Structural Strengthening

Architectural, reinforced-concrete and structural drawings along with other available technical documents are reviewed. We establish whether the drawings exist, whether they are up to date and whether they can be used in the performance assessment. This gives the first technical picture of the building's current state.

Floor plans, storey heights and the positions of columns, beams and shear walls are checked on site and compared with the existing drawings. Any differences are recorded, and the performance calculation is based on the building as it actually stands.

Where no drawings exist, or where they differ significantly from the building, measurements are taken on site and an as-built survey is prepared. The structural system, member dimensions, storey geometry and all other data needed for the analysis are recorded.

Existing concrete strength is determined by testing core samples taken from columns or shear walls. At the comprehensive knowledge level, at least 3 samples are taken on the ground floor, at least 2 on each other floor and at least 9 across the building, with one additional sample for every 400 square metres. Coring is carried out in accordance with TS EN 12504-1.

The diameter, number, layout and concrete cover of longitudinal and transverse reinforcement in columns, beams and shear walls are examined to establish the existing reinforcement arrangement. In line with the scope of investigation set out in TBDY 2018 Chapter 15, data obtained by cover removal and rebar-detection equipment is recorded for use in capacity calculations.

Columns, beams, shear walls, slabs and other structural members are inspected in detail on site. Cracking, crushing, corrosion, deformation and similar deterioration are identified and their locations marked on the survey drawings. The effect of existing damage on seismic behaviour is included in the assessment.

Existing soil investigation reports and other technical data are reviewed to evaluate the foundation system and the properties of the soil. If the foundation system cannot be established from drawings or reliable technical information, inspection pits are opened to determine its type, dimensions and condition in place.

All data gathered on site is transferred into the analysis model. Using a suitable calculation method under TBDY 2018 Chapter 15, the building's performance under earthquake action is determined. The analysis shows whether strengthening is needed, and the results are compiled in a performance report.

The performance analysis results are evaluated to identify structural members that fall short of requirements. The scope of the work needed to reach the target performance level is then defined.

A suitable method is chosen according to the existing structural system and the deficiencies identified. Strengthening of columns and beams, adding new reinforced-concrete shear walls or frames, steel strengthening and fibre-reinforced polymer strengthening are each assessed for the specific building.

Dimensions, reinforcement and connection details are calculated for the columns, beams, shear walls and other members to be strengthened. Joint and anchorage details are designed so that new members work safely together with the existing system.

Existing foundations are assessed against the new loads and seismic actions that follow strengthening. Where required, foundation strengthening and the foundation connections of new members are designed.

The strengthening system is added to the analysis model and the building is analysed again. The check confirms whether the target seismic performance level is achieved.

Once the calculations are complete, the system is turned into structural drawings and details for construction. Members to be strengthened, reinforcement, connections and fabrication details are shown clearly on the drawings.

Calculation and design results are brought together in a strengthening report. The technical specification defines the methods to be used, the materials, the workmanship rules and the quality control requirements. Report, drawings and specification are prepared in line with TBDY 2018 Chapter 15 and the related standards.

Columns and beams that fall short of requirements are strengthened by concrete jacketing or by enlarging their cross section. This increases the load-carrying capacity and seismic resistance of the members.

Columns and beams are wrapped with fibre-reinforced polymer or carbon fibre materials. The application increases the ductility and shear capacity of the members.

New reinforced-concrete shear walls are added to the building. Lateral actions during an earthquake are then carried more safely and the lateral capacity of the structure increases.

New frames of reinforced-concrete columns and beams are added where required. This increases the seismic capacity of the existing structural system.

Steel columns, beams, braces or steel frames are used according to the needs of the building. The seismic resistance of the structural system is increased with these steel members.

Where required, infill walls are strengthened in line with the details set out in the code. This increases their contribution to the seismic behaviour of the building.

Foundations that cannot carry the new loads are improved. This is done either by strengthening the existing foundation or by adding new foundation members.

Where the soil causes bearing capacity, settlement or similar problems, ground improvement is carried out. Methods such as grout injection and jet grouting may be applied for this purpose.