Intermediate Precast vs Special Reinforced Concrete Walls

[Prestressed Guy]

What is the difference in detailing for Intermediate Precast Shear Walls (IPSW) vs Special Reinforced Concrete Walls (SRCW) made from precast elements. Specifically, is Monolithic Emulation required for IPSW or is that the difference between the two systems. My understanding is that SRCW requires monolithic emulation design but IPSW is primarily for typical large panel jointed precast walls which are coupled together for sharing dead load to resist overturning but no special reinforcement provisions other than the 1.5Fy capacity of non-ductile elements of connections.

Secondary question. I have an eor who is only allowing the use of beams which are on 7' - 8' centers to be used for out of plane anchorage per ASCE 7-10 12.11 with no other OOP restraint. The walls are 10' to 12' wide so this means that many of the walls will only have one out-of-plane anchorage and need to lean on the neighbor to remain stable.

 

[Prestressed Guy]

On the second question about restraint. There are some narrow panels that are not attached to any beams and other sections where there are up to three wall panels in a row that each only have one out-of-plane attachment to the roof structure. The EOR is saying that I need to design the precast wall to emulate a monolithic wall so that it can span between the beams on adjoining panels. In his drawings, he has shown a typical joint connection with a embed plate with headed studs on each side and a flat plate welded between. Not sure how that is expected to resist bending.

 

[Prestressed Guy]

I am surprised that no one is taking any nibbles at this one. I have attached a crude schematic diagram of one of the walls at the roof level. The arrows are the roof beam bearing locations that are to provide anchorage to the precast for OOP lateral. The circles are the precast panel joints. The green lines show panels at have two anchorage points from beams. The red lines are panels that only have one support and must get stability from the adjoining panels. The eor has provided the attached joint detail and stated that it is to be used to design the connection to resist bending between anchorages (across panel joints) as required by 12.11.2.1 because the beams are more than 4' oc.

 

[dold]

I don't do any off site precast design, just tiltup.

I'd have to assume there is a roof deck and chord angle (ledger angle)? If so, how is the angle anchored to the wall? Embeds? Post installed anchors? Roof deck can't be used for wall anchorage perpendicular to the deck span per ASCE 7. If i were you, i'd be putting some sort of continuous steel member below his beams. This member would be welded to embeds placed at 48" oc or so. Then the 'strongback/waler' member would be connected to the beams somehow. I wouldnt even consider resisting the bending you're describing with a stitch plate and those anemic embeds he's showing.

When you're designing your out of plane anchorage, don't forget the 1.4 factor applied to the OOP force. ASCE 7-10 SECTION 12.11.2.2.2-STEEL ELEMENTS OF STRUCTURAL WALL ANCHORAGE SYSTEM

For intermediate precast, dont forget about the 10kip hold down "integrity tie" requirement. Unless - i think - if you can show there is no net overturning then it isnt required?

 

[Prestressed Guy]

The beams are spaced at 8'and there is an embed between to attach the ledger to for IP lateral collector at the deck edge but told me in plan review prior to deferred submittal that they cannot be used for OOP loads. The 10k at base is required even if there is no uplift. The ledger is an L4x4x5/8 but I agree with him that it is not strong enough to take OOP loads without reinforcement which he does not want to call out. He had a note on the detail that the wall is to act as a single monolithic wall on a detail that shows a hinge at the vertical joint. He is claiming that the problem is that I am not designing the wall as monolithic emulation but if he wanted emulative design the building should have been specified as a Special reinforced concrete shear wall, not intermediate precast shear wall.
I pretty much do nothing but precast design for most of the past 20 years but have never run across an eor that expected the wall to resist bending across the joints before. Given the flexible deck, Fp = 1.028Wp and the panels weigh 140 pdf. That comes to about 2klf at the roof.