huangyhg

high moments at column/base
hi, when modelling column loads on a foundation slab and the column loads include a moment the model will show high moments local to this applied load. how do you cater for this? i have had a few suggestions, some seem resonable, some i've used in the past but would like to hear the experts view (you guys).
thanks.
this is why most frame bases are modelled as pinned it is often difficult to manage the fully fixed loads..
i agree that the frame should be pinned ideally. however this is not our design (the frame) and there are high loads on the kind of frames which i guess (and would hope) that the steel designer is designing economically. i have also on occasions seen details which are certainly fixed when looking at upgrade work etc.
the steel construction institute used to have a method whereby you model dummy
i am not sure what you are asking. how to analyze; how to detail base plate, anchor bolts or foundation; steel of concrete frame?
sorry. i am looking at the foundation itself. usually piled. in a model i would get very high moment local to load. i.e. the moment applied at the column position is twisting the plate in the model significantly.
are you looking at frame columns sitting on a mat foundation? a large pier/pile cap? if you are modeling a mat/pile cap in safe, for example, how much do the moment magnitudes depend upon the size and aspect ratio of your elements?
(slightly off topic) when you have a "pinned" baseplate connection in a moment frame, how do you avoid a "soft story" at your first story of a multi story building?
ok i take it your talking about the baseplate:
so assuming that the load from the column is uniformly ditributed and completely distributed through the baseplate to the foundation. it would be helpful if you were to state what the column section size was, the moment at the base, the axial load coming down the column and the orientation.
i could help you as far as designing the baseplate, holding down bolts and pad foundation if you could suply me with the information.
you will probably need to create a moment resisting baseplate using side plates or a concrete encasing.
also what is the bearing capacity of the soil, the cohesivness of the soil or if it is on top of a pile any details on the existing pile and pile cap
r. murphy
mice mistructe masce
herewegothen,
are you talking about the concrete footing/pile cap under the concentrated moment?
to take care of this, bring your anchor bolts down to below the horizontal reinforcement and put a plate at the bottom.
you then have a truss with anchor bolt verticals, reinforcing bar horizontals and a diagonal concrete compression strut.
there seems to be some confusion here. i have received column loads from steelwork designers. these include moments. when using a model for a piled or even ground bearing the moment will cause a massive moment in the top of the element. caused i would think by the fact the element in model is a thin plate. how do others rationlize this moment, otherwise you'd have massive reinforcement in top. this is not job specific at the moment. just occured a number of times in past.
dont treat it as a moment, treat it as a push and a pull on your anchor bolts. this will reduce the effect somewhat.
refer my previous post, sorry this is not to uk standards but the principal still applies.

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