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Soil-Structure Interaction

Large civ­il struc­tures such as con­crete dams, nu­clear pow­er plants, high-rise build­ings and bridges are mas­sive enough that their vi­bra­tion due to earth­quake ex­ci­ta­tion af­fects the mo­tion of the soil or rock sup­port­ing them,which in turn fur­ther af­fects the mo­tion of the struc­ture it­self. This in­ter­ac­tion be­tween the struc­ture and the soil needs to be mod­eled ac­cu­rate­ly in or­der to de­sign earth­quake re­sis­tant struc­tures and to cor­rect­ly eval­u­ate the earth­quake safe­ty of ex­ist­ing struc­tures.

Golden Gate Bridge Hoover Dam San Onofre

His­tor­i­cal­ly, en­gi­neer­ing analy­sis of such soil-struc­ture in­ter­ac­tion has had sev­er­al im­ped­i­ments: (i) lim­it­ed knowl­edge of the rel­e­vant earth­quake faults and of the re­gion­al ge­o­log­i­cal fea­tures re­quired to ful­ly char­ac­ter­ize the in­com­ing earth­quake ground mo­tion, (ii) lack of ac­cu­rate earth­quake in­put meth­ods in ex­ist­ing analy­sis soft­ware, and (iii) in­abil­i­ty to ef­fi­cient­ly mod­el the un­bound­ed soil do­main.

LS-DY­NA now has a nov­el method for soil-struc­ture in­ter­ac­tion analy­sis that ap­plies the earth­quake forces in an ef­fi­cient and ra­tio­nal man­ner and mod­els the un­bound­ed do­main ac­cu­rate­ly at low com­pu­ta­tion­al cost, giv­en a free-field ground mo­tion char­ac­ter­iz­ing an earth­quake. It us­es the ef­fec­tive seis­mic in­put method to in­cor­po­rate the earth­quake forces in­to the soil-struc­ture mod­el, us­ing on­ly the free-field ground mo­tion at the soil-struc­ture in­ter­face, and not re­quir­ing any de­con­vo­lu­tion down to depth un­like old­er meth­ods of earth­quake in­put. The un­bound­ed do­main is mod­eled us­ing per­fect­ly matched lay­ers, which ab­sorbs the out­ward-prop­a­gat­ing waves al­most per­fect­ly with on­ly a slight in­crease in cost from the clas­si­cal Lysmer dash­pot bound­aries. These pages ex­plain and demon­strate these tech­niques for seis­mic soil-struc­ture in­ter­ac­tion analy­sis in LS-DY­NA.