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1、Page 1 of 6 Design and Construction of Movable Bridges in the USA Beile Yin, Ph.D. Paul M. Skelton, P.E. Associate Principal Partner Engineer Hardesty & Hanover Hardesty & Hanover New York, NY, USA New York, NY, USA Beile Yin received Paul M. Skelton received his BS degree in his BEME degree in. 196
2、8 from Tsinghu 1985 from State University, China; University of New York Ph.D.in 1986 from NC at Stony Brook, USA State University, USA Robert S. Moses, PE Partner Hardesty & Hanover New York, NY,USA Robert S. Moses received his BSEE degree in 1991 from Bucknell University, New York USA Summary Mova
3、ble bridges are an important part of the transportation infrastructure in the USA and around the world. Some movable bridges have been in service for 60-100 years and remain in good condition. New movable bridges continue to be built yet and existing bridges must be maintained, retrofitted and upgra
4、ded to meet current transportation requirements. Engineers face unique challenges during all phases of movable bridge work from analysis to design and throughout construction, including structural, mechanical and electrical engineering. Keywords: movable, bridge, bascule, lift, swing, electrical, me
5、chanical, trunnion, counterweight. 1 INTRODUCTION There are many types and sub-types of movable bridges but the most popular are the simple trunnion bascule, the center bearing swing bridge, and the vertical lift bridge. The motions of the movable spans are as follows: simple trunnion bascule rotati
6、on about a fixed horizontal axis; center bearing swing bridge rotation about a fixed vertical axis; and vertical lift translation along a fixed vertical axis. Descriptions of many types of movable bridges that have been constructed or proposed, including the machinery to move or stabilize the spans,
7、 may be found elsewhere. 3 4 5 There are a number of concerns arising from features of the movable bridge. The concept of movable bridges can be traced back to a fairly early dates in Europe and Asia. However, the earliest movable bridges, in the modern sense that serve todays transportation needs,
8、are better defined as later 19 century. 3 The first notable vertical lift build in the USA was the South Halstead Street Bridge at Chicago. This bridge, designed by Doctor Waddell in 1892, was constructed soon thereafter, with a span of 130 ft. and a maximum vertical clearance of 155 ft. 名师资料总结 - -
9、-精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 1 页，共 6 页 - - - - - - - - - Page 2 of 6 The Van Buren Street Bridge in Chicago, a Scherzer rolling bascule design, was completed in 1893, and the famous tower bridge in London, a roller bearing, trunion bascule constructed about th
10、e same time may be re-garded as the fore-runners of the modern bascule bridge. Construction of Willis Avenue Swing Bridge soon fol-lowed and was built in 1901. 2DESIGN AND MODELING The AASHTO document that does cover movable bridges is the Standard Specification for Movable Bridges, 1988 (ASD) 1. In
11、 addition, some states have supplements to AASHTO that contain provisions for movable bridges. The bridge engineer shall determine the following: 1. the type of movable bridges (swing, bascule or vertical bridge); 2. for swing bridges, Fig. 1: South Halstead Street Bridge at Chicago the type of cent
12、er (swing bridges shall preferably be the center bearing type); 3. for bascule bridges, the type of bascule; 4. for vertical-lift bridges, the type of tower, the location of the prime mover or movers and the provisions for keeping the moving span level; 5. the system of emergency operation, if any,
13、and the standby power system, if any. Loading conditions and loading combinations are described in 1, for determining the maximum and minimum stresses. Lateral loading such as wind load and seismic load shall also be given due consideration. Particularly, the seismic load is a relatively new issue,
14、which needs engineer s attention. The AASHTO LRFD Specification for Movable Bridges 2 contains significantly more information of the types of structural and mechanical issues than its counterpart 1. Movable bridges can be analyzed with three-dimensional finite element software such as SAP or ADINA.
15、Models are constructed primarily in beam elements, supplemented with shell elements, as necessary. Soil-structure interaction is modeled with foundation springs and dampers. Modeling of nonlinear elements, necessary for movable bridge analysis, is a comprehensive and time-consuming task. Fig. 2: Com
16、puter Model in ADINA This is the computer model using SAP2000 software for Roosevelt Island Lift Bridge in New York. Recently, H & H is performing rehabilitation design for electrical and mechanical system as well as seismic study, because this bridge is the only link between the island and the main
17、land. Fig. 3: Computer Model for Lift Span Bridge 3UNIQUE ISSUES FOR MOVABLE BRIDGE3.1 Structural Foundation and Substructure-Typically, both foundation and substructure of a movable bridge are very massive ensuring long-term performance of the superstructure. With the strong support, the superstruc
18、tures can be operated in a more stable platform. The substructures with large inertias Fig. 1 South Halstead Street BridgeFig. 1 South Halstead Street Bridge名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 2 页，共 6 页 - - - - - - - - - Page 3 of 6 require the foundation
19、having proper stiffness. In turn, foundation forces and the overall structural response are strongly affected by foundation stiffness. Both foundation capacity and foundation stiffness are strongly affected by scour. Movable bridge foundations are frequently located in a navigable stream or waterway
20、, and therefore are more likely to be exposed to strong currents. Most of the horizontal loads from the leaf and counterweight are transferred to the foundations through the trunnion tower. As such, the trunnion tower is a critical component of the structure. Failure of the trunnion tower can repres
21、ent complete failure of the structure. Superstructure - Movable superstructures are designed to be able to open and close, and as such often have unique structural systems. Of particular concern is the load path that vertical and lateral forces from the superstructure and counterweight are taken to
22、the foundations. Bascule bridges, for example, have several key points of vulnerability along the load path from the counterweights to the foundation including the trunnion bearing which supports the movable span in the closed and open positions and the toe joints at the span end. The movable spans
23、are designed to be lightweight, and, typically, have lightweight open steel grid decks, partially filled grid decks, or orthotropic steel plate decks. Open and closed positions - Movable bridges are analyzed in both their open and closed positions, and occasionally are analyzed for positions in betw
24、een. Highway bridges are generally left in their closed position most of the time. The AASHTO Movable Bridge Specification and other codes specify that the seismic load used for the open position may be reduced by 50 percent if the bridge is in that position for less than 10 percent of the time. Cou
25、nterweight - Counterweights are unique for movable bridge which balance the moving span in order to reduce the operating power. Usually found on bascule and lift bridges, these elements require special design considerations. 3.2 Machinery and Mechanical Devices 3.2.1Span Drive MachinerySpan drive ma
26、chinery moves the movable span and auxiliary machinery stabilizes or facilitates the span as a live load carrying structure when it is at rest. For some bridges, span drive machinery also serves to stabilize the movable span in certain positions. Many combinations of electrical, mechanical, and hydr
27、aulic components may be assembled to form span drives. Most US bridges have electro-mechanical span drives. The function of electro-mechanical conventional gear drives is to convert the high-speed low-torque input of an electrical motor to a low-speed high-torque output suitable for moving a heavy m
28、ovable span. There are many arrangements of equipment, but usually an electric motor powers the input shaft of a primary speed reducer (which may contain a differential to permit the output shaft speeds to differ while equalizing output torque). The output shafts of the primary reducer are connected
29、 to two secondary gear reduction units. The output of each secondary reducer rotates a pinion that drives the leaf open or closed, or holds the leaf stationary by means of brakes in the drive train. On older bridges, some or all the gearings may be “open” i.e., not encased in housings. 3.2.2Auxiliar
30、y Drive MachineryAuxiliary machinery supports the movable span to carry live load when it is at rest. The components are usually eletro-mechanical, but fluid power is also used. General examples of auxiliary machinery for various types of movable bridges are: Bascule Bridges- toe and tail locks, cen
31、tering devices, buffers Swing Bridges- center and end wedges Rim Bearing Swing Bridges-tread fastened to undersides of drum girders, tapered roll-ers, tracks, stools and racks, live rings with spiders, pivot posts, center latches or mechanisms, end lifts, rail lifts, buffers, and rigid stops Vertica
32、l Lift Bridges- buffers. 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 3 页，共 6 页 - - - - - - - - - Page 4 of 6 Auxiliary machinery, such as locks, wedges, bumpers, balance wheels and centering devices, are used in movable bridges to fix the structure in place either
33、 before or after it has transitioned from one position to the other. The exact behavior of mechanical device depends on the details of its design and configuration. The use of shear locks or span locks varies in purpose. On double leaf bascules, these devices transfer live loads between leaves. Most
34、 locks are positioned between the two leaves to simply transfer vertical shear. Sometimes, as in the case of some European bridges and a recent Hardesty & Hanover design, they are positioned so as to enable transfer of live load moment also. On lift bridges or single leaf bascules, these devices ass
35、ist in keeping the span seated. On swing bridges, wedges or lift systems perform specific live load function to permit the span to perform reliably. 3.2.3Structural/Mechanical Interface ComponentsFor the various bridges the interfacing details included are: Bascule Bridges- trunnion bearings Rolling
36、 Lift Bridge- segmental girder/track Vertical Lift Bridges- counterweight trunnion bearings, span guides (tower and span) Swing Bridges- pivot bearing/rim bearing For bascule bridges of any trunnion type, the critical connection for transmittal of loads is the trunnion bearing and trunnion shaft sys
37、tem. The issue critical to our case is the translation of the span in its bearing, designed to permit opening about the spans axis of rotation. The computed horizontal load is imparted via the trunnion shaft or trunnion hub into the bearing. Most bearings are the split journal type but even roller b
38、earings will have a jointed bearing base. This requires that the base connections to the support are designed for the full lateral force. For center bearing swing bridges all dead load goes through the pivot bearings. The bearing, whether bronze disk or roller, permits horizontal rotation of the spa
39、n and permits some out of normal rocking due to spherical surfaces. For rim-bearing swing bridges, the dead load is carried either exclusively, or mainly by a series of heavy tapered rollers centered on a post. This assembly, often known as a roller nest, will have spokes of various designs connecti
40、ng their rollers to the central pivot post. 3.3 Electrical System The electrical systems on movable bridges consist of power distribution systems and control systems. Movable bridges powered by electrical motors are serviced by industrial-type utility power or self-contained generator sets, or both.
41、 Electrical power is distributed to the motors, lighting panels, and control components via commercially-available electrical components such as circuit breakers, fuses, transformers, and motor control centers. The principal considerations for movable bridge electrical design involve the control sys
42、tem and the span motor controller. Span motor controllers, also known as span drives, provide proper speed and torque control for the electric motors which operate movable bridges. Four examples of span motor controllers are reviewed: Secondary Resistance Control, Primary Thyristor (SCR) Drive, Rege
43、nerative Direct Current Drive, and Flux Vector Drive. Secondary resistance control is a non-regulated drive system that employs an AC wound rotor motor and contactors. The SCR drive offers speed control, torque control and countertorque capabilities. The DC drive provides stepless, programmable spee
44、d control of a DC motor with similar reduced seating torque, counter-torque control, and feedback loops as the AC SCR drive. Flux vector drive represents the latest in variable frequency drive technology with increasing number of applications in movable bridges. Electrical system redundancy is analy
45、zed by deciding which subsystems are most critical, and providing alternate means of operation. Such subsystems are the power source, the span drives, motors, and their control systems. Redundancy of such subsystems improve operational reliability for waterborne users, vehicular/rail users or both.
46、A brief overview of common components, such 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 4 页，共 6 页 - - - - - - - - - Page 5 of 6 as: Generator Set, Transfer Switch, Transformers, Motor Control Centers, Motors and Drives, other electrical distribution equipment, and
47、 their applications in the movable bridges, is included in the 2000 LRFD AASHTO Standard Specification for Movable Highway Bridges 2. 4BASCULE BRIDGES Hardesty & Hanover designed the new 12-lane bascule bridge to replace the existing Woodrow Wilson Bridge that crosses the Potomac River in Washington
48、 DC. The new bridge comprises four side-by-side double-leaf bascule spans, each with a 270-foot center-to-center trunnion spacing and an overall bridge width of 249 feet. The bascule span is supported on V-shaped concrete bascule piers. Features of the span include a composite concrete deck, moment-
49、resisting span locks, tail Fig. 4: New Woodrow Wilson Bascule Bridge locks and the option of independent or group leaf operation. The bridge has been designed to accommodatefuture plans for a transit system. Contracted by VDOT, H&H performed studies, preliminary and final design for the widening and
50、 design of a new double-leaf bascule bridge. The successfully completed project doubles the traffic capacity of I-264. Large naval vessels can now navigate through the 150-ft. wide channel with ease. Fig. 5: Berkley Bridge Norfolk, VA 5LIFT BRIDGE The new Tomlinson Vertical Lift Bridge recently comp
51、leted con-struction in New Haven Connecticut was designed by H&H. Fig. 6: New Tomlinson Bridge and its Construction, New Haven, CT Marine Parkway Vertical Lift Bridge located in New York is a beautiful signature project linking Brooklyn and Coney Island. Fig. 7: Marine Parkway Lift Bridge Brooklyn,
52、NY 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 5 页，共 6 页 - - - - - - - - - Page 6 of 6 6SWING BRIDGES This is a railroad swing bridge in Connecticut showing full open for navigation. Fig. 8: Railroad Swing Bridge Willis Avenue Swing Bridge, origi-nally built in 19
53、01, connects Man-hattan and Bronx in the city of New York. This bridge carries 70,000 vehicles per day. H & H is currently designing a replacement bridge. This project covers a length ap-proximately 1 mile including Main line, FDR Ramp and Bruckner Blvd. Ramp. The left picture is the pro-posed repla
54、cement plans. Fig. 9: Design plans for replacement of Willis Avenue Bridge The photos to the right are the existing of Third Avenue Bridge and its replacement construction designed by H&H. ACKNOWLEDGEMENT The authors wish to thank and acknowledge many Hardesty & Hanover engineers for their contribut
55、ions and participation in the preparation of this paper. Fig. 10: Construction of Third Avenue Bridge - NY REFERENCES 1 AASHTO, 1988. AASHTO Standard Specifications for Movable Highway Bridges. Washington, DC. American Association of State Highway and Transportation Officials. 2 AASHTO, 2000. AASHTO
56、 LRFD Movable Highway Bridge Design Specifications. Washington, DC. American Association of State Highway and Transportation Officials. 3 Hool, G.A. & Kinne, W.S., 1943 . Movable and Long-Span Steel Bridges. New York, NY. McGraw-Hill. 4 Koglin, T.L., 2003. Movable Bridge Engineering. Hoboken, NJ. Jo
57、hn Wiley & Sons. 5 Waddell, J.A.L., 1916. Bridge Engineering . Vols 1 & 2, New York, NY. McGraw-Hill 6 Altebrando, N.J., Yin, B., Birnstiel, C., & Ludvik, M., 2003. Seismic Analysis of Movable Bridges. 2ndNew York City Bridge Conference. 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 6 页，共 6 页 - - - - - - - - -
