Load Path Concepts
Transcript of Load Path Concepts
Class 2Continuous Load Path Concepts
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Load Paths Loads must go to “ground” Vertical loads
Gravity Uplift
Lateral loads Wind Earthquake Flood
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Load Paths Bridge loads
Headers Beams Girders
Interaction with the ground Shallow – spread, slab, stem wall Deep – piles, caissons, friction, bearing Possible failures – slope failure, liquefaction,
erosion, excessive moisture
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Load PathsVertical
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Deck collapse – gravity failure
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Foundation gravity failure
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Uplift failure
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Uplift column failure
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Flood
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Lateral displacement
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Earthquake
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Wind
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Vertical and Lateral paths OK
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Lateral failure from wind
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Lateral wind failure
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Slope failure
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Masonry piers
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Beams – carrying loads
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Headers:
bridging loads
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WTC-7 (Bridging loads failure) 47 story building
housed city’s OEM some missile impacts burned uncontrolled
for 8 hours 7 story electric
substation diesel fuel in building
in several tanks
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WTC 7 - 7th Floor Plan
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WTC 7
Penthouses start to collapse
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WTC 7
Interior collapse continues - note the “kink”
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Load Path Concepts
Materials chosen with sufficient strength Connections made with sufficient size,
strength, and number Any weak link could be a failure point Load path requires appropriate soil
bearing capacity Soil must be able to maintain bearing
capacity
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Vertical gravity loads
Creates compression in members Creates shear in connections What materials and connections perform
well in compression?
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Vertical gravity loads
Masonry Concrete Steel Wood (of proper size) Reinforcing steel for masonry and
concrete Bolts
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Vertical gravity load
Compression failures are most likely…? Buckling
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Vertical uplift loads
Creates tension in members Creates shear or withdrawal in
connections What materials and connections perform
well in tension?
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Vertical uplift loads
Steel Wood Bolts or welding for steel Bolts for wood
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Lateral loads
Creates compression in wall panels Creates bending in single members Creates shear at panel edges Creates compression in struts between
panels or members
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Homework 1 – Due 9/12/07
Find and mark the load paths on the 2 attached sketches
Sketch headers, girders or beams as bridging loads
Take the loads into the foundation which is a pile system
Name: ____________________________
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Pilelayout
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References
Masonry Structures – text by Drysdale Design of Wood Structures – text by
Breyer ASCE 7 ACI 530 NDS Class web page