Showing 4 results for Lateral Loading
Abbas Niknejad, Mojtaba Firouzi, Hamid Reza Saadat Fard,
Volume 15, Issue 4 (6-2015)
Abstract
This article investigates energy absorption capacity and plastic deformation of lateral flattening process on an aluminum profile with special cross-section under the lateral compressive loading in the quasi-static condition by experimental method. The profile section is a circular tube with two symmetric longitudinal grooves. Different samples with various lengths and outer diameters in three different filling conditions consist of empty, core-filled and full-filled by polyurethane foam were prepared. Some specimens with the same geometry and filling condition but, with different loading angles of 0, 30, 45, 60 and 90o respect to symmetric line of two longitudinal grooves, were laterally compressed. Effects of various parameters such as profile length, outer diameter, three different filling conditions, and loading angle are investigated on lateral loading and specific absorbed energy. Experimental results show that specific absorbed energy is independent of specimen length. At the same displacement, when diameter of samples increases compressive loading decreases. Also, in zero loading angle, presence of the filler enhances lateral load; and consequently, increases specific absorbed energy by the structure. In viewpoint of the design of an energy absorber design, optimum specimen is full-filled profile under a loading angle equal to zero. However, if due to some design limitations, assembling the special profile with loading angle of zero is impossible, assembling the structure in empty condition with loading angle of 90o can be the next suggestion. Experiments show that the highest specific absorbed energy occurs in the profile with different diameters under loading angles of zero and 90o.
Abbas Niknejad, Mojtaba Firouzi, Mohammad Rahim Hematiyan, Sima Ziaee,
Volume 17, Issue 8 (10-2017)
Abstract
This article investigates energy absorption capacity and plastic deformation trend of lateral flattening of an aluminum profile with H-shaped cross section under the quasi-static lateral loading by experimental, numerical and theoretical methods. Samples were prepared with different lengths and three different filling conditions including empty, core-filled and perfectly-filled by polyurethane foam. In addition, samples with the same geometry and filling conditions were laterally compressed with loading angles of 0 and 90 degree. Effect of some parameters such as length, three different filling conditions and loading angle were experimentally investigated on lateral force and specific absorbed energy (SAE). The results show that SAE is independent of samples length. At the loading angle of 90 degree, presence of the filler causes increment of SAE by the structure. Using the perfectly-filled profile under the loading angle of 90 degree is the most optimum condition. Based on two different energy absorption mechanisms, a theoretical equation was derived to estimate total absorbed energy (TAE) by empty sample with loading angle of zero; and predicted results were compared with the experimental samples. Due to present limitations in preparing the samples with different geometrical dimensions, nonlinear ABAQUS software was employed. Some samples with different wall thicknesses were modeled and influence of thickness was investigated on TAE. TAE is directly correlated to the second power of wall thickness; and this relationship can be clearly understood from the theoretical equation and numerical results. High correlation of experimental, numerical and theoretical results indicates precision and accuracy of the performed research.
Volume 19, Issue 4 (11-2019)
Abstract
Wind turbines are considered as an important element of the renewable energy structure. Offshore wind turbines are tending to be more efficient than onshore because wind speed and direction are more consistent. Monopiles are widely used for offshore wind turbines at present. They are always subjected to significant cyclic lateral loads due to wind and wave excitation. Monopiles are hollow cylindrical steel piles with a circular cross-section and a length to diameter ratio of less than 10 (L/D < 10). Currently, the design of monopiles is based on experiments performed on slender piles. Since monopiles behave rigidly, finding their action seems to be very necessary for accurate analysis and design of these structures.
In order to better understand the performance of monopiles under static and cyclic lateral loads, a series of static and cyclic lateral load tests was conducted on a stainless steel monopile in the geotechnical centrifuge. The main goal of this study is the examination of accumulated lateral displacement of a monopile foundation for an offshore wind turbine with a large diameter subjected to wind and wave loads. In this article, the lateral responses of a large diameter monopile under one-way force-controlled cyclic lateral loads are described and accumulated permanent pile shaft lateral displacements caused by cyclic lateral loads are discussed. All tests were performed in beam centrifuge. Monopile was installed in Firoozkooh-161 sand in this study. The centrifuge tests were carried out at different cyclic load and magnitude ratios insights into the ongoing development of net stresses and bending moment.
In this research, 4 Tests were designed and implemented to centrifuge modeling the action of monopiles in sandy soils. Tests were carried at physical modeling laboratory of the school of civil engineering at the University of Tehran. The first experiment was initially conducted to estimate the ultimate capacity of these piles, and then the obtained results compared to similar research findings. Three other experiments were carried out to evaluate their behavior affected by cyclic lateral load and to determine cumulative displacements and deformation state. Consequently, the results were finally compared with findings of other researchers, regulations, and relationships available related to other used piles (with a diameter less than 2 m) in geotechnical projects. Results of the study indicate that the use of available regulations and instructions in estimating the lateral load-bearing capacity of these piles was conservative. However, this fact can lead to the achievement of unreliable and upper-hand results. Thus, the existing relationships and regulations need to be changed to provide accurate results related to these piles.
The major findings of this study are presented below:
-The estimation of the monopile lateral bearing capacity is impossible with existing formulas, and this requires numerical or physical modeling.
-The behavior of the monopile structure under lateral loading is rigid until the failure limit, so the failure mechanism of the monopiles will be similar to the short and rigid piles.
-Cumulative lateral displacement of the monopile head is ascending in the number of cycles, and its rate in all cyclic tests is reducing.
-The monopile has rotated around a point in the depth of 30 to 75 percent of the driving length.
-The maximum bending moment value in all cycles has occurred in the depth of about 20% of the driving length.
Volume 21, Issue 3 (5-2021)
Abstract
One of the most important points of interest for designers in the construction of the tall building is to create a large entrance to the lower floors of the building. The need for such large openings is mainly due to architectural issues such as high traffic congestion, aesthetics, and parking. Creating these large openings, if accompanied by the removal of a column, connects the issue with other structural issues such as the effect of the Construction sequence, progressive collapse, loads during execution, and the presence or absence of auxiliary supports (temporary piles) and making the problem more complex. In this study, 36 regular structures of 10, 20, and 30 floors with a height of 40 to 120 meters were considered with the Moment resistance frame system in the ETABS software. The Iranian National Building Code part 6 has been used for load gravity of structures and the Iranian standard No. 2800 has been used for calculation and loading of earthquake lateral loads. After spectral dynamic analysis and Pushover analysis of the mentioned structures, their behavior was examined from the structural point of view and the effect of using bracing in one to four upper floors of the removed column. In the studied structures, the changes in the process of plastic hinges formation, structural performance level, Demand- Capacity ratio (DCR) of structural elements, period of the first mode, and drift in case of exterior (non-corner) column removal were evaluated. The effect of elimination on the exterior column to create a large entrance to the building on the probability of progressive collapse of the 10-story steel structure was also studied. The results showed that the use of braces to strengthen the large span beam is a convenient and economical solution. In particular, the V braces show better performance compared to the Chevron brace, if the number of braced floors above the desired span is before the inflection point of the building. Because when the braces enter the area adjacent to the inflection point of the building, due to the low ductility in the pressure, with failure in the pressure, they reduce the level of performance of the building. The first plastic hinge at any performance level starts from the inflection point and as a result, the use of low ductility elements in these areas reduces the ductility of the structure. Structures with V brace in most cases have smaller elements than structures with Chevron braces and are more economical. Structures that are reinforced only by increasing the dimensions of the beam and column sections and without adding bracing have more strength than structures with bracing. However, in this case, the dimensions of a large number of sections compared to the braced structures in some cases increase several times, and therefore this increase in strength will be accompanied by a large increase in cost. The results of pushover analysis and performance-based design showed that if the structure is designed from the beginning according to the common code design, assuming the absence of columns, the structure does not experience a reduction in performance and is generally better than to use braces with higher ductility.
