Demolition Analysis Article

DEMOLITION ENGINEER Autumn 2007

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DEMOLITION ENGINEER Autumn 2007

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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