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Though a tiny dot on the map of the world, Hong Kong has one of the highest and fastest growing vehicle densities in the world. There are only 1280 km of roads in this city, but vehicles number more than 300,000. Consequently, the roads are severely congested and, in spite of traffic management schemes of traffic light signals and one-way streets, many locations are so jammed that grade separation has had to be introduced by means of flyovers, elevated highways, and similar structures. Such structures inevitably incorporate many movement joints that have proven in practice to be more troublesome than any other components. The problems experienced with movement joints led to careful scrutiny of movement-joint performance and to a series of different joint installations being made for the purposes of comparison, with the object of providing information for the design, construction, and maintenance of future joint installations. This paper describes the types of joints used in Hong Kong, including their performance, and makes recommendations for specifying movement joints.

In past decades, several types of bridge joints have been installed in Belgian bridge decks. These joint types behave very differently in time, and the lifetime of a bridge joint is determined by numerous interacting factors. Because of the increasing maintenance costs and the difficulties encountered during the repair of these vulnerable structures, a research project on bridge joints was started in 1980 at the Belgian Road Research Center. The objectives of this research are the basis of the present article. These objectives were originally based on the results of visual inspections of bridges, and they have been continuously modified during the past five years. The following topics are addressed: the relationship between the roughness of the road in the vicinity of the joint and the resulting dynamic amplification of traffic load; the movements (both horizontal and vertical) produced at the joint by heavy trucks; the determination of stresses in the anchorage of expansion joints and buried joints by means of computer programs and model studies; the calculation of the lifetime of buried joints by combining displacement spectra resulting from the deformation of the bridge, the Wholer curve of the mix constituting the joint, and the particular stress distribution in the joint; and the application of research results in practice.

The following points guide an engineer in the selection of expansion joints. First, one should take into consideration that there are two different approaches in the field of highway expansion joints--that of companies specializing in waterproof joints (generally elastomeric) and who have extrapolated their technique for applications under traffic conditions and that of construction engineers whose main concern is to protect this vulnerable section that constitutes an opening especially introduced to allow freedom of movement. Second, expansion joints should satisfy a list of criteria: stability, ride, low-noise level, waterproofness, low maintenance costs, and durability. Solutions that more or less satisfy the essential criteria can be considered either as the good qualities or the defects of an expansion joint system. The resolution of one requirement is often made to the detriment of another. The real needs must therefore be clearly defined. Third, a description of the principals selected among a solution presented and that constitute a joint system fitted by prestressing should be offered. In summary, an expansion joint must be both simple, robust, and installed absolutely correctly.

In Denmark, all important concrete bridges are waterproofed and asphalt paved. Joints in bridge surfacing are important details as leakage often starts along the edges and the expansion devices. Practice has shown that with a proper sealant, joint leakage is much more apt to occur between the sealant and the joint sides than due to a break in the sealant. A low elastic modulus of the sealant will reduce the tension between the sealant and the joint sides and is consequently an important property. A suitable primer should always be used, and the shape factor of the joint should be restricted to about 1:1. The present Danish specifications for joint sealants and primers are quoted and discussed. Important details of the workmanship are also specified. Measurements of typical movements in bridge surfacings are reported. Research concerning new specifications is presented. An elaborate device for testing the deformation properties of joint sealants at different temperatures down to -20 C has been constructed. It is intended to use the device to study the influence of such characteristics as aging, water, alkali, and joint geometry. It is expected that the investigation will result in new and more relevant specifications and easier control procedures. The research is directed toward bridge joints, but the results are applicable to joints in concrete roads as well.

Diaphragm walls owing to their method of construction are discontinuous structures. A new technology for the formation of joints between panels has been developed. This new process allows for the construction of diaphragm walls with mechanical and watertight continuity. Within the last 30 years, diaphragm walling has become a construction technique frequently used for the design of major underground works, often in waterbearing grounds, e.g., quay qalls, excavation supporting, and shaft lining.