AVOIDINGTOLERANCETRAPS
WardR.Malisch TechnicalDirector
Whatisatolerance What is a tolerance
Permittedvariationfromaspecified Permitted variation from a specified dimensionorlocation
"No building is ever plumb, level, straight, No and true to dimension – that is, not exactly."
JohnR.Nichols,1940
Thebestistheenemyofthegood The best is the enemy of the good
Best Perfec ction‐‐‐‐
Good
Effortandcost‐‐‐‐‐‐‐‐
Inthebeginning… In the beginning…
Nichol spaperwasthe Nichol's paper was the firstattempttoprovide p p tolerancevaluesfor reinforcedconcrete construction.
Injudginganyproposed In judging any proposed tolerance,however,he tolerance, however, he suggestedthattwo gg q questionsmustbeasked
Firstquestion First question
Isitnecessaryandsufficienttobuild Is it necessary and sufficient to build withinthetolerancesothestructure…
Hasasuitableappearance Satisfiesthepurposeforwhichitwaserected Isstructurallysafe y Accommodatestiling,plaster,orotherfinishes
Secondquestion Second question
Canthetolerancesbe achievedreasonably;that hi d bl th t is,withoutunjustifiedcost is without unjustified cost
Nicholsthensuggestedtolerancevaluesfor propertiessuchas: Memberdimensions..minus1/4,plus1/2in. Plumbness……………………1/4in.inanystory Reinforcingbarplacement…1/4in.vertical g p / Coveroverreinforcement (under1ft.memberthickness)..1/4in. (under 1 ft member thickness) 1/4 in (over1ft.memberthickness)….1/2in. Butheaddedthatdiscussionofhistolerances wouldbeneededbeforetheywereadopted asanACIstandard
InthediscussionoftheNichols In the discussion of the Nichols paper,wefindthefirstinstanceof intelligentdesignbeingdebated inascientificmeeting.Thedebate in a scientific meeting The debate wasrelatedtothe1/4in. / tolerancesonpositioningof reinforcement. i f t
1st engineer: Does that ± in bar engineer:Doesthat± in.bar placementtoleranceapplicable beforeoraftertheconcreteis placed Becausethebarsmovea placed Because the bars move a bitwhenworkerswalkonthem. Nichols:Thefinalpositionofthe Nichols: The final position of the barisallthatmatters.

下一页