wind calculations

huangyhg

wind calculations
background:
wind load calculations as per asce7-02
this is a question related to wind calculations for a project with two adjacent buildings.
both buildings are rectangular in shape. one is 6-story high the other is 3-story high. both are about the same size in plan view. they are next to each others and seperated by a 1" expansion joint. so, the two buildings are completely independent from each others structurally. they have their own independent skin and building envelop.
question:
in this situation, should the wind calculations be based on the two buildings together as if they are one structure? or should each building has its own wind load calculations.
please explain why briefly in either case.
thanks,
do they have the same owner?  with no expectation of one building being torn down, leaving the other exposed to the wind?
daveatkins
you should always do the analysis with no shielding effect from an immediate structure since that structure can be torn down by choice, or destroyed by fire, etc.  you cannot predict the future.
mike mccann
mccann engineering
it would be interesting to do both and see what you get.  while in some ways the taller building shields the lower, you may find that in others you get a worse effect.  components and cladding, for instance, is based on the mrh of the structure.  perhaps the taller building would cause the other to have a greater c&c pressure on one side.  i haven't tried it myself but i think it would be worth investigating.
i take it you have no pounding effects or concerns?
i agree with ucfse.  if it were me i would want to take the time to investigate both conditions and design each for the worst case.
the lateral bracing system should experience the worst case loads assuming the adjacent building is not there, but c&c loads for the smaller building would likely be worse considering it as a portion of the taller one.
yes, as i said the two buildings are on the same project. they are for the same owner and will be built at the same time on the same lot.
considering the fact that it is not practical to predict the future, the asce7 does not allow any considerations of adjacent building shielding and that is stipulated in the code clearly. therefore independent analysis should be done for mwfrs.
based on common engineering sense the c&c calculations should be done based on the two buildings as one. what is not clear is where in the code this requirement is for doing calculations for c&c based on the two buildings combined? in my opinion c&c calculations based on the two buildings as one is questionable and debatable strictly from the asce7 point of view. can anyone prove me wrong?
thanks,
we've considered the expansion joint in a building for a freezer warehouse to not imply two separate buildings but one as the two sections were totally integral with each other in function....i.e. one was a dock area serving a freezer area....there was no consideration that the dock would someday be torn down and leave the freezer as they were functionally dependent on one another.
however, for other cases, there may not be this functional dependence and i would tend to treat them as seperate structures.
l775,
interesting question trying to prove you wrong.  let's try looking at it this way.  you stateed in the op that the two buildings will be separated by a 1" expansion joint.  if that is the case there is no physical gap between the two that wind can hit.  this situation would be analagous to one building with a typical expansion joint located in it.  the fact that each "side" has its own mwfrs wouldn't change that.
the situation you describe is, in fact, one building with two different roof heights.  when/if one gets torn down you still have one building just a smaller one.
two building, or one building with an expansion joint?
i doubt it will make much difference as each main wind force resistance will need to allow for external plus internal pressures (otherwise an internal suction would pull the two sections together).
csd
i have wrestled with this also.
if you apply the mwfrs direct pressure to one building, this will only be a portion of the total mwfrs lateral load. the building on the other side of the expansion joint will receive the suction. shouldn't each building be designed to receive the full mwfrs load? if one building is torn down or is destroyed by fire, the other may still be in use and will now have to resist the full mwfrs.
asce does not allow sheilding because sheilding is less conservative and relies on the assumption that the shielding building will be present for the life of the shielded building.  
asce does not forbid you to use engineering judgment and account for both buildings being present in the wind calculations, as well as accounting for either building acting alone, when doing so could help you identify worse loading conditions.  it is reasonable that both, where both buildings are present or one is razed, situations could arise in the life of either structure.