# Structures Glossary

Terms

load distributed along a linear plane (e.g. column, pile, bracing)

Bending moment

the sum of (force) * (perpendicular distance) to the left of any location along the span of a beam (or the sum of areas in a shear diagram)

= M/S  where, S = bd2/6

Centroid

center of gravity, the point within an object from which the force of gravity appears to act. An object will remain at rest if it is balanced on any point along a vertical line passing through its center of gravity. In terms of moments, the center of gravity of any object is the point around which the moments of the gravitational forces completely cancel one another.

Elasticity

stiffness of a material

Epicenter

point where an earthquake surfaces

Equilibrant

a vector that is equal and opposite to the resultant

Fulcrum

pivot, or center of moment

Hypocenter

focus, or origin of an earthquake

Maximum shear

defines the area of a beam

Maximum moment

defines the depth of a beam

Maxwell diagram

a graphic method to solve a truss, using Bowes Notation

Modulus of Elasticity (E)

the stress to strain ratio of a material; a measure of a material’s resistance to deformation, or its stiffness.  Hint: a stiffer material will have a higher elastic modulus.

Moment

an unbalanced force that causes rotation about a turning point, or fulcrum.   Moment = (Force) * (Perpendicular distance from fulcrum)

Moment  arm

perpendicular distance from a fulcrum, or pivot

Moment of Inertia (I)

a term used to describe the capacity of a cross-section to resist bending. It is always considered with respect to a reference (usually centroidal) axis.

Resultant

a vector sum of forces, or loads

Richter scale

a measure of an earthquake’s magnitude

Shear

the sum of forces to the left of any location along the span of a beam

shear determines area; If shear = 0, then this defines the maximum moment. Shear area = b*d

Slenderness Ratio

The ratio between height or length of a structural element (such as a column, or strut) and the width or thickness of the element.

Hint: The higher the slenderness ratio, the more slender the structural element is. How slender a structural element is allowed to be depends upon the material it is made from. Steel can be more slender than concrete

Strain Gauge

A change of length or shape that measures strain

Stress

the force (load) exerted by a given pressure, P, over a given area, A.

F = P/A

Thermal stress

= (modulus of elasticity) * (coefficient of linear expansion) * (change in temperature, in oF)

Thermal strain

= (coefficient of linear expansion) * (change in temperature, in oF)

Transmissibility

a force sliding along a line of action (L.O.A.) without changes in the reactions

Truss

a structure that controls tension and compression

Acronyms

E = Seismic or earthquake load

F = Load do to fluids, such as an elevated water tank

H = Load due to lateral earth pressure