Chapter 3 Flashcards
What is a Force?
A vector, it has a direction and a Magnitude.
MEASURED: Forces will be in the units of KIPS or POUNDS
What is a Moment?
The tendancy of a force to cause about a given point or axis.
MEASURED: Kip-Feet, Pound-In
What is a force couple?
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.
What is the difference between a moment and a resisting moment.
A resisting moment occurs at the support, while the moment occurs at the edge of the cantilever.
What is a Diaphragm
- 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
T/F, Shear walls CAN be considered a vertical diaphragm.
True.
Flexible Diaphragms
change shape when subjected to lateral loads; its tension chord bends outward and its compression chord bends inward
What is the function of a diaphragm?
To distribute loads to the vertical resisting elements in proportion to their tributary areas.
T/F, Flexible diaphragms ARE considered capable of transmitting torsion to the resisting elements?
False, they cannot transfer torsion loads.
What are some examples of a rigid diaphragms?
Structural concrete systems, concrete filled metal deck over structural steel framing, etc, are considered to be rigid diaphragms.
T/F, Rigid diaphragms ARE considered capable of transmitting torsion to the resisting elements?
True.
What are some examples of flexible diaphragms?
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.
With respect to the design of Columns, the effective length factor “K” is dependent on?
The support at each end of the column.
On a simply supported beam with a uniform load, where does the maximum bending stress occur?
At the mid-span at the extreme fibers
On a simply supported beam with a uniform load, where does the maximum shear stress occur?
The stress is greatest at the neutral axis and is equal along the length of the beam.
T/F Seismic forces ARE NOT applied through the center of mass?
False, Seismic forces “ARE” applied through the center of mass
Torsion is calculated by multiplying what two factors?
Is the difference in distance between the center of gravity and the center of rigidity multiplied by the torsional force.
T/F Torsion only occurs on a rigid diaphragm.
True
During a horizontal load, at what plane do the horizontal loads transfer into the diaphragm?
At the Ceiling/Floor Plane
http://acg.media.mit.edu/people/simong/statics/data/beamLoadingApp.html
shear and moment diagram
T/F When a shear diagram crosses 0, that is a point of maximum moment?
True
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?
The inflection point.
Where does an overturning moment occur
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.
How do you calculate the Factor of Safety?
Resistance x Demand (RM x OTM)
For wind design what is the factor of safety?
1.5 or 2/3 of the dead load
T/F Drag struts will only occur in flexible diaphragms.
False, Drag struts occur in both
T/F Chord Forces only occur in flexible diaphragms
True
What is the primary reason to prestress concrete?
Control the Stresses (Limit the tension stress)
What portion of the load do we prestress or camber a beam for?
A portion of the dead load only typically anywhere between 75%-90%
T/F Never prestress for a variable load (LIVE LOAD)
True
What is the Modulus of Elasticity for steel?
29,000,000 psi
What is the Modulus of Elasticity for concrete?
57,000 FC
What is the Modulus of Elasticity for CMU?
900 fm
What is the Modulus of Elasticity for clay masonry?
750 fm
What is the Modulus of Elasticity?
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.
Hooke’s Law
Delta=PL/AE
Where is Horizontal shear stress at its maximum?
At the neutral axis, and varies in a parabolic shape over the depth of the rectangular axis
T/F Horizontal and vertical shear stress are always equal? What is the long form formula for shear stress?
True, fv= (V Q) / (I b)
What is the formula for the property of a sold rectangular section?
I= (b d^3) / (12)
For a solid rectangular section (wood) what is the shear stress formula?
fv= (1.5 V) / A
For a simply supported beam with a uniform load where can a penetration occur.
Middle 1/3 of the span, and middle 1/3 of the depth.
