%0 Generic
%9 Master's Thesis
%A Wang, Weijin
%D 2013
%F pittir:19300
%K Prestressed concrete, Strand, Debonding, Bridge design
%T Assessment of Partial Debonding Practice for AASHTO Type Girders
%U http://d-scholarship-dev.library.pitt.edu/19300/
%X Pretensioned girders have been commonly used in bridge construction for years. However, some problems remain that hinder the further application of longer and more heavily prestressed girders. The prestressing force can produce large stresses at both the top and bottom surfaces of the girders, especially near the ends where self-weight moments are minimal. Additionally, the transfer of large prestressing forces can cause local cracking. Partial debonding of straight strands, harping strands and/or adding top strands are three common approaches to mitigating such problems. However, harping is limited to those strands aligned with the member web, and adding top strands affects the overall stress state of the section. Comparatively, partial debonding is a simple and preferred approach. The total prestress force is introduced to the member gradually, reducing stress concentrations and associated end-region cracking.  	Even so, partial debonding decreases the longitudinal tension capacity particularly when    a large number of strands is debonded. Excessive debonding, therefore, can also have detrimental effects of the flexure and shear capacity of the girder. This thesis aims to quantify the effects of partial debonding on initial girder stresses and ultimate girder capacity in an effort to identify acceptable prestressing strand debonding details.  	Two series of AASHTO Type III-VI girders having varying spans, amounts of prestressing and different debonding ratios are systematically analysed for their adherence and consistency with present AASHTO LRFD Specification requirements. The analyses use a purpose-written MATLAB program. Analytically obtained girder capacities are validated with initial design capacities from the PCI Bridge Design Manual. An individual case is presented in order to illustrate the analysis procedure. From this study, acceptable partial debonding ranges, satisfying AASHTO-prescribed stress limits, are obtained.   	Conclusions indicate that the upper limit for an acceptable debonding ratio may be increased from the AASHTO-prescribed 25% to perhaps 50%. However the results also indicate that this upper limit is a function of span length and may be greater for longer spans. In many cases no acceptable amount of debonding was found for shorter spans. Further parametric study is required to establish such a relationship and to extend the study to other girder shapes.