Numerical Parametric Study Research Articles

A new robust equation for shear strength of GFRP-RC deep beams using hybrid experimental and synthetic data based-FE quasi-static analysis procedure

The main objective of this article is to propose a new, more robust, and comprehensive design equation for Glass-Fiber-Reinforced-Polymer (GFRP) reinforced concrete (RC) Deep Beams (DBs). The investigation is based on a numerical model using Quasi-Static Two-Dimensional FE simulation of GFRP-RC DBs. The numerical model is validated by calibrating four parameters (concrete dilatation angle ψ, concrete tensile strength fct, fracture energy Gf, mesh size) against data from ten full-scale experiments on GFRP-RC DBs available in the literature. Additionally, a numerical parametric study based on a full factorial design with 5 factors (and between 2 and 5 modalities) is conducted using the validated quasi-static FE model, which includes 360 large-scale GFRP-RC DBs. The impacts of primary design variables on the concrete contribution Vc to the shear capacity of GFRP-RC DBs are assessed. The effects of various geometrical and mechanical variables, such as cross-sectional dimensions (width b × height H), concrete compressive strength grade (fc), GFRP properties (modulus Ef, and strength ffu), GFRP reinforcement ratio (ρf), and shear span to depth ratios (a/df), are examined to understand the shear behavior of GFRP-RC DBs.The numerical simulations demonstrate that the proposed FE model accurately captures the behavior of GFRP-RC DBs. Building upon these findings, a new shear design equation is proposed for DBs, and its accuracy and robustness are compared with five established international design codes (ACI-440.1R-15, ISIS-Canada, CAN/CSA-S806-12, JSCE-1997, and BS-8110). The existing design codes significantly underestimate the concrete contribution to shear capacity, leading to uneconomical designs. In contrast, the new design equation provides a fair prediction of Vc, with a standard error of 7.734 % and 20.84 % compared to the FE and experimental datasets, respectively. This represents a substantial improvement over the existing design guides.

Gas permeability and emission in unsaturated vegetated landfill cover with biochar addition

Plant–biochar interaction has been recognized to affect the hydraulic properties of landfill cover soils, while its influence on landfill gas emission is rarely studied. This study investigated the coupled effects of biochar and vegetation on gas permeability and emission in unsaturated landfill cover through an integrated theoretical modelling and laboratory investigation. First, a gas permeability model was developed for vegetated coarse-grained soils with biochar addition. Then, a well-instrumented laboratory column test and two tests from the literature, considering bare, grass, biochar and grass + biochar conditions, were used for model validation. Finally, a numerical parametric study was conducted to investigate the influence of root growth and drought conditions on the gas emission rate. Results showed that the developed model can satisfactorily capture the gas permeability of unsaturated soils at various degrees of saturation. The lowest water retention capacity, the highest gas permeability and gas emission rate after 24 months of growth were observed in the grassed column. However, adding biochar in vegetated soils can maximize the water retention capacity and decrease the gas permeability, resulting in the lowest gas emission rate. The measured gas emission rates for the four cases meet the recommended value by the design guideline. The parametric study showed that the increased root depth from 0.2 m to 0.4 m improved the gas emission rate by 170% in the grass case but decreased by 97% in the grass + biochar case. Under the severe drought condition with soil suction around 500 kPa, the gas emission rate in the grassed case exceeded the design value by 18%, while those in the biochar cases were far below the allowable value. Therefore, peanut shell biochar should be considered to amend the grassed landfill cover using coarse-grained soils as it can significantly improve engineering performance in reducing gas emissions under extreme drought conditions.Graphical abstract

A parametric numerical study on the performance of polymer electrolyte membrane fuel cell with intermediate‐blocked interdigitated flow field designs

AbstractFlow field design is crucial for achieving higher performance in polymer electrolyte membrane fuel cells (PEMFCs). This study uses a two‐phase, multi‐component, and three‐dimensional model to simulate the performance of PEMFCs that use interdigitated flow field design with intermediate blocks on the cathode side. A detailed parametric study is presented to investigate the effects of various geometric and operational parameters. Of the parameters studied, inlet mass flow rate, relative humidity, and rib width had the greatest impact on cell performance. The results show that increasing the cathode stoichiometric ratio resulted in higher fuel cell performance for blocked interdigitated designs compared to parallel designs. In addition, using cathode channels with higher height values resulted in lower PEMFC performance for all flow fields. Higher values of rib/channel width ratio resulted in lower cell performance due to liquid water accumulation in the rib regions. However, at higher rib/channel width ratios, the positive effect of using interdigitated flow designs was more pronounced. Moreover, at a low relative humidity of RH = 25%, a 10.4% higher performance was obtained for the interdigitated type II compared to cases with RH = 100%, due to more effective over‐rib convection and higher water removal.

Patch Loading Design Recommendations for Titanium–Clad Bimetallic Steel Plate Girder

For steel structures service in corrosive environments, corrosion reduces the mechanical properties and effective thickness of the structural steel, which has a significant effect on the durability of steel structures. Titanium–clad bimetallic steel (TCBS), a bimetallic material composed of titanium alloy and carbon steel with excellent corrosion resistance has been suggested to solve the corrosion issue. The TCBS consisting of the TA1 titanium cladding and Q235 carbon steel substrate was introduced in the plate girder as the web to improve durability in this study. The stress–strain properties and failure performance of TCBS and Q235 carbon steel were discussed. Notably, the separation between the cladding and the substrate in the TCBS was observed during the necking stage in the tensile coupon test. Welding method between TCBS web and Q235 carbon steel flange was suggested for processing the plate girder, which was validated to be appropriate according to the experimental results. No crack in welding and TCBS web of plate girder was observed during the patch loading test. A numerical parametric study on the ultimate resistance of TCBS plate girder subjected to patch loading was conducted using the finite element software ABAQUS, in which three different key parameters were included. A comparison between the numerical and predicted results indicated that the design equations suggested in EN 1993–1–5 were too conservative to be directly used for predicting the ultimate resistance of the TCBS plate girder under patch loading, which was caused by the strain–hardening effect and yield plateau of the structural steel. The current design equations were modified to effectively predict the resistance properties of TCBS plate girders.

Experimental and Numerical Study on Lateral Resistance of Micropile in Sand

Micropile has been increasingly used not only as a reinforcing material for foundations but also as the foundations themselves. Due to the high slenderness ratio (length/diameter (L/D)) of the micropile, the lateral resistance has frequently been neglected or underestimated. However, field measurements in this study revealed that the lateral resistance of a micropile is considerable. In this study, the lateral behavior and lateral bearing capacity of a micropile were investigated by performing field tests, physical model tests, and numerical analysis. It was found that the lateral resistance of the micropile is highly dependent on the slenderness ratio and the installation condition such as inclination. Particularly, the battered micropile showed higher resistance than the vertical pile. The increase in the lateral support of the micropile was obtained when the micropile was inclined 45° in the direction of the load. Based on the numerical parametric study, a simple evaluation method to determine the lateral bearing capacity of a micropile is proposed.

A unified impact displacement prediction model for geometrically similar RC beams: from test specimen to prototype component

Drop hammer impact tests based on the reduced-scale model are the most commonly accepted technique to investigate the impact response of reinforced concrete (RC) beams. However, the scale of RC beam prototypes in actual engineering is much larger than that of test specimens in the laboratory. Whether the analytical results obtained from the small-scaled specimens can be fully extrapolated and evolved to large/full-scaled geometrically similar prototype components needs further discussion. Given a structural scale factor, this study applied numerical simulations on four series of geometrically similar RC beams under different impact energy combinations. The effects of structural scales and energy combinations on the beams' damage modes, midspan displacement response, and energy absorption were numerically investigated. The results indicate that there is a scaling effect on the impact displacement of geometrically similar RC beams, which is influenced by the energy combination. A dimensionless displacement analytical model was developed for single-scaled RC beams under drop weight impact using Buckingham's π-theorem, and it was validated by several drop weight impact results. Then, a unified impact displacement prediction model for geometrically similar RC beams was proposed by considering the coupling effect of structural scales and impact energy combinations. Moreover, the numerical parametric study results preliminarily evaluated the accuracy and safety of the present model. It's worth stating that the proposed model provides a reference for designing and verifying the prototype members.

Numerical Parametric Study on Hysteresis Performance of the Novel Dovetail Joint for Single-layer Grid Shells Subjected to Out-of-Plane Bending Moment

The joint's cyclic behaviour and energy-dissipation capacity are important in lattice shell structures' resisting wind and seismic load capacities. Based on the bending test and FE analysis of the novel steel dovetail joint in the previous study, a full-scaled FE model with six H-shaped beams was analysed using the Abaqus program to determine the boundary conditions for the FE models of hysteric analysis. In the cyclic analysis, 1/6 FE models of the novel steel dovetail joints (NDJGs) were established and analysed based on the boundary conditions of the full FE model in the bending analysis and Quasi-static analysis step. The loading protocol is defined, and the analysis is carried out considering different design parameters, including hub ring thickness, slot edge thickness, and teeth depth. The analysis results indicated that the hub ring thickness does not affect the cyclic bending capacity and stiffness of the novel steel dovetail joint; meanwhile, they increased gradually when the slot edge increased. At the same time, the bending capacity is negatively correlated with the teeth depth, where the bending capacity is reduced when the teeth depth increases. All skeleton curves for all joints of this study are compared, and their energy-dissipation capacities and ductility are calculated. Finally, the novel steel dovetail joint showed an excellent energy-dissipation capacity with high ductility performance under cyclic loads.

A comprehensive study on the effect of reinforcing methods on the flexural behaviour of Concrete-RUHTCC composite beams

A systematic investigation on the effect of various reinforcing methods on the flexural behaviour of concrete-reinforced ultra-high toughness cementitious composites (RUHTCC) composite beams was conducted in this study, combining four-point bending tests, analytical modelling and numerical simulations. Seven specimens with steel reinforcement bars, steel wire mesh, basalt fibre fabrics, were tested, and it was found that the bending capacity of the beam increased with all these reinforcements (up to 152% comparing to that without reinforcement in this study), and various failure modes were captured including cracking in concrete and UHTCC, interfacial shear failure and interfacial peeling. An analytical model including solutions for the ultimate flexural capacity and critical strengths corresponding to interfacial shear failure and interfacial peeling was derived based on the plane-section and good material bonding assumptions. In addition, finite element models were built and used for carrying out parametric studies once they were successfully validated against experimental tests. In the end, the analytical model was further modified referring to the results of numerical parametric studies by integrating the effects of all the possible failure modes in a single expression. Thus, the proposed analytical model can be implemented and used in the design of concrete-RUHTCC composite beams.

Steel Structures Research Update: Slotted-Hidden-Gap Connections and Intentional Eccentricity for Steel Brace Members

Research on alternatives for steel brace members and their connections is highlighted. These studies are a collaboration between Dr. Colin Rogers, Professor and Acting Chair at McGill University, and Dr. Robert Tremblay, Professor at Polytechnique Montreal. Research on braces with intentional eccentricity (BIEs) is motivated by improvements in seismic performance compared to concentrically loaded brace (CLB) members. A brief summary of the background, motivation, and research objectives is presented. Also provided are selected highlights of the experimental program and supplementary finite element study. The slotted-hidden-gap (SHG) connection may eliminate the need to reinforce HSS braces at knife-plate connections, but existing design guidance is limited. Through an extensive, integrated program of numerical parametric studies and physical tests, the research team developed SHG connection design and detailing guidelines.

On the variants of SVM method for the estimation of soil elastic modulus from TSD model: Numerical parametric study

The accurate estimation of the subgrade resilient modulus MR is a crucial element in designing durable and resilient pavements as it quantifies the soil’s bearing capacity to withstand traffic loads without excessive deformation or failure. Conventional methods and devices that are used to estimate MR, such as the Falling Weight Deflectometer (FWD) have several limitations due to operational and security constraints when measuring at the network level. To overcome these limitations, Traffic Speed Deflectometer (TSD) has been developed, which can continuously assess the pavement bearing capacity without requiring traffic control. However, processing the massive amounts of data generated by TSD requires specialized processing techniques such as Machine Learning (ML). Therefore, the primary objective of this paper is to develop an efficient and effective model that can accurately estimate MR by combining two techniques: (TSD + ML). The study uses numerical simulations of deflection velocity slope SV under TSD as the forward model. The research employs Support Vector Machine (SVM) algorithm for ML to classify and estimate MR modulus values from a synthetic and controlled dataset. SVM model exhibits robust performance in both classification and regression analysis, whereas, 95% of the discrepancies between estimated and tested values did not exceed ±15MPa. Advanced numerical validation, sensitivity analysis and parameter estimation methods were also conducted to optimize the model’s performance. Overall, the approach proposed in this paper has the potential to make a significant impact in the field of subgrade evaluation and can facilitate the development of better road infrastructure.

Axial-flexural strength of steel-concrete composite shear walls

A predictive equation is proposed for the axial-flexural strength of rectangular and flanged Composite Plate Shear Walls-Concrete Filled (C-PSW/CF), with and without endplates and boundary elements. The proposed equation is based on plastic stress distribution, adjusted by coefficients to account for influential design parameters. The adjustment coefficients are established by a regression analysis performed on the data developed using an extensive numerical parametric study. The continuum-based finite element model used for the simulations is first validated using the available test data. The effects of various design variables, including the aspect ratio, slenderness ratio, reinforcement ratio, axial load ratio, infill concrete compressive strength, and yielding strength of the steel faceplates on axial-moment are then numerically examined. Four cross-sections, including double skin plate, double skin plate with endplates, double skin plate with boundary elements, and double skin plate with flanges, are considered. The results are used to develop a new predictive equation to obtain the flexural strength of C-PSW/CFs in presence of axial loading. The proposed equation is finally validated using the experimental test data and its accuracy is evaluated by comparing it to available predictive equations and the method proposed by the 2016 AISC Seismic Provisions. The results show that the proposed design equation can well predict the flexural moment capacity of C-PSW/CFs with various cross-sections in presence of axial loading.

Numerical Study on the Bending Resistance of Lightweight Built-Up Steel-Concrete Composite Beams

This paper investigates the bending resistance of an innovative lightweight composite floor system, LWT-FLOOR. The system consists of built-up cold-formed steel elements that are spot-welded and connected to the concrete slab using demountable shear connectors. As the system under investigation is new, the existing standards do not provide guidelines for calculating its bending resistance. This paper gives an overview of different analytical approaches and a comparison of calculated results using bending capacities from the numerical parametric study. Within the numerical parametric study, the influence of the height of the steel beam, the type and degree of shear connection, the connection between the steel elements, and the thickness of the corrugated web used for the bending capacity are investigated. Numerical results for the full shear connections resulted in lower bending capacities than the analytically calculated plastic bending resistances. However, numerically obtained bending capacities for partial shear connections were found to exceed the calculated characteristic non-linear bending resistances and bending resistances for partial shear connections. The obtained results will comprise the basis for further experimental tests, which will support the search for an optimal analytical approach for the bending resistance of the proposed composite system.

Fire design of stainless steel columns with hollow circular and elliptical sections

One of the advantages of stainless steel is its better behaviour under elevated temperatures when compared to the conventional carbon steel, which can be important for structural applications where the fire action should be considered. The second generation of Part 1–2 of Eurocode 3 (prEN 1993-1-2:2021) proposes new calculation formulae resulting from studies on profiles with I-sections. However, it is still important to evaluate the accuracy and safety of the same formulae for columns with circular and elliptical hollow sections (CHS and EHS respectively), whose application in stainless steel structures is common. Hence, this work presents a numerical parametric study on the fire resistance of columns subjected to axial compression, with CHS and EHS, considering different stainless steel grades, cross-sections and member slendernesses, and elevated temperatures. The ultimate load capacities of the columns are obtained by geometrically and materially nonlinear analyses including imperfections, using the SAFIR finite element program and considering the constitutive law based on the two-phase Ramberg-Osgood formulation proposed in prEN 1993-1-2:2021. Based on the comparisons between the numerical results and the methodology of prEN 1993-1-2:2021, small suggestions are proposed to improve the fire design formulae for the cases of CHS and EHS profiles subjected to axial compression.

Antireflection and radiative cooling difunctional coating design for silicon solar cells.

Passive daytime radiative cooling (PDRC) as a zero-energy consumption cooling method has broad application potential. Common commercial crystalline silicon (c-Si) solar cell arrays suffer working efficiency loss due to the incident light loss and overheating. In this work, a radiative cooler with PDMS (polydimethylsiloxane) film and embedded SiO2 microparticles was proposed to use in silicon solar cells. Both anti-reflection and radiative cooling performance can be improved through numerical parametric study. For the best performing of PDMS/SiO2 radiative cooler, the thickness of PDMS layer, volume fraction and radius of the embedded SiO2 particles have been determined as 55 µm, 8% and 500 nm, respectively. 94% of emissivity in first atmospheric window band (8-13 µm) for radiative cooling and 93.4% of solar transmittance at the crystalline silicon absorption band (0.3-1.1 µm) were achieved. We estimated that the PDMS/SiO2 radiative cooler can lower the temperature of a bare c-Si solar cell by 9.5°C, which can avoid 4.28% of efficiency loss. More incident light can enter and be utilized by silicon layer to enhance the efficiency of the solar cells. The proposed difunctional radiative cooling coating may become guidance for next generation encapsulation of crystalline silicon solar cells.

Cold-formed high strength steel CHS-to-RHS T- and X-joints: Performance and design after fire exposures

The post-fire structural performance of cold-formed high strength steel (CFHSS) T- and X-joints with circular hollow section (CHS) braces and square and rectangular hollow section (SHS and RHS) chords is numerically investigated in this study. The tubular members had the nominal 0.2% proof stress of 900 MPa. The CHS-to-RHS T- and X-joints were subjected to compression loads through brace members. The nominal values of peak fire temperatures (ψ) were 300°C, 550°C, 750°C and 900°C. Tests carried out by the authors investigating the post-fire static response of cold-formed S900 steel grade CHS-to-RHS T- and X-joints were formed the basis of the numerical investigation carried out in this study. The test results reported by the authors were used to develop accurate finite element (FE) models. The validated FE models were used to perform extensive numerical parametric studies comprising 768 FE specimens. The validity ranges of critical geometric parameters were extended beyond current limits mentioned in international codes and guides. The residual strengths of test and FE specimens were compared with the nominal resistances predicted from design equations given in Eurocode 3 and Comité International pour le Développement et l’ Etude de la Construction Tubulaire (CIDECT) Design Guide 3 using the measured post-fire residual material properties. Generally, design rules given in Eurocode 3 and CIDECT are shown to be quite conservative with very dispersed and unreliable predictions. As a result, accurate and reliable design rules are proposed in this study.

Numerical simulation and parametric study of pile groups under lateral loads

Numerical simulation and parametric study of pile groups under lateral loads

Simulation and cross-section resistance of stainless steel SHS and RHS at elevated temperatures

This paper investigates the structural response and design of stainless steel square and rectangular hollow sections (SHS and RHS) at elevated temperatures. Finite element models able to replicate the behaviour of stainless steel SHS and RHS members at elevated temperatures are developed and verified against the results from physical experiments, which are then used to perform extensive numerical parametric studies to generate a broad range of benchmark structural performance data on the behaviour of stainless steel SHS and RHS at elevated temperatures. In total, 13860 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel SHS and RHS with a wide range of cross-section properties and subjected to various loading conditions at different elevated temperature levels are considered. A cross-section design method for stainless steel SHS and RHS under different loading conditions at elevated temperatures is proposed, considering the recent design recommendations in [1] for the local buckling assessment of stainless steel plates at elevated temperatures which will be included in the upcoming version of the European structural steel fire design standard EN 1993-1-2. Relative to the current local buckling assessment rules of EN 1993-1-2, the higher accuracy, safety and reliability of the new proposals in the estimations of the ultimate cross-section resistances of stainless steel SHS and RHS at elevated temperatures are demonstrated.

CO2-TBAB semi-clathrate hydrate dissociation behaviour in individual capsules: A new two-stage numerical model and parametric study

Gas hydrates have a wide implementation in the capture, storage, transport and utilisation of a range of gases, in which the dissociation kinetics is of great importance to gas transport and recovery efficiency. Encapsulation has been proven an effective technique to enhance gas–liquid mass transfer and thus improve gas hydrate formation kinetics. However, the dissociation behaviour of gas hydrate in individual capsules remains unknown. In this work, the dissociation kinetics of encapsulated CO2-TBAB semi-clathrate hydrates in different shapes are experimentally investigated under various operating conditions, and, for the first time, a two-stage numerical model is developed which integrates mass transfer, heat transfer and the intrinsic gas hydrate reaction kinetics to simulate the gas hydrate dissociation process. The effects of temperature, pressure, capsule volume and capsule geometry on gas hydrate dissociation kinetics are investigated. The results reveal that the proposed model is capable of capturing two distinct experimentally-observed dissociation stages, a rapid and subsequently slow stage according to the measured dissociation rate. Surface-to-volume ratio of the capsule and the dissociation driving force are the two main factors influencing the dissociation kinetics. The ring-shaped capsule exhibits the most efficient dissociation process due to its high surface-to-volume ratio and long transition time to the slow dissociation stage. This work enhances the understanding of gas hydrate dissociation behaviour in individual capsules and guides the manipulation of dissociation for efficient hydrate-based gas transport and recovery.

Backbone curve variations on steel building seismic response

A 4-story steel moment-frame building designed according to ASCE 7 was used in a numerical parameter study to assess the effects of modeling features on peak drift demands. Features studied included strength, stiffness, ductility, and degradation along with several hysteretic models. Attention was given to ASCE 41-type backbone curves. Of particular interest was exploring the effects of degradation, in which an adaptive backbone curve was used to capture both in-cycle and cyclic degradations. Incremental dynamic analyses (IDAs) were performed using a suite of earthquake records to assess the response over a range of shaking intensities. It was found that in-cycle degradation had more influence on the response compared to cyclic degradation for the set of ground motion records that were employed. Moreover, use of the monotonic backbone alone, with its in-cycle degradation, was sufficient. In addition, it was found that increasing strength, stiffness, and/or ductility resulted in decreased peak drift demands, whereas modifying the hysteretic type (elasto-plastic, stiffness-degrading, and pinching) had little effect on peak drifts. These findings indicate that using backbone curves based on envelopes of first-cycle test data, as done in ASCE 41, can result in overly conservative seismic response predictions.

A numerical parametric study of the effectiveness of the 4-sided impact roller

Rolling dynamic compaction (RDC) is a specific type of dynamic compaction, which involves towing a heavy non-circular module at a relatively constant speed. This paper investigates the effects of module mass, operating speed and varying ground conditions on the effectiveness of the 4-sided impact roller using a developed finite element method (FEM)-discrete element method (DEM) model. Numerical results were analysed from four aspects, namely the energy imparted to the ground, soil velocity vectors, module imprint lengths and soil displacements at different depths. It is found that, a heavier module mass induces greater ground improvement in terms of both energy delivered to the soil per impact and the magnitude of soil displacements. The energy imparted to the underlying soil by the module increases with greater operating speed. The rotational dynamics of the module also change with increasing operating speed, whereby the impacts are delivered by the faces of the module at typical operating speeds; however, at faster speeds the impacts are delivered towards the corners of the module and the behaviour is less reproducible. The modelling showed that soil with a higher initial Young’s modulus and a higher internal angle of friction decreases the magnitude of soil displacements, which confirms that the impact roller is less able to significantly improve soils that are stiff or have a high initial shear strength.