The room is 4m by 2.5m

So have you designed the floor system? What sort of floor live load would you need? Are you an engineer who has designed something like this before?

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Quote (TarikHKJ)

When removing the existing slab... where should I start, from the sides to the center or the opposite?

Demolition of this type can be performed, two ways:

1. Remove large pieces using heavy equipment (typically a crane) for lifting.

2. Remove small pieces by using much hand labor.

Which way depends on job site conditions (such as crane access) and a Contractor's resources (type equipment, worker skills, etc.)

IMHO, the Engineer should NOT specify which method to use. However the Engineer can (probably should) review and accept a Bidder's proposed method before contract award.

AND

A Contractor should NOT bid on a project unless the Contractor has a reasonable plan when the bid is submitted on how to perform the work.

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@JAE I have not designed this floor system.
It's a residential home with 3 kN/m2 L.L.
I am an engineer but I have not designed something like this before (only 2 years experience ;) ).

@SlideruleEra I will use the labor hand tools method because something like a crane is not possible, I was asking which is safer to start from the sides or the center, or does not matter since its a small span.

Thank you for your reply

Quote (TarikHKJ)

I am an engineer...only 2 years experience.

Whether demolition begins in the center or at the perimeter, at some point, the concrete slab that remains will become unstable.

By my calculation the slab (4m x 2.5m x 0.25m) has a mass of about 6,000 kg. Say that the slab becomes unstable when half the concrete has been removed. When you can provide a good answer on how to support and remove the (assumed) 3000 kg of remaining unstable concrete is when to consider which way is "best". This is not an entry level project.

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@SlideRuleEra Thanks for your reply, I know that its no small matter which is the reason I'm asking advise from experienced engineers I know and here on the forum.

This what I have in mind, I will support the slab with formwork supported by braced steel props 50-70 cm apart,
After the concrete is taken apart and the rebar cut, remains will be taken off the formwork by hand off site.

TarikHKJ - It is not wise for us to tell you how to do this project. But we can give you some points to consider.

As I understand the project, slab #1 (labeled in the photo) is to be removed.
The braced props will bear on landing #3 and and stairs.
Your proposal is to demolish the temporarily supported reinforced concrete before removing any of it.

The braced props will fill the entire stairwell (see my sketch below) and will have to support the entire weight of slab #1 (approximately 6000 kg) plus a reasonable construction load. Also, may be some impact when existing rebar are cut.

1. Will landing #3 and the stairs support this loading?

2. The braced props will make access to the work area (from ground level) very difficult. Since a crane cannot be used, I assume there is no access from above. How will the work area be accessed and concrete debris be removed?

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1: The landing and the stairs were designed to live load 5.5 kN/m2 and dead load 2 kN/m2, using this load combination Pu=1.2DL + 1.6LL
The weight of the slab+formork+equipment is approximately 9 kN/m2 on the stairs and landing

2:there is another access point.

Do I understand correctly... the landing / stairs rated live load capacity is 5.5 kN/m² and the applied load is 9 kN/m²? Seems the landing / stairs will be overloaded.
Can not include the rated 2 kN/m² dead load capacity. The landing / stairs have to support themselves.

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