Fastest Possible Nonlinear Time-History Seismic Analysis of Bridge Frame Structures


Abstract eng:
In California and elsewhere, bridge frame structures are designed to respond nonlinearly in high seismic areas, but displacement demand is typically calculated using linear-elastic methods. Nonlinear behavior is often recognized, however, in the displacement capacity determination using a pushover analysis. So there is a clear inconsistency between the way demand and capacity displacements are found, and it arises because of difficulty finding displacement demands using nonlinear analysis methods. A full nonlinear time-history analysis (NTHA) is required to accurately capture the seismic response of a bridge frame over time and to find the maximum displacement – the displacement demand. This more advanced approach of NTHA is solved by the stiffness method, and is not used in the design of everyday highway bridge structures because of the time it takes to run the analysis, instabilities, and overall added difficulty in model preparation, input and output compared to linear-elastic methods. Also because prior to the earthquake the input motion is not known, requiring many different ground motions and analyses to bound the results of a future earthquake. It is just not practical to use NTHA for the design of bridge structures with the currently available analysis tools that are based on the stiffness method. A new method has been developed for NTHA of bridge frame structures that does not depend on the stiffness method or matrix mathematics. Rather it uses closed-form equations that are exact for each time increment. The incremental closed-form method (ICFM) is 1000s of times faster than the traditional stiffness method because (1) there are no simultaneous equations to solve, (2) there is no iteration required and (3) it is a stable solution scheme. This new method was initially presented by the author (prior to completion of the computer program) at the 15th World Conference on Earthquake Engineering (15WCEE) in Lisbon, Portugal and (with the computer program fully working) at the Ninth International Conference on Structural Dynamics (EURODYN 2014) in Porto, Portugal. An example multi-span bridge frame showed that as complexity was added to the model, the ICFM continued to outpace the stiffness approach, while producing the same results; with nonlinear behavior representing plastic hinges at all column ends, as well as banging and soil crushing behind seat-type abutments, the closed-form approach was more than 25,000 times faster than the stiffness method. Such speed increases will allow the ICFM to be used directly by design engineers for NTHA of everyday bridge frame structures, resulting in realistic displacement demands. Because of the tremendous time savings using the ICFM, there is no difficulty running multiple earthquake motions through the structure, one after the other, to determine displacement demand from a future, un-defined earthquake. In the current paper, the author presents and discusses new features of the ICFM, and related computer program, that significantly furthers its capabilities.

Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2791.:
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