In the present work, experimental and numerical investigations were carried out to examine the flexural performance of reinforced concrete (RC) beams after undergoing different degrees of accelerated reinforcement corrosion and strengthened using ultra-high-performance fiber reinforced concrete (UHPFC) layers. The strengthened RC beams were tested under flexure to evaluate the effect of the UHPFC layers (with combinations of three UHPFC layer thicknesses for both options of one-sided and three-sided strengthening) on the failure mode, flexural strength, and stiffness. The flexural strength of the RC beams was significantly enhanced by increasing the thickness of the UHPFC layer. Three-sided strengthening resulted in a higher load-carrying capacity of the RC beams as compared to that of one-sided strengthening. Minimum layer thicknesses required to fully restore the load-carrying capacity of the corroded RC beams were found to be 20 mm and 40 mm for three-sided and one-sided strengthening, respectively. At ultimate load, the mid-span deflections for the strengthened beams were about half of that of the un-strengthened beams due to an increase in the stiffness of the strengthened beams. Finally, the experiment results matched the 3D-FEM predictions, indicating the simulation's accuracy in evaluating corroded-strengthened RC beam flexural performance.
Swelling soils are considered one of the most problematic soils due to their volume changes resulting from variations in the moisture regime. Such volume change tendencies in swelling soils have caused short- and long-term stability issues for civil engineering. The swelling-mechanical behavior is also central in the design of industrial/nuclear waste containment barriers, slope stability of the mudrocks, and gas shale extraction. Several valuable efforts have been undertaken to predict the mechanical behavior of swelling soils at the macro and molecular levels. Still, these models have some limitations due to the partial consideration of complex fabric and structure of natural and compacted swelling soils. Moreover, all macro-level constitutive models require a complete matrix of strength and volume change tests which restrict their application in engineering practice. This paper covers a review, including key features and limitations, of existing models for the mechanical behavior of swelling soils at the macro and molecular levels. Finally, a framework of a nano-level hydro-mechanical constitutive model has also been presented through molecular-level simulations of the structure of the swelling soils. The proposed model can be utilized to predict stiffness moduli for all possible variations in the fabric and structure of swelling soils.
This paper aims to analyze the wave propagation in functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams placed on a viscoelastic foundation utilizing an improved first-order shear deformation theory (FSDT). The material properties are derived from the mixture rule. Four carbon nanotube distribution patterns are considered in the analysis. The extended Hamilton’s Principle is utilized to derive the governing wave equations for the CNTRC beam. A comparison between the present theory results and those in the literature is conducted for validation. The wave dispersion investigation is mainly based on the phase and group velocities. The results illustrate the wave propagation responses for the different CNT configurations. In addition, the influence of the CNTs volume fraction, foundation stiffness parameters, and damping coefficient on the wave characteristics is examined.
Clay minerals in soils and rocks exhibit large volume change upon interaction with water and this behavior becomes even more complex when the strata are being stressed by the engineering and environmental loads. Therefore, a realistic prediction of the hydro-mechanical behavior of the clay-bearing strata is always a challenge due to their coupled swelling-mechanical response in the cases of geotechnical and geoenvironmental engineering problems, nuclear waste storage in clay-bearing rock repositories, shale gas extraction, and other uses of clay in the manufacturing industry. All the existing behavior models have restricted applications in the engineering and other fields of practice mainly due to the partial consideration of the structure and fabric of clay-bearing strata in the model formulation. In this study, a hydro-mechanical behavior model has been formulated using the parameters acquired from the molecular-level simulations and modeling of the volume change and stress-strain behavior of the clay-bearing structure. The Molecular Mechanics and Molecular Dynamic simulations were performed on the natural structure of the clay-bearing strata formulated using Monte Carlo technique. The mathematical model, developed from the simulation results, can predict the overall hydro-mechanical behavior of clay-bearing strata for all possible combinations of clay minerals, non-clay minerals, salts causing cementation of the soil/rock structure, confining pressures, and the induced strain levels. The developed model has successfully been validated through laboratory and field testing on the clay-bearing strata in both the elastic and elasto-plastic regions of the stress-strain behavior and also from the data of two (02) swelling clays (MX-80 and FEBEX Bentonite) from the existing literature, supporting the universal nature of the developed behavior model.
This paper presents the results of a study conducted to investigate the properties of alkali-activated concrete (AAC) mixtures prepared using the optimum combinations of four precursor materials (red mud, limestone powder, silicomanganese fume, and natural pozzolana) and four activation parameters (activator to precursor ratio, silica modulus, sodium hydroxide molarity, and water to precursor ratio). In order to examine the beneficial effects of inclusion of ordinary portland cement (OPC) and curing regimes on the properties of AAC, three dosages of OPC (in the range of 10% to 30% by weight) and two types of curing (steam and air curing) were considered. Tests were conducted on the mixtures of AAC to determine different properties that included the density, void ratio, water absorption, compressive and tensile strengths, modulus of elasticity, drying shrinkage, and loss of weight and strength after exposure to acid and sulfate salt solutions. Additionally, microstructural investigations (x-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy) were conducted on the alkali-activated binders to justify the trends of the experimental data pertaining to different properties of the AAC mixtures. The results of the tests indicated that the properties of AAC were significantly affected by inclusion of OPC and curing regimes. It was found that almost all properties of the AAC were significantly enhanced when the OPC dosage was increased from 10% to 20%. Further, the AAC mixtures having more than 10% OPC exhibited better properties as compared to the traditional OPC concrete mixture.
Composites are commonly used in engineering applications. One example is the polymer-cement composites, where the polymers are used to modify/reinforce the cement mortar and concrete. In this regard, the bottom-up understanding of such complex nano-composites can be achieved through atomistic simulation and modeling at the atomic level. This review discusses the progress of molecular simulation in investigating polymer-cement interactions. Thus, the polymer-cement composites, including polymer-modified cement mortar and polymer-cement interface, as well as other interactions, such as chemical admixtures and corrosion inhibitors, are covered. In addition, the mechanisms involved in the polymer-cement interactions are reviewed. The research challenges in this area are discussed, and the need for future research and development prospects is also presented. To date, no survey on the simulation studies of polymer-cement interactions has been conducted. Thus, this review provides comprehensive molecular-level modeling in this area and, hopefully, it would motivate the researchers to conduct more studies.
This paper presents a study on optimizing the combination of a tuned mass damper inerter and a negative stiffness damper (TMDI-NSD) for better performance of structures against seismic actions. The experimental data obtained from the literature were used in the optimization of a hybrid combination of TMDI-NSD subjected to harmonic excitation considering different stability maximization criteria (SMC). The H2 optimization technique was used to obtain the optimum tunning parameter using the numerical method, while the closed form of the optimum technique was used to obtain the optimum tunning parameter through the SMC optimization technique. The maximum dynamic amplification factor (DAFmax) was considered for a comparison of TMDI-NSD. The results show that the performance of a TMDI-NSD combination is superior compared to that of a TMD. In addition, it is found that the performance of SMC is less compared to H2 & H∞ criteria, but the performance of H2 & H∞ is equivalent. The DAFmax value increases with the increase in the mass ratio for the TMDI-NSD combination, whereas it declines with the rise in the mass ratio for TMD. Besides, the performance of the damped primary system under seismic load with and without the TMDI-NSD combination was analyzed. Twenty real earthquake ground motion data were considered in the analysis. The response of the primary system mitigated with the TMD and TMDI-NSD combination was evaluated in terms of the broad frequency range efficiency and peak value. It is observed that the damped primary system with TMDI-NSD combination using under-optimization criteria is superior to TMDI-NSD with respect to the displacement response. However, when considering the acceleration response, the SMC performs better compared to H2 & H∞ optimization criteria. The acceleration and displacement response for the primary structural system is reduced by 60% and 75%, respectively, by using TMDI-NSD of SMC optimization. Finally, the investigation of the single primary degree of freedom for a system with a TMDI-NSD combination indicates that all three optimization criteria under real seismic excitation perform better.
This paper presents investigation into the behavior of beam-column joints, with the joint region concrete being replaced by steel fiber reinforced concrete (SFRC) and by ultra-high performance concrete (UHPC). A total of ten beam-column joint specimens (BCJ) were tested experimentally to failure under monotonic and cyclic loading, with the beam section being subjected to flexural loading and the column to combined flexural and axial loading. The joint region essentially transferred shear and axial stresses as received from the column. Steel fiber reinforced concrete (SFRC) and ultra-high performance concrete (UHPC) were used as an innovative construction and/or strengthening scheme for some of the BCJ specimens. The reinforced concrete specimens were reinforced with longitudinal steel rebar, 18 mm, and some specimens were reinforced with an additional two ties in the joint region. The results showed that using SFRC and UHPC as a replacement concrete for the BCJ improved the joint shear strength and the load carrying capacity of the hybrid specimens. The mode of failure was also converted from a non-desirable joint shear failure to a preferred beam flexural failure. The effect of the ties in the SFRC and UHPC joint regions could not be observed due to the beam flexural failure. Several models were used in estimating the joint shear strength for different BCJ specimens. The results showed that the existing models yielded wide-ranging values. A new concept to take into account the influence of column axial load on the shear strength of beam-column joints is also presented, which demonstrates that the recommended values for concrete tensile strength for determination of joint shear strength need to be amended for joints subject to moderate to high axial loads. Furthermore, finite element model (FEM) simulation to predict the behaviour of the hybrid BCJ specimens was also carried out in an ABAQUS environment. The result of the FEM modelling showed good agreement with experimental results.
Laser-induced breakdown spectroscopy (LIBS) is a remarkable elemental identification and quantification technique used in multiple sectors, including science, engineering, and medicine. Machine learning techniques have recently sparked widespread interest in the development of calibration-free LIBS due to their ability to generate a defined pattern for complex systems. In geotechnical engineering, understanding soil mechanics in relation to the applications is of paramount importance. The knowledge of soil unconfined compressive strength (UCS) enables engineers to identify the behaviors of a particular soil and propose effective solutions to given geotechnical problems. However, the experimental techniques involved in the measurements of soil UCS are incredibly expensive and time-consuming. In this work, we develop a pioneering technique to estimate the soil unconfined compressive strength using artificial intelligent methods based on the spectra obtained from the LIBS system. Decision tree regression (DTR) and support vector regression learners were initially employed, and consequently, the adaptive boosting method was applied to improve the performance of the two single learners. The prediction power of the established models was determined using the standard performance evaluation metrics such as the root-mean-square error, CC between the predicted and actual soil UCS values, mean absolute error, and R2 score. Our results revealed that the boosted DTR exhibited the highest coefficient of correlation of 99.52% and an R2 value of 99.03% during the testing phase. To validate the models, the UCS values of soils stabilized with lime and cement were predicted with an optimum degree of accuracy, confirming the models' suitability and generalization strength for soil UCS investigations.
This paper reports the results of a study conducted to investigate the flexural behavior of corroded reinforced concrete (RC) beams that were first repaired with different types of cover repairing materials and then strengthened with the carbon fiber-reinforced polymer (CFRP) laminates. Thirteen RC beam specimens were prepared. One specimen was used as a control beam (un-corroded, unrepaired, unstrengthened), and the reinforcing bars in twelve specimens were corroded using an accelerated corrosion setup. While five corroded specimens (two unrepaired and three repaired) were tested without strengthening using CFRP laminates, the other seven corroded specimens (two unrepaired and five repaired) were strengthened with one and two layers of CFRP laminates before testing under flexure. For the RC beams subjected to 10 and 20% corrosion of steel bars (by mass), strengthening using one layer of CFRP laminate enhanced the load-bearing capacities by 89 and 73%, respectively, while strengthening with two CFRP layers improved the load-carrying capacity by 162 and 154%, respectively. Repairing the damaged cover of the corroded RC beams using ultra-high-performance concrete (UHPC) was found to be most effective in enhancing the load-bearing capacity and stiffness, whether the corroded beams were strengthened with CFRP laminates or not. Repairing of the cover using commercial repair material also enhanced the load-carrying capacity and stiffness, with ductility more than that of UHPC. Strengthening of the corroded beams further improved the load-carrying capacity. An analytical model was developed that can predict the load-bearing capacity of the beams with a fair degree of accuracy.
