J1 - Building Science - LT #1 Flashcards
Explain how concrete can be a live load and then a dead load.
Concrete is cast - Live
After curing - Dead load
What is a Live load?
Variable, non-permanent load that acts on a building structure. Live Load may be static, repetitive, or dynamic. Human-caused or environmental.
What is a Static Load? (LIVE)
External forced is applied and held in a fixed position for a period of time.
EX: Static load caused by gravity is the weight of a piece of furniture. Due to being movable or replaced.
What is a repetitive load?
Repeating Load caused by gravity or the momentum of an object.
EX: Cars crossing a bridge place temporary gravitational load on bridge
What is dynamic load?
Load that can be changed over time
EX: Repetitive action of cars braking and accelerating on a bridge.
Wind creates what kind of load on a building?
Both static and dynamic live loads.
EX: Strong gusts of wind place dynamic loads on a building but a steady breeze puts a static live load.
Wind loads create what kind of pressure?
Differential loads across a building draw heated air out of it and rain water into it.
What kind of load do rain and snow create?
Static Live load.
EXL Rain has a greater effect when snow is on the roof, as the snow absorbs the weight and load on the roof.
Specified Snow Load Formula:
S (Cb x Ss) + Sr
Regardless of snow load, no roof may be designed to support less than:
1 kPa
Occupant live loads include:
Furnishings, equipment and people.
What is an example of a dynamic load?
Earthquake.
What is a dead load?
Caused by gravity acting on all the building materials.
Dead loads in a typ. wood framed house include:
Wood framing members, concrete foundation, windows & doors, interior and exterior finish materials and siding and all permanent fixtures.
Dead loads in a wood frame are treated as:
0.5 KPA (10 LB)
Four common stresses acting on a building are:
Compression
Tension
Torsion
Shear
What is compression stress?
Force acting to SQUASH
What is tension stress?
Tension - pulling force
EX Rope used to hoist is under stress
In a joint or beam, the top is under compression and the bottom is under:
Tension
Forces of tension and compression are greates at which part of the beam?
Closest to the edge.
What is a stress of torsion?
Torsion is the force caused when one or both ends of an object are twisted (Torqued).
EX: Extreme winds can result in torsion
How can a bulding reduce effects of torsion stress?
Symmetry
What is shear stress?
When loaded components try to slide. Pushing or pulling forces act in opposite directions on a solid component.
Can be horizontal, vertical or diagonal.
Vertical shear occurs where?
Vertical shear occurs where there are loads, such as those in a beam acting on a supporting member such as a column.
Building components that are under both horizontal and vertical shear stress experience:
Diagonal shear.
Gravity is the force that gives objects what?
Weight
Flat roof can be affected by wind uplift when the wind hits a large wall and has to:
Change directions upward
Hurricane ties connect:
Trusses to top plates, helping to anchor down the roof.
Soil that can be squeezed into a ball and retains shape is:
Cohesive soil
