Chapter 3

Question 1

What is a Force?

Answer 1

A vector, it has a direction and a Magnitude.

MEASURED: Forces will be in the units of KIPS or POUNDS

Question 2

What is a Moment?

Answer 2

The tendancy of a force to cause about a given point or axis.

MEASURED: Kip-Feet, Pound-In

Question 3

What is a force couple?

Answer 3

Two equal forces of opposite magnitude act in an opposite direction and are seperated by some distance.

M + (P) (e)
P= is the eccentricity or distance. In this scenario the engineer is communicating that a moment is being induced into the system and has to be dealt with.

Question 4

What is the difference between a moment and a resisting moment.

Answer 4

A resisting moment occurs at the support, while the moment occurs at the edge of the cantilever.

Question 5

What is a Diaphragm

Answer 5

1. Roof, Floor or other membrane or bracing system acting to transfer the lateral forces to the vertical resisting elements.

• • Typically a planar horizontal or nearly horizontal element that resists shear forces in its own plane and transmits the forces to the vertical lateral load resisting elements.
• Can be Flexible or Rigid
• Shear walls are sometimes referred to as vertical diapragms

Question 6

T/F, Shear walls CAN be considered a vertical diaphragm.

Answer 6

True.

Question 7

Flexible Diaphragms

Answer 7

change shape when subjected to lateral loads; its tension chord bends outward and its compression chord bends inward

Question 8

What is the function of a diaphragm?

Answer 8

To distribute loads to the vertical resisting elements in proportion to their tributary areas.

Question 9

T/F, Flexible diaphragms ARE considered capable of transmitting torsion to the resisting elements?

Answer 9

False, they cannot transfer torsion loads.

Question 10

What are some examples of a rigid diaphragms?

Answer 10

Structural concrete systems, concrete filled metal deck over structural steel framing, etc, are considered to be rigid diaphragms.

Question 11

T/F, Rigid diaphragms ARE considered capable of transmitting torsion to the resisting elements?

Answer 11

True.

Question 12

What are some examples of flexible diaphragms?

Answer 12

Wood structural panels (plywood, osb, etc.) light gauge metal deck or light gauge metal deck with insulating fill such as sonolite are considered to be flexible diaphragms.

Question 13

With respect to the design of Columns, the effective length factor “K” is dependent on?

Answer 13

The support at each end of the column.

Question 14

On a simply supported beam with a uniform load, where does the maximum bending stress occur?

Answer 14

At the mid-span at the extreme fibers

Question 15

On a simply supported beam with a uniform load, where does the maximum shear stress occur?

Answer 15

The stress is greatest at the neutral axis and is equal along the length of the beam.

Question 16

T/F Seismic forces ARE NOT applied through the center of mass?

Answer 16

False, Seismic forces “ARE” applied through the center of mass

Question 17

Torsion is calculated by multiplying what two factors?

Answer 17

Is the difference in distance between the center of gravity and the center of rigidity multiplied by the torsional force.

Question 18

T/F Torsion only occurs on a rigid diaphragm.

Answer 18

True

Question 19

During a horizontal load, at what plane do the horizontal loads transfer into the diaphragm?

Answer 19

At the Ceiling/Floor Plane

Question 20

http://acg.media.mit.edu/people/simong/statics/data/beamLoadingApp.html

Answer 20

shear and moment diagram

Question 21

T/F When a shear diagram crosses 0, that is a point of maximum moment?

Answer 21

True

Question 22

There is a simply supported beam with a uniform load, on a moment diagram what is the point called where the moment diagram crosses 0?

Answer 22

The inflection point.

Question 23

Where does an overturning moment occur

Answer 23

for the whole building, the overturning moment occurs at the ground level.
For each level, the overturning moment occurs at the floor level of the story or stories.

Question 24

How do you calculate the Factor of Safety?

Answer 24

Resistance x Demand (RM x OTM)

Question 25

For wind design what is the factor of safety?

Answer 25

1.5 or 2/3 of the dead load

Question 26

T/F Drag struts will only occur in flexible diaphragms.

Answer 26

False, Drag struts occur in both

Question 27

T/F Chord Forces only occur in flexible diaphragms

Answer 27

True

Question 28

What is the primary reason to prestress concrete?

Answer 28

Control the Stresses (Limit the tension stress)

Question 29

What portion of the load do we prestress or camber a beam for?

Answer 29

A portion of the dead load only typically anywhere between 75%-90%

Question 30

T/F Never prestress for a variable load (LIVE LOAD)

Answer 30

True

Question 31

What is the Modulus of Elasticity for steel?

Answer 31

29,000,000 psi

Question 32

What is the Modulus of Elasticity for concrete?

Answer 32

57,000 FC

Question 33

What is the Modulus of Elasticity for CMU?

Answer 33

900 fm

Question 34

What is the Modulus of Elasticity for clay masonry?

Answer 34

750 fm

Question 35

What is the Modulus of Elasticity?

Answer 35

The ratio of stress to strain characteristic of each material, in ksi or psi.
The modulus of elasticity is a measure of materials resistance to deformation.

Question 36

Hooke’s Law

Answer 36

Delta=PL/AE

Question 37

Where is Horizontal shear stress at its maximum?

Answer 37

At the neutral axis, and varies in a parabolic shape over the depth of the rectangular axis

Question 38

T/F Horizontal and vertical shear stress are always equal? What is the long form formula for shear stress?

Answer 38

True, fv= (V Q) / (I b)

Question 39

What is the formula for the property of a sold rectangular section?

Answer 39

I= (b d^3) / (12)

Question 40

For a solid rectangular section (wood) what is the shear stress formula?

Answer 40

fv= (1.5 V) / A

Question 41

For a simply supported beam with a uniform load where can a penetration occur.

Answer 41

Middle 1/3 of the span, and middle 1/3 of the depth.