Robert D. Hanson

Viscoelastic Mechanical Damping Devices Tested at Real Earthquake Displacements

Experimental steady-state hysteretic characteristics of ten direct shear seismic damping devices (DSSDs) are presented. The devices were tested over a range of frequencies and displacements chosen as representative of building responses during moderate to severe level earthquakes. Three different damping materials, produced by 3M Corporation and Lord Corporation, were used in the devices. Excitation frequency, strain amplitude, damping material initial temperature, temperature change over the test duration, cyclic energy dissipation, and damping material moduli (including complex shear, storage and loss moduli) are reported for all tests performed. The influence of frequency, displacement amplitude, temperature, and cumulative energy absorption on the damping material mechanical properties and hysteretic stability are examined. Methods by which material moduli can be used to design damping devices for specified spring stiffness and equivalent viscous damping are presented. Limitations of the hysteresis model, test results, and design methodology are discussed.

Supplemental damping for improved seismic performance

The results of several studies on the effects of supplemental viscous damping on the response of elastic and elasto-plastic single-degree-of-freedom systems are used to provide insight to the effects of large damping on the earthquake response of buildings and the interpretation of studies reporting the equivalent damping and increased stiffness characteristics of specific types of supplemental energy dissipation devices. Extension to multi-story buildings is discussed briefly. Conversion of the properties of viscous, viscoelastic, friction, and metallic yield device characteristics to equivalent viscous damping are proposed. Specific recommendations for the incorporation of the effects of supplemental energy dissipation devices in the code design process are given.

Evaluation of Reinforced Concrete Members Damaged by Earthquakes

A number of building authorities have included or are proposing to include loss in lateral capacity of the structural system caused by earthquake damage as a basis for requiring specific degrees of seismic repair and upgrades of the damaged members or of the entire structural system. Attempts have been made to apply this criteria through the size of cracks in reinforced concrete walls. This paper reviews experimental results which demonstrate that size of wall crack is not directly related to a reduction in wall capacity. The effectiveness of various wall crack repair techniques on restoring wall characteristics is discussed.

Control Issues for Pseudo Dynamic Testing

The most realistic method to asses the inelastic response characteristics of a test structure, e.g. a building, subjected to seismic ground motions would be to test the full scale structure on a shaking table. Clearly this is not possible with current experimental facilities, nor will it ever be practical for most large structures. Several alternative approaches have been developed. For example, shaking table tests of reduced scale structural models can be used. The shortcomings of such reduced scale tests are obvious; it is sufficient to point out that many structures cannot be adequately represented by reduced scale structural models [1].

Educating engineers for rebuilding rather than building

The subject of this New York Conference on the Infrastructure: Maintenance and Repair of Public Works is timely. The broad-based view represented by the speakers which covers government policies, public financing, influence of maintenance and repair on building codes and standards, and the recognition that reconstruction requires different technological innovations is particularly pertinent to this session on civil engineering education and research. The purpose of this paper is to discuss what civil engineering educators and researchers must do to prepare new engineers for these new challenges. The United States has had a relatively unique position in the technological development arena. Many of our cities and public works were initiated and expanded while the new technologies were being created and improved. Our transportation systems evolved through waterway systems including canals, railroads, auto and truck traffic on dirt roads, and paved highways and expressways, and by air. In almost all of these cases the newest of the technology was applied as additions to or replacements for existing systems. Many parallels exist for water supply and waste treatment. The same is also true for our buildings. The evolution of building technology from timber, stone, and brick through iron, concrete, steel, aluminum, and prestressing has in general left us with a broad supply of building types and materials. Historically, when new facilities were needed the old facilities would be demolished and replaced by newer, bigger, better facilities. Design analysis has had a similar history. Each step of the evolution from simple design analysis procedures through the more complex interconnected systems designs now common followed the development of new analytical capabilities. Even though we now need large digital computers to effectively use our analytical capabilities for the particular problem being studied, we should not forget that earlier designers faced the same decisions that we do now. Many public officials and engineers, not too many years ago, firmly believed that the results of a computer simulation provided the answer for their decisions. At the present time there is a growing recognition that computer modeling and input data are not sufficient to provide the final answer in all cases. However, reevaluation of our past experiences based on current knowledge is necessary. Interaction between our real nonlinear, nonelastic,