AASHTO HB-17 DIVISION II SEC 3-2002 Division II Construction - Temporary Works《临时作业》.pdf

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1、Section 3 TEMPORARY WORKS 3.1 GENERAL 3.1.1 Description This work shall consist of the construction and re- moval of temporary facilities which are generally de- signed by the Contractor and employed by the Contractor in the execution of the work and whose failure to perform properly could adversely

2、 affect the character of the contract work or endanger the safety of adjacent facil- ities, property, or the public. Appropriate reductions in allowable stresses or loads shall be used for design when other than new or undamaged materials are to be used. Such facilities include, but are not limited

3、to, false- work, forms and form travelers, cofferdams, shoring, water control systems, and temporary bridges. The following publications are useful reference docu- ments in the preparation of specifications for the design, review and inspection of temporary works: Synthesis of Falsework, Formwork, a

4、nd Scafolding for Highway Bridge Structures, November 1991, Guide Standard Specijcations for Bridge Temporary Guide Design SpeciJcation for Bridge Temporary Certijcation Program for Bridge Temporary Works, Construction Handbook for Bridge Temporary (FHWA-RD-9 1-062) Works, November 1993, (FHWA-RD-93

5、-031) Works, November 1993, (FHWA-RD-93-032) November 1993, (FHWA-RD-93-033) Works, November 1993, (FHWA-RD-93-034) 3.1.2 Working Drawings Whenever specified or requested by the Engineer, the Contractor shall provide working drawings with design calculations and supporting data in sufficient detail

6、to per- mit a structural review of the proposed design of a tem- porary work. When concrete is involved, such data shall include the sequence and rate of placement. Sufficient copies shall be furnished to meet the needs of the Engi- neer and other entities with review authority. The working drawings

7、 shall be submitted sufficiently in advance of proposed use to allow for their review, revision, if needed, and approval without delay to the work. The Contractor shall not start the construction of any temporary work for which working drawings are required until the drawings have been approved by t

8、he Engineer. Such approval will not relieve the Contractor of responsi- bility for results obtained by use of these drawings or any of his other responsibilities under the contract. 3.1.3 Design The design of temporary works shall conform to the AASHTO Standard Specijcations for Highway Bridges or t

9、he Guide Design Specijcations for Bridge Temporary Works; or to other established and generally accepted de- sign code or specification for such work. When manufactured devices are to be employed, the design shall not result in loads on such devices in excess of the load ratings recommended by their

10、 manufacturer. For equipment where the rated capacity is determined by load testing, the design load shall be as stated in the Guide Design Specijcations for Bridge Temporary Works. The load rating used for special equipment, such as ac- cess scaffolding, may be under the jurisdiction of OSHA and/or

11、 other State/local regulations. However, in no case shall the rating exceed 80% of the maximum load sus- tained during load testing of the equipment. When required by statute or specified in the contract documents, the design shall be prepared and the drawings signed by a Registered Professional Eng

12、ineer. 3.1.4 Construction Temporary works shall be constructed in conformance with the approved working drawings. The Contractor shall verify that the quality of the materials and workmanship employed are consistent with that assumed in the design. 3.1.5 Removal Unless otherwise permitted, all tempo

13、rary works shall be removed and shall remain the property of the Contrac- tor upon completion of their use. The area shall be re- 483 484 HIGHWAY BRIDGES 3.1.5 stored to its original or planned condition and cleaned of all debris. 3.2 FALSEWORK AND FORMS 3.2.1 General Falsework is considered to be a

14、ny temporary structure which supports structural elements of concrete, steel, ma- sonry, or other materials during their construction or erec- tion. Forms are considered to be the enclosures or panels which contain the fluid concrete and withstand the forces due to its placement and consolidation. F

15、orms may in turn be supported on falsework. Form travelers, as used in seg- mental cantilever construction, are considered to be a combination of falsework and forms. Whenever the height of falsework exceeds 14 feet or whenever traffic, other than workmen involved in con- structing the bridge, will

16、travel under the bridge, the working drawings for the falsework shall be prepared and sealed by a Registered Engineer. Falsework and forms shall be of sufficient rigidity and strength to safely support all loads imposed, and produce in the finished structure the lines and grades indicated on the pla

17、ns. Forms shall also impart the required surface texture and rustication, and shall not detract from the uni- formity of color of formed surfaces. 3.2.2 Falsework Design and Construction 3.2.2.1 Loads The design load for falsework shall consist of the sum of dead and live vertical loads, and any hor

18、izontal loads. As a minimum, dead loads shall include the weight of the falsework and all construction material to be sup- ported. The combined weight of concrete, reinforcing and prestressing steel and forms shall be assumed to be not less than 160 pounds per cubic foot of normal weight con- crete

19、or 130 pounds per cubic foot of lightweight concrete that is supported. Live loads shall consist of the actual weight of any equipment to be supported applied as concentrated loads at the points of contact and a uniform load of not less than 20 pounds per square foot applied over the area supported,

20、 plus 75 pounds per linear foot applied at the outside edge of deck overhangs. The horizontal load used for the design of the falsework bracing system shall be the sum of the horizon- tal loads due to equipment, construction sequence, in- cluding unbalanced hydrostatic forces from fluid concrete, st

21、ream flow when applicable, and an allowance for wind. However, in no case shall the horizontal load to be resisted in any direction be less than 2% of the total dead load. For post-tensioned structures, the falsework shall also be designed to support any increased or redistribution of loads caused b

22、y prestressing of the structure. Loads imposed by falsework onto existing, new or par- tially completed structures shall not exceed those permit- ted in Article 8.15, “Application of Loads.” 3.2.2.2 Foundations Falsework shall be founded on a solid footing safe against undermining, protected from so

23、ftening, and capa- ble of supporting the loads imposed on it. When requested by the Engineer, the Contractor shall demonstrate by suit- able load tests that the soil bearing values assumed for the design of the falsework footings do not exceed the sup- porting capacity of the soil. Falsework which c

24、annot be founded on a satisfactory footing shall be supported on piling which shall be spaced, driven, and removed in an approved manner. 3.2.2.3 Deflections For cast-in-place concrete structures, the calculated de- flection of falsework flexural members shall not exceed U240 of their span irrespect

25、ive of the fact that the deflec- tion may be compensated for by camber strips. 3.2.2.4 Clearances Unless otherwise provided, the minimum dimensions of clear openings to be provided through falsework for roadways which are to remain open to traffic during con- struction shall be at least 5 feet great

26、er than the width of the approach traveled way, measured between barriers when used, and 14 feet high, except that the minimum vertical clearance over interstate routes and freeways shall be 14.5 feet. 3.2.2.5 Construction Falsework shall be constructed and set to grades which allow for its anticipa

27、ted settlement and deflection, and for the vertical alignment and camber indicated on the plans or ordered by the Engineer for the permanent structure. Variable depth camber strips shall be used between false- work beams and soffit forms to accomplish this when di- rected by the Engineer. Suitable s

28、crew jacks, pairs of wedges or other devices shall be used at each post to adjust falsework to grade, to permit minor adjustments during the placement of con- 3.2.2.5 DIVISION II-CONSTRUCTION 485 Crete or structural steel should observed settlements de- viate from those anticipated, and to allow for

29、 the gradual release of the falsework. Telltales attached to the forms and extending to the ground, or other means, shall be provided by the Contractor for accurate measurement of falsework settlement during the placing and curing of the concrete. Falsework or formwork for deck slabs on girder bridg

30、es shall be supported directly on the girders so that there will be no appreciable differential settlement during placing of the concrete. Girders shall be braced and tied to resist any forces that would cause rotation or torsion in the girders caused by the placing of concrete for di- aphragms or d

31、eck. Welding of falsework support brackets or braces to structural steel members or reinforcing steel will not be allowed unless specifically permitted. I 3.2.3 Formwork Design and Construction 3.2.3.1 General Forms shall be of wood, steel, or other approved mate- rial and shall be mortar tight and

32、of sufficient rigidity to prevent objectional distortion of the formed concrete sur- face due to pressure of the concrete and other loads inci- dental to the construction operations. Forms for concrete surfaces exposed to view shall pro- duce a smooth surface of uniform texture and color sub- stanti

33、ally equal to that which would be obtained with the use of plywood conforming to the National Institute of Standards and Technology Product Standard PSI for Ex- terior B-B Class I Plywood. Panels lining such forms shall be arranged so that the joint lines form a symmetrical pat- tem conforming to th

34、e general lines of the structure. The same type of form lining material shall be used through- out each element of a structure. Such forms shall be suf- ficiently rigid so that the undulation of the concrete sur- face shall not exceed % inch when checked with a 5-foot-long straightedge or template.

35、All sharp comers shall be filleted with approximately %inch chamfer strips. Concrete shall not be deposited in the forms until all work connected with constructing the forms has been completed, all debris has been removed, all materials to be embedded in the concrete have been placed for the unit to

36、 be cast, and the Engineer has inspected the forms and materials. . 3.2.3.2 Design The structural design of formwork shall conform to AC1 Standard, “Recommended Practice for Concrete Formwork,” (AC1 347) or some other generally accepted standard. In selecting the hydrostatic pressure to be used in t

37、he design of forms, consideration shall be given to the maximum rate of concrete placement to be used, the ef- fects of vibration, the temperature of the concrete and any expected use of set-retarding admixtures or pozzolanic materials in the concrete mix. 3.2.3.3 Construction Forms shall be set and

38、 held true to the dimensions, lines and grades of the structure prior to and during the placement of concrete. Forms may be given a bevel or draft at projections, such as copings, to ensure easy re- moval. Prior to reuse, forms shall be cleaned, inspected for damage and, if necessary, repaired. When

39、 forms ap- pear to be defective in any manner, either before or dur- ing the placement of concrete, the Engineer may order the work stopped until defects have been corrected. Forms shall be treated with form oil or other approved release agent before the reinforcing steel is placed. Mate- rial which

40、 will adhere to or discolor the concrete shall not be used. Except as provided herein, metal ties or anchorages within the forms shall be so constructed as to permit their removal to a depth of at least 1 inch from the face without injury to the concrete. Ordinary wire ties may be used only when the

41、 concrete will not be exposed to view and where the concrete will not come in contact with salts or sulfates. Such wire ties, upon removal of the forms, shall be cut back at least 1/4 inch from the face of the concrete with chisels or nippers; for green concrete, nippers shall be used. Fittings for

42、metal ties shall be of such design that, upon their removal, the cavities that are left will be of the smallest possible size. The cavities shall be filled with ce- ment mortar and the surface left sound, smooth, even, and uniform in color. When epoxy-coated reinforcing steel is required, all metal

43、ties, anchorages or spreaders which will remain in the concrete shall be of corrosion resistant material or coated with a dielectric material. For narrow walls and columns, where the bottom of the form is inaccessible, an access opening shall be provided in the forms for cleaning out extraneous mate

44、rial imme- diately before placing the concrete. 3.2.3.4 -be Forms Tubes used as forms to produce voids in concrete slabs shall be properly designed and fabricated or otherwise treated to make the outside surface waterproof. Prior to concrete placement such tubes shall be protected from the weather a

45、nd stored and installed by methods that prevent distortion or damage. The ends of tube forms shall be cov- 486 HIGHWAY BRIDGES 3.2.3.4 ered with caps that shall be made mortar tight and water- proof. If wood or other material that expands when moist is used for capping tubes, a premolded rubber join

46、t filler Y4 inch in thickness shall be used around the perimeter of the caps to permit expansion. A PVC vent tube shall be provided near each end of each tube. These vents shall be constructed to provide positive venting of the voids. After exterior form removal, the vent tube shall be trimmed to wi

47、thin Y2 inch of the bottom surface of the finished con- crete. Anchors and ties for tube forms shall be adequate to prevent displacement of the tubes during concrete place- ment. 3.2.3.5 Stay-in-Place Forms Stay-in-place deck soffit forms, such as corrugated metal or precast concrete panels, may be

48、used if shown on the plans or approved by the Engineer. Prior to the use of such forms the Contractor shall provide a com- plete set of details to the Engineer for review and approval. The detailed plans for structures, unless other- wise noted, are dimensioned for the use of removable forms and any

49、 changes necessary to accommodate stay-in-place forms, if approved, shall be at the expense of the Contractor. 3.2.4 Removal of Falsework and Forms 3.2.4.1 General Falsework or forms shall not be removed without ap- proval of the Engineer. In the determination of the time for the removal of falsework and forms, consideration shall be given to the location and character of the structure, the weather; the materials used in the mix, and other condi- tions influencing the early strength of the concrete. Methods of removal likely to cause overstressing of the concrete or damage to its surface