Experimental and numerical study on structural behavior of pre-twisted steel box-section beam-column

Evaluation of uncertainty in experimental active buckling control of a slender beam-column with disturbance forces using Weibull analysis

Local-global interaction buckling of square high strength concrete-filled double steel tubular slender beam-columns

This study investigates numerically utilizing nonlinear finite element (ANSYS software) and analytically the shear response of the Reinforced Concrete (RC) beams. Different beams are considered in the current study, such as RC, steel fibre reinforced concrete (SFRC) without web reinforcement, and RC externally reinforced in the shear zone with carbon fibre reinforced polymer (CFRP) sheets. Nonlinear finite element model (FEM) is designed to simulate the performance of the designed beams. The results of FEM are compared to experimental measurements and standard design codes (ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19). According to the experimental approach and nonlinear finite element, the enhancement in the load carrying capacity of SFRC beam due to CFRP strengthening decreases with a volume fraction of steel fibres of 2%. However, the effect of CFRP strengthening on the shear behaviour of RC beams was observed in increased load carrying and ultimate deflection capacities as a result of the CFRP strengthening. The results show that CFRP has a significant contribution to shear strength. At each load increment, the created model accurately reproduced the initial and progressive crack patterns. A comparison of nonlinear finite element and analytical models was conducted using the codes ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19. Numerically, the FEM results showed a high agreement with ACI 440.2R‐17 standard code, with correlation approach to 99%. The comparison experimental load capacity of beams to FEM and ACI 440.2R‐17 shows that the FEM can be significantly used to estimate the shear strength of beams in the X‐Y directions with simulating different scenarios of CFRP and SFRC characteristics. The discrepancy between the nonlinear FEA and the theoretical predictions from the ACI 440.2R‐17 code is less than 1%, from the FIB14 code is less than 2%, from the CNR‐DT200 code is less than 15%, and from the ACI 318‐19 code is less than 30%. The ultimate load capacity evaluated based on ACI 440.2R‐17 code provision shows a good agreement with the experimental data as compared to the others’ code provision. The results of the finite element analysis and analytical models were in good agreement with the experimental results. The most significant advantage of finite element analysis over experimental approaches was that it can aid in the investigation of different output results that cannot be measured experimentally, such as shear stress in the XY direction throughout the beam strengthened in shear with different CFRP properties and steel fibre reinforced concrete (SFRC).

Experimental study on concrete-filled L-shaped steel tubular columns and beam-columns

Behavior of biaxially-loaded rectangular concrete-filled steel tubular slender beam-columns with preload effects

PurposeThis paper aims to develop a non-linear finite element model predicting the response of externally strengthened beams under a three-point flexure test.Design/methodology/approachThe ANSYS software is used for modeling. SOILD65, LINK180, SHELL181 and SOLID185 elements are used, respectively, to model concrete, steel reinforcement, polymer and steel plate support. A parametric study was carried out. The effects of compressive strength, Young’s modulus, layers number and carbon fiber-reinforced polymer thickness on beam behavior are analyzed. A comparative study between the non-linear finite element and analytical models, including the ACI 440.2 R-08 model, and experimental data is also carried out.FindingsA comparative study of the non-linear finite element results with analytical models, including the ACI 440.2 R-08 model and experimental data for different parameters, shows that the strengthened beams possessed better resistance to cracks. In general, the finite element model’s results are in good agreement with the experimental test data.Practical implicationsThis model will predict the strengthened beams behavior and can describe the beams physical conditions, yielding the results that can be interpreted in the structural study context without using a laboratory testing.Originality/valueOn the basis of the results, a good match is found between the model results and experimental data at all stages of loading the tested samples. Crack models obtained in the non-linear finite element model in the beams are also presented. The submitted finite element model can be used to predict the behavior of the reinforced concrete beam. Also, the comparative study between an analytical model proposed by of current code of ACI 440.2 R-08 and finite element analysis is investigated.

The stainless-steel tube has been used to construct Concrete-Filled Steel Tubular (CFST) columns because it has a high resistance to fire and corrosion, good durability, and aesthetic appearance compared to the carbon steel tube. However, there is very little published research on eccentrically loaded circular Concrete-Filled Double-skin Steel Tubular (CFDST) slender beam-columns composed of an outer stainless-steel tube and an inner carbon-steel tube. In line with this, this paper presents a fiber-based simulation model for predicting the structural performance of CFDST slender columns with external circular stainless-steel tube under eccentric compression. The simulation modeling of load-deflection curves and load-moment interaction diagrams for slender CFDST beam-columns is developed and verified by the experimental results. The verified simulation model is then used to study the effects of geometric and material properties on structural performance. The range analysis is applied to the orthogonal design to identify the relative significance of the factors that influence the structural response. The orthogonal design covers CFDST beam-columns with a hollow ratio ranging from 0.1 to 0.8. The results indicate that the column slenderness ratio is the most significant factor, followed by the loading eccentricity ratio, the outer tube thickness, stainless steel proof stress, concrete strength, and carbon steel yield strength. The accuracy of the design method specified in Australian standard AS/NZS 2327, and the proposed design methods are evaluated. The proposed equation provides accurate strength predictions of CFDST slender columns where the external skin is made of stainless steel.

Robust finite element frameworks, which support and allow the users to implement state-of-the-art nonlinear finite element and material models are essential to analyze and design seismically resilient structures and for making better decisions (retrofitting or demolition) during seismic assessments of existing structures. OpenSEEs is an object-oriented software framework for developing applications to simulate the behavior of structures under seismic loading conditions. It supports a TCL-based interpreter for finite element modeling of structures to be analyzed (recently a Python-based interpreter has also been added to the source code). The commands written in TCL/Python automatically call the functions implemented in C++ and provide the required output. Majority of the material models and elements implemented in OpenSEEs do not have proper documentation (examples include hysteretic steel, fiber based nonlinear beam column element, quad element etc.). Hence, it is often difficult to understand and debug the existing implementations to overcome convergence errors encountered in nonlinear finite element analysis (NLFEA). In the present study, a simple yet elegant VC++ wrapper (vcppwrapper) has been developed to efficiently debug the convergence errors encountered in complex NLFEA problems. The nonlinear finite element model can be directly developed and debugged in the C++ language by using the developed wrapper. The advantages and disadvantages of the nonlinear finite element model of an RC panel tested under pure shear loading developed using the newly developed wrapper and the standard TCL-based interpreter has been demonstrated. Few new libraries have also been added to the OpenSEES source code in Visual Studio for various purposes such as data visualization, unit testing, and matrix operations. Their usefulness in the debugging process has also been presented.KeywordsSeismic resilienceOpenSEEsNonlinear finite element modelConvergence issuesDebuggingWrapper

Bayesian updating of complex nonlinear FE models with high-dimensional parameter space using heterogeneous measurements and a batch-recursive approach

This paper describes a novel framework that combines advanced mechanics-based nonlinear (hysteretic) finite element (FE) models and stochastic filtering techniques to estimate unknown time-invariant parameters of nonlinear inelastic material models used in the FE model. Using input-output data recorded during earthquake events, the proposed framework updates the nonlinear FE model of the structure. The updated FE model can be directly used for damage identification and further used for damage prognosis. To update the unknown time-invariant parameters of the FE model, two alternative stochastic filtering methods are used: the extended Kalman filter (EKF) and the unscented Kalman filter (UKF). A three-dimensional, 5-story, 2-by-1 bay reinforced concrete (RC) frame is used to verify the proposed framework. The RC frame is modeled using fiber-section displacement-based beam-column elements with distributed plasticity and is subjected to the ground motion recorded at the Sylmar station during the 1994 Northridge earthquake. The results indicate that the proposed framework accurately estimate the unknown material parameters of the nonlinear FE model. The UKF outperforms the EKF when the relative root-mean-square error of the recorded responses are compared. In addition, the results suggest that the convergence of the estimate of modeling parameters is smoother and faster when the UKF is utilized.

A 3D, nonlinear finite element (FE) model of the diastolic canine heart was constructed from multislice magnetic resonance images (MRI). The model was solved using the p-version of the FE method to predict stress and deformation in diastole. Finite element models were employed in an 'inverse' problem to estimate the nonlinear material properties of intact diastolic myocardium. Additionally, FE models were employed to examine the effects of RV pressure overload on LV pressure-volume (P- V) relationships in the pathologic heart. A 3D, nonlinear FE model had 1,704 degrees of freedom and 8 elements, it had a maximum principal stress value of 429,127 dynes/cm2 and a minimum principal stress of -344,599 dynes/cm2 at p equals 6. Average nonlinear material parameters estimated for 6 dogs were E equals 28,722 +/- 15,984 dynes/cm2 and c equals 0.00182 +/- 0.00232 cm2/dyne. Examination of the effects of RV pressure increase on LV P-V relationships indicated substantially different effects of RV pressure overload on the different pathologic conditions (p < 0.005 by ANOVA) with increasing RV pressure having a more pronounced effect on the dilated heart than the hypertrophied heart. When the mechanical effects of the pericardium were included in the model, at higher RV pressures, all of the pressure-volume (P-V) curves became similar indicating that at higher RV pressures, the P-V curves were independent of ventricular shape and material properties and depended only on the RV pressure. In conclusion, FE models of the heart were constructed from MRI images of the heart and were employed to study diastolic ventricular function in the normal and pathologic heart.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material nonlinearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections

Nonlinear voxel-based finite element model for strength assessment of healthy and metastatic proximal femurs

This paper presents a new framework for output-only nonlinear system and damage identification of civil structures. This framework is based on nonlinear finite element (FE) model updating in the time-domain, using only the sparsely measured structural response to unmeasured or partially measured earthquake excitation. The proposed framework provides a computationally feasible approach for structural health monitoring and damage identification of civil structures when accurate measurement of the input seismic excitations is challenging (e.g., buildings with significant foundation rocking and bridges with piers in deep water) or the measured seismic excitations are erroneous and/or distorted by significant measurement error (e.g., malfunctioning sensors). Grounded on Bayesian inference, the proposed framework estimates the unknown FE model parameters and the ground acceleration time histories simultaneously, using the sparse measured dynamic response of the structure. Two approaches are presented in this study to solve the joint structural system parameter and input identification problem: (a) a sequential maximum likelihood estimation approach, which reduces to a sequential nonlinear constrained optimization method, and (b) a sequential maximum a posteriori estimation approach, which reduces to a sequential iterative extended Kalman filtering method. Both approaches require the computation of FE response sensitivities with respect to the unknown FE model parameters and the values of base acceleration at each time step. The FE response sensitivities are computed efficiently using the direct differentiation method. The two proposed approaches are validated using the seismic response of a 5-story reinforced concrete building structure, numerically simulated using a state-of-the-art mechanics-based nonlinear structural FE modeling technique. The simulated absolute acceleration response time histories of 3 floors and the relative (to the base) roof displacement response time histories of the building to a bidirectional horizontal seismic excitation are polluted with artificial measurement noise. The noisy responses of the structure are then used to estimate the unknown FE model parameters characterizing the nonlinear material constitutive laws of the concrete and reinforcing steel and the (assumed) unknown time history of the ground acceleration in the longitudinal direction of the building. The same nonlinear FE model of the structure is used to simulate the structural response and to estimate the dynamic input and system parameters. Thus, modeling uncertainty is not considered in this paper. Although the validation study demonstrates the estimation accuracy of both approaches, the sequential maximum a posteriori estimation approach is shown to be significantly more efficient computationally than the sequential maximum likelihood estimation approach.

SummaryThis paper presents a novel nonlinear finite element (FE) model updating framework, in which advanced nonlinear structural FE modeling and analysis techniques are used jointly with the extended Kalman filter (EKF) to estimate time‐invariant parameters associated to the nonlinear material constitutive models used in the FE model of the structural system of interest. The EKF as a parameter estimation tool requires the computation of structural FE response sensitivities (total partial derivatives) with respect to the material parameters to be estimated. Employing the direct differentiation method, which is a well‐established procedure for FE response sensitivity analysis, facilitates the application of the EKF in the parameter estimation problem. To verify the proposed nonlinear FE model updating framework, two proof‐of‐concept examples are presented. For each example, the FE‐simulated response of a realistic prototype structure to a set of earthquake ground motions of varying intensity is polluted with artificial measurement noise and used as structural response measurement to estimate the assumed unknown material parameters using the proposed nonlinear FE model updating framework. The first example consists of a cantilever steel bridge column with three unknown material parameters, while a three‐story three‐bay moment resisting steel frame with six unknown material parameters is used as second example. Both examples demonstrate the excellent performance of the proposed parameter estimation framework even in the presence of high measurement noise. Copyright © 2015 John Wiley &amp; Sons, Ltd.