Precast Girder Formwork Technique Direction
Technique Content
Precast girder formwork has advantages of high-precision, simple structure,retractile,easy-demoulding and simple operation. It can be hoisted or dragged to casting site integrally, and demoulded integrally or piecemeal after concrete achieving the strength, then pull out the inner mould from the girder. It is handy installing and debugging, low labor intensity, and high efficient.
(1) Design technique of precasting girder mould
The mould is integrated designed and stress analyzed in concordance with the girder structure,girder span and arrangement of the casting site.The demoulding mechanism is designed by simulating the trajectory of the inner mould.
The girder’s integrally or piecemeal pulling out of mould after precasting is ensured by inner mould structure, connectors, inner mould support system, hydraulic system, demoulding mechanism,guideway system and the segmental design of inner mould.
The design of outer mould structure, way of locomotion, support system of outer mould,pathway of temper mill, disposal of oscillator,stair and rail.
Transport scheme should be considered when design the inner and outer mould segmentation. The applicability of the mould to different girder span .
The material selection: 12mm steel plate for bottom mould and end mould;8mm steel plate for lateral mould and inner mould.
(2)The structure of precasting-girder formwork
1）Precasting-girder formwork consists of later mould, end mould, bottom mould and inner mould. Shown as picture 4.13.1
2）There are two kinds of lateral mould: stationary type and longitudinal slipping type.
3)The end mould will be splitted into segments to transport and assembled on casting site.
4)There are two kinds of bottom mould: stationary type and partial-movable type.Stationary type is always used for casting site with beam hoist and partial-movable suits to the site with bridge crane.
5)Inner mould is divided into beam-above type, beam-below type and no-beam type by structure; integrally-demoulding type and piecemeal-demoulding type by demoulding way; mechanically-demoulding type and hydraulic-demoulding type by automation. Hydraulic mould consists of template, main beam, lifting jack, bracket and hydraulic controlling system.
(4)Girder Mould Assembly
1)Bottom Mould Assembly: Assemble and fix on the concrete pedestal piece by piece from the center to both ends.Set the pre-camber value per quadratic parabola.
2)Outer Lateral Mould Assembly: Lateral mould consists of moulding plate,longitudinal truss, horizontal truss,connecting bolt,trolley,rail, stair,spiral ejection pin etc.Outer mould is welded into a whole after sectional manufacturing and qualified assembly testing.When erecting the outer lateral mould, drag the mould to the pedestal-mould-joint position by winch pulling the trolley. Then, use spiral ejection pin to push the lateral mould from both sides to contact the bottom mould.After horizontally positioning finished, adjust the outer mould vertically to the designed height by spiral ejection pin, then screw up the outer mould and bottom mould. Make sure the mould alignment is suited to the bridge alignment,then screw up all the bolts and nuts.
3) Inner Mould Assembly: The inner mould is manufactured segmentally in factory and assembled together on the casting site, and it should apply to gantry crane and integrity sliding. The inner mould is attached to the main beam, and flexed by controlling the hand reversing lever, which using the hydraulic power provided by a hydraulic pump on main beam through rubber tube.Control the inner mould to distract bottom lateral mould,top lateral mould and top mould orderly, then glide the inner mould into rebar cage. Connect the inner mould and lateral mould by telescopic screw through the vent, in order to keep the inner mould from swaying when pouring the concrete and ensure the thickness of the web plate.Check the thickness of the web plate after assembling, and make sure it is not changed due to laterodeviation.
4) End Mould Assembly: End mould is manufactured segmentally.Check the top mould overall on the casting site to make sure the deviation of the drilled hole is less than 3mm.Before assembling, check the plate for smoothness, deformation, mucilage relict and the neatness of pipeline perforation. Set the end mould to position by gantry crane, and put the rubber extract pipe through the corresponding hole, paying attention not to bend the pipe due to the variety of pipes.Superpose the midlines of end mould and bottom mould.Plumb the end mould and screw up all the fasteners.Recheck the rubber pipes at designed position or not.Do not crash the rebar skeleton when setting the anchor plate, in case it will move the pedestal.
5) Allowable Deviation: Conduct a simulation test when finish assembly to make sure all segments meet the qualification (considering the allowable deviation), then fill in the data per mould checking items as the record of handing-over.When pouring the concrete, there must be on-duty operators to check the mould and fasten the connection bolts and fastener if needed.The allowable deviation shown as below:
|
No.
|
Item
|
Requirement
|
|
1
|
Mould Length
|
±10mm
|
|
2
|
Span Length
|
±10mm
|
|
3
|
Bottom Mould Width
|
+5mm,0
|
|
4
|
Deviation of bottom mould midline
|
≤2mm
|
|
5
|
Deviation of bridge panel with bottom mould midline
|
≤10mm
|
|
6
|
Deviation of web plate midline on plane position
|
≤10mm
|
|
7
|
Deviation of the mould inclination
|
≤3‰
|
|
8
|
Bottom Mould unevenness
|
≤2mm/m
|
|
9
|
Bridge panel Width
|
±10mm
|
|
10
|
Web plate thickness
|
+10mm,0mm
|
|
11
|
Bottom plate thickness
|
+10mm,0mm
|
|
12
|
Top plate thickness
|
+10mm,0mm
|
|
13
|
Mould diagonal deviation
|
±15mm
|
|
14
|
Height deviation of pedestal plates
|
≤2mm
|
(5) Girder Mould Application Notice:
Before every operation cycle
1)Check all the connection screws
2)Check reliability of limit-switches,drag-steel-rope,pulleys and hydraulic system,fluid level,pulleys,walking wheel-axle bearings,lubrication.
3)Check and measure all segments dimension to make sure the dimension and evenness meet the requirement before pouring concrete.
4)When move the mould by drag-trolley,watch the moving direction and make sure no track-skip and no hook on other equipment.
5)Mould operation must follow the procedure provided by factory, and change the hydraulic oil and seals.
2. Technical index:
(1)Arbitrary point normal deviation of actual contour with designed contour ≤2mm；
(2)The mould surface radian is accordant.Deviation of dislocation and gap ≤0.5mm;
(3)Deviation of every single plate manufactured length and width±1mm
(4)Deviation of planeness ≤3mm/2m;
(5)Deviation of mould assembling length ±10mm;
(6)Deviation of bottom mould midline ≤2mm;
(7)Deviation of bridge panel with bottom mould midline ≤10mm
(8)Deviation of web plate midline ≤10mm
(9)Deviation of bulk head center ≤5mm
(10)Mould inclination ≤3‰
(11)Pedestal plates unevenness ≤1mm
(12)Deviation of end mould anchor recess ≤3mm
(13)Turnover frequency: more than 50 times
