definitions Flashcards
centroid/ barycentre
geometric centre of mass/ gravity as defined by x and y coordinates from a reference axis
neutral surface and axis
the neutral surface where the fibers are neither contracted nor extended (under stress), the axis is where this intersects the cross section
second moment of area or the moment of inertia (I)
geometrical property conveying how the points of a section are dispersed with respect to an arbitrary axis in the cross-sectional plane
parallel axis theorem
moments of inertia with respect to different parallel axis can be added together (also with the sums of Ah^2) to find the second moment of area for the whole section
Equilibrium
When a structure is initially at rest and remains at rest when subjected to a system of forces and couples
Couple(t)
a system/ combination of forces with a resultant moment but no resultant force
(Externally) Statical Determinancy
all the support reactions can
be determined by solving the equations of equilibrium
Degree of redundancy
The no. of external restraints greater than the no. of equilibrium equations (3/ more with internal supports)
factor of safety
an indication of a structure’s capacity to withstand load beyond its intended/necessary value
principle of superposition
if a structure of linear elastic material is subjected to loads which do not cause strain beyond the linear elastic region, the resultant effect is equal to the algebraic sum
bending moment
reaction induced by external force or moment causing element to bend
Shear(ing) force
a force that acts parallel or tangential to a surface, causing shear strain (simply: where one surface is pushed one way and the otehr surface the otehr way)
internal resistance across a cross section to a transverse external load
point of contraflexure
the point of zero moment where the moment changes from sagging (+ve) to hogging (-ve) or vice versa
bending stress
longitudinal stresses acting parallel or longitudinal to the beam (tensile or compressive) induced by bending moment application
truss
a pin jointed structural frame of triangles (created by members jointed at nodes)
tension in trusses
joint is being pulled by the member
OR
force pulling member away from the node
compression in trusses
joint is being pushed by the member
OR
force pulling member towards the node
brittle materials
those that fracture without yielding (no elastic deformation region)
ductile materials
those which yield before failing (elastic region in present)
lateral strain
lateral deformation per unit length of the transverse dimension
poisson’s ratio
a ratio value that remains constant for any material that is homogeneous and isotropic (and as long as it remains elastic)
shear strain
the angular distortion
st venant’s principle
nearer to the point of application of a load, the distribution of stress will not be uniform
limit of proportionality
the point at which stress and strain are no longer linearly related
elastic limit
the point beyond which further loading will cause permanent/plastic deformation
plastic deformation
permanant deformation by a load
strain hardening
the flat section of on a stress strain graph where loading does not induce further deformation
dead vs live loads
dead = materials used in the structure
live = additional external loads which may vary
moment of resistance
the sum of moments from internal forces about the neutral axis of the section due to bending moments from an external load
modulus of elasticity
the ratio of direct stress to direct strain
positive shear
sum of forces to left of shear fracture are upwards
negative shear
sum of forces to left of shear fracture are downwards
web
The vertical components that connect horizontal flange components together
flange
A beam section’s horizontal components
