International Concrete Abstracts Portal

The new Dumbarton Bridge is located midway between two major California Faults, each approximately 15 miles from the site. Extensive computer dynamic analysis of both soil and structure indicated that large out-of-phase movements will occur at the deck joints during a major earthquake. This anticipated once-in-a-lifetime large scale movement led to the development of an innovated low cost, but large, movement deck joint design for the over water portion. For the concrete trestle approaches over land, an energy absorbing, force inducing sol id rubber joint of standard design was employed to improve the structure performance during a major earthquake. Construction of the replacement structure paralleling the older bridge started in 1978, with the opening projected for mid-1981.

Graphical procedures are presented for optimum dimensioning of a joint-slab-sealant system coupled with material properties. PART 1 covers an approach for sealing with compression type sealants while PART 2 concentrates on molded-in-place sealants. Horizontal joint movements are emphasized in both cases. While the main emphasis is placed on concrete pavement joint sealing, the methods are also applicable to other joints, such as those in bridges or structures and even cracks. The procedures used to construct each set of curves are given so that the graphs can be adjusted for other joint or crack sealing applications. The paper also outlines areas where more work and data are needed.

This paper outlines the different approaches to road and airfield construction in the U.K. and details how this affects joint spacing, detail and sealant specification. The technical shortcomings of traditional sealant materials are discussed with particular reference to the Standards which exist in the U.S. and U.K. The introduction of the more comprehensive ASTM 3569 Standard is seen as a progressive step towards providing for the use of higher performance sealant materials for road and airfield joints. The properties and U.K. site experience for a sealant complying with ASTM 3569 are discussed.

The concept of base isolation is a natural one based on accepted physical principles. It has not, however, been readily accepted by the structural engineering profession, perhaps because the concept runs counter to accepted methods of aseismic design. In essence, a base-isolated structure is decoupled from the damaging horizontal components of earthquake ground motion by a mechanism which prevents or reduces the transmission of horizontal accelera- tion into the structure. While many base isolation schemes have been proposed over the last one hundred years, virtually all remained unimplemented until the concept became a practical possibility with the recent development of multilayer elastomeric bearings, a development which began with the design of bearings for bridges and those used to isolate structures from ground-borne acoustic vibration. This paper describes the development of base isolation and extensive experimentation on the concept carried out on the shaking table at the Earthquake Engineering Research Center of the University of California, Berkeley. Several isolation systems have been tested, including schemes incorporating handmade isolation bearings of natural rubber as well as commercially manufactured bearings. Two large structural models were used in the tests. The results from these tests have established the effectiveness of this approach to aseismic design and have demonstrated that the peak accelerations experienced by a building on an isolation system are substantially lower than those felt by a conventionally founded structure. Other mechanisms have been tested in combination with the elastomeric bearings, including a mechanical fuse in the form of a notched pin designed to fracture at a specified level of shear force and which acts as a wind restraint, and several forms of energy-absorbing device designed to provide increased levels of damping to the isolation system and which control relative displacements at the bearings. A fail-safe skid system has also been tested; this system produces a Coulomb frictional damping and in the event of earthquake ground motion far greater than that for which the bearings were designed acts to prevent structural collapse.

As earthquakes often occur in Japan, the dimensions of the substructures of bridges and their supports are mainly depending upon seismic load. In order to prevent the fall of superstructure or breaking of bridge seat concrete, the 'Substructure Specifications for Highway Bridges' published in 1968 has defined the necessary distance from the edge of a bearing to the edge of a bridge seat in proportion to span length. Various types of damage to supports resulted from the Miyagiken-oki Earthquake in 1978. In consequence of a detailed investigation, the damage found among substructures could be classified into breakage of bearings and anchor bolts, cracking of bridge seat concrete, and slight damage to supports. The authors have undertaken a series of loading tests on bridge seat concrete to confirm the safety of structures built to present specifications and to examine more effective reinforcements, and have analysed the measured data. They have thus been able to confirm the validity of the specifications and have been able to propose some effective reinforcements.