J-1 Building Sciences

Question 1

What is a Live Load?

Answer 1

Live loads are variable, non-permanent loads that act on a building structure. May be be described as static, repetitive or dynamic. Live loads can be human-caused or they can be environmental.

Question 2

What is a static load?

Answer 2

A static load is an external force that’s applied and held in a fixed position for a specific amount of time.

EX: A static load caused by gravity is the weight of a piece of furniture. This is classified as live load because furniture can be moved or replaced.

Question 3

What is a repetitive load?

Answer 3

A repetitive load is one that repeats itself. A repetitive load may be caused by gravity or the momentum of an object.

EX: Cars crossing a bridge place temporary repetitive gravitational loads on the bridge.

Question 4

What is a dynamic load?

Answer 4

A dynamic load is a load that can cause change over time. An example of a dynamic load is the repetitive action of cars braking and accelerating in a bridge.

Question 5

What is the formula for calculating Snow Load?

Answer 5

S = (Cb x Ss) + Sr

S = specified snow load on the roof
Cb = Basic snow load roof factor, which is .45 where entire width of the roof does not exceed 4.3 and .55 for all other roofs
Ss = 1 in 50 year ground snow load in kPa for the building geographical location
Sr = 1 in 50 year rain load in kPa for the building geographical location

Question 6

Roofs up to 4.3 m (14’ use) use how much of the ground snow load in the calculation?

Answer 6

45% (hence .45)

Question 7

Roofs over 4.3 meters use how much of the snow load in calculation?

Answer 7

55% hence (.55 for beyond 4.3 m in code book)

Question 8

What are occupant live loads?

Answer 8

Considered to be dynamic, because they change as people move about. They include furnishings, equipment and people. Occupancies are usually designed to support specific loads.

EX: Res. occupancies are designed to support 1.9 kPA which is approx. 40 lb per foot.

Where as dance floors are designed to support 4.8 kPA or about 100 lb. per foot.

Question 9

Earthquake is what kind of load?

Answer 9

Earthquakes are a dynamic load, the direction can be either seismic loading (horizontal) but vertical movements are not uncommon.

The shaking of structures can cause huge loads throughout the building frame and cause serious damage.

Question 10

What is a dead load?

Answer 10

Dead loads are caused by gravity on all building materials.

Dead loads are constant, but may shift, move or change should a structure settle or be affected by an earthquake.

In a typical wood-framed house: includes wood framing members, concrete foundation, windows and doors, interior and exterior finish materials etc.

Question 11

What is the dead-load for wood frame construction treated as?

Answer 11

The dead load for wood-frame construction is treated as 0.5 kPA (10 lb per foot).

Question 12

What are the 4 most common stresses acting on a building structure?

Answer 12

1) Compression 2) Tension 3) Torsion 4) Shear

Question 13

Live and dead loads stress a building, left unchecked what will happen?

Answer 13

The building will deform

Question 14

What is compression force?

Answer 14

Force acting to squash an object.

EX: Columns under compression from the loads above. Building components designed to resist compression must be installed plumb.

EX: Point loads (extreme compressive stress)

Uneven loading will induce other stresses that the component may not have been designed to resist.

Question 15

What is the force of tension?

Answer 15

Tension is the pulling force that acts to lengthen an object. For example, a rope used to hoist an object is under tension.

EX: A rope used to hoist an object is under tension. The rope stretches and becomes thinner, if too much tension is applied - the rope may fail.

Question 16

What is compression and tension in horizontal spanning members?

Answer 16

Compression and tension can exist within the same structural member at the same time.

EX: A beam - the top is under compression while the bottom is under tension. These forces are the greatest closest to the edge of the beam.

Question 17

What is torsion?

Answer 17

Torsion is the force caused when one or both ends of an object are twisted (torqued) in opposing directions.

EX: Extreme winds can result in torsion stresses being applied to a building, as they act against wall faces that are structurally anchored to the building’s foundation. Dramatic would be an earthquake.

Question 18

How can you balance torsion?

Answer 18

Symmetry (balance). A balance between stiff and ductile building also helps ease torsion stresses.

Question 19

What is shear stress?

Answer 19

Shear stresses occur when there are pushing or pulling forces acting in opposing directions on a solid component (multiple components in contact with one another).

This direction of shear can be horizontal, vertical, or diagonal.

Question 20

What is horizontal shear?

Answer 20

Horizontal shear occurs when the pushing or pulling forces are acting on a horizontal plane. This is often the rest of deflection and vertical loading.

Question 21

What is vertical shear?

Answer 21

Vertical shear occurs where there are loads, such as in a beam acting on a supporting member such as a column.

Stress on the beam at the edge of the column is a vertical shear.

Question 22

What is diagonal shearing?

Answer 22

Building components that are under both horizontal and vertical shear stresses experience diagonal shear. Overloaded beam under diagonal shear will fail along a diagonal line of approx. 45 degrees.