Week 2 Flashcards
What loads are buildings subjected to?
- Dead loads
- Live loads
- Wind loads
- Earthquake loads
- Loads due to soil pressure
- Loads due to hydrostatic/hydrodynamic pressure
What is hydrostatic pressure?
The pressure exerted by a fluid at equilibrium at any point of time due to the force of gravity
What is hydrodynamic pressure?
The pressure a fluid exerts on an object due to the object’s motion through a fluid
What are the 3 axes of structural elements?
- Longitudinal axis
- Major Axis
- Minor Axis
How is the longitudinal axis viewed?
Parallel to length
What are the types of stresses in building elements?
- Axial stresses
- Bending stresses
- Shear stresses
- Torsional stresses
What is tensile stress?
Pulling apart from two points
What is compressive stress?
Pushing in from two points
What is shear stress?
Pulling apart from 2 points on different planes
What are the characteristics of ‘axial stresses’?
- Load along or in the transverse direction of the line (longitudinal axis)
- Axial loading can be compression or tension
What is the load-stress relationship equation?
Stress = Load / cross-sectional area
What are the characteristics of ‘bending stresses’?
- Transverse loading induces bending stresses
- Top part of beam is subjected to compression
- Bottom part of the beam is subjects to stretching (tensile stress)
What are the characteristics of ‘shear stresses’?
- Developed by transverse loading
- Tends to deform the beam along a plane by slippage
What must buildings adequately have?
- Sound performance
- Heat performance
- Daylight provisions
What are the two types of waves?
- Mechanical waves
- Electromagnetic waves
What are mechanical waves?
Requires a medium (solid, liquid, or gas) to propagate
e.g. Sound
What are electromagnetic waves?
Does not require a medium to propagate
e.g. light
What is the ‘crest’ in reference to wave behavior?
The maximum amount of positive movement from the equilibrium position
What is the ‘trough’ in reference to wave behavior?
The maximum amount of negative movement from the equilibrium position
What is the ‘wave length’ in reference to wave behavior?
the length between two adjacent crests or troughs (i.e. a cycle)
What is the ‘amplitude’ in reference to wave behavior?
The maximum amount of displacement from the equilibrium positions
What is the definition of ‘airborne sounds’?
Noises inside a building without physical impact between the building mass and sound source
e.g. voices
What is the definition of ‘impact sounds’?
Noises that are a result of physical impact on a building mass
e.g. footsetps, slamming doors
How is sound measured?
In dB
What is sound insulation?
Construction elements that: absorb, reflect, or diffuse soundwaves
e.g. walls and floors
What is sound reflection?
- Portion of soundwaves bounced off a construction element
- Reflection is suitable when the sound source is outside the building
- When the sound source is inside, reflection leads to echo effect
What is sound diffusion?
- A larger sound wave is broken into several smaller waves when hit with an irregular surface (e.g. carpet)
- Smaller waves have less energy thus travelling less distance
- Diffusion suitable for reduction of sound inside a building
What is sound absorption?
- Acoustic materials can be engineered to deaden the sound waves (energy)
- Acoustic materials can be engineered to achieve the optimum balance between density and porosity.
What is the ‘Sound Reduction Index (Rw)’?
- Measures the ability of a construction component to insulate airborne noise
- +1 Rw approximately equals -1 dB
- Sound proofing capacity is measured as Rw+Ctr
What is the best form of impact sound insulation?
- Discontinuous construction (reduces vibrations)
- Floor topping has a significant influence on the impact of sound resistance
What is heat balance?
The desired temperature in a building
What are the 3 heat transferring mechanisms?
- Conduction - Transmission of heat between molecules by direct contact
- Convection - Transmission of heat through fluids (liquids & gas)
- Radiation - Transmission of heat from one radiant energy source to another without the need of a medium
What is thermal comfort determined by?
- Thermal mass
- Thermal resistance
What is thermal mass?
The ability of a construction material to absorb and store thermal energy
What is the equation showing the relationship between thermal energy, mass, and temperature rise?
Q = m C ∆T
Q: thermal energy absorbed/released
C: Thermal mass or specific heat
∆T: Temperature difference due to energy absorption or release
What are thermal characteristics of heavy construction materials?
Have a beneficial thermal mass, but thermal resistance is low
What is the term for thermal resistance?
‘R-value’
(insulation has high R values)
What are the characteristics of daylight on buildings?
- Natural light is an advantage
- Unwanted heat gain from sunlight adversely influences thermal comfort
- Major light/heat gaining components (e.g. windows) can be oriented according to sun path
