Behaviour Of Unbonded Post- Tensioned Segmental Box Girders With Dry Joints
Authors:   ,   Cork Institute of Technology, Matson Michael 
Published: September 2024

"The primary objective of this thesis is to examine the capacity of shear keys used in dry jointed precast post-tensioned segmental box girder bridge construction. The use of dry joints, in lieu of the more traditional glued joints, is becoming more popular in climatically suitable countries. The time and cost savings achieved using this construction form arc significant, due to the economies of scale involved. The shear capacity of dry jointed keys is calculated using a number of available formulae. However, in previously published papers, significant differences have been noted in the results obtained from these formulae, deeming further investigation necessary. As part of this thesis, a program of laboratory testing and finite clement modelling was developed to decipher which formula is most appropriate for use. This report firstly looked at the various aspects of precast segmental bridge constmction, from design to construction stages. Techniques and methods used in the casting, storage and transportation of the bridge segments were examined. Erection methods utilised are also detailed and the factors influencing the final choice discussed. A comprehensive literature review was then undertaken on a number of relevant published papers. Following this, formulae used to calculate the capacity of shear keys were described and detailed, with specific reference to the use of dry joints. These formulae were used later in the report on a web section of typical dimension. Having completed this, a program of laboratory testing was undertaken on 4 no. concrete specimens. Each specimen comprised of 2 no. segments, with full scale shear keys, match cast against each other, representing the web section of a typical box girder. These specimens were then prestressed together and laterally loaded to failure, to determine their shear capacity. Relative horizontal displacements, between the two segments, were also recorded at regular load intervals and load-deflection graphs plotted. Finite element models of the laboratory specimens were then developed. The laboratory tests were used to ensure that these models were correctly calibrated. This was achieved by comparing the final failure loads and the crack/crush patterns of each. This enabled results obtained from future finite element models to be presented with a greater degree of certainty. Following this, an Excel spreadsheet was written capable of calculating the capacity of shear keys in accordance with each formula examined. This spreadsheet enabled variable parameters, such as web width, key dimensions, concrete strength and applied prestressing force, to be easily altered. Finally, this spreadsheet was used to calculate the capacity of a section of box girder web, with shear keys of typical size and dimension, in accordance with each formula, for a range of applied prestressing forces. The capacity of this section was also determined using a finite element model. All results, including those got from the laboratory tests, were graphed for easy comparison. The formula deemed to most closely represent the results got from the finite clement modelling and laboratory testing is suggested for use."