Existing buildings and structures, as well as the newly constructed structure, may need bearing replacements and for that purpose, jacking is used. Various elements of work involving buildings and structures require heavy load lifting; like bridge bearing replacement procedures. In replacement of bearings for bridges, jacking is used in order to raise the beams holding the headstock so that the bearings are free for resetting or replacing. Jacking needs to be tight and controlled if any damage to the structure is to be avoided. Alternatively, one bearing at a time may be lifted using flat jacks or hydraulic jacks, in order to eliminate the need for road blocking.
When using this method of jacking for bridge bearing replacement, a hydraulic flat jack is used adjacent to the bearing that is being replaced. The bridge is lifted only a few millimeters. While the bearing is removed, the hydraulic jack holds the weight of the bridge in its place. The bearing is taken off by removing the mortar or pedestal pads. Once the old bearing is removed, another bearing is installed on a flat jack permanently. The flack jack is inflated using epoxy and once the epoxy is strong enough to hold the weight, the hydraulic jacks are removed. In this process, a road closure is needed only for a brief period of time. This strategy is particularly effective on very busy roads that cannot stand long closures.
What are Hydraulic Flat Jacks?
A jack is a mechanical device designed to lift things up by applying great force using hydraulic pressure systems or other such methods. Car jacks, garage, jacks, and floor jacks, are used to lift these heavy objects during mechanical procedures. These devices rely on the use of force multiplication means of heavy lifting. Any device that uses leverage to amplify force is called a jack.
Hydraulic jacks are jacks that use incompressible liquids to build pressure and multiply force. Incompressible liquids commonly used include jack oil and hydraulic fluids. The mechanism involved includes a hydraulic cylinder or a screw thread. A jack is usually rated in terms of the lifting capacity it has because it is used for heavy lifting and its capacity to lift weight determines its usefulness. Floor jacks and bottle jacks are some hydraulic jacks commonly used. The primary component involved in a hydraulic jack includes the following:
1. Buffer tank or reservoir
2. A pump with a plunger or piston
3. Pump handle or lever
4. Check valve
5. Main cylinder/ram
6. Release valve
This is a vessel that carries the incompressible fluid and transfers the pressure that is applied at the handle to the part of the jack that pushes against the structure being lifted. This pump is piston-operated, that can be used by moving the handle or level up and down. Moving the handle in this manner builds up pressure. The pressurized fluid is pushed into the main cylinder through the check valve. The main cylinder, in response to this pressurized fluid, is driven up and out of the hydraulic jack body. This pressure creates the necessary force to lift the object. A release valve is also included in the mechanism to release the pressure that has built up after use. When the object needs to be lowered again, the pressure is released. In some hydraulic jacks, there is also a threaded extension that allows for the unscrewing of the ram extension once it has fully retracted. With this feature, the lifting range is increased, and with it, there is no need to use blocking under the jack once the object has been lifted more than the retracted height of the jack body and ram.
Types of jacks
A conventional hydraulic jack has the capacity of lifting 1000 tonnes of weight. The jack has a swivel head to accommodate for any misalignment in the jacking surface. The hydraulic jack also has a locking collar that lets the hydraulic system be removed after the necessary amount of pressurization is achieved. Hydraulic jacks are very useful devices in bridge bearing replacement procedures. These include the use of either manually operated or powered hydraulic systems. Jacks can be used in both, groups or singly.
Like hydraulic jacks, flat jacks also have a weight capacity of up to 1000 tonnes. These can be used in permanent or temporary situations. A flat jack has two steel plates that are joined at their rims. Inflation between these two plates pushes them apart with great force (up to 15N/mm2). The special feature of these jacks is that they can be used even in places where the gap in which to install the jack is as small as 50mm or even lesser. In flat jacks, for temporary situations, inflation is achieved by hydraulic oil. In permanent jack installation, the jack is inflated using epoxy resin, or first inflated with hydraulic oil and then fused with epoxy resin. Flat jacks are commonly used in construction and building-related repairs. Bridge bearing replacement frequently uses flat jacks.
A Hydraulic flat jack is typically used for bridge bearing replacement procedures. There are numerous products available in the market today for these mechanical processes. When using any hydraulic flat jack, it is important to check that the parts are all normal and that the load is not more than the capacity of the device, and to ensure that there is sufficient oil in the hydraulic pump before use. When using a hydraulic jack, also remember to use support for the object’s weight once it has been lifted sufficiently. Relying solely on the support of the hydraulic jack is not right. Also, try to avoid any violent jack movement while using to avoid damaging the structures involved.
Things to consider when using jacks for bridge bearing replacement
· Take into consideration any bearings that are suffering from serious corrosion that can lower the fixity of the structure.
· Compare the current bearing with the original bearing
· Monitor constantly to prevent any unexpected incidents
· The design of the hydraulic jack being used needs to be appropriate for the purpose.
A hydraulic flat jack is a very useful mechanical device in construction procedures and is frequently used by mechanics and engineers alike. It is necessary to remember precautionary steps when using these in any complicated construction process.