AASHTO WSDOT Questionnaire: Prestressed Girder Design Criteria

not been diligent with keeping ourdesign processes up. Also formany bridges it does not seem tomake any practical difference.1/23/2013lump sum methods were used sincethe lump sum methods of theStandard specifications sometimesdiffered drastically for the stressesand concrete strengths we used (atthe time these were high stresses,strengths, and prestressing levels).Personally I think the detail in thecode detailed method gives theimpression that the predictions aremore accurate than they are, andrequires information only known tothe actual fabricator for the girders,or perhaps not even then. (GIGO)The data set the code is based on isnot broad enough, and concrete andenvironmental conditions are not thatpredictable. When we have donesegmental structures the creep andshrinkage tests were not consistentenough from sample to sample to beof any use whatsoever. If precisionis required for the prediction ofmaterial properties, concrete is thewrong material.District of Columbia DOTKonjit Eskender, P.E. ProjectEngineer 202-671-4568Konjit.Eskender@dc.govFlorida DOTChristina Freeman / DennisGolabekStructures Design Engineer850-414-4190christina.freeman@dot.state.fl.usTransformed SectionPropertiesTransformed SectionPropertiesPer AASHTO LRFD Table5.9.4.2.2-1When analyzing stresses ofsimple span beams, limitstresses in accordance withLRFD Table 5.9.4.1.2-1 withthe exception that for the outer15 percent of the design span,tensile stress at the top of beammay not exceed 12 x squareroot of f'ci at release. Fortransient loads duringconstruction the tensile stresslimit may be taken as 6 xsquare root of f'c. It is notnecessary to check tensilestresses in the top of simplePer AASHTO LRFD Section5.14.1.4 - Bridges Composed ofSimple Span PrecastGirders Made ContinuousFDOT policy is to use only posttensioningto splice beamsegments within simple spansand/or to establish continuitybetween adjacent spans.Furthermore, in the design ofpretensioned beams madecontinuous by field-applied posttensioning,the pretensioning shallbe designed such that, as aminimum, the followingconditions are satisfied:A. The pretensioning shall meetthe minimum steel provisions ofLRFD [5.7.3.3.2].Do not have a policy on timedependentlosses; but followAASHTO (either a or b)Approximate Estimate of Time-Dependent Losses Per AASHTOLRFD Article 5.9.5.3 For simplesupported beams