International Concrete Abstracts Portal

A concept of pot bearing rotation and its relation to vertical load, rotating moment, and eccentricity are examined. At certain low load and rotating combinations, uniform piston contact with the elastomer or the upper element will not occur, resulting in an uneven load transfer and increased eccentricity. Factors that may be traced to this phenomenon are presented. The rotating moment expression used contains an empiric "alpha factor" variable with three known values. Derived from early rotation tests, this "alpha" is based on the diameter-to-height (D/h) ratio of the confined elastomer. An expression for "alpha" was formulated to provide unique factors for each case. Eccentricity and eccentric neutral stress points were computed in all cases. Critical loads are indicated where piston contact loss is possible. This occurs when the eccentricity is less than the eccentric neutral stress point and at the maximum kern of the inner pot section. Piston separation here is likely, due either to the extreme eccentricity or the confined elastomer's resistance to deform at low pressures. Its importance should not be overlooked as future studies may provide substantiation. However, in assuming static equilibrium, complete piston contact is assured so long as the eccentricity remains within the kern of the pot section.

Tests for four circular segmented tunnel linings are described. Two single-ring specimens had the conventional flat joint and the tongue-and-groove joints at the key segment. The three-ring specimens used a staggered arrangement and had circumferential joints with and without tongue-and-groove configurations. The load was applied from the top and the side wall on the single-ring specimens. The measurements of overall deformation, joint slip at the key segment, and joint opening were used in studies of waterproofing joints of several linings. The type of joint configurations that has been proven satisfactory is the key segment with the tongue-and-groove for the longitudinal joint. This selection is based largely on economic factors. Documented field cases observed in the underground excavations carried out for the electric utility tunnels in the urban areas were presented to investigate the applicable watertightening joint of segmented linings.

The Texas State Department of Highways and Public Transportation has developed through laboratory testing a material specification for elastomeric concrete and for use as expansion joint nosing material. The elastomer is specified by physical properties such as tensile stress, elongation, bond strength, and compressive resilience. Physical properties are determined after short-term curing and long-term oven aging. To date, approximately 4000 ft (1219 m) of joint has been placed according to this specification. Although the oldest installation is only one year old, the performance of the joints has been excellent. An experimental installation, scheduled for August 1986, includes four different elastomeric concretes in approximately 1500 ft (457 m) of joint. The performance of these joints will be correlated with physical property testing and used to improve the existing specification.

The background and development of the specialized equipment required for the proper preparation and installation of hot-applied joint sealants is reviewed. The need to use specially designed melter-applicators is embellished. Many of the disastrous field problems resulting from failure to use approved equipment, as well as the appropriate sealant, are discussed in detail. The evaluation of field preparation and application equipment for hot-applied joint fillers and sealants is set forth, from hand pots and so-called tar of roofers' kettles to agitation, recirculation, and extrusion systems of today's melter-applicators. The required specialized laboratory test equipment is also discussed as is the correlation of test results with respect to field installation temperature parameters. Attention is also given to the proper selection of different types of sealants by basic constituents for compatibility with pavement type and previously used sealants and fillers.

The principal cause of deterioration to the superstructure and substructure are the expansion joint systems. Bridge engineers and maintenance personnel have long advocated longer spans with fewer and maintenance-free expansion joints. With longer spans, expansion joints have become greater. In 1978, the New York State Department of Transportation invited manufacturers of six different types of modular expansion systems to install their devices on a new structure crossing the Hudson River at Troy, N.Y. This paper is an up-to-date condition survey of the performance conducted on a regular basis of the six different modular expansion joints.