ASCE 7-10 Chapter 14 Masonry Detailing

[cab7320]

In reviewing Masonry detailing for a project slated to have special reinforced masonry shearwalls in SDC D i have come across a detailing provision that requires no lap splices or weleded splices within the plastic hinge zone of a Special Reinforced Masonry Shearwall.

ASCE 7-10 section 14.4.4.2.2 stipulates no splicing, except mechanical type II in plastic hinge zones. and they define the hinge zone as 15% of the distance btw zero and maximum moment. which for most buidlings would be the base of the wall.

IBC 2012 has a similar requirement in the strength design provision alterations. in ASD they require a 50% increase if stress is above 80% in reinf.

Typically footings would have dowels matching the vertical bar spacing and size. This dowel is lapped with the vertical bars in the plastic hinge zone, apparently.

Does the ASCE 7 provison aiim to eliminate this type of detailing? Does the Dowel from the footing need to be long enough to reach above the plastic hinge zone or have a mechanical type II coupler to the wall reinf.? I don't see this currently being done on jobs i have seen in construction.

Any input is appreciated. or loopholes to this requirement to explain what i currently see being done everywhere.

 

[wannabeSE]

Maybe IBC §1613.1 helps. It excludes chapter 14 of ASCE 7. Where is the similar provision in the IBC? I know they modify the development length requirements (e.g. with strength design, the splice does not need to exceed 72 bar diameters)

FEMA P-750's commentary to ASCE 7 may be useful

C14.4.6.2.2 Splices. In general, the first portion of this section, which prohibits splices in plastic hinge zones, is intended to produce adequate inelastic deformation capacity in those regions. In general, the presence of splices in plastic hinge zones reduces inelastic deformation capacity because the area of steel is doubled at the splice, reducing the extent of yielding. However, there is some controversy concerning the technical validity and necessity for this requirement for masonry walls. Similar requirements apply to plastic hinge zones of reinforced concrete frames, they do not apply to plastic hinge zones of reinforced concrete walls. Also, this requirement does not distinguish between shear-critical and flexurally dominated shear walls. The MSJC is continuing to discuss related requirements for flexurally dominated, highly ductile shear walls.

 

[cab7320]

Thanks on the Chapter 16 exclusion of ASCE 7 Chapter 14.

IBC 2012 Chapter 21 (Masonry) 2107 and 2108 give some added provisions for lap splices.
In ASD 2107 notes the 72 db max as you mention, but also gives the 50% increase if stress is more than 80%
In Stength Design section 2108 notes no welded splices or type I mechanical in plastic hinge zone but actually doesn't limit lap splices. so i guess that is why they are still being used typically.

Your FEMA reference is interesting as well, i guess that is why the building code has chosen not to adopt the provision. However in concrete walls the laps are increased in the expected areas of yeilding (hinge zones) 25%, seems like this would be replicated in masonry walls if the RC analogy is going to be utilized. Also, RC walls typically have confining ties on boundary zones where yeilding will occurs so the long bars are much more confined than in a masonry wall.

 

[cab7320]

Anyone know if IBC 2015 and the new ASCE 5-13 change any of this? I don't have copies of those codes yet.

Thanks,