Deflection

Question 1

What roof top phenomena, which can lead to dangerous

deflections

Answer 1

Ponding

Question 2

if w is in PLF and L is in FT, what is the conversion factor when E is in PSI and I is in IN4?

Answer 2

1728 in3/ft3

Question 3

Cantilevered beams fixed end

Answer 3

Moment = max
Slope = 0
Deflection = 0

Question 4

Cantilever beam free end

Answer 4

Moment = 0
Slope = max
Deflection = max

Question 5

Where does max deflection occur in a all simple beams

Answer 5

At the point of zero slope

Question 6

Three factors that impact structural member stiffness

Answer 6

Material stiffness (E = elastic modulus)
Sectional stiffness (I = moment of inertia)
Beam length (L)

Question 7

Equation for deflection (delta symbol)

Answer 7

Delta = (PL^3)/(48E*I)

P=force
L=length
E=elastic modulus
I=moment of Inertia

Question 8

What is the largest roof deflection due to DL+LL recommended by the International Building Code?

Answer 8

L/120

Question 9

What is the most commonly used limit for floor live load deflections?

Answer 9

Should not exceed L/360

Question 10

The deflection limit of L/360 was originally determined based on the serviceability requirements of what material?

Answer 10

cracking of plaster ceilings. It was determined that plaster ceilings crack with a deflection larger than 1/360 of the span.

Question 11

Code limits on deflection in beams are primarily performed to anticipate which type of structural problems?

Answer 11

Serviceability - It refers to conditions other than the building strength that render the buildings unusable. Serviceability limit state design of structures includes factors such as durability, overall stability, fire resistance, deflection, cracking and excessive vibration.

Question 12

Mathematical sequence of diagrams by integration

Answer 12

Load diagram
Shear diagram
Moment diagram 
Slope diagram
Deflection diagram

Question 13

In a simply supported, symmetrically loaded beam, where does max slope occur

Answer 13

At the ends where the supports are (equal and opposite)

Question 14

What values need to be multiplied with the areas of the moment diagram in order to calculate the angle of the elastic curve (in radians)?

Answer 14

1/(EI)

The inverse of the elastic modulus multiplied by the moment of intertia

Question 15

Slope of beam is a measure of …

Answer 15

Angle in radians of the tangent to the elastic curve

Question 16

What is the slope of the elastic curve at a fixed end condition

Answer 16

Slope is zero

Question 17

For a symmetric, simple span beam using the diagram method, what observation about the slope diagram helps to find the point of maximum deflection?

Answer 17

Slope is always zero at center line

Question 18

Can the diagram method of analysis be used to determine the value of the deflection for a simply supported beam that is not symmetrically loaded?

Answer 18

Yes, although a solution requires some additional work because the point of zero slope cannot be assumed to be at the midspan of the beam.

Question 19

Of the parameter of deflection, which has the greatest effect when changed

Answer 19

Length of beam

Question 20

For simple span beams using the diagram method, what observations about the slope diagram can help in finding the point of maximum deflection?

Answer 20

The positive and negative areas of the diagram will be equal. The point between the left and right parts of diagram will be zero, and will be at the point of maximum deflection.

Question 21

When using superposition of equations to find the maximum deflection of an asymmetrically loaded beam, what must be observed regarding deflection location?

Answer 21

The location of the maximum deflection of each case is not the same as the combined case.

Question 22

Code limits on deflection of beam vary according to what

Answer 22

Application (floor, roof, Dead load, live load)