Special Masonry Shearwall - Joint Reinforcement 1

[engjg]

Is it permissible under IBC 2015/ACI 530-13 to use joint reinforcement to satisfy the horizontal reinforcement ratio of special masonry shearwalls? I see in the 7th ed of the Reinforced Masonry Engineering Handbook they show an example doing this but do address how this satisfied the requirement that horizontal shear reinforcement of special masonry shearwalls must be hooked around the last vertical bar...If you have the last grid of ladder joint reinforcement around this last cell have you provided the same/intent of hooking the bar per code? Also they speak to have the the first course be the first horizontally reinforced course or having this bar be in the footing instead; is the latter stragety addressed in the code

 

[masonrygeek]

If you look at the most recent version of TMS 402-16, Section 6.1.7.1.3 covers joint reinforcement in shear.'

6.1.7.1.3 Joint reinforcement used as shear
reinforcement and needed to satisfy the shear strength
requirements of Section 9.3.4.1.2 shall be anchored
around the edge reinforcing bar in the edge cell, either by
bar placement between adjacent cross-wires or with a 90-
degree bend in longitudinal wires bent around the edge
cell and with at least 3-in. (76-mm) bend extensions in
mortar or grout.

Commentary
6.1.7.1.3 Wire reinforcement should be
anchored around or beyond the edge reinforcing bar. Joint
reinforcement longitudinal wires and wire bends are
placed over masonry unit face shells in mortar and wire
extensions can be placed in edge cell mortar or can extend
into edge cell grout. Both joint reinforcement longitudinal
wires and cross wires can be used to confine vertical
reinforcing bars and grouted cells because wires are
developed within a short length.

I'm not sure about the reinforcing in the foundation.

 

[engjg]

thanks. don't have 402-16 handy and that section of 402-13 doesn't exist...could you tell me what section 9.3.4.1.2 being referenced refers to?

 

[RWW0002]

Section 9.3.4.1.2 appears to be the same in the two versions (13 and 16). The provision quoted above as 6.1.7.1.3 can be found in 9.3.3.3.2.3 in TMS 402-13.

I recently heard a comment in some continuing ed. concerning this topic and it was the presenter's opinion that the requirements of 7.3.2.6 (b) force the use of standard reinforcement in lieu of jt. reinf. for SRMSW. Specifically the term "shall be embedded in grout"

(b)The maximum spacing of horizontal reinforcement required to resist in-plane shear shall be uniformly distributed, shall be the smaller of one-third the length of the shear wall and one-third the height of the shear wall, and shall be embedded in grout. The maximum spacing of horizontal reinforcement shall not exceed 48 in. for masonry laid in running bond and 24 in. for masonry not laid in running bond.

The presenter was very knowledgeable in masonry design and the code committees and quite possibly a frequenter of these forums..

I questioned this interpretation upon returning to the office based on the following:
-Section 9.3 of TMS 402 gives guidance for use of joint. reinf. used as shear reinf in SDC D, E, and F (although I cannot find a similar provision for ASD design in 8.3). Why would there be provisions for jt. reinf. in shear walls in high seismic design categories if it were not allowed for SRMSW??
-Even if it is the intention to limit reinforcement required to resist in-plane shear to standard bars in bond beams, I do not feel like the provision quoted above (9.3.2.6) would apply for reinforcement used solely to meet the minimum horizontal reinforcement requirements (since it specifically says "required to resist in-plane shear").

 

[masonrygeek]

As RWW points out, this is a topic of conversation right now within the TMS 402 Committee with some saying it needs to be embedded in grout. Of course, most joint reinforcement is bedded in mortar since it falls on the face shells of the block. There is also some feeling that the way walls are built you don't get full mortar coverage around joint reinforcement so that could be a concern as well. This discussion will continue until more research is done.