Demetrios M. Cotsovos

Numerical investigation of the effect of infill walls on the structural response of RC frames

The work presented herein sets out to investigate numerically, by means of nonlinear finite element analysis, the effect of un-reinforced concrete or masonry infill walls on the overall structural response of reinforced concrete frames under static monotonic and seismic loading. For this purpose, a nonlinear finite element package purpose built for the analysis of concrete structures is employed in order to predict the nonlinear behaviour of both the infill walls as well as the surrounding frame. Specifically, the dynamic response of a bare two-storey, one-bay frame, whose behaviour has been experimentally established in the past through shake-table testing, is first investigated via nonlinear finite element analy- sis. Subsequently, concrete and masonry walls are introduced into the selected frame in order to investigate numerically how important aspects of structural response such as stiffness, load-carrying capacity, deformation profile, cracking, duc- tility and mode of failure of the frame are affected.

Constitutive modelling of concrete behaviour: need for reappraisal

The present article summarises the fundamental properties 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 experimental data which reveal 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.

A Practical Method For Assessing Reinforced Concrete Members Under Impact

The effect of the loading-rate on the dynamic response of reinforced concrete members under impact loading is investigated numerically through the use of three-dimensional dynamic nonlinear finite element analysis. The package employed is capable of realistically accounting for the triaxiality and the brittle nature characterising concrete material behaviour as well as the characteristics of the problem at hand, a wave propagation problem within a highly nonlinear medium. Due to the availability of tests data, the present study focusses on investigating the effect of impact loading on the behaviour of reinforced concrete beam specimens. The numerical predictions obtained provide detailed insight into the mechanisms underlying RC structural response and offer a quantitative description of the effect of loading-rate on certain important aspects of the exhibited behaviour. Based on the numerical predictions obtained, a physical model is proposed which is capable of realistically describing the behaviour of the RC structural elements under high rates of concentrated loading. The proposed physical model links the observed shift in structural response to the localised experimentally established and/or numerically predicted behaviour with increasing rates of applied loading. Its formulation is based on the use of the Compressive Force Path method which is capable of realistically describing the behaviour of a wide range of reinforced concrete structural configurations at their ultimate limit state under both static and seismic loading conditions.

Statically-Indeterminate SFRC Columns under Cyclic Loads

The present study is aimed at examining the structural response of steel-fibre-reinforced concrete (SFRC) columns under reversed-cyclic loading, which were investigated by means of non-linear finite-element analysis (NLFEA). The focus was on investigating the potential of steel fibres in compensating for reduction in conventional transverse reinforcement [and thus the spacing between shear links was increased by 50% and 100% while the fibre volume fraction (V f ) was increased to 1%, 1.5%, 2% and 2.5%]. This is useful in situations where the latter is required in significant amounts (e.g. in seismic design) leading to congestion and practical difficulties in placing the links. The critical factor in the seismic response is the cyclic nature of the load, which is examined in the present research work. An interesting feature of the present research work is the consideration of statically-indeterminate SFRC columns, information on which is rare as previous research studies have focused on simply-supported beams. To address this, both indeterminacy and axial loads were considered in the present investigation. Calibration work was carried out using existing experimental data and good correlation was established between numerical and test results. Subsequently, parametric studies were carried out using the practical range of fibre dosages, which provided insight into how the steel fibres can help reduce the amount of conventional shear links.

FE modelling of SFRC beams under impact loads

The present work aims at investigating the structural behaviour of steel-fibrereinforced concrete (SFRC) beams under high-rate loading conditions mainly associated with impact problems. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the study. The model is mainly focused on realistically describing the fully brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the postcracking response. The constitutive relations were incorporated into ABAQUS software brittle-cracking concrete model in order to adjust the latter to allow for the effects of fibres. Comparisons of the numerical predictions with their experimental counterparts demonstrated that the model employed herein, despite its simplicity, was capable of providing realistic predictions concerning the structural responses up to failure for different SFRC structural configurations. In the present study, the previous work is extended in order to numerically investigate the structural responses of simply-supported SFRC beams under impact loading. Data obtained from drop-weight tests on RC beams (without fibres) indicates that the response under impact loading differs significantly from that established during equivalent static testing. Essentially, there is (i) an increase in the maximum sustained load and (ii) a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter making it difficult to ascertain the effect of loading rate on various aspects of RC structural response. To achieve this dynamic NLFEA is employed which is capable of realistically accounting for the characteristics of the problem at hand, a wave propagation problem within a highly non-linear medium. Following validation, a further study was conducted to assess the effect of steel fibers (provided at a dosage of Vf = 1%) on key aspects of structural response such as maximum sustained load, load-deflection curves, deformation profiles and ductility) under different rates and intensities of impact loading. The predictions reveal that steel fibers can potentially increase the maximum sustained load, ductility, toughness exhibited by SFRC members under impact loading compared to their RC counterparts. Pegah Behinaein, Ali A. Abbas and Demetris M. Cotsovos