# What is Deflection in FRP?

When used in structural engineering, the term deflection refers to load-induced displacement, which typically affects beam designs. It can be an extremely complicated value to calculate when considering the many variations of boundary conditions and materials.

Furthermore, beams may have constant cross-sections or tapered ends, which brings more complexity to the calculations. Materials can also be non-homogeneous, like a composite (i.e., FRP) or homogeneous (i.e., structural steel).

The utilization of fiber-reinforced polymers (FRP) to manufacture a growing range of structural applications is increasing. In this article, the flexural properties of FRP and how deflection affects the design of FRP beams will be outlined.

## How to Calculate Beam Deflection

A beam deflection calculation is a function of the amount of force that is needed to cause a beam to bend. Knowledge of the beam’s stiffness is needed, and this is defined by the formula of the modulus of elasticity multiplied by the beam’s moment of inertia (E x I).

A typical deflection limit in beam design is that deflection should not exceed the value of the beam span divided by 360 (L/360). These same deflection limits exist for FRP structural members in FRP engineering applications, even though FRP beams are less stiff than steel beams.

Image Credit: Strongwell Corporation

Yet, FRP beams are increasingly used to replace steel beams, owing to their corrosion resistance, satisfactory strength and lower installation costs. This gives FRP members an advantage over steel, whether you are dealing with structural parts or components made up of a number of parallel beams, such as gratings.

## How to Reduce Beam Deflection

There are five primary strategies employed to improve flexural capacity and decrease beam deflection. These are:

1. Stiffen beams
3. Shorten span
4. Change beam support conditions
5. Increase beam depth

It is clearly not always possible to achieve each of these goals, so it is crucial to make improvements where it is most important. Strongwell has taken each of these into consideration for previous applications needing increased loads, lower deflections, longer spans and so on.

## FRP Beams: A Quick Case Study

When the span cannot be decreased, even when a longer span is necessary for larger structural applications, beam stiffness was increased by improving their laminate design, this increased load capacity without increasing deflection.

FRP I-beams which have thick flange construction can also strengthen supports with or without the utilization of additional stiffeners.

## FRP Solutions from Strongwell

Strongwell is proud of its ability to custom-build pultruded FRP solutions that take into consideration customers’ critical design parameters.

This information has been sourced, reviewed and adapted from materials provided by Strongwell Corporation.

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