High Rise Buildings

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25 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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High Rise Buildings

and

Large fires

Structural loads & thermal strain

What 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.

esmunyak@earthlink.net


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 paradigm

for 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
Fires

on 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 fires

20 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, Canada

October 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 Fire

Los 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,
Pa

February 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 2

NYC 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 Building

Caracas, Venezuela

October 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 Windsor

Madrid, 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/res
earch/structures/strucfire/CaseStudy/Historic
Fires/BuildingFires/default.htm



Madrid,Spain12/2/2005

Edificio Windsor Madrid, Spain

Edificio Windsor, Madrid 2/12/2005

Edificio Windsor

After 20 + hour fire


Theorem of Castigliano

Elements 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.

Steel in plastic range

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/ci
nema.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