Ch. 3 Structural Design Features of Buildings

Question 1

The force of GRAVITY …

Answer 1

… is the most common load imposed on a structure via the weight of the structure’s components, contents, and any occupancy activity

Question 2

Vibration

Answer 2

Shaking motion; sources include:

• Natural: Wind, seismic
• Building related: Ventilation system motors
• External: Vehicular traffic, trains

Question 3

Stresses

Answer 3

Tension: Pulls materials apart; tensile strength
Compression: Squeezes materials together; compressive strength
Shear: Slides one plane of a material past an adjacent plane

*Concrete has high Compressive strength but low Tensile strength

Question 4

External forces …

Answer 4

… can be visually identified and evaluated; interior forces must be calculated

Question 5

Unique stresses are caused by ..

Answer 5

… external load alignments including:

• Axial load
• Eccentric load
• Torsional load

Question 6

Load Types

Answer 6

Dead load - fixed in location and quantifiable

Live load - not fixed or permanent; actual weight and distribution of live loads are often not precisely quantifiable

Static load - steady, applied gradually

Dynamic load - involve motion and are capable of delivering energy greatly in excess of weight of the object involved such as:

• Wind
• Moving Vehicles
• Earthquakes
• Vibration
• Falling objects
• Emergency or maintenance work

Question 7

Water at a depth of 3 inches …

Answer 7

… adds a static load of 21 lbs per sq ft

Question 8

Effects of Wind

Answer 8

Direct Pressure - Straight line winds apply force to a surface
Drag - Wind flowing around the object may catch (drag) along a building’s surface
Negative Pressure - Wind may produce a suction effect on the downwind side of the building resulting in outward pressure
Rocking - Wind may cause the building to sway in a back and forth motion
Vibration - Wind passing over a surface, such as a roof, may shake the surface
Clean off - Wind may dislodge or move objects from a building’s surface

Question 9

Directional Movement

Answer 9

Lateral - lateral loads that create horizontal motion are the most significant force generated by an earthquake

Torsional - torsional loads are applied to a structural member that is twisted by seismic motion

Resonant - seismic waves affect some buildings differently than others due to the resonance of the earthquake and each building’s features

Question 10

Structural Accommodations

Answer 10

• Expansion joints
• Damping mechanisms
• Base isolation

Question 11

Active Soil Pressure

Answer 11

• Pressure exerted by the soil against the foundation

Question 12

Passive Soil Pressure

Answer 12

• Force of the foundation against the soil

Question 13

Soil Liquéfaction

Answer 13

• Occurs when sandy soil near water sources is looser and saturated w/water, and entrapped water prevents the sand particles from moving closer together, reducing the ability of the soil to support a structure

Question 14

I - Beams

Answer 14

The top flange of the beam carries compressive stresses and the bottom flange of the beam carries tensile stresses. The center horizontal line of the web is known as the neutral axis because the tension and compression stresses are zero, but the neutral axis is the maximum point of shear stress

Question 15

Columns

Answer 15

Tall, thin columns fail by buckling; short, squat columns fail by crushing