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Re: Dual - System ( frame+wall)

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Jordan is correct.

The moment frames in a "dual system" are intended as a "BACK UP" system to help out a stiffer lateral system elsewhere in the building. The moment frame portion is not supposed to be able to handle 100% of the lateral force considering the stiffer system as 100% completely failed. It's intent is to take up the slack, if any, as the stiff elements begins to deflect excessively ( i.e. yield)

Code requirements (well in the UBC) have use 25% of the total lateral force as the baseshear design value for the moment frames.

They are typically placed at the perimeter, can help lesses torsional irregularities and drift when the stiffer system is primarily in the core.


On Jan 11, 2008 5:02 AM, Jordan Truesdell, PE <seaint2(--nospam--at)> wrote:
Is this borne out by testing?  Aside from the fact that this seems to be a cost-inefficient way to build (walls enough to carry most of the load plus a fully redundant steel moment frame), in a quasi-static case, the walls would be taking a multiple of the load seen by the frame (due to the response factor design methodology), resulting in a sudden collapse as the cmu walls failed.


y.hamida wrote:
yes: the walls will take load as their rigidity but when  the stresses in the walls reinforcement reach mor than
 the yielding point the walls will crack in the plastic phase, and  will loose their rigidty then the frames will
 intervene and take the entire base shear because the frames already design to resist the entire shear.
----- Original Message -----
From: Thor Tandy
Sent: Thursday, January 10, 2008 11:56 AM
Subject: RE: Dual - System ( frame+wall)

... surely the stiffer element will take the load up before the frame deforms enough to carry loads ...?  Or is this suggesting that the base shear of a dual system is greater for frames than for shear walls ...?

Thor A. Tandy P.Eng, MIStructE, Struct Eng
Victoria, BC


-----Original Message-----
From: y.hamida [mailto:y.hamida(--nospam--at)]
Sent: Thursday, January 10, 2008 11:36 AM
To: seaint(--nospam--at)
Subject: Dual - System ( frame+wall)

                                                                  Dual - System
         A  -  code sayes  if you have shear walls and ordinary frames (   beams+columns )  
                               to resist earthquake 
                          You can neglect the ordinary  frames and resist the entire base shear by shear walls 
                            and designe  the ordinary frames just  for axial loads.

       B  -  M y (ph.d) research sayes;

              if you have  moment resisting frames and walls( reinforce concrete or masonary  )
               to resist earthquake You can neglect the walls and resist the entire base shear
               by  moment resisting frames  and the walls design just  for axial loads  
               and minimum reinforcement  for concrete walls and conect the masonary walls to 
                the floor by dowels  .                
                        Dr .hamida

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