Trimmer bars for large slab openings

[Michael Val]

I've been racking my brain for quite some time now over the detailing and design of trimmer bars around an area. For example purposes, I have this slab opening

and the original steel requirement is this :


From what I have read, the proper way to calculate trimmer bars is by determining the disturbed reinforcements and then distributing half of this on each side of the opening. For this example, let's say the vertical bar requirement is H13-200 + H20-200. So, 2700 mm / 2 = 1350 mm, and 1350 mm / 200 mm = approximately 7H13 + 7H20.

Next, calculate the total area of the bars:

7 x area of 13 mm diameter bar + 7 x area of 20 mm diameter bar
7 x 132.732 sq.mm + 7 x 314.159 sq.mm = 3128.237 sq.mm

If the maximum diameter is 25 mm, you can use around 7H25 = 3436.117 sq.mm on the sides of the opening.

My questions are:

1. How do you determine the spacing of these 7H25 rebars?
2. Do I still need to include links as confinement reinforcement for these rebars?
3. How do you know how many diagonal bars are needed?
4. If anyone is using Eurocode, do you have references because I can't find any?

Thank you very much.

 

[KootK]

In general, and particularly at a high demand location like this, it's prudent to think of this as what it primarily is: an offset lap splice between the trimmer bars and the discontinued rebar in front of and behind the opening. Envisaged this way, I suspect that you'll be able to answer most of your questions yourself.

 

[EngDM]

I'd be trying to avoid an opening through a drop panel.