Second European Conference on Earthquake Engineering and Seismology, İstanbul, Turkey, 25 - 29 August 2014, pp.4819-4830
It is widely known that recent earthquakes have significantly influenced lifeline structures such an extent that even if there is not any damage in structures or any facilities on ground, the fracture of gas pipelines resulting in gas leakage leads to fires, economic losses and disability of lifeline networks. Therefore, the possibility of encountering with such a great hazard makes inroads into developing a method to assess the performance of available gas pipeline networks and to envisage the way of reinforcing them in the case of considerable damages under earthquake excitation.
In general, researchers have dealt with the quantification of lifeline hazard in that some of them appeal to the equations which are improved after the occurrence of significant earthquake by computing the number of pipeline breakages/leakages on site with respect to distance. (km) This route allows people to constitute fragility curves including relationship between repair per distance and selected ground motion parameter. (usually PGV) However, this method requires the pipeline damage inventory for a certain specific ground motion(s) and prevents one who does not have any data to develop such relationships. Also, it is customary to model numerically the pipeline and surrounding soil to perform nonlinear time history analysis so that computed strains can be compared with the limiting values given with regard to different types of buried gas pipelines. However, this pipeline – soil interaction model does not make it possible for constructing a rapid response system to be implemented immediate after earthquake.
This paper presents a procedure which bears on the system assuming that pipelines behave as a structural beam and the surrounding soil is modelled as elasto – plastic spring element. (Winkler Foundation System) This is the method released in “Recommended Practices for Earthquake Resistant Design of Gas Pipelines (Draft, 2000) – Japan Gas Association” but modified and further developed to provide compatibility with buried gas pipeline network and seismic hazard data of İstanbul. The Japan Code states that the surrounding soil and pipeline act together under the condition of wave passage, thus paving the way for deriving a transfer equation to calculate pipeline strain with the help of the one occurred in soil. For that purpose, İstanbul is geographically partitioned into grid cells having dimensions of 400mX600m. Pipeline inventory (length, diameter, the number of straight pipelines, bends and tees, pipe coating types, radius of curvature values for bends), real – time spectral acceleration values at 0.2 and 1 sec., soil classification data are extracted from each cell. Finally, this modified procedure is coded by means of VBA in Microsoft Excel in order to perform a rapid analysis with respect to given inventory and data. Results are mapped to supply gas company with a chance to perform immediate treatment to risky areas after earthquake.