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Safety Format for Non-linear Analysis of RC Structures Subjected to Multiple Failure Modes
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis treats the safety format for non-linear analysis of reinforced concrete (RC) structures subjected to multiple failure modes. The purpose is to identify questions which are poorly understood and ambiguous about the behaviour of structures that may fail due to a number of possible failure modes (e.g., bending, shear, buckling, crack propagation, fatigue) which might be used as a focus for the development of a more comprehensive approach to the evaluation of the structural safety level.

Nowadays non-linear analysis in concrete structures cannot be considered only as a research tool to improve the understanding of structural behaviour, but it is also a useful mean to design more and more enhanced structures and to estimate the actual safety level in existing structures. As a consequence, semi-probabilistic safety formats for the non-linear analysis of RC structures are of great practical interest for structural engineers.

Safety formats for non-linear analysis have mainly been tested on beams and columns subjected to normal forces and bending moments. Only recently there has been a noticeable effort in understanding whether available safety formats lead to the intended reliability when they are applied to structures that also may fail due to shear forces. However, the road ahead is still long and challenging.

The definition of a suitable safety format involves the clarification of (i) which values of geometric and material properties should be used in the non-linear analysis, considering that they all influence both the resistance and the ultimate behaviour of the whole system, (ii) when the incremental process of non-linear analysis should stop, and (iii) how to derive from the failure load the ultimate load that can be carried by the structure with the safety margins that are required by the semi-probabilistic approach. This thesis considers in some sense all three of these aspects.

The following major conclusions are based on the studies described in the appended papers: (1) the scatter of the shear capacity of RC slender members seems to be mainly due to the randomness of both tensile strength of concrete and shrinkage; (2) the structural behaviour at ultimate load of RC structures designed according to Eurocodes 2 is not unambiguous and may significantly vary depending on the structural system, load configuration, and capacity design; (3) the resistance of RC structures subjected to flexural and shear failure modes seems to be mainly influenced by the combination of mechanical properties of both longitudinal reinforcement and stirrups, and tensile strength of concrete; and (4) the resistance of RC structures subjected to multiple failure modes may have a general multimodal probability density function, in which each mode represents a specific failure mechanism.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 45 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 127
National Category
Infrastructure Engineering
Identifiers
URN: urn:nbn:se:kth:diva-164304OAI: oai:DiVA.org:kth-164304DiVA: diva2:805416
Public defence
2015-05-06, Aula Albenga, Corso Duca degli Abruzzi 24, Torino, Italy, 10:00 (English)
Opponent
Supervisors
Note

QC 20150416

Available from: 2015-04-16 Created: 2015-04-15 Last updated: 2015-04-16Bibliographically approved
List of papers
1. Assessment of the ACI-DAfStb Database of Shear Tests on Slender Reinforced Concrete Beams without Stirrups for Investigations on the Shear Capacity Scatter
Open this publication in new window or tab >>Assessment of the ACI-DAfStb Database of Shear Tests on Slender Reinforced Concrete Beams without Stirrups for Investigations on the Shear Capacity Scatter
2014 (English)In: Athens Journal of Technology & Engineering, ISSN 2241-8237, Vol. 1, no 3, 181-197 p.Article in journal (Refereed) Published
Abstract [en]

The shear transfer mechanism of RC slender members without stirrups still presents very high uncertainties and the question has generated many controversies and debates since the beginning of the last century. Regrettably, until now the real causes of this problem are not yet clear to the scientific community and the issue is still important to investigate, especially nowadays that the minimizing of natural resources is of uppermost global interest.

Due to the increased laboratory costs, actual studies are more and more often devoted to numerical simulations based on previous experiments. Unfortunately, it is difficult to find test results suitable for investigations on the shear capacity scatter in the available specialized literature.

Therefore, the objective of this paper is to provide different adequate sets of reported test results containing tests performed on almost identical beams. The ACI-DAfStb database of shear tests on slender reinforced concrete beams without stirrups is considered and analyzed through the use of both multivariate statistical methods and clustering data mining techniques. The database was firstly visually explored by scatterplots and investigated through both univariate and correlation statistical procedures, and then processed by clustering using the k-means algorithm. Similar sets of data were collected in groups of comparable experiments. Clusters containing less than six data sets48were removed. The criteria to establish the rate of similarity between each set of data were chosen according to the JCSS Probabilistic Model Code.

The study has led to the formation of 13 groups of comparable experiments each group containing a number of tests between 6 and 43, performed generally by different field workers. These groups of reported test results will be of great importance both for the continuation of the authors' research and for other researchers who investigate the causes of the shear failure scatter or develop improved shear design methods.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164299 (URN)
Note

QC 20150415

Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2015-04-16Bibliographically approved
2. Scatter in the Shear Capacity of RC Slender Members without Web Reinforcement: Overview Study
Open this publication in new window or tab >>Scatter in the Shear Capacity of RC Slender Members without Web Reinforcement: Overview Study
2015 (English)In: Structural Concrete, ISSN 1464-4177, E-ISSN 1751-7648Article in journal (Refereed) Accepted
Abstract [en]

All researchers that have tested the shear capacity of RC members without stirrups have observed a large scatter in the results.

The objective of this paper is to conduct an overview study of the causes to the great shear failure scatter of RC beams without stirrups. Thirteen groups of shear tests on comparable experiments, extracted from the ACI-DAfStb evaluation database, are considered. The amount of data available is increased numerically. To this end, based on Eurocode 2 equations for shear resistance and shrinkage strain, a full probabilistic model according to JCSS Probabilistic Model Code is defined. A multivariate statistical evaluation of outcomes is then performed.

The investigation highlights that both tensile strength of concrete and high values of shrinkage may be useful to be considered for more in-depth studies of the phenomenon, whereas geometrical properties and concrete compressive strength seem to be less important or can even be neglected.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164300 (URN)
Note

QP 201504

Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved
3. Probabilistic Investigation on the Ultimate Load Behaviour of RC Structures Designed According to EN 1992-1-1 and Subjected to Multiple Failure Modes
Open this publication in new window or tab >>Probabilistic Investigation on the Ultimate Load Behaviour of RC Structures Designed According to EN 1992-1-1 and Subjected to Multiple Failure Modes
2015 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323Article in journal (Other academic) Submitted
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164301 (URN)
Note

QS 2015

Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved
4. Resistance and Sub-Resistances of RC Beams Subjected to Multiple Failure Modes
Open this publication in new window or tab >>Resistance and Sub-Resistances of RC Beams Subjected to Multiple Failure Modes
2015 (English)In: World Academy of Science, Engineering and Technology: An International Journal of Science, Engineering and Technology, ISSN 2010-376X, E-ISSN 2070-3740, Vol. 9, no 2, 145-153 p.Article in journal (Refereed) Published
Abstract [en]

Geometric and mechanical properties all influence the resistance of RC structures and may, in certain combination of property values, increase the risk of a brittle failure of the whole system.

This paper presents a statistical and probabilistic investigation on the resistance of RC beams designed according to Eurocodes 2 and 8, and subjected to multiple failure modes, under both the natural variation of material properties and the uncertainty associated with cross-section and transverse reinforcement geometry. A full probabilistic model based on JCSS Probabilistic Model Code is derived. Different beams are studied through material nonlinear analysis via Monte Carlo simulations. The resistance model is consistent with Eurocode 2. Both a multivariate statistical evaluation and the data clustering analysis of outcomes are then performed.

Results show that the ultimate load behaviour of RC beams subjected to flexural and shear failure modes seems to be mainly influenced by the combination of the mechanical properties of both longitudinal reinforcement and stirrups, and the tensile strength of concrete, of which the latter appears to affect the overall response of the system in a nonlinear way. The model uncertainty of the resistance model used in the analysis plays undoubtedly an important role in interpreting results.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164302 (URN)
Note

QC 20150415

Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2017-12-04Bibliographically approved
5. Safety Format for Non-Linear Analysis of RC Structures: Resistance PDF of Structural Systems
Open this publication in new window or tab >>Safety Format for Non-Linear Analysis of RC Structures: Resistance PDF of Structural Systems
(English)In: ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil EngineeringArticle in journal (Other academic) Submitted
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164303 (URN)
Note

QS 2015

Available from: 2015-04-15 Created: 2015-04-15 Last updated: 2015-04-16Bibliographically approved

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