collapse of world trade centre

8/14/2019 COLLAPSE OF WORLD TRADE CENTRE

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K.L.S SAHABANDUSPECIALIST ENGINEER (STRUCTURAL DESIGNS)

CENTRAL ENGINEERING CONSULTANCY BUREAU

THE WORLD TRADE

CENTER DISASTER


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At 8:55 a.m

first plane crashes into the North Tower


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At 9:03a.m

Second plane

crashes into the

South Tower.


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At 9:50 a.m

South Tower begins

to collapse.

`


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At 10:29 a.m

North Tower begins to collapse


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Remains of the facade of Two World

Trade Centre is all that stands after

Tuesday's terrorist attack

Wednesday, Sept. 12, 2001 in New

York. (AP Photo/Nick Finely)


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Fire-fighters work in the rubble of

the World Trade Centre towers in

New York, Wednesday, Sept. 12,2001. The towers collapsed

Tuesday after being struck by two

commercial aircraft's in a terrorist

attack. (AP Photo/Virgil Case)


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TYPICAL ARRANGEMENT OF THE

TOWER


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TYPICL FLOOR ARRANGEMENT


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FLOOR / BEAM / COLUMN

ARRANGEMENT


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TYPICAL DETAILS OF COLUMN

FOUNDATIONS


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BASEMENT TYPICAL DETAILS

WORLD TRADE CENTER AND


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WORLD TRADE CENTER AND

SURROUNDING BUILDINGSDAMAGE STATUS


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STRUCTURAL ASSESSMENT

Structural Assessment done on 406 Buildings by 24

teams with total 170 engineers

No structural damages - 382 Nos.

Superficial and non-structural - 19 Nos.

Major structural damages - 5 Nos.


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AS BUILT DRAWINGS

WHETHER DEBRIS WOULD SUPPORT CRANES,

WHETHER HEAVILY DAMAGED BUILDING WOULD STAY

STANDING.

WHETHER SURRYWALL WOULD STAND WITHOUT SUPPORT O

THE DEBRIS.

FOLLOWING INFORMATION WERE REQUIRED

ORGINALS STORED IN THE WTC TOWERSHAMPERED THE RESCUE OPERATIONS


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RESCUE OPERATION

STRUCTURAL ENGINEERS ROLE

STRUCTURAL ENGINEERS WORKING ROUND THECLOCK ARE QUESTIONED :

CAN THIS PIECE OF STEEL BE REMOVED.

WILL THIS STRETCH OF RUBBLE SUPPORT ACRANE.

CAN PEPOLE WORK UNDERNEATH THE FACADEOF BUILDINGS WHERE HUGE PIECES OF STEELDEBRIS PROTRUDING FROM THE CLADDING.


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PROBLEMS ASSOCIATED WITH

REMOVAL OF DEBRIS

STABIL I TY OF THE DIAPHRAGM WALL

During construction supported by Tieback Anchors.

After construction propped by basement slabs.

(Tiebacks are disconnected )

During the collapse of towers propped basementslabs were destroyed by fallen debris and wall was

restrained by well packed debris.


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Removal of debris was not possible which

would destabilize the wall.

* Endangering the adjoining buildings

* flooding of the basement .* flooding of the under ground tunnels.

New anchor system was foreseen to stabilize the

slury wall.


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POSSIBLE REASONS FOR

PROGRESSIVE COLLAPSE

Impact of the planes - No.

Lost of load bearing elements during the crash ofplanes.

Fire softening of steel load bearing elements andthe impact of collapsing of the top part of the tower

on to the bottom part.


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FIRE SOFTENING OF LOAD BEARING

ELEMENTS

SOFTENING OF FLOOR MEMBERS.

* Collapsing of floor.

* Buckling of columns due to increase

of unsupported height.

SOFTENING OF COLUMNS.


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SOLUTIONS TO MINIMISE THE

DAMAGES

OBJECT - Not to save the Building.

But to save human lives.

Improvement of fire ratings (five to six hours )and

robustness of the structure.

Improvement of evacuation methods.

Solutions for services , ventilation and access routes in

crisis situation.


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STRUCTURE

Safety of the structure ( to complete the total evacuation)

* Higher fire rating for the structure

* Reliable fire protection system.

* Designing a level of structure every 10 floors to carry the weight of

nine collapsing floors above.

* Compartmentalizing buildings using a secondary structure as a fall

back if the main structure fails.

(i.e having concrete core able to stay after loosing the floors

and perimeter frame.)


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EVACUATION

Present philosophy - Partial evacuation.

Future Aim - Total (Simultaneous)evacuation.

Emergency access / stair case arrangements* Ventilation

* Lighting

* New method of evacuations

# Use of helicopters

# Use of parachutes

Time Requirement for evacuation.


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SERVICES

Artificial ventilation.

Artificial lighting.

Sprinkler system and water for fire fighting.

* Reliability - In question

* Solutions

# Passive means of fire protection.# Natural ventilation and lighting.


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7thInternational Conference on

INSPECTION, APPRAISAL, REPAIR ANDMAINTENANCE OF BUILDINGS ANDSTRUCTURES

1113 September 2001At The Nottingham Trent UniversityUnited Kingdom.

DAMAGE ASSESMENT AND REPAIRTECHNIQUES USED IN BOMB AND FIRE

DAMAGED CENTRAL BANK BUILDING INSRI LANKA


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K.L.S. Sahabandu, an expert in

blast and fire damage from SriLanka at the conference,told The

Structural Engineer, It was the

fire,not the impact of the planes

that caused the progressive

collapse. We need to the review the

fire resistance and services of such

structures, and the evacuation

plans,in future.


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THE END

collapse of world trade centre

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