IBC/UBC seismic warning - Structural Analysis and Design - Forum - Structural Analysis and Design - Bentley Communities

IBC/UBC seismic warning

"**WARNING: IF THIS UBC/IBC ANALYSIS HAS TENSION/COMPRESSION OR REPEAT LOAD OR RE-ANALYSIS OR SELECT OPTIMIZE, THEN EACH UBC/IBC CASE SHOULD BE FOLLOWED BY PERFORM ANALYSIS & CHANGE."

 I did not understand anything from that warning but it contd to analize the structure. I wanna ask you that is my seismic analysis correct?

P.s: I entered 0.8s period values on purpose. And i know my modal analysis is wrong.

12 Replies

  • In STAAD, when you analyse a model containing UBC, IBC, IS1893, and various other seismic loads, the program has to first generate lateral loads per the rules of that code.

    If subsequently, there are other load cases which refer to the above cases through the means of a REPEAT LOAD command, as in cases 21 and 22 below

    LOAD 1
    IBC LOAD X 1.0
    LOAD 2
    IBC LOAD Z 1.0
    LOAD 3 GRAVITY
    SELF Y -1.0
    LOAD 4 LIVE
    MEMBER LOAD
    ..
    ..

    LOAD 21 DEAD + SEISMIC IN X
    REPEAT LOAD
    1 1.0 3 1.0

    LOAD 22 DEAD + SEISMIC IN Z
    REPEAT LOAD
    2 1.0 3 1.0

    then, load cases 21 and 22 must have access to the lateral load values generated in cases 1 and 2 respectively.

    This means that STAAD must be told to retain those generated load values. If it is not told to do so, it will simply "forget" those load values once it has finished processing cases 1 and 2. Consequently, cases 21 and 22 will not reflect any effects of the seismic loads.

    Another instance where STAAD needs to remember those generated lateral loads due to seismic cases is when a re-analysis has to be done following a member selection in steel design, as in

    LOAD 1
    IBC LOAD X 1.0
    LOAD 2
    IBC LOAD Z 1.0
    LOAD 3 GRAVITY
    SELF Y -1.0
    LOAD 4 LIVE
    MEMBER LOAD
    ..
    ..
    PERFORM ANALYSIS
    PARAMETER
    CODE AISC
    ..
    SELECT ALL
    PERFORM ANALYSIS

    The analysis instruction which follows the SELECT ALL command is called re-analysis. During re-analysis, all previously defined load cases are re-analysed using the member properties which resulted from the member selection.

    The warning message you saw earlier is merely intended to remind you of these facts.

    The means by which you can tell STAAD that it has to "remember" the generated load values is to specify a PERFORM ANALYSIS and CHANGE commands following those individual seismic cases, as shown below.

    LOAD 1
    IBC LOAD X 1.0

    PERFORM ANALYSIS
    CHANGE

    LOAD 2
    IBC LOAD Z 1.0

    PERFORM ANALYSIS
    CHANGE

    LOAD 3 GRAVITY
    SELF Y -1.0
    LOAD 4 LIVE
    MEMBER LOAD
    ..
    LOAD 5
    ..
    LOAD 21 DEAD + SEISMIC IN X
    REPEAT LOAD
    1 1.0 3 1.0

    LOAD 22 DEAD + SEISMIC IN Z
    REPEAT LOAD
    2 1.0 3 1.0

    PERFORM ANALYSIS
    CHANGE

     

    Sudip Narayan Choudhury

  • Thank you so much, your answer is very clear. Is everything allright with this input?

     

    LOAD 1 LOADTYPE Seismic TITLE SEISMIC X
    UBC LOAD X 1
    PERFORM ANALYSIS
    CHANGE
    LOAD 2 LOADTYPE Seismic TITLE SEISMIC Z
    UBC LOAD Z 1
    PERFORM ANALYSIS
    CHANGE
    LOAD 5 LOADTYPE Seismic TITLE SEISMIC -X
    UBC LOAD X -1
    PERFORM ANALYSIS
    CHANGE
    LOAD 6 LOADTYPE Seismic TITLE SEISMIC -Z
    UBC LOAD Z -1
    PERFORM ANALYSIS
    CHANGE
    LOAD 3 LOADTYPE Dead TITLE DEAD
    ELEMENT LOAD
    51 TO 59 61 63 TO 71 73 75 TO 83 85 87 TO 95 97 99 TO 107 109 111 TO 119 121 -
    123 TO 131 133 135 TO 143 145 147 TO 155 157 159 TO 167 169 171 TO 179 181 -
    268 TO 276 278 TO 287 289 TO 298 300 TO 309 311 TO 320 322 TO 331 -
    333 TO 343 364 TO 383 415 416 418 419 421 422 424 425 427 428 430 TO 433 -
    435 436 439 441 443 445 447 449 451 453 455 457 469 471 472 474 475 477 478 -
    480 TO 482 486 488 490 492 TO 508 510 512 514 516 517 519 521 523 525 527 -
    529 531 533 535 537 563 565 567 569 571 573 575 577 579 581 583 585 TO 597 -
    599 601 603 605 TO 621 623 625 627 629 630 632 TO 641 643 TO 652 654 TO 663 -
    665 TO 684 740 TO 748 750 752 TO 760 762 764 TO 772 774 776 TO 784 786 788 -
    789 TO 796 798 800 TO 808 810 TO 820 823 TO 831 833 TO 843 845 TO 853 855 -
    856 TO 864 866 TO 875 877 921 923 925 927 929 TO 942 984 985 987 989 990 992 -
    994 995 997 999 1000 1002 1004 1005 1007 1009 1010 1012 1014 1015 1017 1019 -
    1020 1022 1024 1025 1027 1029 1030 1032 1034 1035 1037 TO 1040 1042 TO 1050 -
    1064 1066 1068 1070 TO 1081 1103 1104 1106 1107 1109 1110 1134 1136 1138 -
    1140 1142 1144 1146 1148 1150 1152 1154 1156 1158 1160 1162 1164 1166 1168 -
    1170 1172 PR GY -0.35
    1174 1176 TO 1178 1216 TO 1222 1226 TO 1232 1236 TO 1242 1246 TO 1252 1256 -
    1257 TO 1262 1266 TO 1272 1276 TO 1282 1286 TO 1292 1296 TO 1302 1306 TO 1312 -
    1316 TO 1322 1446 TO 1452 1471 TO 1490 1497 TO 1522 1529 TO 1573 -
    1586 TO 1684 1715 TO 1834 1865 TO 1882 1910 TO 1954 1964 TO 1978 -
    1994 TO 1999 2012 TO 2145 2176 TO 2190 2520 TO 2601 2603 TO 2646 2649 2650 -
    2661 TO 2734 2813 TO 3683 PR GY -0.35
    SELFWEIGHT Y -1 LIST 51 TO 59 61 63 TO 71 73 75 TO 83 85 87 TO 95 97 -
    99 TO 107 109 111 TO 119 121 123 TO 131 133 135 TO 143 145 147 TO 155 157 -
    159 TO 167 169 171 TO 179 181 183 TO 191 193 195 TO 203 205 207 209 211 213 -
    215 217 219 221 223 224 227 229 231 233 235 237 239 241 243 245 TO 254 256 -
    257 TO 265 267 TO 276 278 TO 287 289 TO 298 300 TO 309 311 TO 320 322 TO 331 -
    333 TO 343 346 348 350 352 TO 383 406 407 409 410 412 413 415 416 418 419 -
    421 422 424 425 427 428 430 TO 433 435 436 439 441 443 445 447 449 451 453 -
    455 457 459 461 463 465 467 TO 469 471 472 474 475 477 478 480 TO 482 486 -
    488 490 492 TO 508 510 512 514 516 517 519 521 523 525 527 529 531 533 535 -
    537 539 541 543 545 547 548 551 553 563 565 567 569 571 573 575 577 579 581 -
    583 585 TO 597 599 601 603 605 TO 621 623 625 627 629 630 632 TO 641 643 -
    644 TO 652 654 TO 663 665 TO 684 688 691 694 697 700 703 706 709 712 714 716 -
    717 TO 724 726 728 TO 736 738 740 TO 748 750 752 TO 760 762 764 TO 772 774 -
    776 TO 784 786 788 TO 796 798 800 TO 808 810 TO 820 823 TO 831 833 TO 843 -
    845 TO 853 855 TO 864 866 TO 875 877 TO 886 888
    SELFWEIGHT Y -1 LIST 889 TO 897 899 901 903 905 907 909 911 913 915 917 918 -
    921 923 925 927 929 TO 954 956 958 960 962 964 965 968 970 972 974 975 977 -
    979 980 982 984 985 987 989 990 992 994 995 997 999 1000 1002 1004 1005 1007 -
    1009 1010 1012 1014 1015 1017 1019 1020 1022 1024 1025 1027 1029 1030 1032 -
    1034 1035 1037 TO 1040 1042 TO 1056 1058 1060 1061 1064 1066 1068 -
    1070 TO 1091 1093 1095 1097 1099 1100 1103 1104 1106 1107 1109 1110 1118 -
    1119 1122 1124 1134 1136 1138 1140 1142 1144 1146 1148 1150 1152 1154 1156 -
    1158 1160 1162 1164 1166 1168 1170 1172 1174 1176 TO 1178 1184 TO 1190 1192 -
    1193 1196 1197 1199 TO 1205 1208 TO 1210 1214 1216 TO 1222 1226 TO 1232 1236 -
    1237 TO 1242 1246 TO 1252 1256 TO 1262 1266 TO 1272 1276 TO 1282 1286 TO 1292 -
    1296 TO 1302 1306 TO 1312 1316 TO 1322 1446 TO 1452 1471 TO 1490 -
    1497 TO 1522 1529 TO 1573 1586 TO 1684 1715 TO 1834 1865 TO 1882 -
    1910 TO 1954 1964 TO 1978 1994 TO 1999 2012 TO 2145 2176 TO 2190 -
    2520 TO 2601 2603 TO 2654 2656 2658 TO 2744 2746 TO 2792 2794 TO 2808 2810 -
    2811 TO 3837 3839 TO 3964 3966 TO 3973
    LOAD 4 LOADTYPE Live REDUCIBLE TITLE LIVE
    ELEMENT LOAD
    51 TO 59 61 63 TO 71 73 75 TO 83 85 87 TO 95 97 99 TO 107 109 111 TO 119 121 -
    123 TO 131 133 135 TO 143 145 147 TO 155 157 159 TO 167 169 171 TO 179 181 -
    183 TO 191 193 195 TO 203 205 207 209 211 213 215 217 219 221 223 224 227 -
    229 231 233 235 237 239 241 243 245 TO 254 256 TO 265 267 TO 276 278 TO 287 -
    289 TO 298 300 TO 309 311 TO 320 322 TO 331 333 TO 343 346 348 350 -
    352 TO 383 406 407 409 410 412 413 415 416 418 419 421 422 424 425 427 428 -
    430 TO 433 435 436 439 441 443 445 447 449 451 453 455 457 459 461 463 465 -
    467 TO 469 471 472 474 475 477 478 480 TO 482 486 488 490 492 TO 508 510 -
    512 514 516 517 519 521 523 525 527 529 531 533 535 537 539 541 543 545 547 -
    548 551 553 563 565 567 569 571 573 575 577 579 581 583 585 TO 597 599 601 -
    603 605 TO 621 623 625 627 629 630 632 TO 641 643 TO 652 654 TO 663 -
    665 TO 684 688 691 694 697 700 703 706 709 712 714 716 TO 724 726 -
    728 TO 736 738 740 TO 748 750 752 TO 760 762 764 TO 772 774 776 TO 784 786 -
    788 TO 796 798 800 TO 808 810 TO 820 823 TO 831 833 TO 843 845 TO 853 855 -
    856 TO 864 866 TO 875 877 TO 886 888 PR GY -5
    889 TO 897 899 901 903 905 907 909 911 913 915 917 918 921 923 925 927 929 -
    930 TO 954 956 958 960 962 964 965 968 970 972 974 975 977 979 980 982 984 -
    985 987 989 990 992 994 995 997 999 1000 1002 1004 1005 1007 1009 1010 1012 -
    1014 1015 1017 1019 1020 1022 1024 1025 1027 1029 1030 1032 1034 1035 1037 -
    1038 TO 1040 1042 TO 1056 1058 1060 1061 1064 1066 1068 1070 TO 1091 1093 -
    1095 1097 1099 1100 1103 1104 1106 1107 1109 1110 1118 1119 1122 1124 1134 -
    1136 1138 1140 1142 1144 1146 1148 1150 1152 1154 1156 1158 1160 1162 1164 -
    1166 1168 1170 1172 1174 1176 TO 1178 1216 TO 1222 1226 TO 1232 1236 TO 1242 -
    1246 TO 1252 1256 TO 1262 1266 TO 1272 1276 TO 1282 1286 TO 1292 -
    1296 TO 1302 1306 TO 1312 1316 TO 1322 1446 TO 1452 1471 TO 1490 -
    1497 TO 1522 1529 TO 1573 1586 TO 1684 1715 TO 1834 1865 TO 1882 -
    1910 TO 1954 1964 TO 1978 1994 TO 1999 2012 TO 2145 2176 TO 2190 -
    2520 TO 2601 2603 TO 2654 2656 2658 TO 2734 2813 TO 3683 PR GY -5
    2813 TO 3640 3642 TO 3683 PR GY -3.25
    LOAD COMB 7 GENERATED ACI TABLE1 1
    3 1.4
    LOAD COMB 8 GENERATED ACI TABLE1 2
    3 1.2 4 1.6
    LOAD COMB 9 GENERATED ACI TABLE1 3
    3 1.2 4 1.0
    LOAD COMB 10 GENERATED ACI TABLE1 4
    3 1.2
    LOAD COMB 11 GENERATED ACI TABLE1 5
    3 1.2 4 1.0 1 1.0
    LOAD COMB 12 GENERATED ACI TABLE1 6
    3 1.2 4 1.0 2 1.0
    LOAD COMB 13 GENERATED ACI TABLE1 7
    3 1.2 4 1.0 5 1.0
    LOAD COMB 14 GENERATED ACI TABLE1 8
    3 1.2 4 1.0 6 1.0
    LOAD COMB 15 GENERATED ACI TABLE1 9
    3 0.9
    LOAD COMB 16 GENERATED ACI TABLE1 10
    3 0.9 1 1.0
    LOAD COMB 17 GENERATED ACI TABLE1 11
    3 0.9 2 1.0
    LOAD COMB 18 GENERATED ACI TABLE1 12
    3 0.9 5 1.0
    LOAD COMB 19 GENERATED ACI TABLE1 13
    3 0.9 6 1.0
    PERFORM ANALYSIS
    CHANGE
    FINISH 

  • In reply to GBaltali:

    The last "CHANGE" command, just before the command "FINISH", is not required. The presence of it is not a problem though.

    The rest of the input looks alright.

    Sudip Narayan Choudhury

  • I have a problem on this either.. but my tutor said it does not affect the safety of the design. Cab anyone expound on this?
  • In reply to etnickstudio:

    Sorry, we did not understand the question. Can you please elaborate?

     

    Biswa

  • In reply to Geeky biswa:

    Hi!    

    I'm new with STAAD and i'm using 2005. I'm having trouble with some errors and i do not know how to correct them :

    1. "... if the UBC/IBC  has tension/compression.. " - Error notice

    2. " density not provided, self weight ignored.. "

    Please enlighten me on these errors, What does it mean and How do I correct it ?

     

  • You can find answers to your first question on this topic. 

    You should check your material properties for concrete that you have used in your model.

  • In reply to etnickstudio:

    1. When UBC/IBC load cases are present in the model, each such load case must be followed by a PERFORM ANALYSIS and CHANGE command. For example LOAD 1 IBC LOAD X PERFORM ANALYSIS CHANGE LOAD 2 IBC LOAD X PERFORM ANALYSIS CHANGE LOAD 3 SELF Y -1 LOAD 4 FLOOR LOAD YRA 13.9 14.2 FLOAD -3.2 .. .. 2. In the DEFINE MATERIAL command, check whether you have specified DENSITY for the material. If you have not, the warning you encountered will appear. Without density, the weight of the entities to which that material is assigned cannot be calculated.

  • In reply to saraswathi.l:

    It worked perfectly THANK YOU !!!!. :-)

    Hmmmm... now i'm into slab. It keeps failing. 

    first, i made a 0.18m thick slab and assigned it to the most critical slab surface in my structure.

    then I designed it with the following properties :  fc=20700kn/sqm             fyld=276000Kn/sqm         bars from D10-d12

                                                                                           I chose max. moment for the design, and selected DL and LL for loadings

    The span is only 3m by 4m, i even tried 2m x 3 m span and it keeps failing. Is there something i should look into to correct this failure ?

     

     

     

  • This question is out of topic. Can you send your file in a related topic?
  • hI !    I have some few questions here:

    1. I would like to know if STAAD is considering rigidity of the structure due to slab when inputting slab coordinates like y range 3 3.... and so on and so forth. What i meant was by inputting y range for floor loads, is the rigidity of the slab already been considered.

    2. In connection to question one, how can I make a hole in the slab ?   I've placed y range for floor loads and it does assume the whole floor rigid-slab ?   How about the stairwell, atrium or simply floor openings?

  • In reply to etnickstudio:

    Answer to question 1 :

    YRANGE or XRANGE or ZRANGE is merely a way by which one tells the program the portion of the structure where the FLOOR LOAD is being applied. A structure can have many floors, and on each floor, there can be loads of various intensities on different parts of the floor. So, if the program is to be told which region a specific load intensity is to be applied, there has to be a way by which to identify that location. XRANGE, YRANGE and ZRANGE is one of the means to identify that region. Another method is the FLOOR GROUP.

    If a slab is present on a region, and if the slab is modeled using plate elements, you can apply the load using ELEMENT LOAD instead of FLOOR LOAD. The stiffness of the slab is accounted for through the stiffness of the elements which gets calculated during the assembly of the stiffness matrix.

     

    Answer to question 2 :

    If the slab is modeled using plate elements, an opening in the slab can be modeled by ensuring that there are no elements in the region of the opening. In other words, a hole is nothing but an absence of elements on the region defined by the opening.

    If the slab is not included in the model (and thus there are no elements to model the slab), and you want to exclude the region of the opening while applying the floor load, use the appropriate values for XRANGE and ZRANGE. YRANGE is usually for identifying the elevation of the floor.

     

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