What Does Lift Slab Mean In Construction?
What Does Lift Slab Mean In Construction?
Lift slab construction is a method of constructing concrete buildings in which the floor or roof slab is cast on top of the previous slab and then raised (jacked) into place with hydraulic jacks.
This method of construction allows for much of the work to be completed at ground level, eliminating the need to form floors in place.
The ability to create monolithic concrete slabs makes lift slab construction a useful technique for quickly creating structures with repetitive form work, like parking ramps.
Where Was Lift Slab Used?
The building located at 2150 Shattuck Avenue in Berkeley, CA (or First Savings Building) is an example of lift slab construction used in the Bay Area during the mid-twentieth century.
Built in 1969, the fourteen story high First Savings Building uses this construction technique where a system of trusses support various concrete slab floors.
These trusses extend out from two reinforced concrete cores that provide main structural support for the entire building.
Lift slab construction was also involved in the L’Ambiance Plaza collapse in Bridgeport, Connecticut, in 1987 which caused a nationwide federal investigation into this construction technique in the United States.
As a result of the failure of the structure, Connecticut temporarily imposed a moratorium on lift slab construction.
The instability of steel columns meant to support the floors has been attributed as the primary cause of collapse.
What Is The Slab Lifting Process?
A concrete slab is first poured on the ground level. Lifting collars are set around each of the columns and cast into place as the slab is poured around them.
The lifting collars will later be used to support the slab as it is raised and secured in place. Subsequent floors and the roof are then poured and formed on top of the initial ground slab.
Bond breakers are used between each floor plate to allow the slabs to separate as they are raised.
Along with reducing the formwork required to create the slabs, slabs can be easily protected from inclement weather since all of the slabs remain together during the curing process.
Once the slabs have been raised to their desired height, the lifting collars are welded to the columns, along with shear blocks to support the slab from beneath.
To assure the security of a structure during the raising of the slabs, hydraulic jacks, attached to the top of the columns, use synchronized consoles to lift the slabs at an even rate.
The conventional method of mounting jacks to columns requires that the jacks be removed before continuing to raise the slabs.
A more recent approach is to utilize welded plates that are separated from the columns to support the jack.
What Is The Advantage Of Lift Slab Construction?
There are various reasons homeowners are highly dependable on concrete lifting. This process is also known as mud jacking or slab jacking. Some advantages and disadvantages of this method include:
-It is quite affordable; concrete lifting service will never add to your financial worry and it does not take much time to complete. You also do not have to pay for hours as you have to do in other projects.
There is only a minimal cost for the materials needed, such as grout for filling the gaps underneath the slab.
-It is quick and effective; in this method, you do not have to wait for days for your concrete to cure.
Once the treatment is done, you can drive on the surface on the same day. It works on the most dramatically sunken slab.
What Is The Disadvantage Of Lift Slab?
As a home concrete repair method, concrete lifting is one of the best options. However, you should think about its long-term effectiveness and compare it to other methods before you invest any money in this repair – even if the cost is minimal.
Be sure to address the underlying reason your concrete is sinking. For example, if soil erosion due to poor drainage is washing away the earth that supports your concrete slab, concrete lifting won’t be effective for long. You’ll only have the same problem again.
If you’re able to solve the root problem causing the sinking concrete, the fix will last much longer.