Seismic design of ventilated facades in Georgia: what the regulation requires and how we detail it
Georgia sits in a seismic region, and a cladding panel is the part of a building most likely to fall on someone. This article explains how the Georgian seismic regulation treats facades and what that means for brackets, anchors and joints.
Where the requirement comes from
The seismic rules sit in the technical regulation "Seismic-resistant construction", Annex 3 to Government of Georgia Resolution No. 71 of 15 January 2014. It uses the MSK-64 intensity scale and lists a design intensity and a coefficient A for each settlement. The regulation allows these values to be refined by microzoning of the site.
The regulation does not describe ventilated facades as a system. What it does contain is the provision on non-structural elements (Article 6, paragraph 8): parapets, gables, cornices, infill walls, partitions, equipment, enclosures and similar parts whose collapse could cause casualties are checked for the design seismic action together with their supports. A facade cladding panel hanging on a bracket is exactly such an element, and we apply the provision to it. This is our engineering reading, not a quotation: there is no Georgian text on facade systems to cite.
The seismic method of the regulation is the spectral one. Eurocode 8 (EN 1998-1) is not the national basis; it can be used as a reference, see Eurocodes in Georgia, but the intensity and the coefficient come from the Georgian tables.
Design intensity in the main cities
| City | Intensity, MSK-64 | Coefficient A |
|---|---|---|
| Tbilisi | 8 | 0.17 |
| Kutaisi | 8 | 0.13 |
| Batumi | 7 | 0.09 |
Tbilisi and Kutaisi share the same intensity but not the same coefficient, so the calculated inertial load on a panel in Tbilisi is higher. Take the values for other settlements from the regulation itself and check them for the actual plot. A full city-by-city comparison is in Tbilisi, Batumi and Kutaisi: design conditions.
What an earthquake does to a facade
Two effects act on the cladding at the same time.
- Inertial force. The panel, its subframe and the insulation have mass, and the ground motion pushes them horizontally, mostly out of the plane of the wall. The force grows with the mass of the cladding.
- Imposed drift. The structure of the building deforms. Floor slabs move relative to each other, and the wall behind the facade shears. A rigid subframe fixed to two different floors is forced to follow this movement or break.
The first effect is checked by calculation. The second is solved by detailing: the system has to be able to move without losing a single panel.
Design principles
Keep the mass down
Inertial load is proportional to weight, so a light cladding helps in every connection. Aluminium cassettes, aluminium composite, HPL and thin fibre cement boards load the brackets far less than natural stone or thick porcelain stoneware. The choice between materials is covered in choosing a facade system; in a seismic city the weight of the cladding is one of the criteria, not a footnote.
Fix to the structure, not to the infill
The anchors must go into elements that remain in place during the shaking: reinforced concrete walls, columns and slab edges. Brackets in aerated concrete, hollow blocks or partition masonry carry the load only as long as that masonry survives, and the masonry is exactly the part that cracks. Where the wall is infill, the bracket line is moved to the slab edge or the anchoring is designed against the actual test results; see anchors and substrates.
Allow controlled movement
The usual solutions are slotted holes in brackets and profiles, a combination of fixed and sliding points on every vertical profile, joints in the cladding wider than thermal movement alone would require, and a vertical break in the subframe at every movement joint of the building. The same elements serve thermal expansion; the basics are in movement joints. The seismic case simply asks for a larger travel.
Add a second line of retention for heavy panels
Where a panel falls onto a pavement or an entrance, a hook, a safety clip or a secondary rail that holds the panel if the primary fixing fails is justified. This is a design decision for the dangerous zones (entrances, passages, balconies above public space), not a rule for the entire facade.
Calculation sequence
- Take the design intensity and coefficient A for the site from the regulation; check whether microzoning exists.
- Collect the masses: cladding, subframe, insulation, fixings, per square metre of facade.
- Calculate the horizontal seismic force on the panel and on the subframe with the method of the regulation, applying the factors for a non-structural element and for the height of the attachment point (the higher the floor, the larger the amplification).
- Combine it with dead load and wind in the seismic design situation and check panel fixings, brackets, profiles and anchors, see structural calculation.
- Check the imposed drift: the clearance of slotted holes and of panel joints must cover the relative displacement of the floors the subframe spans.
- Record the assumptions in the calculation note so that the expert reviewer can retrace them.
The exact formulas, factors and combinations must be taken from the current text of the regulation; we do not reproduce them here.
Checklist for the designer
| Item | What to check |
|---|---|
| Site data | Intensity and A for the settlement; microzoning report if available |
| Cladding mass | kg/m² of the finished system including fixings, not only the board |
| Anchor base | Reinforced concrete vs. masonry; pull-out tests where the wall is unknown |
| Bracket slots | Travel at least equal to the relative floor displacement |
| Joints | Facade joints aligned with the building movement joints |
| Dangerous zones | Entrances, passages, public space: secondary retention |
| Corners and parapets | Parapet cladding and returns checked as separate non-structural elements |
| Products | ETA or declaration of performance for brackets and anchors, see Resolution No. 476 |
Typical mistakes
- Checking the main frame of the building for earthquakes and leaving the facade as "architectural".
- Using the same bracket spacing in Batumi and in Tbilisi without looking at the coefficient.
- Anchoring into partition walls because the slab edge is covered by a curtain wall detail.
- Slotted holes drawn on the detail but tightened to a fixed clamp by the installer; the shop drawings and the installation instruction must say which points are sliding, see shop drawings.
- Rigid panel joints with sealant filling the whole gap, so that adjacent panels collide.
- Ignoring the parapet and the roof edge, where the acceleration is highest and the support is weakest.
Evidence and testing
Georgia has no dedicated seismic test standard for facade systems. In practice the designer relies on the calculation, the ETA and test reports of the subframe manufacturer and the on-site pull-out tests of anchors. Ask the supplier which loads the declared capacities refer to and whether the test report covers cyclic or only static loading. If the system has been tested for seismic displacement in projects in Central Asia or Europe, the report is a useful supporting document, but it does not replace the calculation for the actual building.
Send the building height, the structural frame and the wall material with your request and we will say which of these points govern the design: request a calculation.