Journal of Numerical Methods in Civil Engineering
Volume:5 Issue: 3, Mar 2021

Today, numerical simulation can be used as a suitable tool to measure large quantities that are very expensive and, in some cases, impossible to measure. One of the important issues in predicting rock mass boreability in excavation with full face tunnel boring machines is estimating the discchr('39')s forces for rock cutting. For this purpose, the linear cutting test is  employed. However, limited access to equipment and the high cost of this test have resulted in a decline in its use. In this research, linear cutting tests have been simulated using numerical methods using ABAQUS 6-14 software, which is based on the finite element method. In this simulation, according to the dynamic analysis, for the explicit solution method and the behavior of the rock, the Johnson–Holmquist-II model (JH-2) is used. Subsequently, after solving the model, the forces acting on a fixed cross-sectional disc are estimated, and then, for validation, the results of numerical modeling are compared with laboratory results and theoretical model. Comparison of the results shows that the cutting forces obtained from the simulation have a deviation of 7% and 11% with normal and rolling forces compared to the mean forces in laboratory work, respectively.

In recent years, lightweight steel framed (LSF) structures are designed to resist fire, earthquakes, and storm events. This system has entered the field of construction due to advantages of light members. Based on these advantages, such a system is also used for buildings with special importance. Structural health monitoring (SHM) implements a damage detection and characterization strategy for engineering structures.  In the present study, a multi-objective numerical method for optimal sensor placement based on the combination of Modal Assurance Criteria (MAC) and maximum stress has been proposed. Genetic Algorithm (GA) was employed to determine the location of sensors on the structure based on the structural dynamic response of the LSF system. To show the efficiency of the proposed method, a very large irregular museum building, which was built by using LSF system, has been considered. To improve the proposed method, dominant frequencies are identified and the number of sensors is decreased using the Fourier Transform (FT) of the ground motions time history. Results show that the proposed method can provide the optimal sensor locations and remarkably reduce the number of required sensors and also improve their optimum location.

Tubular structural systems are one of the most common types of systems in high-rise structures. In the early days of this system, there were imperfections in its design which were overcome over time. The most important modification to rectify these defects is the use of a series of internal frames in addition to the peripheral frames and new systems in the center of the plan to eliminate design weaknesses over time. The central frames such as the inner tube, enhance the final rigidity and durability of the system. In this paper, high-rise buildings of 30, 40 and 50 floors have been subjected to static linear analysis and resistive design and their key design parameters have been investigated. The method is in a way that several samples with real dimensions are selected and the variables of height and the inner tube dimensions are numerically compared. The results revealed that the inner tube dimensions play an important role in improving the design parameters and the best dimension of the inner tube in a square plan is equal to half of the dimension of the outer tube.

The local site conditions and the geological properties of soil materials on which buildings are constructed might play a pivotal role in changing the characteristics of input seismic ground motions, and subsequently affect the seismic performance of the structures. These effects should be considered in the seismic evaluation of structures, especially those equipped with damping devices. As a matter of fact, these devices are designed to increase the energy dissipation capacity of the buildings through certain inelastic mechanisms, which are highly dependent on the input ground motions. Friction dampers are one of the cost-efficient controlling devices in which whose performance mostly depends on the story displacements. Hence, the variation in seismic excitations caused by the local site effects might have an impact on how they mitigate the earthquake hazard in addition to their efficiency. Shedding light on the above facts, this paper evaluates the influence of site effects on the seismic performance of a 10-story intermediate friction-damped steel moment frame under near-field excitations. Nonlinear time-history analyses are done using ten ground motions, which have been originally recorded at bedrock, while variation in their properties is calculated by passing them through a soil profile, which is modelled using the equivalent linear method. The result indicates that considering the site soil effects has a major consequence on ground motions as well as the performance of dampers insofar as it leads to a rise in the amount of input energy and the story drifts. Nevertheless, the seismic performance of the dampers remain quite efficient and reliable.

Performance-based optimization of energy dissipation devices in structures necessitates massive and repetitive dynamic ‎analyses. In the endurance time method known as a rather fast dynamic analysis procedure, structures are subjected to ‎intensifying dynamic excitations and their response at multiple intensity levels is estimated by a minimal number of analyses. ‎So, this method significantly reduces computational endeavors. In this paper, the endurance time method is employed to determine the optimal placement of viscous dampers in a weak structure to achieve the desired performance at various hazard levels, simultaneously. The viscous damper is one of the energy dissipation systems which can dissipate a large amount of seismic input energy to the ‎structure. To this end, hysteretic energy compatible endurance time ‎ ‎excitation functions are used and the validity of the results is investigated by comparing them with the results obtained from a suite of ground motions. To optimize the placement of the dampers, the genetic algorithm is used. The damping coefficients of the dampers are considered as design variables in the optimization procedure and determined ‎in such a way that the sum of them has a minimum value. The behavior of the weak structure before and after rehabilitation is also investigated using endurance ‎time and nonlinear time history analysis procedures in different hazard levels.‎

In most cases, concrete arch dams in the presence of suitable abutments, have high bearing capacity and more appropriate safety regarding the cost aspects, when compared to the other types of dams. However, according to the dam failure statistics, site specific conditions and abutment instability are the main factors of concrete dam’s failure. In this paper, the effects of two important factors on earthquake response of high arch dams are considered. These factors are: effects of contraction joints opening between the dam monoliths and appropriate rock foundation boundary conditions. Nonlinear seismic response of dam  reservoir foundation system includes dam-canyon interaction, dam body contraction joint opening, discontinuities (sliding planes) of foundation rock and failure of the jointed rock and concrete materials. Therefore, a finite element program for nonlinear dynamic analysis of 3D dam reservoir  foundation system was developed. Karun 4 Dam as a case study was analyzed and the results revealed the essential role of modeling discontinuities and boundary conditions of rock foundation under seismic excitation. Also, The results demonstrate that the contraction joint openings during strong earthquakes are substantial and greatly change the arch to cantilever stress distribution in the dam body.