# Changes for page Seismic analysis

Last modified by IwonaBudny on 2018/09/28 08:53

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 ... ... @@ -284,4 +284,26 @@ 284 284 285 285 = **Useful tips, which method to use?** = 286 286 287 - 287 +((( 288 +(% style="text-align: justify;" %) 289 +To answer this question is hard even for experienced engineers. However some basic concept can be formulated: 290 + 291 +(% class="box successmessage" %) 292 +((( 293 +Before any decision, always run the Eigenfrequencies calculation. From these results you will experience how the structure behaves in aspect of dynamics. 294 + 295 +Always check the effective masses, if you calculate the structure for seismic effect in the first occasion or make changes in the geometry or in the mass distribution. 296 + 297 +If you see that the effective masses shows larger value than 100% com- pare them to the Total mass and not to the Reduced mass. 298 + 299 +If the sum of the selected effective masses is less than the prescribed minimum (in EC8 this is 90%), calculate more mode shape. 300 + 301 +If the sum of effective masses in case of large number mode shapes doesnâ€™t approach to the prescribed value use the static, linear shape or static, mode shape if the code allow. 302 + 303 +If the building has large importance or it has special geometry try to apply the modal analysis. 304 + 305 +If the building is not too high, any of the static methods will give reliable results avoiding longer run time calculation in eigenfrequencies. 306 + 307 +It is not always necessary to analyze the 3D model in all directions, sometimes one or two planar model is enough. 308 +))) 309 +)))

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