Application Of Measures About Temperature And Shrinkage Crack Control For Super-long Concrete Frame Structures

More effectivedesign and constructionmethods are needed, to control the cracks inlong concretestructures, especially for the rapidly increasing over-long concretestructures without traditional seams, like large commercialcomplexes and airports.As tolong concreteframe structures with redundant constraints,the slabs may crackforlargetensile stress, raised bythe actions of shrinkage and thermal effects.In this study by finite element software SAP2000, a series of simulation analysis ofeffects caused by temperature and shrinkage have been done, based on over-longconcrete frame structures whose length range from300m to500m, and thedistributioncharacteristics of internal forcesandstress have been summarized.Then the crack control measures, such as using shrinkage-compensating concreteor prestressed technology, adopting appropriate layout ofpost-cast strip and otherconstruction details, have been examined.①The compensation effect of shrinkage-compensatingconcrete has been analyzed,and its’ application principles for longconcrete structures are summarized.②Intermsof prestressedtechnology,designprinciplesof the pre-stressedtechnologyin the over-longstructure have been summarized,the minor axialforce ofthepre-stressingeffect has been analyzed, and coefficientranges of the minor axialforcehave been proposedin the frame structure.③A new layout of post-cast strip has been proposed, by taking tensioned tendoninto consideration, and been evaluated based on the analysis of a model structure.④Performance of the measure which sets several row of directionally slidingbearings in the ends of the structure has been examined through another modelstructure.What’s more, a complete design steps for the over-long concreteframes have beenproposed, and validated though the analyses of a500m long modelstructure.Base on the analyses above,the following conclusions can be drawn.①With the action of uniformcooling effect, the distributions ofinternal forcescaused by temperature in the300m to500m long concrete structures are similar. Fromtheendsto the middle of the structure, the nodedeformation and max internal forcesorstress of slabs and columns decrease, while the averageinternal forcesandstress of slabsincrease.The max tensile stress ofcolumns, beams and slabs appear at the bottomsection ofthe edge column, thesection ofedge beamnear the column, thesection ofthe axis ofsymmetryin the structure, respectively. The decrease of effects caused by temperatureandshrinkage in multi-frames, are significant on first two stories and can been ignoredon above stories.②When design the prestressed tendons, thelosses of pre-stress should beconsidered,but alsothe adversely effect of the added axis force should be taken intoaccount. Tensioningtendons can provide stronger pre-pressure effects with the help ofappropriate layout of post-cast strip, andthe added axis force can be reduced.Thus, thenew principles of layout of post-cast strip can be proposed, which are: the first structureshould be divided with long and short units to minimize the spans of prestressedtendons in each stages, and second, the tendons in the middle of the structure should bewith few spans.③We know that it was reducedin the largeramplitude at the ends of thestructure.The more was the lower about weakeningeffectofthe thermal stress tomiddleof the structure.setting several row of directionally sliding bearings in the ends of thestructure, can reduced the shrinkage and thermal effects significantly, while with moreclose to the middle of structure the reduced amplitude becomes more smaller.④A510m×150m concrete frame mode that adoptspre-stressedtechnology and iswith post-cast strip and directionally sliding bearings set, designed by the proposedlongstructuraldesign approach, can achieve thecrack control objective which suggeststhat the proposed design approach for500mlong concreteframes is feasible.