Lesson 2 Advantages and Disadvantages of Statically Indeterminate

Lesson 2 Advantages and Disadvantages of Statically Indeterminate Structures

Advantages/Disadvantages

Geometric changes cause indirect stresses

Geometric changes cause indirect stresses Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error If this is accidentally Fabricated too long… Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error If this is accidentally Fabricated too long… All joints just move to New positions Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error If this is accidentally Fabricated too long… Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error If this is accidentally Fabricated too long… Then it must be Compressed into place Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses Which puts these in tension 1. Fabrication Error If this is accidentally Fabricated too long… Then it must be Compressed into place Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error Which puts forces on all members If this is accidentally Fabricated too long… Then it must be Compressed into place Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 1. Fabrication Error Which puts forces on all members No Stresses. Members go together. Statically Determinate Members must be forced to fit. Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 2. Temperature Changes SUN Heated Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 2. Temperature Changes SUN Heated No Stresses. Positions just change Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses Joints restricted by truss-action 2. Temperature Changes SUN Heated No Stresses. Positions just change Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 2. Temperature Changes SUN Heated No Stresses. Positions just change Statically Determinate Heated Thermal causes stresses Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 2. Temperature Changes SUN If Expansion Joint does not Allow expansion, this duct Is statically indeterminate SUN Heated No Stresses. Positions just change Statically Determinate Heated Thermal causes stresses Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 2. Temperature Changes SUN If Expansion Joint does not Allow expansion, this duct Is statically indeterminate SUN Heated No Stresses. Positions just change Statically Determinate Heated 800 F high-temperature gas causes it to Thermal causes stresses Crumple like a beer can Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses Simple Beam Pier Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 3. Foundation Settlement Simple Beam Pier Any Settlement: Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 3. Foundation Settlement Simple Beam Pier Any Settlement: No Curvature. No moment Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 3. Foundation Settlement Simple Beam Pier Any Settlement: No Curvature. No moment Statically Determinate Statically Indeterminate

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 3. Foundation Settlement Simple Beam Continuous Beam Statically Determinate Statically Indeterminate Pier Pier Any Settlement: No Curvature. No moment

Statically Indeterminate Disadvantages Geometric changes cause indirect stresses 3. Foundation Settlement Simple Beam Continuous Beam Any Settlement: Curvature! Moment! Statically Indeterminate Pier Statically Determinate Pier Any Settlement: No Curvature. No moment

Statically Indeterminate Pier Pier Statically Determinate

Statically Indeterminate Advantages M Statically Determinate Statically Indeterminate Pier Pier M

Statically Indeterminate Advantages M M Statically Determinate Statically Indeterminate Pier Pier w. L 2/8

Statically Indeterminate Advantages 1. Lower Stresses Pier Pier w. L 2/8 M w. L 2/21. 4 M M Statically Determinate M Statically Indeterminate

Statically Indeterminate Advantages 2. Greater Stiffness Statically Determinate Statically Indeterminate Pier Pier D=

Statically Indeterminate Advantages 2. Greater Stiffness Statically Determinate Statically Indeterminate Pier Pier D = 5 w. L 4/384 EI

Statically Indeterminate Advantages 2. Greater Stiffness Statically Determinate Statically Indeterminate Pier Pier D = 5 w. L 4/384 EI

Statically Indeterminate Advantages 2. Greater Stiffness D = 2. 1 w. L 4/384 EI Statically Indeterminate Pier Statically Determinate Pier D= 5 w. L 4/384 EI

Statically Indeterminate Advantages 2. Greater Stiffness Statically Indeterminate Pier Pier Statically Determinate DOIs = ? ?

Statically Indeterminate Advantages 2. Greater Stiffness Statically Indeterminate DOIs = 1 Pier Pier Statically Determinate DOIs = 0

Statically Indeterminate Advantages Pier A catastrophic event eliminates the middle pier Statically Determinate DOIs = 0 Statically Indeterminate DOIs = 1

Statically Indeterminate Advantages 3. Greater Robustness – May survive redundant loss of massive overload Pier Will NOT Survive (zero redundancy) MAY Survive (if the beam can take a Substantial increase in moment) A catastrophic event eliminates the middle pier Statically Determinate DOIs = 0 Statically Indeterminate DOIs = 1