BEAM TO BEAM FLOORING SYSTEM –FLOOR DÉCOR KENYA

INTRODUCTION

Beam-to-beam flooring (BBF) can be described as an economic, safe and functional system currently being utilized in slab construction both locally and internationally. It comprises of high performance pre-stressed concrete beams, concrete hollow blocks and a topping that work together to result in a robust slab. The pre-stressed concrete T-beams have a 100mm wide and 50mm deep flange with a web that is 50mm wide and 100mm deep. It is these T-beam joists that work in tandem with the concrete hollow blocks to support the 50mm topping and all manner of design loads imposed on them. 

How it works

The hollow blocks used in this system have a high compressive load i.e. 7N/mm2 thus function as structural elements unlike your typical hollow blocks that function as “fillers” meant to achieve required structural depth. These hollow blocks lock by 100mm on either side of the pre-stressed concrete beams. The load path is therefore from the topping to the hollow blocks to the pre-stressed beams to the reinforced concrete beams of that particular floor to the columns and finally to the foundations. 

Production

The pre-stressed concrete T-beams are cast in a pre-stressing yard where all the necessary design parameters are controlled to achieve a high quality product. A concrete mix design that achieves class 60 i.e. a compressive load of 60N/mm2 is used. 5mm tendons are stretched between stable end-anchorage points and concreted over a casting bed before being allowed to sufficiently cure. The tendons are released after the concrete has achieved minimum desired strength. The length requirements for each beam is determined prior to casting to avoid wastage. 

Usually, all stresses induced by loads on reinforced concrete structures are mainly carried by reinforcement bars. However, in pre-stressed members such as the beams in BBF the stresses are induced in the entire member. The end result is a structural product that is better at managing vibrations and shocks compared to conventional concrete. 

Applications

Pre-stressing is typically used to allow for longer spans and/or minimize the structural depth of beams and slabs. Pre-stressed elements are commonly used in the following areas, span being a major consideration; floor beams, bridges, water tanks, runways, roofs, railroad ties, poles etc. A key benefit is that pre-stressed concrete elements can more economically span longer distances than conventionally-reinforced concrete elements. This is of benefit in infrastructure e.g. bridges as well as in buildings with respect to beams and slabs.

Benefits

The benefits of utilizing BBF system are:

1. Foundation excavation – The system minimizes mass excavation that would have otherwise been performed underneath the ground slab for sites situated in areas with predominant expansive soils such as black cotton soil. This means that it minimizes labor cost that would have been incurred for doing the actual excavation and consequently backfilling of the same. Transportation for hauling the excavated material to a dumpsite is also eliminated.
2. Steel fixing- BBF system realizes a time and labor cost saving that would have been incurred in cut and bend for reinforcement bars of the slab and concreting for the same.
3. Construction material – BBF system eliminates the need to use BRC mesh in the topping but rather uses fibre mesh. This saves cost for the client as fibre mesh is significantly cheaper compared to BRC mesh. It also eliminates labor that would have been incurred in handling BRC mesh on site. 
4. Shuttering and propping – It reduces the traditional use of shuttering and props because the concrete hollow block lock onto the pre-stressed beams that in turn rest of reinforced concrete beams of a building’s floor. Essentially, only the reinforced concrete floor beams remain propped. 
5. Increased head-room – There is an increased floor to floor height because the floor system rests on top of the reinforced concrete beams of the building’s frame. 
6. Sound insulation – The concrete hollow blocks help in insulating the slab by breaking sound waves resulting in buildings that are quieter.
7. Fire rating – The pre-stressed beams in BBF help in increasing the fire rating of buildings due to the large cover provided for the tendons. 
8. Assembly time – There is time saving realized with BBF system because the elements are pre-cast. Assembly takes a very short time resulting in faster construction timelines. This positively impacts program of works.
9. Structural benefits – The pre-stressed beams minimize potential cracks, decreases the risk that would have been presented by reinforcement corrosion and also lengthens the service life of a building.