International Concrete Abstracts Portal

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.

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.

What does an engineer do when a defective pot bearing needs replacing? This particular situation was encountered on two recent construction jobs. Several of the pot bearings on the Cline Avenue Project in East Chicago, Ind., needed to be replaced because the elastomer was extruding from the pot. On the I-285 project in Atlanta, Ga., six pot bearings were misaligned and had to be readjusted. The superstructure on both projects was cast in place prestressed concrete box girders. The performance of replacing the pot bearings required designing, fabricating, and installing temporary steel frames, performing special jacking operations, and removing and replacing the pot bearings. This paper describes the operation for both projects in hopes that the solutions illustrated herein may be used by others to help solve similar problems.

Central to the design of the Intermountain Power Project (IPP) mechanical cooling towers was the ability to configure connections between precast concrete members so that large horizontal seismic forces could be transferred between beams and girders and between girders and columns. Complicating the task of connection design were substantial thermal loads and severe environmental conditions. To solve these and related design questions, a testing program was undertaken using «-scale models of certain key joints in the structure. This paper presents a description of the testing program, a brief description of the structural system in which the joints were located, and the results and conclusions of the tests. Principal among the conclusions is the recognition that embedded metal pins used to transfer forces between discrete members must not only be carefully detailed, but they also must accommodate substantial elastic deformation at the joint if failure below acceptable force levels is to be avoided. In the IPP, this was accomplished by the introduction of a confined viscoelastic medium surrounding the pin. This simple addition to the joint configuration increased the force transferred through the connection by a factor of 2.5 to 3 while limiting deformation to acceptable values.

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.