# Changes for page Seismic analysis

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edited by IwonaBudny
on 2018/09/10 11:19
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edited by IwonaBudny
on 2018/09/10 11:37
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 ... ... @@ -468,7 +468,7 @@ 468 468 (% class="wikigeneratedid" %) 469 469 == Other setting possibilities == 470 470 471 -(% style="font-size:18px" %)Horizontal direction setting for seismic calculation 471 +=== Horizontal direction setting for seismic calculation === 472 472 473 473 Generally codes speak about the seismic calculation in X-Y directions. However results in these directions give the maximum effect if the mass and elastic properties of the structure ensure that the calculated mode shapes lay in X-Z or Y-Z plane. Nevertheless it is not always achieved in practice. To achieve the unfavorable direction, where the results from a ground motion are maximum, the user can Set the Alpha angle or may get the program suggestion by using Auto but- ton. 474 474 ... ... @@ -484,7 +484,7 @@ 484 484 Of course this also can be reached if the user rotates the whole geometry with a specified angle. 485 485 486 486 487 -(% style="font-size:18px" %)Effective mass setting 487 +=== Effective mass setting === 488 488 489 489 FEM-Design always takes into account the entire mass of the structure in the calculation of base shear force which was mentioned in Lateral force method. It was also mentioned, EC8 defines the total mass without the basement, this is called Reduced mass in this manual. The effective masses are generally compared to the Reduced mass, but this is not valid for the massive basement with elastic foundation. 490 490 ... ... @@ -495,6 +495,9 @@ 495 495 496 496 It is uninteresting from the calculation point of view that effective masses are compared to the total or the reduced mass because these values are given in percentage and only gives information about which mode shape is the fundamental or which shapes are dominant in a given direction. 497 497 498 +---- 499 + 500 +(% class="wikigeneratedid" %) 498 498 == Combination rule, rotation and second order effects == 499 499 500 500 (% style="text-align: justify;" %) ... ... @@ -505,8 +505,8 @@ 505 505 (% style="text-align: justify;" %) 506 506 The first rule which is called SRSS is implemented to all the other codes than EC8 and NS3491-12 and there is no possibility for rule selection. 507 507 508 -(% style="text-align: justify;" %) 509 -=== (% style="font-size:18px" %)**Torsional effect**(%%) === 511 +(% id="HTorsionaleffect" %) 512 +=== **Torsional effect** === 510 510 511 511 (% style="text-align: justify;" %) 512 512 According to EC8 4.3.2 the program gives possibility to take into account the accidental mass distribution of the structure by the calculation of the torsional effect. This means that from the horizontal seismic forces a Z directional torsional moment can be calculated according to EC8 4.3.3.3.3 (EC8 4.17 equation) as follows: ... ... @@ -544,7 +544,8 @@ 544 544 (% style="text-align: justify;" %) 545 545 It was seen that the influence of uncertainties of mass position was modeled by the rotation effect. According to our experiment using the FE method, when a plate, a wall and beams are divided into several elements the accidental torsional effect is not reasonable. 546 546 547 -=== (% style="font-size:18px" %)**Second-order effects (P-∆ effects)**(%%) === 550 +(% id="HSecond-ordereffects28P-2206effects29" %) 551 +=== **Second-order effects (P-∆ effects)** === 548 548 549 549 (% style="text-align: justify;" %) 550 550 Only EC8 gives a possibility to calculate the second order effect which is done according to 4.4.2.2(2). The second order effect is ignored if the following condition is fulfilled in all storeys and all horizontal directions: ... ... @@ -579,6 +579,8 @@ 579 579 * To calculate thesecond order effect, storey(s) should be defined. 580 580 ))) 581 581 586 +---- 587 + 582 582 == Displacement calculation == 583 583 584 584 (% style="text-align: justify;" %)