Extension of direct displacement-based design methodology for bridges to account for higher mode effects

An improvement is suggested to the direct displacement-based design (DDBD) procedure for bridges to account for higher mode effects, the key idea being not only the proper prediction of a target-displacement profile through the effective mode shape (EMS) method (wherein all significant modes are considered), but also the proper definition of the corresponding peak structural response. The proposed methodology is then applied to an actual concrete bridge wherein the different pier heights and the unrestrained transverse displacement at the abutments result in an increased contribution of the second mode. A comparison between the extended and the 'standard' DDBD is conducted, while further issues such as the proper consideration of the degree of fixity at the pier’s top and the effect of the deck’s torsional stiffness are also investigated. The proposed methodology and resulting designs are evaluated using nonlinear response-history analysis (NLRHA) for a number of spectrum-compatible motions. Unlike the 'standard' DDBD, the extended procedure adequately reproduced the target-displacement profile providing at the same time a good estimate of results regarding additional design quantities such as yield displacements, displacement ductilities etc., closely matching the results of the more rigorous NLRHA. However, the need for additional iterations clearly indicates that practical application of the proposed procedure is feasible only if it is fully 'automated', i.e. implemented in a software package

334-3313 (in the Washington metropolitan area); Internet www.nap.edu.

and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported by the National Institute of Standards and Technology under contract No. SB134106Z0011. The opinions, findings, and conclusions or recommendations contained in this document are those of the authors and do not necessarily reflect the views of the National Institute of Standards and Technology

Volcanic Eruptions Repose, and Their Unrest, Precursors, and Timing

Volcanic eruptions are common, with more than 50 volcanic eruptions in the United States alone in the past 31 years. These eruptions can have devastating economic and social consequences, even at great distances from the volcano. Fortunately many eruptions are preceded by unrest that can be detected using ground, airborne, and spaceborne instruments. Data from these instruments, combined with basic understanding of how volcanoes work, form the basis for forecasting eruptions—where, when, how big, how long, and the consequences. Accurate forecasts of the likelihood and magnitude of an eruption in a specified timeframe are rooted in a scientific understanding of the processes that govern the storage, ascent, and eruption of magma. Yet our understanding of volcanic systems is incomplete and biased by the limited number of volcanoes and eruption styles observed with advanced instrumentation. Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing identifies key science questions, research and observation priorities, and approaches for building a volcano science community capable of tackling them. This report presents goals for making major advances in volcano science.https://scholarworks.boisestate.edu/fac_books/1473/thumbnail.jp