Skip to main content

Seismic Input in LS-DYNA

Ef­fec­tive seis­mic in­put has been im­ple­ment­ed in LS-DY­NA, with IN­TER­FACE_­SSI cards used to iden­ti­fy the soil-struc­ture in­ter­face, and LOAD_­SEIS­MIC_­SSI used to spec­i­fy the ground mo­tion on such an in­ter­face. Typ­i­cal­ly, on­ly ground ac­cel­er­a­tion his­to­ries are re­quired to spec­i­fy the ground mo­tion, but if ground ve­loc­i­ty and dis­place­ment curves are al­so avail­able from sig­nal pro­cess­ing of the ac­celero­grams, then the ground mo­tion may be spec­i­fied us­ing DE­FINE_­GROUND_­MO­TION. 

The vari­a­tions on the IN­TER­FACE_­SSI cards (_­AUX, _­AUX_­EM­BED­DED and _­STA­T­IC) are meant for dif­fer­ent stages in the analy­sis. All the IN­TER­FACE_­SSI cards (ex­cept for _­AUX) cre­ate a tied-con­tact in­ter­face be­tween two spec­i­fied seg­ment sets, the mas­ter sur­face be­ing on the soil side and the slave on the struc­ture side. 

Soil-struc­ture in­ter­ac­tion analy­sis un­der earth­quake ex­ci­ta­tion may then be car­ried out in LS-DY­NA us­ing these cards as fol­lows:

0. Car­ry out a sta­t­ic analy­sis of the soil-struc­ture sys­tem (e.g. us­ing dy­nam­ic re­lax­ation; see *CON­TROL_­DY­NAM­IC_­RE­LAX­ATION), with the soil-struc­ture in­ter­face iden­ti­fied us­ing *IN­TER­FACE_­SSI_­STA­T­IC_­ID. 

Op­tion­al­ly, car­ry out a free-field analy­sis to record free-field mo­tions on the fu­ture soil-struc­ture in­ter­face, us­ing ei­ther *IN­TER­FACE_­SSI_­AUX or *IN­TER­FACE_­SSI_­AUX_­EM­BED­DED, for sur­face-sup­port­ed or em­bed­ded struc­tures re­spec­tive­ly.

1. Car­ry out the tran­sient analy­sis as a full-deck restart job (see *RESTART), with on­ly the struc­ture ini­tial­ized to its sta­t­ic stress state (see *STRESS_­INI­TIAL­IZA­TION), and the same soil-struc­ture in­ter­face iden­ti­fied us­ing *IN­TER­FACE_­SSI_­ID with the same ID as in sta­t­ic analy­sis:

  1. The struc­ture mesh must be iden­ti­cal to the one used for sta­t­ic analy­sis.
  2. The soil mesh is ex­pect­ed to be dif­fer­ent from the one used for sta­t­ic analy­sis, es­pe­cial­ly be­cause non-re­flect­ing bound­ary mod­els may be used for tran­sient analy­sis.
  3. The mesh­es for the struc­ture and the soil need not match at the in­ter­face.
  4. On­ly the struc­ture must be sub­ject­ed to sta­t­ic loads, via *LOAD_­BODY_­PARTS.
  5. The earth­quake ground mo­tion is spec­i­fied us­ing *LOAD_­SEIS­MIC_­SSI, and/­or read from mo­tions record­ed from a pre­vi­ous analy­sis us­ing *IN­TER­FACE_­SSI_­AUX or *IN­TER­FACE_­SSI_­AUX_­EM­BED­DED.

 NOTE: Please ig­nore er­ror mes­sages from LS-Pre­post flag­ging the IN­TER­FACE_­SSI cards as in­valid.