What is a Rigid Frame?

A rigid frame is a structural configuration consisting of a frame in which the connections between all of the frame pieces are fixed at particular angles that do not change. Steel structural pieces are most common, but other types of frame pieces may also be used, including concrete structural pieces in bridges. This type of frame is particularly desirable because of its relatively high strength compared to other types of frames.

Stationary structures such as buildings and bridges are the most typical applications in which this type of construction is used. Warehouses and office buildings, retail spaces, recreational facilities, airplane hangars and more may be built with this type of frame. Bridges that take advantage of this design may be found around the globe. Ontario, Canada, in particular, is home to a number of historic rigid frame bridges. Rigid frame design may also be incorporated into non-stationary applications such as wheelchairs, bicycles, motorcycles, and industrial trucks.

There are some notable advantages to this style of building design. For instance, the typical square or rectangular construction of a rigid frame building yields more usable space than a comparable rounded frame building such as one that utilizes arch construction. Rounded structural pieces of an arch-style building reduce available head space and side space where the structural pieces curve. Larger unobstructed spaces are possible with rigid frames than with building styles that require interior columns for support. Buildings constructed this way do, however, require an unyielding foundation and uneven settling is not readily accommodated by this type of design.

Bridges may be built using rigid frame construction to take advantage of the inherent strength and stability of the configuration. Other advantages of this type of frame that are desirable in bridge construction are reduced deflection and vibration of structural members under loads. Environmental considerations may also be involved in the selection of rigid frame construction for a given bridge design. Given that a wider span is possible without a support column at the center, a bridge of this type may be used over a waterway without disturbing the natural flow of the water and causing damaging environmental effects.

Strength, weight, and efficiency are also important factors taken into consideration when incorporating a rigid frame into a vehicle design. All of the structural pieces are fixed, so no energy is wasted by flexing, moving parts and all is instead applied toward propelling the vehicle forward. The comparably higher strength of a rigid frame as compared to other types of frames also means the vehicle can be built with a lighter frame. These considerations may be particularly important in certain applications, such as for a disabled person who wants to wheel his wheelchair up a ramp. Rigid frames do, however, tend to provide bumpy rides, because shock experienced from going over bumps cannot be absorbed as readily by fixed structural pieces.