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1、ACI 345.2R-98 supersedes 345.2R-92 and became effective September 18, 1998. Copyright 1998, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical devic
2、e, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidanc
3、e in planning, de- signing, executing, and inspecting construction. This doc- ument is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept re- sponsibility for the application of the material it con
4、tains. The American Concrete Institute disclaims any and all re- sponsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in con- tract documents. If items found in this document are de- sired by
5、the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer. 345.2R-1 Many highway bridges become functionally obsolete due to inadequate width before they become structurally deficient. Because widening is a
6、lmost always more economical than complete replacement, there is a need to make available the results of research and field experience pertaining to the widening of bridges. This guide discusses many problems unique to the widening of concrete bridges and bridges with concrete decks. The primary foc
7、us of this document is on bridge decks. Substructure issues, however, also are raised and discussed. The effects of differential movements between the existing and new portions, including movements due to traffic on the existing structure during construction, are discussed. General recommendations a
8、re made pertaining to the choice of structure type, design details, and construction methods and materials. Keywords: bridge decks; bridge widening; bridges (structures); concrete construction; deflection; formwork (construction); reinforced concrete; reinforcing steels; substructures; superstructur
9、es; traffic vibrations. CONTENTS Chapter 1Introduction, p. 345.2R-1 1.1Purpose 1.2Common widening considerations Guide for Widening Highway Bridges ACI 345.2R-98 (Reapproved 2005) Reported by ACI Committee 345 Michael M. Sprinkel Chairman Khaled S. Soubra Subcommittee Chairman John AllenByron T. Dan
10、leyGert E. Hoppe Irfan A. AlviRalph L. DuncanHarry L. Patterson Gerald H. AndersonPhillip D. FreyOrrin Riley James C. AndersonRobert Vernon GeveckerHarold R. Sandberg John L. CarratoRobert J. GulyasVirendra K. Varma Paul D. CarterAllan C. HarwoodYash P. Virmani Reid W. CastrodaleKenneth A. HerrRicha
11、rd E. Weyers Chapter 2General design considerations, p. 345.2R-4 2.1General 2.2Selection of structure type Chapter 3Design and construction details, p. 345.2R-6 3.1General 3.2Concrete removal 3.3Refinishing exposed areas of the deck 3.4Traffic-induced vibrations and deflections 3.5Avoidance of damag
12、e due to dead load deflections 3.6Closure placement details 3.7Substructure details Chapter 4Summary of recommendations, p. 345.2R-13 Chapter 5References, p. 345.2R-14 5.1Recommended references 5.2Cited references CHAPTER 1INTRODUCTION 1.1Purpose The widening of highway bridges has become common. Se
13、veral factors contribute to this demand for wider bridges: a. Increased traffic volumes requiring additional lanes; b. Safety hazards of narrow bridges requiring wider shoulders; and c. Provision for bikeways and pedestrian ways. 345.2R-2ACI COMMITTEE REPORT The availability of funds under special p
14、rograms, such as the Intermodal Surface Transportation Efficiency Act (ISTEA), is enabling public agencies to widen many func- tionally obsolete bridges as needed to eliminate safety prob- lems. If a bridge was designed for current live loads and has not deteriorated appreciably, widening is likely
15、more cost-ef- fective than complete replacement. Many problems unique to bridge widening are not encoun- tered in work on new bridges. Failures or serious mainte- nance problems can be created by misunderstanding these problems. Each bridge widening is unique. This report pro- vides the designer and
16、 constructor with general guidelines for bridge widening. Emphasis is placed on construction practices, but because construction sequence, structure type, framing details, and other decisions critical to the success of the work are deter- mined during the design phase, some discussion of design conc
17、epts must be included. Structural analysis and design for bridge widenings is not addressed. Much of the discussion that follows also applies to new bridges constructed in stages, part width at a time. 1.2Common widening considerations When a bridge is to be widened, several potential problems shoul
18、d be considered by design and construction engineers. These include retention of bridge elements, traffic control, struc- tural constraints, and construction limitations. Moreover, certain elementary procedures should be followed for all structures: Review the record drawings and specifications of t
19、he original structure. Review any change orders that might have been approved during the original construction. Thoroughly inspect the structure and note changes in site conditions, such as bank scour. Obtain additional subsurface information, including borings, when footings are to be widened. The
20、first consideration for bridge widening is whether to retain structurally sound parts of the deck. Entire deck re- placement should be considered if the remaining old deck will become less than half of the new deck width, or the deck is severely deteriorated, or both (Operation, 1992; Seible, 1991).
21、 If the deck is to be retained, the design should provide for moment and shear transfer through the longitudinal joint be- tween the new and old portions of the deck. 1.2.1 Maintenance of trafficPrime concerns are the safe- ty and convenience of the traveling public, the safety of con- struction per
22、sonnel, and potential damage to the work. Another consideration is the effect of the widening on the safety of the public using the roadway or railway beneath the bridge and any traffic-related impact that the widening can have on that roadway. Ideally, a convenient alternate route should be used as
23、 a detour during bridge widening operations, so that all traffic can be kept off the bridge. However, this is seldom the case. Due to the high cost of a temporary detour bridge, economy usually dictates that traffic be carried on the bridge during widening. This creates congestion at the work site,
24、and re- sulting vibrations and deflections from live loads on the bridge can affect concrete in the new work (Transportation Research Board, 1981; Furr, 1981; Deaver, 1982; Arnold, 1980; Whiffen, 1971; Harsh, 1983; Silfwerbrand, 1992). Vi- brations can cause settlement and other movement of fresh co
25、ncrete and fractures in hardened concrete although exam- ples of the latter are rare. 1.2.2 Prevention of damage to existing structureBridge widenings generally involve shored excavation immediately adjacent to the existing bridge and removal of portions of the existing bridge (Fig. 1.1). Shoring of
26、 excavations is usually the responsibility of the contractor. Construction engineers should monitor this phase of the work carefully because public safety and safety of the existing bridge or adjacent highway facilities can be jeopar- dized by failure of shoring. Specifications should require that s
27、horing be designed and monitored by licensed engineers. De- signers should minimize lengths and widths of excavations. 1.2.3 Differential foundation settlementThe amount of tolerable differential foundation settlement between old and new construction depends on the configuration of the widen- ing. I
28、f the joint between the existing structure and the new structure is outside of the traveled way (that is, in the medi- an) or if rigid attachment of the widening to the existing structure is not required for overall stability, the existing and new structures can be left unconnected and differential
29、set- tlements tolerated. It is usually necessary, however, for the new foundation to be compatible with the existing one. This means that the new foundation must be designed to settle very little, dictating piles or drilled shafts, unless rock is present near the surface. 1.2.4 Differential superstr
30、ucture deflectionsDifferential deflections between new and existing superstructures are not a problem if the joint between the two occurs in a median or untraveled area. Generally in such cases, the superstructures are not connected. Joints should be located out of the traveled lanes whenever possib
31、le, but most frequently the joint between new and existing decks does occur within the traveled way. If decks are not connected, differential deflections will create offsets in the riding surface that could result in potentially Fig. 1.1Shoring to protect roadway during abutment wid- ening. 345.2R-3
32、GUIDE FOR WIDENING HIGHWAY BRIDGES hazardous vehicle control problems. Fig. 1.2 and 1.3 show two different views of a joint with differential deflection. Fig. 1.4 and 1.5 show attempts to minimize such differences; however, such situations should be avoided. Maintenance of joint seals in such workin
33、g joints can be difficult, hazardous to workers, and expensive. A new deck should be connected structurally to the exist- ing deck, if deicing salts are to be used, because leakage through the joint allows corrosion-inducing materials to reach the girders and substructure (Fig. 1.6). Whenever the ne
34、w deck joins the existing deck within the roadway, the two should be structurally connected (Transportation Research Board, 1981; Furr, 1981; Deaver, 1982; Arnold, 1980; Whiffen, 1971; Harsh, 1983; Concrete Repair Digest, 1997; McMahon, 1965; Shaw, 1974). If proper attention is not given to construc
35、tion sequence and details (for example, use of closure placements between the new deck and the existing deck), large differential deflections can cause overloading of the existing structure or distress in the new work along the joint line (Fig. 1.7). The deflections can be elastic deflections result
36、ing from the release of the falsework, or time-dependent deflections due to creep. 1.2.5 Differential longitudinal shorteningFor cast-in-place, post-tensioned concrete widenings, it is essential that the new work be allowed to shorten longitudinally without restraint from the existing bridge. Restra
37、ints will cause some of the stressing force to be transferred into the existing bridge, creat- ing undesirable stresses in it, and possibly reducing the pre- stressing force in the new work. When the two are to be rigidly connected in their completed state, a specific con- Fig. 1.2Transverse view sh
38、owing vertical lip. Fig. 1.3Longitudinal view showing proximity of wheel path. Fig. 1.4One view of an unsatisfactory attempt to minimize differential deflections by means of a continuous bituminous wedge. Fig. 1.5Another view of an unsatisfactory attempt to mini- mize differential deflections by mea
39、ns of a continuous bitu- minous wedge. 345.2R-4ACI COMMITTEE REPORT been more desirable to have scarified the old deck surface and repaired it as part of a combined bridge-widening and rehabilitation plan. CHAPTER 2GENERAL DESIGN CONSIDERATIONS 2.1General Certain aspects of structural type selection
40、, framing consid- erations, and design details are unique to bridge widenings. For specific design guidance, refer to the American Associa- tion of State Highway and Transportation Officials (AASH- TO) Load Resistance Factor Design (LRFD) Bridge Design Specifications and other standards and guides (
41、Silano, 1992) as noted in the references. Among the questions that a design- er should investigate prior to commencing design are: a. Can the widening be accomplished solely on the super- structure, or does the substructure also require widening? b. If widening the substructure is necessary, was thi
42、s fore- seen in the original design? c. Should one or both sides be widened? d. Is a parallel structure justified as an alternative to widening? e. Does widening the structure provide adequate vertical clearance? In general, current design codes and loadings applicable to the route on which the stru
43、cture is located should be used for bridge widenings. If the original bridge was designed using outdated codes or smaller than current live loadings, design- ing the widening to the old codes and loadings perpetuates a deficiency. Constructing widenings to current standards cre- ates the opportunity
44、 of later replacing or strengthening all or portions of the original bridge so that the entire structure can be upgraded. Bridges on private lands or outside the limits of the United States can require designing for higher loadings Fig. 1.6Chloride damage under leaking longitudinal deck joint. Fig.
45、1.7Deck soffit spalls under reinforcing steel dowels. struction sequence and the use of delayed closure placements are mandatory. 1.2.6 Vibrations from trafficTraffic-induced vibration has been blamed for distress occasionally observed in new construction that connects to structures carrying live lo
46、ads. Research (Effects, 1981; Furr, 1981; Deaver, 1982; Arnold, 1980; Whiffen, 1971; Harsh, 1983) indicates that such dam- age is relatively rare and can be eliminated by the use of a proper construction sequence and correct design details. See Section 3.4 for an extended discussion. 1.2.7 Removal o
47、f deck surfacesGenerally, bridge widen- ings involve removal of curbs, sidewalks, or railings. This often exposes a rough surface not suitable for traffic. The deck in these areas may have been intentionally left rough or may have been damaged during removal work, and should be restored to a smooth
48、profile in conjunction with the wid- ening work. This is best resolved by removing concrete to a minimum depth of 11/2 in. (38 mm) below grade and casting a new surface to match the adjacent grade. Saw cuts at least 1 in. (25 mm) below final grade should be used to provide any necessary hardened con
49、crete vertical faces to cast the new concrete against. Fig. 1.8, 1.9, and 1.10 show unsatisfactory patches adja- cent to a newly widened deck. In such cases, it would have -,-,- 345.2R-5GUIDE FOR WIDENING HIGHWAY BRIDGES than AASHTO standards due to industrial loads, a lack of load limits, or a lack of enforcement of load limits. 2.2Selection of structure type Many factors influence the designers choice of type of structure for a widening. The natural choice is to use the same type as the original, but this