Structure

Question 1

2 Design Methodologies: ASD vs LRFD

Answer 1

Allowable Strength Design (ASD): apply service loads (D+L). Calculated stress must be less than allowable stress.
Load and Resistance Factor (LRFD): apply factor loads. These are DESIGN strengths. Apply resistance factor, phi, in most cases

Question 2

Typical Factored Load Equation

Answer 2

Mu = 1.2Md + 1.6Ml (also true for loads)

Question 3

How many reactions from roller, pin, and fixed ends?

Answer 3

Rolled: 1 vertical reaction
Pin: 1 horizontal and 1 vertical reaction
Fixed: 1 horizontal and 1 vertical reaction and 1 moment

Question 4

Where on a truss is in compression and where in tension?

Answer 4

Top of a truss is in compression, whereas bottom of truss is in tension

Question 5

Shear Diagrams - when constant, when linear, etc

Answer 5

Shear is constant under unloaded portions. Point load - shear reacts at constant rate. Uniform load - shear is linear
Slope of the shear diagram = load at that point

Question 6

Moment Diagrams

Answer 6

Clockwise moments are +
In positive moment (smiley face) - top is in compression
For constant shear - moment is linear
For linear shear - moment is parabolic
Change in moment = area under shear diagram
0 shear = max moment

Question 7

Is tension positive or negative in Truss Analysis?

Answer 7

Tension is POSITIVE

Question 8

4 rules to identify Zero Force truss members

Answer 8

1. If there are ONLY two non-collinear members at joint with no external load
2. If there are only 3 members at joint and 2 are collinear and no external force, 3rd is 0
   3: Once zero force is identified - you can assume it doesn’t exist and “delete it”
   4: if there are only 1 horizontal member connected to roller with NO DIAGONALS, horizontal must be zero-force

Question 9

Moment of Inertia Definition

Answer 9

Moment of Inertia is a measure of section resistance to bending and deflection –> bigger inertia = more resistance

Question 10

Bending Stress in Beams - where is max stress?

Answer 10

Center of beam has 0 bending stress. Max stress is furthest from center of beam

Question 11

E of steel?

Answer 11

E of steel = 29,000 kips

Question 12

Beam Design - ASD or LRFD?

Answer 12

Beam design uses ONLY LRFD!

Question 13

Ultimate strain for concrete? (once this is hit the concrete has lost all strength)

Answer 13

ultimate strain = 0.003

Question 14

What is the neutral axis in a beam?

Answer 14

Where tension and compression forces are equal and opposite

Question 15

What is local buckling?

Answer 15

When member yields before you reach plastic moment

Question 16

What is design of steel beams controlled by?

Answer 16

Deflections (Total Deflection limited by L / 240 in

Controlled by bending moment requirements (deflection) - shear checked second as typically not a problem with steel

Question 17

One-way vs Two-way Slab

Answer 17

One Way Slab –> L is greater than 2B
where B = 12 in

Question 18

Net allowable pressure = ?

Answer 18

Gross - weight of soil - weight of column on footing
Net = Total load / Area of footing

Question 19

Area of footing designed using Service or factored?
Thickness/reinforcement design?

Answer 19

Area of footing designed using Service loads
Thickness/reinforcement designed using Factored loads

Question 20

What is a determinate structure?

Answer 20

Implies there are enough equations of equilibrium to determine support reactions (Fy, Fx, and Moment)

Question 21

Truss Analysis - Equation to Determine if Structure is determinate, unstable, or indeterminate

Answer 21

m + r = 2j

where m = # members
r = # reaction components
J = # joints

if less than 2j –> unstable
if more than 2j –> indeterminate

*Note - if truss bay is not triangular –> unstable

Question 22

Wide Flanged Members - Stress Distribution

Answer 22

0 shear stress in flange. Web has all shear stress

Max shear stress occurs at mid depth

avg shear stress = Total Shear stress/ (web thickness * web length)

Question 23

How to reduce buckling potential?

Answer 23

Increase width of beam
Lateral braces

Question 24

What is stable equilibrium

Answer 24

Ability of structure to return to initial position

Question 25

How to calculate Moment of inertia (T-beam)

Answer 25

sum of Critical moment of inertia + sum of A*d^2

where d is the distance centroid of total structure to centroid of sub-area