Slip joint
Encyclopedia
A slip joint is a mechanical construction allowing extension and compression in a linear structure.
s, hiking poles, or similar telescoping
device. The position is fixed using a clamping mechanism based on a cam
, a set screw
or similar locking mechanism. Slip joints can also be non-telescoping, such as the joints on some older wooden surveyor's levelling rods. These use a joint that keeps the sections offset from each other but able to be slid together for transport.
Examples of continuous slip joints are given below.
at some high level, there are two options in structural engineering. If the buildings are identical in mass and elasticity they will tend to respond similarly to ground motion induced by earthquake
s. In this case it may be appropriate to construct a rigid connection between the buildings, although this may require additional supporting members within the structures. On the other hand, a lower cost connection may be made by using a lightweight structure that is not coupled rigidly but instead which is allowed to slide or "float" relative to one or both structures. This is especially suitable where the two structures may respond differently to ground motion. The structure will not be completely free to move but rather may use elastic materials to locate it near the center of its range of motion and viscous
shock absorber
s to absorb energy and to restrict the speed of relative motion. When a sliding connection is used it is extremely important that there be sufficient range of motion without failure to accommodate the maximum credible relative motion of the structures. Additional "fail safe" flexible connections may be added to ensure that the structure does not fall, although it may be damaged to a point of being unservicable or unrepairable
Slip joints are common under conditions where temperature changes can cause expansion and contraction that may overstress a structure. These are generally referred to as expansion joint
s. Bridges and overpasses frequently have sliding joints that allow a deck to move relative to piers or abutments. The joints can be constructed with elastomeric pads that permit motion or can use rollers on flat surfaces to allow the ends to move smoothly. The exact details are limited by the imagination of the designer.
. Pipe supports often are slip joints to allow for the thermal expansion or contraction or the pipe relative to the support.
General forms
Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment from one temporarily fixed position to another. Examples of the latter are tripodTripod (photography)
In photography, a tripod is used to stabilize and elevate a camera, or to support flashes or other photographic equipment. All photographic tripods have three legs and a mounting head to couple with a camera...
s, hiking poles, or similar telescoping
Telescoping (mechanics)
Telescoping in mechanics describes the movement of one part sliding out from another, lengthening an object from its rest state. In modern equipment, this is often done by hydraulics....
device. The position is fixed using a clamping mechanism based on a cam
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
, a set screw
Set screw
A set screw is a type of screw generally used to secure an object within or against another object. The most common examples are securing a pulley or gear to a shaft. Set screws are most often headless , meaning that the screw is fully threaded and has no head projecting past the major diameter of...
or similar locking mechanism. Slip joints can also be non-telescoping, such as the joints on some older wooden surveyor's levelling rods. These use a joint that keeps the sections offset from each other but able to be slid together for transport.
Examples of continuous slip joints are given below.
Civil Engineering
Slip joints in large structures are used to allow independent motion of large components while enabling them to be joined in some way. For example, if two tall buildings are to be joined with a pedestrian skywaySkyway
In an urban setting, a skyway, catwalk, sky bridge, or skywalk is a type of pedway consisting of an enclosed or covered bridge between two buildings. This protects pedestrians from the weather. These skyways are usually owned by businesses, and are therefore not public spaces...
at some high level, there are two options in structural engineering. If the buildings are identical in mass and elasticity they will tend to respond similarly to ground motion induced by earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s. In this case it may be appropriate to construct a rigid connection between the buildings, although this may require additional supporting members within the structures. On the other hand, a lower cost connection may be made by using a lightweight structure that is not coupled rigidly but instead which is allowed to slide or "float" relative to one or both structures. This is especially suitable where the two structures may respond differently to ground motion. The structure will not be completely free to move but rather may use elastic materials to locate it near the center of its range of motion and viscous
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
s to absorb energy and to restrict the speed of relative motion. When a sliding connection is used it is extremely important that there be sufficient range of motion without failure to accommodate the maximum credible relative motion of the structures. Additional "fail safe" flexible connections may be added to ensure that the structure does not fall, although it may be damaged to a point of being unservicable or unrepairable
Slip joints are common under conditions where temperature changes can cause expansion and contraction that may overstress a structure. These are generally referred to as expansion joint
Expansion joint
An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, to hold certain parts together, or to allow movement due to ground settlement or earthquakes...
s. Bridges and overpasses frequently have sliding joints that allow a deck to move relative to piers or abutments. The joints can be constructed with elastomeric pads that permit motion or can use rollers on flat surfaces to allow the ends to move smoothly. The exact details are limited by the imagination of the designer.
Mechanical Engineering
Slip joints are sometimes found in tubular structures such as piping, but are generally avoided for this application due to requirements for sealing against leakage, instead using either a large loop that is allowed to flex or a semi-rigid bellowsBellows
A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...
. Pipe supports often are slip joints to allow for the thermal expansion or contraction or the pipe relative to the support.