Transcript
DEMOLITION ENGINEER Autumn 2007
8
DEMOLITION ENGINEER Autumn 2007
9
Demolition is becoming ever morecomplicated because of bothmodern structural systems andadditional safety regulations. As aresult, many demolitioncontractors and municipalities arelooking for ways to overcomethese challenges.
Until recently technical limitations prevented the
accurate calculation and presentation of
structural behaviour during post-failure stages
and collapse. Therefore, simulating demolition
plans has not been a viable option.
However, Applied Science International (ASI),
an engineering analysis firm based in the United
States, is helping demolition contractors by
simulating and visualising their plans using
Extreme Loading® analysis technology.
Extreme Loading® an exclusive technology
based on the Applied Element Method (AEM)
analyses a structure’s behaviour during pre- and
post-failure stages in 3D, in addition to
calculating changes in the structure as elements
fail, tracking the propagation of cracks, and
simulating progressive collapse.
COLLAPSE BEHAVIOURRecognising value in the capabilities of this
technology engineers, security experts, and over
50 universities worldwide are using Extreme
Loading® analysis to study concrete, steel,
masonry and composite structures under
extreme events such as explosions, earthquakes,
hurricanes, impact, and demolition.
“Demolition contractors are facing more
challenges with projects in dense urban
environments, and the ageing of complex
structures. Safety and quality standards are
requiring additional analysis of demolition plans.
That’s where our simulations can help,” says
Steve Bruns, business development manager for
ASI. “By modeling a structure and then running
the demolition plan, we can generate simulations
that allow demolition contractors to test several
different plans and ‘What-if ’ scenarios to identify
safety perimeters, and communicate their plans.”
ASI’s demolition simulations replicate each
element of the structure to determine its
behaviour during demolition and collapse. This
reveals the collapse behaviour of composites,
post-tensioned elements, precast elements, rebar,
concrete strength, and structural deterioration.
When there is a concern for the contribution of
nonstructural elements during demolition, walls,
elevator shafts, and windows are modeled into
the analysis and their effects on the demolition
are also simulated.
ASI’s simulation capabilities have primarily
attracted explosive demolition projects because of
the associated risk but the scope of applications
include: pull downs, wrecking ball, and
deconstruction projects.
EXTREME LOADINGFor example in deconstruction projects ASI
simulates how a building behaves when heavy
equipment, often exceeding the weight limits of a
building, removes portions of a building piece by
piece creating a potentially unstable and
dangerous environment. Extreme Loading®
technology simulates the sequence of removing
structural members and the movement of the
equipment within the building to illustrate the
impact on the remaining supports. Diagrams of
colour contours are generated representing the
changes in stresses and strain on the structure,
and highlighting zones where there is risk of
sudden collapse.
Last month the world‘s largest domed arena at
time of construction ‘the Hive’ former home of
the Charlotte Hornets basketball team was taken
down by explosive demolition. The 24,000 seat
arena was built of steel, composite columns,
composite girders, masonry walls, and a dome
made from an intricate web of space trusses. The
primary challenge facing the demolition
contractor was weakening the dome truss so that
it remains intact during the demolition long
enough for it to pull the perimeter of the
coliseum inward as the supporting columns are
blasted. Any mistake in the plan would have
significantly increased removal time and costs.
BLAST SPECIALISTSASI studied the case from every angle, examining
the structure’s main elements and gathering
information from blueprints and site visits.
“We modeled the coliseum including its steel and
composite sections, space trusses, reinforcement
details, and even compensated for deterioration.”
“We also modeled the plans for weakening the
structure, modeling all the cuts in the steel
columns and trusses,” says Patrick Lea, ASI
structural engineer.
The blast plan was modeled into the computer
simulation by using a method called immaculate
element removal. This method is to remove
elements from the model in the same sequence
the blast specialist would detonate the charges.
The program then runs computations to
determine the overall behaviour of the structure.
The project took about three weeks to complete
from start to finish.
“We were able to illustrate the collapse mode and
debris field to the owners and help the blaster
adjust the sequence to maintain momentum thru
the collapse and bring the dome down more
completely,” says Patrick.
When the video of the real implosion and simulation
were compared, (http://www.appliedscienceint.com/
Charlotte Coliseum.shtml#Movie) it was immediately
evident that the simulation accurately resembled the
actual implosion.
EVENT ATTRACTIONEvents like this also draw significant attention
from the media who now have the ability to see
beyond the dust of the actual demolition and
inside the structure as it collapses.
Lately, ASI has been working closely with
engineers on planning the demolition of an
industrial facility in Australia. The facility, retired
over three years ago, is five meters away from a
reactor that must remain standing after the
demolition. The challenge is in the structure’s
complex braced frame used to support large
industrial equipment much of which will remain,
and to provide a stable base until the final stage
at which point complete structural collapse is
required. The consulting engineers were limited
to using linear static finite element analysis to
study the demolition plans, which cannot
determine collapse modes. ASI was hired to help
calculate the required pulling force to bring down
the structure safely, determine the dynamic
behaviour, and simulate collapse modes. ASI is
testing multiple scenarios and the final
demolition plan is in the works.
CATCHING UP WITH THEFUTUREDemolition is known to accelerate the future;
finally, the future has caught up with demolition.
By using computer simulations to visualise
demolition plans, demolition safety standards
have been elevated to new heights.
See the simulation of the Charlotte Coliseum
and find updates about the Australia project at
ASI’s website: www.extremeloading.com.
See it come down…before it comes down
top related