Recently Completed Projects

As the mechanical properties of reinforced concrete change significantly at elevated temperatures, and as most of the international building codes are getting more concerned with performance-based design having fire-performance criteria, investigating the behaviour of reinforced concrete structures under elevated temperatures and fire is the major area of Fady ElMohandes’ research.   Thermal analysis is being incorporated in VecTor3 software, the part of the VecTor analysis software responsible for the analysis of three-dimensional reinforced concrete solid elements. In addition, dynamic analysis capabilities including blast and impact loading are also being included in the software. For the sake of the corroboration of VecTor3, an intensive experimental program is planned, where various types of elements will be tested with different types of concrete, levels of sustained loading, confinement levels and temperature loading profiles.

The complete details of the research program can be viewed in ElMohandes (2013).
Fady
By Fady ElMohandes, Ph.D.
E mail: fady.elmohandes@utoronto.ca
Shock tube blast loading of reinforced concrete slab
Effect of Temperature on Compression Strength of Carbonate Aggregate Concrete (Abrams, 1971)

There is a growing need for analytical tools which are capable of accurately modelling reinforced concrete (RC) structures under generalized loading conditions. The analytical procedures forming most of the available commercial programs have often been met with limited success as they often require complex and expensive micro-modelling approaches, results are often highly sensitive to user-selected behavioural models and analysis parameters, and many of the programs have demonstrated inabilities in capturing the brittle concrete response of shear-critical elements.

A procedure for improved nonlinear analysis of RC slab and shell structures has been developed and implemented within the framework of the nonlinear finite element program VecTor4. The program employs a layered thick-shell formulation which considers out-of-plane (through-thickness) shear forces, a feature which makes it notably different from most shell analysis programs. Previous versions of the program were of somewhat limited use due to their inabilities to accurately capture out-of-plane shear failures, and because analyses were restricted to monotonic loading conditions. The work performed in this research program was focused on addressing these limitations, and implementing new analysis features extending the range of structures and loading conditions that can be considered. The accuracy of the resulting program was verified using test specimens presented in the literature spanning various member types and loading conditions. The new program features are shown to enhance modelling capabilities and provide accurate assessments of shear-critical structures.

In addition to the analytical study, an experimental program consisting of RC and FRC slab specimens under dynamic loading conditions was performed. Eight intermediate-scale slabs were constructed and tested to failure under sequential high-mass low-velocity impact. The data from the testing program were used to verify the dynamic and FRC modelling procedures developed, and to contribute to a research area which is currently limited within the database of literature: the global response of RC and FRC elements under impact. Test results showed that the addition of end-hooked steel fibres was effective in increasing the capacities of the slabs, reducing crack widths and spacings, and mitigating the development of local damage under repeated impact loading. VecTor4 analyses of the slabs showed that high accuracy estimates can be obtained for RC and FRC elements under impact using basic modelling techniques and simple finite element meshes.

Details regarding the shell structure analysis program VecTor4 and the companion experimental study are presented in Hrynyk (2013). The unfiltered digital data collected during the impact testing program are also provided: Slab Digital Data.
trevor
By Trevor Hrynyk, Ph.D.
E mail: thrynyk@utexas.edu

One of the key benefits from the addition of steel fibres to reinforced concrete is in improving the shear resistance of the structural element; hence, it is important to investigate the behaviour of steel fibre reinforced concrete (SFRC) under pure shear conditions without the obscuring effects of flexure. An experimental test program has been established to accomplish this goal. A series of in-plane panel specimens (890x890x70 mm) will be tested using University of Toronto’s Panel Element Tester, one of the few facilities in the world capable of isolating shear-related mechanisms. The panels will have varying steel fibre volume fractions, fibre lengths and fibre tensile strengths. The loading protocols include monotonic shear and reversed cyclic shear.

Results from this experimental study will be used to improve constitutive models for SFRC. Namely, the goal is to study the effects of the presence of steel fibres and conventional reinforcements on cracking characteristics, post-cracking rotation of principal stresses and principal strains, slip along the crack surface, tension stiffening, tension softening, compression softening and post-peak ductility. Ultimately, the constitutive models developed will be implemented into the VecTor suite of nonlinear finite element analysis programs to allow for more accurate analysis of SFRC structures.

Details regarding the research program is provided in Luo (2014).
Fady
By william Luo, M.A.Sc.
E mail: William.luo@mail.utoronto.ca

Finite element analysis (FEA) programs facilitate the analysis of complex structures which may not be readily designed by traditional means, generating vast arrays of data in approximately predicting the behaviour of a given under a desired loading scenario. Contemporary FEA programs, such as the VecTor software suite, utilize post-processor programs to allow for the multitude of numerical information to be comprehensively displayed graphically for ease of data synthesis, interpretation and verification of results. The proposed Janus post-processor program will be used to augment the existing VecTor structural analysis programs, providing the user with the capability to display both two-dimensional and three-dimensional global structural response characteristics such as: crack patterns, stress contours, deflections, and load patterns. The Janus post-processor will not only allow for the user to comprehensively recall and manipulate structural analysis results on a global scale, but will also have the capacity to display pertinent information for individual specified elements of interest as well.

Details regarding the research program is provided in Chak (2013).
Ivan
By Ivan Chak, M.A.Sc.
E mail: ivan.chak@utoronto.ca
Storage silo displaced shape
Janus post-processor: Storage silo displaced shape

The benefits of fibre reinforced concrete (FRC) have been thoroughly investigated. Much of this work has focussed on steel FRC subjected to monotonic loads. Data on the structural behaviour of macro-synthetic FRC or FRC under cyclic loads is scarce.

A pilot investigation on the shear behaviour of macro-synthetic FRC and on the behaviour of FRC under reversed cyclic in-plane shear loading was carried out. Five in-plane shear panel tests were performed. The parameters under study were the fibre material type (steel or macro-synthetic) and loading protocol. Additionally, a number of compression, direct tension, and flexural tests were performed to determine the material properties of the concretes for comparison. The material response of 2.0% by volume of macro-synthetic FRC matched closely with 1.0% steel FRC.

Finally, building upon an existing steel FRC model, a model for macro-synthetic FRC in tension was proposed and a short verification study was undertaken.

Details regarding the research program is provided in Carnovale (2013).
David
By David Carnovale, M.A.Sc.
E mail: david.carnovale@utoronto.ca

The analysis of reinforced concrete structures under blast and impact loads is an area of research that has become increasingly relevant in recent years. Complex hydrocodes are typically used for impact analyses, although single-degree-of-freedom methods have also been developed. There are a number of disadvantages associated withboth methods, and the Canadian Nuclear Safety Commission (CNSC) is looking for a tool thatcan be used in conjunction with hydrocodes to analyze hard and soft missile impacts, with target damage ranging from flexural cracking to perforation.

The VecTor programs, a suite of nonlinear finite element programs developed at the University of Toronto for the analysis of reinforced concrete structures, can potentially be developed into such tools. The analytical work done in this studyserves to investigate the current impact and impulse loading analysis capabilities in VecTor2 and VecTor3, and to identify areas where work should be focused in the future.

The complete details of the research program can be viewed in Trommels (2013).
Heather
By Heather Trommels, M.A.Sc.
E mail: heather.trommels@utoronto.ca
Shock tube blast loading of reinforced concrete slab

The first objective of this study was to develop an updated version of FormWorks, FormWorks 3.8, which is more user-friendly and compatible with newer versions of VecTor2. The second objective was to create a new version of FormWorks, FormWorks-Plus, capable of modeling different types of structures including 2D Membrane Structures, 3D Solid Structures, Shell Structures, Plane Frame Structures, and Axisymmetric Solid Structures.

FormWorks 3.8 was mainly developed to model the different types of materials now available in VecTor2 including Reinforced Concrete, Structural Steel, Masonry, Wood, Concrete-Steel Laminate, Concrete-SFRC Laminate, Masonry-SFRC Laminate, Concrete-Ortho Laminate, Reinforcement, and Bond. In addition, the Job Page was updated with the most recent behavioural models and analysis parameters. The zooming feature of FormWorks was improved to display the geometry of the finite element model properly. A new load type, Nodal Thermal Load, was added to the program allowing the user to define thermal loads for nodes. The performance of the truss and rectangular elements was improved. Finally, updated dialog boxes for nodes, elements, restraints, and load types were added to facilitate the modifying process of finite element model.

FormWorks-Plus is a new version of FormWorks, compatible with entire suite of VecTor programs. In addition to the XY, XZ, and ZY plane views, sectional and projection views were added to the program, greatly contributing to its utility. FormWorks-Plus also uses a supporting program called 3D View which is written with the MFC library and OpenGL (Open Graphics Library), allowing the user to see a 3D view of the structural model. In addition, four different types of node coordinate definitions, five types of elements, several load types, and new material properties are added to the software, making it compatible with the remaining VecTor programs.

The complete details of the research program can be viewed in Sadeghian (2012).
FormWorks-Plus
Vahid
By Vahid Sadeghian, M.A.Sc.
E mail: vahid.sadeghian@utoronto.ca

There are many researchers who derived tension stiffening models to evaluate the average tensile stress of concrete. Most of them have focused on tensile behaviour before yielding of reinforcement. After the yielding of reinforcement at the crack surface, the average tensile stress of concrete is reduced because the reinforcement stress is limited to its yield strength (line B-C in Figure). Without this equilibrium check, the capacity of concrete members or structures could be not correct because of an overestimation of concrete tensile stress. With this limitation, after the average strain of reinforcement reaches the yield strain, the average tensile stress of concrete becomes zero. Hence, once the average stresses of reinforcement have reached yield, the contribution of concrete on tensile behaviour is ignored, so the tensile behaviour of reinforced concrete members after yielding of reinforcement becomes the same as that of bare steel bars. Consequently, the equilibrium check on the crack surface makes the ultimate strength and strain identical to those of the bare steel bar (line C-D in Figure). However, tensile stress of concrete still exists even after yielding of reinforcement because of bond behaviour between concrete and steel reinforcement. The contribution of concrete tensile stress after yielding of reinforcement makes the strain at the ultimate condition less than that of the bare steel bar (line C-E in Figure). Therefore, the tensile stress of concrete after the yielding of reinforcement should be considered for a more reasonable and precise prediction of structural behaviour of concrete members and structures.

The main objective of this research is on the development of a tension stiffening model which is applicable to the prediction of the post-yield behaviour of RC members. The model to be developed will be implemented on VecTor2.

lee
By Seong-Cheol Lee, Ph.D.
E mail: wook0903@snu.ac.kr
Behaviour of RC members subject to uniaxial tension
Behaviour of RC members subject to uniaxial tension

Fibres have been used in concrete structures to compensate for the weak point of concrete; its brittle tensile behaviour. One of the most important effects of the application of fibres in concrete structures is that non-brittle behaviour after concrete cracking can be achieved. When evaluating the stress-crack opening displacement response due to fibres, the direct tension specimens tested are generally of a small size. Therefore, the effect of the restriction of fibre orientation should be considered in order to apply test results from small specimens to the analysis of real structures with fibre reinforced concrete. Moreover, some of fibres crossing crack surfaces are engaged in tension while the others are not engaged, so the effectiveness of fibres should be also considered.

The objective of this research is on the derivation of a tensile behaviour model for fibre reinforced concrete which takes account of the member size effect, the effectiveness of the fibres, the fibres' random orientation, and so on, all at once. The model to be derived will be expanded into the derivation of a tension stiffening model for fibre reinforced concrete with ordinary deformed steel reinforcing bars. The model to be derived will be implemented in the VecTor analysis programs.

lee
By Seong-Cheol Lee, Ph.D.
E mail: wook0903@snu.ac.kr
Tensile behaviour of fibre reinforced concrete
Tensile behaviour of fibre reinforced concrete

A research program was conducted which focused on improving the ability to model the cracking behaviour of steel fibre reinforced concrete members containing conventional deformed steel reinforcing bars. The objective of this experimental program was to observe the changes in crack widths and spacings caused by the inclusion of steel fibres, as well as to observe the effect of steel fibres on the tensile stress-strain response of reinforced concrete.

The uniaxial tension test specimens had the following dimensions. The specimens were one metre in length, with 250 mm of reinforcing bar protruding from each end for gripping in the testing machine. The square concrete cross section was varied from 50 mm x 50 mm to 200 mm x 200 mm, and the reinforcing bar size was varied from 10M to 30M (Canadian bar sizes). The steel fibre types and volume contents were also varied. Dramix RC-80/30-BP (high-strength 30mm fibres, l/d~80) were used primarily, but the effect of using RL-45/50-BN (normal-strength 50mm fibres, l/d~45) and ZP 305 (normal-strength 30mm fibres, l/d~55) were also investigated. A duplicate of each specimen was produced and tested in order to minimize statistical variance. A total of 60 uniaxial tension tests were performed.

It was observed that crack widths and spacings decreased with increasing fibre content, increasing fibre aspect ratio, increasing conventional reinforcement ratio, and decreasing conventional reinforcing bar diameter. These observations were developed into a stabilized mean crack spacing model which accounts for the influence of steel fibres on cracking behaviour. This model was based on the CEB-FIP 1978 Model Code formulation. This new analytical cracking behaviour model was found to predict stabilized crack spacings with far greater accuracy than those currently available in the literature. The complete details of the research program can be viewed in Deluce (2011).
jordon
By Jordon Deluce, M.A.Sc.
E mail: jordon.deluce@utoronto.ca
Uniaxial Tension Test Setup
Uniaxial Tension Test Setup
Tension Test Specimen Dimensions
Tension Test Specimen Dimensions
Comparison Between Measured Crack Spacings and Those Predicted by Proposed Model
Comparison Between Measured Crack Spacings and Those Predicted by the Proposed Model

Extensive work was conducted to investigate the effectiveness of hooked-end steel fibres to control cracks. Seven types of material tests were performed: uniaxial tension test, cylinder compression test, modulus of rupture test, splitting test, free and autogenous shrinkage test, and restrained shrinkage test. In addition, ten 890×890×70 mm concrete panels were tested under in-plane pure-shear loading using the Panel Element Tester. The parameters of study were the fibre volume content (0.5%, 1.0%, and 1.5%), the concrete compressive strength (50 and 80 MPa), and the fibre geometry and tensile strength. In addition to the experimental study, a model was developed to investigate the behaviour of a 1D restrained FRC member subjected to shrinkage.

The experimental results indicated that the addition of fibres significantly improved the behaviour of the concrete, particularly the crack control characteristics, the post-peak compressive response, the post-cracking tensile response, the toughness, and the ductility of the concrete. The results also indicated that steel fibres were as effective as conventional reinforcement in controlling shrinkage cracking, provided that sufficient fibre volume content was added to the concrete. For example, in order to achieve a maximum crack width of 0.35 mm, a minimum fibre content of 0.9% and 1.1% should be provided for 50 MPa FRC containing high aspect ratio fibres and low aspect ratio fibres, respectively. In addition, the results indicated the importance of fibre content and fibre aspect ratio on the effectiveness of fibre reinforcement.
jimmy
By Jimmy Susetyo, Ph.D.
E mail: jimmy_susetyo@yahoo.fr
Failure Crack Pattern of Non-FRC Panel (f’c=50 MPa, rx=3.3%, ry=0.4%)
Failure Crack Pattern of Non-FRC Panel (f’c=50 MPa, rx=3.3%, ry=0.4%)
Failure Crack Pattern of FRC Panel (f’c=50 MPa, rx=3.3%, 1.5% DRAMIX RC 80/50)
Failure Crack Pattern of FRC Panel (f’c=50 MPa, rx=3.3%, 1.5% DRAMIX RC 80/50)

Although modern design codes typically require concrete frame structures to be designed to be ductile and flexure-critical in their behaviour, many situations arise in practice where shear-related mechanisms play a significant role in the response of structures. Advanced analytical tools that rigorously consider shear behaviour are required for a comprehensive and accurate assessment of the performance of such frames. However, the typical analysis tools currently available either ignore shear mechanisms altogether, employ opaque and overly-simplistic formulations, or are overly-complex requiring the selection of numerous parameters and supporting calculations prior to the analysis. Most neglect shear deformations by default.

A research initiative was undertaken to develop a nonlinear analysis procedure, VecTor5, for plane frames that accurately accounts for shear effects, but one that does not require extensive pre-selection of analysis options, material models and failure modes nor extensive supporting analyses or calculations prior to the analysis. The procedure developed is capable of considering static loads (i.e., monotonic, cyclic and reversed-cyclic) as well as dynamic loads (i.e., base accelerations, impulse, impact and blast forces, initial mass velocities, and constant mass accelerations). The advantage of the procedure lies in its simple modelling, and inherent and accurate consideration of shear effects. Complete details of the formulation, application and verification of the procedure is provided by Guner (2008).
Duong et al. Frame
guner
By Serhan Guner, Ph.D.
E mail: sguner@ryerson.ca

The analysis and design of reinforced concrete (RC) structures against extreme loads, such as earthquakes, blasts, and impacts, has been an objective of many researchers and designers. As a result of recently elevated terror threat levels in the world, demand for the impact resistant design of buildings has increased. Numerous studies have been conducted to-date for understanding and developing methodologies predicting the behaviour of RC structures under impact loads. However, lack of complete understanding of shear behaviour under high dynamic conditions hindered the efforts for accurate prediction of impact behaviour, since severe shear mechanisms may dominate the behaviour of RC structures when subjected to impact loads.

This study aimed to apply one of the more successful methods of static reinforced concrete shear analysis, the Modified Compression Field Theory (MCFT), to the analysis of dynamic loads, and thus, develop an efficient and reliable tool for impact analysis of RC structures. Two-dimensional nonlinear finite element analysis program for reinforced concrete, VecTor2, developed previously at the University of Toronto for static loads, was modified to include the consideration of dynamic loads, including impacts. VecTor2 uses the MCFT for its computational methodology, along with a wide array of material and behavioural models for reinforced concrete. To verify the performance of VecTor2 and its computational methodology under impact loads, an experimental program was also undertaken to provide data for corroboration. Eight reinforced concrete beam specimens, four pairs, were tested under free falling drop-weights, impacting the specimens at the mid-span. All specimens had identical longitudinal reinforcement, but varying shear reinforcement ratio, intended to investigate the effects of shear capacity on the impact behaviour. A total of 20 tests were conducted, including multiple tests on each specimen. The test results showed that the shear characteristics of the specimens played an important role in their overall behaviour. All specimens, regardless of their shear capacity, developed severe diagonal shear cracks, forming a shear-plug under the impact point. The VecTor2 analyses of the test specimens were satisfactory in predicting damage levels, and maximum and residual displacements. The methodology employed by VecTor2, based on the MCFT, proved to be successful in predicting the shear-dominant behaviour of the specimens under impact.
saatci
By Selcuk Saatci, Ph.D.
E mail:  selcuksaatci@iyte.edu.tr

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Saatci: Augustus screenshot
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