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The prevention ofdisproportionate collapse using

catenary action

Mike Byfield BEng, PhD, CEng, MICE, MIStructEand

Sakthivel Paramasivam BEng, MSc

School of Civil Engineering and the Environment

University of Southampton, United Kingdom

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1983 US Marine Corps HQ, Lebanon - 241 dead + 60 wounded

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1995 Federal Murrah Building

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Catenary

Action

Steel

columns

Bomb

Damage

Steel

columns

Catenary

Action

Bomb

Damage

Catenary ActionRedistribution of perimeter columnloads through hat truss in WTC1

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Accidental limit state load = 1.05 gk + 0.33 qkUK approachDAF = 1Pinned jointsFull reliance oncatenary actionPinned Joint

Tying Force Method

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Design tying load Catenary loadRupture

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Notes:

All columns 356 x 406 x 235 UC

All main beams 533 x 210 x 82 UBAll secondary beam 457 x 191 x 67 UB

Steel grade S355

Concrete grade C35

Imposed load 5 kN/m2

Partition load 1 kN/m2

3 m 3 m 3 m

533 x 210 x 82 UB

457x191x67UB

Support to column removed by brisance

3 m 3 m 3 m

12m

0.5 m

356 x 406 x 235 UC

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

533 x 210 x 82 UB

3 m 3 m 3 m

533 x 210 x 82 UB

457x191x67UB

Support to column removed by brisance

3 m 3 m 3 m

12m

0.5 m

356 x 406 x 235 UC

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

457x191x67UB

533 x 210 x 82 UB

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Design rotation

capacity = 4o

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The Best Guess Scenario, FoS = 0.12

Full tensile strength of the slab included

DAF = 1.5

202 kN

6.36 kN/m

A BC

202 kN 154.2 kN 202 kN 202 kN

Internal Hinge

4o

4569 kN

0.124569

528 ==FoS

202 kN

6.36 kN/m

A BC

202 kN 154.2 kN 202 kN 202 kN

Internal Hinge

4o

4569 kN

202 kN

6.36 kN/m

A BC

202 kN 154.2 kN 202 kN 202 kN

Internal Hinge

4o

4569 kN

0.124569

528 ==FoS

Accidental limit state load = 1.05 gk + 0.33 qk

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The Best Case Scenario, FoS = 0.19

Full tensile strength of the slab included

DAF = 1.0

The Worst Case Scenario, FoS = 0.08

Tensile strength of the slab ignored

DAF = 2.0 in accordance with US practice

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202 kN

6.36 kN/m

A B

C

202 kN 140 kN 202 kN 202 kN

Internal Hinge

24.4o

528 kN

202 kN

6.36 kN/m

A B

C

202 kN 140 kN 202 kN 202 kN

Internal Hinge

24.4o

528 kN

DLF=1.5

Slab strength included

What if we have unlimited ductility in the connections?

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Joint A Joint C

A

C

24o 3.84 m

DLF=1.5Slab strength included

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(b) Joint A (c) Joint C

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Unsupported columns

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Unsupported columns

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1995 Federal Murrah Building

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Typical Canary

Wharf Tower

Flexible cladding

No stiff internalpartitions

No columns betweenservice cores andperimeter

Number of columnsminimised by use of

transfer beams Low stiffness slab Low ductility Pinned

connections

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Rupture

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Rigid Joint

Partial strength Semi-rigid Joint

Beam remains elastic

Plastic Hinge

Available rotation capacity for industry standard semi-rigid composite connections limited to:1.80o for S355 beams1.43o for S275 beams

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203 x 86 UC

End plate (Detail 2)

75

55

20mm stiffener

533 x 210 x 82 UB

8

610

100

4T16 rebars

Detail 2

60 8

5

90

90

20090

300

6 No. holes 22

for M20 bolts

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ConclusionsConclusionsConclusions Tying capacity of industry standard connections is

generally determined in the absence of beamrotations.

Connections can develop a prying action that leadsto rapid failure.

Tying method will not prevent progressive collapsewhen used with low ductility connections

Semi-rigid (partial strength) connections haveinsufficient ductility to survive the demands ofcatenary action