WB Equipment Inc. - Supplier of Hydraulic and Pneumatic Jacking Systems for Jacking, Hoisting, Lifting & Moving. Tel: 866-522-5464
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FLAT JACKS

Flat Jack Rentals

Temporary Flat Jacks • Permanent Flat Jacks
Complex Flat Jack System • Calibrated Flat Jacks & Weighing

General Description
Flat Jacks are simple, practical devices for the civil or structural engineer wherever
the application or control of large forces is required. They are frequently used in the
solution of unforeseen problems such as in remedial measures or structural additions.

They are as often used in new constructions in which they form part of the structural concept.

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In the years since their invention by Eugene Freyssinet in 1934, many techniques
have been evolved for applications such as (click images for a larger view) :

 
                       
 
   
                       
Click here to see the FLAT JACK SELECTION CHART  
  1. The flat jack consists of a mild steel capsule, circular in plan, with a cross
    section that is initially dumb-bell shaped. The dished portions are fitted
    with ground steel thrust plates before the jack is placed between the
    surfaces to be jacked apart.

    When the jack is inflated with a liquid the hydrostatic pressure is trans-
    mitted by the flat portions of the capsule through the thrust plates while
    the toroidal rim of the jack deforms to allow the flat faces to move apart.

  2. The maximum operating pressure is only 150 bar (2,200psi).
    Flat jacks thereby exert low bearing pressures on the jacked faces.

  3. The maximum recommended opening stroke of a flat jack is equal to
    the depth of the toroidal rim - about 25mm (1in).

  4. Two pipe connections are welded into the jack rim usually at 90o to
    one another. One provides the inlet for inflation and the other serves
    as a vent during filling and is subsequently capped off.
  

Advantages

- Known Forces
- Precise Control
- Low Height For Limited Access Situations
- Low Bearing Stresses
- Out Of Parallel Tolerance 
  Between Jacking Surfaces
- Temporary, Removable Jacks
- Permanent, Sacrificial Jacks
- Structural Lifting
- Underpinning
- Control Of Thrust Forces
- Maintenance Of ConstantThrust
- Adjustment Of Support  Reactions
- Pretressing
- Structural Pre-Loading
- Loading Of Seismic Isolators
- Arch De-Centering
- Control Of Settlement
- Measurement Of Forces
- Weighing Of Offshore Structures
- Permanent Shimming
               
 
 
Temporary Flat Jacks
Oil Inflation - When flat jacks are to be used for a limited period and subsequently removed inflation is usually done with hydraulic fluid. For small numbers of jacks, requiring relatively small volumes of oil, simple hand pumps may be used for inflation. Larger jacks or large numbers of jacks may require electric or diesel powered pumps.Top
 
         
  Hydraulic Circuits - Single or multiple flat jacks can be inflated individually or on inter-connected circuits. Each jack has a needle valve for locking off and may be fitted with a pressure gauge if required.
         
 

Permanent Flat Jacks
Where a force is required to be permanently applied to a structure, flat jacks are inflated under pressure with an epoxy resin by means of a special resin injection cylinder. The epoxy resin hardens over a period of time to leave the force permanently applied. This type of application is suitable for pre-loading new or additional steelwork in structures, underpinning works and structural bearing installation.

This method is often used where sufficient room is not available for wedging or grouting the jacking gap.

In certain circumstances, it may be necessary to carry out the initial inflation on hydraulic oil with resin inflation being carried out at a later date. An oil to resin transfusion system is then required. Top

         
  Complex Flat Jack System  
         
 

 

In applications using multiple flat jacks the hydraulic pumping circuitry can be arranged appropriately using pipe and compression fitting or flexible hoses and quick release couplings.

Individual jacks are usually fitted with manual needle valves. Pressure gauges may be fitted to individual jacks, downstream of their needle valves, instead of or in addition to a common ring main gauge. Differing loads in neighboring jacks may thus be locked in and monitored as necessary. Top
         
  For especially complex operations solenoid valves, electronic pressure transducers and computer control, monitoring and data logging systems may be used.
         
 
         
 

Calibrated Flat Jacks & Weighing
A flat jack which has been pre-opened, fitted with a pressure gauge or transducer, sealed and then calibrated in a press can be used as a robust, accurate load cell. This load cell can be placed in tandem with a standard flat jack of the same size.

The twin jacks are then installed beneath a structure at weighing positions. The weight of the structure taken by inflation of the standard flat jack registers a pressure in the calibrated flat jack which, by reference to its calibration graph, provides an accurate weight.

         
 
   
         
  Using this principle, offshore structures ranging from modules of several hundred tonnes to complete integrated decks of over 30,000 tonnes to an accuracy of +/- 1%. Where necessary for lighter structures, an arrangement is available with greater accuracy. Top
         
 
 
               

 
 
W.B. Equipment Service Company, Inc. ▪ Tel: 866-522-5464 ▪ Fax: 201-438-7830 ▪ E-Mail: info@wbequipment.com