SURVEYS, TESTS AND CHECKS IN CONSTRUCTION_P1

 

Before I list the tests likely to be performed on masonry structures, I would like to introduce briefly the reasons why a Client should want to test. As a matter of fact, several Clients are still not aware enough of the importance of planning and performing tests accurately.
Many testing equipment used in construction are borrowed from medicine (e.g. georadar, videoendoscope, ultrasound, contrast medium, etc...), but the parallelism between a human body and a building is not that widely accepted in the end. We may all have experienced medical examinations followed by screening tests (in the construction industry we would call them on-site surveys), aimed at understanding the causes of a disorder and choosing the best therapy. Well, in construction this is not clear enough and needs to be reaffirmed strongly all the time. More often, expensive consolidation works are preferred to proper diagnostics, which is, more or less consciously, a discarded practice. The idea of spending money in something with no direct concrete benefits is not in the mind-set of several Clients.
In the last few years, the Italian legislators have tried to offset this oddity with a view to reducing the need to make changes during works, and the resulting growth in costs, that could be easily avoided with accurate diagnostics. To this end, they introduced the notion of Knowledge Levels (LC1, LC2 and LC3), whereby the higher the level of knowledge about an existing structure, which is also gained through an appropriate diagnostic phase, the greater the economic benefits (possibility to use lower Confidence Factors during engineering). Therefore, the best diagnostic phase must be conveniently planned by the same engineers who will perform structural analysis (not by the companies who will carry out the tests, who may be assigned the role of advisers) and must be aimed at acquiring all the parameters that are really useful for the subsequent calculus analysis. Today, technology makes available increasingly reliable equipment and the real issue is to strike a balance between costs and benefits while respecting the concerned monument. This said, hoping that the awareness of the need to perform proper diagnostics will increase in the future, I offer below a brief introduction to the most commonly used practices in construction surveys.

 

ON-SITE AND LAB TESTS

TESTS ON MASONRY STRUCTURES (figures 1 and 2)

  • Video-endoscopic surveys
  • Stress state and compressive strength tests by means of flat jacks
  • Shear strength of masonry
  • Assessment of mortar strength by means of dynamic penetration testing
  • Sonic tests to check masonry homogeneity
  • Georadar surveys

TESTS ON REINFORCED CONCRETE STRUCTURES (figures 3-5)

  • Tests for mechanical characterization of concrete, by means of:

            _ Windsor probe
            _Ultrasound survey
            _Sclerometric survey
            _Pullout test
            _Carbonation depth test

  • concrete sample collection with diamond crown core drill
  • lab tests on concrete specimens to determine chemical, physical and mechanical properties

TESTS ON STEEL STRUCTURES (figure 6)

  • Testing with penetrating fluids to detect surface flaws
  • Magnetoscopic test to detect deep cracks and flaws
  • Chemical-metallographic analysis (micrography, S.E.M. electronic microscopy, chemical attack and EDS analysis of cracks, verification of weldability)
  • Tensile and bend test in ambient temperature
  • Verification of tightening torque of bolted joints by means of dynamometric key
  • Ultrasound surveys/thickness gauge surveys

TESTS ON SOIL (figures 7 and 8)

  • (Simple or double) continuous core drilling with collection of undisturbed samples
  • On-site testing of strength and deformability
  • Surveys for geotechnical characterization, lab tests of strength and deformability
  • Down-hole prospecting by means of miniature TV probe

 

MONITORING AND CHECKING METHODS FOR BUILDINGS

MONITORING METHODS TO CHECK THE PRINCIPAL PHYSICAL PARAMETERS (figures 9 and 10)

  • Static and dynamic monitoring methods to check the variability in time of some physical parameters

                  _Verticality of walls, towers and bell towers
                  _Opening of cracks
                  _Relative temperature and humidity
                  _Vertical subsidence
                  _Maximum pull of chains
                  _Tensile strain in structural elements
                  _Contact pressure
                  _Groundwater levels
                  _Motion of slopes, escarpments, elevations

PRECISION LEVELLING AND CHECKS ON VERTICALITY (figures 11 and 12)

  • Topographic measurement to check building verticality
  • Precision levelling to check subsidence with time

 

STATIC AND DYNAMIC LOAD TESTS

STATIC AND DYNAMIC LOAD TESTS (figures 13-16)

  • Load testing with water weight bags. Measurement of deformation by means of transducers and data acquisition methods capable of offering real-time load-deformation curves.
  • Load testing with contrast beams
  • Tearing strength test to check scaffold anchors
  • Dynamic tests of buildings and viaducts under natural excitation (wind, earthquake, traffic) or induced by external agents (vibrodyne, controlled impact)

[by Alessandro Bozzetti and Cristiano Russo]