High Rise Buildingsand Large fires Structural loads & thermal strainWhat can happen? As presented to the Northern California-Nevada Chapter of the Society of Fire Protection Engineers On April 21, 2006 in Walnut Creek, California. by Edward Munyak, P.E.firstname.lastname@example.org
Probable Maximum Loss • PML assumes a fire scenario with a loss of one suppression system and a delay in manual fire fighting. • The 9/11 Commission report ignores the collapse of WTC 7 • The NIST Report on WTC 1,2 & 7 implies that global collapse was inevitable for these steel structures.
Is there a new paradigmfor building collapse? • What follows is a study of steel frame building response to maximum fire conditions based on: • Historical catastrophic fires in high rise buildings from 1986 to 2005 • Actual fire tests in steel frame buildings in the UK • Thermodynamic simulations
Fire Resistance • Unprotected steel that resists high winds and seismic forces has considerable fire resistance. • Adding dead weight at a cost of 20% ? • Structures need to be designed to resist higher wind, seismic loads and increased fire resistance will automatically follow.
Inherent fire resistance • “In many instances, particularly in tall buildings or massive structures, the mass of steel required to support loads and resist moments is very large and thus the thermal mass of the steel itself provides inherent resistance to weakening by fire fire exposure for periods of time that can be determined by engineering analysis” page 17 NIST structural steel report GCR 04-872 7/2004
ASTM E-119 is the standard test for full size structural components. • Oven temperature(not structure) versus time. • One side of the structure is exposed to heat. • If temperature on unexposed side is excessive or if deflection is above a certain limit after the test duration, the component fails. • Structure is always within the elastic range
ASTM vs “Real” fires • Recent and historical large fires in steel frame buildings have demonstrated that actual fire performance of the structural system is much better than results of the test of a single component. • Broadgate Fire in UK occurred prior to fire proofing. Structure exceeded 650 degree C. but did not collapse.
Simulations of Standard Fireson whole frame design Performance based approach deleted fire proofing on most secondary steel. Catenary action on beams and Tensile membrane action of floor slabs compensated for the reduction of strength at higher temperatures
High rise Building fires20 year time span • Montreal, Canada 1986, 15 stories • Los Angeles, 1988, First Interstate Bank • One Meridian Plaza, Philadelphia, 1991 • WTC 1, 2 & 7, NYC. 9/11/2001 • Parque Central, Caracas, Venezuela 2004 • Edificio Madrid, Spain 2005
Montreal, CanadaOctober 26, 1986 • 15 story SFRM Steel frame building with a fire load estimated to be at least twice WTC ( 10 - 11 lbs/sq ft vs 4 lbs/ sq ft in WTC) • Fire burned for over 13 hours on multiple floor levels due to vertical openings. • A 30ft x 40ft section on the 11th floor fell to the 10th floor when welded clips failed. No inelastic deformation noted on surrounding structure. • Loss demonstrated the need for automatic sprinkler protection and protection of vertical openings. • Interesting example of girder to column failure of weld clip.
First Interstate Bank FireLos Angeles, May 4, 1988 • 62 story type II. SFRM steel frame, open floor plan • Fire duration was 3 1/2 hours • Fire spread vertically from 12 th to 15th floors internally and externally. • Many broken windows resulted in a severe fire and auto-ignition • Smoke spread throughout building but there was no structural frame damage. • Fire damper in HVAC failed at critical point
One Meridian Plaza, Philadelphia, PaFebruary 23, 1991 • Fire gutted 8 floors of a 38 story building • 3 fire fighters died,$100 million in direct fire loss, $ 4 billion civil damage • Fire burned for over 19 hours • Major power and water supply failure • Severe fire broke most windows on the fire floors • Fire spread externally by auto-ignition • Fire was stopped by automatic sprinklers on the 30th floor. • Vertical columns were not damaged, horizontal beams sagged as much as 3 feet.
WTC 1 and 2NYC Sept 11, 2001 • Applying the equal-area principle for the time-temperature curve, fires were not as severe as ASTM standard and less than all other examples. • Each tower was more massive than other high rise examples. • NIST report, page 77, estimates a fuel loading of 4 lbs/ sq ft or 60 tons of combustibles per floor.
WTC 1 & 2 Structure • Designed in accordance with the 1968 NYC building code with a 50 year wind storm of just under 100 mph which exceeds existing and current codes. • Designed to resist the impact of a Boeing 707@ 600 mph • Originally designed with gypsum board and SFRM to protect core. • Building core supported gravity load, external high strength columns could be under compression or tension
ASTM vs WTC South After the initial fireball 1050 C for 2min. Fuel burns off in 10 minutes 4 lbs/ ft fire load equates To 30-40 min duration.
NIST analysis of WTC collapse • “The towers withstood the impact and would have remained standing if not for the dislodged insulation(fire proofing) and subsequent multi-floor fires.” • Towers were built in accordance with 1968 NYC Building Code. • Recommended objective should be survival of an uncontrollable fire without local or global collapse.
WTC Tower structure • Gravity loads were supported by 47 steel columns in the core. • Wind loads were resisted by 59 columns on each of 4 sides that could be in compression or tension. • The floors were composite concrete and steel. Steel trusses had viscoelastic dampers on bottom chord.
Thermal simulation of south tower • A steel frame building with the mass of WTC 1 or 2 could have partial structural collapse after aircraft impact only if the heat output was at least 100 times the heat release rate of the accountable fuel load and ventilation conditions in the south tower. • This fire would need to involve every floor from impact floor to the roof with most windows broken and providing plenty of oxygen as in the Edificio Windsor fire in Madrid. • This most severe fire would need to burn for at least 12 hours before loss of strength from heat; and thermal strains from expansion and contraction caused partial collapse.
Anomalies within an Anomaly • Unprecedented total collapse of a steel frame building. • The tower with the least structural damage and smallest fire collapsed first. • If lack of fire proofing brought down WTC 1 & 2 why did intact fire proofing not help WTC 7? • On the scene professional fire fighters knew that the building was not damaged to the verge of collapse.
WTC 7 • WTC 7 was one city block away from Towers • No damage to fire proofing • Small fires were observed • Global collapse was initiated on the lowest level • Different structure
Parque Central Office BuildingCaracas, VenezuelaOctober 15, 2004 • South America’s Tallest building at 56 stories • Automatic sprinkler system impaired • The fire burned for over 24 hours and consumed 17 floors at a rate one floor every 2 1/2 hours. • Five spray fire proofed structural steel sections were sandwiched between concrete protected steel macro slabs that were supported by exterior reinforced columns • Fire spread by auto-ignition and through unrated floor panels in the two hour rated floors. Total glass breakage on fire floors.. • Two floor areas partially collapsed, fire chief ordered fire fighters to abandon interior fire fighting but there was no further collapse.
Edificio WindsorMadrid, Spain 12 Feb, 2005 • Fire started on the 21 st floor of a 32 story concrete core column building with unprotected steel beams on perimeter with unprotected perimeter columns • Building was being renovated; there were large unprotected vertical openings. • Unknown fire load but judging by the 18- 20 hour fire duration, and massive flames, the fire load must have been high. • The suspicious fire spread from the 21 floor to the top 32nd floor within one hour and then downward to the lowest floor(4th) within the next 10 + hours. • Property was valued at 72 million Euros before the fire that gutted it. • A portion of the floor slabs above the 17th floor that was supported by unprotected steel beams collapsed but the reinforced concrete core columns performed well. http://www.mace.manchester.ac.uk/project/research/structures/strucfire/CaseStudy/HistoricFires/BuildingFires/default.htm
Theorem of CastiglianoElements of Strength of Materials by Timoshenko & Young 4th edition page, p. 246-263 Strain energy that must be overcome before limit collapse is complete is proportional to all forces squared and inversely proportional to high strength modulus of elasticity. Integration of area under the stress-strain curve represents a massive amount of strain energy that must be overcome before collapse is complete in the case WTC 1, 2 & 7. The only available source of energy of that magnitude is the potential energy of at least 10 floors and it had to be released in a sudden impulse.
Energy available for release • Fire tests in the UK shown the structure under load at very high temperatures slowly releasing potential energy of mass and height by plastic deformation of the heated steel. • Chemical energy in the fuel and potential energy (mass x height) is released by plastic deformation where temperatures are hottest. • The load path then shifts to surrounding structures in rather slow process.
Magnitude of Available Energy sources Chemical energy in jet fuel(2 planes)=6.9.e+10 metric joules (applied over 5 -10 minute time duration) Kinetic energy (2 planes) = 1.9 e+9 metric joules (less than one second) Potential energy (2 towers) =6.8 e=11 metric joules (controlled demolition can release this in less than one second)
Releasing Gravitational Energy • Collapse in WTC was initiated near the floors of Impact. • The center core suddenly dropped without any resistance from the structures below. • If column severing energy was sequentially timed so that as the total mass accelerating down met minimal resistance for 2 or 3 floor enough potential energy will be converted into downward momentum so that in the words of the NIST report “global collapse was inevitable.” • All potential energy was suddenly released and available for inelastic deformation of steel and simultaneous pulverizing of concrete within a time span of about 10 seconds
Recommendation Reimbursement of any loss must be contingent upon access to and analysis of fire damaged structure: • The wreckage of WTC 1, 2 & 7 was worth hundreds of millions of dollars in terms of research and practical knowledge. • There was evidence of sulfadation on beams from explosive material • The severed ends of beams were observed to be partially molten for days after clean-up. This is characteristic of thermite.
WTC Collapse Professor Steven Jones of BYU Department of Physics and Astronomy “WTC 7 collapsed rapidly and symmetrically-even though fires were randomly scattered in the building” “Where is the delay that must be expected due to conservation of momentum-one of the foundational laws of physics”
http://www.implosionworld.com/cinema.htm • What is incredible in the fire effects continua is routine in the world of controlled demolition. • “Even with explosives, achieving such results requires a great deal of pre-planning and expertise” • “The explosive demolition hypothesis better satisfies tests of repeatability and parsimony” states Professor Steven Jones http://www.physics.byu.edu/research/energy/htm7.html
To be continued • For additional information contact • Edward Munyak, P.E. • esmunyak@ earthlink.net • (650)948-8035
References • NFPA Journal, March/April 2005 “Fire Unchecked” page 47 Caracas, Venezuela Fire • Culver, Charles, “Characteristics of fire loads in office buildings” Fire Technology 1978, Vol 14, No.1 pages 51-60 • NFPA investigation of High Rise office Building Fire, Montreal, Canada, October 26, 1986 • NFPA investigations of May 4, 1988 First Bank Building Bank Fire, Los Angeles, Ca • WWW. Implosionworld.com • http://911reserach.wtc7.net • “Building Regulatory Systems in a post-September 11 World” by Richard Bukowski, P.E. NIST Building and Fire Research Laboratory • http://www.mace.manchester.ac.uk/project/research/structures/casestudy/historic fires/building fires/default.htm • http://www.physics.byu.edu/research/energy/htm7.html • “Fire Protection of Structural Steel in High Rise Buildings”, NIST GCR 04-872 • Moscatelli, Frank, WETC energy calculations • 9/11 Commission Report, Omissions and Distortions. David Ray Griffin • 9/11 Synthetic Terror-Made in the USA, Webster Griffin Tarpley