Shear force

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Shearing forces push in one direction at the top, and the opposite direction at the bottom, causing shearing deformation. Simple shear in 2D.svg
Shearing forces push in one direction at the top, and the opposite direction at the bottom, causing shearing deformation.
A crack or tear may develop in a body from parallel shearing forces pushing in opposite directions at different points of the body. If the forces were aligned and aimed straight into each other, they would pinch or compress the body, rather than tear or crack it. Shear crack.svg
A crack or tear may develop in a body from parallel shearing forces pushing in opposite directions at different points of the body. If the forces were aligned and aimed straight into each other, they would pinch or compress the body, rather than tear or crack it.

Shearing forces are unaligned forces pushing one part of a body in one specific direction, and another part of the body in the opposite direction. When the forces are aligned into each other, they are called compression forces. An example is a deck of cards being pushed one way on the top, and the other at the bottom, causing the cards to slide. Another example is when wind blows at the side of a peaked roof of a house - the side walls experience a force at their top pushing in the direction of the wind, and their bottom in the opposite direction, from the ground or foundation. William A. Nash defines shear force in terms of planes: "If a plane is passed through a body, a force acting along this plane is called a shear force or shearing force." [1]

Force Any action that tends to maintain or alter the motion of an object

In physics, a force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity, i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newtons and represented by the symbol F.

Plane (geometry) Flat, two-dimensional surface

In mathematics, a plane is a flat, two-dimensional surface that extends infinitely far. A plane is the two-dimensional analogue of a point, a line and three-dimensional space. Planes can arise as subspaces of some higher-dimensional space, as with a room's walls extended infinitely far, or they may enjoy an independent existence in their own right, as in the setting of Euclidean geometry.

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Shear force of steel and bolts

Here follows a short example of how to work out the shear force of a piece of steel. The factor of 0.6 used to change from tensile to shear force could vary from 0.58–0.62 and will depend on application.

Steel called EN8 bright has a tensile strength of 800 MPa and mild steel has a tensile strength of 400 MPa.

To work out the force to shear a 25 mm diameter round steel EN8 bright;

Area of the 25 mm round steel in mm2 = (12.52)(π) ≈ 490.8 mm2
0.8 kN/mm2 × 490.8 mm2 = 392.64 kN ≈ 40 tonne-force
40 tonne-force × 0.6 (to change force from tensile to shear) = 24 tonne-force

When working with a riveted or tensioned bolted joint, the strength comes from friction between the materials bolted together. Bolts are correctly torqued to maintain the friction. The shear force only becomes relevant when the bolts are not torqued.

Rivet Permanent mechanical fastener

A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the tail. On installation, the rivet is placed in a punched or drilled hole, and the tail is upset, or bucked, so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, pounding creates a new "head" on the other end by smashing the "tail" material flatter, resulting in a rivet that is roughly a dumbbell shape. To distinguish between the two ends of the rivet, the original head is called the factory head and the deformed end is called the shop head or buck-tail.

Bolted joint type of fastener

Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads.

A bolt with property class 12.9 has a tensile strength of 1200 MPa (1 MPa = 1 N/mm2) or 1.2 kN/mm2 and the yield strength is 0.90 times tensile strength, 1080 MPa in this case.

A bolt with property class 4.6 has a tensile strength of 400 MPa (1 MPa = 1 N/mm2) or 0.4 kN/mm2 and yield strength is 0.60 times tensile strength, 240 MPa in this case.

In case of fasteners, proof load is specified as it gives a real-life picture about the characteristics of the bolt.

See also

ASTM F568M is an ASTM International standard for metric bolts, screws and studs that are used in general engineering applications. It is titled: Standard Specification for Carbon and Alloy Steel Externally Threaded Metric Fasteners. It defines mechanical properties for fasteners that range from M1.6 to 100 in diameter. The standard was withdrawn in 2012. and has been replaced by ISO 898-1

The Cantilever method is an approximate method for calculating shear forces and moments developed in beams and columns of a frame or structure due to lateral loads. The applied lateral loads typically include wind loads and earthquake loads, which must be taken into consideration while designing buildings. The assumptions used in this method are that the points of contraflexure in both the vertical and horizontal members are located at the midpoint of the member, and that the direct stresses in the columns are proportional to their distances from the centroidal axis of the frame. The frame is analysed in step-wise (iterative) fashion, and the results can then be described by force diagrams drawn up at the end of the process. The method is quite versatile and can be used to analyse frames of any number of storeys or floors.

The Resal effect is a structural engineering term which refers to the way the compressive force acting on a flange of a tapered beam reduces the effective shear force acting on the beam.

Related Research Articles

Stress (mechanics) physical quantity that expresses internal forces in a continuous material

In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighbouring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material which is not a physical quantity. For example, when a solid vertical bar is supporting an overhead weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a closed container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface push against them in (Newtonian) reaction. These macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Stress is frequently represented by a lowercase Greek letter sigma (σ).

Rebar steel bar or mesh used within concrete

Rebar, known when massed as reinforcing steel or reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has weak tensile strength. Rebar significantly increases the tensile strength of the structure. Rebar's surface is often deformed to promote a better bond with the concrete.

Strength of materials, also called mechanics of materials, is a subject which deals with the behavior of solid objects subject to stresses and strains. The complete theory began with the consideration of the behavior of one and two dimensional members of structures, whose states of stress can be approximated as two dimensional, and was then generalized to three dimensions to develop a more complete theory of the elastic and plastic behavior of materials. An important founding pioneer in mechanics of materials was Stephen Timoshenko.

Work hardening strengthening of a metal by plastic deformation

Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context.

Shear strength strength of a material or component against the type of yield or structural failure when the material or component fails in shear

In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shear.

Wire rope rope made from wire

Wire rope is several strands of metal wire twisted into a helix forming a composite "rope", in a pattern known as "laid rope". Larger diameter wire rope consists of multiple strands of such laid rope in a pattern known as "cable laid".

The yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear deformation begins. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

Fracture (geology) Geologic structure

A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.

A514 is a particular type of high strength steel, which is quenched and tempered alloy steel, with a yield strength of 100,000 psi. The ArcelorMittal trademarked name is T-1. A514 is primarily used as a structural steel for building construction. A517 is a closely related alloy that is used for the production of high-strength pressure vessels.

A36 steel is a common structural steel in the United States. The A36 standard was established by the ASTM International.

Anchor bolt

Anchor bolts are used to connect structural and non-structural elements to the concrete. The connection is made by an assembling of different components such as: anchor bolts, steel plates, stiffeners. Anchor bolts transfer different types of load: tension forces and shear forces. A connection between structural elements can be represented by steel column attached to reinforced concrete foundation. Whereas, a common case of non-structural element attached to a structural one is represented by the connection between a facade system and a reinforced concrete wall.

ABS Steels are types of structural steel which are standardized by the American Bureau of Shipping for use in shipbuilding.

Screw type of fastener characterized by a thread wrapped around a cylinder

A screw is a type of fastener, in some ways similar to a bolt, typically made of metal, and characterized by a helical ridge, known as a male thread. Screws are used to fasten materials by digging in and wedging into a material when turned, while the thread cuts grooves in the fastened material that may help pull fastened materials together and prevent pull-out. There are many screws for a variety of materials; those commonly fastened by screws include wood, sheet metal, and plastic.

ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 12 to 1 12 inches in diameter.

ASTM A490 and ASTM A490M are ASTM International standards for heavy hex structural bolts made from alloy steel. The imperial standard is officially titled Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength, while the metric standard (M) is titled Standard Specification for High-Strength Steel Bolts, Classes 10.9 and 10.9.3, for Structural Steel Joints.

Pounds per square inch unit of pressure or stress

The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m2.

A threaded rod, also known as a stud, is a relatively long rod that is threaded on both ends; the thread may extend along the complete length of the rod. They are designed to be used in tension. Threaded rod in bar stock form is often called all-thread.

A mechanical joint is a section of a machine which is used to connect one or more mechanical part to another. Mechanical joints may be temporary or permanent, most types are designed to be disassembled. Most mechanical joints are designed to allow relative movement of these mechanical parts of the machine in one degree of freedom, and restrict movement in one or more others. Mechanical joints are much cheaper and are usually bought ready assembled.

References

  1. William A. Nash (1 July 1998). Schaum's Outline of Theory and Problems of Strength of Materials. McGraw-Hill Professional. p. 82. ISBN   978-0-07-046617-3 . Retrieved 20 May 2012.