a706 bars for masonry

[SeanMD]

In reviewing ACI ch 21.2.5, it seems unless a615 bars meet certain criteria we should be using a706 bars in concrete for moment frames and wall boundry elements.

This is used, I think, because the a706 bars are more ductile. Is there a similar criteria for masonry? I cant seem to find it if there is. Should we be using a 706 bars for the ends of masonry shear walls too?

 

[ishvaaag]

Some ductilty it needs have, other thing is being of "more" or "special" ductility. For reinforced concrete in Spain it is maybe since EHE 1998 that we use steel that is simultaneously weldable and ductile, yet there are one of special ductility. The requirement of being weldable surely appeared as an acknowledgement of that many off-site rebar was prepared with ties and stirrups welded to main rebar, something not explicitly prohibited by the code for buildings (and I am not currently aware on what status for bridges).

Now, frankly, I don't think for a masonry wall any special ductility is required. See, special ductility may what, extend the elongation over the yield point by 20% ? By the limit elongation of an ordinary steel, any masonry would be rubble at, say, 8% elongation. You have hair cracking since 1/1700! The elongation to rupture of some ordinary steel is 136 times that, so one must expect that adding a proportionate amount of steel to masonry is made thinking in the outfit remaining in the elastic limit. There's no advantage whatsoever in providing very ductile steels to reinforced masonry.

 

[ishvaaag]

Pears with pears. Look at griffis table ...

Tile, Hollow Clay Brick, supporting sructural element Wind frame, deformation type Shear Strain (DMI) Recommended Limit H/2000. Now, limit strain is limit strain and other thing is shear deformation, so I must correct myself.

Limit tensile strain for brickwork lesser but in the order of magnitude of concrete. The difference is that reinforced concrete is designed to remain organized and with ultimate strength devices till its ultimate strength. Concrete itself with moderately ductile steel has a ratio of ultimate strains (steel to concrete) of say 25. So think you have (whilst we look for a value) 50 times elongation for steel to fail than brickwork. When treated as reinforcement to walls etc, the ultimate strains meant what in the above post said: disorganizatio of the masonry; no cage to contain the fractioned elements. So no gain in going more and more ductile for masonries.

Furthermore, it is interesting to distinguish between structural ductility and steel ductility. For example a pole prestressed with wire can behave interestingly in ductile way whilst the actual prestress at the wire stays around half the stress of rupture, entirely in the elastic realm and far from the realm of plasticity and strain hardening etc and yet gets for the structure the desired behaviour.