03 thuyet minh cantilever span

Môc lôc GMS Ben Luc Long Thanh Expressway Project Package A5 Civil Works Km 32+450 to Km 35+900 METHOD STATEMENT OF CANTILEVER SPAN CONSTRUCTION TABLE OF CONTENTS I FLOW CHART FOR CANTILEVER CONSTRUCT[.]

METHOD STATEMENT OF CANTILEVER SPAN CONSTRUCTION

TABLE OF CONTENTS

I FLOW CHART FOR CANTILEVER CONSTRUCTION

II ASSEMBLING PROCEDURE FOR FORM TRAVELER

III CONSTRUCTION OF GIRDER

IV SAFETY CONTROL

I FLOW CHART FOR CANTILEVER CONSTRUCTION:

Assembly of Form Traveler Setting of Formwork

Disassembly of bracket Construction of K0, K1 segment by bracket

Construction of segments

Disassembly of Form traveler and Formwork

Center closure Side closure

II ASSEMBLING PROCEDURE FOR FORM TRAVELER

Flow Chart procedure for assembling of Form traveler is shown below

Preparation works Installation of Rail beam

Installation of Main truss

Installation of Transverse beam/truss

Installation of Transverse beam/truss

Installation of Lower deck form Installation of Platform

Adjustment of Lower deck form

Installation of External form

Adjustment of External form

Installation of Top slab form

Construction work

III CONSTRUCTION OF GIRDER

1 K0 segment by Bracket

Assembly of Supporting Installation of form for bottom slab

Installation of External form for web

Assembly of re-bar for bottom, web

Casting Concrete

Assembly of Internal supporting

Curing, Chipping

Assembly of re-bar for bottom slab, web

Installation of Internal form

Assembly of re-bar and PC for top slab

Casting Concrete

Curing, Chipping

Prestressing

Removal of formwork

2 K1 segment – K10 segment by Form Traveler

Setting of Form traveler

Assembly of re-bar and PC (bottom slab & web)

Installation of internal form

Curing

Prestressing works

Launching form traveler to next segment

Setting of Formwork

Assembly of re-bar and PC (top slab)

Casting concrete

Removal of inner form

Removal of outer form

3 KT segment by scaffolding

This segment is constructed on the scaffolding

Concreting work for segments casting on the scaffolding:

- Stage 1: pour concrete for bottom clab

- Stage 2: pour concrete for wall clab, top slab

3.1 Foundation

Replacement of soil (2m), backfill and compacted to the requirement K95 and in according the requirement of Engineer;

Casting in site a RC plate

3.2 Erection of scaffolding system

Scaffolding system are erected on RC plate

3.3 Load test of scaffolding system

A crane is used to lift concrete blocks 1x1x2m, for load test of scaffolding system (method statement of load test is in separate document) Re-adjust the scaffolding system

3.4 Concreting construction of segment casting on the scaffolding in stage 1

Erect bottom formwork, window formwork: use a crane to lift bottom formwork to place into position Adjust exactly elevation, longitudinal centerline, cross centerline

of bottom formwork

Erect formwork of external wall: it must be ensured geometric dimensions of casting segment Formwork plates of external wall are fixed into external scaffolding system Installation of rebars, pipes is done after accepting elevation and position of formwork At positions of thick rebars, compacting work must be ensured compliance with Specifications of Project

Concrete curing: curing work is begun since redundant water on concrete surface has already completed evaporating Time for continuous curing is within 7 days

3.5 Concreting construction of segment casting on the scaffolding in stage 2

Sequence of core formwork erection: core formworks are fixed by bracings and through bars Erect formwork of top slab Rebars and duct installation is only done when geometric dimensions of fromwork are accepted

Then, pour concrete in stage 2, cure concrete

3.6 Stretching of pre-stressing tendon of segment casting on scaffolding

Pre-stressing tendon is carried out stretching when concrete strength met 90% of design strength Beofor stretching pre-stressing tendon, formworks of external wall and internal wall must be removed from concrete surface Exceptedly, bottom formwork and scaffolding system are only removed after completion of segment closure

4 Construction of closure segment

Closure segment is the last segment to connect cantilever girder segments and gider segments casting on scaffolding system or connect canlilever girder segments together

to form continuous girder Construction sequence of the closure segment contains following steps:

4.1 Adjustment of elevation at closure segment

During construction process, because of affected factors, especially affect of shrinkage and creep of concrete, deflection of canlilever girder has deviation of elevation time to time Moreover, girder segment casting on scaffolding can have deviation of elevation because of settlement of foundation Therefore, we should adjust elevations at elevation of closure segmen This adjustment is done by form traveler or loading depending on each of specific case

Place cross barcing PC tendon to stabilize longitudinally (prevent pendulating of cantilever girder wing) and stretch them with a force 10T for each bar

PC tendon for girder fixing longitudinally

4.2 Arrangement of scaffolding and formwork and installation of rebars for closure

segment

Formwork is hung by supporting beams and PC tendon through waiting holes at head

of box girder The formwork is structured as same as formwork of segment casting on the scaffolding Installation of rebars for closure segment is carried out similarly to other segments

4.3 Placing of temporary brace

Temporary barce is structured from combination shaped steels, placed on closure segment for duty of accepting compressing force caused by stretching bottom trand before concreting

Upper brace: is placed into respective position of lower brace After 2 bottom trands are stretched respectively 75% and 50% of stretching force, non-shrink grout is filled into 2 ends of bar

Arrangement of brace when constructing closure segment

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4.4 Temporary stretching of trands of box bottom slab when concreting

Stretching of bottom trand before concreting has purpose of "link" girders together and create a forecompressive force at below part of closure segment not to appear stretching stress at this part during concreting process

Bottom strand is only stretched when grout strength at head of brace meets requirements of 330 kG/cm2 Before stretching bottom strand, bolts for connection of

2 bearings must be removed to be able to move freely during tretching cable (for side span)

Sequence of stretching for bottom trand before concreting will be determined by Designer While stretching, 2 guages for displacement are installed into 2 lower braces

to measure compressive displacement of bar under affecting of stretching force of trand Value of displacement will be recored and monitored at the time before and after stretching in purpose of preventing apperance of stretching stress at lower part of closure segment during concreting process

Pour concrete for bottom slab and wall Monitor frequently gauges of displacement measure If concreting for box wall completed but dial indicator is still far from the first position, it means that lower part has only compressive stress, we keep on concreting for surface slab If dial indicator backs near its first position, it means that it

is going to appear stretching stress, we keep on stretching bottom trand to 75% of design stretching force, at that time, pour concrete for surface slab

4.5 Cutting of lower brace

When concrete strength met 90%, carry out cutting lower brace

4.6 Stretching of remaining trands

Before stretching, formwork must be removed from concrete, except bottom formwork Stretching sequence will be determined by design consultant

4.7 Cutting of redundant cable end, concreting for anchor head sealing and grouti

strands

Carry out similarly to prevuous segments

4.8 Removal of form traveler:

The form traveler is removed with reverse sequence of its assembling sequence:

- Pay attention to following points:

 Because of many different causes, construction process can have errors,

this requires to adjust elevation at closure segment Adjustment of elevation can use charging method and load of more charging shall be determined by designer

 During construction process, cantilever girders on next piers should be

monitored frequently affect of shrinkage, creep of concrete time to time and camber of cantilever girder when completing construction to adjust timely the girder

 Sequence of cable stretching at first, during, and after concrete follows

design requirements Measurement of elongation of trands is same as states above part

5 Work Sequence for Cantilever construction by Form Traveler

5.1 Survey Works:

Preparation:

The surveyor shall check the whole survey points and coordinates network

Determine the centerline of the formwork:

- Provide marking point for centerline of the form traveler by offsetting from the end of the old cast segment, the longitudinal centerline of the form traveler shall match to the centerline of the bridge/pier

- Set rail beam in its exact layout base on dimension of the form traveler

- After the rail beams confirm its exact location, the form traveler can start assembling

5.2 Assembling Form traveler and Formworks

5.2.1 Work sequence:

Preparation works:

- Prepare all necessary materials and equipments to be used for form traveler erection

- Assemble all necessary formworks & structures on ground for easy installation

- All form surfaces shall be cleaned and applied with the approved form release

- Before installation, the location of the form traveler shall be located determined

by the survey

Installation and assembling of Form traveler:

- Installed the rail beam and fixed it with PC bars passing through the top slab of box girder Installed the main beam (I1000) and fixed it with PC bar passing throught the rail beam

5.2.2 Main cantilever truss shall be set by the use of crane then check the vertical position

Main truss shall be fixed to rail beam

- Main cantilever truss must be supported temporary by chain block or lever block for easy adjustment to attain its vertical alignment

- Install the transverse beams and all necessary structural supports for Main cantilever truss

- Installed all necessary PC bars and supports prior for installation of formworks

- Install the lower deck form; it shall be fixed and supported by the PC bars or high tensile stress bar provided before installation Set the elevation of the deck forms to its exact elevation by using hydraulic jacks After confirming the condition of the lower deck form the external side deck form shall be installed

- Install the external side deck form, this form shall be supported by the PC bars provided at the top portion and fixed at the bottom by the adjustable support or jacks for horizontal adjustment

- When external forms were set, the dimension of the box girder should be check

by the survey Considering its exact position, level, and alignment according to the planned pre-camber calculation

- Install the top slab bottom forms and fixed it with the PC bars provided

- Define the level of formwork prior for the installation of rebars

- Assembled and installed external end forms

5.2.3 Rebar works

Installation of reinforcement bars:

- Install the lower transverse rebars of bottom slab

- Install the longitudinal bars for bottom and fixed to transverse rebars by a tie wire

- Install the stirrups and longitudinal bars for the web Web stirrups shall be temporarily supported by a rebar until all longitudinal bars installed

- Install the upper rebars for the bottom slab

- Install the lower rebars for top slab.(Same procedure as bottom slab)

- Install the upper rebar for top slab and rebars for parapet Install the transverse tendons, transverse tendons shall be fixed and kept in correct position by using rebar spacers or by hanging using tie wire Install longitudinal tendons, it shall

be supported by steel racks and fixed with tie wire

- Assemble and install the internal side forms Fixed internal forms by using tie rod

- Final checking for box girder dimension and elevation shall be done immediately prior for casting

Cleaning inside formworks:

- Before casting, cleaning inside forms shall be done

Installation of necessary block out:

- Install the block out for drainage inlet

- Install the pipe sleeves or block out for PC bars to be used for fixing the form traveler

5.2.4 Preventive measures for rebars and forms:

For long time waiting for next step, exposed rebar shall be treated by applying

cement grout to prevent rust

Forms shall be treated in case there is a gap in between, this gap shall be filled with cement paste

5.3 Curing, Finishing, and Construction joint:

5.3.1 Concrete curing:

After casting, cover the fresh concrete by vinyl sheet For exposed surfaces such as slab and other structure it must be covered for a period of 7 days The vinyl sheet shall

be kept thoroughly wet for the entire period of curing

5.3.2 Finishing Concrete:

Immediately after placing concrete, top deck surface shall be struck-off with templates

to provide proper transverse section and shall be hand finished smooth to the concrete levels Finishing shall slightly but uniformly roughened by broom

5.3.4 Surface Treatment for Construction Joint:

Before the installations of end forms for construction joint Rugasol F shall be applied for the surface of the end forms This retarder is used to delay the settlement of the concrete surface without affecting the strength of the concrete After removal of end forms, the surface of construction joint could be treated easily by spraying water pressure

5.4 Pre-stressing

Grouting Works

Measuring cast block:

- For defining the level in this stage data must accepted by the Engineer The differential between the design and actual level should be attested in measuring segment deflection in early morning

- All measurement must keep going until the forms adjustment meet the requirement and raging from allowable limit

6 Safety Control

6.1 General Safety Provisions

Safety protection for staff:

- All workers should wear Personal Protective Equipment (PPE) during working and safety belt when required

Safety Protection for Equipment:

- Concrete pumps, especially its condition, tremie pipes and elbow pipes and truck mixers shall be regularly maintained and checked by sub-contractors before mobilization Spare parts such as tremie or elbow pipe shall be stocked on site for emergency cases

Safety rail on working platforms:

- Working platforms and safety rails shall be provided on high working area for workers to prevent accident of falling down according to local safety regulations Safety nets shall be provided underneath the form traveler

Prepare lighting system for emergency use or in night operation

6.2 Before placing concrete

Electrical connection shall be checked thoroughly

A numbers of hand lights shall be provided in case the electricity shut down

6.3 During placing concrete

Communications between pump operators and person-in-charge in placing concrete shall be closely done with walky-talky receiver or loud microphone, if the operator cannot see concreting place

When the concrete pump shifts to another location, the tip of the hose shall be covered so that the remaining concrete inside the discharge hose will not fall down

on workers

Workers shall not stand under the boom and discharging hose

6.4 Safety measures before and during Pre stressing works:

Before pre stressing:

- PC strands, PC bars, hydraulic jacks, and other materials to be used shall beperiodically checked and the equipment must maintained its good condition

- If unsuitable condition is found, material and equipment shall be replaced immediately

- Provide working platforms for workers for good working convenience

- All equipment to be used must be calibrated by the local authorized calibration

- When jack already set for pre stressing Provide safety board in front of extended strand to prevent accident, just in case if the strand suddenly cut during stressing

- All work shall be done by skilled and well-trained workers