Hollowcore slab
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The document discusses several types of concrete slabs, including hollowcore slabs, hardy slabs, and waffle slabs. Hardy slabs use hollow concrete blocks to reduce weight and increase insulation. They are constructed by placing blocks in formwork, adding reinforcement in gaps, and pouring concrete. Waffle slabs contain square grids that create a waffle-like appearance. PVC trays are placed in formwork and concrete is poured, leaving hollow spaces. Waffle slabs can span longer distances than flat slabs and are lighter. Both hardy slabs and waffle slabs offer advantages of reduced weight and increased load capacity compared to conventional slabs.
Hollowcore slab
- 1. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 133 Hollowcore slab Disadvantages: 1. If not properly handled, the hollow core ribbed slab units may be damaged during transport. 2. It becomes difficult to produce satisfactory connections between the precast members. 3. It is necessary to arrange for special equipment for lifting and moving of the precast units. 4. Not economic for small spans. 5. Difficult to repair and strengthen 4. Hardy Slab:- Hardy slabs are generally seen in Dubai and China. Hardy slab is constructed by hardy Bricks. Hardy bricks are hollow bricks and made up of concrete Hollow blocks. These blocks are used to fill portions of the slab. Hardy slabs saves the amount of concrete and hence the own weight of the slab is reduced. This kind of slab has a more thickness 0.27m when compared with the conventional one. The method of installing Hardy slab is different from normal and it is clearly explained below:
- 2. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 134 The process of hardy blocks execution is as follows: Step 1 : Formwork is arranged and then shutters are fixed on the formwork. Step 2 : Hardy blocks are placed on the shutter with one brick gap on the entire shutter. Step 3 : The gaps between the bricks are called a rib. Reinforcement is provided in a form of the beam within the gap. Step 4 : After placing the rib, the plane steel mesh is placed on entire slab area resting on ribs. Step 5 : Now pouring of concrete is done on a slab.
- 3. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 135 Hardy slab can be used where temperatures are very high. To resist the temperature from top of the slab thickness is increased. The heat coming from walls are resisted by using special bricks which has thermacol in it. Thermacol is the best insulator of sunlight. Advantages of Hardy Slab: 1. Reducing slab weight by reducing the amount of concrete below neutral axis. 2. Ease of construction, especially when all beams are hidden beams. 3. Economic for spans > 5m with moderate live load: hospitals, office and residential buildings. 4. Improved insulation for sound and heat. Disadvantages of Hardy Slab: 1. If not properly handled, the hollow core ribbed brick units may be damaged during transport. 2. Not economic for small spans. 3. Difficult to repair and strengthen Hardy slabs are further classified into two types: • One way Hardy Slab • Two way Hardy slab
- 4. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 136 Waffle Slab:- Waffle slab is a reinforced concrete roof or floor containing square grids with deep sides and it is also called as grid slabs. This kind of slab is majorly used at the entrance of hotels, Malls, Restaurants for good pictorial view and to install artificial lighting. This a type of slab where we find a hollow hole in the slab when the formwork is removed. Firstly PVC trays (pods) are placed on shuttering then reinforcement is provided between the pods and steel mesh is provided at top of the pods and then concrete is filled. After concrete sets, the formwork is removed and PVC pods are not removed. The concrete waffle slab is often used for industrial and commercial buildings while wood and metal waffle slabs are used in many other construction sites. This is a one of the types of concrete slabs.
- 5. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 137 Where to use Waffle Slab & Waffle slab details: A waffle slab has a holes underneath, giving an appearance of waffles. It is usually used where large spans are required (e.g auditorium, cinema halls) to avoid many columns interfering with space. Hence thick slabs spanning between wide beams (to avoid the beams protruding below for aesthetic reasons) are required. The main purpose of employing this technology is for its strong foundation characteristics of crack and sagging resistance. Waffle slab also holds a greater amount of load compared with conventional concrete slabs.
- 6. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 138 Types of Waffle slabs: Based on the shape of Pods (PVC Trays) They are classified into different types some of them are: 1.Triangular pod system 2.Square pod system
- 7. Erbil Polytechnic University Civil Engineering Department Saad.bilbas@epu.edu.iq 139 Advantages of Waffle slabs: 1. Waffle slabs are able to carry heavier loads and span longer distances than flat slabs as these systems are light in weight. 2. Waffle slab can be used as both ceiling and floor slab. 3. Suitable for spans of 7m-16m ;longer spans may be possible with posttensioning. 4. These systems are light in weight and hence considerable saving is ensured in the framework as the light framework is required Disadvantages of Waffle slabs: 1. Waffle slab is not used in typical construction projects. 2. The casting forms or moulds required for pre- cast units are very costly and hence only economical when large scale production of similar units are desired. 3. Construction requires strict supervision and skilled labour.