6.11.4 Earthquake walls
In multi-mode seismic load cases, the signs of all influences (M and N sign) are always
positive. The program designs such load cases for all four combinations of these two influences
symbol - M>0 i N>0, M>0 i N<0, M<0 i N>0, M<0 i N – and, as a result, adopts the
reinforcement from the least favourable case.
The metod is corect, but the results is not correct for all section cuts!
We have just received the exact question from our representative from Bulgaria - we analyzed it and here is the conclusion:
Calculation of reinforcement is absolutely correct, and in accordance with designed behavior which is alternating mutual signs of M and N.
In the other words, the reinforcement is calculated for 4 combinations - sub-cases (not just 2).
a) I + II + III (M>0,N>0)
b) I + II + III (M<0,N>0)
c) I + II - III (M<0,N<0)
d) I + II - III (M>0,N<0)
The only error is in report - wrong sub-case was displayed for a least favorable load case, and we will correct this.
As you can see, in both sections calculated reinforcements are the same, and you can be absolutely sure that calculated reinforcement is OK.
Influences in proxy object in multimodal seismic (MMS) loadcase combinations are under question. As you know, the only valid method for elaboration of influences in MMS loadcase is through variation of mutual signs of M and N performed during reinforcement calculation. So, it is under big question, which combination of signs should be used for one and only diagram of forces in a proxy object.
Because of this ambiguity, there is no code implemented for special handling of MMS loadcase combinations either for influence in sections, influences in indirect elements and influences in proxy objects.
If we do the implementation of integration of influences for MMS loadcase combination, it would be irregular. Example:
LC 1) - ordinary loadcase: M = -300, N = -100
LC 2) - MMS loadcase M = 100, N = 10
In combination I + II it would be wrong if we display this as M = -200 and N = -90, because this is not necessary the less favourable variation of influences.
So, we will solve this by disabling commands for showing influences in cross section, indirect elements and proxy object for MMS load combination. We will leave this option on for showing influences for single MMS load case.
Odgovor na pitanje koje je glasilo: "Uticaji u reduktoru za seizmicke kombinacije takodje nisu dobri. Mozete li to popraviti ?" (pod pojmom seizmicki misli se na multimodalni seizmicki proracun, prim. b.milan)
Uticaji u reduktoru za multimodalne seizmicke (MMS) kombinacije opterecenja su pod znakom pitanja. Kao sto znate, jedini ispravan metod za analizu uticaja u MMS sl. opterecenja je kroz varijaciju uzajamnih znakova momanata i normalnih sila (M i N) koje se vrsi za vreme dimenzionisanja. Prema tome, pod velikim pitanjem je koja kombinaciju znakova uticaja treba da se upotrebi prilikom linearnog kombinovanja uticaja u prikazivanju jednih jedinstvenih uticaja u reduktoru.
Zbog te viseznacnosti, u programu Tower nije postojao kod koji je na poseban nacin obradjivao MMS kombinacije opterecenja za uticaje u presecima, uticaje u indirektnim elementima i uticajima u reduktoru.
Ako i uradimo implementaciju integracije uticaja za MMS kombinacije opterecenja to bi bilo nepravilno. Evo primera:
S.0. 1) obican slucaj opterecenja: M = -300, N = -100
S.0. 2) MMS slucaj opterecenja: M = 100, N = 10
U kombinaciji I + II bilo bi pogresno ako bi ispisali kao M = -200 i N = -90, zato sto ovo nije neophodno najnepovoljnija varijacija uticaja.
Zbog toga, mi cemo ovo resiti onemogucavanjem prikazivanja uticaja u presecima, u indirektnim elementima i u reduktoru za MMS kombinacije opterecenja. Prikazivanje uticaja ce i dalje biti omoguceno za pojedinacni MMS slucaj opterecenja.
