Performance and management of post-tensioned structures

Post-tensioned structures have performed well for some 60 years and justified their early promise. There have, however, been instances of brittle fractures of cold-quenched steel experienced in Germany, cracking and deflection of cantilever bridges, defective grouting, and corrosion of the post-tensioning steel in most countries. These problems have been responsible for isolated failures of various structures including buildings, walkways and bridges. The embargo on new construction of post-tensioned bridges in the UK, placed by the Highways Agency in 1992, had a salutary effect on the industry and led to a determined effort to improve standards. The resulting research and development showed that one of the main shortfalls has been caused by the use of unstable grouts coupled with standard performance tests that have been inadequate. The instability has led to bleeding and formation of voids which expose the steel strands to potential corrosion. The work has led to the development of improved formulations of grout and more discriminating performance tests. Also, it has been shown that the quality assurance of the grouting operations can be improved by use of equipment such as flowmeters to measure the rate and quantity of grout injected into each duct, and pressure sensors to identify blockages and leaks. With these improved procedures there should be no reason for defective grouting in the future. For the management of existing structures, there are suites of methods to enable post-tensioning to be inspected, monitored, refurbished, repaired and strengthened.