Stresses within a glass and concrete slab
Stresses within a glass and concrete slab
(OP)
Dear Engineers
I am wanting to check the design of a reinforced concrete-slab that has glass-block voids and a band of insulation (please see attached). The slab is constructed in two parts; with the glass-blocks laid out, the bottom rib, which contains the reinforcement, is poured first and the dowels fitted. The insulation is pushed over the dowels when the concrete is sufficiently set and the top layer of concrete is poured.
The slabs will be expected to span 2.5-m (11-blocks x 11-blocks)
I have assumed that the the dowels and concrete-blocks will allow the slab to act as a whole and that the mode of failure would be through the glass-block where it meets the concrete (X-X in the diagram).
The insulation will be in the 'tension' area of the section.
The section would be evaluated by taking moments around the N.A. The glass will only be expected to resist shear. Dowels are to be used to hold the two skins of concrete together.
Would I be right in my analysis of the mode of failure, please?
Regards
I am wanting to check the design of a reinforced concrete-slab that has glass-block voids and a band of insulation (please see attached). The slab is constructed in two parts; with the glass-blocks laid out, the bottom rib, which contains the reinforcement, is poured first and the dowels fitted. The insulation is pushed over the dowels when the concrete is sufficiently set and the top layer of concrete is poured.
The slabs will be expected to span 2.5-m (11-blocks x 11-blocks)
I have assumed that the the dowels and concrete-blocks will allow the slab to act as a whole and that the mode of failure would be through the glass-block where it meets the concrete (X-X in the diagram).
The insulation will be in the 'tension' area of the section.
The section would be evaluated by taking moments around the N.A. The glass will only be expected to resist shear. Dowels are to be used to hold the two skins of concrete together.
Would I be right in my analysis of the mode of failure, please?
Regards






RE: Stresses within a glass and concrete slab
Where you have the insulation, you have two individual 45mm thick slabs/beams, not a 110mm thick section. The dowels across the insulation need to transfer horizontal shear to make the two pieces composite, and they will simply bend across the gap. You can back calculate a composite (110mm) section strength based on what horizontal shear you can transfer through bending of the dowels. It will not be very much.
RE: Stresses within a glass and concrete slab
I do not think the top and bottom concrete can be assumed to work together as a slab the way it is detailed.
If you got rid of the insulation, it could work as a ribbed slab!
RE: Stresses within a glass and concrete slab
You seem to be ignoring the glass-blocks. The blocks have a known structural strength and will provide the stability required, including in the transverse direction. The blocks will have to resist the strain of deformation, not the insulation. The strength of the insulation is irrelevant; only its location is important.
The neutral-axis will be calculated for the cracked section with only the compressive-concrete and tension-steel being considered in the equations but, as the glass-blocks are holding the whole slab together, the blocks need to be checked for failure but not factored into the functions. I think the blocks would be the primary failure mode; a brittle fracture below the neutral-axis. The block would not fail where encased in concrete. The walls of the glass-blocks may be 20-mm thick but I doubt if the steel would fail first.
As for not using insulation and casting the rib in concrete - that's what I do every day for a living. I make pavement-lights. This insulation is being requested more and more in my work and I am trying to assess the strength of the slab. I blame global-warming for this extra work.
Regards
RE: Stresses within a glass and concrete slab
RE: Stresses within a glass and concrete slab
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Stresses within a glass and concrete slab
The glass blocks are voids as Hokie said!
RE: Stresses within a glass and concrete slab
You have NO composite section.