Génie civil - Publications // Civil Engineering - Publications

Permanent URI for this collectionhttps://hdl.handle.net/10393/32831

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Impact evaluation of instream bar management using morphodynamic modelling
(2022-07-17) Yu, Qingcheng; Rennie, Colin; Slaney, Jonathan; Parsapour-Moghaddam, Parna
The Bow River’s 2013 flood was the costliest natural disaster in the City of Calgary’s history. Flood-induced bar growth and subsequent riparian vegetation colonization at many locations has constricted the river channel, which increases flood risk. Although bar removal has been widely employed as a flood mitigation strategy, its effectiveness and associated impacts are still uncertain. This study employs Delft3D to develop a two-dimensional (2D) morphodynamic model in order to evaluate the impacts of a conventional plan of bar removal and a novel plan of bar realignment in terms of flood mitigation, aquatic habitat protection and river recreation realization. A hydrodynamic model was firstly developed and calibrated using post-flood spatially distributed velocimetry data. A morphodynamic model was then developed and validated using post-flood bed elevation survey data. Then, the future channel response and flood peak levels using different bar management plans were modelled and compared. Results show that appropriate bar realignment can protect aquatic habitat and provide river recreation opportunities while bar removal performs the better in terms of lowering the future flood peak level. The findings indicate that manipulation on instream bars has little morphological impact to downstream reach and creating a less obstructed channel is the fundamental strategy in flood mitigation.
Reynolds flux modeling; new numerical insights into inclined dense jets
(2023) Tahmooresi, Sina; Mohammadian, Ablodmajid; Nistor, Ioan; Kheirkhah Gildeh, Hossein
This paper aims to provide a more detailed representation of the scalar flux modeling (SFM) approach for modeling turbulent inclined negatively buoyant jets. The SFM approach addresses the limitations of eddy viscosity models in terms of the mean concentration field and turbulent scalar flux within the context of Reynolds-averaged Navier–Stokes modeling. In this study, the contribution of the involved terms in the transport equation of the turbulent scalar flux vector was evaluated, and the geometrical and mixing parameters of concentration and velocity of 45 inclined negatively buoyant jets were verified. The SFM approach, along with the required modification for momentum flux modeling, was implemented in OpenFOAM v6. Results showed that the SFM approach can accurately predict mixing parameters due to the complex interactions between different turbulence contributors of the flow involved in the model. In comparison to simpler approaches, such as gradient-type models, that only correlate the gradient of the scalar field with turbulence, the SFM approach’s capability to predict mixing parameters is significantly higher.
Numerical Study on the Effect of Port Orientation on Multiple Inclined Dense Jets
(2022) Saeidi Hosseini, Seyed Ahmad Reza; Mohammadian, Abdolmajid; Roberts, Philip J. W.; Abessi, Ozeair
Wastewaters are commonly discharged into the seas and oceans through multiport diffusers. Accurate prediction of the complex interactions of multiport diffusers with the receiving water bodies is significant for the optimal design of outfall systems and has yet to be fully illuminated. In the current study, the mixing and dilution characteristics of multiple inclined dense jets are studied using a three-dimensional numerical simulation. The Launder, Reece, and Rodi (LRR) turbulence model is employed to perform the simulations, and the predictions are compared against available experimental data. The results indicate that the LRR turbulence model is a promising tool for the study of inclined dense jets discharged from multiport diffusers, and it can provide more accurate predictions of the mixing behavior than standard and re-normalization group (RNG) k-ε turbulence models. The model is further employed to evaluate and compare the dispersion capabilities of multiport diffusers with uniform and non-uniform jet orientation to the horizontal, as a novel idea. The comparisons demonstrate the middle discharge may have a longer trajectory (7% and 5% increase in terminal rise height and impact point distance, respectively) and therefore a higher dilution rate (14% increase in impact dilution) when its adjacent jets are disposed with a different angle, compared to that of uniform discharges. The outcomes may be favorable for outfall systems applications involving dilution.
Numerical Investigation of Tsunami Bore Effects on Structures, Part I: Drag Coefficients
(2019) Asadollahi, Nora; Nistor, Ioan; Mohammadian, Abdolmajid
Recent tsunami disasters caused devastating damage to non-engineered as well as engineered coastal infrastructure. In fact, previous design guidelines containing provisions for tsunami loading did not provide accurate estimations of tsunami loads in order to design structures capable of withstanding tsunami impacts. The drag coefficient plays a significant role in the calculation of tsunami hydrodynamic forces. This coefficient is traditionally calculated based on a steady flow analogy. However, tsunami-induced coastal inundation is a typical case of rapidly varying unsteady flows. The present study aims at investigating the tsunami forces exerted on structures with different geometries in order to provide realistic guidelines to estimate drag coefficients for unsteady flows. In this paper, a dam-break wave is used to investigate the tsunami-induced bore interaction with structures. A three-dimensional multiphase numerical model is implemented to study the tsunami loading on rectangular-shaped structures with various aspect ratios (width/depth) and orientations. The numerical model results are validated using measured forces and bore surface elevations from physical experiments previously carried out by some of the authors of this paper. A scaled-up domain is then modeled in order to assess the performance of the model and the induced tsunami loading at prototype scale. The drag coefficient relations for various structural geometries and bore depths are further provided. The calculated hydrodynamic forces and associated drag coefficients are compared with data in the existing literature and current design codes.
Numerical investigation of tsunami bore effects on structures, part II: effects of bed condition on loading onto circular structures
(2019) Asadollahi, Nora; Nistor, Ioan; Mohammadian, Abdolmajid
In this paper, a multiphase three-dimensional numerical reproduction of a large-scale laboratory experiment of tsunami-like bore interaction with a surface-piercing circular column is presented. The numerical simulation is conducted using OpenFOAM. A dam-break mechanism is implemented in order to generate tsunami-like bores. The numerical model is validated using the results of experiments performed at the Canadian Hydraulics Center of the National Research Council in Ottawa, Canada. Unsteady Reynolds-Averaged Navier–Stokes equations are used in order to treat the turbulence effects. The Shear Stress Transport k–ω turbulence model showed a high level of accuracy in replicating the bore–structure interactions. A scaled-up domain is used to investigate the influence of bed condition in terms of various downstream depths and roughnesses. Finally, a broad investigation on bore propagation characteristics is performed. The stream-wise forces exerted on the structural column as well as the bore velocity are compared and analyzed for smooth, rough, dry and wet beds with varying depths.
The Impact of Geostrophic Transport on the Temporal and Spatial Structure of Wind-Driven Coastal Upwelling/ Downwelling over the Persian Gulf
(2023) Eshghi, Nasrin; Mohammad Mahdizadeh, Mahdi; Mohammadian, Abdolmajid
Geostrophic transport can affect the structure of thewind-driven coastal upwelling/downwelling. Focusing on quantifying this impact is vital to understanding circulation dynamics in the Persian Gulf. To this end, in this study, after the investigation of wind patterns, the temporal and spatial structure of coastal upwelling/downwelling using the Ekman transport upwelling index, and the intra-annual vertical variability of temperature are investigated based on the daily wind, and monthly temperature data time series of 28 years (1993–2020). Then, the geostrophic transport using an improved methodology and the total cross-shore transport as a sum of Ekman and geostrophic transport are estimated based on the monthly SLA data time series. The results indicated that the region, located around 51.5 and 28 (48 and 29 and 50.5 and 25.5) experienced the most intense coastal upwelling (downwelling) at a peak in June with larger mixed and thermocline layers than other regions. The intensity of Ekman transport is higher than the geostrophic transport in the Persian Gulf due to the presence of the prevailing wind and the shallowness of the mixed layers’ depth. We found that the intensity of the coastal upwelling (downwelling) decreases (increases) under favorable spatial and temporal conditions by considering the geostrophic transport in the upwelling index.
The effect of Ekman and geostrophic surface current on the distribution of SST variability over the Persian Gulf
(2022) Eshghi, Nasrin; Mohammadian, Abdolmajid; Mohammad Mahdizadeh, Mahdi
Ekman and geostrophic surface currents are often associated with mesoscale eddy activity and upwelling jets, due to their effect on the variability of SST, in the Persian Gulf. Therefore, understanding the distribution of geostrophic and Ekman surface currents and how they are related to SST variability is a vital step for understanding circulation dynamics in the Persian Gulf. This study aims to quantify the importance of components of current on the distribution of SST variability over the Persian Gulf. To this end, intra-annual variability of Ekman, geostrophic and total currents, and SST have been investigated based on the daily time series of 21 years (2000–2020). As well, a correlation analysis was done on the components of current and SST, the results indicated that Ekman current has more intensity in the winter months than the summer months due to the Winter Shamal events, and the maximum value of this current component is seen in the center of the Persian Gulf in all months. In addition, the direction of the Ekman surface currents is toward the sea in the northern region of the Persian Gulf so the Ekman current gives rise to the formation of coastal upwelling currents. The maximum value of the geostrophic component is seen in the northwestern part of the Persian Gulf (near the mouths of rivers) as well as the easternmost region of the Persian Gulf (Strait of Hormuz) in all months due to the difference in surface density in these areas and geostrophic component plays an important role in the formation of the total and main current in this region. The maximum value of total current is seen in the northwestern Persian Gulf in June. A negative (positive) correlation between Ekman (geostrophic) current and SST is found over the Persian Gulf (in the northern coastal regions) and certain parts of the northern Persian Gulf (about 52.5° E–53.5°), which have the strongest relationship between the components of current and SST, implying that there is a possibility of the upwelling and mesoscale eddy creation at the same time.
Numerical modeling of dam-break flood flows for dry and wet sloped beds
(2022) Bigdeli, Mostafa; Taheri, Mercedeh; Mohammadian, Abdolmajid
Investigation of the effects of sloping dry and wet immobile beds on downstream dam-break flows is of great importance given the destructive power of these flows. Such investigation can lead to the adoption of appropriate measures and timely control strategies. In this study, numerical simulations of experimental wave propagation were carried out using four models, i.e., k-ω-SST-RANS, realizable k-ε-RANS, Smagorinsky-LES, and k-ω-SST-DES on sloped beds, for the first time as its novelty, with respect to upstream water and different downstream tail-water depths. The k-ω-SST-DES exhibited the best performance in the simulation of wave peak patterns and mean velocities. Taylor diagrams showed that all models were similar in estimating the highest R values and lowest centered root-mean-square errors for dry beds. However, for wet beds with higher downstream tail-water depths, the CRMSE were higher. For lower depths, the standard deviations of the models were generally closer to those of the flume experimental measurements conducted by Liu et al. (2020). The present study has shed light on the levels of turbulence models’ accuracy in simulation of dam-break flows on dry and wet sloping beds, and can be taken as a basis for further understanding of the flood flow behavior in future studies.
Stationary complementary energy high-order theory for the static analysis of beams
(2019) Pham, Phe Van; Mohareb, Magdi; Fam, Amir
A high-order theory is developed for the analysis of beams with general mono-symmetric cross-sections. The theory represents the nonlinear distribution of the longitudinal normal stress across the section depth by a polynomial series expansion up to any order as specified by the analyst. The corresponding shear and transverse normal stresses are obtained by satisfying the 2D infinitesimal stress-flow equilibrium conditions. The resulting statically admissible stress fields are then used in conjunction with the principle of stationary complementary strain energy to formulate the governing compatibility equations and boundary conditions. Closed form solutions are then developed for general loading and boundary conditions. Comparisons with the theory of elasticity and 3D finite element analysis predictions showcase the ability of the present theory to naturally capture shear deformation effects, transverse normal stress effects, nonlinear longitudinal normal stress distributions in deep beams, as well as the effect of support height. Unlike conventional beam solutions that are based on postulated kinematic assumptions, which tend to converge to the displacement response from below, the present theory avoids introducing any kinematic assumptions and is shown to converge to the solution from above. The theory is applicable to beams with doubly symmetric or mono-symmetric cross-sections, with isotropic or orthotropic materials, and subjected to general loading and boundary conditions. The theory is shown to offer advantages compared to other theories when modelling deep beams and/or beams with supports that are offset from the centroidal axis.
Sway Model for the Lateral Torsional Buckling Analysis of Wooden Twin-beam-deck Systems
(2019) Du, Yang; Mohareb, Magdi; Doudak, Ghasan
The present study develops a finite element model for the lateral torsional buckling analysis of wooden twin beams braced by deck boards subjected to gravity or wind uplift loading. The restraining action of the deck boards is modelled as continuous partial lateral and twist restraints provided at the top of both beams that capture the interaction between both beams. A parametric study is then conducted to examine the effects of beam and deck spans, load type, load height, lateral restraint height and stiffness and number of beam spans on the overall buckling capacity. The results indicate that the restraining effects of deck boards significantly improve the lateral torsional buckling capacity of twin-beam-deck assemblies.
Generalized theory for the dynamic analysis of thin shells with application to circular cylindrical geometries
(2019) Salahifar, Raydin; Mohareb, Magdi
A generalized theory is formulated for the analysis of thin shells of general curvatures based on the variational form of the Hamiltonian functional in conjunction with tensor calculus. Simplifying approximations and subtle inconsistencies made at the early stages of common classical formulations are avoided herein, and hence, the present treatment leads to field equations and boundary conditions that are accurate and consistent. The theory is then specialized to circular cylindrical shells. The well -known field equations of Flugge and Donnell-Mushtari-Vlasov (DMV) theories are recovered as consistent approximations from the present theory. Closed form solutions are then developed for the present and past cylindrical shell theories by Flugge, Timoshenko, and DMV. A comparative study is conducted to assess and quantify the effects of approximations made in classical theories on the predicted displacements and stresses.
Lateral torsional buckling analysis of moment resisting plane frames
(2019) Sahraei, Arash; Mohareb, Magdi
A finite element formulation is developed to predict the lateral torsional buckling resistance of plane frames with moment connections. The solution focuses on the simple characterization the elastic warping behavior of moment connections in a manner that allows them to interface seamlessly with existing beam buckling finite elements, thus providing means for realistically modelling the lateral torsional buckling of plane frames. Special attention is devoted to the joint rotation effects. The technique successfully captures the interaction between beams and columns of frames, an effect that is neglected in present design methodologies based on individual member checks. The solution is shown to provide lateral torsional buckling resistance predictions in very good agreement with shell based finite element solutions at a fraction of the modelling and computational effort. For typical frames that are laterally supported at the joints, the study suggests that present design methodologies that isolate the member from the rest of the structure provide conservative buckling resistance predictions. Conversely, for frames with no lateral restraints at some of the joints, the present solution predicts lateral torsional buckling resistances that are significantly different from those based on design standard equations, suggesting the need to account for interaction effects in such situations.
Lateral Torsional Buckling of Wooden Beams with Mid-span Lateral Bracing offset from Section Mid-height
(2017) Hu, Ye; Mohareb, Magdi; Doudak, Ghasan
An energy-based solution is developed for the lateral torsional buckling analysis of wooden beams with a mid-span lateral brace subjected to uniformly distributed loads or mid-span point load. The predicted critical moments and mode shapes are shown to agree with results based on three- dimensional finite element analysis. The study indicates that such beams are prone to two buckling patterns: a symmetric mode and an anti-symmetric mode. Whether the symmetric or the anti-symmetric mode governs the critical moment capacity is shown to depend on the bracing height. A technique is then developed to determine the threshold bracing height required to maximize the critical moment. A parametric study is then conducted to investigate the effect of lateral bracing and load height effects on the critical moments. Simple design equations are developed to predict critical moments for a practical range of cases. The limitations of the simplified procedure are discussed. For cases outside the scope of the simplified procedure, designers are recommended to adopt the more detailed energy-based solution. Design examples are provided to illustrate the merits and applicability of the proposed procedure in practical situations.
Distortional Lateral torsional buckling analysis of beams with overhangs
(2019) Pezeshky, Payam; Sahraei, Arash; Mohareb, Magdi
The present study investigates the effect of web distortion on the lateral torsional buckling strength of Gerber systems. Towards this goal, a number of modifications are introduced into two finite element formulations for the distortional and non-distortional lateral torsional buckling analysis. The distortional formulation treats the web as a thin plate and the flanges as Gjelsvik members, and captures load height effects. The non-distortional formulation is based on the Vlasov beam kinematics and enables the enforcement of lateral restraints offset from the shear center while preserving the positive definiteness of the stiffness matrices. Both models are validated against shell finite element solutions and then utilized to develop moment gradient coefficients for Gerber beams, assess the web distortional effects, and quantify the influence of various lateral bracing scenarios, on the elastic lateral torsional buckling strength. Unlike rolled simply supported beams where web distortion is considered to be insignificant, the present study indicates that web distortion heavily influences the lateral torsional buckling strength of Gerber beams.
Effect of Eccentric Lateral Bracing Stiffness on Lateral Torsional Buckling Resistance of Wooden Beams
(2018) Hu, Ye; Mohareb, Magdi; Doudak, Ghasan
An energy based solution is developed for the lateral torsional buckling analysis of wooden beams with flexible mid-span lateral bracing offset from section mid-height and subjected to uniformly distributed or mid-span point load. The study shows that such beams are prone to two potential buckling modes; symmetric or anti-symmetric. The symmetric mode is shown to govern the capacity of the beam for low bracing stiffness while the anti-symmetric mode governs the capacity when the bracing stiffness exceeds a threshold value. Under the present formulation, the threshold bracing stiffness required to suppress the symmetric mode and maximize the critical moments is directly obtained by solving a special eigenvalue problem in the unknown bracing stiffness. The technique thus eliminates the need for trial and error in standard solutions. A parametric study is conducted to investigate the effect of bracing height, load height, and bracing stiffness on the critical moments. A large database of runs is generated and used to develop simple expressions for determining the threshold bracing stiffness required to maximize the elastic lateral torsional buckling resistance.
Elastic Analysis of Steel Beams Strengthened with GFRP Plates Including Preexisting Loading Effects
(2017) Pham, Phe Van; Mohareb, Magdi; Fam, Amir
The present study develops a theory for the elastic analysis of a pre-loaded wide flange steel beam, strengthened with two Glass Fiber Reinforced Polymer (GFRP) plates bonded to both flanges, then subjected to additional loads. Starting with the principle of stationary potential energy, the governing equilibrium equations and corresponding boundary conditions are formulated prior to and after GFRP strengthening. The resulting theory involves four coupled equilibrium equations and 10 boundary conditions. A general closed form solution is then provided for general loading and boundary conditions. Detailed comparisons with three-dimensional finite element solutions show that the theory provides reliable predictions for the displacements and stresses. A parametric study is then developed to quantify the effects of strengthening, GFRP plate thicknesses, and pre-existing loads, on the capacity of the strengthened beam.
Lateral torsional buckling of STEEL beams strengthened with GFRP plate
(2018) Pham, Phe Van; Mohareb, Magdi; Fam, Amir
The present study investigates the lateral-torsional buckling of wide flange steel members strengthened by a Glass Fiber Reinforced Polymer (GFRP) plate bonded to one of the flanges through an adhesive layer. A variational formulation and two finite elements are developed for the problem. The formulation captures global and local warping effects, shear deformation due to bending and twist, and partial interaction between the steel and GFRP provided by the flexible layer of adhesive. The destabilizing effects due to strong axis bending, axial force and load height effect are incorporated into the formulation. The first element involves two nodes and 16 buckling degrees of freedom (DOFs) while the second element involves three nodes and 14 DOFs. Comparisons of present model results against those based on 3D finite element analysis based on solid elements demonstrate the ability of the present models to accurately predict the buckling loads and mode shapes at a fraction of the modelling and computational efforts. Practical examples quantify the gain in elastic buckling strength achieved by GFRP strengthening, and characterize the moment gradient factors and load height effects. Elastic buckling interaction diagrams are developed for beam-columns and comparisons are provided to interaction diagrams of un-strengthened beams.
Nonsway Model for Lateral Torsional Buckling of Wooden Beams under Wind Uplift
(2016) Du, Yang; Mohareb, Magdi; Doudak, Ghasan
Simply supported wooden beams nailed to deck boards subjected to wind uplift forces are subjected to compressive stresses at their bottom fibers. Because the restraining action provided by decking is at the top fibers, it is unclear to what extent such restraints are effective in controlling lateral torsional buckling as a possible mode of failure under wind uplift. Present design standards do not have provisions for such cases. Thus, the present study aims to quantify the effect of restraints provided by the deck boards on the lateral torsional buckling capacity of twin-beam-deck systems under wind uplift. Toward this goal, a series of analytical and numerical models were formulated. All models capture the continuous rigid lateral restraint and partial twisting restraint provided by the deck boards. The effects of load type and load position were investigated. The bending stiffness of deck boards was observed to have a significant influence on the lateral torsional buckling capacity of twin-beam-deck systems.
Finite element formulation for the analysis of multilayered beams based on the principle of stationary complementary strain energy
(2018) Pham, Phe Van; Mohareb, Magdi; Fam, Amir
A family of finite elements for the analysis of orthotropic multilayered beams with mono-symmetric cross-sections is developed based on the principle of stationary complementary energy. The longitudinal normal stress field is postulated as polynomial and Heaviside step function series and substituted into the infinitesimal equilibrium conditions to develop expressions for the shear and transverse stress fields. The statically admissible stress fields thus derived are then adopted within the complementary energy variational principle framework to develop a family of finite elements. The distinguishing features of the solution are: (i) it captures the nonlinear distribution of the stress fields along the section depth and steep stress gradients typically occurring near bondline ends of multilayer beams, (ii) unlike conventional solutions based on the principle of stationary potential energy which predict jumps in the shear and peeling stresses at interfaces of adjacent layers, the present solution satisfies equilibrium in an exact infinitesimal sense at layer interfaces and thus ensures continuity of the stress fields across the interface, (iii) it naturally captures the effects of transverse shear and transverse normal stresses, and (iv) it consistently converges to the displacements from above, in contrast to conventional finite element solutions where convergence is typically from below. The versatility of the solution is then illustrated in applications involving wood beams and steel beams strengthened with GFRP plates and sandwich beams with soft cores.
Upper and lower bound solutions for lateral-torsional buckling of doubly symmetric members
(2016) Sahraei, Arash; Mohareb, Magdi
A family of three finite elements is developed for the lateral-torsional buckling analysis of thin-walled members with doubly symmetric cross-sections. The elements are based on a recently derived variational principle which incorporates shear deformation effects in conjunction with a special interpolation scheme ensuring C1 continuity. One of the elements is developed such that it consistently converges from above while another element is intended to consistently converge from below. The third element exhibits fast convergence characteristics compared to other shear deformable elements but cannot be guaranteed to provide either an upper or a lower bound solution. The formulation can incorporate any set of linear multi-point kinematic constraints. The validity of the solution is established through comparisons with other well-established numerical solutions. The elements are then used to solve practical problems involving simply supported beams, cantilevers and continuous beams under a variety of loading conditions including concentrated loads, linear bending moments and uniformly distributed loads. The effect of lateral and torsional restraints and the location of lateral restraint along the section height on lateral-torsional buckling capacity of beams are also examined through examples.

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