Assessing concrete strength variability in existing structures based on the results of NDTs

In reinforced concrete (RC) structures, the compressive strength of concrete can play a crucial role in seismic performance and is usually difficult to estimate. Major seismic codes prescribe that concrete strength must be determined essentially from in situ and laboratory tests. Mean values obtained from such tests are the reference design values when assessing existing structures under seismic actions. The variability of concrete strength can also play an important role, generally requiring that various homogeneous domains are identified in a single structure, in each of which a specific mean value should be assumed as representative. This study analyzes the inter- and intra-variability of the concrete strength of existing buildings using a very large database made up of approximately 1600 core tests extracted from RC buildings located in the Basilicata region (Southern Italy). The analysis highlighted that concrete strength variability was dependent on the structures’ dimensions as well as on the number of storeys. Moreover, the concrete strength of cores extracted from columns was found to be, on average, lower than that from beams, thus justifying the usual practice to extract cores mainly from columns, which results in a conservative approach as well as a more feasible one. Finally, some case studies were analyzed, specifically focusing on the effects of the within-storey variability. Conservative strength values, to be used especially in the case of vertical members subjected to high axial loads, are suggested.

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The Concrete Strength Variability as Source of Irregularity for RC Existing Buildings

Seismic Behaviour and Design of Irregular and Complex Civil Structures II - Geotechnical, Geological and Earthquake Engineering ◽

10.1007/978-3-319-14246-3_13 ◽

2016 ◽

pp. 149-158 ◽

Cited By ~ 2

Author(s):

Stefania Viti ◽

Marco Tanganelli ◽

Marco De Stefano

Keyword(s):

Concrete Strength ◽

Existing Buildings ◽

Strength Variability

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Concrete Strength Variability in Italian RC Buildings: Analysis of a Large DataBase of Core Tests

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.597.283 ◽

2014 ◽

Vol 597 ◽

pp. 283-290 ◽

Cited By ~ 14

Author(s):

Angelo Masi ◽

Andrea Digrisolo ◽

Giuseppe Santarsiero

Keyword(s):

Large Scale ◽

Seismic Vulnerability ◽

Concrete Strength ◽

Discrete Distributions ◽

Existing Buildings ◽

Large Database ◽

Public Buildings ◽

Rc Structures ◽

Actual Strength ◽

Strength Variability

The knowledge of the materials’ mechanical properties is a preliminary and important step in the seismic vulnerability assessment of existing buildings. In RC structures, the compressive strength of concrete can have a crucial role on the seismic performance and is usually difficult to estimate. Major seismic codes prescribe that concrete strength has to be determined essentially from in-situ and laboratory tests. In some cases such estimation can be complemented by default values in accordance to standards at the time of construction, therefore analysing the actual concrete properties typically found in RC existing buildings realized in different periods can make available useful data. To this end, in this paper attention has been addressed to public buildings, namely schools and hospitals. A large database made up of about 1500 test results on concrete cores extracted from about 300 RC public buildings located in Basilicata region (Italy), has been prepared and analysed. The relationships between the actual strength values (mean and dispersion) and the construction period of buildings have been studied. Theoretical distributions to approximate the discrete distributions of strength values in different construction periods have been determined, thus providing relevant data for the structural assessment of individual buildings and, especially, for large scale vulnerability evaluations.

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The Structural Diagnosis of Existing RC Buildings: The Role of Nondestructive Tests in the Case of Low Concrete Strength

Infrastructures ◽

10.3390/infrastructures5110100 ◽

2020 ◽

Vol 5 (11) ◽

pp. 100

Author(s):

Silvia Santini ◽

Angelo Forte ◽

Lorena Sguerri

Keyword(s):

Mechanical Properties ◽

Concrete Strength ◽

High Strength ◽

Ultrasonic Pulse ◽

Assessment Process ◽

Structural Safety ◽

Existing Structures ◽

Nondestructive Tests ◽

Compression Properties ◽

Pull Out

In the structural safety assessment process of existing structures, knowledge of the mechanical properties of the materials is key. Different experimental activities carried out on materials extracted from existing reinforced concrete buildings show a high strength variability, especially concrete. In the past, the lack of standardized quality control for materials and workmanship caused nonuniform and homogeneous properties within the same structure. The most accurate and reliable experimental technique consists of performing direct tests on the materials, but these are considerably expensive and invasive. In this paper, alternative indirect methods that estimate material properties by correlating different physical measures were proved to reduce invasive inspections on existing buildings and infrastructures, especially in built heritage. A complete experimental activity concerning destructive and nondestructive tests was conducted on elements (four portions of a column and a beam portion) removed from an Italian school building built in 1940. Destructive and nondestructive methods were compared and appropriate correlation laws developed to predict the main mechanical properties of the studied material. Reliable correlations were identified considering the pull-out test, Sonic–Rebound (SonReb) combined method and ultrasonic pulse velocities (UPVs). The latter were mapped by tomography, which highlighted the compression properties of concrete in the different structural sections.

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Rebound Hammer Test: An Investigation into Its Reliability in Applications on Concrete Structures

Advances in Materials Science and Engineering ◽

10.1155/2020/6450183 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Antonio Brencich ◽

Rossella Bovolenta ◽

Valeria Ghiggi ◽

Davide Pera ◽

Paolo Redaelli

Keyword(s):

Building Materials ◽

Concrete Strength ◽

Research Work ◽

Third Party ◽

Test Reliability ◽

Surface Finishing ◽

Engineering Practice ◽

Rebound Hammer ◽

Existing Structures ◽

Concrete Maturity

The issue of concrete strength often arises in civil engineering practice, either due to quality control of new constructions or due to the assessment of existing structures. To this aim, one of the most widely spread techniques is the rebound hammer (Schmidt hammer) test, for which calibration is still related to the original Schmidt curve dating back to the early 50’s. In spite of the large amount of research work performed in the last decades, the uncertainties of the rebound test are still not clearly quantified and open to further insight. This paper presents and discusses a wide research campaign on laboratory specimens and on third-party specimens delivered to the Laboratory for Building Materials of the University of Genoa, Italy, for standard quality controls. While it is well known that moisture content, surface finishing, and concrete maturity strongly affect the test result, the effect of the stress state has not yet been studied and is found in this research to be a further parameter affecting the test reliability. The final outcome of all the uncertainties is variability in estimated concrete strength as large as ±70%; additionally, some issues are discussed on the intrinsic uncertainty of this test. As already demonstrated by many authors, the results of this research also show that a universal calibration curve to be used for any concrete, in any condition, conceptually does not exist.

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