The objective of this study is to compare conventional models used for estimating the load carryi... more The objective of this study is to compare conventional models used for estimating the load carrying capacity of reinforced concrete (RC) members, i.e., Current Design Codes (CDCs), with the method based on different assumptions, i.e., the Compressive Force Path (CFP) method and a non-conventional problem solver, i.e., an Artificial Neural Network (ANN). For this purpose, four different databases with the details of the critical parameters of (i) RC beams in simply supported conditions without transverse steel or stirrups (BWOS) and RC beams in simply supported conditions with transverse steel or stirrups (BWS), (ii) RC columns with cantilever-supported conditions (CWA), (iii) RC T-beams in simply supported conditions without transverse steel or stirrups (TBWOS) and RC T-beams in simply supported conditions with transverse steel or stirrups (TBWS) and (iv) RC flat slabs in simply supported conditions under a punching load (SCS) are developed based on the data from available experimen...
International Journal of Protective Structures, 2019
Published experimental work reveals that the out-of-plane behaviour of unreinforced masonry walls... more Published experimental work reveals that the out-of-plane behaviour of unreinforced masonry walls under impact loading can be significantly enhanced through the use of engineered cementitious composite layers fully bonded to the surface of the masonry. The disadvantage of this method is associated with the localised cracking exhibited by the engineered cementitious composite layer close to the joints forming between bricks. This cracking is associated with the bond developing between the masonry and the engineered cementitious composite layer and does not allow the latter layer to achieve its full potential, thus resulting in its premature failure. In an attempt to address this problem, a series of drop-weight tests were carried on masonry prismatic specimens strengthened with a layer of engineered cementitious composite partially bonded to the surface of the masonry acting in tension. The latter prismatic specimens consist of a stack of bricks connected with mortar joints. The spec...
Proceedings of the Institution of Civil Engineers - Structures and Buildings, 2019
A comparison of the predicted and experimentally-established behaviour of over 150 reinforced con... more A comparison of the predicted and experimentally-established behaviour of over 150 reinforced concrete beam specimens (selected from 465 test results considered) revealed that around 20% of the specimens exhibited shear failure rather than the expected flexural failure. The work presented in this paper investigated the possibility that the causes of shear failure reflected shortcomings of the code methods adopted for calculating flexural capacity. It was found that the predicted values of flexural capacity tended to underestimate their experimentally-established counterparts by up to 17% on average. It was shown that by accounting for the triaxial stress conditions invariably developing in the compressive zone through a simple modification of code-proposed stress blocks, the correlation between predicted and experimental values was similar to the best possible one resulting from the development and use of an artificial neural network model.
This work is based on a nonlinear finite-element model with proven capacity for yielding realisti... more This work is based on a nonlinear finite-element model with proven capacity for yielding realistic predictions of the response of reinforced-concrete structures under static monotonically-increasing loading. In it, the material description relies essentially on the two key properties of triaxiality and brittleness and, thus, is simpler than those of most other material models in use. In this article, the finite-element program is successfully used in investigating the behaviour of a series of RC walls under static cyclic loading. This type of loading offers a more strenuous test of the validity of the proposed program since cracks continuously form and close during each load cycle. Such a test is considered to be essential before attempting to use the program for the analysis of concrete structures under seismic excitation in order to ensure that the solution procedure adopted is numerically stable and can accurately predict the behaviour of RC structures under such earthquake-loading conditions. This is achieved through a comparative study between the numerical predictions obtained presently from the program and available experimental data.
The present article summarises the fundamental characteristics of concrete behaviour which underl... more The present article summarises the fundamental characteristics of concrete behaviour which underlie the formulation of an engineering finite element model capable of realistically predicting the behaviour of (plain or reinforced) concrete structural forms in a wide range of problems ranging from static to impact loading without the need of any kind of re-calibration. The already published evidence supporting the proposed formulation is complemented by four additional typical case studies presented herein; for each case, a comparative study is carried out between numerical predictions and the experimental data which reveals good agreement. Such evidence validates the material characteristics upon which the FE model`s formulation is based and provides an alternative explanation regarding the behaviour of structural concrete and how it should be modelled which contradicts the presently (widely) accepted assumptions adopted in the majority of FE models used to predict the behaviour of concrete.
Most finite-element models of reinforced-concrete structures attribute to concrete material chara... more Most finite-element models of reinforced-concrete structures attribute to concrete material characteristics which are in conflict with true behaviour established from valid experimental information. As a result the constitutive models adopted are case-study dependent. The present work summarizes already published work which shows that the use of realistic concrete properties coupled with well-tried numerical techniques can yield a finite-element model characterised by both generality and objectivity.
The structural behaviour of steel-fibre-reinforced concrete (SFRC) beams was studied using non-li... more The structural behaviour of steel-fibre-reinforced concrete (SFRC) beams was studied using non-linear finite-element analysis (NLFEA) and existing experimental data. The work aim was to examine the potential of using steel fibres to reduce the amount of conventional transverse steel reinforcement without compromising ductility and strength requirements set out in design codes. To achieve this, the spacing between shear links was increased while steel fibres were added as a substitute. A material model was selected and implemented into the commercial NLFEA software package ABAQUS. The numerical model was carefully calibrated against existing experimental data to ensure the reliability of its predictions. Parametric studies were subsequently carried out and comparisons were also made with Eurocode 2 predictions. It was concluded that the addition of steel fibres enhanced the load-carrying capacity and also altered the failure mode from a brittle shear mode to a flexural ductile one. T...
ABSTRACT The present article assesses the various techniques which have been employed to date in ... more ABSTRACT The present article assesses the various techniques which have been employed to date in order to investigate the nonlinear response of multidrum columns supporting statues at their tip when subjected to ground excitation. The article focuses on identifying the most practical and accurate semi-analytical method for the solution of above problem.
ABSTRACT The work described in the present article focuses on an investigation of the effect of t... more ABSTRACT The work described in the present article focuses on an investigation of the effect of the rate of applied loading on various aspects of structural response exhibited by reinforced concrete beams when subjected to high rates of concentrated loading. For the purpose of the numerical investigation, two finite-element packages are employed suitable for both static and dynamic three-dimensional nonlinear finite element analyses. A key feature of both packages employed is that they adopt the assumption that, for the case of high-rate-loading problems, the material properties of concrete and steel reinforcement are essentially independent of the loading rate and that the effects of the latter on structural response are primarily due to the inertia forces developing within the structural member, rather than to the loading-rate sensitivity of the mechanical characteristics of the materials involved. The agreement between numerical predictions and available experimental data is considered as evidence of the validity of the numerical predictions obtained.
Proceedings of the ICE - Structures and Buildings, 2010
This two-part set of papers reports some recent experiences in the design of jet-grouted piles (u... more This two-part set of papers reports some recent experiences in the design of jet-grouted piles (under predominantly lateral load) when their intended use is primarily structural, as is certainly the case when reinforcing steel is present. Although unusual, a number of such design solutions have been documented – several of them recent and applied to major structures. In the absence of specialist rules for the design of jet-grouted piles with steel reinforcement, codes of practice for reinforced concrete (RC) are usually adopted and applied as discussed in this paper. However, certain important differences between concrete and jet-grouted soil (fully discussed in the companion paper) must be clearly understood and allowed for by designers with the result that analysis and design from first principles should be undertaken instead of relying automatically on RC codes of practice. This use of first principles must be combined with a refined construction method to improve the accuracy of...
Proceedings of the ICE - Structures and Buildings, 2010
Part 1 of this two-part set of papers was intended to raise awareness of the specific problems en... more Part 1 of this two-part set of papers was intended to raise awareness of the specific problems encountered with the design of jet-grouted piles, the latter being usually based on reinforced concrete codes, as there is a lack of specialist documents on the subject. Among the problems identified in Part 1, those associated with the variability and uncertainty of both the material characteristics and the construction tolerances are prominent. The present article discusses the implications of the latter problems for the design of reinforced-concrete grouting structures and proposes guidelines that aim to minimise the risk of inappropriate design solutions, which are usually among the main causes of structural failures.
The objective of this study is to compare conventional models used for estimating the load carryi... more The objective of this study is to compare conventional models used for estimating the load carrying capacity of reinforced concrete (RC) members, i.e., Current Design Codes (CDCs), with the method based on different assumptions, i.e., the Compressive Force Path (CFP) method and a non-conventional problem solver, i.e., an Artificial Neural Network (ANN). For this purpose, four different databases with the details of the critical parameters of (i) RC beams in simply supported conditions without transverse steel or stirrups (BWOS) and RC beams in simply supported conditions with transverse steel or stirrups (BWS), (ii) RC columns with cantilever-supported conditions (CWA), (iii) RC T-beams in simply supported conditions without transverse steel or stirrups (TBWOS) and RC T-beams in simply supported conditions with transverse steel or stirrups (TBWS) and (iv) RC flat slabs in simply supported conditions under a punching load (SCS) are developed based on the data from available experimen...
International Journal of Protective Structures, 2019
Published experimental work reveals that the out-of-plane behaviour of unreinforced masonry walls... more Published experimental work reveals that the out-of-plane behaviour of unreinforced masonry walls under impact loading can be significantly enhanced through the use of engineered cementitious composite layers fully bonded to the surface of the masonry. The disadvantage of this method is associated with the localised cracking exhibited by the engineered cementitious composite layer close to the joints forming between bricks. This cracking is associated with the bond developing between the masonry and the engineered cementitious composite layer and does not allow the latter layer to achieve its full potential, thus resulting in its premature failure. In an attempt to address this problem, a series of drop-weight tests were carried on masonry prismatic specimens strengthened with a layer of engineered cementitious composite partially bonded to the surface of the masonry acting in tension. The latter prismatic specimens consist of a stack of bricks connected with mortar joints. The spec...
Proceedings of the Institution of Civil Engineers - Structures and Buildings, 2019
A comparison of the predicted and experimentally-established behaviour of over 150 reinforced con... more A comparison of the predicted and experimentally-established behaviour of over 150 reinforced concrete beam specimens (selected from 465 test results considered) revealed that around 20% of the specimens exhibited shear failure rather than the expected flexural failure. The work presented in this paper investigated the possibility that the causes of shear failure reflected shortcomings of the code methods adopted for calculating flexural capacity. It was found that the predicted values of flexural capacity tended to underestimate their experimentally-established counterparts by up to 17% on average. It was shown that by accounting for the triaxial stress conditions invariably developing in the compressive zone through a simple modification of code-proposed stress blocks, the correlation between predicted and experimental values was similar to the best possible one resulting from the development and use of an artificial neural network model.
This work is based on a nonlinear finite-element model with proven capacity for yielding realisti... more This work is based on a nonlinear finite-element model with proven capacity for yielding realistic predictions of the response of reinforced-concrete structures under static monotonically-increasing loading. In it, the material description relies essentially on the two key properties of triaxiality and brittleness and, thus, is simpler than those of most other material models in use. In this article, the finite-element program is successfully used in investigating the behaviour of a series of RC walls under static cyclic loading. This type of loading offers a more strenuous test of the validity of the proposed program since cracks continuously form and close during each load cycle. Such a test is considered to be essential before attempting to use the program for the analysis of concrete structures under seismic excitation in order to ensure that the solution procedure adopted is numerically stable and can accurately predict the behaviour of RC structures under such earthquake-loading conditions. This is achieved through a comparative study between the numerical predictions obtained presently from the program and available experimental data.
The present article summarises the fundamental characteristics of concrete behaviour which underl... more The present article summarises the fundamental characteristics of concrete behaviour which underlie the formulation of an engineering finite element model capable of realistically predicting the behaviour of (plain or reinforced) concrete structural forms in a wide range of problems ranging from static to impact loading without the need of any kind of re-calibration. The already published evidence supporting the proposed formulation is complemented by four additional typical case studies presented herein; for each case, a comparative study is carried out between numerical predictions and the experimental data which reveals good agreement. Such evidence validates the material characteristics upon which the FE model`s formulation is based and provides an alternative explanation regarding the behaviour of structural concrete and how it should be modelled which contradicts the presently (widely) accepted assumptions adopted in the majority of FE models used to predict the behaviour of concrete.
Most finite-element models of reinforced-concrete structures attribute to concrete material chara... more Most finite-element models of reinforced-concrete structures attribute to concrete material characteristics which are in conflict with true behaviour established from valid experimental information. As a result the constitutive models adopted are case-study dependent. The present work summarizes already published work which shows that the use of realistic concrete properties coupled with well-tried numerical techniques can yield a finite-element model characterised by both generality and objectivity.
The structural behaviour of steel-fibre-reinforced concrete (SFRC) beams was studied using non-li... more The structural behaviour of steel-fibre-reinforced concrete (SFRC) beams was studied using non-linear finite-element analysis (NLFEA) and existing experimental data. The work aim was to examine the potential of using steel fibres to reduce the amount of conventional transverse steel reinforcement without compromising ductility and strength requirements set out in design codes. To achieve this, the spacing between shear links was increased while steel fibres were added as a substitute. A material model was selected and implemented into the commercial NLFEA software package ABAQUS. The numerical model was carefully calibrated against existing experimental data to ensure the reliability of its predictions. Parametric studies were subsequently carried out and comparisons were also made with Eurocode 2 predictions. It was concluded that the addition of steel fibres enhanced the load-carrying capacity and also altered the failure mode from a brittle shear mode to a flexural ductile one. T...
ABSTRACT The present article assesses the various techniques which have been employed to date in ... more ABSTRACT The present article assesses the various techniques which have been employed to date in order to investigate the nonlinear response of multidrum columns supporting statues at their tip when subjected to ground excitation. The article focuses on identifying the most practical and accurate semi-analytical method for the solution of above problem.
ABSTRACT The work described in the present article focuses on an investigation of the effect of t... more ABSTRACT The work described in the present article focuses on an investigation of the effect of the rate of applied loading on various aspects of structural response exhibited by reinforced concrete beams when subjected to high rates of concentrated loading. For the purpose of the numerical investigation, two finite-element packages are employed suitable for both static and dynamic three-dimensional nonlinear finite element analyses. A key feature of both packages employed is that they adopt the assumption that, for the case of high-rate-loading problems, the material properties of concrete and steel reinforcement are essentially independent of the loading rate and that the effects of the latter on structural response are primarily due to the inertia forces developing within the structural member, rather than to the loading-rate sensitivity of the mechanical characteristics of the materials involved. The agreement between numerical predictions and available experimental data is considered as evidence of the validity of the numerical predictions obtained.
Proceedings of the ICE - Structures and Buildings, 2010
This two-part set of papers reports some recent experiences in the design of jet-grouted piles (u... more This two-part set of papers reports some recent experiences in the design of jet-grouted piles (under predominantly lateral load) when their intended use is primarily structural, as is certainly the case when reinforcing steel is present. Although unusual, a number of such design solutions have been documented – several of them recent and applied to major structures. In the absence of specialist rules for the design of jet-grouted piles with steel reinforcement, codes of practice for reinforced concrete (RC) are usually adopted and applied as discussed in this paper. However, certain important differences between concrete and jet-grouted soil (fully discussed in the companion paper) must be clearly understood and allowed for by designers with the result that analysis and design from first principles should be undertaken instead of relying automatically on RC codes of practice. This use of first principles must be combined with a refined construction method to improve the accuracy of...
Proceedings of the ICE - Structures and Buildings, 2010
Part 1 of this two-part set of papers was intended to raise awareness of the specific problems en... more Part 1 of this two-part set of papers was intended to raise awareness of the specific problems encountered with the design of jet-grouted piles, the latter being usually based on reinforced concrete codes, as there is a lack of specialist documents on the subject. Among the problems identified in Part 1, those associated with the variability and uncertainty of both the material characteristics and the construction tolerances are prominent. The present article discusses the implications of the latter problems for the design of reinforced-concrete grouting structures and proposes guidelines that aim to minimise the risk of inappropriate design solutions, which are usually among the main causes of structural failures.
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Papers by Demetrios Cotsovos