The static mapping of the building in a non-destructive way using scanning equipment, creates with precision the static identity of the building, which is the unique tool, for any future intervention.

 Stages of inspection:

• Level I: Visual Inspection, General Checks and Self-frequency measurement.
• Level II: Data Acquisition through use of NDT Equipment and other testing methods.
• Level III: Structural Analysis / design of the retrofitting (upon request)

 Inspection Level I / Visual Inspection and Documentation of findings

Visual inspection is the most basic NDT method and typically the first step in the evaluation of concrete structures. It can provide a huge amount of information, crucial to form a strategy for the inspections to follow. Broad knowledge of structural engineering, concrete materials and construction methods are needed to extract the most information possible. It is generally used for the identification of cracks, peeling and other imperfections on the surface and interior of the concrete. Simple tools for concrete crack size measurements might be needed.

The visual inspection method, although very simple and cheap, is extremely efficient, especially when combined with a different method.

It has the obvious limitation that only visible surface can be inspected. Internal defects cannot be noticed and no quantitative information is obtained about the properties of the concrete.

During a visual inspection, structural damage is detected, and recorded through drawings, pictures and videos, such as:

• Cracks (position and size)
• Corroded reinforcement bars
• Moisture problems
• Anomalies on concrete and steel (concrete peeling, material continuity and uniformity, signs of steel corrosion and concrete carbonation, exposed/broken rebars)
• Measurement of the building’s frequency is performed, in order to create an evaluation tool, following any future structure alterations.

All the outputs of level I inspection, are provided in a detailed “Level I Technical Assessment Report”.

Inspection Level II / Data Acquisition

This procedure is more involved and time-consuming. It includes visual checks, measurements of building and soil properties and simplified analysis.

This inspection makes use of non-destructive testing (NDT) equipment, such as concrete magnetic/ultrasonic scanners and rebound hammers to provide additional and more reliable information of the concrete’s and rebars’ condition.

The Inspection Level 2 for existing buildings, can also include Destructive Tests, depending of the NDT results and the results of Level 1 Inspection.

All the outputs of level II inspection, are provided in a detailed “Level II Technical Assessment Report”.

ADVANCED NON-DESTRUCTIVE TESTING on CONCRETE & REINFORCEMENT STEEL

A. Non-destructive tests on concrete

• Concrete rebound hammer: This method is applied with the impact of a metallic mass on the surface of the examined material. Its rebound is measured on a calibrated gauge which translates it to compressive strength. It is applied to:
  • Estimate the material’s strength.
  • Estimate the material’s homogeneity.
  • Compare the quality of a structural elements, one to another.

• Nail extraction test: A nail launcher penetrates the concrete with a nail of specified dimensions. After 10 min, the force required for its extraction is measured with a dynamometer and translated to compressive strength. The method is applied to:
  • Estimate the concrete’s strength.
  • Estimate the concrete’s homogeneity.

• Ultrasonic Pulse Velocity test (UPV): This method is based on the propagation of stress waves through concrete. A transmitter produces ultrasonic waves which are received by a receiver. The wave propagation velocity is estimated by the wave’s travel time. The wave propagation velocity is directly correlated to the Yound’s modulus, Poisson’s ratio, density and geometry of the material. The maximum measuring range is 15 m depending on the concrete’s quality. The method is applied to:
  • Estimate the concrete’s/masonry’s thickness.
  • Estimate the material’s Young’s modulus, Poisson’s ratio, density.
  • Detect concrete internal discontinuities.
  • Detect pipes.
  • Estimate cracks’ size.
  • Estimate the depth of damaged layers.
• Phenolphthalein carbonation test: The rebars are protected against corrosion, through a very thin surface layer of iron oxide, which is created by the high alkalinity of its surrounding concrete. Concrete carbonation is the chemical reaction between the calcium hydroxide that exists in the concrete’s water and the atmosphere’s carbon dioxide, which leads to the loss of this layer. It is a sign that the rebars’ corrosion takes place and an indicator of the concrete’s durability. Carbonation can be detected with the use of phenolphthalein spray.
• Infrared Thermography: This method is based on the principle that heat flows at a different rate on different materials. This leads to differences on the surface temperatures. An infrared thermography camera is able to ‘see’ and measure the infrared energy radiated by these surfaces, which is invisible to the human eye. It has proven to be an accurate and efficient method with many applications in civil engineering, as to:
• Detect delamination on the material’s surface.
• Predict buckling, caused by thermal expanding, of exterior tiles on tall buildings.
• Detect voids in the concrete’s core.
• Detect concrete bands in brick walls.
• Detect underfloor heating and thermal bridges, to assess the energy performance of buildings.
• Detect moisture and heat leak caused by insulation problems of buildings.
• Measure the liquid level of tanks.
• Detect slab leaks.

B. Non-destructive tests on reinforcement steel:

• Magnet scanners: Magnet scanners’ function is based on the interaction of the reinforcement bars and a low frequency electromagnetic field. The detection depth is up to 40 cm. The method is applied to:
  • Detect reinforcement bars.
  • Estimation of the bars’ diameters.
  • Estimation of the concrete’s cover.

• Eddy Current Testing: The steel is exposed to electric current. Defects such as cracks disrupt the path of eddy currents and weaken their strength, allowing for their detection. The detection depth is up to 10 cm. The interpretation of these changes gives information about:
  • The imperfections and surface cracks on the steel.
  • The hardness of the steel.
  • The paint thicknesses.
• Pulse Response Analysis:  The steel is exposed to AC current. The current’s frequency is alternating between low and high values and the results are interpreted with an advanced & inovative system. The detection depth range is up to 10 cm or more. It is applied to:
  • Estimate the reinforcement bars’ corrosion rate.
  • Estimate the concrete’s resistivity.
  • Measure the half-cell potential.

• Rebound hardness test: A defined mass impacts with a known energy on steel. The steel’s hardness is estimated by the energy loss after the impact.

• Method UCI (Ultrasonic Contact Impedance): This method is performed by a device containing an oscillating mass that comes in contact with the steel. Following this, the surface hardness is estimated as a function of the change in natural frequency of the oscillator, before and after the impact.

• Differentiated Electric current method: Electric current is applied to two positions on the concrete’s surface. The voltage response of a corroded bar is different when compared to a non-corroded one. The method is applied to:
  • Detect rebar’s corrosion.
  • Measure rebar’s corrosion potential.
  • Measure rebar’s corrosion rate.
  • Measure the concrete’s resistivity.

Our services are exclusively addressed to Companies and Engineering Offices. Not reserved for privet customers.

EQ-FAST inspection and classification of buildings

INSTRUMENTAL SEISMIC VULNERABILITY ASSESSMENT OF EXISTING BUILDINGS

Swiss Approval introduces the innovative, exclusive and patented method EQ-Fast, based on the recommendations of Euro code 8, for measuring the seismic hazard in construction by conducting measurements of fundamental natural frequencies (resonance frequencies) of both the building and its territory.

It is an internationally patented tool of non-destructive instrumental assessment concerning the seismic risk of constructions and it is the most reliable method used to extract realistic rates of the damage likelihood. (Germany Patent No 1182301 (EU), 552368/02 (JP) and 10/362, 649(USA)). The assessment can be performed at two different evaluation levels, depending on the customer’s choice for accuracy, reliability, available time and cost.

A vulnerability assessment can be carried out at two different levels, depending on the scope and the accuracy required:

• Level I, simple and quick (time requirement for assessment less than one hour per building), suitable for determining risk for a large number of buildings. Only general building data – such as the age and the type of building – is taken into account at this level.
• Level II, detailed and more time-consuming (time requirement for assessment in the order of half a day per building). At this level, a number of measurements of the building’s properties (e.g. natural frequencies, building height, cross-sections of the shear walls, etc.) may also be required.

Results

Taking into account the above data and the other discrepancies which are entered into the specific program interface, EQ-Fast Expert System, gives information about the mean damage ratio of buildings for different modified mercalli intensities and classifies buildings as:

• A. Low risk,
• B. Acceptable risk,
• C. High risk),
• D. Very high risk.

After calculations, a Report will be presented to Clients, which contains the building’s deficiencies and if there is any requirement about retrofitting of the building.

Swiss Approval is also able to support Customers throughout the life cycle of buildings estimation. We provide vulnerability inspection services against earthquakes, as well as objective assessments and accessibility audits in accordance with international standards and local legislation.