forensic engineering - causes of distress in concrete.pdf

8/10/2019 Forensic Engineering - Causes of Distress in Concrete.pdf

1/115

Forensic En ineerin =Forensic En ineerin =

1

Causes of Distress in ConcreteCauses of Distress in Concrete

David W. FowlerThe University of Texas at Austin

[email protected]


2/115

What is forensic engineeringForensic engineeringscience

concerned with the relations betweenengineering and the law.Forensic en ineerin is a

2

specialized discipline which is arelatively new and unfamiliar field to

the public.More common definition: activitiesrelated to failure investigation


3/115

Forensic engineers performautopsies on components and

materials or full-sized buildings,bridges, foundations, and otheren ineered constructed works in

3

order to determine the cause andextent of failure.

A secondary purpose is todetermine methods ofrepair/rehabilitation/replacement.


4/115

What are the qualifications of forensicengineers?

Must be expert. Must be ethical

M lik iv

4

Must enjoy digging for the truth

Must think outside the box


5/115

So if you want to be anengineering Sherlock Holmes,

lets go further

5


6/115

How is failure defined?


7/115

What is a failure?

When a facility, structure or material does

not perform in the manner it was intended.

It does not have to collapse or cause

7

be a failure


8/115

Failure Examples A floor vibrates when people walk on it.

One room in the building is not cooled by

the air conditioning system A parking area ponds water when it rains

8

The foundation moves differentially,

causing cracking in the interior and

exterior wall.


9/115

Famous Failures

Tower of Pisa, Italy

Tay Bridge, Scotland

Hyatt Regency Hotel Walkway, Kansas

9

ty Big Dig (Boston) Tunnel Ceiling Panels


10/115

Famous FailuresTower of Pisa (1173 to present)

200 ft (60 m) tall

Inclined 5.5

Extensive efforts to

10

Many efforts tocorrect problem


11/115

Famous FailuresTay Bridge, Scotland (1879)

Completed in 1828

Length: 10,321 ft. (3146 m) 85 simply supported iron lattice-truss spans

Failure occurred during a major storm

11

Train was passing over bridge 75 people died

Cause of failure: improper estimation of wind

force in design 10 psf (0.5 kPa) instead of 50 psf (2.5 kPa)


12/115

Famous FailuresTay Bridge, Scotland (1879)

12


13/115

Famous FailuresHyatt Regency Hotel in Kansas City

(1981)

Hanging walkway supported by steel rods

Colla sed killin 113 eo le

13

Cause: poor connection detail

Poor communication between engineer

and steel fabricator involved


14/115

Famous Failures

Hyatt Regency Hotel in Kansas City(1981)

14


15/115

Famous Failures


15


16/115

Famous Failures


16Hanger rod box beamconnection


17/115

Ultimate Capacity ofConnection

Original Design: Ultimate capacity of

connection only 60% of required capacity As Built: Ultimate capacity was just a little

17

Either way, connection was bound to fail!


18/115

Famous Failures

Big Dig Ceiling Panel Failure

On 11 pm, July 10, 2006, four sections of

precast concrete ceiling panels fell in aconnector tunnel in Boston.

18

- - ,to Logan Airport with her husband, waskilled.

The epoxy anchors holding the ceilingpanels failed due to faulty construction anddesign.


19/115

The Accident Scene

19


20/115

Car Crushed by Ceiling Panel

20


21/115

HoweverHowever

These are very dramatic butThese are very dramatic but

spectacular!spectacular!


22/115

Why Did I Fail?


23/115

Scientific Method for Solving

Forensics Problems State the problem

Make observations

State the likely causes of the failure

Test the likely causes by making moreobservations, performing tests, doingcalculations, doing a literature search, etc.

Develop the most likely cause or causes


24/115

Often the anxwer will be yes, maybe orno, maybe.

There may be more than one contributing

factor

Developing a simple matrix is helpful in

com ng o e mos e y causes.


25/115


26/115

Symptom Cause

Cracking shortly (minutes to hours)after placing (before setting)

Plastic shrinkage cracking (rate ofevaporation > rate of bleeding)


27/115

Symptom Cause

Cracking shortly (hours to days)

after placing (after hardening)

Drying/thermal cracking (improper timing

of spacing of joints)


28/115

Symptom Cause

Cracking occurring after structure

is in service

Structural cracking (improper placing or

insufficient reinforcement)


29/115

Symptom Cause

Map cracking typically

occurring after 5 to 10 years

Volumetric expansion of concrete (in this

case ASR)


30/115

Symptom Cause

Map cracking typically

occurring after 5 to 10 years

Volumetric expansion of concrete (in this

case ASR & DEF)


31/115

Symptom Cause

Map cracking occurring

anytime from weeks to years

Excessive drying shrinkage


32/115

Compare with map-cracking due to ASRwhere extrusion of

joint sealantprovides evidence ofexpansion


33/115

Symptom Cause

Map cracking typically occurring

anytime from months to years

Freeze-thaw attack (non-air-entrained

concrete that was also hit by truck)


34/115

Symptom Cause

Surface scaling occurring after

approximately 5 years

Abrasion by vehicular traffic (in wheel

path)


35/115

Symptom Cause

Surface scaling occurring after decades Water abrasion


36/115

Symptom Cause

Severe spalling of concrete

surface

Fire damage (petroleum tanker crashed

into bridge pier and ignited)


37/115

Symptom Cause

Severe erosion of concrete

occurring after years

Sewer-pipe corrosion (chemical-biogenic

attack of paste by sulfuric acid)


38/115

Symptom Cause

Spalling and disintegration

occurring after a few years

Freeze-thaw attack (non-air-entrained

concrete)


39/115

Symptom Cause

Shearing of concrete column and

spalling of concrete cover

Shoving of foundation due to expansion

of adjacent pavement (ASR)


40/115

Symptom Cause

Spalling of concrete over rebar Corrosion of rebar initiated by chlorides

(from roadway above)


41/115

Symptom Cause

Spalling of concrete over rebar Corrosion of rebar initiated by chlorides

(from unwashed sea-dredged sand)


42/115


43/115


44/115


45/115


46/115


47/115


48/115


49/115


50/115


51/115

Case of the

Ruptured Slab


52/115

Background Residence located in South Texas

Construction date unknown: estimated tobe before 1950

Owners purchased in 1992 Construction

Slab on grade

Wood framing

Stucco exterior


53/115

Observations: Owner Interview Owner discovered that no water pressure

existed on April 15, 2000 Water going through meter; meter turned off

n pr , p um er ocate ea eneatlaundry room slab.

Broke slab and found copper water supply

pipe had completely separated Pipe was repaired.


54/115

Observations: Owner Interview

Owner had found N-S crack through slabearlier, before loss of pressure occurred.

,

door to bedroom stuck. Shortly after leak was found, owner heard

loud noise and found that front of househad a severe crack and stucco had fallenoff house.


55/115

Observations: Owner Interview

Another noise was heard and crack was

was broken.


56/115

Visual Observations

N-S slab crack extending from north wallthrough house to utility

Crack was in line with location of leaklocation

Numerous other cracks in floor and walls

N S Slab Crack: Looking down on


57/115

N-S Slab Crack: Looking down on

crack after carpet removed


58/115

Location of Pipe Separation


59/115

Cut Out Section of Pipe


60/115

Repaired Water Pipe


61/115

Separation of Cabinet at Ceiling

Door Frame Planed due to


62/115

Door Frame Planed due toSticking Door


63/115

Wall-Ceiling Crack


64/115

Severe Wall Cracking on North Side


65/115

Cracking at NE Corner


66/115

Stucco Cracking at Window


67/115

Findings: Floor Level Survey

Floor levels were taken in June 2000b defendants ex ert showed a

mound in vicinity of leak. Floor levels taken by me in December

2000 were similar to those taken bydefendants expert.


68/115


69/115

LeakLeakLeakLeak


70/115

Findings: Water UsageMonth BilledMonth BilledMonth BilledMonth Billed 1999199919991999 2000200020002000

JanuaryJanuaryJanuaryJanuary 18,00018,00018,00018,000 23,00023,00023,00023,000

,,,, ,,,,

MarchMarchMarchMarch 18,00018,00018,00018,000 17,00017,00017,00017,000

AprilAprilAprilApril 21, 00021, 00021, 00021, 000 18,00018,00018,00018,000

MayMayMayMay 20,00020,00020,00020,000 26,00026,00026,00026,000


71/115


72/115

Defendant Expert Findings Plumbing leaks did not contribute to

cracking. Causes of cracking attributed to:

Differential soil movement due toseasonal climatic effects

Inadequate compaction of soil

Infrequent water pattern around house

Trees near foundation


73/115


74/115


75/115


76/115

OutcomeOutcomeOutcomeOutcome

Initially, no money offered

After my report was presented, $39,000 After some serious negotiation, $140,000


77/115

A 12-STORY BUILDING LYING


78/115

ON THE GROUND in CHINA


79/115


80/115


81/115


82/115


83/115

Heavy rains resulted in waterseeping into the ground.

The building began to shiftand the concrete pilings

were snappeddue to the uneven lateralpressures.


84/115

The building began totilt.

And thus came the eighthwonder of the world


85/115


86/115


87/115


88/115


89/115


90/115


91/115

On Piers and Still Problems


92/115

An educational building for a church was

constructed on expansive clay. The structural engineer had a soil

piers to go about 20 ft. into the clay.

Pier as designed


93/115


94/115


95/115

Pier as built


96/115


97/115

Design of Pier Foundations


98/115

When the drought broke the moistured lli f th il th l i th


99/115

When the drought broke, the moisturecaused swelling of the soil, the clay in theactive zone created skin friction on the

surface of the pier and lifted it up. But how could the skin friction uplift break

the concrete?

How much force would it take to break thepier?

How much stress would it take to breakthe concrete?


100/115


101/115

The total uplifge providec by the soil on

the pier is over 100 000 lbs


102/115

the pier is over 100,000 lbs. Had the steel been placed to the bottom of

the bell, it would not have stopped thecrack from forming but it would have keeph r k fr m nin wi .

The bell would have served as an anchorpreventing the pier from moving upward.

But this illustrates the force clay can exert

in lifting up a structure.

Foundation Solution


103/115

AlternateDesign

A f fi l f il f


104/115

A few final failures for your

viewing pleasure.

104

2.

Where does the stair go?


105/115

105

5.

How do I get up these stairs?


106/115

106

6.

Escalator for very short people


107/115

107

9.

Someone forgot about the light pole


108/115

108

11.

We need to grow taller people


109/115

109


110/115

And the winner is . . .

110


111/115

You may be the next engineering

Sherlock Holmes!


112/115

112

Does it pay well?

2001 Salaries


113/115

General Civil $73,000

Civil (Structural) 75,000

Geotechnical 68,000

Forensic 143,500

View these as relative, but they arehigher than in 2001.


114/115

Questions?


115/115

Winner: Not My Job Award

forensic engineering - causes of distress in concrete.pdf

Documents