Massachusetts Institute of Technology Cambridge, MA, USA The Collapse of Twin Towers: Causes and Effects Keynote Lecture EFCA 2004 CONFERENCE AND GAM May 22-May 25, 2004 Istanbul, Turkey Keynote Lecture EFCA 2004 CONFERENCE AND GAM May 22-May 25, 2004 Istanbul, Turkey Dr. Oral Buyukozturk Professor of Civil and Environmental Engineering Dr. Oguz Gunes Dr. Oral Buyukozturk Professor of Civil and Environmental Engineering Dr. Oguz Gunes

WTC Causes Effects Lessons Conclusion OUTLINE WTC DESCRIPTION CAUSES OF COLLAPSE –IMPACT –FIRE –PROGRESSIVE FAILURE EFFECTS OF COLLAPSE –CASUALTIES –STRUCTURAL –TRANSPORTATION –ECONOMIC/BUSINESS –COMMUNICATION –LOGISTICS LESSONS LEARNED CONCLUSION WTC

Causes Effects Lessons Conclusion WTC Facts Consist of Seven Buildings Own zipcode: & Owner Port Authority of NY and NJ Architect: Minoru Yamasaki & Associates Engineer John Skilling & Leslie Robertson Contractor Tishman Construction Company Ground Breaking August 5, 1966 Opened April 4, 1973 WTC

Causes Effects Lessons Conclusion WTC Facts Area of WTC complex 65,000 m 2 (16 acres) Total rentable office area 1.1 million m 2 (12 million foot 2 ) Tower floor dimensions 63 m (207 ft) sides Tower heights 110 stories, 417 (N) and 415 (S) m (1368 and 1362 ft) Antenna 110 m (360 ft) Earth work 920,000 m 3 (1.2 million cubic yards) Steel weight 200,000 tons Concrete 325,000 m 3 (425,000 cubic yards) Total weight 500,000 tons WTC

Causes Effects Lessons Conclusion WTC Facts 3 exit stairways in the core of each tower 99 elevators and 16 escalators in each tower 43,600 windows/tower >350 businesses 50,000 employees in twin towers 150,000 daily visitors WTC

Causes Effects Lessons Conclusion Innovations in Design of WTC A basement like a bathtub A building like a tube An elevator system like a subway system Viscoelastic dampers (10,000 in each tower) Outrigger space frame to support antenna Wind tunnel study for wind loads First commercial building designed to resist plane impact WTC

Causes Effects Lessons Conclusion Earthquake Load Wind Load Blast Load Impact Load Gravity Loads Structural Loads Gravity loads –Dead loads –Live loads –Snow loads Lateral loads –Wind loads –Seismic loads Special load cases –Impact loads –Blast loads Design wind speed: 240 km/h (150 m/h) Design impact object: Boeing 707 WTC

Causes Effects Lessons Conclusion Structural System Framed tube construction principle: load bearing external walls stiffened by the floors to form a flexurally and torsionally rigid tube WTC 63.1 m (72’ 2”) 42 m (137 ft) 26.5 m (87 ft) Core area (Steel Frame) Outer steel lattice Cross-braced floors

WTC Causes Effects Lessons Conclusion Exterior Column System WTC Assembly of the external wall units and floor units Wall units alternately staggered in one-storey heights (FEMA 403)

WTC Causes Effects Lessons Conclusion Erection of Prefabricated Components Prefabricated column unitsErection of floor framing WTC (FEMA 403)

WTC Causes Effects Lessons Conclusion Floor Joists (Trusses) WTC (FEMA 403) (10,000 viscoelastic dampers used in each tower)

WTC Causes Effects Lessons Conclusion CAUSES OF COLLAPSE IMPACT FIRE PROGRESSIVE FAILURE Causes

WTC Causes Effects Lessons Conclusion Timeline of Events in :46 a.m. - Plane hits North Tower 9:03 a.m. - Plane hits South Tower 9:17 a.m. - FAA shuts down NYC airports 9:17 a.m. - Amtrak suspends all service 9:17 a.m. - NY DOT shuts down highways 9:21 a.m. - Port Authority closes bridges and tunnels 9:40 a.m. - FAA grounds all flights 9:43 a.m. - Plane hits Pentagon 9:59 a.m. - South Tower collapses 10:00 a.m. - Armed forces put on high alert 10:20 a.m. - NYC Transit shut down 10:29 a.m. - North Tower collapses 10:30 a.m. - NJ Transit stops rail service to Penn Station 10:37 a.m. - Fourth plane crashes in Pennsylvania 10:45 a.m. - All PATH operations stop 10:50 a.m. - All remaining bridges and tunnels close Causes

WTC Causes Effects Lessons Conclusion Impact Configuration Causes (FEMA 403)

WTC Causes Effects Lessons Conclusion TargetFlightAircraft Impact Time Approximate Velocity km/hrm/s North Tower AA-11 Boeing :46 AM South Tower UA-175 Boeing :03 AM Impact Velocity Causes Estimated Impact Velocities

WTC Causes Effects Lessons Conclusion Conservation of linear momentum Impulse = change in momentum v m Boeing ER 14 m (46 ft) 5.5 m (18 ft) 48.5 m (159.2 ft) F = collision force F = mv / t d = ½ mv 2 / d ≈ 12,500 ton d = distance traveled by plane to a stop ≈ 50 m v = velocity of plane ≈ 250 m/s m = mass ≈ 200 ton (weight of each floor ≈ 2,500 ton) E k = kinetic energy t d = duration of collision = 2 d / v ≈ 0.4 s Characteristics of Plane Impact Causes

WTC Causes Effects Lessons Conclusion Impact Damage to North Tower Floors Causes (FEMA 403)

WTC Causes Effects Lessons Conclusion Impact Damage to South Tower Floors Causes (FEMA 403)

WTC Causes Effects Lessons Conclusion Impact Induced Fires Estimated 38,000 liters (10,000 gallons) of jet fuel in each plane at impact. Causes (FEMA 403)

WTC Causes Effects Lessons Conclusion Column Safety Under Service Loads Safety against yielding Buckling stress Safety against buckling Causes

WTC Causes Effects Lessons Conclusion Behavior of Materials under Heat Temperature (C) Material property Modulus of Elasticity Compressive Strength Concrete Temperature (C) Material Property Yield Strength Modulus of Elasticity Steel Causes Diffusion Conduction Steel Concrete Substrate Fire proofing 6-8 times more fire proofing required for steel

WTC Causes Effects Lessons Conclusion Fire Type and Protection Time (Minutes) Temperature (C) Fire Temperature Unprotected steel Protected Steel Causes Time (Minutes) Temperature (C) Cellulosic fire Petrochemical fire Jet fuel fire provides more heat than typical office fire. Degree of fire proofing significantly affects the time for evacuation

WTC Causes Effects Lessons Conclusion A Possible Failure Mechanism Causes

WTC Causes Effects Lessons Conclusion Collapse of the Towers South tower: 9:59 a.m. North tower: 10:29 a.m. Causes (FEMA 403) Collapse of South Tower

WTC Causes Effects Lessons Conclusion EFFECTS OF COLLAPSE CASUALTIES STRUCTURAL TRANSPORTATION ECONOMIC/BUSINESS COMMUNICATION LOGISTICS Effects

WTC Causes Effects Lessons Conclusion Casualties Estimated 58,000 Present 2,830 Died All but four people above the crash zones died Nearly everyone below the crash zones lived Most people died in the North Tower, which was hit first Nearly 500 rescue workers died when two towers collapsed Victims were 78% male and 22% female

WTC Causes Effects Lessons Conclusion Structural Damage Effects Collapsed or Destroyed One World Trade Center (North Tower) Two World Trade Center (South Tower) Marriott Hotel (3 WTC) Five World Trade Center Seven World Trade Center Partially Collapsed Four World Trade Center Six World Trade Center Major Damage One Liberty Plaza East River Savings Bank N.J. Kalikow and Co. Building and Millennium Hotel Federal Building N.Y. Telephone Building One World Financial Center Two World Financial Center Three World Financial Center St. Nicholas Greek Orthodox Church 90 West Street Bankers Trust

WTC Causes Effects Lessons Conclusion Critical Infrastructures Affected by 9-11 Effects Government Operations Emergency Services Transportation Water Supply Systems Telecommunication Energy Supply Banking and Finance Gas & Oil Storage and Delivery

WTC Causes Effects Lessons Conclusion U.S. Air Traffic on 9/11 Morning 9:17 a.m. FAA shut down NYC airports 9:40 a.m. FAA grounded all flights Transportation 8:48 a.m. – AA-11 hit WTC 1 9:04 a.m. – UA-175 hit WTC a.m. – AA-77 hit Pentagon 10:20 a.m. – UA-93 crashed First shut down of all air transportation Effects 10:00 a.m. 3,181 Aircrafts aloft 10:17 a.m. 2,201 Aircrafts aloft 10:31 a.m. 1,240 Aircrafts aloft 10:40 a.m. 820 Aircrafts aloft 10:55 a.m. 680 Aircrafts aloft 11:40 a.m. No commercial aircrafts aloft

WTC Causes Effects Lessons Conclusion Transportation 3 million commute to NYC everyday Damage to 1/9 Line (serves 600,000 people daily) –WTC subway & PATH station destroyed –427 m (1400 feet) of tunnel destroyed –two fan plants destroyed –Transportation disruptions for up to 14 days Effects

WTC Causes Effects Lessons Conclusion Economic/Business Big economy of the Big Apple –Over 8 Million people reside in NYC –$42.3 Billion budget –350,000 City employees in 38 Agencies 50,000 office workers at the WTC each day Six banks, five large investment firms, and three insurance companies had their headquarters in the towers. The Port Authority of New York and New Jersey had its headquarters in the building. American Express had three floors in the WTC. Major damage to World Financial Center next to the WTC site. Effects

WTC Causes Effects Lessons Conclusion Hardware & Software failure Data corruption Telecommunication failure Site physical facility problems Security failure Effects Business Continuity What companies had planned for before 9-11 What was not anticipated? Collapse of the building Long-term outage Transportation failure Logistics failure People support issues Loss of key personnel Many companies which did not have alternate sites and trained personnel are gone!

WTC Causes Effects Lessons Conclusion Telecommunications Challenges Significant destruction of Verizon Central Office at 140 West Street –Between 9000 and businesses left without service (IDC Flash) –300,000 voice lines (200k for homes/small businesses) –3.5 million data circuits, 2 million that “pass through” –1,737 employees (all evacuated) –Water from broken mains and fire hoses flooded basement vaults, shorting cables that had not been cut by the falling debris Effects –Ducts outside were covered by 30 foot high debris, denying Verizon access for several days Power outages

WTC Causes Effects Lessons Conclusion LESSONS LEARNED Vulnerability assessment Design against vulnerabilities Redundancy Structural Egress paths Transportation Communication Energy Business continuity Preparedness Lessons

WTC Causes Effects Lessons Conclusion Vulnerability and Risk Assessment Probabilistic risk assessment (PRA) and decision making have been effectively used in nuclear engineering, manufacturing, seismic loss estimation etc. Probabilistic, nonlinear, and coupled evaluation of building vulnerability is needed for identified hazards. Hazard identification, prioritization and evaluation Vulnerability analysis Risk assessment & Loss estimation Optimum mitigation strategy Decision & Implementation Lessons

WTC Causes Effects Lessons Conclusion Design for Fire Old: Prescriptive-Based Design –Design based on fire rating of materials used –Fire rating of material from tables –Compliance with a code specified value New: Performance-Based Design –Evaluate the strength and stiffness for a particular design fire –Coupled stress-thermal analysis –Specialized design for fire effects –Use of fire retardant materials, advanced coatings and ceramics Lessons

WTC Causes Effects Lessons Conclusion Performance Evaluation Under Fire Coupled structural/fire analysis Structural loads Thermal analysisStress analysis Fire modeling Deformations, damage, collapse Elastic/strength properties Thermal properties Structural Model Geometry Demand Time: 20 min Onset of fire Time: 35 min Time: 45 min Weakest link Lessons

WTC Causes Effects Lessons Conclusion Design for Impact Loading Engineering problems related to impact loads: Modeling of impact Assessment of impact damage Evaluation of structural safety after impact Modeling of potential fire after impact Coupled evaluation of structural integrity and collapse potential Lessons

WTC Causes Effects Lessons Conclusion Impact Modeling Velocity Total kinetic energy Fuselage cutting force MIT Impact and Crashworthiness Laboratory Exterior columns Core columns Boeing Floor Core area Boeing Max. takeoff weight: 395,000 lb (180 ton) Max. fuel capacity: 24,000 gal (91,000 liter) Cruise speed: 530 mph (237 m/s) Lessons

WTC Causes Effects Lessons Conclusion The initial kinetic energy of the plane is dissipated through Permanent plastic deformation (crushing) Generated Heat Fracture and fragmentation (creating new surfaces) Friction Residual velocity Elastic vibrations Energy Dissipation During Impact Core columns 28% Aircraft 25% Exterior columns 3% Floor structure 53% Estimated distribution of energy dissipation May be used as a design tool MIT Impact and Crashworthiness Laboratory Lessons

WTC Causes Effects Lessons Conclusion Redundancy and Progressive Failure Redundancy in column system Redundancy in floor system System Redundancy (Global frame) Local Redundancy (Local joints) Improved local redundancy FEMA 403 Lessons

WTC Causes Effects Lessons Conclusion Emergency Egress Strategies Elevated passages to neighboring buildings Refuge floors/rooms with fire escape elevators Perimeter wall rescue vehicles Fire resistant escape chutes Flying rescue platforms Individual fire resistant parachutes Lessons

WTC Causes Effects Lessons Conclusion Lessons for Business Continuity Establish multiple physical sites (redundancy) Assign same level workers over two or more physical sites. Favor distributed networks Cross train high level manages (IT) in each other’s duties. Have a clear order of succession. Regularly rehearse full disaster drills. Lessons

WTC Causes Effects Lessons Conclusion Lessons for Logistics What can go wrong? What is the likelihood of a disruption? What are the consequences if it happens? How do we recover? Assess vulnerability to special events Keywords: Redundancy and flexibility Strategic planning - locations Operational security Public-private partnerships Awareness culture Reduce probability of disruption Lessons

WTC Causes Effects Lessons Conclusion Conclusions Conclusion Causes Effects Lessons Large scale casualties, structural damage, infrastructure disruption, and economic loss Worldwide impact on way of human life Rigorous engineering paradigms Preparedness Effective emergency management and disaster recovery planning Vulnerability to unexpected events in physical and social dimensions Progressive and time-sensitive nature of destruction

WTC Causes Effects Lessons Conclusion Lesson Learned Expect the unexpected. Be prepared! Conclusion