International Journal of Advanced Structural Engineering
Volume:12 Issue: 1, Spring 2022

With current progress in engineering science and in order to improve the performance of structures, the issue of strengthening of extant structures has caught many researchers’ attention due to different reasons such as application change, loading increase after construction, and modification of regulations. In this study, the role of pre-stressed cables made of steel and Nitinol in a steel beam under dynamic and static loads along with some different mechanisms was examined. Initially, to locate optimal points, a three-floor structure was designed as the extant structure. Then, a beam was arbitrarily modeled using some different mechanisms that included strengthening with steel and Nitinol pre-stressed cables placed under the lower beam wing at the end of it in V-shaped form from the two sides of the beam to its center. Finally, the structure was analyzed and examined via non-linear static and dynamic analysis of time history. The obtained results finally indicated a positive role of applied mechanisms in the steel beam. Further, the results also showed that the performance of steel beam strengthened with steel and Nitinol pre-stressed cables was better than that of the beam with steel cables. In general, it might be observed that the deflection of the beam center in static and dynamic states had an average reduction of 55 and 60% when compared with the ordinary state.

The problem of overcrowding at the junction of the rebars is very significant, particularly for seismic details. Mechanical couplers can, thus offer an appealing solution that eliminates the disadvantages of traditional reinforcement splicing. By identifying the target area for bar failure, the potential area for failure could be modified with this in mind, it is very useful in assessing the position of the reinforced concrete (RC) plastic hinge. In this context, the present study focuses on the numerical and analytical modelling of the experimentally obtained response of Integrated bar (without coupler) and bars with mechanical coupler to tensile uniaxial tests. Simulation results showed agreement with the experimental response in terms of load–elongation curve, Von Mises yield and failure mode .After validating the model, alternative designs (diameter, height and thickness of mechanical couplers and bar) were numerically tested to study the influence of the geometry of the structural system on the failures mechanical coupler. Overall results indicated that the optimum design would be the one with an increased diameter in the thread area of both the bar and the mechanical coupler. For this improved configuration, the load-bearing capacity was Similar to the Integrated bar (without coupler) Cases.

Researchers have combined passive control systems of differing stiffness with each other to provide multistory passive control systems. Each system absorbs and dissipates the applied energy according to its stiffness. This study investigates the multistory control system with the modern pipe in pipe passive damper, and combining them with braces, which are able to change stiffness and absorb energy under various loads to reduce seismic structural vibrations. Their performance in 5, 10 and 15 story 3D steel structures on type 1, 2 and 3 soil was evaluated with nonlinear time history analysis and referred to as the structure’s seismic responses. Results showed that using a combination of dampers and braces in 5, 10 and 15 story steel structures can be a suitable substitute for traditional bracing systems. For example, using pipe in pipe dampers instead of dual structures in 5, 10 and 15 story structures on type 3 soil reduced base shear by 45%, 51%, and 55%, and roof acceleration by 39%, 35% and 50%. Compared to dual structures, a combination of dampers in lower stories and braces in higher stories on type 3 soil reduced base shear by 36%, 36% and 46%, and roof acceleration by 38%, 32% and 41% in the 5, 10 and 15 story structures.

The paper aimed to quantify the compressive strength of cementitious materials using in-situ “pull-off” and “twist-off” tests. Apart from determining the correlation coefficient, calibration plots and equations are presented to convert the results of in-situ tests to mortar compressive strength. The crack distribution was calculated in the tests using the nonlinear ABAQUS software. Additionally, the methods mentioned above were used to investigate the effect of pre-compression on mortar/concrete shear and tensile adhesion strength. Thus, the effect of pre-compression on the tensile and shear adhesion strength of mortar/substrate concrete was investigated using the scanning electron microscopy (SEM) method and physical adsorption theory. The results indicated that pre-compression positively affected adhesion and could be measured using the simple twist-off machine instead of the other machine. By applying 0.1 kg/cm2 of pre-compress, the tensile and shear adhesion between the mortar and concrete layers increased by 5.8% and 8.8%, respectively, after 90 days. Additionally, a linear relationship between the results of “twist-off” and “pull-off” tests and those obtained from experimental tests was observed.

Most of the hilly regions are situated in high seismic zones of India. Such a threat compels the need to keep a check on the performance of buildings that suffer extensive damages or even collapse during strong ground shaking on account of near-fault pulses. The present research work is related to the construction of an ensemble of fragility curves for buildings lying on 15⁰, 30⁰ and 45⁰ slopes. In order to mitigate the damages caused by near-field earthquakes, base isolation system using lead rubber bearing has been provided at the foundation level. The responses of the buildings are obtained by incremental dynamic analysis and linear regression is performed to obtain the probabilistic seismic demand models to find out the median intensity and the uncertain parameters. All the buildings are analysed for slight, moderate, extensive and collapse damage states for which the corresponding fragility curves are obtained. Base isolator was able to significantly reduce the seismic demand measures by imparting flexibility to the system and therefore can be recommended as an alternative to conventional fixed base type buildings located on sloping terrain experiencing near-fault motions.

In this article, the application of artificial neural networks in predicting the degree of concrete compressive strength of High Strength Concrete (HSC) was investigated. For this purpose, use was made of the pattern recognition neural network and the obtained data from the experimental tests for predicting the compressive strength degree of HSC. Five inputs from the HSC mix design were utilized for predicting the degree of compressive strength, by application of the scaled conjugate gradient backpropagation algorithm in neural network. The outputs were classified into 5 strength groups of M1, M2, M3, M4 and M5. The simulation results shows 97.9% accuracy in classifying the different predefined degrees of HSC using the confusion matrix diagram. Moreover, the cross-entropy error obtained from testing the neural network (NN) model and correlation coefficient (R2) of GEP for predicting compressive strength of the HSC were evaluated at 0.042096 and 0.9795, respectively, indicating high accuracy of the model. Application of this model could greatly help the persons, companies and research centers in terms of preparation and making of HSC with desired compressive strength, that are in need of this type of concrete.