Shoring 18 Story Building Loads at Ground Floor Level - Steel Shear Collar Design

[Enable]

So here's the situation. P1 slab is being fully replaced in an underground parking garage. The slab abuts a 300mm x 600mm corner building column. This column is significantly deteriorated at its base and once the removal of the P1 slab occurs it is likely much of that column will come with it. Based on preliminary drilling at least half of the column is in questionable shape.

Thus the shoring needs to be designed to pickup the entirety of the column load in case the worst should happen. Problem being this is an occupied apartment complex and going above the ground floor level is a no-go.

The P1 column has a 812mm x 300mm beam above it plus a 200mm slab that can be used to transfer the vertical load to adjacent vertical shoring. But the factored loads are about 3x the shear capacity of these members so I need a way to transfer the load from the P1 column to my steel shoring structure (see loads below). I'm thinking a steel collar with post-installed anchors and taking the vertical shoring to the footing.

Below are some sketches of the elevation / proposed collar. It seems a bit clunky so before I go full monty and start to calc it all out I just wanted to get insight from the team to see if there is a better way to do this (that's why details on welds and such are sparse this is more conceptual at the moment). I'm assuming that the slab + beam will pick up their full shear capacities / transfer that to the vertical shoring, and so the collar anchorage is designed for the net (about 1000kN).

Engineering particulars:

fc = 20 mPa
factored load on column = 1500 kN
200mm ground floor slab with Vr = Vc = 230 kN
812mm x 300mm beam above P1 column with Vr = 237 kN = Vc + Vs

Here's the elevation sketch

Here's the plan of the collar

Here's section A-A

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[hokie66]

I would not depend on the horizontal elements. They are designed just to resist the gravity forces at that floor only. So my approach would be to support all the 1500 kN on the connections to the column.

 

[Enable]

That's probably prudent and I think can be reasonably handled. I can bring the plates down as much as I need to accommodate additional bolt rows.

One thing that concerns me is that the threaded rod installation precludes precision. I mean, the contractor will have to take a template of idealized anchorage locations (once scanning identifies bar locations) mark where to drill on the column, drill the holes with an oversize bit, grout the anchors into place and then slip the bracket assembly overtop.

Seems like lining things up without significant hole tolerance would be a nightmare. But if I give a lot of tolerance then they become slip critical and I dont like that much at all. I would much prefer bearing in this application.

I could have them weld plate washers on each bolt after installation. Would that be the best way to achieve bearing condition or is there a better way to do that? At the moment this thing is getting pretty beefy with all the field welds!

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[HTURKAK]

Dear Enable (Structural),

I would prefer the jacketing of the subject column with high performance concrete for two storeys with following steps,

- Shoring of the beams at GFL to the foundation level ( with through props )

- Shoring of the P1 slab ( which will be replaced )

- Stripping of the cover of column, provide an empty pad around column at P1 slab level

- Reinforcement cage for two storeys and jacketing of the column say 100 mm thk.

- Take out the beam probs for 1st basement level,

- Demolish the P1 slab and construct new slab.

Good luck..

 

[dhengr]

Enable:
As a temporary construction situation, can you justify/tolerate 75 or 80% of the max. column cap’y. as being o.k. during part of this process? Maybe by doing one col. at a time. Could you remove 2 or 3’ of vert. conc. rebar cover, to fit your bracket vertically, all around the entire col., into & exposing the col. tie stl., thus the reduced cap’y? This would allow you to inset your temp. support brackets/frame, thus allowing 1.5” or so of bracket bearing all around the col., at the bracket top. Drypack the top of the bracket to the conc. col. notch, and now you have some bearing, and the A.B’s. The top of the bracket could just be a heavy stl. pl., as you seem to show, which just canti’s. in 1.5”, or so, for the bearing of the conc. above. I would like to move the 4 tube cols. out about .75” from your current positioning, so that I could push forming plywd. behind them to form the new conc. col.

Edit:
Once you know where the rebar stl. is, then lay out and drill your vert. bracket pls., install the entire bracket/frame, and use it as a template for drilling and injection grouting the A.B. holes. Put some sort of a soft rubber (o-ring, soft rubber flat washer) gasket around/on each holes in the vert. stl. bracket pl. to conform with the chipped conc. and to retain the grout/epoxy.

 

[bones206]

A couple conceptual ideas:

1) Core holes into column face and grout-in some high strength through-bolts. Attach some big channels on opposing faces of the column. Set the channels a couple inches below the beam soffit and dry pack with grout. Install shoring steel to carry load from channels to foundation.

2) Core holes into column and grout in some stiff steel "needle beams" (heaviest WF section that can safely pass through the rebar cage) that protrude to provide lugs from each face of the column. Install shoring steel to carry load from needle beams to foundation.