An Experimental Investigation of Ultra-High-Performance Concrete Rectangular Columns

This study presents the development and evaluation of an Artificial Neural Network (ANN) model for predicting the shear strength of reinforced concrete (RC) beam–column joints subjected to seismic loading. A comprehensive experimental database was compiled from more than 120 RC beam–column joint test specimens reported in the literature and used to train, validate, and test the ANN within MATLAB’s Neural Network Toolbox environment. The model employed the Levenberg–Marquardt backpropagation algorithm, a single hidden layer with an optimized number of neurons, a hyperbolic tangent sigmoid transfer function in the hidden layer, and a linear activation function at the output layer. Input parameters included concrete grade, reinforcement ratio, axial load, and joint geometry, while the output corresponded to joint shear strength. The ANN achieved outstanding predictive performance, with a coefficient of determination (R²) exceeding 0.99 and minimal error metrics (MSE = 0.000105), outperforming multiple regression models and ten widely adopted international design codes. Sensitivity analysis further revealed that reinforcement ratio and axial load were the most influential predictors of joint shear capacity. In addition to numerical prediction, the ANN demonstrated strong generalization capability and robustness across different concrete grades (M25–M40) and design standards. The results highlight the superior adaptability of machine learning compared to conventional design approaches, offering an innovative, data-driven framework for seismic performance assessment. This research contributes to the advancement of performance-based design methodologies by integrating artificial intelligence into structural engineering, paving the way for more accurate, efficient, and reliable seismic safety evaluations of RC joints.

To assess the performance of femoral orthopedic implants, they are often attached to cadaveric femurs, and biomechanical testing is performed. To identify areas of high stress, stress shielding, and to facilitate implant redesign, these tests are often accompanied by finite element (FE) models of the bone/implant system. However, cadaveric bone suffers from wide specimen to specimen variability both in terms of bone geometry and mechanical properties, making it virtually impossible for experimental results to be reproduced. An alternative approach is to utilize synthetic femurs of standardized geometry, having material behavior approximating that of human bone, but with very small specimen to specimen variability. This approach allows for repeatable experimental results and a standard geometry for use in accompanying FE models. While the synthetic bones appear to be of appropriate geometry to simulate bone mechanical behavior, it has not, however, been established what bone quality they most resemble, i.e., osteoporotic or osteopenic versus healthy bone. Furthermore, it is also of interest to determine whether FE models of synthetic bones, with appropriate adjustments in input material properties or geometric size, could be used to simulate the mechanical behavior of a wider range of bone quality and size. To shed light on these questions, the axial and torsional stiffness of cadaveric femurs were compared to those measured on synthetic femurs. A FE model, previously validated by the authors to represent the geometry of a synthetic femur, was then used with a range of input material properties and change in geometric size, to establish whether cadaveric results could be simulated. Axial and torsional stiffnesses and rigidities were measured for 25 human cadaveric femurs (simulating poor bone stock) and three synthetic "third generation composite" femurs (3GCF) (simulating normal healthy bone stock) in the midstance orientation. The measured results were compared, under identical loading conditions, to those predicted by a previously validated three-dimensional finite element model of the 3GCF at a variety of Young's modulus values. A smaller FE model of the 3GCF was also created to examine the effects of a simple change in bone size. The 3GCF was found to be significantly stiffer (2.3 times in torsional loading, 1.7 times in axial loading) than the presently utilized cadaveric samples. Nevertheless, the FE model was able to successfully simulate both the behavior of the 3GCF, and a wide range of cadaveric bone data scatter by an appropriate adjustment of Young's modulus or geometric size. The synthetic femur had a significantly higher stiffness than the cadaveric bone samples. The finite element model provided a good estimate of upper and lower bounds for the axial and torsional stiffness of human femurs because it was effective at reproducing the geometric properties of a femur. Cadaveric bone experiments can be used to calibrate FE models' input material properties so that bones of varying quality can be simulated.

Finite element (FE) models of long bones are widely used to analyze implant designs. Experimental validation has been used to examine the accuracy of FE models of cadaveric femurs; however, although convergence tests have been carried out, no FE models of an intact and implanted human cadaveric tibia have been validated using a range of experimental loading conditions. The aim of the current study was to create FE models of a human cadaveric tibia, both intact and implanted with a unicompartmental knee replacement, and to validate the models against results obtained from a comprehensive set of experiments. Seventeen strain rosettes were attached to a human cadaveric tibia. Surface strains and displacements were measured under 17 loading conditions, which consisted of axial, torsional, and bending loads. The tibia was tested both before and after implantation of the knee replacement. FE models were created based on computed tomography (CT) scans of the cadaveric tibia. The models consisted of ten-node tetrahedral elements and used 600 material properties derived from the CT scans. The experiments were simulated on the models and the results compared to experimental results. Experimental strain measurements were highly repeatable and the measured stiffnesses compared well to published results. For the intact tibia under axial loading, the regression line through a plot of strains predicted by the FE model versus experimentally measured strains had a slope of 1.15, an intercept of 5.5 microstrain, and an R(2) value of 0.98. For the implanted tibia, the comparable regression line had a slope of 1.25, an intercept of 12.3 microstrain, and an R(2) value of 0.97. The root mean square errors were 6.0% and 8.8% for the intact and implanted models under axial loads, respectively. The model produced by the current study provides a tool for simulating mechanical test conditions on a human tibia. This has considerable value in reducing the costs of physical testing by pre-selecting the most appropriate test conditions or most favorable prosthetic designs for final mechanical testing. It can also be used to gain insight into the results of physical testing, by allowing the prediction of those variables difficult or impossible to measure directly.

To investigate the seismic performance of hollow reinforced concrete (RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges (JTG/T B02-01-2008). The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

Blast load and its effects on transportation infrastructure especially bridge structures have received considerable attention in recent years. The RC bridge columns are considered as the most critical structural members because their failure leads to collapse of the bridge. Although RC bridge columns are typical axial load-carrying components, the studies on blast-resistant capacity of RC bridge columns usually neglect the axial load effect since it is commonly assumed that neglecting the axial load leads to conservative predictions of column responses. This assumption is true when column failure is governed by flexural response since axial compressive load generates a prestress in column which compensates concrete tensile stress induced by bending response. When subjected to blast loads, column response however could be governed by shear response. In this case neglecting axial loading effect does not necessarily lead to conservative predictions of column responses. In this study, high-fidelity finite element (FE) models for both non-contact explosion and contact explosion were developed in LS-DYNA. The FE models were validated with field blast test data. Subsequently, intensive simulations of the RC bridge columns with and without axial load subjected to a wider range of blast loading scenarios, including far-field, near-field and contact explosion were conducted. The influence of axial load on the dynamic performance of RC bridge columns corresponding to different blast loading scenarios was discussed.

Numerical investigation on the seismic behaviour of GFRP-reinforced concrete rectangular columns

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

Pendulum impact tests were conducted on a reinforced concrete (RC) frame column and four RC free-standing columns. The effects of the axial compression ratio and reinforcement ratio on the impact resistance of the columns were compared using the dynamic time curves of framed and freestanding columns under impact. The test results show that for the same impact load, although the presence of axial loads can play a positive role (e.g., reducing the residual displacement), it may lead to more severe local damage. In addition, compared with free-standing columns, frame columns can be considered as a protective structure because of their greater lateral stiffness and stronger crashworthiness. The corresponding finite element models are developed, and the influence of the axial loads on the cross-section force responses under impact excitation was deeply explored. Axial loads can significantly affect the distribution of moment, shear force, and damage to the column.

Performance of axially loaded reinforced concrete rectangular columns strengthened with GFRP strips

: Stress analyses of lumbar vertebrae were performed by a three dimensional finite element method for the purposes of (i) evaluating simplified models of the vertebrae which are suitable as injury post processors, and (ii) gaining a better understanding of injury mechanisms. The finite element analyses were linear and elastic. Axial and moment loads were applied over the end plates to simulate G sub z impact and on the facets to simulate load transmission between the articular facets and the vertebral bodies. The finite element model predicts that the maximum stresses under axial load are perpendicular to the axis of the vertebral body, which are called axial stresses; this is consistent with the predominance of compressive and wedge fractures. However, the maximum stresses predicted by the finite element model are only about a third of those predicted by the simplified injury model. This discrepancy is due to the fact that a substantial portion of the total load is transmitted through the vertebral centrum which is neglected in the simplified model. Furthermore, the finite element model exhibits a rather complex pattern of deformation even under axial load, which cannot be incorporated easily in a simplified model. The stresses predicted by the finite element model for bending also differ substantially from those given by the simplified model for the same reasons. Good agreement between the finite element model and simplified model is only achieved for torsion loads.

Experimental and numerical study of T-shaped irregularly concrete-filled steel tube columns under combined axial loads and moments

The paper describes the development of a simple theoretical approach in estimating the capacity of short reinforced concrete (RC) columns under biaxial bending and axial load. The developed approach considers the nonlinear stress-strain relations of concrete and reinforcing steel and does not make the assumption about the limiting strain of extreme compression fiber of concrete. The solution is obtained using a nonlinearly constrained optimization algorithm. The approach was used to estimate the theoretical capacities of many tested RC columns found in the literature. A probabilistic analysis of the modeling errors was carried out using the ratios of the test-to-predicted results. The probabilistic analysis was extended to include two simplified theoretical methods: the reciprocal load method given by Bresler and the failure surface method given by Hsu.Key words: biaxial bending, modeling error, optimization, probability distribution.

Crashworthiness design for multi-cell circumferentially corrugated thin-walled tubes with sub-sections under multiple loading conditions

High strength reinforced concrete (HSRC) has been used more frequently in the construction of high rise buildings and other concrete structures in recent decades due to its advantages and excellent performance over normal strength and conventional reinforced concrete. Some of these advantages include: higher strength, better durability and allowance for provision of using less concrete and smaller section sizes. Although HSRC performs better than normal strength reinforced concrete (NSRC) at ambient temperatures, NSRC has been found to perform better than HSRC at elevated temperatures and fire conditions. Provision of adequate fire resistance for reinforced concrete (RC) structures is essential as fire represents an extreme loading and hazardous condition to which a structure might be exposed during its life span. The fire resistance of RC members is evaluated using a prescriptive approach which is irrational and conservative. Current codes of practice and construction in industry are moving towards performance based fire design method with computing software, which is a rationally based method with each structure designed to meets its own need. This method requires comprehensive knowledge and modelling of concrete and reinforcement material behaviour and their response at elevated temperatures. The fire resistance of HSRC members (columns and beams) in this study was evaluated using a three-dimensional Finite Element (FE) model created in ANSYS. The stress – strain behaviour of concrete proposed in this research was used in modelling the behaviour of concrete in ANSYS, while other concrete and steel material properties were accounted for by using models proposed by other researchers. The fire resistance of the HSRC members is evaluated using coupled field analysis (thermal – structural analysis) with performance based failure criteria provided in the code of practice. The accuracy of the FE model was verified by comparing the thermal response, structural response and predicted fire resistance with fire test results obtained. Using the validated FE model, parametric studies were conducted to investigate the influence of various parameters affecting the fire performance of HSRC members exposed to fire. From the parametric studies conducted, simplified calculation models were developed for evaluating the resistance of HSRC members (columns and beams) exposed to fire. These models were validated with results from ANSYS and a fire resistance test. The simple model accounts for major factors such as member size, load ratio and fire scenario, and therefore can be easily incorporated into structural design. The FE model and simple calculation model provide a rational approach for evaluating the fire resistance of HSRC (members) and predict a more accurate fire resistance than the prescriptive approach.

This study involves the development of three-dimensional nonlinear Finite Element (FE) models of strengthened Reinforced Concrete (RC) beams with different anchorage systems, obtained from experimental testing. The aim of this investigation was to simulate the flexural behavior of strengthened RC beam, and compare FE and experimental results using load deflection response plots, maximum attained loads, and corresponding deflections. Three FE models were developed, which include: a reference RC beam, beam externally bonded (EB) with Aluminum Alloy (AA) plate along the soffit of the beam, and another strengthened beam with an AA plate EB to the soffit of the beam and anchored at its ends using Carbon Fiber Reinforced Polymers (CFRP) U-wraps. The developed FE models integrated nonlinear material properties and fundamental constitutive laws. The results obtained from the FE models closely agreed with those obtained from the experiment. Therefore, successful FE modeling has proven to provide great insight on the flexural behavior strengthened RC specimens. The performance of AA plated beams would be used as a valid platform to study the effect of different variables.