A major rehabilitation of the reinforced concrete approach viaduct to the Pattullo Bridge has been successfully completed over the last nine years. A condition inspection revealed that extensive cracking had taken place over the years,especially at the bridge girder ends due mainly to frozen bearings. A program of bearing replacement was carried out at all girder ends along with seismic improvements and general concrete repairs. An elaborate falsework system was designed which was easily adaptable to the varying geometry along the viaduct. Load transfer to the falsework to implement the rehabilitation was achieved using a hydraulic jacking system. The work was carried out in a series of six contracts and the project was completed without any bridge traffic closures during the assignment.

A design method has been proposed that considers the interaction of the superstructure with the abutments. The superstructure sways freely under moderate intensity ground shaking. At this stage, the piers are considered to be taxed at 70 percent of their capacity. Under the design earthquake, the piers hinge and bang against the abutments. The soil passive resistance behind the abutment back wall is mobilized, which is considered as elastic springs in the computer model. The sway of the superstructure is carefully monitored to limit the displacement of the abutment to avoid stability problems. The maximum resistance of the soil behind the backwall is also limited. Since the maximum longitudinal sway is known, the demand on ductility of the pier is quantified by plastic analysis. This demand is checked against the realistic thrust-moment-curvature relationship of the pier. Iterations may be performed to satisfy the constraints and achieve acceptable results.

Soldier Field, located on Chicago's lakefront, is one of the most historically significant buildings in the city. Opened to the public in 1924, the stadium features classic Roman colonnades above the main stands on each side of the playing field. Sixty years of exposure to harsh northern climate took its toll on the reinforced concrete structure. The tread-and-riser system was deteriorating due to reinforcement corrosion and freeze-thaw exposure. Also, ground water fluctuations accelerated the deterioration of the highly permeable concrete at the base of the columns. A major rehabilitation effort was started in the early 1980s. The concrete frames were strengthened and the stands were reinforced with an overlay of latex-modified concrete. The overlay system was designed to support its own weight, the weight of the original stands, and the expected live load. The underside of the structure was repaired with shotcrete. Circularly reinforced collars were installed at the deteriorated column bases, and the existing wood pile foundations were tested to verify their capacity to support the additional dead load. The repairs are holding up very well after 10 years of service.

The Hong Kong Housing Authority's annual maintenance budget currently runs at around US$140m, approximately US$13m of which is expended on patch repairs to spalled and delaminated concrete, totalling 65,000 mý per annum. In recent years, a large number of different proprietary brands of repair material, both prebagged and site-mixed, have been used and new materials are continually being introduced. Two basic problems have been encountered: determining the suitability of materials for various applications, and controlling the preparation and application of repair mortars. Manufacturers of proprietary materials tend to use different tests and standards against which to evaluate the performance of their products and, with regard to the assessment of the performance and quality of repairs as applied, there are presently very few internationally accepted testing standards. The Housing Department has, therefore, developed its own series of tests and administrative procedures for classifying concrete repair mortars and controlling the quality of repairs. These include prequalification tests and routine quality control tests required to be undertaken by materials suppliers, the establishment of an approved list of materials, field trials undertaken at the commencement of repair contracts, and quality control tests undertaken during the contracts. This paper describes the background to and development of these procedures. Avenues for further development are also discussed.

According to the trade literature, the determinations of location, direction, and the cover thickness over a single steel bar in concrete are relatively easy and reliable from a magnetic measurement if the bar diameter is known. The estimation of the bar diameter is also possible if the cover thickness is known, although these results are less reliable. Only recent publications suggest double measurements from which both the cover thickness and the bar diameter can be estimated without previous knowledge of either of them. Unfortunately, the accuracy of diameter determination remains unimproved even with these methods. This paper attempts to present the further improvement of the magnetic determination of bar characteristics. The basic idea is to combine a magnetic device with a computer that calculates, without any previous knowledge about the bar: 1) the thickness of the concrete cover above the bar and, 2) the diameter of the bar. Preliminary data also indicate that distinction can be made whether the tested area is above a single bar or multiple bars, although this is not discussed in this paper. Experimental data obtained on laboratory specimens illustrate the new method.