# Changes for page Seismic analysis

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 ... ... @@ -266,6 +266,7 @@ 266 266 267 267 (% style="text-align: justify;" %) 268 268 Calculation input parameters can be set in the Calculation dialog in Analysis/ Seismic analysis in the Setup as can be seen below. 269 + 269 269 270 270 (% style="text-align: justify;" %) 271 271 [[image:1536569776410-536.png||height="76" width="250"]] ... ... @@ -300,7 +300,7 @@ 300 300 * Modal response spectrum analysis (Modal analysis). 301 301 302 302 (% id="H1.Lateralforcemethod" %) 303 -=== 1. Lateral force method === 304 +=== Lateral force method === 304 304 305 305 In some codes called equivalent static analysis.EC8 as well NS3491-12 uses this method. The user may not use this method in other codes. 306 306 ... ... @@ -336,7 +336,7 @@ 336 336 337 337 ))) 338 338 339 -==== a. Linear distribution of horizontal seismic forces (Static, linear shape) ==== 340 +==== Linear distribution of horizontal seismic forces (Static, linear shape) ==== 340 340 341 341 In this method the distribution of base shear force happens according to a simplified fundamental mode shape which is approximated by horizontal displacements that increased linearly along the height (see EC8 4.3.3.2.3(3)). The seismic action effects shall be determined by applying to the x' or y' direction. The horizontal forces are: 342 342 ... ... @@ -378,13 +378,14 @@ 378 378 * unusable if the horizontal foundation is elastic 379 379 ))) 380 380 381 -== [[image:1536570428267-379.png||height="205" width="330"]] == 382 +(% class="wikigeneratedid" id="H" %) 383 +[[image:1536570428267-379.png||height="205" width="330"]] 382 382 383 383 (% style="text-align: justify;" %) 384 384 If any of the above mentioned situations happen, the static, mode shape or modal analysis should be used. 385 385 386 386 387 -==== b. Distribution of seismic forces according to fundamental mode shapes (Static, mode shape) ==== 389 +==== Distribution of seismic forces according to fundamental mode shapes (Static, mode shape) ==== 388 388 389 389 (% style="text-align: justify;" %) 390 390 In this method the distribution of base shear force happens according to the base vibration shape (see EC8 4.3.3.2.3(2)P). The horizontal forces acting on the place of mi are: ... ... @@ -412,15 +412,19 @@ 412 412 ((( 413 413 Remarks: 414 414 415 -* The calculation of base shear force is performed according to the total mass of the structure and not the effective mass, as was introduced earlier in Lateral force method. 417 +* The calculation of base shear force is performed according to the total mass of the structure and not the effective mass, as was introduced earlier in** Lateral force method**. 416 416 ))) 417 417 418 -=== 2. Modal response spectrum analysis (modal analysis) === 420 +=== 421 +Modal response spectrum analysis (modal analysis) === 419 419 420 420 (% style="text-align: justify;" %) 421 -This method can be used in all national codes. The essence of the method is the calculation of the structural response for different ground motions by the sufficient summation of more vibration shapes. Method gives possibility to take into account full x, y and z direction investigation. In the table below, more vibration mode shape could be selected in x', y' and z' directions if necessary. The last row of the table shows that in a given ground motion direction how large is the sum of the considered effective masses compared to the total or reduced mass of the structure. 424 +This method can be used in all national codes. 422 422 423 423 (% style="text-align: justify;" %) 427 +The essence of the method is the calculation of the structural response for different ground motions by the sufficient summation of more vibration shapes. Method gives possibility to take into account full x, y and z direction investigation. In the table below, more vibration mode shape could be selected in x', y' and z' directions if necessary. The last row of the table shows that in a given ground motion direction how large is the sum of the considered effective masses compared to the total or reduced mass of the structure. 428 + 429 +(% style="text-align: justify;" %) 424 424 According to EC8 4.3.3.3.1(3) and NS3491-12 sum of the effective mass of the chosen mode shapes - at least in horizontal direction - should reach 90% of total mass. Additionally every mode shape has to be taken into account which effective mass is larger than 5%. 425 425 426 426 (% style="text-align: justify;" %) ... ... @@ -457,7 +457,6 @@ 457 457 T,,j ,,/ T,,i ,,> 0,9 with T,,j ,,≤ T,,i,, 458 458 459 459 460 - 461 461 FEM-Design always applies the selected rule for the summation except if the **Automatic **is highlighted. If the **Automatic **is selected then the rule selection procedure is as follows: 462 462 463 463 * ((( ... ... @@ -469,7 +469,6 @@ 469 469 If at least one dependent situation exists in a direction, the program automatically uses the CQC rule for all mode shapes in that direction, otherwise SRSS rule is used. 470 470 ))) 471 471 472 ----- 473 473 474 474 == Other setting possibilities == 475 475 ... ... @@ -499,9 +499,8 @@ 499 499 In FEM-Design Reduced mass means the difference between the total mass of the structure and the basement mass. The basement mass is the sum of all masses which lay on the foundation level which can be set in the Others tab of seismic load. 500 500 501 501 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. 506 + 502 502 503 ----- 504 - 505 505 == Combination rule, rotation and second order effects == 506 506 507 507 (% style="text-align: justify;" %) ... ... @@ -513,7 +513,7 @@ 513 513 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. 514 514 515 515 (% id="HTorsionaleffect" %) 516 -=== **Torsional effect** === 519 +=== Torsional effect === 517 517 518 518 (% style="text-align: justify;" %) 519 519 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: ... ... @@ -552,7 +552,7 @@ 552 552 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. 553 553 554 554 (% id="HSecond-ordereffects28P-2206effects29" %) 555 -=== **Second-order effects (P-∆ effects)** === 558 +=== Second-order effects (P-∆ effects) === 556 556 557 557 (% style="text-align: justify;" %) 558 558 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: ... ... @@ -587,10 +587,9 @@ 587 587 * To calculate thesecond order effect, storey(s) should be defined. 588 588 ))) 589 589 590 ----- 593 +== 594 +Displacement calculation == 591 591 592 -== Displacement calculation == 593 - 594 594 (% style="text-align: justify;" %) 595 595 The displacement calculation is made according to EC8 4.3.4 using the following formula: 596 596