Beam (structure)

beam, deflecting (sagging) under a uniformly distributed load, which includes its own weight A beam is a structural element designed to carry loads perpendicular to its long (or "horizontal") axis. This contrasts with a strut or column, which bears its load perpendicular to its short (or "vertical") axis. A beam's mode of deflection is primarily by bending, as loads produce reaction forces at the beam's support points and internal bending moments, shear, stresses, strains, and deflections. Beams are characterized by their manner of support, profile (shape of cross-section), equilibrium conditions, length, and material. Any structural element, in any orientation, that primarily resists loads applied laterally across the element's axis is a beam. While beams are most commonly found in architecture and civil engineering, they are also found in automobile frames, aircraft components, machine frames, and many other mechanical or structural systems.

beam, deflecting (sagging) under a uniformly distributed load, which includes its own weight]] A beam is a structural element designed to carry loads perpendicular to its long (or "horizontal") axis. This contrasts with a strut or column, which bears its load perpendicular to its short (or "vertical") axis. A beam's mode of deflection is primarily by bending, as loads produce reaction forces at the beam's support points and internal bending moments, shear, stresses, strains, and deflections. Beams are characterized by their manner of support, profile (shape of cross-section), equilibrium conditions, length, and material. Any structural element, in any orientation, that primarily resists loads applied laterally across the element's axis is a beam. While beams are most commonly found in architecture and civil engineering, they are also found in automobile frames, aircraft components, machine frames, and many other mechanical or structural systems. ==Classification based on supports== In engineering, beams are of several types: Simply supported – a beam supported on the ends which are free to rotate and have no moment resistance. Fixed or encastré (encastrated) – a beam supported on both ends and restrained from rotation. Overhanging – a simple beam extending beyond its support on one end. Double overhanging – a simple beam with both ends extending beyond its supports on both ends. Continuous – a beam extending over more than two supports. Cantilever – a projecting beam fixed only at one end. Trussed – a beam strengthened by adding a cable or rod to form a truss. Beam on spring supports Beam on elastic foundation ==Beam area measurement== In the beam equation, the variable I represents the second moment of area or moment of inertia: it is the sum, along the axis, of dA·r 2 , where r is the distance from the neutral axis and dA is a small patch of area. It measures not only the total area of the beam section, but the square of each patch's distance from the axis. A larger value of I indicates a stiffer beam, more resistant to bending. ==General shapes== Most beams in reinforced concrete buildings have rectangular cross sections, but a more efficient cross section for a beam is an I-beam or H-shaped section which is typically seen in steel construction. Because of the parallel axis theorem and the fact that most of the material is away from the neutral axis, the second moment of area of the beam increases, which in turn increases the stiffness. supporting a bridge]] An I-beam is only the most efficient shape in its "I" orientation; turned on its side, it functions as an 'H', where it is less efficient. The most efficient shape for both directions in 2D is a box (a square shell); the most efficient shape for bending in any direction, however, is a cylindrical shell or tube. For unidirectional bending, the I-beam or wide flange beam is superior. Efficiency means that for the same cross sectional area (volume of beam per length) subjected to the same loading conditions, the beam deflects less. Other shapes, like L-beam (angles), C (channels), T-beam and double-T or tubes, are also used in construction when there are special requirements. ==Walers and struts== This system provides horizontal bracing for small trenches, ensuring the secure installation of utilities. It's specifically designed to work in conjunction with steel trench sheets, or with a concrete retaining wall. In an idealised case, the lateral pressure due to the soil imposes a uniformly distributed load on the waler, which is then propped up by the struts with designated spacing between them. Therefore, the waler generally experiences shear forces and bending moment, while the struts experiences axial loads transferred from the waler. Usually, steel I-beams are used, owing to their efficiency. Some deeper excavations may require multiple layers of walers and struts. The design of struts and walers plays a very important part in excavation projects. In 2004, the collapse of the excavation site for the Nicoll Highway Station in Singapore was initiated due to a failure of the strut-waler system, whereby several walers buckled and leading to a cave-in of the earth retaining walls, killing 4 workers. The inquiry into the collapse also reported inadequate monitoring of the forces of the struts and walers. Possible measures are to use load cells and strain gauges to monitor the forces in the most critical (usually the sections with the longest span, as they are most vulnerable to buckling) sections of the excavation cite, to ensure ample warning before a possible failure. ==History== ==See also== Airy points Beam engine Building code Cantilever Classical mechanics Deflection (engineering) Elasticity (physics) and Plasticity (physics) Euler–Bernoulli beam theory Finite element method in structural mechanics Flexural modulus Free body diagram Influence line Materials science and Strength of materials Moment (physics) Poisson's ratio Post and lintel Shear strength Statics and Statically indeterminate Stress (mechanics) and Strain (materials science) Thin-shell structure Timber framing Truss Ultimate tensile strength and Hooke's law Yield (engineering) ==References== ==External links== American Wood Council: Free Download Library Wood Construction Data Introduction to Structural Design , U. Virginia Dept. Architecture Glossary Course Sampler Lectures, Projects, Tests Beams and Bending review points (follow using next buttons) Structural Behavior and Design Approaches lectures (follow using next buttons) U. Wisconsin–Stout, Strength of Materials online lectures, problems, tests/solutions, links, software Beams I – Shear Forces and Bending Moments

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