Civil and Environmental Engineering

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9906

This is the collection for the University of Waterloo's Department of Civil and Environmental Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 7 of 7

Computational Systems Mechanobiology of Tumor-Induced Angiogenesis
(University of Waterloo, 2019-05-21) Mostofinejad, Amirmahdi; Al-Mayah, Adil
Tumour-induced angiogenesis is affected by an interplay between different cell types, the mechanical stresses in the extracellular matrix (ECM), and the cell signalling networks. The morphology of the newly-created cells is highly dependent on the tip cells’ movements, yet the mechanical aspect of tip cell migration is not very well studied. The model developed here is one of the first phase-field models of angiogenesis incorporating the mechanics of the phenomenon. Besides, it is the only model to make a connection between the movement of the tip cell and the formation of matrix pathways in the extracellular matrix. Here, fracture formulas handle the modelling of the formation of matrix pathways. Furthermore, the model integrates the biochemical elements into the mechanical progression of the tip cells. This framework uses a set of equations to model different aspects of the phenomenon categorized into three modules; biomechanical, biochemical, and the vascular network module. The biomechanical module is simply a set of two partial differential equations (PDEs); the linear momentum balance equation and a phase-field equation for handling the two phases, the endothelial cells (ECs) and the ECM. We used an energy-based criterion for soft material for the fracture of the ECM. The biochemical module consists of four advection-diffusion-reaction equations, each of which is responsible for the concentration of one of the elements involved in the process namely: oxygen, TAF (tumour angiogenesis factor), MMP (matrix metalloproteinases), the ECM. The vascular network describes the movement of the tip cells and possible branching. This module uses a nonlinear equation solver and a stochastic function to find the location of the tip cell in each step. The results of this modelling approach conform with the results available from older computational models and experimental models.
Development, Analysis and Testing of Innovative Mechanical Prestressing Anchors for CFRP Plates for Structural Rehabilitation and Retrofitting
(University of Waterloo, 2017-01-18) Mohee, Faizul Mohammad; Al-Mayah, Adil
This thesis presents the development, analysis and experimental investigation of three innovative, easy-to-install, low cost, epoxy-free, mechanical, friction-based, compact, high-strength, prestressing anchors for carbon fibre-reinforced-polymer (CFRP) plates. Two anchors (anchor #1 and #2) were developed to prestress the popular and commercially available 50 mm ⨉ 1.2 mm CFRP plates with 2,800 MPa strength, while the third anchor (anchor #3) was for the 50 mm ⨉ 1.4 mm CFRP plates with 2,900 MPa strength. Two anchors (anchor #1 and #3) were made of heat-treated H13 steel. Anchor #2 was the corrosion resistant anchor, and it was made of heat-treated 440C stainless steel. Each anchor consists of a CFRP plate, two annealed copper sleeves, two steel wedges and a steel barrel. The novel CFRP plate anchors were designed and analyzed by means of: (1) experimental friction tests; (2) finite element numerical modelling; (3) mathematics-based analytical modelling; and (4) experimental investigations of the anchor prototypes. Friction tests were conducted to characterize the tribological behaviour and to determine the coefficient of friction values between the CFRP plate and two types of copper plates (as-received and annealed). Finite element numerical models were developed to investigate the mechanics of the three anchors. A parametric study, using the numerical models, was carried out in order to optimize the anchor design. A unique mathematics-based analytical model was developed to predict the contact pressure distribution on the CFRP plate inside the anchor under loading. A manufacturability study was also conducted for the new anchors including the selection of materials, the heat-treatment procedure and 3-D rapid prototyping. This thesis also presents the experimental results of twenty-nine tension tests to measure the performance of the anchors under loading. The new anchors were optimized through a sequential testing program for different design parameters. All three new anchors carried a load of more than 100% of the guaranteed ultimate tensile strength of the CFRP plate without any premature failure or slip of the CFRP plate from the anchor. The average failure load was 187±6 kN, 187±5 kN and 231±6 kN for anchor #1, #2 and #3, respectively. The failure mode of all of the anchors was the tensile rupture of the CFRP plate at its free length outside of the anchors. The results show that the anchors do not require any pre-setting equipment. The new anchors can be used for new construction and for the repair, rehabilitation and retrofitting of aging infrastructure by prestressing the CFRP plate in bridges, buildings, tunnels, dams, marine structures and other structures.
Evaluation of X-Ray Computed Tomography and Finite Element Models for Fatigue Experimental Hot Mix Asphalt Characterization
(University of Waterloo, 2016-01-15) Shaheen, Magdy; Tighe, Susan; Al-Mayah, Adil
Fatigue cracking is one of the major distresses of surface hot mix asphalt (HMA) pavement that shorten pavement service life. Under typical Canadian weather conditions, fatigue distress requires frequent and high-cost maintenance and is therefore always a key concern for pavement construction and design engineers. The primary focus of this thesis was the development of an advanced understanding of the mechanisms underlying fatigue resistance in surface HMA materials. The research objectives have been achieved through extensive experimental evaluation, advanced image-based characterization techniques, and three-dimensional (3D) image-based microstructural finite element (FE) modelling. The findings of this study can therefore be considered a guide for the development of HMA that exhibits superior fatigue performance for use in pavement designs that might lead to longer-lasting pavements and enhanced performance. The experimental work involved an evaluation of the sensitivity of the fatigue resistance of surface HMA mixes to three primary design variables. Aggregate type, binder type, and binder content as well as their interaction have been quantified with respect to their effects on HMA fatigue life, rutting resistance, and stiffness. The objective was to optimize the design by extending fatigue performance while reducing the confounded negative effect on rutting resistance. Two aggregate types were used in the evaluation: Superpave SP12.5 and high friction SP12.5FC2. Two performance graded binders (PG 64-28) were also employed: a modified binder (PG Plus) that meets Ontario Laboratory Standards (LS) specifications and an unmodified binder at two binder levels (optimum and optimum plus 0.5 %). The results show that when a high friction aggregate is used, the value of modifying the binder to produce softer mixes can be compromised due to the irregular shape associated with the texture, which produces stiffer mixes. A slight adjustment to the amount of binder (+ 0.5%) can decrease this effect. Superior HMA fatigue performance was exhibited by the regular 12.5 aggregate and the PG Plus at the optimum binder content plus the additional 0.5 %. This conclusion was reached through the integration of the positive effects of the variables investigated. The experimental findings also revealed only an insignificant reversible impact on rutting resistance. A high friction aggregate provided a better internal structural characteristic as well as superior rutting resistance and stiffness in the HMA mixes. The use of PG Plus and the addition of 0.5% to the optimum binder content negatively affected HMA stiffness and rutting resistance. However, the levels of rutting resistance for all mixes were acceptable (rut depth < 12.5 mm), even when shear upheave was considered. Three imaging techniques were utilized for an advanced image-based investigation of HMA characteristics and performance: scanning electron microscopy (SEM), a combination of a simple scanner and Ipas2 software to depict the two-dimensional (2D) internal structure of the test specimens, and nondestructive X-ray computed tomography (CT) for 3D analysis. Aggregate texture was compared using 3D visualization of the SEM images, a technique that provides very high resolution. The rutting resistance of the HMA mixes was investigated using 2D images of the experimentally tested specimens, which involved estimating the number of aggregate contacts, the total contact length, and the Internal Structure Index (ISI). The ISIs measured were effective for capturing changes in the internal HMA structure with respect to aggregate type and asphalt cement content. A framework was established for employing X-ray CT for the assessment of HMA fatigue damage. The analyses were carried out on asphalt beams in order to quantify the damage created by four-point bending loads. A new algorithm was developed for calculating the thresholding levels of the images acquired before and after testing. The thresholding levels prior to testing were estimated using laboratory air voids. To determine the post-testing thresholding levels, the proposed algorithm matches 16-bit image histograms obtained before and after the testing. This process is implemented only for the portion of the histogram that represents the aggregate colour intensities that remain unchanged during the testing. The results and analysis reveal that the developed technique is a valid method for successfully quantifying and evaluating HMA fatigue damage in large specimens. Because of the high degree of precision they provide, 16-bit images are recommended for this type of analysis. It was found that the distribution of both air voids and damage is non-uniform in asphalt beams and that it varies significantly throughout the length of a single beam as well as from beam to beam. This study also confirms the effectiveness of X-ray CT for quantifying HMA fatigue damage in asphalt beams following crack propagation. A microstructural FE model based on 3D X-ray CT images was developed as a means of investigating the effect of asphalt mixture constituents on mechanical responses. The model takes into account the complex 3D geometry, spatial distribution, volume fraction, and mechanical behaviour of each individual component of the asphalt mixture. Three mixture components were modelled: the aggregate, the fine aggregate asphalt matrix (FAM), and the air voids. The primary objective of developing this model was to quantify and enable the visualization of the effect of air voids and the aggregate modulus on the FAM phase, which is the domain in which fatigue cracking initiates and propagates. The results demonstrate that air void distribution and the aggregate modulus have a strong impact on local stress concentrations that occur in the FAM domain. The developed 3D microstructural model has notable potential to enhance HMA design methods.
Experimental and Analytical Investigation of the Cavity Expansion Method for Mechanical Characterization of Soft Materials
(University of Waterloo, 2016-03-17) Nafo, Wanis; Al-Mayah, Adil
In biomedical engineering, the mechanical properties of biological tissues are commonly determined by using conventional methods such as tensile stretching, confined and unconfined compression, indentation and elastography. With the exception of elastography, most techniques are implemented on ex-vivo soft tissue samples. This study evaluated a newly developed technique that has the potential to measure the mechanical properties of soft tissues in their in-vivo condition. This technique is based on the mechanics of internal spherical cavity expansion inside soft materials. Experimental, mathematical and numerical investigations were conducted. Experimentally, the pressure-cavity volume relationship was measured using two types of polyvinyl alcohol (PVA) hydrogels of different stiffnesses, namely Sample1 and Sample 2. In addition, unconfined compression tests were conducted to measure the stress-strain relationship of the two gels. Based on the cavity expansion test results, the measured pressure-volume data was translated into the stress-strain relationship using a mathematical model. The stiffness of the two gels was then compared to that determined by the unconfined compression technique. The resulting stiffness of the two techniques was then compared at overlapping range of strains, with the average percentage of difference being 8.46% for Sample1 and 5.36% for Sample 2. A numerical model was developed to investigate the analytical solution of the new technique. This investigation was based on verifying the displacement predicted by the analytical solution. The promising outcome of the technique encouraged extending this study to include bovine liver tissues. A tissue sample was extracted from a bovine liver and subjected to tensile loading to evaluate its stiffness. The result was a stiffness of 76.92 kPa. A second sample of the same bovine liver was evaluated using the spherical expansion technique which resulted in a stiffness of 87.94 kPa.
The Fatigue Behaviour of Tension Lap Spliced Reinforced Concrete Beams Strengthened with Fibre Reinforced Polymer Wrapping
(University of Waterloo, 2016-10-25) Alyousef, Rayed; Topper, Tim; Al-Mayah, Adil; Soudki, Khaled
Many reinforced concrete structures containing lap splices were constructed before modern bond and fatigue design codes came into existence and are subjected to fatigue loading, which may lead to a bond failure even when the applied load is far below the ultimate load for a bond failure under a monotonic loading. Fatigue loads result in a deterioration of the bond interaction between the steel and concrete and interrupt the force transfer mechanism resulting in an increased deflection, an increased number of cracks and their widths, and a decreased load carrying capacity of reinforced concrete elements of structures. Some of these structures require strengthening to enhance their bond strength at lap splices. This study was aimed at increasing our understanding of the behaviour of the bond between the steel bar and the concrete along the lap splice region for structures subjected to cyclic loading. An additional aim of the study was to investigate the effect of fatigue loading on the bond between concrete and steel, and the ability of the new high and low modulus fiber-reinforced polymer (FRP) sheets to enhance the fatigue performance of a tension lap splice. Fifty three beams were cast and tested under monotonic and fatigue loading. The beams dimensions were 2200 mm in length, 350 mm in height and 250 mm in width. Each beam was reinforced with two 20M bars lap spliced in the constant moment region of the tension zone and two 10M bars in the compression zone outside the constant moment region. The test variables were the concrete cover, the presence or absence of FRP wrapping, the type of the FRP wrapping glass or carbon fiber-reinforced polymer (GFRP or CFRP), the type of loading and the fatigue load range. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to obtain fatigue lives between 1,000 and 1,000,000 cycles. The test frequency for all cyclic tests was 1.3 Hz. The results of the tests under monotonic load showed that the GFRP wrapped beams had an increase in bond strength of approximately 25% compared to the unwrapped beams for each of the concrete covers. However, the CFRP wrapped beams had a percentage increase in bond strength that decreased as the concrete cover increased. The CFRP wrapped beams had increases in bond strength of 71%, 60% and 44% compared to the unwrapped beams for concrete covers of 20 mm, 30 mm and 50 mm, respectively. The results of the tests under fatigue load showed that all beams failed by a bond failure except for those beams that exceeded the fatigue life limits for a longitudinal bar. As expected, these beams failed by fatigue rupture of the longitudinal steel bars. The GFRP and CFRP sheets increased the fatigue strength (measured as the applied load range for a given fatigue life) of the wrapped beams for all concrete covers compared to that of the unwrapped beams. The longitudinal splitting cracks for the FRP wrapped beams were finer in width and larger in number compared to those cracks for the unwrapped beams. A crack growth model was developed to calculate the fatigue life of the bond specimens and to calculate the slip and the deflection due to stress changes in the steel and concrete due to cracking, and compare it to the measured slip and deflection. There is also a good agreement between the calculated number of cycles with the actual fatigue data for all different wrapping conditions and all different concrete cover thicknesses. Also, only a small amount of the inelastic slip and the inelastic deflection are due to the stress changes in the steel and concrete due to splitting cracking. The remaining inelastic slip and inelastic deflection which are due to deformation of the concrete in front of the steel rebar lugs is much larger.
Finite Element Modelling of RC Beams Strengthened with Prestressed NSM CFRP Plate
(University of Waterloo, 2021-04-30) Alfaidi, Hamed; Al-Mayah, Adil
Near Surface mounted (NSM) carbon fibre reinforced polymer (CFRP) reinforcement has become a promising flexural strengthening technique for reinforced concrete (RC) elements. The prestressing of a CFRP plate can be used to provide RC members with further enhancements in the flexural capacity. The aim of this study was to introduce a three-dimensional nonlinear finite element analysis (FEA) of RC beam strengthened by prestressed CFRP plate. Although there is a wide range of commercial programs for three-dimensional nonlinear FEA, they have different capabilities to model complex behaviour of composite materials such as RC beams strengthened with prestressed CFRP plate and the contact interaction. Therefore, the ABAQUS finite element package was used in this study due to its known accuracy to model the behaviour of a variety of materials such as concrete and its powerful contact algorithms. Concrete material was modelled using concrete damage plasticity (CDP) constitutive model, and steel reinforcements were modelled as elastic-perfectly plastic material. The CFRP plate was modelled as perfectly elastic material that fails at maximum tensile strain. Perfect bond was assumed between concrete and steel reinforcement, and a contact model was used to represent the behaviour between concrete and the CFRP plate. The results of the FEA were validated against experiment results reported in the literature. The results were compared in terms of the load-deflection behaviour, crack patterns, and mode of failure (rupture or debonding of CFRP plate). Based on the validation, the proposed FEA model was capable of capturing the behaviour of RC beams strengthened with prestressed CFRP plate. A parametric study was conducted to investigate the effect of prestressing levels, steel grades, and thickness, width, and length of the CFRP plate. It was observed that increasing prestressing of the CFRP plate improved the strength of the RC beam especially for the ultimate load. However, as the prestressing increased, the mode of failure changed to the rupture of the CFRP plate which limited further increase of the ultimate load. Using a higher steel grade improved the load carrying capacity. Increasing the width of the CFRP plate improved the load carrying capacity by delaying the debonding at the CFRP-concrete interface. Increasing CFRP plate thickness further improved the load carrying capacity of the beam. Increasing the length of the CFRP plate developed the general load carrying capacity; however, it was found that covering 25% of the shear span of RC beams provided sufficient and cost effective strengthening. The FE model offers a reasonable representation of the experimental results for load-deflection curve, failure modes and crack patterns.
Mechanical Characterization of Soft Materials Using Volume-Controlled Cavitation
(University of Waterloo, 2020-03-31) Nafo, Wanis; Al-Mayah, Adil
The mechanical properties of soft materials are used in a wide range of fields and applications including biomedical engineering, sports, and automobile industry, in addition to medical applications. Therefore, several methods have been used to measure these properties including tension, compression, and indentation. This study focuses on the application of multiaxial loading using cavitation mechanics to measure nonlinear mechanical properties of soft materials. It was found that applying controlled cavitation within the internal structure of soft materials provided enough information to characterize their mechanical behavior. This is done by inserting a needle-balloon tool inside the tested material while being attached to a system that allows for injections of an incompressible fluid (water) into the balloon. To establish this methodology as a robust characterization technique of the mechanics of soft materials, it was used in a four-stages investigation: developing an analytical framework to characterize the non-linear elastic behavior of rubber-like materials (elastomeric gels), measuring the hyperelastic properties of soft biological tissues (porcine liver), comparing the cavity expansion test with a conventional uniaxial tensile testing, and establishing an analytical framework to characterize the time-dependent behavior of viscoelastic materials. In the first stage, a solution that relates the applied radial loads and tangential deformation is introduced. This solution allows the calibration of hyperelastic strain energy functions (SEF), which were Yeoh, Arruda-Boyce and Ogden (used in all stages). Finite element simulations were used to validate the material parameters of the three hyperelastic models. Computed tomography (CT) imaging was used to validate the spherical configuration assumption of the inflated balloon inside the sample. The validation process considered the two types of stresses generated during the test, radial and hoop stresses. It was observed that the radial stresses were insignificant compared to the hoop stresses. In the second stage, a smaller balloon was used to test porcine liver tissues; however, the protocol of this stage was similar to the first stage. Few changes were introduced to the definition of the deformation term, as a result, the measured deformations in the cavity test coincided with the deformation levels reported in literature. In addition, the three hyperelastic models predicted initial shear moduli that agreed with their counterparts reported in literature using conventional testing techniques. To understand the similarities and differences between the cavity expansion test and conventional axial loading, the third stage addressed the comparison between the cavitation and uniaxial tension characterization. The comparison focused on the stress levels, range of strains as well as the initial shear moduli. It was found that the strain levels in the hydrogels were similar up to the failure point. In addition, the hoop stresses generated due to cavity loads were similar to the tensile stresses generated in uniaxial tension up to a strain level of 45%. Afterward, hoop stresses increased exponentially reaching a peak magnitude that was twice that observed in the uniaxial tension. Since the radial stresses were insignificant, the previous two observations provided an indication to the equi-biaxial nature of the cavity expansion test. The final stage of this study addressed the characterization of the viscoelastic properties of rubber-like materials. In this stage, linear viscoelastic theory was used. The cavitation rheology is used to measure the non-linear elastic response of the hydrogels at three different strain rates. The simple shear relaxation test was used to measure the viscous response of the hydrogels. While the elastic material parameters were calibrated using the same method used in previous stages, the viscous coefficients of the Prony series were determined using Abaqus’ calibration tool. Afterward, the elastic parameters and viscous coefficients were used to reproduce the experimental data numerically using FE simulations, and analytically using Matlab code. The agreement between experimental data, FE simulations and the analytical code showed that the cavity expansion test was capable of measuring the time-dependent response of rubber-like materials.

Browse

Browsing Civil and Environmental Engineering by Author "Al-Mayah, Adil"