Biện pháp mô tả chi tiết quy trình thi công đúc sẵn dầm Bản Cầu. Được biên soạn dựa trên chỉ dẫn kỹ thuật dự án, Tiêu chuẩn AASHTO, TCVN
GENERAL DESCRIPTION
Introduction
This method statement outlines the process, personnel, equipment, materials, and documentation required for the construction of box culverts It also includes quality and measurement verification procedures, safety precautions, and environmental protection measures to ensure the project's successful execution.
Project Information
The project road connects Tbong Khmum district to Kratie province of the Cambodia, stretching along the northern, to Kratie province The road passes on a comfortable alignment through flat/wavy terrain along the toe of hilly land Four (4) rather sharp curves along the road are considered non-critical due to adequate super-elevation of the road way and appropriate signage The traffic on the road is a medium mix of private cars and quite heavy trucks that contribute mainly to the road wear The PR.377 and PR377A of RCIP are located in Kratie province The length of the PR377 is 35.00 km and the PR377A is 13.593km The location of the packages is shown in Figure-1
Figure 1.2 Location of Contract Package on CW-3(PR377 & PR377A)
Project Objective
The objective of the project is to ensure continued effective use of the rehabilitated national and provincial road network in support of the economic development in Cambodia It will do so by improving the institutional and technical capacity of the Ministry of Public Works and Transport for road maintenance planning, budgeting and operations as well as by expanding of strengthening maintenance activities.
The project seeks to contribute to cultivating a road asset management culture within the sector by:
(i) expanding maintenance of the national road infrastructure nationwide and facilitating interventions in priority areas, (ii) allocating adequate maintenance funding during the budgeting process; (iii). knowledge building in MPWT on road network management, maintenance technology and contract management; and (iv) private sector involvement in competitive bidding and performance quality.
Project is expected to bring significant benefits to local residents in six Cambodian provinces,Kampong chham, Tbong Phmum, Kratie, Mondulkiri, Ratanakiri and Stung treng province; by reduced travel times and cost, less arduous journeys and better connectivity along the national road network It is intended that the benefits to local populations are maximized, and to ensure that the benefits are shared by local communities.
Topography and Climate
The topography in the project area is mainly flat with some hilly sections and the road elevation varies from minimum 23.52m to maximum 50.95meter The maximum temperature is around 40°C, the annual temperature fluctuates more than 10°C and from 6 – 7°C in a day In hot weather the absolute high temperature may be up to 39°C (in April) By contrast, in January the absolute low temperature may descend to 16°C.
Rainfall Records
The available hydrometeorological data such as rainfall are obtained from the Kratie Provincial Department of Water Resources and Meteorology (PDoWRAM) The rainfall station is located at (Xa0976, Y79728) The data ranged from 1980 to 2019 is considered to conduct frequency analysis for hydrologic modeling The 24hr maximum annual rainfall over 3 decades were extracted for the analysis as shown in Figure 4.1 and 4.2 below From the figure below, it’s clearly observed that the highest rainfall over the period was in the year of 1988 with a value above 250mm, followed by the year of 1982 as the second highest with the precipitation of above 270mm The year 2009 is observed to have above 150mm which was the highest rate over the 10 year after 1992 and it was revealed during the Ketsana storm In 2001 was noted as lowest rainfall, it’s reflected to the Drought period.
Figure 1.5.1 Daily Rainfall Ditribution in Kratie 1980-2019
DESCRIPTION OF WORKS
Scope of Works
This is Method Statement for production of Prestressed Concrete Deck (PSC Deck) for superstructure
Summary table of PSC Deck :
No Type of Beam Number Bridge Package
BR-07 (PK23+673.04) CW3-PR377 2 PSC Deck type B, 18m 4
BR-11 (PK30+920.54) CW3-PR377 4 PSC Deck type B, 18m 4
BR-12 (PK31+868.04) CW3-PR3776 PSC Deck type B, 18m 4
Standards and Technical specification related
CAM PW 04-102-99 Bridge Design Standard (Cambodia, 2003) AASHTO, 2002 Standard Specifications for Highway Bridges Other Standards related b) Technical specification
+ Section 5.1: Concrete of Specifications + Section 5.2: Reinforcement of Specifications + Section 5.4: Prestressed Concrete
Construction Schedule
Construction Schedule shall be referred to latest approved Schedule.
ORGANIZATION CHART
Organization Chart is as follow:
MANPOWER AND EQUIPMENT
Equipment
Plants and equipments proposed as in Table below:
No Description Model Quantit y Remarks
2 Bar Cutter Max dia 32mm 2
3 Bar Bender Max dia 32mm 2
14 Air Compressor 7kg/cm 2 1 Cleaning work
Above stated schedule of equipment shall be increased in quantity if required and necessary Actual equipment mobilized shall be subjected to inspection and approved of the Engineer.
Calibration of pre-stressing Jacks and pumps shall be implemented at least one time per year and after repairing And extra calibration shall be conducted if each pre-stressing result or group control of pre-stressing show abnormal phenomenon or the Engineer’s request.
Manpower
Workforce to be mobilized for construction work as below:
Notes: This manpower will be increased according to the site requirements
MATERIALS
List of main materials used for constructing
1 Portland Cement 2 Course of Aggregate 3 Fine Aggregate 4 Water
5 Admixtures (if any) 6 Steel Bars
7 Steel Strands8 Anchorages9 Other supplies
Technical requirements of the material
Cement shall conform to the requirements of AASHTO Standard Specification M85 The use of high alumina cement is not allowed Cement shall conform to Type I unless specifically otherwise stated in the Special Provisions, or on the Drawings Supply of cement shall be submitted for approval before use, with respect to origin and quality Subsequent deliveries shall be also subject to quality control testing as work proceeds.
Approval of origin and quality shall be given only on presentation of test results showing that the cement factory proposed is able to supply a product which will consistently meet the physical and chemical qualities specified Quality control tests shall be made on each cement delivery, in order to determine the following characteristics:
+ Specific gravity + Specific surface by means of air permeability + Heat loss
+ Hot and cold expansion properties + Compressive strength at 3, 7 and 28 days + Setting time
The Contractor shall provide suitable means of storing and protecting the cement against dampness that shall be subject to the approval of the Engineer.
The Contractor shall store consecutive deliveries of cement separately and shall ensure that cement is used in chronological order of delivery.
The Engineer may reject cement which is more than eight weeks old or which has become partially set or which contains lumps of caked cement The use of cement reclaimed from discarded or used bags will not be permitted b) Water
Water used in mixing and curing concrete shall be subjected to approval of the Engineer and shall be clean and free from oil, salt, acid, alkali, sugar, vegetable, or other substances injurious to concrete or steel Generally, water that is suitable for drinking is satisfactory for use in concrete.
Water shall be tested by methods described in AASHTO T26, and shall not contain concentrations of dissolved solids, chlorides expressed as Cl, and sulphates expressed as S04 in excess of the following limits:
Application Dissolved Solids Concentrations in ppm
Water which contains a high content of suspended solids shall be allowed to stand in a settling basin before use The turgidity of water shall not exceed 2,000 ppm. c) Coarse Aggregate
Coarse aggregate shall consist of clean, hard, durable rounded natural aggregates or crushed rock It shall comply with the requirements of AASHTO M80, Coarse Aggregate for Portland Cement Concrete, in respect of bulk density, unit mass, water absorption, stability, soundness, material finer than 75 microns, deleterious materials, sulphur content, physical properties and particle shape If required, aggregate shall be washed to satisfy these requirements.
The coarse aggregate shall have a Los Angeles abrasion coefficient, after 500 revolutions, below 35
% (AASHTO T-96) and a water absorption capacity < 5 % (AASHTO T-85)
The aggregates shall include as few as possible of flat and elongated particles The testing for checking the amount of particles with an incorrect shape shall be carried out either by determining the average volumetric coefficient of the aggregate, or by any other equivalent method approved by the Engineer
The coarse aggregate for use in concrete structures shall not contain any materials that are deleteriously reactive with the alkalis in the cement in an amount sufficient to cause excessive expansion of mortar or concrete, except that, if such materials are present in injurious amounts, the coarse aggregate may be used with a cement containing less than 0.6 percent alkalis calculated as sodium oxide or with the addition of the material that has been shown to prevent harmful expansion due to alkali-aggregate reaction d) Fine Aggregate
Fine aggregate shall consist of either a sand resulting from the crushing of the rock used for the fabrication of coarse aggregates with a Los Angeles abrasion coefficient lower than 35 % at 500 revolutions (AASHTO T 96) and a water absorption capacity lower than 5 % (AASHTO T 84), or a natural river sand The use of marine sand is not allowed
Fine aggregate shall conform to all the requirements of AASHTO Standard Specification M6 e) Admixtures
Admixtures or any other additions shall not be used except with the written approval of the Engineer
The contractor must provide specifications and samples of proposed admixtures or additives to the engineer at least 28 days before the project's start or manufacturing of the specific structure where they intend to use such materials This requirement ensures that the engineer has ample time to review and approve the materials, ensuring their suitability and compliance with project specifications.
The concrete mix is tested under the supervision of a supervisory consultant and meets the project's technical requirements
The design testing of concrete mix composition is carried out in the field laboratory.
Before designing concrete mix, must submit to the consulting engineer the origin of the materials, together with the factory certificate as well as the material test results When taking samples for testing, they must be witnessed by the supervision consultant, make a record of taking samples for testing and fully signed by the parties before they can be tested.
Concrete mix design results must be reported in writing.
The composition and strength of concrete must satisfy the requirements in the following table:
Slump (mm) Coarse Aggregate AASHTO M 43
Note: The air content for concrete Class A1, A2, B1, B2 and B3 shall not be more than 4, +/- 1 percent
A trial mix for a particular class shall be acceptable when the strengths of each specimen from three sets of three specimens made from different batches, cured and tested after the age specified, in a laboratory approved by the Engineer, and when the slump tested on the concrete from the same batches, are not below the particular requirements specified in Table 5.2.2.
Table 5.2.2: Trial Mix Characteristic Properties
3-Day 7-Day 28-Day 3-Day 7-Day 28-Day Non vibrated
The flexural strength is expressed as the modulus of rupture MR = K f’c , with K=0.7 to 0.8, and f’ c in Mpa. g) Mortar
Any mortar used in conjunction with concrete work shall be a 1:3:5 mix mortar, conforming to SubClause 5.4.2.12 (Technical Specification), unless otherwise indicated. h) Reinforcement
The Contractor shall submit the name of the proposed supplier (or suppliers) of the reinforcement and necessary information concerning the supplier as soon as possible to the Engineer for his approval.
According to AASHTO M 31M, concrete reinforcement bars must meet specified material properties Deformed billet-steel bars are designated Grade 400, while plain round bars are classified as Grade 300.
Wire and Wire Mesh: Wire shall conform to the requirements of AASHTO Standard
Specification M 32 –Cold Drawn Steel Wire for Concrete Reinforcement Wire mesh shall conform to the requirements of AASHTO Standard Specification M 55 - Welded Steel Wire Fabric for Concrete Reinforcemen.
Bar Mat Reinforcement: Bar mat reinforcement for concrete shall conform to the requirements of
AASHTO Standard Specification M 54 - Fabricated Steel Bar or Rod Mats for Concrete Reinforcement. i) Pre-Stressing Reinforcement
High Tensile Strength Steel Strand - High Tensile Strength Steel Strand shall conform to the requirements of AASHTO M203 Uncoated Seven-Wire Low Relaxation Stress-Relieved Strand for Prestressed Concrete Strand shall be delivered in coils of sufficiently large diameter to ensure that it pulls off straight They shall be stored clear of the ground and protected from the weather and any other potentially harmful effects.
High Tensile Strength Steel Bars - High Tensile Strength Steel Bars for pre-stressed concrete shall conform to AASHTO M275 Uncoated High Strength Steel Bar for Pre-stressing Concrete j) Anchorage Assemblies
TESTING AND SAMPLING
Lab
The contractor will submit to the consultant a qualified testing unit The profile will be submitted separately by the contractor The experimental unit will serve the project with the approval of the consultant.
Testing Standard
Unless otherwise specified, all tests shall be performed in accordance with the methods used by AASHTO/ASTM and shall be made by the Engineer or his designated representative.
List table of sampling and test frequency reference Table 1.7 “Concrete”, Table 1.8
“Reinforcement” and Table 1.9 “Pre-stressing steel” at Sub-clauses 1.1.7 of Technical Specification ofProject.
Experimental Work
Contractor will provide full test certificates, origin of all supplier's materials.
The material criteria shall conform to the requirements in item “5: Materials” and the requirements of the technical instructions.
All tests shall be conducted in a manner approved by the engineer and shall be conducted in the contractor's laboratory. a) For concrete mix:
All concrete used in the Works shall be subject to sampling and testing strictly in the manner prescribed in AASHTO Testing Specifications T-22, T-23, T-97, T-126, T-119 and T-141 and in accordance with the requirements as detailed in Tecnical Specifications.
Samples shall be taken from separate batches of concrete selected at random during the placing operation Two cylinders (minimum) shall be cast from each sample in purpose-made steel moulds conforming to AASHTO T-23 and identified as a matched set Each cylinder shall be identified with the batch and/or lot as directed by the Engineer and a written record made of the location of each batch within the structure In addition, for precast concrete, the cylinders shall be so marked that they can be readily identified with the corresponding structural unit at all times. b) For reinforcement:
Samples of the steel lot delivered to the site will be taken for testing at the request of the engineer.
The frequency of testing for reinforcement shall not be less than the following frequency: 1 time/ each type of diameter/ each batch of steel delivered to the site Additional tests may be required by the engineer.
All rebar tests shall conform to the requirements and specifications of the AASHTO standards. c) For Prestressing Reinforcement:
High Tensile Strength Steel Strand - At least one specimen for test shall be taken from each 20 tons production lot of finished strand Test specimens shall be cut from the outside end of reels or either end of coils of strand Any specimen found to contain a wire joint should be discarded and a new specimen obtained.
The specimens shall be tested to determine compliance with the requirements of the relevant AASHTO Specifications. d) Testing of Pre-Stressed Beams:
When directed by the Engineer one or more beams shall be subjected to a loading test The Contractor shall obtain the prior approval of the Engineer to the detailed arrangements for the testing.
A beam that is to undergo testing shall be supported at its design points of’ bearing and the upward deflection due to the pre-stressing force measured relative to a line joining these points.
Equal loads shall then be applied at the third points in ten equal increments, the total being sustained for 5 minutes The beam shall then be unloaded
The mid-span deflection relative to the reference line shall be measured for each increment of load.
The load deflection curve plotted from these values must show no appreciable variation from a straight line The Drawings shall show, or the Engineer shall direct, the loads to be applied and the corresponding deflections that must not be exceeded.
Any beam which fails to satisfy the Engineer under the prescribed test shall be rejected
The Contractor shall supply to the Engineer record sheets of the tests showing date of test, the loads, deflections, and load deflection curves, calculated values of “E”, and the strength of the concrete at release as indicated by the relevant cube test results
The tests are to be carried out on units selected by and in the presence of the Engineer after he has agreed the method of testing and form of records.
CONSTRUCTION REQUIREMENT
Reinforcement
Each bundle of steel shall be tagged at the mill with an identifying mill tag showing the name of the mill and the melt or heat number The Contractor shall also make available for review, when requested by the Engineer, a copy of the certified mill test report for each heat and size of reinforcing steel showing physical and chemical analysis
Reinforcement for structures shall be handled and stored in a manner that will prevent bending out of the desired shape and the unnecessary accumulation of dust, oil and paint
All reinforcing steel shall be stored under cover and protected from the weather, and no reinforcing steel shall be stored in direct contact with the ground nor with water.
Before concrete is placed, the reinforcement to be embedded shall be free of mortar, oil, dirt, loose mill scale and loose rust, and other coatings of any character that would destroy or reduce the bond. b) Cutting and Bending
Bars shall be cut and bent cold to the dimensions indicated and with equipment and methods approved by the Engineer.
Bars shall be bent around a circular pin having the following diameters (D) in relation to the diameter of the bar (d):
To ensure structural integrity, bends and hooks in stirrups or ties should be formed around a pin with a diameter of at least twice the bar's nominal diameter Hook configurations must adhere to the guidelines outlined in Section 906 of the American Concrete Institute's Standard Building Code Requirements for Reinforced Concrete (ACI 318), or as specified in the construction drawings.
Reinforcement shall conform accurately to the dimensions shown on the Drawings Bars shall not be bent and straightened in a manner that will injure the material In particular, it shall not be authorized to straighten back deformed bars which have been previously bent Bars with kinks or improper bends shall not be used.
All reinforcement bars shall be sheared; flame cutting will not be permitted unless approved by the Engineer c) Placing, Supporting, and Fastening
Before commencing concrete placing, all bar reinforcement must be positioned, braced, and secured Prior placement approval from an Engineer is required to ensure compliance The minimum spacing between bars must exceed 1.33 times the largest coarse aggregate particle size Subsequent bar insertion into the concrete is prohibited Metal supports or mortar blocks with embedded tie wires (1:3 cement-sand ratio) should support horizontal reinforcement Mortar blocks are required for supports adjacent to concrete surfaces, excluding small stones or wood blocks Wire ties guarantee proper positioning and spacing of reinforcement, as per construction drawings.
Wire ties shall be securely tied and folded so that they do not project beyond the planes formed by the reinforcing bars The adequacy of the supports and ties to secure the reinforcement properly shall be subject to the approval of the Engineer.
The concrete cover shall be in accordance with the requirements of the AASHTO LRFD Bridge Design Specifications, Section 5, Table 5.12.3-1, unless otherwise indicated in the Drawings. d) Splicing
Reinforcement shall be furnished in the lengths indicated on the Drawings Lap splicing except where shown on the Drawings will not be permitted without written approval from the Engineer, and if additional lap splices are used the additional weight occasioned by such lap splices with not be included in the measurement of reinforcement for payment.
All splices shall have a lap length of not less than 40 diameters of the bars for tensile reinforcement and 32 diameters for compressive reinforcement or as shown on the Drawings Lap splices shall generally be located at points of minimum tensile strength Except where otherwise shown on the Drawings lap splices shall be made with the bars placed in contact and wired securely together.
Welding of reinforcing steel shall not normally be permitted and shall only be done if detailed on the Drawings or approved in writing by the Engineer Before the Engineer will approve of welding, the Contractor shall submit such samples as the Engineer may require for testing and make allowance for the time elapsing before test results are available.
Welding of reinforcing steel, if permitted, shall conform to the Structural Welding Code AWS Dl.4 of the American Welding Society and applicable special provisions and shall only be done where shown, specified, or permitted by the Engineer Every welder shall possess a welding certificate issued by an internationally recognized authority acceptable to the Engineer e) Substitutions
Substitution of different size bars will be permitted only with specific authorization by theEngineer If steel is substituted, it shall have a cross sectional area equivalent to the design area or larger.
Formwork
Molds shall be made of metal and shall be substantial enough so that they shall not deflect beyond the tolerance limits during casting Chamfers shall be straight and true to shape and line.
Core for forming transverse holes in the finished work, or other forming devices which would restrict longitudinal strains in the member shall be loosened so that concrete shrinkage or thermal movements are not restrained.
For enduring structural integrity, internal ties should facilitate removal up to 25 mm from the concrete surface, ensuring no damage occurs To prevent corrosion and maintain concrete durability, permanently embedded metal elements must maintain a minimum cover of 25 mm from the finished concrete surface.
Formwork shall be so constructed that easy cleaning out of any extraneous material inside the formwork can be achieved without disturbing formwork already checked and approved by the Engineer.
Formwork shall be treated with approved non-staining oil or saturated with water at the discretion of the Engineer before placing concrete Form oil will only be used after the approval of the Engineer has been given The Engineer may require trials to be carried out before approval is given for the use of a particular form oil, to ascertain that the form oil proposed by the Contractor will not discolor or injure the finished concrete face in any way.
Seals shall be fitted to prevent loss of cement past through joints in the formwork.
Removal of Formwork and False-work
General - Formwork shall be constructed such that the side forms of members can be removed without disturbing the soffit forms and, if props are to be left in place when the soffit forms are removed, the props shall not be disturbed during striking All formwork shall be removed without damage to the concrete.
Time of removal - Forms and false-work shall not be removed without the approval of the
Engineer To facilitate finishing, side forms may be removed at time after 24 hours completion of the placing of concrete.
Patching - As soon as the forms are removed, all wire or metal devices used for securing the formwork which project from or appear on the surface of the finished concrete shall be removed or cut back at least 25 mm from the finished surface of the concrete All holes and pockets so formed shall be filled with cement mortar mixed in the same proportions as the fine aggregate to cement of the concrete mix used for that particular section of the structure, after the surface to be patched has been thoroughly cleaned and wetted to receive the patch.
General Concrete Problems
After having carefully accepted the formwork, reinforcement and approved by the consultant and supervisory engineer, the contractor is allowed to proceed with the concreting work.
Inspection of the exact position of the heart, the core, the waiting details to ensure that after the concrete is poured, the formwork and the rear formwork are installed without deviation.
Concrete employed in construction is sourced from dedicated "cement concrete batching plants," ensuring adherence to technical specifications during the mixing and transportation processes These specifications govern the optimal ratios of ingredients, mixing time, and transportation conditions to guarantee the integrity and durability of the concrete upon its arrival at the construction site.
The thickness of the concrete layers is suitable for the size of the structure and compaction tools but must not exceed 35cm according to the pouring speed (v < 25m 3 /h).
Workers will pour concrete under the guidance of field staff to ensure that the concrete work is performed in the correct order, reasonable specifications, and regulations.
Do not distort position of reinforcement, formwork, position of waiting details and thickness of protective concrete layer.
If the reinforcement is bent or warped, it must be straightened before concreting.
Do not step on or stepping directly on the reinforcement, causing damage to the reinforcement.
Ensure accuracy in concrete surface level during pouring, adhering to designated elevations marked prior to concreting Avoid deviations from the design specifications, ensuring neither excessive height nor insufficient depth Pay meticulous attention to concrete surface finishing with cardboard, achieving a smooth and uniform result.
Concrete mix fabrication, concrete mixing and concrete transportation:
These works shall be in accordance with the directive section 5.1 “Concrete” – in the TechnicalSpecifications of the project
Pre-Tensioning Method
The pre-stressing elements shall be accurately held in position and stressed by jacks Stressing shall be applied to produce the stresses required in the wires immediately after the anchorage as shown on the Drawings or as directed by the Engineer Suitable allowances shall be made for friction in the jacks and for slip and yield in the grips or anchorages A record shall be kept of the jacking forces and the elongations produced thereby and the minimum age in hours of the concrete in the line at the time the tendons were released.
Several units may be cast in one continuous line and stressed at one time Sufficient space shall be left between ends of units to permit access for cutting after the concrete has attained the required strength No bond stress shall be transferred to the concrete, nor shall end anchors be released, until the concrete has attained a compressive strength of at least 75% of the ultimate compressive strength obtained when testing standard cylinders and cured in the manner identical to the curing of the members.
The elements shall be cut or released in such an order that eccentricity of pre-stress will be a minimum.
Construction Tolerances
The construction tolerances for concrete works shall be as follows:
1 Length of concrete members (beams & slabs):
+ Overall length up to 6 m : - 0 and +
+ Overall length over 6 m :- 0 and + 15mm
2 Width, depth & thickness (beams & slabs) : - 0 and +
1 Squareness (difference in diagonal lengths) : 10mm
2 Straightness or bow (deviation of intended line)
+ For length up to 3 m : 12mm
+ For length from 3 m to 5 : 15mm
PRODUCTION PROCEDURE
Construction sequence
Construction of pre-tension prestressed reinforced concrete slab beams:
Prefabricated PSC Deck at the site's beam casting yard have been pre-designed according to the following steps:
1) Construction of the beam casting yard at the approved location At the beam casting yard location, the casting pedestal and the girder storage yard shall be constructed.
2) Install and adjust the tensioning platform, beam formwork.
3) Fabrication nd installation of normal reinforcement, prestressed reinforcement.
4) Completion and acceptance of formwork, normal reinforcement.
5) High tensile steel tension, acceptance test.
6) Acceptance of preparation for concrete pouring and concrete pouring 7) Curing concrete, Remove the side form
8) Cut prestressed steel when concrete reaches over 75% of design strength 9) Remove the formwork at the end of the beam.
10) Measure beam deflection and basic dimensions.
11) General technical acceptance test before putting beams into use.
12) Transport finishing beams to girder storage yard, process curing and subsequent casting of beams.
Description of work sequence
Preparation of Prefabricated beam yard
Site preparation for production yard shall be carried out before mobilization of necessary materials and equipments for the production of PSC Deck.
Site layout: After the site is selected according to the allocation of the number of precast concrete girders, the site should be leveled and cleaned up Test the precast site to see if all aspects of the bearing capacity meet the specification requirements and set up temporary drainage facilities to ensure that the site is not waterlogged Ensure the concrete girder precast site is supplied with water and electricity.
To meet the demands of pre-tensioned pre-stressed structure production, a well-designed casting bed guarantees user convenience and safety By prioritizing strength, rigidity, and stability, this design maintains the structure's quality while facilitating uniform mass production.
The design of the casting bed must ensure that it is convenient to place the normal reinforcement and the prestressed reinforcement in the right position to ensure convenience and enough space for erecting and dismantling of formwork, concrete supply, concrete construction and the crane lifts the finished structure.
The position of casting bed must be in a high place, ensuring good drainage so that the area around the casting bed is always dry.
For beams fabricated by the pre-tensioning method on the cast pedestal, it is necessary to test the pedestal load before casting the beam to determine the necessary specifications for tensioning the high-strength reinforcement bundles to the correct design values.
Figure 8.2-1: Production Area for Beam
The girder storage yard is built with enough area to accommodate the beams to ensure compliance with the casting and installation progress of the beams.
Beams stacked in the storage yard are placed at the pillow position and fixed in position by struts to ensure that the beam does not fall.
The Contractor shall provide all equipment necessary for the construction and the prestressing.
Prestressing shall be done with approved jacking equipment If hydraulic jacks are used, they shall be equipped with accurately reading pressure gauges The combination of jack and gauge shall be calibrated and a graph or table showing the calibration shall be furnished to the Engineer Should other types of jacks be used, calibrated proving rings or other devises shall be furnished so that the jacking forces may be accurately known. b) Fabrication and erection of formwork and tensioning pedestal
The formwork and tensioning pedestal are designed and constructed to ensure the required strength and stiffness, ensuring the accuracy of the shape, size and location of the reinforced concrete structure.
Formwork shall be reasonable forming, easy to erect, dismantle or adjust when necessary
The design and construction of formwork, tensioning pedestal as well as their exploitation shall be ensured absolute safety for people and related equipment.
Formwork is made of steel plate.
Tensioning pedestal made of reinforcement concrete
Formwork is designed with precise shape and position Formwork should be easy to erect and dismantle Joints shall be parallel or perpendicular to the beam axis and shall be sufficiently sealed to prevent mortar leakage The formwork must be chamfered where there are corners.
Formwork parts must be firmly connected to each other by bolts or steel bars Such bolt heads and bar ends shall not be exposed to the surface of the concrete after the formwork is removed.
Formworks shall be installed by Truck-Mounted Crane following the layout markings on the bottom form.
Forms shall be properly fixed by braces and support to keep the shape and dimension shown on approved working drawing.
Holes on side form be made at proper location with proper dimension in accordance with approved working drawings.
All joint between the part of side form, between the side form and bottom form, form for girder top should have rubber cushion for preventing leakage cement water.
For optimal concrete aesthetics and durability, careful selection of formwork release agents is crucial These compounds facilitate form removal, ensuring smooth concrete surfaces with minimal defects Additionally, they prevent corrosion of the concrete during the curing process, preserving its integrity and desired coloration.
Inspection and approval by the Engineer shall be done prior to casting concrete.
Formwork, tensioning pedestal shall be checked before pouring concrete as well as during concrete pouring Any damage must be promptly repaired such as: bulging formwork, leaking mortar, tilted formwork or tension platform, settlement, broken connections.
During prestressed reinforcement tensioning, meticulous monitoring of deformation and displacement is crucial for both safety and quality assurance This applies not only to the tensioning pedestal but also to all connecting components and welds Regular inspections help ensure that the entire system remains within acceptable limits, minimizing potential risks and ensuring the integrity of the tensioning operation.
The permissible error after installing the formwork shall be in accordance with the construction specifications. c) Processing and erection of normal reinforcement and prestressed steel
Materials supplied to the construction site must conform to the type specified in the design project.
The supply schedule must be consistent with the general construction schedule and be clearly stated in the construction plan as well as in the contract of delivery of materials.
Before processing the reinforced frame system, each reinforcement must be brushed and cleaned of all dirt, grease, paint The reinforcement must not have cracks, fractures, bends.
Rebar shall be fabricated in accordance with the shape and dimension as shown on approved working drawing
Bar cutter equipment, bending equipment shall be used to cutting rebar, bending rebar.
Fabrication of rebar shall be carried out by cold cutting and cold bending Rebar fabrication by application of heat shall be in accordance with the Engineer’s instruction.
Reinforcement bar shall be installed in accordance with approved working drawing
Concrete blocks with whip shall be installed at bottom and side of rebar in order to keep the appropriate concrete covering
Fixing and splicing of rebar shall be done by iron wire 0.9mm or larger diameter
Splicing length and location shall be in accordance with working drawing
Rebar shall be tied at all intersections to prevent dislocation during casting.
Fixing by welding shall only be carried out if it is shown on approved working drawing or as instructed by the Engineer.
Installed rebar shall be free from rust, dirt, oil or other material that might reduce the bond.
Temporary embedded material such as PVC pipe for support of decks slabs form shall be installed at proper location
Prestressed reinforcement shall be made according to the exact shape and size as specified in the technical specification without reducing the quality of the material.
Prohibit the use of reinforcements that have been excessively bent, affected by sudden temperature changes or by high temperatures.
When cutting, mechanical cutting method should be used It is strictly forbidden to cut with a soldering iron.
Reinforcing steel surface shall be cleaned before use, avoiding rust, grease, dirt and other harmful substances that can cause corrosion or reduce adhesion of reinforcement to concrete.
Before placing prestressed reinforcements, isolate the base slab with membranes and geotextiles These membranes effectively prevent release agents from contaminating steel strands, thereby preserving the bond between concrete and steel If contamination occurs, use appropriate solvents to restore the integrity of the strands.
During laying, the appearances of the steel strands shall be observed from time to time If any local damages or severe rust is discovered, the steel strands shall be put out of use immediately and new steel strands shall be blanked and laid according to the requirements.
Before tensioning of the steel strands, the transverse reinforcements of the base slab at the hollow slab part, the embedded steel plates, etc Shall be placed in advance according to the design, so as to prevent failure in installing partial base slab reinforcements and embedded steel plates to the design positions after completion of tensioning. d) Prestressed reinforcement tensioning
Adjustment of tensioning beams and placement of anchor holders and tensioning equipment:
After completion of laying of the tensioning steel strands, the positions of the cross beams shall be adjusted to guarantee the accuracy of the positions of the steel strands During construction, the clips in the connector anchor plates shall be often checked for damages If any damages are discovered, they shall be replaced immediately to prevent the steel strands from sliding and causing injuries
QUALITY CONTROL
Quality control of equipment and materials
a) Strictly control raw material supply quality
The technical indicators of cement used in mixing concrete must conform to the corresponding national standards The cement delivered to the site should include the factory test report provided by the supplier, and be inspected and accepted in batches according to the cement variety, label number and factory number The overdue cement needs to be reinspected and unqualified cement shall not be used.
Mixed concrete should be made of hard, durable natural coarse sand as fine aggregate; fine aggregate to the site, should be stored in batches according to different origin, specifications and varieties The test department should provide the report.
The coarse aggregate used for concrete should be hard and durable crushed stone, and the technical indexes must meet the standard.
The water used for mixing and curing concrete must conform to the relevant provisions All drinkable water may be used for mixing and curing concrete.
In order to improve the technical performance of concrete, concrete can be mixed with appropriate chemical admixtures; a variety of admixtures should be provided by the specialized production companies; admixtures to the site whether solid, liquid, should have appropriate packaging containers And with the product identification certificate, store the admixtures after being classified, to prevent deterioration Before using, the admixtures must be carefully checked, mixed and confirmed.
The technical conditions, acceptance standards and test methods of steel must conform to the current national and metallurgical Ministry standards respectively The steel entering the site should be accompanied by the manufacturer's quality certificate or acceptance report The site test engineer shall inspect the purchased steel in accordance with relevant regulations, and fill out the "Steel Bar Test Identification Report" as the basis for the use of this batch of steel In the process of transportation and storage should prevent corrosion, pollution, avoid bending, according to the factory name, level, specification batch pile in the warehouse, and off the ground, hanging identification plate. b) Quality assurance measures for formwork and steel bar production and processing
Formwork is essential in construction, ensuring the accuracy of structural dimensions, strength, rigidity, and stability It must withstand the loads encountered during concrete pouring Simplicity, ease of installation and disassembly are crucial for efficient construction, and durability allows for multiple uses, reducing costs and environmental impact.
The combination should be tight and there should be no leakage Every time the formwork is used, someone should be assigned to clean it up and apply a release agent for the next use.
The steel bar should be straightened before processing, and the oil stains and rust on the surface should be cleaned. c) Concrete Quality Assurance Measures
The concrete shall be stirred evenly and the color shall be consistent, and the mixing time shall comply with the regulations.
Concrete should not segregate, leak and bleed during transportation The inner wall of the vehicle should be flat and smooth, and the road should be as smooth as possible.
Before pouring concrete, various inspections and records should be made according to regulations, and sundries on formwork and steel bars should be removed The pouring thickness is appropriate, and the poured concrete should be compacted with a combination of an attached vibrator and an inserted vibrator During the concrete pouring construction, special personnel shall be appointed to check the status of formwork, steel bars, embedded parts and reserved holes, etc. d) Prestressed Construction Quality Assurance Measures
Arrange experienced technicians to guide the prestressed tensioning operation full-time All personnel operating prestressing equipment shall undergo induction training and conduct standardized training through the use of equipment to master operating techniques.
Before operation, calibrate the tensioning equipment and force measuring facilities, and carry out regular inspection and calibration according to the regulations When the temperature drops below 5°C without insulation measures, tensioning work is prohibited.
When stretching, make the line of action of the tension force of the jack coincide with the axis of the prestressed steel strand; for curved prestressed steel strands, the line of action of the tension force should coincide with the tangent line at the end of the center line of the tunnel, and make detailed records.
The prestress should be stretched at a slow and uniform speed, and both ends should be carried out at the same time When the prestress stretches to the specified value of the design and reaches the anchorage of the supervisory engineer.
Construction site quality management and implementation control
In order to achieve quality goals, we will take the following quality assurance measures in terms of project site quality management and implementation:
Establish a sound quality responsibility system for the project manager department, decompose the quality objectives, and decompose them layer by layer according to the specific quality requirements of creating excellence by unit project-division project-sub-item project-construction process, and implement the quality responsibility to the utmost grassroots.
Formulate practical and feasible management systems, including joint review of drawings and technical disclosure systems; on-site quality management systems; process management systems; scheme data management systems;
Strict quality procedural management, including: project quality plan, document and data control procedures, material management procedures, process control procedures, inspection and test procedures, non-conforming control procedures, quality record procedures, and standardize various quality with strict procedures management work.
To enhance quality assurance, it is crucial to implement stringent process control mechanisms, encompassing a comprehensive process control plan, rigorous quality inspection plan, and clearly defined acceptance quality control guidelines Additionally, monthly quality reports and summaries of new materials and process control procedures serve as valuable tools for monitoring and improving quality standards.
During the implementation process, strictly implement the three-level inspection system; strictly implement reasonable process arrangement and management; the use of unqualified materials and equipment is absolutely prohibited, and the processes that fail to meet the standard requirements are completely reworked without mercy.
Strengthen the quality control of incoming inspection and testing of raw materials, strengthen the quality inspection of the construction process and the quality control of testing, strengthen the management of construction technology, and conscientiously implement process standards and operating procedures, so as to improve the stability of project quality and ensure the realization ofAll elements of quality objectives are under control.
Construction Process Quality Control
Before the start of construction, according to the actual situation of the project, the project department will prepare the "Construction Organization Design" (construction plan), which will be approved by the engineering department of the company, and if necessary, by the chief engineer or deputy chief engineer.
For successful construction, a comprehensive quality plan is crucial This plan outlines specific quality goals, establishes the construction schedule, and defines the processes to be followed during construction To ensure project quality, the plan includes stringent quality assurance measures, inspection, and testing protocols It also specifies the required construction equipment, detailed material specifications, and necessary personnel qualifications Safety and environmental concerns are addressed through safety assurance measures and environmental compliance requirements.
Carry out three-level technical disclosure:
According to the "Quality Plan" and the requirements of regulations, before each process starts, the engineering and technical personnel of the company or office shall first disclose to the engineering and technical personnel of the project department, and then the engineering and technical personnel of the project department shall report to the team The leader will explain the truth, and finally the team leader will explain the truth to the operating personnel.
Implementation method of quality control
Before construction, the technical person in charge organizes the foreman, internal workers, and quality and safety personnel to study the relevant specifications, construction technology and operating procedures carefully, familiarize themselves with the drawings, do a good job in the joint review of the drawings, and prepare the construction organization design in a targeted manner.
In view of the key points and difficulties of this project, establish a QC team, formulate a detailed construction process card, and strictly follow the card construction to ensure the quality of the project.
Strictly follow the construction drawings.
To ensure efficient operations, the technology manager should regularly review records and reports, promptly addressing any identified issues The office data clerk is responsible for organizing and maintaining various documents On construction sites, the foreman documents progress and observations in a construction diary.
TRAFFIC SAFETY CONTROL
Traffic Closing Basis
The lanes shall be closed to execute, traffic will be maintained and guaranteed on the detour road.
The detour road shall be design based on the principles of facilitating the construction vehicles to enter or leave the site and the passing vehicles to pass smoothly.
Site Layout
The lanes shall be closed to execute, traffic will be maintained and guaranteed on the detour road.
Traffic Control of Blocked Sections
For construction personnel in accordance with the safety regulations for construction.
No drinking, slippers, and sandals are allowed on site.
The insurance fee shall be paid on time and warning flashlights be installed for the construction vehicles.
The traffic rules shall be com plied with and no parking on the lane or turning around randomly be permitted for construction vehicles.
The finished sections shall be protected carefully, and roadblocks or warning signs shall be placed if necessary.
The damaged safety signs which affect the expression of the safety information shall be replaced in time.
Safety signs shall be placed in bright environment and at a proper distance from the danger location so that the relevant people have enough time to note the information that it represents.
The safety signs with dirt, grease shall be cleaned timely to ensure the safety information without the mistakable messages.
The safety signs with displacement shall be adjusted in place to avoid accidents, which result from the relevant people's not quickly noticing and understanding the safety information.
ENVIROMENT AND SAFETY CONTROL
Safety Control
Prior to starting of construction works, Warning signs and instruction boards shall be fully installed either inside or surrounding the construction site and the following particular matters are to be through to all members working in the construction site in order to complete the work efficiently without any accident or casualty. a) Joint Meeting
Prior to start any activity, a joint meeting with relevant staffs shall be held for the purpose of general explanation on the whole contents of works as well as the method for the implementation of efficient work. b) Basic Instruction
All workers shall always wear Personal Protective Equipment (PPE), such as hardhat (helmet), safety shoes, hand gloves and working uniform. c) Prevention of Accident by Heavy Machine
Only skilled operator shall be allowed to operate equipment on site In case of new operators, a test of skill shall be conducted first prior to his acceptance to the job Preventive maintenance check shall be done regularly at equipment working at site prior to full operation Stability of working area and foundation of equipment shall be checked particularly at locations of outrigger and track pad of cranes. d) Prevention of Accident of Electrocution
Electric generating equipment shall be properly protected and properly installed with earth connection Electric wires shall relate to electrical tapes to prevent electric leakage Only skilled operator shall be allowed to operate equipment on site. e) Prevention of Accident in Night Shift Works
Enough lighting system shall be provided for night shift works especially installed at working platforms If necessary, all the surrounding working area shall be lighted up The people who work on the site must wear reflective jacket, if worked at night. f) Existing Facilities
Existing facilities especially existing overhead electric line, water line, telecommunication line and other important facilities at surrounding area shall be taken with care not to damage.
Environmental Control
Responsibility for surrounding environment during Substructure work and shall comply with the Condition of Contract on Protection of Environment.
If any other problems occurred in the site, applicable counter measures or prevention action shall be considered immediately and executed as soon as possible.
The Contractor shall be responsible for implementing and managing mitigation measures during the construction of the Works The recommended mitigation measures are presented below. a) Ambient air quality
Exhaust emissions from construction equipment shall be strictly controlled in accordance The Contractors are requested to use standard equipment.
Where possible the Contractor ’s chosen access routes to and from the site should avoid residential areas Vehicles carrying sand, aggregates or other loose materials shall be fully covered Brushing and watering shall be used where required to control dust and the spraying of mud.
Stockpiles should be covered or kept damp to avoid windblown dust.
The Contractor is responsible for collaborating with local environmental agencies to monitor and regulate ambient air quality as part of the regional pollution control program They must also monitor and control the water environment to maintain compliance with environmental standards and regulations By working closely with environmental authorities, the Contractor ensures that construction activities minimize their impact on the surrounding environment and contribute to the overall environmental protection efforts in the region.
To ensure the water quality of local watercourses, ponds, and lakes the Contractors shall comply with the following environmental protection measures Care shall be taken with fuels and oils.
No waste material of any kind shall be disposed of into local watercourses, ponds, or lakes.
Stationary construction equipment, offices and accommodation, workshops and storage areas and other temporary facilities shall not be located near to local watercourses, ponds, and lakes.