF-THE-ART ANALYSIS AND DESIGN OF A THREE DIMENSIONAL-PRESTRESSED STEEL ARCH BRIDGE

Salib, Sameh1,4, Archibald, Brent2 and Liu, Karen3

1,2,3 Parsons, Markham, Ontario, Canada

Abstract: Since the Romans, and before, arches have introduced an effective load carrying system.

Herein, a steel arch was a key element to replace an existing 100-year-old bridge with a landmark structure in the Niagara Region, Ontario, Canada, where a blend of geotechnical, environmental and traffic conditions posed numerous challenges to the bridge design The arch carries twin composite steel box girders within the largest span (125m) through transverse floor beams connected to the arch by cables The girders are continuous over 7 spans and supported by tall concrete piers and deep foundations (concrete caissons) The arch span is prestressed longitudinally (through arch tie), transversally (through cables embedded in the superstructure) and vertically (through arch hangers) To the knowledge of the authors, this design introduced the first steel arch bridge in Canada that is prestressed in the spatial three dimensions Further, the longitudinal prestressing was intentionally designed to be applied after the steel arch is fully anchored/ integral with the piers that the substructure and foundations benefit from the applied prestressing as well This concept had a significant impact on optimizing the design of the arch piers and their foundations A sophisticated three-Dimensional Finite Element Model (3D-FEM) was developed for static, dynamic and staged construction analyses to determine the optimum construction sequence including the prestressing stages It is believed that the present paper introduces an innovative approach for an optimum design of medium-span arch bridges under unique construction conditions The bridge structure was completed and opened for service in 2016

Arches have been utilized in bridges for thousands of years The era of the Roman Empire is considered the prime period for the evolution and development of long and multi-span arch bridges (O’Connor 1994) Herein, the subject bridge (Burgoyne Bridge) presently carries Regional Road 81 (St Paul Street West), over Twelve Mile Creek and Highway 406 in the City of St Catharines The bridge has a steel truss structure built in about 1915 and it is approximately 400m long It includes multiple steel truss spans supported on steel truss towers together with steel girder spans flanking the main structure The structural condition of the bridge was examined and it showed significant signs of deterioration due to heavy corrosion, rust packing, section loss, and deformation Consequently, it has reached the point where major work of replacement or rehabilitation of the structure is required As a result of the condition of the structure, life cycle cost analyses and the overall safety and risks associated with rehabilitation, it was concluded that the preferred structural option was the replacement of the bridge with a new structure adjacent to the existing structure

The new structure was envisaged to allow for two lanes of traffic to be maintained during construction, to maintain this integral link within the Region, and to create the possibility of providing a legacy for the future through a picturesque gateway structure The evaluation of alternative bridge/roadway cross sections was based on existing and future traffic requirements, the need to accommodate various modes

of traffic along the corridor (eg pedestrians, cyclists, mobility scooters), access for emergency service and maintenance vehicles, user safety, cost and input received from the public and technical agencies Further, considerable investigation was carried out to determine the optimum structure type While many conventional bridge structural configurations proved to be practical, they did not fulfill the requirement that the new bridge have in the aggregate a strong positive environmental effect by virtue of it being a landmark and iconic structure (Delcan 2011)

When all of these and other engineering and architectural aspects were considered, there arose several features which were believed to be ideally combined in a single iconic or landmark bridge at the Burgoyne Bridge site (Delcan 2011), namely:

• The incorporation of the arch theme with reference to the Glenridge Bridge;

• The incorporation of the truss theme with reference to the Burgoyne Bridge and the old swing bridge;

• The incorporation of inclined hangers with reference to the old swing bridge; and

• The incorporation of girders which comprise a reference to the existing Burgoyne Bridge

With these thoughts in mind, the new bridge configurations were crystallized (Figure 1) as detailed through the following paragraphs

Figure 1: New bridge rendered aerial views (left: Overall view and right: Arch span approach)

The bridge has 7 spans ranging between 20m and 125m The main span (125m) includes single central steel truss-arch supporting twin girders (Figure 2) The girders are carried by inclined hangers connected

to the soffit of the arch and to the top of the steel beams between the girders in the transverse direction (Figure 3) The arch consists of three curved steel tubes braced together to form an arched truss with a single tube as bottom chord and double tubes for the top chord Within the arch span, each girder has a composite concrete-steel closed box section The transverse beams are of a steel closed box section and bolted at each end to the inside web of the girders (Figure 3) For the other spans, the girders have the same exterior profile of those within the main span while the steel section is of an open type (Figure 4) The bridge superstructure is supported by reinforced concrete piers of variable cross section through their height for aesthetic purposes The bridge piers (piers 2 to 4), as shown in Figure 2, are relatively high where pier 2 reaches a height of approximately 24m As a combination of the significant loads carried by the substructure and the poor top soil conditions, deep concrete caissons are used for the bridge foundations The length of the caissons reaches about 50m at the North abutment The bridge approaches are supported by concrete retaining walls on steel caissons

Figure 2: New bridge elevation

Figure 3: New bridge cross section within the arch span

Figure 4: New bridge cross section within the arch span approaches

3 FINITE ELEMENT MODELLING (FEM)

The FEM of the bridge was developed through MIDAS software (MIDAS CIVIL 2012-2016) The selection

of each model element type was based on geometry and material properties as well as on its expected behaviour and desired output results The piles, piers, girders, floor beams, and arch members were modelled as beam elements while the pile caps and pier caps were modelled as shell elements Solid elements were used to model the concrete blocks that anchor the arch ends with the pier caps The soil-pile interaction was represented by spring elements along the length of each soil-pile Various types of analysis were conducted through the developed model in order to have full understanding of the bridge behaviour and to achieve an optimum design under construction, serviceability and ultimate loading conditions

4.1 Staged Construction Analysis

4.1.1 General

One of the exceptional features of the subject bridge is that not only the construction stages are part of construction but also some of these stages should serve as a fully constructed bridge carrying vehicular traffic and supported by what is traditionally called ‘temporary’ shoring The developed FEM was utilized

to represent the non-linear characteristics of the proposed construction staging Figures 5 to 8 show the FEM of the major construction phases Phase 1 represents the construction of the east side of the entire bridge along with the associated temporary piers/supports to support the east girder carrying 2 lanes of vehicular traffic during the demolition of the existing bridge The west girder, carrying 2 additional lanes of vehicular traffic, along with additional towers at the temporary piers and the construction of permanent pier caps/arch anchor concrete blocks (at piers 4 & 5; Figure 6) marks the completion of phase 2 The introduction of the arch anchored to the end concrete blocks at the permanent pier caps and supported by temporary shoring along with the installation of the floor beams and their pre-tensioned ties represents phase 3 as shown in Figure 7 Thereafter, a series of interacting construction stages takes place in order

to install the arch tie and the stay cables and to implement their prestressing forces while lowering the bearings between the girders and the temporary piers in a specific sequence and with specific magnitude until the full removal of the support introduced by the temporary piers Such sophisticated construction sequence was essential to maintain the bridge straining actions and deformations within acceptable limits After the removal of all the temporary shoring and piers, the construction is considered completed as shown in Figure 8

Figure 5: FEM – construction phase 1

Temporary supports

Figure 6: FEM – construction phase 2

Figure 7: FEM – construction phase 3

Figure 8: FEM – full construction

4.1.1 Prestressing

To the knowledge of the authors, this design introduces the first steel arch bridge in Canada that is prestressed in the spatial three dimensions The arch span is prestressed transversally through cables embedded in the superstructure/floor beams The effect is illustrated in Figure 9 where specific straining actions are developed to counteract most of the loads applied on the floor beams Also, in the longitudinal

Temporary supports

Temporary supports

direction, the arch span is prestressed through the arch tie cables The associated series of stages, through which this prestressing is applied, are intentionally designed to take place after the steel arch is fully anchored/ integral with the piers that the substructure and foundations benefit from the applied prestressing as well (Figure 10) The prestressing of the hangers between the arch and superstructure provides mainly a vertical prestressing component as well as a secondary (additional) transverse component (Figure 11) This innovative prestressing approach has a substantial impact on optimizing the design, weight and cost of the superstructure/arch, arch piers and their foundations Further, it significantly improves the overall stiffness and integrity of the bridge

Figure 9: Rendered FEM-floor beams deformed shape (left: before prestressing, middle: after transverse

prestressing and right: after completed construction)

Figure 10: FEM-arch span deformed shape (left: before prestressing and right: after first stage of

longitudinal prestressing)

Figure 11: FEM-arch span deformed shape (left: before prestressing and right: after first stage of hangers

prestressing)

4.2 Serviceability and Ultimate Design Analysis

The bridge in its final configuration after completion of construction was subject to analysis and design for both serviceability and ultimate limit states as per the Canadian Highway Bridge Design Code, CHBDC, (CSA-S6-06) Further, due to the special nature of the subject bridge, both permanent bridge members

and temporary piers received the same analysis and design based on the applied loads at each construction stage

4.3 Stress Analysis

Understanding the global structural behaviour of the bridge and obtaining the design straining actions (Bending moments, shear forces, axial loads) at each component were the major objectives of most of the types of the conducted analyses However, few locations in the bridge were considered quite critical and were qualified for more sophisticated presentation of their details through the FEM Figure 12 shows one

of these locations which represents the connection details between the top of the arch hangers and the soffit of the bottom pipe of the arch In order to capture the stress flow in the connection and, hence, verify not only its strength but also its fatigue capacity, the main gusset plates, the transverse stiffeners, the plate holes and the structure of the pipe were modelled and analysed under their corresponding loads

Figure 12: FEM of top stay-arch connection (left: model and right: stress contours)

4.4 Buckling Analysis

One of the major criterion of designing members subjected mainly to compressive forces such as arches

is the buckling capacity Few analytical methods were adopted to evaluate the maximum loads that can

be applied on an arch prior to buckling (Timoshenko and Gere 1961) However, most of these methods are accurate for simply loaded arches When the arch is subject to loads in both in-plane and out-of-plane, complex boundary conditions and various straining actions, then FEM is considered a practical approach to address buckling issues A FEM buckling analysis can predict the modes of buckling of the entire bridge and those for the individual members along with the corresponding buckling load (Pi and Trahair 1998 and 2000, Wu et al 2005, Qiu et al 2010) Figure 13 shows the first mode of buckling (corresponds to the lowest buckling load of the bridge) w.r.t an at rest bridge (Figure 14) A global buckling of the entire bridge structure can be seen in the shape of a lateral transverse sway of the arch/girders assembly

Figure 13: FEM - plan view (1st mode of buckling)

Figure 14: FEM - plan view (undeformed)

The relatively long arch span (125m) in addition to the topography of the site and the unique arch/girders assembly can introduce dynamic behaviour and wind effects that cannot be captured by the standard wind loads of the area (CSA-S6-06) Two phases of study were dedicated to evaluate the dynamic response of the bridge under wind loads The first phase was to have an understanding of the dynamic characteristics of bridge through the developed FEM, especially its fundamental Modes Of Vibration (MOV) (Brownjohn et al 1999, Ribeiro 2012) Figures 15 and 16 show the first and second MOV respectively It can be seen that the first MOV represents the longitudinal direction as the major vibration reference where the girders are sliding longitudinally over the substructure On the other hand, the flexural characteristics of the arch/girders assembly in the vertical plan dominates the second MOV

Figure 15: FEM – isometric view (1st MOV; 0.95 Hz)

Figure 16: FEM – isometric view (2nd MOV; 1.16 Hz)

The second phase of studying the dynamic-wind interaction of the bridge was through a wind tunnel testing (Figure 17) carried out by Rowan Williams Davies & Irwin Inc (RWDI) The main objectives of this phase were as follows:

• Determine the design wind speeds for wind loading;

• Evaluate the basic aerodynamic characteristics of the completed deck by performing sectional model tests;

• Conduct a buffeting analysis to obtain equivalent static wind loads on the completed bridge; and

• Assess the potential for pedestrians to initiate vibrations of the bridge

The study derived 29 different equivalent static load cases for the bridge design These loads included the effects of wind gusts and the dynamic response of the bridge Also, a total of 52 different scenarios modeling crowds walking and running on the bridge were established and targeted each of the modes of vibration identified as potentially sensitive to this type of excitation A review of the different applicable codes was done to establish comfort criteria for vertical and lateral motion based on the acceleration of the bridge (RWDI 2013)

Figure 17: Wind tunnel testing of the bridge

The present paper threw the light on a recent arch bridge design that was completed recently for the Niagara Region, Ontario, Canada A major objective was to replace an existing 100-year-old bridge with a landmark structure To achieve such objective along with overcoming the major challenges introduced by the combination of geotechnical, environmental and traffic conditions, the following can be concluded:

• Considering the various engineering and architectural aspects of the project as well as the surrounding existing and old bridges; a truss-arch carrying a twin girder through inclined cables within the main span while only girders of the same profile form the superstructure of the rest of the bridge was believed to be

an optimum option that bears iconic features of the desired landmark bridge at the subject site;

• The bridge design had to accommodate for two lanes of traffic to be maintained during construction to maintain this integral link within the Region Therefore, the construction stages were designed not only for construction purposes but also to serve carrying two lanes of vehicular traffic until the installation of the arch-tie-hangers system;

• Controlling the straining actions and associated deformations of the structure during construction mandated a unique design of a series of interacting construction stages The installation of the arch tie and stay cables and the implementation of their prestressing forces are designed to take place while lowering the bearings between the girders and the temporary piers in a specific sequence and with specific magnitude until the full removal of the support introduced by the temporary piers;

• A sophisticated 3D-FEM was developed to represent the non-linear characteristics of the proposed construction staging Further, various other types of analysis were performed in order to capture the unique behaviour of the bridge in both global and individual modes of buckling, to determine the stress concentration and fatigue capacity at critical connections and to evaluate the dynamic characteristics of the bridge; and

• A wind tunnel testing of the bridge was carried out to gain a comprehensive understanding of the wind effects under the complex bridge geometry and the irregular surrounding terrain Among the objectives fulfilled by the testing were conducting a buffeting analysis to obtain equivalent static design wind loads and assessing the bridge vibration sensitivity under various scenarios of pedestrians’ activities