A strut is a structural component commonly found in

engineering Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...

aeronautics Aeronautics is the science or art involved with the study, design process, design, and manufacturing of air flight-capable machines, and the techniques of operating aircraft and rockets within the atmosphere. While the term originally referred ...

architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...

and

anatomy Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

. Struts generally work by resisting longitudinal

compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...

, but they may also serve in tension. A stay is sometimes used as a synonym for strut, but some sources distinguish that struts are braces for holding compressive forces apart, while stays are braces for keeping stretching forces together.

Human anatomy

Part of the functionality of the

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

is to serve as a strut between the

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

and

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

, resisting forces that would otherwise bring the

upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digit (anatomy), digits, including all the musc ...

close to the

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...

. Keeping the upper limb away from the thorax is vital for its

range of motion Range of motion (or ROM) is the linear or angular distance that a moving object may normally travel while properly attached to another. In biomechanics and strength training, ROM refers to the angular distance and direction a joint can move be ...

. Complete lack of clavicles may be seen in

cleidocranial dysostosis Cleidocranial dysostosis (CCD), also called cleidocranial dysplasia, is a congenital disorder, birth defect that mostly affects the bones and teeth. The collarbones are typically either poorly developed or absent, which allows the shoulders to be ...

, and the abnormal proximity of the shoulders to the

median plane Whether in reference to the anatomy of the human or other members of the Bilateria, the median plane, also called the midsagittal plane and related terms, is used to describe the sagittal plane as it bisects the body vertically through the midline ...

in cases of this genetic condition exemplifies the clavicle's importance as a strut.

Architecture and construction

Strut is a common name in

timber framing Timber framing () and "post-and-beam" construction are traditional methods of building with heavy Beam (structure), timbers, creating structures using squared-off and carefully fitted and Woodworking joints, joined timbers with joints secure ...

for a support or brace of

scantling Scantling is a measurement of prescribed size, dimensions, or cross sectional areas. When used in regard to timber, the scantling is (also "the scantlings are") the thickness and breadth, the sectional dimensions; in the case of stone it refers t ...

s lighter than a post. Frequently struts are found in roof framing from either a tie beam or a king post to a principal rafter. Struts may be vertically plumb or leaning (then called canted, raking, or angled) and may be straight or curved. In the U.K., strut is generally used in a sense of a lighter duty piece: a king post carries a ridge beam but a king strut does not, a queen post carries a plate but a queen strut does not, a crown post carries a crown plate but a crown strut does not. Strutting or blocking between floor joists adds strength to the floor system. Struts provide outwards-facing support in their lengthwise direction, which can be used to keep two other components separate, performing the opposite function of a ''

tie Tie has two principal meanings: * Tie (draw), a finish to a competition with identical results, particularly sports * Necktie, a long piece of cloth worn around the neck or shoulders Tie or TIE may also refer to: Engineering and technology * T ...

''. In piping, struts restrain movement of a component in one direction while allowing movement or contraction in another direction.

Strut channel Strut channel, often referred to colloquially by one of several manufacturer trade names, is a standardized formed structural system used in the construction and electrical industries for light structural support, often for supporting wiring, plum ...

made from

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

, or

fibre-reinforced plastic Fibre-reinforced plastic (FRP; also called fibre-reinforced polymer, or in American English ''fiber'') is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fibre ...

is used heavily in the building industry and is often used in the support of

cable tray In the electrical wiring of buildings, a cable tray system is used to support insulated electrical cables used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or electrical conduit system ...

s and other forms of

cable management Cable management refers to management of electrical or optical cable in a cabinet or an installation. The term is used for products, workmanship or planning. Cables can easily become tangled, making them difficult to work with, sometimes ...

, and pipes support systems.

Aircraft

Bracing struts and wires of many kinds were extensively used in early

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

to stiffen and strengthen, and sometimes even to form, the main functional airframe. Throughout the 1920s and 1930s they fell out of use in favour of the low drag

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

construction. Most aircraft bracing struts are principally loaded in compression, with wires taking the tension loads. Lift struts came into increasing use during the changeover period and remain in use on smaller aircraft today where ultimate performance is not an issue. Typically, they are applied to a high wing

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple wings. A monoplane has inherently the highest efficiency and lowest drag of any wing con ...

and act in tension during flight. Struts have also been widely used for purely structural reasons to attach engines,

landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for taxiing, takeoff or landing. For aircraft, it is generally needed for all three of these. It was also formerly called ''alighting gear'' by some manufacturers, s ...

and other loads. The oil-sprung legs of retractable landing gear are still called ''

Oleo strut An oleo strut is a pneumatic air–oil hydraulic shock absorber used on the landing gear of most large aircraft and many smaller ones. This design cushions the impacts of landing and damps out vertical oscillations. It is undesirable for an air ...

s''.

Automobiles

As components of an automobile

chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of a manufactured object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...

, struts can be passive braces to reinforce the chassis and/or body, or active components of the suspension. An example of an active unit would be a

coilover A coilover is an automobile suspension (vehicle), suspension device. The name coilover is an abbreviation of "coil over shock absorber". Description Coilovers are found on many vehicles, from Radio-controlled car, RC cars to normal passenger ...

design in an automotive suspension. The

combines a shock absorber and a spring in a single unit. A common form of automotive suspension strut in an automobile is the

MacPherson strut The MacPherson strut is a type of automotive suspension system that uses the top of a telescopic damper as the upper steering pivot. It is widely used in the front suspension of modern vehicles. The name comes from American automotive engineer ...

. MacPherson struts are often purchased by the automakers in sets of four completed sub-assemblies: These can be mounted on the car bodies as part of the manufacturers' own assembly operations. A MacPherson strut combines the primary function of a

shock absorber A shock absorber or damper is a mechanical or hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...

(as a

damper A damper is a device that deadens, restrains, or depresses. It may refer to: Music * Damper pedal, a device that mutes musical tones, particularly in stringed instruments * A mute for various brass instruments Structure * Damper (flow), a mech ...

), with the ability to support sideways loads not along its axis of compression, somewhat similar to a sliding pillar suspension, thus eliminating the need for an upper suspension arm. This means that a strut must have a more rugged design, with mounting points near its middle for attachment of such loads. Another common type of strut used in

air suspension Air suspension is a type of vehicle suspension powered by an electric or engine-driven air pump or compressor. This compressor pumps the air into a flexible bellows, usually made from textile-reinforced rubber. Unlike hydropneumatic suspensio ...

is an air strut which combines the shock absorber with an air spring and can be designed in the same fashion as a

device. These come available in most types of suspension setups including

beam axle A beam axle, rigid axle, or solid axle is a suspension (vehicle), dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but hist ...

and

style design. Transportation-related struts are used in "load bearing" applications ranging from both highway and off-road suspensions to automobile hood and hatch window supports to aircraft wing supports. The majority of struts feature a bearing, but only for the cases, when the strut mounts operate as steering pivots. For such struts, the bearing is the wear item, as it is subject to constant impact of vibration and its condition reflects both wheel alignment and steering response. In vehicle suspension systems, struts are most commonly an assembly of coil-over spring and shock absorber. Other variants to using a coil-over spring as the compressible load bearer include support via pressurized nitrogen gas acting as the spring, and rigid (hard tail) support which provides neither longitudinal compression/extension nor damping.

History

Struts were created in the 1970s in which automakers transitioned from large rear-wheeled drive vehicles to more fuel-efficient front-wheeled drive vehicles. The entire suspension system was changed in accordance to meet the new style of vehicles. The new styles of vehicles left less room for the traditional system, which was called the short-arm/ long-arm suspension systems. This caused the

system to become the new standard for all automobiles including front-wheeled and rear-wheeled vehicles. The

system does not require an upper control arm, bushings, or a pivot shaft like previous models.

Options on vehicles

Struts are not necessarily needed components on vehicles which separate the springs and shock absorbers, while the shocks support no weight. There are also some vehicles with the option of only having one pair of struts on one set of wheels while the other pair uses a separate selection of shocks and springs. This singular pair of struts are almost always a

. These choices are made for various reasons including the balance of initial cost, performance, and other elements. Some vehicles use a "double wishbone," suspension system which exclusively uses shock absorbers. Sports cars seem to favor this suspension style; however, the Porsche 911 favors traditional struts.

Maintenance

Struts keeps your suspension aligned, along with numerous other functions. To check if a set of struts is failing; simply walk to each side of the wheel and begin to bounce the car up and down. As the car is pushed down, let it bounce back into position. If it continues to bounce up and down, consider taking your vehicle to a mechanic for replacement. You can also check your strut car to see if it's leaking oil. Bad struts could possibly lead to many issues including the breaking of a wheel, flattening of a tire, damaged power steering, broken springs, broken joints, and many more issues in your suspension system. Keep all of these in mind as you drive your vehicle with bad struts.

Gallery

File:Strut.jpg, ORI strut, off-road application of strut File:Strut bar2.JPG, Strut bar File:Wing Brace strut.JPG, Compression strut on Piper Pawnee (low-wing aircraft) File:Shorts360airsey.jpg, Tension strut on Shorts 360 (high-wing aircraft) File:MacPhersonStrut.jpg, MacPherson strut suspension File:Su-30MKI nosewheel.jpeg, Nosewheel oleo strut on Su-30MKI aircraft

References

{{Authority control Automotive suspension technologies Timber framing ja:ストラット式サスペンション