Bridge Bearing Replacement

John A. Van Lund, Washington State Department of Transportation

The Washington State Department of Transportation perstructure lifting recommendations are given. Jacks are (WSDOT) has removed and replaced nonfunctioning sized for at least 1.5 times the calculated lifting loads. Bear• bridge bearings to extend the service lives of existing ing design loads, replacement bearing costs, and costs for bridges. Inoperable roller nests and seismically vulnerable lifting bridge superstructures are presented. steel rocker bearings with excessive tipping have been re• moved and replaced to restore expansion capability. The superstructure must be raised to replace bridge bearings. ^ I 1 he Washington State Department of Transpor- Case studies that show three recent bridge bearing replace• I tation (WSDOT) has removed and replaced ment projects designed by WSDOT are presented. In the JL nonfunctioning bridge bearings on older steel first case study, a 113.0-m single-span truss built in 1925 truss bridges. After 60 to 70 years of service, the steel was raised from below by placing two hydraulic jacks and roller nests, which were used to provide for expansion the upper steel distribution plates directly under the bear• and contraction, are inoperable because of excessive tip• ing pin gusset plates. The unreinforced pier cap was post- ping and extensive corrosion. In addition, tipping tensioned to prevent spalling. A sliding disc bearing was rocker bearings are seismically vulnerable and are re• installed in place of the frozen roller nest. In the second placed with more stable bearings. As shown in the sec• case study, the bearings were removed and were replaced ond case study, removal and replacement of nonfunc• as part of an overall structural rehabilitation project. The tioning bearings can be included as part of bridge existing concrete deck was removed and the ends of seven rehabilitation or seismic retrofit projects. Replacement 54.9-m single-span trusses were lifted sequentially from bearings include multirotational disc bearings, fabric above with a pair of jacking beams consisting of two W36 pads with polytetrafluoroethylene (TFE) and stainless X 245 steel beams. Hanger rods were attached directly to steel sliding surfaces, elastomeric bearings, and lead- the jacking beams and the floor beam top flange. Four 50- core isolation bearings. It is WSDOT's policy to remove metric-ton jacks (two per jacking beam) simultaneously and replace defective or seismically vulnerable bearings raised the ends of the trusses. Sliding fabric pad bearings to extend the service lives of existing bridges. were used to replace the frozen expansion roller nests. In To replace bridge bearings, the superstructure must the final case study, seismically vulnerable tipping rocker be raised. Hydraulic jacks have been used to raise ex• bearings were replaced with elastomeric bearings. Jacking isting bridge superstructures so that defective pot bear• diaphragms were located in the exterior bays at the girder ings could be removed and replaced (1). In Washington centerline of bearings so that the lifting loads would not State jacks were used to raise one bridge superstructure cause tipping of the pier. Additional shelf width was pro• by as much as 6.3 m so that avalanches could pass be• vided by adding a continuous corbel to the pier cap. Su• low the bridge without hitting the girders. On another

122 VAN LUND 123

project jacking was used as a means of transferring the moving and replacing the frozen roller nests at the ex• dead load of the superstructure from one existing sub• pansion end of the truss span. The trusses were raised structure to another. Jacks with a capacity of 1.5 to 2 by jacking from the top of the existing pier cap. Before times the calculated lifting loads are used (2). Generally, raising the bridge, the unreinforced pier cap was post- jacking under a live load is not recommended. However, tensioned with two 35-mm-diameter high-strength bars traffic is permitted on the bridge after the girders have to prevent spalling of the pier cap concrete. The post- been safely blocked. Blocking and member connections tensioning bars were located directly under the truss must be designed for the total dead and live loads. On gusset plates and jacks (Figure 2). one recent WSDOT project, jacking was done under a The end of each truss was raised individually to pre• live load. Initially, jacking was done at night, and later vent possible lateral movements that might have oc• the operation was expanded to permit jacking under curred if both trusses were raised simultaneously. Anal• traffic during daylight hours. ysis showed that there was no overstress in the end WSDOT shares responsibility with the contractor for portal and connections when the trusses were lifted in• the success of the lifting operation by designing the dependently. The differential vertical deflection between most practical lifting procedure based on past experi• the jacked and the unjacked bearing was not to exceed ence. As the owner, WSDOT is concerned that no dam• 25 mm, and no jacking was permitted when the wind age to the bridge should occur during a lifting opera• speed exceeded 40 km/hr. Two 180-metric-ton locknut tion. In most cases the WSDOT-designed lifting jacks were placed as close as possible to the bearing pin. procedure is used, but the contractor may propose an Locknut jacks were used because no suitable blocking alternate procedure. In either case the contractor sub• points were available. The jacking cylinders were cen• mits working plans and independent calculations, tered directly under the gusset plates. A steel distribu• which are stamped by a registered professional engineer. tion plate and an epoxy leveling course were used to The following case studies show three recent bridge provide a level jacking surface, because the bottoms of bearing replacement projects designed by WSDOT. the gusset plates were uneven (Figure 3). The purpose of the epoxy leveling course was to distribute the lifting load uniformly to the gusset plates and to prevent over- CASE STUDY 1: PUYALLUP RIVER BRIDGE, BRIDGE stressing of individual gusset plates during the lifting No. 167/20E, PIERCE COUNTY, WASHINGTON operation. The epoxy leveling course was a two- component epoxy consisting of a resin and a catalyst The Puyallup River Bridge, originally the Meridian similar to that used in the wire rope industry for resin Street Bridge, was built in 1925. The bridge consists of socketing. The resin-catalyst was pourable and hard• a 113.0-m single-span steel truss that spans the river ened within 15 min with a fully cured compressive and two 5.8-m timber approach spans at each end of strength of 131 MPa. The lifting load, based on hy• the main span (Figure 1). The two trusses are narrowly draulic pressure gauge readings, was approximately 150 spaced at 7.3 m and are 19.0 m high at the midspan. percent greater than the calculated dead load, which In 1991 the bridge was closed to traffic and was re• may be attributed to heavy rusting of the roller nests, habilitated. Part of the rehabilitation effort involved re• internal friction forces in the jacks caused by binding.

Centerline Centerline of Brg's of Brg's 113.0 m

High Wateriine

FIGURE 1 Case Study 1: elevation, Puyallup River Bridge. Centerline truss

Gusset plates Centerline pin

Upper bearing See Figure 3 assembly

Tipping roller nest

Top of pier cap - Lower bearing bolster

!V_ Centerline 180 Anchor Plate, Tonne jacks 305 X 305 X 50 \ \ Centerline 33mm dia. post-tensioning bars

200 200 Post-tension bars and lock off at 734kN Lift load: Dead load 172 tonnes/bearing

All dimensions in mm

FIGURE 2 Case Study 1: pier cap post-tensioning and jack location, Puyallup River Bridge.

Gusset plates

- Epoxy Filler

22mm epoxy leveling course

Level

Plate 32 X 152 X 152 mm

Centerline jack

FIGURE 3 Case Study 1: epoxy leveling course. VAN LUND 125

or faulty gauges. During the lifting operation, the pier Raising trusses from above is a practical lifting tech• was monitored for potential tipping because the jacks nique during rehabilitation projects after the existing were positioned 560 mm from the pier centerhne. No deck slab has been removed. In this case study, the tipping from the eccentric lifting loads was observed. weight of the deck slab accounted for 70 percent of the However, just as the truss started to rise, the epoxy lev• truss dead load. Smaller jacking beams and jacks were eling course cracked but supported the truss without used because of this reduction in dead load. Raising failing. The roller nests were removed, the new sliding these trusses from above with the deck slab in place was disc bearings were installed. not feasible because the end floor beams and floor If epoxy is used as a leveling course for uneven gusset beam-to-truss connections would be overstressed and plates, it should be confined along each side to prevent would require extensive reinforcement. failure. Steel confinement bars can be welded to the up• per load distribution plate. The depth of confinement should be equal to one-half the height of the leveling course to prevent spalling. It is also important to have CASE STUDY 3: KALAMA RIVER BRIDGE, BRIDGE temporary blocking available to be installed in the space No. 5/113, COWLITZ COUNTY, WASHINGTON formerly occupied by the bearing in case the epoxy lev• eling course fails. Steel shims, which require careful ma• The Kalama River Bridge, which was built in 1970, is chining, could also be used in heu of epoxies to obtain a two-span steel plate girder bridge that spans over In• a level bearing surface for uneven gusset plates. terstate 5. There are four plate girders with simple spans of 44.5 m, and fixity is provided at the end abutments. Two sets of rocker bearings permit expansion at the CASE STUDY 2: SNOHOMISH RIVER BRIDGE, intermediate pier. Shortly after construction it was ob• BRIDGE NO. 529/lOE, SNOHOMISH COUNTY, served that the rocker bearings at the intermediate pier WASHINGTON had tipped toward the west. The tipping occurred be• cause of 0.3 to 0.6 m of settlement of the west approach The Snohomish River Bridge was built in 1926 and con• fill, which continued after construction because of un• sists of a 44.5-m steel lift span, eight single-span steel derlying organic soil. In early 1972 the bridge was trusses (seven with spans of 54.9 m and one with a span jacked, the base plates were slotted, and the rocker of 42.9 m), and numerous reinforced concrete approach bearings were plumbed. The tipping continued and was spans. The overall length of the bridge is 816.8 m. In monitored for the next two decades until the settlement 1994 the bridge was closed to traffic and rehabilitated stabihzed. at a cost of $6.0 million. The concrete deck, steel string• In 1995 the tipping rocker bearings were replaced ers and floor beams, and truss panel point gusset plates with reinforced elastomeric bearings. Plate girder dia• were removed and replaced. phragms, which had been installed to raise the bridge The expansion ends of the trusses were raised se• in 1972 and which had been left in place as permanent quentially with a pair of steel jacking beams so that the bracing, were again used to raise the ends of the girders frozen expansion bearing roller nests could be removed (Figure 6). The jacking diaphragms were located in the and replaced (Figure 4). The jacking beams consisted of exterior bays at the girder centerline of bearings so that two W36 X 245 steel beams placed side by side and the lifting loads would not cause tipping of the pier. had a mechanical advantage of 2 to 1. Each jacking Additional shelf width was provided by post-tensioning beam weighed 11.5 metric tons and could be placed a new 305-mm-thick continuous corbel to the pier cap. anywhere on the bridge by an overhead crane, which The bridge was raised 25 mm by four 90-metric-ton was supported by rails attached to the upper chords of jacks located adjacent to each girder. The existing the trusses. rocker bearing was removed, and the upper bearing Four 25.4-mm-diameter high-strength hanger rods block, which was welded to the bottom flange of the connected the jacking beam and the floor beam (Figure plate girder, was cut free by arc gouging and was 5). Four 50-metric-ton jacks (two per jacking beam) si• ground smooth to remove any excess weld metal. A multaneously raised the ends of the jacking beams 50 concrete pedestal, which was integral with the contin• mm. Adequate space was provided between the jacks to uous corbel, was constructed because the height of the install blocking so that the jack's cylinders could be new elastomeric bearing is 230 mm less than that of the lowered. The roller nests were removed, and new fabric original rocker bearing. The plan dimensions of the new pad bearings with TFE and stainless steel sliding sur• elastomeric bearing are 305 by 650 mm, and the height faces were installed. The maximum lifting load was is 78 mm. Six 14-gauge steel shims reinforce the 12.7- 91.0 metric tons, and the maximum jacking beam de• mm-thick internal elastomer layers. The external elas• flection was approximately 8 to 10 mm. tomer thickness is 6.4 mm. 126 FOURTH INTERNATIONAL BRIDGE ENGINEERING CONFERENCE

Jacking Procedure 1. Remove concrete deck 2. Remove and replace floorbeams and stringers 3. Install jacking beams 4. Use two 50 tonne jacks at each jacking point 5. Raise the superstructure not more than 50mm and block 6. Do not jack when wind speed exceeds 40km/hr 7. Coordinate jacking with utility companies

Jacking beam 2-W36 X 245

2-50 tonne jacks

Support point Jacking point

Lifting point Truss expansion roller nest to be removed

FIGURE 4 Case Study 2: elevation of jacking scheme, Snohomish River Bridge.

SUPERSTRUCTURE LIFTING RECOMMENDATIONS providing positive restraining systems and by adding temporary cross bracing to prevent member distortion. Lifting recommendations based on WSDOT's experi• This may be particularly important for bridges on steep ence (2,3) and on guidelines from Orr (4) are as follows: grades, in wind-prone areas, or with high supereleva• tions. Targets and tilt meters can be placed on the struc• 1. Show details in the plans for the most practical ture to monitor any movement. lifting procedure, and permit the contractor to propose 5. Block and shim during the lifting operation. an alternate procedure. Show the lifting points and in• WSDOT uses locknut jacks whenever space is not avail• dicate the lifting loads in the contract plans. The effects able to block the structure. Generally, the structure is of wind loading, construction loading, and live loading, shimmed tight or the locknuts are secured after incre• if any, should be included in the calculated lifting loads. mental lifts of 3 mm. In the event of a jack failure, there 2. Size jacks for at least 1.5 times the calculated lift• will be no significant differential settlement and a ing load and require backup jacks. If a jack fails, it can backup jack can be quickly installed. readily be replaced if backup jacks are available. The 6. For safety reasons do not permit traffic on the manufacturer's nameplate and the rated capacity of the bridge or the presence of any unnecessary construction jack should be attached to each jack. The schematic personnel near the bridge during lifting. Occasionally, hydraulic layout, including gauges, valves, manifolds, WSDOT has permitted jacking under traffic. Extreme and other equipment, should be shown in the contrac• care, advance planning, careful coordination, cribbing, tor's working drawings. and locknut jacks are required when lifting under traf• 3. Control relative vertical displacements so as not fic. A temporary ramp, usually constructed of asphalt, to overstress the existing structural members and con• may be required at the approaches if the total height of nections during lifting. Indicate the maximum vertical the lift exceeds 20 mm. displacement and the relative vertical displacements per• 7. Disconnect any utilities, railing, traffic barrier mitted between adjacent lifting points and between ad• cover plates, and sliding expansion joint plates that will jacent girders. prevent the lifting of the structure. 4. Determine maximum permissible deflections. Pre• 8. The working drawings, jacking procedures, and vent excessive longitudinal and lateral movement by calculations should be prepared, stamped, and signed VAN LUND 127

Centerline jacking beams Centerline W 36 x 245

50mm

25mm dia. high strength rods

Centerline truss Stiffener plates

Plate 25 X 300

HP 12x84

Plate 75 X 300

New floorbeam W27x 161

Plate 25 x 300 930 mm Double nuts top and bottom

FIGURE 5 Case Study 2: details at lifting point, Snohomish River Bridge.

by a professional engineer licensed in the state where rocker bearings when the expansion and contraction are the lifting is to take place. The engineer should inspect less than ±50 mm. all aspects of the lifting operation and be present during High-load elastomeric bearings can also be used for the lifting. expansion bearings for trusses, provided that the load and expansion limits are not exceeded. For new bridges WSDOT has designed high-load elastomeric bearings REPLACEMENT BEARDSTG AND LIFTING COSTS with a maximum elastomer height of 150 mm and for service loads of up to 360 metric tons in accordance with The design service load limits and costs for various AASHTO's Method B (5). Elastomeric bearings can also bearing types used by WSDOT are given in Table 1. be designed as isolation bearings that will reduce the seis• These costs are per metric ton of the design service load. mic forces acting between the superstructure and sub• The lowest cost of $3 to $5/metric ton is for elastomeric structure. Elastomeric bearings show excellent promise bearings, and the highest cost of $13 to $20/metric ton as replacement bearings because they are corrosion re• is for multirotational and seismic isolation bearings. sistant, durable, easy to install, maintenance-free, and Since 1987 WSDOT has not permitted the use of pot more economical than any other bearing type. bearings because of poor performance, which may be Table 2 provides the lifting costs per bearing per met• related to overrotation during construction. WSDOT ric ton for the three case studies. The costs range from has used fabric pad bearings with a TFE and stainless a low of $22 to a high of $78/metric ton. The figure of steel sliding surface and multirotational disc bearings as $22/metric ton is low because the contractor had un• replacement bearings for frozen truss expansion roller balanced the bid by overpricing the disc bearings. When nests. Elastomeric bearings have been used as replace• the bearing unit price is decreased to reflect a reasonable ment bearings for steel girder bridges with tipping price for disc bearings, the lifting cost would be ap- 128 FOURTH INTERNATIONAL BRIDGE ENGINEERING CONFERENCE

Centerline Centerline Centerline Centerline exterior girder lift point lift point interior girder

864 mm 864 mm

Jacking diagram

Beanng Stiffeners

Top of pier cap

Centerline Centerline jack jack 584 mm 584 mm

Centerline Centerline blocking Centerline bearing bearing

- Tipping rocker bearing to be Centerline blocking removed and replaced with an elastomeric bearing

FIGURE 6 Case Study 3: jacking details, Kalama River Road Overcrossing.

proximately $50/metric ton. The high cost of $78/met- procedure. Generally, jacking under Uve load traffic is ric ton included the fabrication of the jacking beams not recommended. used for raising the Snohomish River Bridge. 4. Hydraulic jacks are used as a means of Ufting bridges so that defective or frozen bearings can be re• moved. Jacks should be sized for a minimum of 1.5 times the calculated lifting loads to account for discrep• SUMMARY ancies between hydraulic gauge readings and calculated

1. It is WSDOT's policy to remove and replace non• functioning or seismically vulnerable tipping rocker TABLE 1 Bearing Design Loads and Costs, 1991 to bearings to extend the service lives of existing bridges. 1995 2. Details of three recent bearing replacement proj• Bearing Type Design Service Load Cost/tonne ects in Washington State are presented. Case studies de• (tonnes)" ($ U.S.) scribe three different Ufting approaches: direct bearing on truss gusset plates, the use of a jacking beam as a Elastomeric^ <360 3-5 pry bar with a mechanical advantage of 2 to 1, and the Fabric Pad* <270 5-10 use of jacking diaphragms placed between the ends of plate girders. Steel Pin >270 6-20 3. WSDOT shares responsibility for the success of Disc or Spherical* >360 10-20 the lifting operation by including details in the plans for the most practical Ufting procedure on the basis of past Seismic Isolation* <360 13-20 experience. As the owner WSDOT is concerned that no damage to the bridge should occur during a Ufting op• All loads are in tonnes (metric tons). eration. The contractor may propose an alternate lifting *Replacement bearing types used by WSDOT. VAN LUND 129

TABLE 2 Superstructure Lifting Costs, 1991 to 1995

Case Bridge Description Cost/tonne Study ($ U.S.)

1 Puyallup River Bridge Jacking against truss 22" Br. No. 167/20E gusset plates

2 Snohomish River Bridge Jacking beams 78* Br, No. 529/lOE 2-W36X245

3 Kalama River Bridge Jacking diaphragms 58 Br. No. 5/113 between girders

'Contractor unbalanced bid by overpricing the disc bearings. When a reasonable disc bearing price is used, the lifting cost is increased to SSO/tonne. »Include. s fabrication of jacking beams.

lifting loads. The gauge readings indicate that heavier WSDOT, and were checked by the author. The Snoho• lifting loads occur and may be attributed to the in• mish River lifting and bearing replacement project was creased force required to break the bond caused by designed by Jugesh Kapur and was checked by John heavy rusting of the roller nests, internal friction in the LaBranche, WSDOT. Rick Liptak, WSDOT, was the jacks caused by binding, or faulty gauges. Bridge Technical Advisor for the Snohomish River 5. In the first case study, epoxy was used as a lev• Bridge project. Progressive Contractors, Inc., did the eling course for uneven gusset plates. This was the first lifting and bearing replacement on the Puyallup River time that WSDOT specified an epoxy as a means of and Snohomish River bridges. Mowat Construction uniformly distributing lifting loads. To prevent spalling, Company was the contractor for the Kalama River the epoxy leveling course should be confined by steel Bridge bearing replacement. bars along each side for a depth equal to one-half height The author thanks WSDOT for support in preparing of the leveling course. this paper. The bearing replacement designs were pre• 6. Bridge bearing replacement is simplified if it is co• pared under the direction of Allan H. Walley, former ordinated with rehabilitation projects. As shown in the WSDOT Bridge and Structures Engineer, and M. Myint second case study, it was easier to lift the bridge from Lwin, current WSDOT Bridge and Structures Engineer. above with jacking beams after the concrete deck was Their support and encouragement are very much removed because the deck accounted for 70 percent of appreciated. the dead load. Smaller jacking beams and jacks were used because of the reduced dead load. 7. Replacement bearings include multirotational disc REFERENCES bearings, fabric pads with TFE and stainless steel sliding surfaces, elastomeric bearings, and lead-core isolation 1. Redfield, C, and C. Seim. Pot Bearing Replacements— Two Case Studies: Cline Avenue Interchange and 1-285/ bearings. Elastomeric bearings show promise as replace• 1-85 Interchange. Joint Sealing and Bearing Systems for ment bearings because they are corrosion resistant, du• Concrete Structures, Vol. 2, SP-94. American Concrete In• rable, easy to install, maintenance-free, and more eco• stitute, Detroit, Mich., 1986, pp. 817-823. nomical than other bearing types. 2. Van Lund, J. A. Jacking Steel Bridge Superstructures in 8. Maximum design loads for replacement bearings, Washington State. In Transportation Research Record costs for replacement bearings, and costs for lifting 1319, TRB, National Research Council, Washington, bridges are given. D.C., 1991, pp. 94-101. 3. Structural Lifting Operations. Bridge Special Provision, Washington State Department of Transportation, Jan. 1991. ACKNOWLEDGMENTS 4. Orr, J. Planning, Knowledge Keys to Safe Bridge Lifting. Roads & Bridges, Vol. 26, No. 4, April 1988, pp. 85-87. The Puyallup River and Kalama River bearing replace• 5. Standard Specifications for Highway Bridges, 15th ed. ment projects were designed by Munindra Talukdar, AASHTO, Washington, D.C., 1992, pp. 294-299.