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