A seismic ring beam and frame reinforcement in Batumi

Where reinforcement works in a house

In a seismic area a house is held together not by concrete or blocks but by reinforcement tied into one system. Concrete works in compression, and when the house sways, the steel takes the tension and bending. So the engineer designs the reinforcement of every part to the Georgian code, and our job on site is to build it with no deviations. The general principles of earthquake resistance are on the page about earthquake-resistant construction; here we cover the work itself.

• Frame columns and beams: longitudinal bars and stirrups, placed closer together near the joints.
• Floor slabs: two meshes with extra bars over the columns and round openings.
• A seismic ring beam along the top of the masonry on each storey in a house with load-bearing walls.
• Vertical concrete cores at corners, wall junctions and wide openings.
• Lintels over windows and doors.

A seismic ring beam in a block house

A ring beam is a closed reinforced concrete beam running along all the load-bearing walls at the level of each floor. It ties the walls into a box so they do not part at the corners in an earthquake, and spreads the load from the floor onto the masonry. It must be continuous: if it is broken over a wide window or the staircase, the wall at that point works separately from the rest.

In a house with a cast-in-place concrete frame the role of the ring beam is played by the beams and the slab, and the masonry between the columns is anchored to the frame. How the walls themselves are built is described on the page about load-bearing walls and partitions, and the frame with brick infill is covered in the section on concrete frame and brick construction.

Joints, laps and concrete cover

Most mistakes happen not in the long bars but at the joints. Where a column meets a beam, stirrups are placed at reduced spacing, and they must not be left out even if space is tight. We make bar laps the length and in the places shown on the drawings, not wherever a bar happened to end. Structural reinforcement is not welded: welding at a joint changes the properties of the steel, so cages are tied with wire.

The concrete cover over the reinforcement is held by plastic spacers of the right height. By the sea this matters especially: if a bar lies on the formwork, in a few years rust at that spot will split the concrete from inside.

How we check the reinforcement

Before every pour the site foreman goes over the cage with the drawings and checks diameters, spacing, stirrups at joints, laps, starter bars for the next storey and spacers. Everything is photographed grid line by grid line, and you get the photos in the report before the concrete arrives. If you have hired your own site inspection engineer, we time the reinforcement sign-off for when they can come or join a video call.

Mistakes we see on other sites

• stirrups at column joints placed at the same spacing as mid-height, or left out;
• all column laps made at one level, although the drawing staggers them;
• a ring beam broken over an opening or not closed at a corner;
• reinforcement lying on the formwork without spacers;
• rusty bars with flaking mill scale used without cleaning.

If another contractor started the shell, where possible we open up and check such places before carrying on.

How much seismic ring beams and reinforcement cost

A seismic ring beam on masonry with formwork, reinforcement and concrete costs from 100 ₾ per linear metre. Cast-in-place columns and beams are from 1,410 ₾ per m³, a lintel over an opening from 100 ₾ per linear metre, and a concrete frame without walls from 650 ₾ per m² of floor area. If old masonry needs strengthening, mesh with sprayed concrete is from 235 ₾ per m². The structural section of the design with a seismic calculation is from 27 ₾ per m². The final cost is set from the design, after agreement on the estimate.