Experimental background behind new AASHTO LRFD specifications for partially debonded strands

[摘要] In prestressed concrete bridge girder fabrication, the following four methods are commonly used to meet limitson the extreme fiber concrete tensile stress at prestressstrand release:• partial debonding of several strands near the girder end• harping some strands• adding top strands• a combination of these methodsStrands that can be harped are limited to those alignedwithin the member webs and may be further limited by thecasting bed. For some girder shapes, such as boxes, harpingis not practical. The preference for partial debonding orharping to relieve extreme-fiber tensile stress varies amongstates.1 Partial debonding may also be used to satisfy theAmerican Association of State Highway and TransportationOfficials’ AASHTO LRFD Bridge Design Specifications2article 5.9.4.4.1 requirements for splitting resistance at theends of prestressed concrete girders, which require transverse confining reinforcement sufficient to resist 4% of thetotal prestressing force at transfer to be located within h/4of the girder end, where h is the component depth. Partialdebonding reduces the prestressing force, which can potentially cause splitting at the end of the girder. In addition,partial debonding can be used to relieve the compressivestress (AASHTO LRFD Specifications article 5.9.2.3.1a) atthe end region when required.

[学科分类] 建筑学