Boundary zone detailing of shear wall as per UBC 1997

[dollarbulldog]

Greetings

I 'd like to ask a question regarding boundary zone in special concrete wall as per UBC 1997.

1) Is that correct that the vertical reinforcement layout in boundary zone be controlled by the requirement of confinement spacing?

2) Can we still include the rebar outside boundary zone to compute interaction diagram as usual done by may building analysis & design package?

So is it correct to conclude that the boundary zone is just a matter of detailing not the matter of strength evaluation?

Please suggest.

Thank you

 

[ishvaaag]

(Not looking at UBC at the moment but Ghosh and Dormel book

Design of Concrete Buildings for Earthquake and wind forces
pca

The formula used to define hoop stirrups is one of confinement, hence confinement is asked for the boundary zone. It protects against non ductile failure by excess of compression stress in the concrete without adequate reinforcement and so is of course a matter of detailing as well.

See also that sometimes maximum separations are mandated in the same intent.

http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1420&context=engpapers

In that light I think that counting additional steel in the web of the shearwall to flexural purposes -even if technically correct- would be cheating the intent; i.e., I think that every rebar in the compression head should be protected by the special confinement. Yet to not be excessively conservative, I might consider the vertical -along the height- rebar in the web for normal stresses equilibrium as long it is uniform, i.e., using a closer regular mesh would look acceptable to me, but not a weak mesh in the web and then significant additional vertical rebar outside the confined nucleus just to ameliorate the behaviur under the earthquake drive.

This is of course an inconsistence against the principle of compatibility of deformations for some case, admitting it in one case to lower concrete stresses and then not in another. However in light of the intent it may not be illogical. By the boundary elements you are protecting against brusque compressive failure; it is accepted the web (that has own requirements) at some earthquake, not being protected by confinement reinforcement will show more cracking; but throwing to the web required protected steel in the boundary zone might produce the brusque compressive kind of failure that is wanted barred.