Abstract in English:Abstract This paper describes the experimental performance of the bolted stiffened end-plate (BSEP) and bolted flange-plate (BFP) connections using European hot-rolled profiles and built-up profiles. Four connections are designed and constructed according to FEMA-350 and are performed under cyclic loading. The influence of using different member profiles (European profiles and built-up profiles) in both the BSEP and BFP connections are examined. The obtained test results, including failure modes, hysteretic curves, ultimate moment and rotation values and panel zone extensions were reported and the performance of different connections is compared. It was found out, based on the obtained test results, that using hot-rolled or built-up profiles in the connection does not affect its global behavior.
Abstract in English:Abstract The use of tensegrity structures in soft robotics has seen an increased interest in recent years thanks to their mechanical properties, but the control of these systems remains an open problem. This paper presents a reconfiguration strategy for actuated multi-stage tensegrity structures. The algorithm works on the principle of using the infinitesimal mechanisms of the structure to generate a path of positions along which a multi-stage tensegrity structure can change its shape while maintaining the self-equilibrium. Combining the force density method with a marching procedure, the solution to the equilibrium problem is given by a set of differential equations that define the kinematic constraints of the structure. Beginning from an initial stable position, the algorithm calculates a small displacement until a new stable configuration is reached, and recurrently repeats the process during a given interval of time. By means of three numerical examples, we show the efficacy of our algorithm for reconfiguring a two-stage tensegrity mast along different directions.
Abstract in English:Abstract Leakage resistance of casing connections can be evaluated by extremely expensive testing procedures. Although testing is required for connection validation, significant amount of resources can be saved by complementing testing with Finite Element (FE) analysis. In this regard, a broadly accepted criterion to characterize leaks in FE simulation is still required. This paper proposes an objective and accurate criterion to characterize leakage resistance of casing connections in axisymmetric FE simulation. The criterion is based on stab flank contact pressures and stab flank engaged length parameters. The criterion is tested in application to API 8 Round LTC connections (5 ½ J55 14lb/ft), and confronted with test results. Leakage envelopes are obtained considering make-up torque and tensile axial loads. The influence of taper on connection sealability is also investigated. The long term goal of the investigation is to derive probabilistic leakage envelopes of casing connections considering manufacturing tolerances, effect of thermal cycles, and seal ovalization due to bending during assembly.
Abstract in English:Abstract Structural fuses and rocking system are used in order to reduce the building response to earthquakes and damage guidance. In the proposed seesaw motion system, which is similar to the rocking system, the building columns, in top of the foundation, have been removed and a central support and structural fuses are used around the building instead of them. The main purpose of creating this system is that the structural components remain elastic during the earthquake and nonlinear deformations occur in circumferential structural fuses it means that, it is possible to replace damaged fuses after the earthquake and exploit the building in a short time and at a lower cost than the construction cost of the whole building. In this research, the specification of a kind of structural fuse have been investigated and its application in the building with a seesaw system is studied under the influence of the near-field earthquake. After reviewing the fuses, it was observed that, the maximum absolute acceleration of roof and the base shear are significantly reduced in this system; however, the relative drift of floors in some buildings has increased but is lower than the permitted limit.
Abstract in English:Abstract The high prediction accuracy of FEM calculations is an important prerequisite for their growing use in the field of crash load cases for vehicle body design. Although the simulation accuracy of crash calculations for steel structures already is at a high standard, continuous improvements and a further development of the simulation models are crucial in the field of vehicle design. Existing studies on the simulation accuracy for steel structures under crash load focus on the deformation behaviour of idealized component-like structures. These studies do not allow for conclusions on the simulation accuracy of crash calculations based on vehicle-related components with increased geometric complexity as well as with different material combinations, joining techniques and bead structures. This was the reason for conducting the experimental and numerical investigations on crash boxes outlined in this paper. The goal was to investigate whether the FE code is capable of increasing the accuracy of the simulation of the experimental results by considering the information obtained from technical measurements.
Abstract in English:Abstract The use of recycled Reclaimed Asphalt Pavement (RAP) material into flexible pavement contributes to sustainable development with environmental and economic benefits. In the present work, Semi-Circular Bending (SCB) specimen has been adopted to study the flexural strength and mode-I fracture toughness of flexible pavement with and without RAP. Two different resources of RAP, namely KS and KF, with two different percentages (20% and 40%) have been examined. Smooth and cracked specimens have been cast to measure the flexural strength and mode-I fracture of flexible pavement containing RAP, respectively. Smooth and cracked specimens for flexible pavement without RAP, as control beams, have been cast for the sake of comparisons. The experimental results showed that, the flexural strength and mode-I fracture toughness of flexible pavement containing 40% RAP are higher than those of flexible pavement without RAP, for the two types of RAP. Comparison between the of work of fracture calculated based on AASHTO TP 105-13 and AASHTO TP 124-16 showed that, the calculation based on AASHTO TP 105-13 is more accurate than that based on AASHTO TP 124-16. Furthermore, the suggested quad-linear relation to work of fracture predictions is easier and more reasonable for presenting the experimental results especially for the descending part of P-LLD curve than that suggested as exponential curve by AASHTO TP 124-16. For all groups, the type of failure is intergranular-mode fracture.
Abstract in English:Abstract In this paper, a new hybrid approach is presented based on the combination of the power series expansions and the Rayleigh-Ritz method for stability and free vibration analyses of axially functionally graded non-uniform beams resting on constant Winkler-Pasternak elastic foundation. In the proposed novel technique, the power series approximation is first adopted to solve the motion equation. Regarding this numerical methodology, the transverse displacement and all mechanical properties are expanded in terms of power series of a known degree. By solving the eigenvalue problem, one can acquire the fundamental natural frequencies. According to aforementioned method, the expression of vibrational mode shape is also determined. Based on the similarities existing between the vibrational and buckling deformation shapes, Rayleigh-Ritz method is finally employed to construct eigenvalue problem for obtaining the critical loads. In order to illustrate the correctness and convergence of the method, several numerical examples of axially non-homogeneous and homogeneous beams are conducted. The obtained outcomes are compared to the results of Finite Element Analysis in terms of ANSYS software and those of other available numerical and analytical solutions. The accuracy of the method is then remarked.
Abstract in English:Abstract The behavior and response of pipelines subjected to slip fault movement is studied by numerical simulations as well as experimental setup. A finite element modeling is also developed via ABAQUS software. In this study, an artificial accelerogram is applied to the system and matched against the response spectrum according to the standard No. 2800 (Iranian code of practice for seismic resistant design of buildings, 2014). Three different pipe nominal sizes and thicknesses (1 ½”, 2” and 4”) are considered in the experiments on the shaking table. According to the results, plastic hinge as well as the extremum stress and strain is formed in the fixed soil wedge and at locations close to the fault line. Further, as the pipe D/t ratio increases, the plastic hinge forms further away from the fault line. According to the results, the pipe-soil strain ratio (εp/s) has lower values at larger pipe diameters. Also, the axial strains would be greater for the systems with higher (εp/s) ratios.
Abstract in English:Abstract The effect of fabric anisotropy on strength has not been considered in most strength criterions for granular material. Some criterions can describe the variation of material strength with stress-induced anisotropy, but micro-mechanism and physical meanings are undefined. Some criterions consider the effect of fabric anisotropy, but the evolution of fabric is ignored during loading by assuming a constant fabric tensor. Based on strength mechanical characteristics of granular material, in this paper, the relationship between macro stress and micro contact force of granular material is derived by micromechanics. Then, the concept of true stress tensor is proposed. An anisotropic strength criterion of granular material considering fabric evolution is established and its applicability is validated by comparing with test results for different granular materials. The analysis results indicate that the proposed anisotropic criterion can be utilized to describe the strength feature of anisotropic granular materials, which gives a way for the cause analysis of the strength of granular materials from the perspective of Microscopic mechanism.