1. Final Project - Structural Flashcards
What is the internal resistance to an external force?
Stress. (Tension, Compression, Shear, Torsion, Bending, Combined Stresses)
Stress f = total force P / total area A
What are the three basic types of stress?
Tension, compression, and shear
What is tension?
Tension is stress in which the particles of the member tend to pull a part under load.
What is compression?
Compression is stress in which the particles of the member are pushed together and the member tends to shorten.
What is the deformation of a material caused by external forces?
Strain (e)
strain (e) = total strain e / original length L
What is shear?
Shear is stress in which the particles of a member slide past one another.
What is Hooke’s law?
As a force is applied to a material, the deformation (strain) is directly proportional to the stress, up to a certain point.
Ultimate Strength
The failing point of a given material.
Yield Point
On a stress-strain graph, the point at which the material begins to deform with minimal increase in load (stress).
Elastic Limit
On a stress-strain graph, the point at which the material will experience deformation faster. (Prior to to this point stress and strain are directly proportional.)
Coefficient of Expansion
Thermal Stress
plastic, acrylic = 0.0000450
aluminum = 0.0000128 in/in-F
bronze = 0.0000101
structural steel = 0.0000065
concrete = 0.0000055
glass = 0.0000051
marble = 0.0000045
brick = 0.0000034
Question: What is the applied force called in the following diagram?
→ ▯ ←
A) Shear
B) Compression
C) Torsion
D) Traction
B) Compression
Newton’s 3rd law
For every force acting on a body (building) there is an equal force of opposite magnitude.
List & define the 3 types of forces which may impact a structural body.
1 - COLLINEAR = along the same line of action *sum of vectors = magnitude along same line of action
2 - CONCURRENT = vectors that intersect at one point *sum of vectors with parallelogram polygon method
3 - NON-CONCURRENT = moment or rotation forces *sum of vectors = moment arm = F X d
Shear & moment forces are best resisted with which construction types?
- RIGID CONNECTIONS (Least efficient, only good for small buildings)
- SHEAR PLANES
- BRACING
2 types of loads
Static & dynamic
2 types of static loads
Dead & Live
4 types of live loads
1 - Occupant & moveable furniture / equipment
2 - Snow
3 - Rain
4 - Impact (kinetic loads of short duration - cosidered static by Code *amplify load to compensate for its dynamic nature)
2 Common types of dynamic loads
Wind & seismic
- Name 3 criteria governing the choice and use of a construction material.
- How should these criteria be for a material to be the most advantageous?
- Resistance
- Elasticity
- Rigidity
- The most beneficial materials of construction provide optimal elasticity and rigidity.
Elasticity
- Ability of a material to deform under stress - bending, elongation or compression - and to return to its original shape when the stress is removed.
- Any material has a yield point beyond which it breaks or permanently deforms.
Explain: ductile material vs brittle material
Ductile Material: Undergoes plastic deformation before breaking.
Brittle or fragile material: weak elastic limit and, without noticeable visible deformation, breaks under a load.
- Less resistant than ductile materials, brittle materials are not very suitable for the construction of buildings.
Rigidity
Why is it important?
Measurement of the compressive or tensile force that must be exerted on a material for it to reach its elastic limit.
The stiffness / rigidity of a material and the stiffness of its cross-section are very important when it comes to the relationship between span and deflection under load.
The dimensional stability of a material determines what?
The degree of dimensional stability of a material subjected to variations in temperature and humidity determines how it will be shaped and joined to other materials.
3 types of structural systems & materials typically used for each
1 - LINEAR - columns & beams (steel/timber/concrete beams)
2 - PLANAR - walls & slabs (light wood/steel framing/masonry/concrete walls & slabs)
3 - COMPOSITE - columns/walls & beams/slabs
3 main types of shear strength in high rise construction
1 - CONVENTIONAL - shear walls/bracing & or rigid frames
2 - CORE - vertical circulation key to lateral strength
3 - TUBE - lateral bracing along perimeter
Best construction type for tall buildings in seismic zones
STEEL = DUCTILE & LIGHT
NOT CONCRETE = HEAVY & BRITTLE
2 types of dampening
1 - TUNED MASS DAMPER - heavy mass on rollers towards the top of a tall building
2 - BASE ISOLATION - isolate the base from the ground so building can ‘float’ - prevents resonance
Effective structural building materials comprise of
- Stiffness w Elasticity
- Resist Dimensional Instability due to Humidity & Temp.
Qualities of wood as a structural material
- small • renewable • flexible
- light • exposed timbed
* GOOD IN COMPRESSION & TENSION
Qualities of concrete as a structural material
- Freedom of form • Naturally fire protected
- Exposed structure • Inexpensive
* GOOD IN COMPRESSION - MUST BE PAIRED WITH STEEL REINFORCING FOR TENSION
Qualities of steel as a structural material
- Repetitious modular • Long spans
- Light • Stiff & elastic
Describe the typical assembly for a concrete slab
TOP
- 100min slab thickness
- welded wire fabric reinforcement midway
- controls thermal stress: shrinking /cracking
- grid of bars needed for heavy floor loads
- 6 mil poly
- 50mm sand
- soak up water during curing
- 100mm min base course of gravel/crushed stone
- stable uniformly dense soil
- prevents capillary rise of groundwater
What are the 3 main concrete joints?
-
Isolation (aka expansion)
- allows MVMT btwn concrete slab + adj. columns walls
-
Construction (also serve as control/isolation)
- allows a place for construction to stop and start again @ later time
- keyed or doweled
-
Control
- creates lines of weakness so cracking from tensile stress occurs along predetermined lines
Describe the typical spacing of control joints, and 3 common types.
typ. spaced 4500-6100(15’-20’) or where required:
- irregular slab shape
- openings
- Sawn Joint
- Premolded or metal strip inserted into concrete
- Keyed Joint
- prevent bond by applying metal or plastic joint material or applying curing agent to one side
Modulus of Elasticity
A stress to strain ratio of a given material. €
e = PL/AE
Total strain (deformation) of a material under a given load.
A = total area P = total force L = original length e = total strain
Moment
The tendency of a force to cause rotation about a point.
