Axial load in beams due to offset

[Bill2001]

Dear STAAD.PRO experts!
It's urgent!
I'm doing an bridge analysis. I offset all the beams below the transverse beams in different distance which matches the real case. The results show large axial forces in almost all the beams plus horizontal reaction forces. If I delete all the offset, the axial forces are gone. But I don't think it is a good way to do this because it obviously doesn't fit for the real case.
Could somebody here help me with this situation?
Below is the input file:

STAAD SPACE
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 17 0 0; 3 0 0 1; 4 17 0 1; 5 0 0 2; 6 17 0 2; 7 0 0 3; 8 17 0 3;
9 1 0 0; 10 1 0 3; 11 2 0 0; 12 2 0 3; 13 3 0 0; 14 3 0 3; 15 4 0 0; 16 4 0 3;
17 5 0 0; 18 5 0 3; 19 6 0 0; 20 6 0 3; 21 7 0 0; 22 7 0 3; 23 8 0 0; 24 8 0 3;
25 9 0 0; 26 9 0 3; 27 10 0 0; 28 10 0 3; 29 11 0 0; 30 11 0 3; 31 12 0 0;
32 12 0 3; 33 13 0 0; 34 13 0 3; 35 14 0 0; 36 14 0 3; 37 15 0 0; 38 15 0 3;
39 16 0 0; 40 16 0 3; 41 16 0 1; 42 15 0 1; 43 14 0 1; 44 13 0 1; 45 12 0 1;
46 11 0 1; 47 10 0 1; 48 9 0 1; 49 8 0 1; 50 7 0 1; 51 6 0 1; 52 5 0 1;
53 4 0 1; 54 3 0 1; 55 2 0 1; 56 1 0 1; 57 16 0 2; 58 15 0 2; 59 14 0 2;
60 13 0 2; 61 12 0 2; 62 11 0 2; 63 10 0 2; 64 9 0 2; 65 8 0 2; 66 7 0 2;
67 6 0 2; 68 5 0 2; 69 4 0 2; 70 3 0 2; 71 2 0 2; 72 1 0 2;
MEMBER INCIDENCES
100 1 9; 200 3 56; 300 5 72; 400 7 10; 500 1 3; 501 9 11; 502 10 12; 503 9 56;
504 11 13; 505 12 14; 506 11 55; 507 13 15; 508 14 16; 509 13 54; 510 15 17;
511 16 18; 512 15 53; 513 17 19; 514 18 20; 515 17 52; 516 19 21; 517 20 22;
518 19 51; 519 21 23; 520 22 24; 521 21 50; 522 23 25; 523 24 26; 524 23 49;
525 25 27; 526 26 28; 527 25 48; 528 27 29; 529 28 30; 530 27 47; 531 29 31;
532 30 32; 533 29 46; 534 31 33; 535 32 34; 536 31 45; 537 33 35; 538 34 36;
539 33 44; 540 35 37; 541 36 38; 542 35 43; 543 37 39; 544 38 40; 545 37 42;
546 39 2; 547 40 8; 548 39 41; 549 2 4; 550 41 4; 551 42 41; 552 43 42;
553 44 43; 554 45 44; 555 46 45; 556 47 46; 557 48 47; 558 49 48; 559 50 49;
560 51 50; 561 52 51; 562 53 52; 563 54 53; 564 55 54; 565 56 55; 566 57 6;
567 58 57; 568 59 58; 569 60 59; 570 61 60; 571 62 61; 572 63 62; 573 64 63;
574 65 64; 575 66 65; 576 67 66; 577 68 67; 578 69 68; 579 70 69; 580 71 70;
581 72 71; 582 5 7; 583 3 5; 584 72 10; 585 56 72; 586 71 12; 587 55 71;
588 70 14; 589 54 70; 590 69 16; 591 53 69; 592 68 18; 593 52 68; 594 67 20;
595 51 67; 596 66 22; 597 50 66; 598 65 24; 599 49 65; 600 64 26; 601 48 64;
602 63 28; 603 47 63; 604 62 30; 605 46 62; 606 61 32; 607 45 61; 608 60 34;
609 44 60; 610 59 36; 611 43 59; 612 58 38; 613 42 58; 614 57 40; 615 41 57;
616 6 8; 617 4 6;
MEMBER PROPERTY EUROPEAN
100 200 300 400 501 502 504 505 507 508 510 511 513 514 516 517 519 520 522 -
523 525 526 528 529 531 532 534 535 537 538 540 541 543 544 546 547 -
550 TO 581 TABLE ST HE450B
500 503 506 509 512 515 518 521 524 527 530 533 536 539 542 545 548 549 582 -
583 TO 617 TABLE ST HE200B
SUPPORTS
1 3 5 7 PINNED
2 4 6 8 FIXED BUT FX MZ
DEFINE MATERIAL START
ISOTROPIC S355
E 2.1e+008
POISSON 0.3
DENSITY 78.5
ALPHA 1.2e-005
DAMP 0.03
END DEFINE MATERIAL
CONSTANTS
MATERIAL S355 MEMB 100 200 300 400 500 TO 617
MEMBER OFFSET
100 200 300 400 501 502 504 505 507 508 510 511 513 514 516 517 519 520 522 -
523 525 526 528 529 531 532 534 535 537 538 540 541 543 544 546 547 -
550 TO 581 START 0 -0.325 0
100 200 300 400 501 502 504 505 507 508 510 511 513 514 516 517 519 520 522 -
523 525 526 528 529 531 532 534 535 537 538 540 541 543 544 546 547 -
550 TO 581 END 0 -0.325 0
CUT OFF MODE SHAPE 6
LOAD 1 Vertical_Load
JOINT LOAD
24 49 FY -100
LOAD 2 LOADTYPE Mass TITLE Self_weight
SELFWEIGHT Y -1
MODAL CALCULATION REQUESTED
PERFORM ANALYSIS PRINT STATICS CHECK
LOAD LIST 1
PRINT MEMBER FORCES LIST 100 200 300 400 500 503 582 TO 585
PRINT SUPPORT REACTION LIST 1 TO 8
FINISH

 

[edward1]

Download a 30 day trial of the program for bridge analysis from MDX. You can run the analysis as a grid or finite elements. This will give you the results you need.