26 research outputs found
Response of steel fibre reinforced concrete structural elements under high rate loading
No full textThe work presented in the subject Thesis investigates experimentally and numerically the potential benefits stemming from the introduction of steel fibres into the concrete mix in order to enhance the material properties of structural concrete and improve the response of RC structural elements under static and high rate (impact) loading. The effect of a number of parameters associated with the fibres used (e.g. aspect ratio and volume fraction) on the exhibited structural response is studied experimentally, by carrying out a series of drop-weight testing on RC beam specimens (with and without steel fibres being introduced into the concrete mix), and numerically, through the use of dynamic Nonlinear Finite Element Analysis (NLFEA). The investigation mainly focuses on studying how certain aspects of the behaviour exhibited by the beam specimens under impact loading are affected from the use of steel fibres.
The use of steel fibres, at different volume fractions, results in increase of load carrying capacity and energy absorption of the structural elements under impact. The deflection at the beam mid-span also increases compared to the RC case indicating the ductility provided by the steel fibres. The extent of the effective length around the point of application of the impact load also increases due to the addition of fibres
Numerical modelling of structural concrete under dynamic (earthquake and impact) loading
No full textDynamic response of RC structural elements under impact loading
No full textThe effect of loading rate on the dynamic response of reinforced concrete (RC) beams
under impact loading is investigated experimentally, via drop-weight testing, and
numerically, through the use of three-dimensional (3D) dynamic nonlinear finite element
analysis (NLFEA). During drop-weight testing, the behaviour of each specimen is
established through the combined use of conventional instrumentations and a high-speed
(HS) camera. The primary objective of the experimental work is to investigate the reasons
that trigger the observed shift in specimen behaviour (compared to that established during
static testing), once certain thresholds of applied loading rate and intensity are surpassed.
The analysis of the test data suggests that the observed shift in specimen behaviour is
largely attributed to the nature of the problem at hand (i.e. a wave propagation problem
within a highly nonlinear medium) as well as the inertia forces developing along the
element span (during the application of the impact load) and the ensuing localised
response. The strain-rate sensitivity of the material properties of concrete does not appear
to have a significant effect on the behaviour of the specimens tested as high values of
strain-rate appear to be associated with the development of cracking along the element
span.
The data obtained from the drop-tests conducted on slender and short beams reveal that
the response exhibited under impact loading differs significantly from that established
during equivalent static testing. This shift in structural response predominantly takes the
form of an increase in the maximum sustained load as well as a reduction in the portion
(span) of the beam reacting to the imposed action which tends to concentrate around the
area of impact. However, measurements obtained from the drop-weight tests, concerning
certain important aspects of RC structural response (e.g. maximum sustained load or
deflection) often correspond to a specimen physical-state characterised by high concrete
disintegration in combination with low residual load-bearing capacity and stiffness. This
stage of structural response has little practical significance as it depends heavily on post-failure mechanisms for transferring the applied load to the specimen supports. In view of
the above, the available test data cannot provide insight into the mechanisms underlying
RC structural response nor can it identify the true ultimate limit state of the specimens
when subjected to impact loading. To achieve further insight into the mechanics underlying RC structural response under
impact loading a well-established structural analysis packages (ADINA version 9.3.1) is
employed which is capable of carrying out three-dimensional dynamic nonlinear finite
element analysis while realistically accounting for the nonlinear behaviour of concrete
and steel. The numerical predictions obtained are validated against available data
obtained from the drop-weight tests. The validated models are then used to conduct a
parametric investigation to study the dynamic response exhibited by RC beams when
subjected to different rates and intensities of impact loading. The latter investigation
reveals that ‘true’ load-carrying capacity is often significantly lower than the maximum
sustained load recorded experimentally. In fact, the higher the loading rate and intensity
characterising the impact load imposed the larger the latter difference becomes.
Based on the available test data and the numerical predictions obtained, a simplified
model is proposed aiming to describe the behaviour of the RC beams under impact
loading. The model attempts to link the observed shift in structural response to the
localised behaviour exhibited by the beams with increasing rates of applied loading. A
comparison of the predictions obtained with the relevant test data reveals good agreement.School of Energy, Geoscience, Infrastructure and Society (EGIS), Heriot-Watt
University scholarship
Subsea pipes under high-mass low-velocity impacts
No full textSubsea steel pipes are often used to form networks for transporting oil and gas over large distances. Such pipes can potentially be subjected to actions characterised by high loading rates and intensities stemming from accidental loads caused by high-mass low-velocity impacts. In order to ensure that such networks can continue to operate after being subjected to such extreme loading conditions, it is essential that the behaviour of the pipes is characterised by a certain level of resilience. The short duration and high intensity that often characterises impact loads can potentially result in large strain-rates being exhibited within the pipes. To study the effects of the loading-rate on the material behaviour of steel and identify the causes that trigger the experimentally observed shift in specimen behaviour with increasing loading rates compared to that established under equivalent static testing, a review of the relevant experimental evidence is carried out. A review reveals that the specimen behaviour is significantly affected by the developing inertia forces and the interaction with the experimental setup. This suggests that the available test data describes structural rather than material behaviour, thus raising concerns regarding the validity of current practices to employ such data for the development of constitutive models capable of predicting material behaviour under high loading rates.
A numerical study is carried out investigating the behaviour exhibited by steel pipes under impact loading, accompanied by a limited number of drop-weight tests. The numerical predictions, which are validated against relevant test data reveal that number of parameters associated with the characteristics of the impacting object, the geometry and the support conditions of the pipes, the level of axial loading as well as the level of internal and external pressure imposed onto the walls of the pipes can significantly affect, often detrimentally, the exhibited behaviour under impact loading. Existing assessment methods employed in practice for predicting the level of damage sustained by pipes during impact do not accurately consider the effect of the above parameters. As a result questions rise concerning their ability to realistically predict the level of damage sustained by such pipes under impact. The numerical predictions are presented in the form of simple diagrams quantifying the individual and combined effect of the above parameters on the level of damage sustained by the pipes when subjected to impact. The latter predictions can potentially form the basis for the development of more advanced analysis methods suitable for practice and leading to the development of more effective design solutions capable of safeguarding the intended level of resilience required to characterise the behaviour of subsea pipes. Finally, it is shown that the use of coatings, constructed from reinforced concrete or engineered cementitious composites, can potentially further reduce the level of damage sustained by pipes due to impact loading, however, further – more detailed – studies are required in order to accurately quantify these benefits
Investigating the mechanical properties of indigenous softwood timber used in construction in Scotland
No full textScotland has a rich and diverse heritage in terms of buildings (ranging from single-storey
houses to castles) that needs to be preserved as it represents a unique tradition in design
and construction practice. Different types of softwood, such as Scott Pine, have been
traditionally used as a construction material in Scotland’s built heritage. However, over
time, it can deteriorate causing its properties to change which can in turn, compromise
structural integrity. Before performing any repairs or other conservation activities on an
existing timber building, the current state of the structure must be assessed to identify the
form and the condition of the structural system employed for transferring the imposed
loads to the foundations as well as the type and properties of the construction materials
used. Through this process, decay zones within the structure and their underlying causes
are identified. Subsequently, the level of damage sustained and its impact on material
properties and structural performance is assessed. Depending on the level of deterioration
identified appropriate methods of intervention are employed that can range from typical
conservation to full restoration/strengthening.
Present work focuses on assessing the material properties of timber using non-destructive
testing (NDT) for realistically determining its mechanical properties as well as the extent
of the damage sustained. The measurements obtained from these tests are calibrated
against data obtained from destructive tests. The experimental study carried out focuses
on determining the properties of three types of softwood (Scot Pine, Douglas Fir and to a
lesser extent Spruce) which are indigenous to Scotland and are used in the construction
industry. A series of samples were either retrieved from existing structures undergoing
refurbishment or have been obtained from newly cut logs. Specimens were subjected to
a combination of non-destructive tests (NDTs) and destructive tests (DTs) to investigate
the behaviour of the different types of timber considered under different loading
conditions while at the same time calibrating the results obtained from the NDTs against the those achieved from the destructive tests. The latter study will allow NDTs to be more
effectively used for assessing heritage timber buildings
Novel structural details to mitigate progressive collapse in steel nominally-pinned joints
No full textSteel structures are frequently used worldwide. The beam-column connections play a vital
role in those structures. In a case of column removal due to blast, fire or vehicle impact,
the disproportionate collapse can occur if the robustness of the joint is not enough and the
failure propagates to other members. Current design practices require that the beam-column joints shall withstand a minimum tie force to prevent progressive collapse.
However, several pieces of research have shown that nominally pinned joints which are
commonly used in steel frames cannot provide the required tie force while undergoing
significant rotations imposed by a column removal event. The present thesis proposes a
set of novel structural detail to be added to the steel nominally pinned joints to arrest
progressive collapse by enhancing both their tensile resistance and rotation capacity. The
proposed structural details exploit the exceptional strength and ductility of Duplex
stainless steel pins (SSPs) under bending which allows them to withstand excessive
deformation prior to their fracture. First, the monotonic fracture capacity of SSPs was
experimentally evaluated followed by the calibration of numerical models with the
capability of predicting fracture of SSPs. Employing the calibrated numerical models, a
set of parametric study was carried out on various geometry properties of SSPs to develop
a design procedure to reliably achieve the required levels of tie force and rotation in a
joint. An experimental programme including static and dynamic tests on the proposed
joint was presented, discussed, and simulated in Abaqus. In addition, more analyses were
conducted to determine the Dynamic Increase Factor (DIF). Finally, the proposed joint
was modelled as a 3D connection including the primary and secondary directions. It was
observed that the proposed joint significantly increases the joint rotation while providing
appreciable tie force compared to standard fin plate connection.Heriot-Watt University scholarshi
Reinforced concrete (RC) structures analysis and assessment with artificial neural networks (ANNs)
No full textThis project aims to develop a radically new stable, robust and computationally efficient structural analysis procedure capable of realistically and objectively predicting the nonlinear response of reinforced concrete (RC) structures. This procedure will be suitable for both research and practical applications and will be capable of effectively solving design optimization and reliability problems which require extensive parametric studies. For this purpose, Artificial Neural Networks (ANNs) are employed which require significantly less computational resources compared to more traditional approaches of structural analysis based on the non-linear finite element analysis (NLFEA). The procedure is based on the simulation of the nonlinear behaviour of each RC element (ranging from which include typical beams and column) through the use of a model which consist of a finite element incorporating an ANN the latter predicting brittle modes of failure and the associated load-carrying capacity.
For this purpose, databases consisting of test data obtained from experiments carried out on a range of simple (determinate) structural configurations (e.g.; Beam, Column, T-beam and Slab) are developed. Subsequently the published test data is used for training the ANN models. The predictions obtained from the trained ANN models are then compared to the predictions of the relevant design codes and alternative assessment methods concerning specific aspects of RC structural behaviour at the ultimate limit state (ULS). For validation of these ANN models, limited nonlinear finite-element analyses are also conducted. These models are then used to form ANN-FEA models to simulate more intricate RC structural configurations consisting of more than one structural elements. In the latter ANN-FE models, ANNs are essentially used as a failure criteria when conducting non-linear static push over analysis.
The stability and robustness of the proposed structural analysis method, as well as the validity and objectivity of its predictions, is ensured through a comparative study of the predicted behaviour of RC frames under static loads with its experimentally and numerically established counterparts. The predictions obtained from ANN-FE models are compared to their counterparts obtained from professional and research analysis packages for the case of a number RC structures. The proposed procedure employs the ANNs as failure criteria defining the loadbearing capacity and mode of failure exhibited by the individual RC beams and columns during the pushover analysis. The results show that the ANN-FE model predicts the structural response of RC at ULS with more accurately as compared to industrial tools (i.e., SAP 2000) and in less amount of time without requiring the high computational resources as compare to research tools (i.e., ABAQUS)
Drop-weight testing of slender reinforced concrete beams
No full textThe work presented herein sets out to investigate experimentally, via drop-weight testing, the behavior of slender reinforced concrete (RC) beam specimens under impact loading. During testing, the behavior of each specimen is established through the combined use of conventional instrumentation and a high-speed video camera. The primary objective of this work is to investigate the reasons that trigger the observed shift in specimen behavior (compared to that established from static tests) with increasing levels of applied loading rate and intensity. Analysis of the test data reveals that during drop-weight testing only a portion of the element span reacts to the applied load (as indicated by the deformation and cracking profiles recorded) which in turn affects the mechanics underlying specimen behavior and therefore, significantly influencing the mode of failure ultimately exhibited. The observed localized response becomes more prominent by increasing the loading rate and intensity of the imposed impact loading. In addition to the above, the strain-rate sensitivity of the material properties of concrete does not appear to have a significant effect on the behavior of the specimens tested. The aforementioned observations appear to be in conflict with current design practice raising questions concerning the effectives of the design solutions produced.</p
Out-of-plane retrofitting of masonry wall using engineered cementitious composites.
No full textThe contribution of infill masonry walls to the overall behaviour of frame structures has been acknowledged through numerous published experimental and numerical investigations. Both the in-plane and out-of-plane response of such walls have a significant effect on the overall structural performance of frames and can be subjected to a range of in-plane and out-of-plane actions (e.g. wind, earthquakes, impact and blast loads) characterised by different time-histories, loading-frequencies and intensities. Infill walls are particularly vulnerable to the application of loads in the out-of-plain direction and often sustain significant damage (in the form of cracking) which can result in failure and collapse. It is interesting to note that after sustaining a certain level of damage due to the load applied in the out-of-plane direction, an infill wall can no longer contribute to the in-plane response of a frame. In an attempt to enhance the overall behaviour of infill walls, present work sets out to develop a method for improving the out-of-plain behaviour of such elements. This is achieved through the use of a thin layer of engineered cementitious composite (ECC) which is fully or partially bonded on the face of the wall which is in tension (opposite to the face on which the out-of-plane action is applied) or on both faces of the wall. For this purpose, an ECC mix is initially developed employing materials available in the UK. Its behaviour is then established experimentally under increasing loading rates and temperatures. This material is then used to strengthen a series of beam-like masonry specimens under different loading rates by conducting a series of static and dynamic 4-
point bending tests. The test data obtained is then employed to develop a numerical model of the problem at hand capable of realistically predicting the experimentally established behaviour through the use of nonlinear dynamic finite element analysis. Both, experimental and numerical studies, reveal that in all cases considered the use of ECC resulted in a significant enhancement of the out-of-plain behaviour of the specimens in terms of strength, stiffness and ductility. Furthermore, the specimens with a partially bonded ECC layer performed better compared to those with a fully ECC layer. In addition, the performance of these specimens under impact load was further enhanced when adding a second layer on the other face of the specimen. Finally, a parametric numerical investigation is conducted to assess the effect of a range of parameters (associated with the boundary conditions imposed onto the specimen, the properties of the materials involved, the geometry of the specimen and loading rate) on the behaviour of the specimens
Assessing the performance of existing RC beam-column joints
No full textThe work presented herein sets out to study the behaviour of external beam-column joints with different reinforcement configurations that form part of existing RC structures and are often not been designed in accordance with current code provisions. The work is concerned with a numerical investigation of the behaviour of reinforced-concrete beam-column sub-assemblages under monotonic loading to assess the effect of crack-formation within the joint region on the overall response of the structural configurations considered. The behaviour of the latter specimens is investigated numerically using a nonlinear finite element analysis package (ADINA) which is capable of realistically accounting for the nonlinear behaviour of concrete and steel. The predictions of the numerical models developed are initially validated against published test data. The validated models are subsequently employed to provide insight into the mechanics underlying specimen behaviour as they approach their ultimate limit state. Each specimen is modelled twice, once with their joint region being modelled as a reinforced concrete member and then (a second time) with the joint region being assigned elastic properties. In most cases studies presented, the joints were found to suffer considerable cracking that initiated at early load stages. This led to an increase of the overall displacement values which was dependent however, on the configuration of the reinforcement provided. This indicates that the assumption of 'rigid joint', which is essentially implicit in methods used for the practical analysis of frames, is not always applicable when employed for the analysis of concrete structures.</p
