strength of structure
- materials behavior
- the capacity of the structural system to withstand the load that is applied to it
- first function
stability of structure
- equilibrium for all forces and moments
- the capacity of a structural system to transmit various loadings safely to the ground
- second function
strength failure
if the legs of a chair cannot support the applied load they will fracture or break
- not bearing the load
stability failure
the stability of the system of elements depends upon the orientation of the chair in space
if tilted, the structural system loses its equilibrium
- loss of equilibrium
stability
structures may be in equilibrium but not stable
arrangement of parts critical
adding bracing will not make structure fall, such as internally bracing (high rise building )
and externally bracing (wide+low rise buildings like bridges)
what is a load?
load is a force that acts on a structure.
2 types of loads - primary - secondary
primary load
- primary load - dead load - self-weight of structure - fixed building elements like columns
- primary load - live load - occupancy (moving people) - environmental/ variable
Secondary load
-secondary load- thermal
-secondary load - settlement
(accounts for secondary load only once)
concentrated load vs distributed load
concentrated = example standing on a table distributed = example laying down on table
principle of transmissibility
all loads are finally transmitted and resisted by the ground
equilibrium
two types of equilibrium
- external = encompasses all loads and reactions of the structural system as a whole
- internal = encompasses all the forces within every member of the system
parabolic curves
a curve genrated by evenly distributed load along a horizontal axis.
examples a suspension bridge
catenary curve
a curve generated by evenly distributed loads (own weight) along the length of a curve.
funicular curves
a curve generated by point loads distributed at various points (not evenly) along a curve
examples Gaudi’s hanging structures
difference between tensions + compression
tension = force that pulls materials apart. force is exerted out compression = force that squeezes materials together. force is exerted down
resistance: BENDING
- lateral
- torsional
- vertical
modes of failure
- steel bottim of concrete structure avoids tensions and cracking
material behaviours
- stress
- strain
- elasticity - plasticity
- safety factors
stress + strain
Force - causes - stress
stress - puts material under - strain
strain - results in - deformation
3 zones of stress + strain
- elastic region - goes back to normal condition.
- plastic region - dent - deformed material
- failure region - brake material
Brittle vs ductile
Brittle = shorter deformation zone - concrete or glass ductile = long deformation zone - mild steel or metal
ductility
the ability to sustain large plastic deformations without failing. ex : gold, aluminum
brittleness
the ability sustain very little deformation before fracturing or failing
ex: glass, ceramics
yield strength
the point where a material under stress will not return to its original shape. no going back
