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ACI error survey: Canadian data

A C I ERROR SURVEY

-

CANADIAN DATA

by

D.E. Allen

One hundred and eighty-eight cases of errors in concrete structurcs,

29 of which resulted in collapse and 118 in distress, d e t e r i o r a t i o n ,

excessive cracking, spalling, deflection or settlement, were collected from consulting engineers and government deparrments across Canada as

part o f a larger survey of the American Concrete Institute. The Canadian s u r v e y indicated t h a t about h a l f t h e errors o r i g i n a t e d in t h e design and the o t h e r half were due t o faulty c o n s t r u c t i o n . Most of the

collapses occurred d u r i n g construction, mainly as a r e s u l t of inadequate

formwork or temporary b r a c i n g . A number of callapses were due to

detailing errors in design. Most. s e m i c e a b i l i t y failu~es, on t h e o t h e r

hand, occurred d u r i n g use, many of which were due to a lack o f

consideration i n design of serviceability problems or of t h e e f f e c t s of

temperature, shrinkage and creep. SURVEY

T h i s survey forms part o f a l a r g e r survey organized by A C I

Commitzcc 348 across North America in an attempt to '"develop a profile

of t h e practices, a c t i v i t i e s and circumstances making up the design and

c o n s t r u c t i o n of concrete structures that tend to lead to e r r o r s . ' " Appendix A contains an explanation of the survey and the questionnaire which, far each case, obtains information about the type o f member and

construction, structural o r serviceability characteristic affected, t y p e

o f error, its d e t e c t i o n , i t s consequences and t h e _{control exercised.}

In Canada, t h e questionnaire and explanation were s e n t to

approximately 250 c o n s u l t i n g engineering firms, to a l l federal and

provincial government departments of highways, public works, and

agriculture, and to building departments of municipalities of g r e a t e r t h a n 100,000 population. The responses from various sources are givcn

an Table 1. The 188 cases were obtained from about 50 sources r a n g i n g

from 1 to 22 cases each.

The responses ranged f r o m d e t a i l e d and i l l u m i n a t i n g to vague and

occasionally ambiguous. 'Phis made it d i f f i c u l t t o analyze the information. A l s o correspondence from participants showed t h a t the

qucstionnairc was n o t as clear as it might have been.

(1) unless extra information is provided under i t c m P, i t is oftcn

d i f f i c u l t to determine what went wrong and what the errors werc. For example, a detailing e r r o r in d e s i g n would fit i n t o any h~t t h c

last c a t e g o r i e s of item E;

( 2 ) by "failure" in Item I , it i s not clear whether t h i s is meant to i n c l u d e serviceability failures in a d d i t i o n to s t r e n g t h failures; (3) the scope of t h e survey tends to exclude construction f a i l u r e s

due t o formwork failure or inadequate temporary bracing since such failures do n o t "affect the i n t e n d e d usage of a reinforced

s t r u c t u r e t 7 (see Appendix A ) , Quite a number of such cases wcrc repasted but t h e responsc may not be representative;

( 4 ) t h e scope of the survey does, ho~vcver, i n c l u d e errors that were

caught b e f o r e construction during checking, approval, drawing

p r e p a r a t i o n and building permit review. Although a large number o f these k i n d s of errors occur, only 8 of this type were reported,

presumably because records of such errors are

not

u s u a I l y made.

Therefore t h e survey does not provide representative i n f o m a t i a n on e r r o r s corrected in time.

Desplre such shortcomings the survey provides much useful

information. A n encouraging f e a t u r e o f t h e responses was t h e frankness

of many d e s i g engineers (about 401 r e p o r t i n g design e r r o r s made i n t h e i r orrm o f f i c e s . Anonymity was assured ts survey respondents since

n o names o r places were requested fn t h e responses.

The responses a r e sutmnarized in A~pendices B (buildings),

C (tanks, r e t a i n i n g walls, e t c . ) and D (bridges). Tables 2 to 7

summarize t h e information contained in Appendices B , C and D. DISCUSSTON OF RESULTS

Tables 2 and 3 provide a breakdown o f type o f c o n s t r u c t i o n and t y p e o f element affected. Table 4 g i v e s , f a r failures that occurscd,

a breakdown according to limit s t a t e , whether failure occurred during

use o r during construction and a l s o a breakdown

of

t h e kinds

of

errors

l c a d i n g to failure.

The r e s u l t s show that most c o l l a ~ s e s occur d u r i n g construction, primarily due to formnark failure or inadequate temporary bracing. A number of c o l l a p s e s occurred because of detailing error in d e s i g n . Of t h e 6 collapses that occurred during use, 2 were due to d e t a i l i n g e r r o r and 2 to

no

c o n s i d e r a t i o n of lateral load. Most serviceability

e r r o r s , i . e . , cracking and d e f l e c t i o n , occur during use and are

primarily t h e fault of d e s i g n errors. Deflection problems most o f t e n

a r i s c d u e to i n a d e q u a t e consideraZion o f deflection o r of the e f f e c t s

of d e f l e c t i o n . The category t'distressr' i.s somewhat vague b u t ranges from imminent collapse t o e x c e s s i v e cracking or displacement, C a s e s of "distress" were separated from cracking, s p a l l i n g , deflection and

settlement (serviceability l i m i t s t a t e s ] in Table 4 a n d Appendices B , C and D i f insufficient strzrctural s a f e t y was e v i d e n t i n thc responses, The o n l y 7 cases of deterioration reported in t h i s survcy a r e n o t

representative of haw widespread it i s in practice,

Table 5 gives a breakdown of a l l errors reported. About h a l f were design errors and h a l f were c o n s t r u c t i o n errors

with some

overlap

(204 e r r o r s vs 188 cases] because of multiple eTrors for a single

failure. Most design errors were classified as "analysis a n d / o r d e s i g n " or 'kaalculationT' in the questionnaire but a number of these were probably

what would be called " d e t a i l i n g " e r r o r s , i.e., inadequate consideration of connections, anchorages and reinforcing d e t a i l s . A number of

detailing errors, some of which l e d to collapse, were caused by a l a c k o f consideration of the e f f e c t s of temperature or shrinkage or o f

eccentric forces.

Morc dctailed descriptions of the errors, where t h e y were g i v e n in

t h e responses, a r e contained in T a b l e 6 . These are self-explanatory and are worth studying to understand t h e k i n d s af troubles t h a t a r i s e in

concrete structures

i n

Canada. The r e s u l t s indicate that most d e s i g n

e r r o r s , and this would include design of temporary supports or b r a c i n g

during construction, are due to misconception or f o r g e t t i n g t h e general

hehaviour of a connection, member o r stmcture as a whole and the k i n d s

o f f o r c e s that w i l l occur. As one engineer s a i d , the care we t a k e t o

d e s i g n a beam o r column is sometimes not carried i n t o the rest o f the

structure.

Nevertheless, as almost any d e s i g n e r h a s personally experienced,

mistakes will be made because of the complexity of c i v i l e n g i n e e r i n g

structures, t h e quest f o r economy and the pressure to f i n i s h t h e job. Table T gives a _{summary breakdown of t h e "control" r e p o r t e d , whcre} control refers to c h e c k i n g or reviewing of design and d r a w i n g s if the e r r o r was primarily a d e s i g n error, and to s i t e i n s p e c t i o n i f thc e r r o r

w a s primarily a construction error. T h e questionnaire d i d nor ~rovjdc

information on c o n t r o l o f fsrmuork or ternposnry b r a c i n g as this was n o t

asked and usually is not t h e rcsponsihility of t h e cngineer or architect.

F o r a nurnhcr o f o t h e r cascs, it w a s n o t clcar whether thc control scportcd p e r t a i n e d t a the errof. that was made, f o r example a detailing e r r o r in 3 p r e c a s t clement may not be t h e responsibility of t h e building engineer. The questionnaire might be improved by a s k i n g more s p e c i f i c a l l y

what were t h c control procedures and responsibilities p e r t a i n i n g to t h e e r r o r s t h a t occurred, since responsibilities change with type of

construction, nature of the s t r u c t u r e and l o c a l practice.

CONCLUSIONS

Although t h e r e are a number o f shortcomings

in

t h e s u r v e y proccdurc and questionnaire which came to l f g h r from t h e responses and correspondence, some u s e f u l i n f o m a t i o n on errors l e a d i n g t o f a i l u r e s of concrete

s t r u c t u r e s in Canada was obtained and i s summarized in T a b l e s 2 to 6.

' r s h l e h, i n particular, providcs n list of the kinds o f errors t h a t a r e causing !,trouhlr: in Canadian concrete s t r u c t u r e s .

Of

t h e 188 cases r e p o r t e d , 29 resulted i n collapses and 118 i n

distress, deterioration, excessive c r a c k i n g , s p a l l i n g , d e f l e c t i o n OT

settlement. About half t h e errors r e p o r t e d o r i g i n a t e d in the d e s i g n

and about h a l f were due t o f a u l t y c o n s t r u c t i o n . Most of t h e collapses

r e p o r t e d occurred d u r i n g construction p r i m a r i l y because of i n a d e q u a t e

formwork o r temporary b r a c i n g and a number were due to design detailing e r r o r s . Most serviceability failures, on the o t h e r hand, o c c u r d u r i n g u x e and are primarily due ta d e s i g n errors. Deflection problems were

most o f t e n caused b y inadequate conside~ation of d e f l e c t i o n d u r i n g

desi gn.

R c r c s u l ts i n d j c a t c t h a t most dcsign e r r o r s , i n c l ~ i d ing Jcs ign o f tctnlwrsry supports o r I ~ r - n c i n g , arc duc t o :r rrmi s c o n c c p t ion of or

forgcttiny, thc gcncral Ischaviour o f t h c s t r t r c t u r c a s 3 wholc o r o f

i t s nicrnkers or dctaiIs and o f thc kinds o f forces t h a t n i l 1 o c c u r .

E r r o r s leading to deterioration, howevcr, a r e not adcquatcly covcrcd i n

t h i s survey.

I t is recommended t h a t a f t e r the r e s u l t s of t h e A C I error survey have been analyzed, a new questionnaire be prepared which could be used

t o c o l l e c t f u r t h e r i n f o r m a t i a n on structural failures. There is no d o u b t t h a t t h e e f f o r t will p r o v i d e u s e f u l information for designers and code writcrs.

ACKNUIVLEDGEMENT

-

'She a u t h o r would l i k e to thank t h e more t h a n 50 r e s p o n d e n t s f o r

p r o v i d i n g t h e v a l u a b l e information on errors in concrete structures,

TABLE 1

RES I'ONSES

Consulting Engineers ( a few from Testing Labs.) 3 42

hlunici.pal Building Departments 13

Provincial Highway Departments 16

Government Public Works and Hydro Depts. 1 2

Government Agricultural Depaflments 5

T o t a l _- 188 TABLE 2 TYPE OF CONSTRUCTION Cast-in-place Construction reinforced concrete post-tensioned concrete composite construction plain concrete concrete black Precast Cmstruction ~cinforced C O I I C T ~ ~ ~ prestressed concrete 'I'A BLE 3 COk!PONENT AFFECTED S l a b Bridge deck Beam Column P i l e o r pier Wall

R e t a i n i n g , tank o r basement wall Foundation

Connection

TABLE 5

ERRORS FROM ALL CASES

Design - t o t a l --

Loading (including temp.

G

shrinkage) Analysis

G

dcsign

D e t a i l i n g

Construction - t o t a l

Formwork, bracing, supports Installation of reinforcing C o n c r e t i n g

Overloading

o r

impact

Contractor's interpretation of working drawings

'Ilsc - Overloading

-

No. Cases 103 2 2 G 0 2 5 92 2 7 3 1 2 1 8 1

a

1

TABLE 6

DESCRIPTIONS OF ERRORS

E r r o r Description

1. Design

d c t n iling error--col lapse

I n t c r ~ t l l o n d i n ~ n o t l~sol>crP y ccms idcrcd

Z;rtcral s u p p o r t n o t p r o p c r l y considcscd

n e g l e c t of temperature, shrinkage or crccp e f f e c t s inadequate s o i l investigation

h y d r o s t a t i c uplift or soil swelling

neglect o f d e f l e c t i o n e f f e c t s

p l a i n concrete

or

block walls subject to e a r t h pressure

c o n c r e t e specification (no a i r entrainment, sulphate attack)

leakage p r o t e c t i o n

overloekcd wcight o f masonry w i l l 1

avalanche forces greater than predicted

l a c k of overflow device--hydrostatic t m k pressurc neglected radial temperatuse movements i n curved

b r i d g e (cracked p i e r )

neglected tension across tapered p i e r

skew reinforcing--corner c r a c k i n g of b r i d g e deck

no i n s i d e reinforcing in cylindrical shear wall-- leakage

e c c e n t r i c loading neglected by precaster

no stirrups

s h a r p curves in prestress splice detail--cracking unstable hangar supports for T beams

detailing--bar congestion

p a n e l s bowed out at c o r n e r of building--leakage

TARLI; 6 ( c o n t ' d )

Error Description

Construction

formwork failure--collapse

t h a w i n g of ground below mudsills--collapse

inadcqu;ltc tcmporasy bracing-- col l a p s e

overloading rlrrrin~ construction

impact duri ng c o n s t r u c t i on

cnncrctc m i x f r o z c n concrete

i nadcquate chair supports f o r reinforcing

wrong stcel

settlement or s l i d i n g due to improper construction methods

N o . oI'

(:EISCS

Misc.

unbalanced construction loads--wharf caisson cracked

s l i d i n g bearing concreted i n

wooden pegs left in concrete--leakage in waffle slab

mud i n p i c r s h a f t

w a l l form 1/3 rcrluircd thicknc-ss

h l o c k w:i l l form not b r ; ~ c c d against concrctc pressure

o l d concrcte surface n o t clcaned--crack duc t o bond failure

r e i n f o r c i n g placed u p s i d e down

overexcavation o f ground intended t o prevent sliding f r o s t penetration below f o o t i n g reduced sail s t r e n g t h contractor substituted bearing materials--corrosion flying forms not anchored--flew off

i n a d c q u a t c temporary f a s t e n i n g of p r e c a s t panel

contractor l e f t o u t p o s t tensioning anchor stirrups no e r c c t i o n b r a c i n g betwccn box g i r d c r s

TABLE 6 ( c o n t W)

Error Description

3 . Misc.

overloading during use ice formed i n bolt sleeves

concrete or anchorage failure d u r i n g p o s t tensioning

soil erosion due t o watermain leak

C o n t r o l Yes Spot check None Unknown TABLE 7 CONTROL Failure Occurred Failure Prevented No. of Crr s c s -- TOTAL

APPENDIX A

Survey of Errors

in

t h e Design-Build Process

(Explanation E Questionnaire) A C I Committee 348,

Structural

S a f e t y

1975

PURPOSE

This survey i s an attempt to develop a p r o f i l e of those p r a c t i c e s ,

activities, and c i r c u m s t a n c e s making up t h e d e s i g n and canstruction of concrete structures that tend to lead to errors. The idea behind t h i s

survey is not .to call attention to any p a r t i c u l a r peTsons or groups

involved in concrete construction by publishing details of an error that they made, nor to obtain a statistically valid sample. Rather it is the sincere hope of A C I Committee 348, Structural S a f e t y , t h a t the

presentation of an objective sampling of the cirtumstances behind given i n s t a n c e s of error wauld be h e l p f u l to those ACI members involved in

t h e design-build process; this idea is, in fact, part of the mission of

our committee.

SCOPE

The survey scope encompasses design or construction errors of a serious enough n a t u r e as to affect t h e _{intended usage of a reinforced}

concrete structure.

The

usage of t h e structure could have been a f f e c t e d

with r e g a r d s t o i t s structural safety or its serviceability. Errors

a f f e c t i n g only appearance are not being considered in this particular survey,

The survey, hopefully, covers a l l phases of the design-build process so t h a t not only architects, engineers, and c o n t r a c t o r s , b u t

a l s o reinforcing bar detailers, building officials, and many o t h e r s may

c o n t r i b u t e t o it. Errors caught before construction are included. RESPONSE

In order to avoid duplication or incompleteness, respondents should confine themselves to i n c i d e n t s of error o f which t h e y possess

first-hand, complete information. A respondent may cover as many

separate i n c i d e n t s as he wishes by xeroxing the survey q u e s t i o n form, u s i n g one form for each error. The authors are aware t h a t it may have been a combination of circumstances that l e d t o a detrimental situation and have attempted t o structure t h e survey f o r this possibility.

Anonymity is assured f o r survey respondents since n e i t h e r name,

title or b u s i n e s s a f f i l i a t i o n of t h e respondent n o r geographical location

of t h e structure involved are required. Furthermore, survey r e s u l t s will

h e grouped so that no particular incident will be d i s c e r n i b l e .

T f you wish to make s i g n e d comments on t h e q u e s t i o n n a i r e , p l e a s e

send separately to Chairman, ACI 3 4 8 , c / o American Concrete Institute.

SURVEY

QUESTIONS

(Place d in the appropriate b l a n k s )

A

.

The structure o r element affected was: Bridge or building foundation

...

wall f o o t i n g 1

..

column f o o t i n g

...

2

...

drilled pier 3

...

concrete-filled steel shell pile 4

...

p i l e cap 5 Below g r a d e s t r u c t u r e basement wall

...

G

...

tank wall

...

7 bridge pier

...

8 grade beam

...*...

9 r e t a i n i n g w a l l

..

...

10

Compress ion member u n d e r a x i a l load only

...

I I

...

under axial and flexural loading 12 compression ring

...

13 shear wall

...

14

Flexural member interior location

...,

15 spandrel location

...

16

...

cantilever 17 F l o o r o r roof system

...

bridge deck 18 one-way s l a b

...

19 two-way s l a b

...

20 joist-girder system

...*....

21

...

two-way j o i s t (waffle) system 22 flat s l a b

...,...

23

...

f l a t plate 2 4 composite concrete s l a b with steel beams

.

25 s h e l l

...

26

kliscellaneous elements c o n n e c t i o n or j o i n t

...

27

...

opening in a slab. wall or beam 28 s l a b on grade or pavement slab

...

29

B

.

The structural characteristic affected was: tension in r e i n f o r c i n g

...*...

1

...

compression in r e i n f o r c i n g 2 tension

in

concrete

...

3 compression in concrete

...

4 bond

o r

anchorage

...

5 b e a r i n g

...*..

6 beam shear

...

7 punching shear

...

8 t o r s i o n

...

9

C

.

The serviceability characteristic principally affected: settlement

...

...

1 live load d e f l e c t i o n

...

...

2 creep d e f l e c t i o n

...

3 vibration

...

4 cracking

...

5 spalling

...

6 leakage

...

7 deterioration

...

8 other. specify

...

9

D

.

The type o f construction involved was: cast-in-place concrete * with deformed bar reinforcing

...,...m...

1

precast concrete with deformed bar r e i n f o r c i n g

...II.

..

2

precast. pretensioned concrete

...

3

precast. past-tensioned concrete

...

4

cast.in-place. post-tensioned concrete

...

5

concrete slab composite with s t e e l beams

...

6

concrete masonry units

...

7

E

.

71c crror occurred d u r i n g t h c design phase. spccifical l y : dcsign load selection

...

I analysis and/or design

...

2

calculation

. ...

3

structural working drawings (dimensions. schedules or details)

...

4

re para ti an of shop drawings

...

5

F

.

The e r r o r occurred during the construction phase. specifically:

contractorts interpretation of working

d r a ~ ~ i n g s

...

1 installation of f o m i n g / s h o r i n g

...

2 installation o f r e i n f o r c i n g

...,..

3 cancretc mix

...,,.

4 c o n c r e t i n g procedures

...

5

...

concrete c u r i n g and p r o t e c t i o n G form rcmoval and/or r e s h o r i n g

...

7

G

.

Thc error was dctccted by: t h e architect

...

1

t h e d e s i g n e n g i n e e r

...*.

2

t h e shop drawing prepaxor

...

3

the building o f f i c i a l

...*...

4

t h e contractor

...

5

o t h e r . s p e c i f y

.

...

6

H

.

The e r r o r was detected during: design

...

1

b i d d i n g

...

2

building permit review

...

3

shop drawing preparation

...

4

construction

...*..

5

occupancy

...

6

I

.

Consequences of t h e e r r o r : Would have been. i f not detected in time f a i l u r e

...

1

distress

...

2

reduction in s t r e n g t h

...

3

r e d u c t i o n i n serviceability

...

4

limitation of usage

... ...,,....

5

required remedial work

...

6

Actually were f a i l u r e

...

7 distress

..

...*..n.*.

..

8 reduction in strength

...

9 reduction in serviceability

...

10 l i m t t a t i m of usage

...

I I required remedial work

...

12

J. The a r c h i t e c t l e n g i n e e r review-check system o f design and u o r k i n g

drawings consisted o f :

detailed review of calculations and drawings. 1

spot check of both calculations and drawings. 2

spot check o f drawings o n l y

...

3

no check er review..,..

...-,...

4

respondent doesn't know

...

5

K. Architectlengineer review-check system af shop drawings consisted o f : a11 details, including dimensions

...

X general review for conformance to concept only 2 no check or review. . . . l . . . 3

respondent doesn't know..

...

4

L. S h o ~ drawings f o r t h e s t r u c t u r e were reviewed by the following part i e s _: t h e architect

...,...,.*.-....-.-.-....*..

1

t h e e n g i n e e r

...

_. 2

the c o n t r a c t o r

...,..*...-.-...-...+....

5

M. ArchitectJengineer construction phase involvement f o r the s t r u c t u r e c o n s i s t e d o f : d a i l y site visits . . . , . . . - . . . - . I , It weekly site visits

...

2

no site visits

...-...

3

full-time architect" representative

...

4

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APPENDIX C: A C I Error Survey

-

Canadian Data: Tanks, Retaining Walls, e t c . Construction design--drawings rnents neglected struts amikted during c o n s t . flow device