Fibre has been used in beam design for more than 35 years to improve and reinforce existing properties. For example, fibre-reinforced concrete, also known as FRC, is commonplace. Concrete as a material has little tensile strength, as we mentioned in our guide to concrete beams. While usually reinforcement bars are an acceptable solution, fibre reinforcement is much more effective in designs with complex geometries.

Likewise, FRPs like fibreglass or carbon-fibre are innovative materials that have been used for seismic retrofits for years. They are especially common in restoring old buildings like wooden structures, where the wood beam design can be strengthened with FRP.

In this guide, we take a look at and explain why fibre reinforcement is becoming a popular technique for structural engineers and different applications for the materials in beam design and restoration.

Why Fibre Reinforcement is so Popular

Beam design in an old hall

Most materials used in beam design have advantages and disadvantages. Typically, one of the biggest problems with using concrete and plastic beams is that they are vulnerable to cracking. Both plastic and hardened concrete struggle with crack control, for example.

Fibre reinforcement remains somewhat uncommon due to the high cost of production and the high amount of skill needed to distribute polymers among a beam uniformly. However, when necessary, fibre reinforced beams can be extremely useful to a structural engineer’s project.

 

Fibre Reinforced Concrete

Concrete beam design in an attic

Fibre-reinforced concrete is a mix of water, cement, construction aggregate, and discontinuous fibres. The first fibre mixed with concrete for reinforcement was asbestos in the early 20th century, though for obvious reasons we do not use asbestos nowadays. Instead, structural engineers typically use synthetic fibres, cellulose, sisal or jute for FRC.

Unreinforced concrete is a brittle material. It has a high compressive strength, but low tensile strength, meaning it typically requires reinforcement to be effective. Ordinary reinforcement bars are one effective way to increase the load-carrying capacity in the shear and tensile areas of a bar. However, reinforcement bars are rigid, and for unorthodox-shaped buildings, they can be cumbersome and restrictive to beam design.

Instead, by mixing short fibres into the concrete mix, the concrete becomes remarkably more ductile. As a result, cracks become less likely to form, and so the concrete is less likely to give way under pressure.

The most common fibres mixed with concrete are synthetic ones made out of stainless steel. They have little effect on the compressive or tensile strength of beams but improve the toughness of the concrete and post-cracking behaviour. Most common in ground slabs or tunnel linings, much work is being done to implement steel fibre reinforced concrete beams into structural engineering design.

 

Fibre Reinforced Plastics

Fibre reinforced timber beams

Fibre reinforced plastic (FRP) beam designs are an effective and cheaper mode of beam design, but the lack of official guidance still makes them difficult to use. FRPs like fibreglass, carbon fibre, aramid, or basalt behave differently depending on the materials used in production but have a variety of benefits.

Fibre reinforced plastics are lightweight, not magnetic, not corrosive, do not conduct electricity, have high strength, high fatigue life, high durability, and are suitable for buildings at risk of earthquakes or otherwise need a seismic response. Furthermore, more and more modern technologies like fibre optics are easily integrated into FRPs. When steel is vulnerable to corrosion, has high labour costs, high energy consumption, causes environmental pollution, and is weak to earthquakes, FRPs are an effective alternative material for beam design.

FRP still needs more analysis and guidance before it becomes widespread in beam design. However, this demonstrates that fibre reinforcement has many uses and works well with many materials. Expect in the near future, that the structural engineering industry will pivot more towards fibre reinforcement.

We hope this blog post on fibre reinforcement in beam design has proved useful to you. Fibre reinforcement is increasingly common among in redevelopment or building projects with unique and complex structural engineering requirements. It can be a difficult material to use effectively, but it can be fantastic when used correctly. If you need a South West structural engineer, get in touch, and we will be happy to provide our expertise.