DESIGN OF STRUCTURAL STRENGTHENING

The strength, reliability and stability of every building and facility depend on its load-bearing structure, which is made up of two groups of elements: vertical and horizontal. Strengthening the load-bearing structure of buildings and facilities is an important, demanding and high-risk task. Under the action of various external factors — operating conditions (aggressiveness of the environment), climate, extreme events (seismicity, floods, high winds, heavy snow, accidents, fire, etc.) — load-bearing structures gradually deteriorate (wear out). Strengthening the load-bearing structures of existing buildings and facilities is also required in the following cases:

When adding extra storeys or deepening ground-floor and basement levels;
When building new floor levels in mezzanines (galleries) or sufficiently high rooms;
In case of change of use, loads (additional equipment) or building structures (reconstructions);
In case of defects and damages during the operation of the buildings and facilities leading to a decrease in bearing capacity, strength, stiffness or resistance to cracking (settlement, sagging, cracks, local failures, etc.);
After a technological failure, after a fire, after an earthquake, after a flood or after another extreme event;
In case of deviations from the design, errors in the design, deviations in the quality and quantity of the materials used or deviations from the construction technology;
At the client's request to meet modern safety and security requirements of building structures;

Baseline data for the preparation of a structural strengthening design are the results of a detailed (instrumental) survey and the original or re-created design documentation. The structural strengthening works shall be carried out according to a special detailed design and a special design concerning the technology and sequence of execution. In general, the principles for structural strengthening are:

Restoring the design load-bearing capacity by:
Replacing whole elements with new ones; restoring cross-sections (repairing cracks, defects, damage, etc.); restoring connection details and anchorages; restoring surface protection (waterproofing, thermal insulation, corrosion protection, fire protection); restoring a normal temperature and moisture regime; increasing foundation capacity (protection from surface and groundwater, strengthening of the subsoil, repair and strengthening of the foundations, etc.); and similar measures.
Design of off-loading and replacement structures.
This method introduces new, duplicate structures that take part or all of the load. Its main drawback is significant alteration of the interior and reduced room dimensions.
Design of strengthening that increases the inherent load-bearing capacity by:
- Keeping the structural scheme unchanged — by means of: reinforced-concrete jackets, steel cages (frames), one-sided thickening of elements, strengthening of joints, externally bonded reinforcement fabrics and laminates (glass, aramid, carbon), and similar techniques;
- Modifying the structural scheme — by means of: introducing new structural elements (columns, beams, connections, slabs, walls, etc.), additional supports, strut (raking-shore) systems, tie rods or reinforced-concrete tie beams, tying separate structures together, and other tailored solutions;
- Modifying the stress state — by means of: additional horizontal or trussed prestressed reinforcement, prestressed diagonals (braces), prestressed bolts and clamps (yokes), and other tailored solutions.

Strengthening and/or reinforcement of buildings and facilities designed and carried out by firms without sufficient experience in this work can lead to local — and even total — damage to and failure of building structures. Carrying out strengthening or reinforcement without a competently prepared design (relying on contractor design-and-build) carries a high risk of (local or total) collapse, injury, and even loss of life!