Most floor tiles are not nominally reinforced or reinforced to control the width of cracks. For this reason, concrete slab strengthening and strengthening methods must be used. One of these methods is the use of steel reinforcement, when the steel reinforcement is placed at the top or above the thickness of the slab, and to introduce random cracks that may occur due to concrete shrinkage and temperature restrictions, and to stabilize the foundation, increased applied loads or problems will be created again, this limits.
This article focuses on introducing concrete slab strengthening methods such as steel rebar and welding wire reinforcement to control crack width.
Types of methods for strengthening concrete slabs
For most structural slabs on the ground, two reinforcement layers of steel reinforcement are considered at the top and bottom, which is suitable for controlling the crack width and bearing the increased load.
Reinforcing bars do not prevent concrete slabs and welded reinforcement from cracking. The hardener is essentially inactive until the concrete cracks. After cracking, it activates and controls crack width by limiting crack growth
Reinforcement is generally not required if slabs are placed on good quality, uniformly reinforced layers consisting of low-shrinkage concrete with appropriate joints spaced 15 feet or less.
Under these conditions, some random or out-of-joint cracks may develop, but random cracks remain relatively tolerable without increasing, because joint spacing is limited and concrete shrinkage is small, resulting in the need for reinforcement. Fixed in the future.
But when slabs are placed on problem foundations that have risks such as irregular support, medium to high shrinkage concrete is used in the structure, or joints are spaced more than 15 feet apart, if cracks occur, hardener must be used for a limited purpose, which is used to widen the cracks.
Crack control options in concrete slab reinforcement
In general, there are two options for crack control in concrete slab reinforcement
1) Control the incision location by installing shrink joints
In this method of strengthening concrete slab, we adjust the slab so that the location of the crack is clear and the width of the shrinkage joints or cracks in the joints can be largely controlled by the distance of the joints and the shrinkage of the concrete.
By increasing joint spacing and shrinkage of concrete, the joint width increases. Similar to cracks, if the joint width approaches approximately 35 mils, the effectiveness of aggregate interlocking to transfer loads and prevent differential vertical movements across the joints can be significantly reduced.
For this reason, many designers use load transfer devices such as steel dowels, plates, or concrete slab reinforcement in conjunction with shrinkage joints to ensure positive load transfer and limit vertical differential movements between joints.
Concrete slab reinforcement
2) Control the width of the crack by installing the stiffener
Controlling the crack width by installing hardeners is another way to strengthen the concrete slab, through which we allow the slab to crack randomly, but we control the crack width by using reinforcement bars for the concrete slab or welding wire reinforcement.
Typically, shrinkage joints are not installed with this option. Instead, cracking occurs randomly, creating multiple, tightly packed cracks. Due to its somewhat unsightly appearance, this crack control method should always be used with the owner’s permission.
Concrete slab reinforcement site
Concrete slab reinforcement bars and welded reinforcing wires should be placed in the upper third of the slab thickness because shrinkage and temperature cracks originate from the slab surface. The cracks are wider in surface and narrow in depth.
Therefore, crack control hardeners should never be placed below the center depth of the slab. The stiffener should also be placed low enough so as not to cause the stiffener to break.
To reinforce welded wire, it is recommended to place the steel about 2 inches below the surface or at the top third of the slab thickness, whichever is closest to the surface.
Designers usually determine the location of the stiffener by specifying a concrete cover (1/2 to 2 inches) for the stiffener. It is not recommended to apply a single layer of hardener at the center or mid-depth of the slab to strengthen a concrete slab (except for 4-inch thick slabs).
Strengthening methods are usually implemented in addition to controlling the width of cracks, with the aim of increasing the load capacity of the slab. However, placing the stiffener in the middle of the slab does not cover either target effectively.
Concrete slab reinforcement
Effect of FRP fibers and composites on concrete slab reinforcement
Fiber reinforced polymer (FRP) or FRP composites, also fiber reinforced plastic, is a composite material made of a fiber-reinforced polymer matrix.
These fibers are usually glass, carbon, or aramid, although other fibers such as paper, wood, or asbestos are sometimes used.
The polymer is usually an epoxy, vinyl ester or thermoplastic polyester, and phenol-formaldehyde resins are also currently used. FRPs are commonly used in the aerospace, automotive, marine and construction industries.
Another way to strengthen concrete slabs is to use FRP materials because these materials have high tensile strength while being light.
FRP composite materials can be applied as strips or sheets to roofs, and longitudinally supported one-way slabs can be strengthened by gluing FRP strips or sheets to their undersides.
FRP composites consist of two or more components with very different physical or chemical properties that act separately and distinctly in the final structure.
Characteristics of each method of strengthening concrete slab
Adding steel clips
Adding steel clips to strengthen the concrete slab reduces the need for ductility. In general, the use of clamp systems in strengthening is not common due to the high cost and difficulties in implementing and supplying beams. However, it is possible to use a variety of closely spaced clamp systems that also help strengthen the concrete slab.
Add a curved frame
The technique of adding a bending frame is done to remove the local or general strength of the building or to strengthen the concrete slab in general.
Bending frames should not be placed in other unstable locations or on floors higher than the first floor
Seismic isolator in building improvement
Seismic isolation systems are one way to build resistance against seismic loads.
Seismic isolators include structural elements that separate the units of the upper floors from the units on the seismic bed, thus ensuring the integrated and safe performance of the building against earthquakes.
last word
Considering that the slabs must be connected horizontally to all strong side elements, a strong connection between the slab and the shear wall is necessary, and the concrete slab can be strengthened with rebar or reinforced steel.
In general, you can refer to our website and communicate with our experts to get the necessary advice on issues related to concrete slab reinforcement and FRP compounds on concrete slab reinforcement.