Design-Construction Feature

The Twelve Mile Creek Precast Prestressed Segmental Bridges

Kris G. Bassi Head, Design Section Structural Office Ministry of Transportation -And Communications Toronto, Ontario

Watone L. Lin Design Engineer (Central) Structural Office Ministry of Transportation and Communications Toronto, Ontario

he Twelve Mile Creek Bridges, lo- The twisting alignment and profile of T cated on Highway 406 linking the the new divided highway at the creek City of St. Catherines, Ontario, to the crossing was dictated by an adjacent in- Queen Elizabeth Way, were completed terchange, site terrain, poor soil condi- in 1982. For the last two years the tions, and property constraints. The size, bridges have been used for access and number, and location of piers in the hauling fill before being opened to the waterway also were restricted and the public this past October. requirement for a mimimum vertical The route of the new highway, which clearance above the creek had to be met. follows the valley through which the In addition, the proximity of the adja- creek flows (as shown in Fig. 1), was cent interchange required part of the selected for economy and minimum so- roadway on the bridge to be flared to cial and environmental impact. The accommodate the ramps. Therefore, Twelve Mile Creek originally formed where the divided highway crosses the part of the Welland Canal, connecting creek, two bridges, one for the north- Lake Erie to Lake Ontario. Today, it is bound lanes and the other for the south- part of a fast flowing tailrace for a bound lanes, were necessary to meet the generating station. specified requirements.

30 Synopsis Describes the overall design of the bridges plus the fabrication and erection of the segments. A special feature of these structures is the use of transverse ribs along both segment faces to accommodate the deck flare. Problems encountered during construction and their method of solution are also discussed.

AI-Ba=i Senior Structural Engineer ctural Office Ministry of Transportation and Communications Toronto, Ontario

(Stru

Osmo E. Ramakko Head, Structural Section Northwestern Region Ministry of Transpoilation F and Communications Thunder Bay, Ontario

Several alternative types of bridges 76, 52 in) while the southbound lanes were investigated during the prelimi- structure is on a horizontal S-curve with nary design stage. The precast post- six continuous spans of 155, 250, 250, tensioned segmental concrete box 250, 250, 155 ft (47, 76, 76, 76, 76, 47 m). girder bridges were selected for their The southbound lanes structure is con- ability to economically satisfy the com- siderably longer than the northbound plex geometry, restricted construction Ianes structure because neither fill or an depth, and the variable roadway width embankment retaining wall at the south requirements. approach was permitted to encroach on the waterway. The layout of the bridges Description of Bridges is given in Fig. 2. Both bridges were designed for three The bridges consist of a 594 ft (181 m) 12 ft (3.66 rn) lanes of traffic; two 3 ft 3 long northbound lanes structure and a in. (0.99 m) shoulders; and 1 ft 8 in. (0.51 1310 ft (399 in) long southbound lanes m) safety barriers giving an overall structure. The northbound lanes struc- width of45 $10 in. (13.97 m). However, ure is on a horizontal curve with three to accommodate the on and off ramps continuous spans of 172, 250, 172 ft (52, from the adjoining interchange, the

PCI JOURNAUNovember-December 1984 31 Fig. 1. Aerial view of the completed bridges.

decks are flared towards the north nearby interchange and the restricted abutments to a maximum of 48 ft 8% in. soffit elevation required for creek flow. (14.85 m) for the northbound lanes Two spherical rotational bearings structure and 54 ft 4 in. (16.56 m) for the with TFE sliding surfaces were pro- southbound lanes structure. Both vided at each abutment and pier with bridges are on a slight grade towards the. the exception of the bearings at Pier 1 north. for the northbound lanes structure and Each bridge consists of a single cell Pier 4 for the southbound lanes struc- box girder having a constant depth of9 ft ture. Those bearings were fixed for 3 in, (2.82 m) and a constant out to out translation. web width of 25 ft (7.62 m). The cross A special design feature of the bridges section of the superstructure is given in is the transverse ribs located along both Fig. 3. The extremely shallow construc- segment faces as shown in Fig. 4. The tion depth (span to depth ratio of 27:1) decision to use transverse ribs was was dictated by the roadway profile primarily due to the need to flare the which was controlled by both the decks towards the north abutments

32

b NORTH FOR CONSTRUCTION

Z F L E VAT ION - NORTHBOUND BRIDGE

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5. ASl3T.6RG5 PIER 3 PIEr! 2 PtBR l 1 x= -_ PIER 4 I g lEP ^I J Sp5 PLAN N

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ELEVATION - SOU T HBOU ND B RI DGE Note: I FT.= 0305. Fig. 2. General layout of bridges; plan and elevation_ 1 IN. : 25.4 _ . 4 HWY 4118 W 9. RIDGE S.B. RIDGE

IR_.A,..0

Note: 1 FT. _ 305. 1 IN, • 25,4.. Fig. 3. Typical cross section of bridges.

where the normal deck cantilever over- 229 m) and then remains constant for the hang of 10 ft 5 in. (3.17 m) increases to a remaining segments which are 8 ft5 in. maximum of 14 ft 8 in. (4.47 m). The (2.57 m) long. transverse post-tensioned ribs with a 7 The abutment and pier segments in- in. (178 mm) thick top slab were ex- clude transversely post-tensioned solid tended to accommodate the deck flare diaphragms with access openings. The and resulted in a 10 percent reduction in concrete in the diaphragms was placed the segment weight, Without the ribs, after erection of these segments to keep the deck flare would have required a the segment weights within the capacity considerably thicker top slab. of the launching truss. The two bridges were constructed by Multiple shear keys without any re- the balanced cantilever method. The inforcement and spread over the seg- northbound lanes bridge has 74 precast ment faces were provided to resist the segments and three cast-in-place closure vertical shear forces during construc- segments. The southbound lanes bridge tion. They were chosen over a single has 163 precast segments and six cast- large shear key due to the lack of space in-place closure segments. in the shallow webs where anchorages The pier and abutment segments are 6 for the draped longitudinal tendons also ft 8 in. and 6 ft (2.03 and 1.83 m) long, were located. respectively, The first segments adja- Longitudinal cast-in-place fascia cent to the pier segments are also 6 ft 8 beams were provided at the edges of the in. (2.03 m) long. They are followed by deck to cover the transverse post- four segments, each 7 ft (2.13 m) long. tensioning anchorages and to give the The thickness of the bottom slab for the structure an aesthetically pleasing ap- five segments adjacent to the pier seg- pearance. The fascia beams also help to ment varies front 2 ft 4 in. to 9 in. (686 to distribute the wheel live loads.

34 C) SEI;MENT 0 ^rr 1" C 2 z 1

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MAX

VARIES 1 1 IES 4 -3ri 0 TO 4 TO -J^7 r 1 12=6" 1 7-e"

NOTE: I FT.= •705 . 1 IN, =2S.4—

CTI Fig. 4. Details of segment showing shear keys.

rn

PIER 4 ABUT. ERGS. 172-0 NB. BRIDGE +- i5s- 05.B.BRIOGE _ TYP. BALANCED CANTILEVER_UNIT I

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ELEVATION INTERI OR SPAN (TYP.) Note 1 FT.: 0305. Fig. 5. Details of span segments showing location of post-tensioning. 1 IN. = 75,4 •. Design Considerations of the southbound lanes structure as they are located in the fast flowing The bridges were designed for all water. The construction sequence of normal AASHTO loads. The longitudi- these piers was established from a scale nal analysis of the box girders was car- model study of creek flow to minimize ried out using the BC computer pro- flow restriction and scour. gram. 2 Three groups of tendons (19/0.6 The piers are supported on either strands) were used for longitudinal spread footings or footings with piles post-tensioning (Fig. 5). The function of driven to bedrock. The abutment foot- the first group, where the tendons are ings are supported on piles driven to draped and anchored in the webs, was to bedrock. resist the negative moments during con- The design strength of the concrete struction by the balanced cantilever was 6000 psi (41.3 MPa) for the precast method. The tendons for the second segments and 5000 psi (34.4 MPa) for group, located in the girder bottom to the pier caps. No tension was allowed in resist the positive moments for the con- the design of the prestressed concrete tinuous structure, are draped and an- box girder and pier caps during con- chored in the deck slab. The third group struction and under AASHTO 1 loads. of tendons, located in the top slab, were provided to resist negative moments Fabrication of Segments along the span arising from live load in adjoining spans. The segments were precast in a tem- The transverse design was based on a porary all-weather building near the finite element analysis and a modified bridge site. Two short-Iine casting beds version of the procedures given in the located on the same base line, one to Precast Segmental Box Girder Bridge produce the standard 8 ft 5 in. (2.57 m) Manual. 3 Transverse post-tensioning long segments and the other to produce tendons (110.6 strands) were provided in nonstandard segments, were used. The the ribs as well as in the deck slab. The survey tower to control the horizontal bottom slab of the box girder was rein- and vertical alignments of the segments forced with mild steel reinforcement. was located between the two casting The design for shear in the webs of beds. the box girder was based on the CEB- Each casting form consisted of a fixed FtP Model Code for Concrete Struc- vertical bulkhead, soffit, two wing tures. 4 A combination of vertical post- forms, and a retractable mandrel carry- tensioning consisting of 1 in. (25 mm) ing the expanding interior forms. Each diameter Dywidag bars, stressed from segment was cast between the fixed the top, and mild steel reinforcement bulkhead and its adjacent or countercast was used in the first six segments on segment. Horizontal and vertical align- each side of the pier to resist shear. The ment was achieved by adjusting the remaining segments were provided with orientation of the countercast segment mild steel stirrups. prior to casting the new segment. All piers consist of 10 ft (3.05 m) di- A tolerance of ±16 in. (1.59 mm), con- ameter round columns with post- sidered to be too fine by the contractor, tensioned pier caps. Circular single col- was enforced both horizontally and ver- umn piers were chosen to suit the skew tically for the setting up of the counter- crossing and to minimize any effect on cast segment priorto placing concrete in the creek flow, a concern of the nearby the new segment. Due to the move- upstream generating station. Piers I and ments caused by the concreting opera- 2 of the northbound lanes structure were tion, the resulting as-cast tolerance was aligned with Piers 4 and 5, respectively, -t%a in. (4.76 mm). Although it was time

PCI JOURNAL/November-December 1984 37 consuming to meet the initial tolerance Initially, two segments were erected of ±lhs in. (1.59 mm), the resulting during a normal working day. This in- bridge alignment was satisfactory. creased to four segments per day by the The reinforcing steel cages, with the time the northbound lanes structure was post-tensioning ducts in place, were completed. prefabricated in a wooden mock-up of The temporary stressing system used the segment before moving them into to clamp the segments onto the growing the casting beds. cantilevers, until permanent tendons The forms were stripped when the could be installed, was a combination of concrete strength reached 1500 psi (10.3 strand and high strength bar tendons lo- MPa). The countercast segment was cated in either existing ducts or in ducts moved into a storage area and the newly especially provided for this purpose. cast segment was then moved into the Due to the presence of the transverse countercast position. ribs, the large contact area at the seg- The segments were vertically and ment joints was provided with addi- transversely post-tensioned and grouted tional short prestressing bars to provide in the storage area after the concrete the required 30 to 50 psi (0.21 to 0.34 reached a strength of 5000 psi (34.4 MPa) temporary contact pressure. MPa). Epoxy adhesive was used to bond the An average of 1.5 segments per day segments during erection. Two formu- were produced over a period of about 10 lations were used; one for faster setting months. The maximum segment weight, during cool weather and the other for excluding the cast-in-place diaphragms, setting during warmer weather. A dili- was 72 tons (65 t). gent inspection, testing, and curing pro- cedure in accordance with AASHTO Erection of Segments specifications was followed to ensure success. The abutment segments and the adja- After completion of cantilevers in cent segments (up to the first cast-in- each span and removal of all loads from place closure segment) were erected on the spans, stabilizing clamping beams falsework using a crawler crane. The were used to connect the two canti- entire balanced cantilever over Pier I of lever tips or the cantilever tip in the end the southbound lanes structure, which is spans to segments resting on temporary situated over the creek shoreline, was falsework. The concrete in the closure erected by a crawler crane using a mov- segments was placed during periods of able temporary support and stabilizing stable ambient temperature, which was concrete blocks. usually around midnight. When the The remaining segments were concrete in the closure segment reached erected by a launching truss. The steel a strength of 1000 psi (6.9 MPa), four of launching truss which had previously the tendons were stressed. The re- been used on two other straight seg- maining tendons were stressed when mental bridges in Ontario had a length the concrete strength reached 4000 psi of 377 ft (114.9 m) and an approximate (27.6 MPa), weight of 463 tons (420 t). Major modifications were required to Problems and Solutions enable the truss to travel and erect seg- ments on the horizontally curved During precasting of the segments bridges. The launching truss stabilized and erection of the superstructure sev- the balanced cantilevers, delivered seg- eral problems were encountered. Dis- ments, and supported the work plat- cussed below are the difficulties and forms and post-tensioning hardware. their method of solution.

38

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^ 1 1 ^

36 K r ^1 l ^

SYMMETRY I ^1

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:4.4 NEWTOM5 0-305 rn = 25 4r"

Fig. 6. Shear distribution due to segment weight and construction load.

Precasting not until about 20 percent of the seg- ments had been cast) by adjusting the During the separation of the counter- method of separation, increasing the cast segments from the new segments, depth of shear keys from 4 to 6 in. (102 to some of the shear keys were damaged. 152 mm), and careful application of the This was due to the method of separa- bond breaker. tion employed which caused the seg- The damage to the shear keys neces- ments to slightly rotate relative to one sitated a reassessment of the capacity of another, resulting in unanticipated the remaining undamaged shear keys. forces on the shear keys when the con- Tests were carried out on a number of crete strength was only 1500 psi (10.3 concrete blocks with 4 in. (102 mm) MPa). This problem was resolved (but deep shear keys. A minimum shear

PCI JOURNAL/November- December 1984 39 Fig. 7. Completed northbound bridge with southbound bridge under construction. Note mislocated Pier 4 with Pier 5 in the foreground.

capacity of 2.5 ^J{ psi (0.2 , MPa) ing grouting of the tendons. was established from these tests and was The longitudinal tendon ducts were used in assessing the shear capacity of displaced between the segment faces the undamaged shear keys. during concrete placement even though Most of the damaged shear keys were they were well fixed and inflatable rub- in the webs. A finite element analysis ber hoses were inserted into the ducts. was used to check the shear distribution This resulted in excessive friction dur- at the remaining keys located in the top ing post-tensioning. and bottom slabs and is shown in Fig. The transverse tendons in two seg- 6. The analysis confirmed that only ments were accidentally grouted before about 20 percent of the shear force was they were stressed. In the process of transferred through these keys. It was, removing these segments from the stor- therefore, decided to hold the segments age area, the boom of the lifting crane with the damaged keys in place until the collapsed and severely damaged epoxy cured since the keys could not be another two segments. Since these four relied upon to transfer shear forces segments were to be located near the tip across the joint. This resulted in a slow- of one of the cantilevers, it was only down of segment erection. necessary to recast these four segments. The fixed bulkhead had a 5 in. (127 The original design called for the mm) protruding ledge which formed transverse reinforcing bars crossing the part of the bottom pallet for the segment anchorage recesses for longitudinal forms. During separation, large pieces of post-tensioning in the top slab to extend concrete often were broken off by the into the recesses and he spliced by field ledge. These breaks were subsequently welding after longitudinal post-tension- repaired but caused fit-up problems ing. However, for construction it was during erection and led to leakage dur- decided to place prebent bars through

40 4 C) PIER 3 Ii L plfR A 1 0 NORTH x FOR CONSTRUCTION ERECMC^0,C5 AST FROM z CAHTti EC1QN^ CORRECT LOCATION Z ^. y - 0 c 1101 EOE AFSEP. ^^^^ ^ ^{F^6- BRIDGE C (CORRECT LOCATION) B CD e^S CD B CD •-CAST-IN-PLACE SEGMENT

BRGS SHI 2 -5 EAST I CORRECT LOCA BALAN EO CANTILEVERS ROTATED AFTER ERECTION DRGS SHIFT L-o"EAST ^-" _- • ^[ 5. B. BRIDGE CORRECT LOCA1 - -- (CORRECT LOCATION)

NOTE 1 FT. = 0.305 m N 1 IN.=2R4mm L Fig. B. Alignment adjustment for mislocated Pier 4. i C S.B.BRIDGE

WEST EAST

PIER 4 CORRECT LOCATION

t S.E BRIDGE (CORRECT LOCATION)

F SEGMENT AS ERECTED

WEST EAST

PIER 4 AS CONSTRUCTED

NOTE 1 FT. a0.305m 1 IN.= 25.4 mm

Fig. 9. Pier segment and bearings at mislocated Pier 4.

42 Fig. 10. Typical pier segment with cast-in-place diaphragm and erection oS adjacent segment.

the recess formers and bend them down joints, some strand wires did break. to form a lap splice after longitudinal Where it was not possible to increase post-tensioning. This caused the the jacking force for subsequent ten- bent-up bars to interfere with construc- dons, especially near the ends of the tion and many of them were broken off. cantilevers, the temporary prestressing In retrospect, the original design detail tendons connecting the last few seg- would have been better. ments were left in place and grouted. Provision should be made in all seg- mental bridge designs to provide addi- Erection tional prestressing to compensate for As noted earlier, the longitudinal ten- any excessive friction or for future don ducts had displaced between the strengthening. segment faces during precasting and the Due to the breakage and patching of friction loss was higher than anticipated. the concrete in the bottom slab at the since low-relaxation strands were used segment joint during segment separa- on this project, it was decided to in- tion from the bulkhead and possibly crease the jacking force from 0.08f f to other reasons, numerous interconnec- 0.85 f„ for subsequent tendons to com- tions and leaks were discovered during pensate for the higher friction loss. the process of water pressure testing the Due to sharp kinks at some segment ducts prior to grouting. The original de-

PCI JOURNAL)November-December 1984 43 Fig. 11. Delivering segment on completed cantilever for erection by launching truss.

sign called for the negative moment veloped in some segments on each side tendons in the cantilevers to be grouted of Piers 4 and 5. after the completion of each balanced Where heating for grouting purposes cantilever. However, due to the possi- is likely to be required, the design bility of duct interconnection, the should allow for the anticipated thermal grouting was delayed and the tendons g_ rradient. were protected against corrosion by The vertical alignment of the canti- coating them with a water soluble oil levers was controlled by insertion of prior to installation. stainless steel wire mesh between the The northbound lanes structure was segment faces and the resulting canti- grouted in one stage after completion of lever tip elevation was within 1 in. (25 superstructure erection. The south- mm) of the theoretical value. Atone clo- bound lanes structure was grouted in sure segment, the clamping beams be- two stages due to the approaching tween the cantilever tips moved during winter. The grouting for the first stage the concreting operation, resulting in a extended to the vicinity of Pier 3. The step of about 2 in. (51 mm) across the grouting for the second stage, which in- closure segment. cluded the remaining tendons, was car- The alignment control pins in top of ried out in December during cold the deck along the segment centerline weather. The structure was heated from were set about 2 in. (51 mm) from the inside the box to prevent freezing of the segment faces. Since the horizontal grout. The required heat exceeded the alignment computations were based on temperature differential between the the actual segment lengths, rather than interior and exterior of the box girder as- the pin to pin lengths, the erected sumed in design and fine cracks de- curved cantilever tips curled inwards.

44 Fig. 12. Underside view of completed bridges showing the transverse ribs.

The maximum horizontal alignment de- bearing shift of 9 in. (0.32 m) relative to viation at the forward tip (with the rear the segment and completing the bal- tip in the correct position) was 6 in. (152 anced cantilevers as usual, as shown in mm), This error was split between two Figs. 8 and 9. closure segments by rotating the bal- The completed cantilever at Pier 4 anced cantilever in plan and the devia- was then rotated to line up with the pre- tion is unnoticeable. viously completed cantilever at Pier 3 A serious problem on this project was and the closure segment was concreted. the discovery of a survey error, which The pier segment on the correctly lo- had located Pier 4 of the southbound cated Pier 5 was also shifted eastward by lanes structure about 3 ft 6 in. (1.07 m) 1 ft 9 in. (0.53 m) from its correct location east of its correct location, as the canti- with an easterly bearings shift of 1 ft levers at Pier 3 were nearing completion (0.30 m). The completed cantilever at (Fig. 7). Since the alignment of the this pier was then rotated to bring the bridge was curved, the problem could forward cantilever tip to its correct posi- be resolved by altering the horizontal tion. On inspection, the shift in the alignment of the bridge between the curved alignment is not noticeable. forward cantilever at Pier 3 and the It was fortunate that the bridge was on north abutment. By allowing some ten- a curved alignment and some adjust- sion in the top ofthe post-tensioned pier ments could be taken up by the piers caps and reassessing the pier column and the cast-in-place closure segments. and footing design, it was possible to With any other type of construction, it shift the pier segment at Pier 4 eastward probably would have been necessary to from its theoretically correct location by demolish Pier 4 and reconstruct it in its 1 ft 9 in. (0.63 ni) with a further easterly correct location, resulting in increased

PCI JOURNAUNovember-December 1984 45 Fig. 13. View of completed bridge.

costs and considerable delay in com- sons learned from the design and con- pleting the bridges. struction of these bridges have en- Figs. 10 through 13 show various hanced the future of this type of con- phases of the bridges during construc- struction in Ontario. tion and after completion. The total cost of the bridges (in Cana- dian dollars) was $8,970,000 or $100/ft2 ($10761m 2). The cost of the superstruc- Closing Comments ture was $88/ft2 ($947/m2). In 1984 the Twelve Mile Creek The Twelve Mile Creek Bridges were Bridges received national awards from the first precast segmental concrete both the Prestressed Concrete Institute bridges to be constructed by the Ontario and the Post-Tensioning Institute. Ministry of Transportation and Com- The bridges were opened to traffic in munications. The restricted construc- tion depth and the curved and twisted October 1984 on completion of Highway 406 to the Queen Elizabeth Way. alignment combined with flared decks near the north abutments, provided a challenge that was satisfactorily met by Credits using precast prestressed concrete seg- mental construction. Owner: Ministry of Transportation and The experience gained and the les- Communications, Ontario.

46 Engineer: Structural Office, Ministry of References Transportation and Communications, 1. Standard Specifications for Highway Ontario. Bridges, American Association of State Special Consultant to Owner: Precon- Highway and Transportation Officials, sult Canada. Washington, D.C., 1977. General Contracator and Manufacturer 2. Bridge Construction (BC) Computer Pro- of Precast Segments: Kilmer Van gram, Europe Gecti Etudes, France. Nostrand Company Ltd., Downsview, 3. Precast Segmental Box Girder Bridge Manual, Published jointly by the Pre- Ontario. stressed Concrete Institute, Chicago, Il- Special Consultant to Contractor: DRC linois, and the Post-Tensioning Institute, Consultants, New York City, New Phoenix, Arizona, 1978. York. 4. CEB-FIP Model Code for Concrete Post-Tensioning Supplier: Canadian Structures, Comite Euro-International du BBR (1980) Inc., Toronto, Ontario. IB^ton, Paris, 1978.

NOTE: Discussion of this paper is invited. Please submit your comments to PCI Headquarters by July 1, 1985.

PCI JOURNAL.lNovember-December 1984 47