Balance Equal distribution or equivalence of load, stress, stain, weight, etc.; symmetry; equality.
Bar A small rolled steel shape, usually round or rectangular in cross section; a rolled steel shape used for reinforcing concrete.
Beam When a straight beam of uniform cross-sectional area is subjected to a perpendicular load, the beam bends. If shear is negligible, the vertical deflection is largely due to bending. Fibers on the convex side of the beam lengthen, and fibers on the concave side compress.
There is a neutral surface within any beam that contains the centroids of all sections and is perpendicular to the plane of the load for such deflections. In a uniform, symmetrical beam, the neutral axis of the beam is the horizontal, central axis. Tensile or compressive stress and strain on the neutral axis are essentially zero. At all other points within the beam, the stress is a tensile stress if the point lies between the neutral axis and convex surfaces of the beam, and is a compressive stress if the point lies between the neutral axis and concave surfaces of the beam, see the Bending of a Beam illustration below.
The fiber stress σ for any point (q) within the beam is calculated using the equation:
The maximum fiber stress in any section occurs at the points farthest from the neutral surface and at the section of greatest bending moment, i.e., when z = Max z, and M = Max M. Maximum fiber stress is given by the equation:
Such equations are valid if:
- The beam is of homogeneous material, so that it has the same modulus of elasticity in tension and compression.
- Plane sections remain planar.
If several loads are applied at the same time, the total stress and deflection at any point are found by superimposition. Compute the stress and deflection for each load acting on the point, and add them together.
Click to enlarge images below.
Bend Deflect.
Bending (or flexural) Strength The maximum stress that can be applied to a beam in pure bending before permanent deformation occurs. It is most commonly used to describe flexure properties of cast iron and wood products.
Bending Moment The moment that causes a beam or other structural member to bend; algebraic sum of moments about the neutral axis of any cross section of a beam.
Bending stress A compressive and/or tensile stress resulting from the application of a nonaxial force to a structural member.
Binder Resin or cementing constituent of a plastic compound which holds the other components together.
Biomaterial Material used for or suitable for use in prostheses that come in direct contact with living tissues.
Biomimetic The construction of artificial materials that mimic natural forms.
Biomimetric The construction of artificial materials using measurements prevalent in nature.
Blend A mixture or kind produced by mixing smoothly and inseparably.
Box Frame A structure formed of pieces joined at right angles.
Brace, Bracing Diagonal member, either temporary or permanent, installed to stabilize a structure against lateral load.
Break To apply sufficient stress to a material to cause it to fail in either tension or compression.
Breaking Load Load that causes fracture in a tension, compression, flexure or torsion test. In tensile tests of thin sheet materials or materials in form of small diameter wire, it is difficult to distinguish between breaking load and the maximum load developed, so the latter is considered the breaking load.
Brittle Having hardness and rigidity but little tensile strength. A brittle material breaks readily under excessive load with a comparatively smooth fracture, as glass does.
Brittleness/Ductility/Toughness The characteristics of a brittle material - seen from the stress-strain curves - are a steep initial linear slope, low failure strain and little or no yielding. Ductile materials show a reduced initial slope, drastic deviation from linearity and a high failure strain. Toughness is the measure of a material’s ability to absorb energy during plastic deformation without showing brittle failure. Toughness can be calculated by the area beneath a stress/strain curve.
Bubble A globule of air or gas in a thin liquid envelope.
Buckling Structural failure by gross lateral deflection of a slender element under bending stress, such as the sideward buckling of a long, slender column or the buckling of a beam in the lower center of its span.
Bulk Magnitude in three dimensions, especially when great.
Bulk Modulus of Elasticity Ratio of stress to change in volume of a material subjected to axial loading. Related to Modulus of Elasticity (E) and Poisson's Ratio (r) by the following equation: Bending Strength K = Er 3(1-2r).
Buttress A structural device of masonry or concrete that resists the diagonal forces from an arch or vault; abutment.