Identification of the Confidence level (§3.6)

For the purpose of choosing the admissible type of analysis, the appropriate safety factors as well as the properties of the materials used in the structure under consideration, the following three Confidence levels are defined:

1. Higher Confidence level
2. Satisfactory Confidence level
3. Lower (tolerable) Confidence level

Geometrical and detailing properties (§3.5.2)

In situ testing and in situ inspection should yield the following information:

• the overall structural geometry,
• detailing and geometry of non structural members,
• structural detailing (amount of steel in beams, columns and walls, amount and detailing of confining steel in critical regions, anchorages, splices, concrete covers etc.)

When the original construction drawings and any subsequent modifications are readily available, only a limited in situ inspection should be used. In particular, in order to identify the structural details of the structure, it should be verified that the detailing of (at least) 3 incisions per structural type (beams, columns, walls, foundation elements) follow the available construction drawings.  

When the original construction drawings and any subsequent modifications are not available, or when the as-build structure deviates substantially from the original construction drawings, a full survey is needed resulting in the production of structural drawings that describe the geometry of the structure, allowing for identification of structural and non structural components and their dimensions, as well as the structural system to resist both vertical and lateral actions. In such a case, it is often almost impossible to identify the structural detailing along the whole structure, thus it is advisable, to follow a rather extended in-situ inspection. It is sometimes useful in such cases to increase the intensity of the in-situ inspection in those members whose integrity is more important for the structure as a whole (i.e. columns, walls supporting a large number of floors etc.)

Concrete Properties (§3.7.1)

A combination of non-destructive and semi-destructive methods (core sampling and testing).

For relatively small buildings (not more than 2 floors), the minimum number of concrete cores is 3, taken out of the same structural member types. For higher buildings, the minimum requirement is for 3 cores every two floors. In that case, 3 cores should be taken from the most critical (in terms of earthquake resistance behavior) floor. In most cases, this is the ground floor, especially when a “pilotis” like configuration is used.

Core testing results should only be used in order to calibrate the accompanying non-destructive methods used.

As far as the semi destructive testing methods of concrete is concerned, KAN.EPE. advices that at least one of the Schmidt Rebound hammer or the ultrasonic pulse velocity method to be used. Preferably, a combination of those two might be used as well. 1D structural members (columns, beams) should be tested via a semi destructive method in both ends of them (critical regions). Walls should be checked in every floor at their bases.

The higher Confidence level for the concrete strength, can be achieved if non-destructive testing is performed as follows:

• 45% of the vertical structural elements of each floor (columns, walls),
• 25% of the horizontal structural elements (beams, slabs).

Satisfactory Confidence level for the concrete strength can be achieved if non-destructive testing is performed as follows:

• 30% of the vertical structural elements of each floor (columns, walls),
• 15% of the horizontal structural elements (beams, slabs)

Whenever the results of this test exhibit a rather low standard deviation (S≤0.20X), the Confidence level can be considered as high.

Lower (tolerable) Confidence level for the concrete strength can be achieved if non-destructive testing is performed as follows:

• 15% of the vertical structural elements of each floor (columns, walls)
• 7.5% of the horizontal structural elements (beams, slabs).

Whenever the results of this test exhibit a rather low standard deviation (S≤0.20X), the Confidence level can be considered as Satisfactory.

Reinforcing Steel Properties (§3.7.2)

Reinforcing steel Category can simply be certified via visual inspection taken into consideration the configuration of the ribs (if any) along the steel bar surface as well as the (approximate) date of construction. Visual inspection leads to Satisfactory Confidence level.

Whenever there is need for a more thorough investigation, at least 3 samples of reinforcing steel should be tested. These bar samples have to be extracted from structural members of the critical floor (normally the ground floor) and should have almost the same nominal diameter.  In that case, Confidence level can be considered as high.

Infill walls properties (§3.7.3)

Investigation of infill wall properties is necessary only if the walls are to be considered as part of the structural system.

Visual inspection should come first. Geometry of the infill walls are to be inspected in at least 2 places per floor (minimum dimensions 0.7x0.7m).

Of special interest in terms of the structural behavior of the infill walls, is the compressive strength, the shear strength and corresponding Modulus E and G. When their values are calculated via empirical or semi-empirical methods (see EN 1996-1 for example), Confidence level can be no more the Satisfactory.

Lower (tolerable) Confidence level is not permitted.

Higher Confidence level can be achieved only under a relatively fringed in situ and laboratory testing program.

Ground properties identification (§3.5.4)

Whenever a geotechnical investigation is already available, and there is no sign of any possible foundation failure, there is no need for further investigations.

Either way, the following table should be advised and be followed.

Geotechnical investigation	Foundation behavior	Intervention that imposes extra actions on the ground	Need for new geotechnical investigation
Available	bad		yes
Non Available	good	no	no
		yes	yes
	bad		yes

Confidence levels for geometrical and detailing properties (§3.7.4)

Geometrical and detailing properties include in general the following: identification of the lateral resisting system in both directions, size of structural members, configuration of infill elements, amount of longitudinal steel in beams, columns and walls, anchorages, splices and concrete covers.

Confidence level depends on how the data is extracted. The following table should be advised.

Original constru ction drawings

Data extraction

Geometry of the structural resisting system and foundation

Knowledge of additional self weights, infill elements geometry etc.

Steel Reinforcing details

Avail able

No avail able

Low er

Satis facto ry

High

Low er

Satis factory

High

Low er

Satis facto ry

High

✓

1

Data is extracted from the original construction drawings which were implemented without major modifications.

(1)

✓

✓

✓

✓

2

Data is extracted from the original construction drawings which were implemented with some limited modifications.

(2)

✓

✓

✓

✓

3

Data extracted from a special reference or key of the original drawings (i.e. a note, a general table etc.)

(3)

✓

✓

✓

✓

4

Data which is extracted from an in situ test or measurement.

(4)

✓

✓

✓

✓

5

Data which is extracted indirectly, but adequately reliably.

(5)

✓

✓

✓

✓

6

Data which is based on simple engineering judgement.

(6)

✓

✓

✓

✓

✓

✓