The Beauharnois Bridge, Montreal, Canada

The Beauharnois Bridge, Montreal, Canada Alejandro Acerete, Civil Eng. MSc, Acciona Infraestructuras—Civil-Works and Structures, Madrid, Spain; Javier Ayala, Director, Acciona—Engineering Area-Civil-Works and Structures, Madrid, Spain; Gabriel Menendez Pidal, Civil Eng. MSc, Dragados, Madrid, Spain and Luis Peset, Civil Eng. MSc, Dragados, Madrid, Spain. Contact: aacerete@acciona.es DOI: 10.2749/101686614X13854694314685 Abstract The bridge over the Beauharnois Canal (BHC) is the main structure of the Nouvelle Autoroute 30 project, with a total length of 2551 m. It crosses the BHC and the Saint Laurent Seaway (SLS). This paper describes the development of the design and construction process of the Beauharnois Bridge carried out by a leading construction company in Montreal. It describes the construction procedures carried out to achieve the works in a schedule severely limited by the technical clauses of the contract and winter conditions. This paper emphasizes the different prefabrication systems employed in the construction of the bridge and the incremental launching technique used to erect the steel box-girders of the east part over the BHC and the SLS. The bridge superstructure is divided into two parts: the east part, formed by a closed composite structure with a steel box-girder spanning over 82 m, and the west part, designed with a concrete deck composed of five concrete prefabricated beams spanning a typical length of 45 m. The east part, with a length of 1456 m, was designed with no expansion joints. This side of the deck includes the main span of 150 m and was entirely assembled at the east abutment and erected in place using the incremental launching technique. Keywords: Incremental launching; precast piers; hybrid joints; deck without joints. Structure Description The bridge, with a total length of 2551 m, crosses from east to west of the Beauharnois Canal (BHC) and the Saint Laurent Seaway (SLS) canal with a twin deck. The SLS is an international navigational infrastructure connecting the Great Lakes of North America with the Atlantic Ocean through the 402 Technical Report Québec region in Canada. This strategic point governs the conditions under which the Beauharnois Bridge has been designed and built (Fig. 1). The bridge length is divided into three parts: • West approach, over land, from the west abutment (axis 1) to the transition pier 26 • Area of the main span over the SLS between piers 26 and 31 • East approach, over the BHC waters, between pier 31 and the east abutment (axis 44). The design of the bridge, carried out by a multinational professional services firm in London, was divided into two parts: the east part that includes the area of the 150 m main span and the east approach with typical spans of 82 m. The 14 m wide twin composite decks are formed by a steel box-girder. The west approach has 1094 m divided into 25 typical spans of approximately 44,5 m. It is composed of continuous decks with five precast concrete beams. Foundations Design The pier’s foundation design on the water side presented an important challenge. The rock was located 14 m under water level and it was composed of quartzitic sandstone with siliceous cement of high compressive strength (average values of 150–200 MPa up to 350 MPa); besides, it was very abrasive. (Fig. 2). The design took advantage of the highstrength rock, transmitting important forces through the rock socket; and to confirm these assumptions, two load tests using a high-capacity sacrificial loading device were carried out. over the water when compared with other underwater solutions using cofferdams. – The environment permit required minimum surface distortion at the canal bottom. – The hydroelectric power plant located downstream required minimum head losses as a result of the bridge construction, so minimum interferance in the canal waters flow was sought. Each pile cap consisted of two groups of three piles placed in an equilateral triangle and interconnected by a tie beam. Foundations of the west approach were designed with 96 steel-driven piles and a double T-shaped pile cap with a configuration similar to that described. Construction Piles were cast with steel casing embedded on the rock. The piles were drilled from barges and their position was controlled and located using the GPS system. The construction rate achieved was one pile/week and machine. The pile caps were cast in two phases in order to minimize the formwork structure. The soffit was supported on piles with sand jacks to ease formwork removal. The first pour of the pile caps were 1 m high. Once the strength was reached, the soffit formwork was removed using the sand jacks. The formwork was moved to the next pier so that the second phase of casting could take place. Besides reducing the concrete weight supported by the formwork, this system also allowed work on two piers in parallel. Also, the reduced concrete volume had, as a consequence, less hydration heat produced in the concrete mass. The design was based on piles and pile caps over the water for different reasons: Piers – Because piles were drilled from a barge, they were easier to construct Typical void piers of the bridge are 3,6 m in diameter and 400 mm in Typical piers Structural Engineering International 3/2014 67700 44 thickness and their height varies along the longitudinal profile of the bridge between 4 and 38 m. 40 81900 41 81900 42 81900 43 The design of the piers was originally based on in situ construction, but a precast alternative was developed in 2009 as a means to speed up construction and improve quality in view of the site conditions. 39 81900 Each precast column had two parts: 5m 81900 38 81900 81900 35 81900 34 1456700 36 81900 t-109 t par Wes 37 1050500 81900 • The base, with an in situ part divided into two lifts: the first lift of the pier is where plastic hinges could be formed during an earthquake; the second is where the anchorages of the post-tension system are located. • The precast segments, designed with post-tension tendons and using the match cast technique, to attach together all elements of the top part. 64500 31 81900 32 81900 33 Once the in situ part was built, the assembling of all the precast elements reached a production rate of one pier per day and crane crew. The transition between the two different decks is done at pier 26 with a singular pier head that combines the support for both decks at two different levels (Fig. 3). 63700 28 406200 150000 29 63000 Main span 30 Transition Pier 26 m 457 art-1 p East 33250 37850 1 Structural Engineering International 3/2014 Fig. 1: Beauharnois Bridge general view 2498 2 33250 45000 45000 45000 44200 44500 44500 44500 44500 44500 44500 44500 44200 44200 44500 44500 44500 44500 44500 44500 44500 44500 44500 44500 44500 65000 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 4 4A 5 Main Piers 10696 3 13180 1094700 This pier has been designed as a mobile point on the west approach and as a fixed point on the east part. This double function is achieved with a seismic retainer that links the boxgirder with the pier head. The volume of this pier head made it impossible to prefabricate, but the rest of the column shaft was prefabricated. The main piers are the fixed points of the east part; as there are no expansion joints, they attract most of the seismic forces of the 1457 m deck. The combination of ductility and resistance required for these piers has been balanced by providing a strong connection with the deck and the foundation and slender double columns (diapason columns) (Fig. 4). The connection between the main piers and the deck combines different elements: (a) a massive pier head 20 m long and 8,5 m wide, (b) a concrete block cast inside the box-girder to connect the pier head with the deck, and (c) steel haunches bolted to the bottom of the box-girder. Several construction stages were needed to cast the pier head. The last Technical Report 403 23 220 2830 1500 Ø2400 Bridge Pont 2500 1500 3000 1500 2500 4000 B Point D’implantation SOP Fall Fall pente pente 4000 Voir note 3 See note 3 ÉL. A + 45 mm 3000 4500 ÉL. A PLAN Pile Pier Pile Pier B Fig. 2: Construction of foundations on the water (Units: mm) ch West approa East part Main span Fig. 3: Transition Pier 26 two stages of the connection with the deck were (a) the erection of the haunches (a reinforcement of the steel section with a nose shape) and connection to the pier head and (b) the cast of the concrete block inside the boxgirder. These operations were carried 404 Technical Report out once the incremental launching was finished. West Deck The west deck was designed with precast concrete beams using a standard bulb-T-shaped girder section with 2000 mm depth beams. The total length of 1094 m has 25 typical spans of 44,5 m and it is divided into three segments by the expansion joints located at axis 1, 8, 17, and 26. Structural Engineering International 3/2014 28 259,0 m3 20,2 m3 1,90 nom. 16 m3 0,7 m 89,7 m3 4,5 m3 2,00 m 169,0 m3 2,00 m 107,4 m3 Top of column Fig. 4: Main Piers 13 770 3275 7220 3275 5060 Demi-dalle préfabriquée precast semi-slab 1000 (typ.) (+0,000) (–0,075) 250 dalle 250 slab Conduit ducts CJP 2% (–0,628) 2% Contreventment horizontal (W310×97 profilé) Horizontal bracing (W310×97 section) CJP Trou pour its conduit hole for its duct 3675 Profondeur de poutre girder depth (–0,686) 2160 Passerelle D’accés access walkway R200 CJP CJP 190 CJP 5400 (–4,303) 190 Fig. 5: East deck construction (Units: mm) The deck is 14,2 m wide and is continuous over the piers. East Deck The east deck is 13,7 m wide and has a composite section with a steel boxgirder 8,2 m wide and 3,7 m height. The entire length of 1457 m is divided into 18 spans with typical spans of 82 m and the main span of 150 m; it is continuous, with no intermediate expansion joints. The box-girder was assembled at the east abutment and erected with the launching technique described subsequently (Fig. 5). The concrete deck was designed with full-width precast prestressed slabs. All the elements required for the drainage support were also included in the precast slab. The purpose of the design was to maximize the deck elements included in the precast section of the deck. The objective was to improve productivity on-site. With this system, once the slabs were installed, the rest of the deck was cast at the rate of 82 m every 3 days and concreting crew. • The 150 m main span over the SLS channel was erected without affecting ship traffic, using the launching technique. • Hybrid steel mechanical joints were used, combining welding and bolting. Construction Singularities The construction of the Beauharnois Bridge was a challenge from different points of view. The various constraints introduced the following singularities in the bridge design and construction: • Partial precast piers with the anchorage zone in the in situ base of the column instead of in the foundation (Fig. 6). • The east part, constructed with no expansion joints and using the launching procedure. The assembly and launch operations were singular because of the variable curvature of the longitudinal elevation profile. Structural Engineering International 3/2014 Partial Precast Piers The typical piers were prefabricated with two peculiarities: 1. The post-tension system that joins all the precast elements has the anchor block at the base of the pier. Usually the anchors are located at the foundation, where there is enough concrete volume to be able to spread the concentrated loads of the post-tension system. This design was chosen so that the precast solution could be introduced without affecting the foundation’s design (prepared for in situ piers). Technical Report 405 H4 Top segment H1 4000 length precast segment Second last top segment H5 C.J. H2 in-stiu bottom lift C.J. 1800 1800 ÉL. B Fig. 6: Partial precast piers critical areas Fig. 7: Launch over the Beauharnois canal these pier heads were reduced to 100 t over water, and to 150 t and 250 t (expansion joint pier heads) on land. At the base of the pier, the first in situ lift was designed to be able to develop plastic hinges in case of an earthquake. The partial precast piers solution proved efficient to advance works in winter conditions. It allows working in parallel with the in situ part and the fabrication at the shop. Incremental Launching Fig. 8: Launching over the main span 2. The transition between the in situ and the precast part was solved with a “wet joint.” This joint was cast in place with high-strength and nonshrinkage grout. The leveling operations of the first precast segments 406 Technical Report were critical in achieving the proper alignment of the pier. 3. The pier heads were designed prefabricated with the requirement of being able to lift them with standard cranes. As a result, the weight of Initially, the constraints of the contract only left a 3 month winter construction season per year over the navigational channel. For this reason, incremental launching was selected as the most adequate construction method to erect the steel structure over the water. Nonstandard launching design and equipment were required to achieve what has been a launching record in Canada and North America, including a Structural Engineering International 3/2014 Fig. 9: Launching over the Beauharnois canal hybrid joint with two technological obstacles: 1. If welding was done first with no constraints from the bolting, the geometry of the joint could not have been controlled, as the weld deformation introduced important variations in the joint angle. 2. If bolting was fixed at the beginning of the operations, the welding introduced important tensions in the nearer bolts that were not considered in the joint design. The final method statement was sought through a process to fix the geometry with some bolts and pins introduced at the holes surrounding the weld. These pins were removed when the first passes of the weld were completed. Fig. 10: Hybrid mechanical joints Conclusion temporary stayed tower and special temporary supports combined with jacks. The operations were carried in 20 different launching stages (10 per deck). At each stage, 160 m were put in place with an average speed of 7 m/h. This method allowed erecting a total of 2900 m of steel box-girders in less than a year, with production peaks of 270 m per month. In order to cross the main span (150 m) with the launching, it was decided to install four temporary bearings with 850 t jacks in the main piers. Each pair of bearing on each side of the pier was 20 m apart and connected hydraulically. The result was a “swing bearing system” that reduced the effective span to launch to 130 m. The steel box-girder cross section was selected for the typical span. This section was designed to resist the launching forces of the typical span of 82 m, but it was not enough to launch the box-girder over the main span. For this reason, a temporary stayed tower had to be used to provide enough resistance to the box-girder. This tower also allowed controlling the deflection at the tip of the launching nose (Figs 7–9). The different construction singularities used to design and construct the bridge allowed the owner to open the bridge to traffic on schedule in December 2012. Assembling with Hybrid Mechanical Joints When winter and technical requirements introduced important constraints to the schedule, precast and industrialized solutions for construction proved to be the key to the success. The longitudinal profile of the boxgirder is divided into 40 segments, with lengths that range from 18 m to 41,7 m. Each pair of segments was joined using a hybrid mechanical joint that combines welding and bolted techniques in the same joint: top flanges and webs were bolted and the bottom flange was partially welded and bolted. The reason for using this system was to be able to slide the box-girder supported on the bottom flange. This 300 mm wide sliding area was required to be continuous all along the entire length of the bridge with no bolts. For this reason, the sliding area had to be welded at each mechanical joint. On the other hand, to optimize assembling works, especially during winter, all other parts of the section had to be bolted (Fig. 10). This double constraint introduced in the project a new concept of Structural Engineering International 3/2014 SEI Data Block Owner: Ministère de Transport du Québec & Nouvell Autorute 30 S.E.N.C (Acciona-Iridium) Contractor: Nouvell Autorute 30 CJV (Dragados-Acciona-Aecon-Verrault) Steel (t): 15 500 3 Concrete (m ): 70 000 Precast concrete (m3): 25 000 Rebar steel (t): 21 000 Estimated cost (USD million): 275 USD (300 CAD) Service date: December 2012 Technical Report 407