Finding worst loaded element in model with MAXIMA

Hi all

I have a model of a steel truss bridge with potentially hundreds of elements, and I have introduced the eurocode 1990 combinations in Maxima (shown below).

Now I need to extract the forces of the worst loaded elements, but I dont know which element this is. I’ve had a look at TRAC, but it seems I can find the largest forces in a specific element, where I would want to go the other way around (I dont know the position (element no.) where the largest force is present.

How would one find the worst loaded element?

+prog maxima urs:42.1
$ECHO chck


COMB 1 EXTR EXPL BASE 1000 TYPE DESI TITL 'ULS 6.10a: Self weight'
    ADD TYPE G FACU 1.25*KFI FACF 1.00

COMB 2 EXTR EXPL BASE 2000 TYPE DESI TITL 'ULS 6.10b-1: Area load'
    ADD TYPE G    FACU 1.00*KFI FACF 0.90
    ADD TYPE Q_1  FACU 1.40*KFI FACF 0
    ADD TYPE W    FACU 0.45*KFI FACF 0
    ADD TYPE T    FACU 0.90*KFI FACF 0

COMB 3 EXTR DESI BASE 3000 type stan TITL 'ULS - 6.10b-2: Service vehicle'
    ACT 'G_1'   GAMU 1.00*#KFI GAMF 0.9 SUP PERM psi0 1 psi1 1 psi2 1    // ALL LOAD CATEGORIES PERMANENTLY INCLUDED
    ACT 'G_2'   GAMU 1.00*#KFI GAMF 0.9 SUP PERM psi0 1 psi1 1 psi2 1    // ALL LOAD CATEGORIES PERMANENTLY INCLUDED
    ACT 'Q_2'   GAMU 1.40*#KFI GAMF 0.0 SUP ALEX psi0 1 psi1 1 psi2 1    // EXCLUSIVE WITHIN CATEGORY
    ACT 'W'     GAMU 0.45*#KFI GAMF 0.0          psi0 1 psi1 1 psi2 1
    ACT 'T'     GAMU 0.90*#KFI GAMF 0.0          psi0 1 psi1 1 psi2 1


the worst forces elements are dependent from the superposition values – record SUPP. E.g. for beams the maximum bending moment My lies at another position than the maximum shear force Vz.

In order to get the resulting load case combination with record TRAC for a worst force element we recommended following workflow:

  • Use ECHO CHCK for the superposition of specific action combinations
    This prints the most unfavourable positions in dependence on the superposition value, e.g. for bending moment My of beams two positions – one for max. My and one for min.My. In the extended MAXIMA printout all necessary information about the determination of leading and accompanying actions as well as the resulting factors per load cases are available.

  • MAXIMA record TRAC
    In a further MAXIMA run the with ECHO CHCK determined element or beam with its x position can be defined.
    e.g. TRAC LC xxxx ETYP BEAM ELEM number from MAXiMA printput ECHO CHCK X x-position of the beam

I hope this information is useful for you.

With kind regards
Sabine Fahrendholz
Senior Product Manager

1 Like

Using ECHO CHCK I do get the worst loaded element for each force. But:

  1. How do can I select this element in the system viewer by inputting element no.?

  2. I dont want to scroll through literally hundreds of pages to manually find each force and corresponding element. Especially as the worst element is likely to change as the design moves forward. How can I “automatically” use TRAC on the presented elements in “relevant forces” from ECHO CHCK?

  1. Currently it is not possible to select this element in the system viewer.
  2. I know that many tables are generated with ECHO CHCK if many action combinations as for bridge design are available. That’s why we recommend to define single SUPP records only for ECHO CHCK.
    SUPP NO xxx EXTR MAMI ETYP BEAM TYPE MY → printout of two decisive points: max My + min My
    ECHO CHCK no
    SUPP NO xxx … → other SUPP records without printout for decisive points

The record ECHO can be defined differently for each SUPP record.

The easiest way is probably to:

  • Run maxima
  • Select the relevant load case in the result viewer and sort for the loading your interested in (e.g. My)
  • Search for the element by number in in wingraf