Abstract
This thesis descibes the development of an indirect stressmeter for measuring the in-situ stresses in concrete bridge structures - especially bridge decks. These stresses are invariably required to be known in the case of prestressed concrete bridges to determine whether the level of stress is as expected based on the original design, or whether there has been a significant loss of prestress for one reason or another. The technique described is based on the stress relief principle and involves producing a discontinuity in a member under stress by drilling a hole. This disturbs the stress field in the vicinity and changes can be measured by the use of an instrumented inclusion which is bonded into the hole and then overcored. The annulus of concrete within the core is stress relieved and the inclusion is stressed. Strain gauges within the body of the inclusion measure the associated strain changes from which the original stress in the concrete can be determined. The design; fabrication; testing and use of the device are described. The device consisted essentally of a solid steel cylinder assembled from discrete sections with rosette strain gauges bonded to diametrically opposite faces of each section. Finite element simulations were carried out to aid understanding of the behaviour of the inclusion in concrete, and the device was used in practice to measure the stresses in a local prestressed concrete bridge deck. The inclusion technique has been proved to be a viable way of measuring stresses in existing structures but further research is recommended in order to refine it and to improve its reliability.