Showing 1–12 of 650 results
A Level Set Method for Structural Shape and Topology Optimization Using Radial Basis Functions
In this paper, the cرایگان!
In this paper, the conventional level set method is extended as an effective approach for shape and topology optimization by the introduction of the radial basis functions (RBFs). We apply the RBFs to represent the implicit level set modeling to reconstruct the shape and topology of an admissible design in a parametric way. This scheme converts the original PDE based level set method into a set of much easier ODE system and makes the level set method more efficient to implement. Numerical examples show the convergence speed and insensitivity to initial designs of proposed method in shape and topology optimization of 2D problems.
A Robust Approach to Estimate the Uniaxial Compressive Strength of Intact Rocks
The uniaxial compres...رایگان!
The uniaxial compressive strength of intact rocks is extensively used in many rock engineering projects. High-quality core samples are required for the uniaxial compressive strength determinations. However, such core samples cannot always be obtained from weak rocks. For this reason, the predictive models are often employed to estimate indirectly. In present study, various models have been developed in order to predict uniaxial compressive strength. For this purpose different tests were accomplished. The root mean square error index was calculated as 6.1 from the neuro-fuzzy model and 13.63 from the multiple regression model. As a result, performance index reveled that the neuro-fuzzy exhibited a very high prediction capacity
Assessment of Equivalent Static Earthquake Analysis Procedure for Structures with Mass Irregularity in Height
Sudden changes in st...رایگان!
Sudden changes in structural dimensions and mass irregularities are inevitable in urban buildings. Most building codes have different analysis and design previsions for such buildings. In this article, such provisions based on the Iranian seismic code of practice (Standard No. 2800), which is to a great extent similar to UBC-97 model code, are verified in order to assess the provisions for different types of structures. Thus, four two-dimensional residential type steel structures with 4, 8, 12 and 16 stories and with different forms of mass irregularities in height are designed using the standard equivalent static procedure per the Iranian Seismic Code of practice. The designed structures, then, were subjected to different nonlinear static (pushover) and dynamic analyses. Two levels of irregularities, i.e. 150 and 300 percents, located at the heights equal to 50% and 75% of the overall height of the structures, have been considered. The results show that the static procedure adapted in the code results in much higher internal forces, story shears and overturning moments in various parts of the structures compared to the dynamic results. Also, this study shows that lateral inter-story drifts obtained using the equivalent static procedure and dynamic analyses are quite comparable for short buildings. For taller buildings, in contrast, dynamic analyses showed less inter-story drifts. It is also observed that mass irregularities in height could be responsible for more contribution of higher modes in seismic response of such structures
Bee Colony Optimization of Tuned Mass Dampers for Earthquake Vibrations of High-rise Buildings Including Soil Structure Interaction
This paper investigaرایگان!
This paper investigates the optimization of Tuned Mass Dampers (TMDs) for high-rise buildings. The model is assumed as a 40 story building with 160m height considering the translation and rotation of foundation. The Soil Structure Interaction (SSI) is considered for the better prediction of building’s response. To illustrate the results, Bam earthquake data is applied to the model. The three soil types, i.e. soft, medium and dense soil are utilized, and the results are compared with the fixed based model. The model is based on time domain analysis, and Newmark method is used to obtain the displacement, velocity and acceleration of different elements. The Artificial Bee Colony (ABC), a heuristic method based on the behavior of bees forage for food, is employed to obtain the best parameters for TMD device. The design variables are assumed as mass, damping and spring stiffness quantity. The objective is to decrease both the maximum displacement and acceleration of the building. The results show that the presented model can be effectively applied to evaluate the response of high-rise buildings including SSI effects. It is indicated that the results obtained by this model is more accurate than the results of fixed based model. The effects of TMD on the oscillations of structures including different soil characteristics are also investigated. It is shown that the TMD is more effective for soft soil foundations. It is also shown that how the bee colony optimization technique can be employed to design the optimum TMD for the minimum displacement and acceleration. This study leads the researchers to the better understanding of earthquake oscillations of the high-rise buildings, and helps the designers to achieve the optimized TMD for the structures.
Comparison between Seismic Behavior of Suspended Zipper Braced Frames and Various EBF Systems
Zipper frames are in...رایگان!
Zipper frames are intended to improve on the behavior of conventional inverted-V-braced frames, which show poor performance taking place from the early buckling of braces in the lower story. A zipper frame affords better performance by forcing simultaneous buckling of all braces. In this article, seismic behaviors of zipper braced frames and three types of eccentrically braced frames are evaluated using finite element simulation. Two dimensional finite element models have been created for three-story onebay frames for various bay lengths and different arrangement of braces. Seismic response of frames subjected to near-fault ground motions (LA21) has been studied through dynamic analysis, considering no nlinearity of geometry and materials. For this purpose, SAP2000 has been used. Results have been ompared and structural response of steel frames and some other parameters such as ductility of frames, maximum base shear and optimized link length have been investigated. Against other researches, in this article, the ratio of maximum shear over the weight of structure and its relation to behavior of structure has also been studied. It was found that optimized link length in EBF systems which caused to maximum du ctility of frame is about 30 percent of the bay length. Moreover, the results showed that zipper frames provide desirable post buckling behavior and exhibit more ductility.
Compliance of Rigid Arbitrary Shape Foundations Using 1 DOF BEM
In this study the reرایگان!
In this study the relationship between the dynamic force and displacement (impedance or compliance) is evaluated for rigid foundations with arbitrary shape resting on a half-space medium, consisting of homogeneous, isotropic, linear elastic materials with constant Boundary Element Method, (1 DOF). Green’s function is computed for half-space and presented in explicit form. By using BEM formulation the stress beneath foundations and compliance of them are obtained. The vertical compliance of a rigid circular disc which is calculated by this method is compared by semi-closed form solution and verifies the accuracy and efficiency of this method. the vertical and rocking compliance functions for rigid rectangular and some arbitrary shape foundations are obtained. And also, the variation of stress distribution pattern beneath square and circular foundations with frequency is studied and these results are compared with the results of the other methods.
Ductility Demand Distribution of Asymmetric Multi-Story R/C Buildings
To evaluate the infl...رایگان!
To evaluate the influences of the number of stories on the torsional response and ductility demand distribution in the plan and the height of plan asymmetric RC dual lateral load resistant multi-story buildings, three categories of structural models that contain 8-, 14- nd 20-stories buildings (with the wide range of eccentricity values) are subjected to an assemblage of ordinary and near-fault ground motions. The approach of modeling has been used, is more accurate for multi-storey R/C structures, because it redefines the stiffness from the strength in each time step. According to the findings, the torsional effects, decreases for high-rise structures where the lateral natural period increases
Effect of Steel Plate Jacketing of Columns in Seismic Behavior of Concrete Beam-Column Connections
Design philosophy ofرایگان!
Design philosophy of having weak beam – strong column is recommended almost in all design codes. But in some ases, in prior buildings, this philosophy is ignored. In these structures, during major earthquakes, failure mechanism would begin from columns leading to sever damages. To avoid this event, column in the connection zone must be strengthened to conduct the plastic zone to the beams. There is several ways for strengthening concrete columns and one of the efficient ways is using steel plates surrounding column in the critical zone. In this paper, using steel plates for seismic upgrading of Concrete Beam-Column connections has been investigated numerically. Effect of plate thickness, length and beam-column dimensions is taken into account. Some empirical results are used to verify the finite element approach. Analyses are conducted with the use of some modeling methods including various geometrical models and material behaviors. The results from various methods are compared and the suitable model is proposed
Effects of Circular Opening Dimensions on the Behavior of Steel Plate Shear Walls (SPSWs)
In recent years ther...رایگان!
In recent years there is a developing attention to steel plate shear walls (SPSWs) thanks to their proper function exposing to lateral wind and earthquake loads. Furthermore, their application in steel and concrete structures in order to strengthening them has raised a lot of focus upon. In some cases existence of opening is unavoidable due to architectural reasons or installed heating and cooling systems on the walls. That leads to a decrease in capacity and improper functioning of these systems that also results in an intense variation in inplane stress distribution. In this paper impact of circular opening dimensions on behavior of steel plate shear walls has been closely studied. On this purpose using ABAQUS finite element method a nonlinear analysis has been conducted considering geometrical and material nonlinearity in the models. Analyzed models indicate that the reduction factor (1-D/H)S and (1-D/H) respectively for resistance value and stiffness value predict lower error versus the increases in opening diameter
Evaluation of Base Shear Absorption of Combined System; RC Frame & Precast 3d Panels with Irregularities in Vertical
The current study inرایگان!
The current study investigates the base shear absorption of combined systems, RC frame pre-cast 3D wall sandwich panels in both linear and non-linear material properties. The seismic behavior of building constructed by 3D panels is studied using numerical approach finite element method. The obtained results are compared with regular bending RC frames, complete box type sandwich wall panels system, and present the differences of behavior and absorbance in each system and also the variation of vertical stiffness on structural response is examined. The material nonlinearities simulated with drucker-prager and von-misses failure criteria. The validation of FEM analysis is test with those obtained through experimental
Evaluation of Horizontal Seismic Hazard of ABADE, Iran
This paper presentsرایگان!
This paper presents probabilistic horizontal seismic hazard assessment of Abade, Iran. It displays the probabilistic estimate of Peak Ground Horizontal Acceleration (PGHA) for the return period of 475 and 2475 years. The output of the probabilistic seismic hazard analysis is based on peak ground acceleration (PGA), which is the most common criterion in designing of buildings. A catalogue of seismic events that includes both historical and instrumental events was developed and covering the period from 840 to 2007 is used. he seismic sources that affect the hazard in Abade were identified within the radius of 150 km and the recurrence relationships of these sources were generated by Kijko and Sellevoll . Finally four maps have been prepared to indicate the earthquake hazard of Abade in the form of iso-acceleration contour lines for different hazard levels by using SEISRISK III
Experimental Investigation of Time-Dependent Effect on Shear Strength Parameters of Sand–Geotextile Interface
The time-dependent bرایگان!
The time-dependent behavior of soils has been investigated extensively using one-dimensional and triaxial tests. The phenomena associated with time effects in soils are creep, relaxation, strain rate and rearrangement effects. The engineering properties of soil are often improved significantly with the time elapse. The objective of this paper is to investigate the time-dependent effect on the shear strength parameters of sand–geosynthetic interface using large direct shear test apparatus. For this purpose, the geotextile layer has been adhered gently on a piece of wood with a thickness such that a half of the shear test box has been occupied. The other half of the box has been filled with the sand and the test has been performed. Three normal stresses of 30, 45, and 60 kPa have been applied in all tests. The shear stress has subsequently been applied in different times to the failure stage. In all tests, the shearing velocity has been kept the same. The results of these experiments show that the stiffness and friction angle of the dry sand– geotextile interface increases up to 12.6% and 3.9% at 720 minutes after the sample is poured in the mold