Abstract in English:Abstract The construction of the cross passage changes the main tunnels segment from a complete cylindrical structure to a notched unstable stressed structure. Thus, the overall force (bending and shearing) performance of the main tunnels is considerably decreased. The excavation of the cross passage also destroys the stability of the original soil layer and main tunnels and causes difficulty in avoiding the settlement of the surface and main tunnels. Numerical simulation analysis of the mechanical characteristics and influencing factors analysis were carried out using FLAC3D. Results show that (1) the construction of the cross passage largely disturbs the main tunnels. The settlement of the intersection part of the main tunnels and cross passage is mainly concentrated from −7 m to 7 m. (2) During the construction of the cross passage, the original main tunnels are subjected to stress redistribution, which causes stress concentration in the intersecting segments, especially in the opening side segment has an unfavorable force form in which the upper and lower sections are integrally pulled. (3) The construction of the cross passage causes a large tensile stress area in the structure as well. As a result, the overall tension of the upper and lower sections of the structure and the compression of the hance are unfavorable. (4) The influence of the excavation of the cross passage on the surface and main tunnels is related to the buried depth, intersection angle, excavation method, and grouting range. Therefore, the influence of different parameters can be analyzed by changing the model parameters.
Abstract in English:Abstract This study focuses on performance of CFT column to foundation connections subjected to combined axial and lateral cyclic loading. Experimental investigations were carried out on five specimens with exposed column base and embedded column base connections. The parameters considered were number of stiffeners and embedment depth of CFT column. The force - displacement response of all the specimens were compared. Providing increased number of stiffeners, increase the strength of connection. An additional mesh provided on the embedded connection was found to be good in improving the ductility of the connection which is a feasible solution for composite structures in earthquake prone regions.
Abstract in English:Abstract This paper presents and discusses the design of a vibration control device for a 120 m high steel tubular tower of onshore Horizontal Axis Wind Turbine (HAWT). The tower is modeled using beam (own code), and shell and solid finite elements (via ANSYS). The Dynamic Vibration Absorber (DVA) is designed to be attached to the tower top, aiming to analyze Tuned Mass Damper (TMD), Active Mass Damper (AMD), and Hybrid Mass Damper (HMD). The theory proposed by Den Hartog is used to determine the coefficients of the absorber and the Linear Quadratic Regulator (LQR) is applied to obtain the optimal control variables introduced by the hydraulic actuators. The HMD, the main contribuition of this paper, reaches excellent levels of vibration reduction for the tower submitted to harmonic actions, in a transient and permanent (stationary) regime, resonant to the first vibration mode of the structure without control.
Abstract in English:Abstract This paper presents cyclic load test of five exterior reinforced concrete frames. All the specimens represent a substandard single-span, low-rise reinforced concrete frame building which behaves a weak column-strong beam mechanism under a strong seismic loading. The first three exterior frames M1, M2 and M3 were designed for the joint shear critical to investigate the effect of joint reinforcement. They are similar except the joint reinforcement detailing. The fourth specimen M4 was an exterior frame with a very small column member. The fifth specimen U5 was the seismic upgrade of M4 specimen using externally attached steel column. From the first three tests, the increase in shear capacity due to the reinforcement provided in the beam-column joint was negligible when the column size was small leading to high joint shear stress. The shear capacity of the specimens was agreed well with the calculation formula provided by ACI318 (ACI, 2008) ignoring the contribution from the reinforcement. The upgraded frame markedly indicated the increased capacity of 2.02 times of the strength of M4 specimen. However, the ductility of the upgraded frame was decreased. It was the result from that the failure mode of the specimen was shifted from the joint failure to the column damage at the section next to the end of the attached steel column.
Abstract in English:Abstract The dynamic behavior of cylindrical shells is essential in many practical applications. These include in-vacuum and coupled vibrations of structures with contained fluids. Closed-form solutions are extremely complex since they involve many terms and algebraic operations that require numerical solvers. In this work, a simplified closed-form solution for the free vibration analysis of an empty or filled with an inviscid and incompressible fluid cylindrical tank is presented. The proposed analytical method is developed for a simply supported cylindrical shell, based on an energy formulation obtained with variational calculus, and provides explicit expressions for natural frequencies, which can be easily programmed in a spreadsheet. The fluid is represented by an acoustic cavity, modeled by the wave equation, and the fluid-structure interaction is reduced to an added mass of fluid in the uncoupled shell equations of motion. A finite element model was built using ANSYS software to validate the proposed procedure. The natural frequencies and mode shapes were studied, and the results obtained are consistent with analytical, numerical and experimental results.
Abstract in English:Abstract The use of integrally stiffened panels (ISP's) in wings of small and medium-sized aircraft is frequent in aviation. These thin-walled structures are often subjected to compressive loads during their life-time and, although the finite element method has become an important tool for engineers to obtain the buckling load of structural members, some results based in charts published by NACA are still used in the preliminary stages of the wing design in many aircraft companies. However, these charts used for calculation of the critical compressive stress consider only idealized stiffened panels and neglect geometric details as the fillet radius used in the current design of ISP's. The objectives of this paper are twofold: (i) to show that the charts published by NACA provide good results for the critical buckling stresses for several geometries of ISP's, when compared to finite element results with proper boundary conditions, providing fillet radii are also neglected in the finite element models and (ii) to show that the values of the critical buckling stresses for local instability of ISP's may be significantly increased when one considers the effect of the fillet radius, meaning that this parameter should also be considered in the optimal design of such structures. Several numerical results obtained with finite element simulations based on different geometrical parameters of ISP's are presented in this study.
Abstract in English:Abstract Geotechnical engineering has often been challenged by demands from technically and economically bold construction projects, such as that of tall buildings. The architectural requirements of these buildings have increased and concentrated the loads from structural systems without proportionally increasing plant area. New forms of using load capacity and settlement control have been assessed to optimize conventional designs. Thus, piled foundations started to allow for the contribution of block-soil contact, being conceptually named piled raft. In this sense, this study analyzed the contribution of contact in piled foundations composed of one, two, three and four instrumented bore piles 25 cm in diameter (ϕ) and 5 m in length (L). Experimental results showed a 21% average contribution of block-soil in relation to the total piled foundation capacity. This result demonstrates the need to re-evaluate traditional calculation requirements, aiming at rationalizing the geotechnical design and improving the overall safety/stability of the system.
Abstract in English:Abstract This paper investigates the crack and mechanical behavior of CFRP plate-reinforced bridge roof under high temperature with different anchoring measures. Six CFRP-reinforced test beams with different anchoring schemes were designed and constructed. The beam specimens, after the high temperature effects, were tested under four-point bending loads. The crack propagation, beam deflection, mid-span strain and the damage modes were observed and recorded until failure. The stiffness variation and the debonding failure mechanism of the test beams were comparatively investigated. The results indicate that the debonding bearing capacity of the specimens can be improved by the additional anchoring measures. The concrete shrinkage at the crack and the average crack spacing are more effectively reduced, when the additional anchoring measures are placed at the mid-span and the support position. In addition, a theoretical model is proposed for calculating the intermediate crack debonding bearing capacity. Based on the comparative analysis of various models and test results, it is shown that the proposed model could accurately calculate the intermediate crack debonding bearing capacity of the test specimens.
Abstract in English:Abstract In this article, third- and fourth-order accurate explicit time integration methods are developed for effective analyses of various linear and nonlinear dynamic problems stated by second-order ordinary differential equations in time. Two sets of the new methods are developed by employing the collocation approach in the time domain. To remedy some shortcomings of using the explicit Runge-Kutta methods for second-order ordinary differential equations in time, the new methods are designed to introduce small period and damping errors in the important low-frequency range. For linear cases, the explicitness of the new methods is not affected by the presence of non-diagonal damping matrix. For nonlinear cases, the new methods can handle velocity dependent problems explicitly without decreasing order of accuracy. The new methods do not have any undetermined algorithmic parameters. Improved numerical solutions are obtained when they are applied to various linear and nonlinear problems.
Abstract in English:Abstract This paper deals with a deep circular tunnel excavated in infinite homogeneous and isotropic elasto-viscoplastic rock mass subjected to a hydrostatic initial stresses. The tunnel is divided into the initial plastic, viscoplastic, and elastic zones. By combining the generalized Bingham model with Mohr-Coulomb yield criteria, analytical solutions of the circular tunnel are derived with the consideration of non-associated flow rule and elasto-viscoplasticity. The initial plastic zone is defined as the instantaneous change of rock mass excavation. Based on the initial plastic zone, the stresses in viscoplastic zone are transferred to the deep surrounding rock with time due to the initial earth stresses. The results are compared with the elastic-brittle solution at static conditions, and the solutions of this paper are validated. Moreover, the presented results shows that the stress and displacement of the surrounding rock varies with time, and the solutions can be obtained at different instants of time.