Detailed 3D Nonlinear Finite Element Research Articles

Numerical investigation on RC T-beams strengthened in the negative moment region using NSM FRP rods at various depth of embedment

The application of Near Surface Mounted (NSM) method to strengthen reinforced concrete (RC) members in flexure through the use of Fiber Reinforced Polymer (FRP) rods has become a subject of interest to designers and researchers over the past few years. This technique has been extensively applied, and there is still a need for more experiments, analytical, and numerical studies to determine the effects of their parameters on the flexural performance of RC members. Therefore, a detailed 3D nonlinear finite element (FE) numerical model was developed in this study to predict the load-carrying capacity and the response of RC T-beams strengthened in the negative moment region accurately through the use of NSM FRP rods at different depth of embedment which are placed under three-point bending loading. The model was, however, designed with due consideration for the nonlinear constitutive material properties of concrete, yielding of steel reinforcement, NSM rods, and cohesive behaviors to simulate the contact between two neighboring materials. Moreover, the findings of the numerical simulations were compared with those from the experiments by other investigators which involve two specimens strengthened with NSM FRP rods added to one unstrengthened control specimen. The results, however, showed that the mid-span deflection responses of the predicted FE were in line with the corresponding data from the experiment for all the flexural loading stages. This was followed by the use of the validated FE models to analyze the effect of several properties of the FRP materials to provide more information than the limited experimental data available. It was discovered that the FE model developed is appropriate to be applied practically and economically with more focus on the parametric studies based on design to precisely model and analyze flexural negative moment strengthening for the RC members through the use of NSM FRP rods.

Experimental and analytical investigation of geo-grid confined RC beams with glass fiber reinforced concrete

The application of geosynthetics in infrastructure is an innovative development in concrete with the usage of geo-grid. In the plastic hinge region of Reinforced Concrete (RC) beams the additional shear reinforcement was provided by using glass fibers. The present study is carried out for the RC beam specimens, in which the additional shear confinement was given by geo-grid of various sizes was studied. In RC beams, less labor work only needed for the confinement and with the usage of geo-grid and also for the confinement the usage of geo-grid will be an effective solution. The effect of geo-grid with the glass fiber reinforced concrete has also been investigated by experimental observations and non-linear finite element simulations. Detailed 3D non-linear finite element analyses with perfect bonding of RC beam confined with geo-grid in ANSYS was carried out. One conventional beam, one conventional beam with glass fiber and three beams with a different configuration of geo-grid and volume of glass fiber were casted. For studying load–deflection behaviour, the single point loading was carried out for the geo-grid specimens and conventional beam specimens under flexure. Depend upon the usage of glass fibers and geo-grid confinement in the beam specimens, the experimental test results show that there is an enhancement in the post-yield behaviour and strength. The flexure test on beam specimens reveals that the strength of the geo-grid and its size plays a vital role in improving the load-deformation behaviour as well as crack propagation. The load–displacement behaviour and damage predicted from finite element analysis almost agree with the experimental result. Hence geo-grid seem to be an alternative material which having great ductile behaviour for the strengthening of RC beam.

Experimental and numerical investigation on cyclic behaviour of RC beam column joints reinforced with geogrid material

This article investigates the effectiveness of geogrid material on upgrading the cyclic performance of nonductile exterior reinforced concrete (RC) beam-column joints by experimental observations and non-linear finite element simulations. Conventional RC beam-column joints without seismic detailing confined internally with geogrid material and compared these specimens with control RC beam-column joint specimens with and without seismic detailing. A detailed 3D non-linear finite element (FE) analyses of the RC beam-column joints internally confined with geogrid in ANSYS are carried out. All the beam-column specimens are subjected to reverse cyclic loading under controlled amplitudes to explore the cyclic performance on the parameters such as failure patterns; load–displacement envelope curve; ductility factor. The test results showed that internal geogrid confinement are effective for enhancing the load-carrying capacity and also ductility of the test specimens. The load–displacement behaviour and damage predicted from finite element analysis almost show the similar behaviour with the experimental result. Hence geogrid with conventional steel bar can be used as a hybrid reinforcement which having excellent ductile behaviour for increasing the seismic performance of RC beam-column joints.

Moment-rotation model for steel-timber composite connections with slab continuity steel rods

Detailed 3D nonlinear finite element (FE) analyses of steel-timber composite (STC) cruciform subassemblies including material, geometrical and contact nonlinearities are carried out. In the STC subassemblies, the steel beams are connected to the column flange by fin plates and/or double web-cleats and the continuity of the cross laminated timber (CLT) slabs across the column is preserved by mechanically anchored rods. The FE models are verified against experimental data and it is shown the adopted constitutive law of materials (i.e. steel and timber) and proposed modelling strategies accurately predict the failure mode, local (load-strain) and global (bending moment-rotation) response of the STC connections. Variables influencing the bending moment-rotation response of the STC connections are identified and considered in a parametric study and a mathematical model for the moment-rotation of the STC joints is developed by non-linear regression of the data obtained from the parametric study. The calibrated mathematical model is employed for blind prediction of the moment-rotation of the STC connections and the accuracy of the model compared to the detailed 3D nonlinear FE models is demonstrated by a few examples. Lastly, nonlinear FE analysis of a multi-storey STC frame with nominally pinned connections is carried out and it is shown that the continuity steel rods (anchored in the CLT slabs) reduce the mid-span deflection of the STC beams by approximately one-third.

Compressive performance of ECC-concrete encased high strength steel composite columns

The use of high strength steel (HSS) in the construction of concrete encased steel (CES) composite columns is often limited by the strain incompatibility issue between HSS and concrete at peak-load. This study proposes an alternative approach to confine the high strength concrete with Engineered Cementitious Composite (ECC) to improve its compatibility with high strength steel. The main purpose of this study is to experimentally evaluate the axial compressive performance of the proposed composite column cross-section configuration. Behaviours of fifteen short columns including twelve ECC-CES columns are investigated in terms of failure modes, load-deformation curves, ductility and energy absorption capacity. The test parameters included ECC and concrete strengths, ECC cover thickness, steel section shape and column section’s aspect ratio. It was found that ECC generally improved the failure behaviour of high strength steel CES columns and increased the deformation and energy absorption capacity. On average ECC-CES columns showed around 12% and 8% higher ductility and toughness than control concrete column, respectively. A detailed 3D nonlinear finite element model was developed and validated against experimental results. Applicability of current design codes to predict the ultimate strength of ECC-CES columns was also evaluated. Finally, a method to calculate the ECC-CES column’s capacity considering effective material stresses at peak-load was proposed.

Force and Deformation Demands of Bolts in Steel Bolted Bracket Moment Connections

The behavior of pretentioned bolts at bracket-to-column in steel bolted bracket moment connections was investigated through detailed 3D non-linear finite element analysis. Analysis results indicated the significant increase of axial force in the bolt was caused by prying action due to column flange local bending. Tension force in the bolt was noted up to 166% of the initial bolt pretension, which corresponded to 125% of the nominal strength of the bolt. In addition, local deformation at bolt threads resulted in high strain demand at nut-to-column flange, which is the potential hazard of bolt fracture. A subsequent parametric study demonstrated that the strain concentration in the bolt could be shifted away from the critical location to the unthreaded shank by simply adding a 25 mm thick gang washer on the back side of column flange. But the tensile force demand in the bolts could not be reduced with additional gang washer plates. Reducing initial bolt pretension (i.e., sung-tight condition) does not contribute to the reduction in bolt tension force demand as well.

Numerical study of steel sandwich plates with RPF and VR cores materials under free air blast loads

One of the most important design criteria in military tunnels and armoured doors is to resist the blast loads with minimum structural weight. This can be achieved by using steel sandwich panels. In this paper, the nonlinear behaviour of steel sandwich panels, with different core materials: (1) Hollow (no core material); (2) Rigid Polyurethane Foam (RPF); and (3) Vulcanized Rubber (VR) under free air blast loads, was investigated using detailed 3D nonlinear finite element models in Ansys Autodyn. The accuracy of the finite element model proposed was verified using available experimental test data of a similar steel sandwich panel tested. The results show the developed finite element model can be reliably used to simulate the nonlinear behaviour of the steel sandwich panels under free air blast loads. The verified finite element model was used to examine the different parameters of the steel sandwich panel with different core materials. The result shows that the sandwich panel with RPF core material is more efficient than the VR sandwich panel followed by the Hollow sandwich panels. The average maximum displacement of RPF sandwich panel under different ranges of TNT charge (1 kg to 10 kg at a standoff distance of 1 m) is 49% and 53% less than the VR and Hollow sandwich panels, respectively. Detailed empirical design equations were provided to quantify the maximum deformation of the steel sandwich panels with different core materials and core thickness under a different range of blast loads. The developed equations can be used as a guide for engineer to design steel sandwich panels with RPF and VR core material under a different range of free air blast loads.

Experimental and numerical investigations on the performance evaluation of shear deficient and GFRP strengthened reinforced concrete beams

The present study is focused on the experimental investigation and nonlinear finite element simulations of shear deficient and glass fibre reinforced plastic (GFRP) strengthened reinforced concrete beams. Three levels of shear deficiency are considered in the design. Two layers of GFRP fabric are used for strengthening in the shear zone. The behavior of control, shear deficient and GFRP strengthened beams under two-point monotonic loading is studied. Detailed 3D non-linear finite element analyses with perfect bonding as well as with cohesive zone modelling are carried out to simulate the behavior of shear deficient beams. The responses, in terms of load-deflection behavior, failure loads and crack patterns, obtained from numerical simulations are validated with that of the experimental investigations. The validated numerical models are then used for studying the efficacy and effectiveness of various strengthening schemes using epoxy impregnated GFRP fabric where the number of layers, orientation and distribution of fibres are considered as parameters.Based on the parametric studies, the schemes which provide optimum improvement in performance for strengthening of the shear deficient beams are identified. For all three classes of deficient beams, greatest improvement in strength is attained for 45° orientation in single ply, 45°–90° orientation in double ply and 90°–45°–90° orientation in triple ply strengthening schemes. In all GFRP strengthened beams, mode of failure changed from shear to flexural failure and showed great improvement in the ductile behavior.

Joint strength of gasketed bolted pipe flange joint under combined internal pressure plus axial load with different (industrial and ASME) bolt-up strategy

Gasketed bolted flange joints are used in process industry for connecting pressure vessels and pipes. Design procedures available in the literature mostly discuss structural strength, while sealing failure is still a big concern in industries. Similarly, limited work is found in the literature regarding performance of gasketed bolted joints under combined loading. A detailed 3D nonlinear finite element analysis is performed to study the strength and sealing of a gasketed bolted flanged pipe joint under different bolt-up strategy (Industrial and ASME) and under combined internal pressure and axial loading.

Nonlinear Finite Element Analysis for the Flexural Behavior of Concrete Beams Strengthened with NSM CFRP-PCPs Composite Bars

This paper presents the development of a detailed 3D nonlinear finite element (FE) numerical model that can accurately predict the load-carrying capacity and response of RC beams strengthened with NSM CFRP-PCPs composite bars subjected to four-point bending loading. The predicted FE mid-span deflection responses agreed very well with the corresponding measured experimental tested data at all stages of flexural loading.

A step towards the 3D component method for modelling beam‐to‐column joints

AbstractThis paper deals with the component method for the structural design of steel joints in the 3D modelling of loads. The essential features of the method are presented in terms of the local and global analysis model. There is a discussion about the location of the local joint model, the definition of generalized joint displacements and the generic nature of the method. The proposed method is verified for a beam‐to‐column joint. Verification is carried out by a detailed 3D non‐linear finite element analysis of a single joint. Other results in the literature are discussed briefly. One of the new components used in 3D modelling is introduced here. The proposed 3D component method seems to work rather well for moment resistances of joints in both ambient and fire conditions. Initial rotational stiffness needs to be studied more. Validation of the 3D component method is continuing with experiments on the end plate splice joints of rectangular tubular structures.

Service reliability of offshore wind turbines

A probabilistic formulation is proposed to assess the performance of the support structure of offshore wind turbines based on their probability and expected time of exceeding specified drift thresholds. To this end, novel probabilistic models are developed to predict the mean and standard deviation of the drift ratio response of wind turbine support structures operating under day-to-day loads as a function of the wind turbine geometry and material properties, and loading conditions. The proposed models are assessed using a database of virtual experiments generated using detailed three-dimensional (3D) nonlinear finite element (FE) models of a set of representative wind turbine configurations. The developed models are then used in a random vibration formulation to estimate the probability and expected time of exceeding specified drift thresholds. As an example, the probability and expected time of exceeding specified drift thresholds are estimated for a typical offshore wind turbine at different wind speeds. A comparison is made between the results obtained based on the proposed models, those obtained using simulators commonly used in practice and detailed 3D nonlinear FE analyses.

Nonlinear finite element modeling of RC beams strengthened with NSM FRP rods

The introduction of Near Surface Mounted (NSM) strengthening technique to retrofit reinforced concrete (RC) members in flexure using Carbon Fiber-Reinforced Polymer (CFRP) rods is becoming more attractive to both researchers and designers in recent years. Although NSM strengthening systems has been used extensively, still further experimental, analytical, and numerical research is warranted to understand the effect of the several strengthening parameters on the flexural performance of RC members. This paper presents the development of a detailed 3D nonlinear finite element (FE) numerical model that can accurately predict the load-carrying capacity and response of RC beams strengthened with NSM FRP rods subjected to four-point bending loading. The developed FE model considers the nonlinear constitutive material properties of concrete, yielding of steel reinforcement, cracking of the filler bonding materials, bond slip of the steel and NSM reinforcements with the adjacent concrete surfaces, and bond at the interface between the filling materials and concrete. The numerical FE simulations were compared with experimental measurement tested by other investigators comprising of seven specimen strengthened with NSM CFRP rods in addition to one un-strengthened control specimen. Overall, the predicted FE mid-span deflection responses agreed very well with the corresponding measured experimental tested data at all stages of flexural loading. Furthermore, the developed models were also capable of predicting the failure mode of the strengthened tested specimen such as NSM rod debonding (peeling off) and concrete cover separation. The validated FE models are then used to study the effect of different NSM material bar types and sizes to provide further information over the limited available experimental data. It is concluded that the developed FE model is suitable as a practical and economical tool especially in design-oriented parametric studies for accurate modeling and analysis of flexural strengthening of RC members with NSM reinforcement.

Modeling of nonlinear cyclic response of shear-deficient RC T-beams strengthened with side bonded CFRP fabric strips

The use of Carbon Fiber Reinforced Polymers (CFRP) to strengthen reinforced concrete beams under bending and shear has gained rapid growth in recent years. The performance of shear strengthened beams with externally bonded CFRP laminate or fabric strips is raising many concerns when the beam is loaded under cyclic loading. Such concerns warrant experimental, analytical and numerical investigation of such beams under cyclic loading. To date, limited investigations have been carried out to address this concern. This paper presents a numerical investigation by developing a nonlinear finite element (FE) model to study the response of a cantilever reinforced concrete T-beam strengthened in shear with side bonded CFRP fabric strips and subjected to cyclic loading. A detailed 3D nonlinear finite element model that takes into account the orthotropic nature of the polymer`s fibers is developed. In order to simulate the bond between the CFRP sheets and concrete, a layer having the material properties of the adhesive epoxy resin is introduced in the model as an interface between the CFRP sheets and concrete surface. Appropriate numerical modeling strategies were used and the response envelope and the load-displacement hysteresis loops of the FE model were compared with the experimental response at all stages of the cyclic loading. It is observed that the responses of the FE beam model are in good agreement with those of the experimental test. A parametric study was conducted using the validated FE model to investigate the effect of spacing between CFRP sheets, number of CFRP layers, and fiber orientation on the overall performance of the T-beam. It is concluded that successful FE modeling provides a practical and economical tool to investigate the behavior of such strengthened beams when subjected to cyclic loading.

Ductile crack growth and constraint in pipelines subject to combined loadings

An important failure mode of offshore pipelines is ductile fracture of the pipe wall triggered by a hypothetical welding defect. In this study, pipelines having an external part-through semi-circumferential crack of various sizes, subject to combined internal pressure and inelastic bending are considered. This is done to assess the response of pipelines during both their installation and operational conditions. Detailed 3D nonlinear finite element (FE) models of pipelines are developed. A row of elements ahead of the initial crack front are modeled using a voided plasticity material model, which enables simulation of crack growth and the subsequent fracture failure mode (denoted by the critical curvature, κ crit ). After discussing the typical response characteristics of such pipelines, the FE model is used to parametrically investigate the influence of varying pipe and crack dimensions, and also the internal pressure levels, on κ crit . In the second part of this paper, the crack tip constraint ahead of a growing crack in such pipes is evaluated and systematically compared to the crack tip constraint of both the traditionally used deeply cracked Single Edge Notch Bend (SENB) specimens and the constraint-matched Single Edge Notch Tensile (SENT) specimens. This is achieved by comparing the crack resistance curves ( R-curves) along with stress triaxiality and equivalent plastic strain fields evaluated ahead of a growing crack of the three systems. The results present grounds for justification of usage of SENT specimens in fracture assessment of such pipes as an alternative to the traditional overly conservative SENB specimens.