Article · Seismic safety
Seismic strengthening of buildings: methods and when it's needed
Almaty is a seismic region, and many existing buildings fall short of the required seismic resistance. We explain when seismic strengthening is needed and by which methods structures are strengthened.
Many buildings in Almaty were built to outdated codes or have accumulated defects over years of use, so their actual seismic resistance is below what is required for the seismic zone. Seismic strengthening is a set of measures that increase the ability of structures to withstand seismic loads without collapse.
When seismic strengthening is needed
- when an inspection reveals a seismic-resistance deficit;
- before reconstruction, floor addition or a change of use (loads increase);
- after an earthquake, accident or the appearance of dangerous cracks;
- for properties of increased responsibility — schools, kindergartens, hospitals, retail and public buildings;
- when commissioning a reconstructed property at the request of expert review.
How to tell strengthening is necessary
The need for and extent of strengthening is determined not by a visual inspection but by a verification calculation of the building for seismic actions for its seismic zone. The calculation shows which elements fall short, and by how much.
Seismic strengthening always rests on a seismic report — an assessment of seismic resistance with a calculation. Without it, strengthening risks being either insufficient or excessive and costly. See the service “Seismic assessment of a building”.
Methods of seismic strengthening
Strengthening foundations and bases. Widening the footing, installing piles, grouting the soil.
Strengthening columns and piers. Steel and reinforced-concrete jackets, increasing the cross-section.
Additional bracing and stiffening diaphragms. So the building works as a single spatial system.
Strengthening floor slabs and nodes, anti-seismic belts. Improving the connectivity and robustness of the frame.
Composite materials (carbon fibre, laminates). Where it is important not to increase the section and weight of the structures.
The process: from inspection to the strengthening design
The correct sequence: inspection → verification calculation for seismic actions → seismic report with the deficit and recommendations → strengthening design → works. KAZNICEP LLP carries out the inspection and the seismic assessment and prepares strengthening recommendations that the designer uses as the basis for the design. Related material: inspection before reconstruction and strengthening and work with load-bearing structures.
Frequently asked questions
When does a building need seismic strengthening?
Seismic strengthening is needed when a verification calculation shows a seismic-resistance deficit for the seismic zone, and also before reconstruction, floor addition and a change of use, after earthquakes and accidents, and when dangerous cracks appear. For schools, hospitals and public buildings the requirements are especially strict.
By which methods are structures strengthened?
The main methods: strengthening foundations (widening, piles), jackets and increasing the cross-section of columns and piers, additional bracing and stiffening diaphragms, anti-seismic belts, and composite materials (carbon fibre). The method is chosen based on the verification calculation.
Is an inspection needed before seismic strengthening?
Yes. The extent and method of strengthening is determined by a verification calculation for seismic loads, carried out as part of the seismic report. Without an inspection, strengthening risks being insufficient or excessive and unjustifiably costly.
How much does the assessment before strengthening cost and how long does it take?
A seismic assessment with a calculation is from 200,000 KZT and 1 to 6 weeks depending on the floor area, number of storeys and structural scheme. An exact price is given after an inspection and clarification of the task.
Seismic
assessment of a building
We carry out the inspection and a verification calculation for seismic loads, and prepare strengthening recommendations — input data for the design.