Showing 13–24 of 726 results
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 Number of Contributed Modes on Accuracy of MultiModal Pushover Seismic Analysis of Irregular Frames
One of well-establisرایگان!
One of well-established static procedures for seismic evaluation and design of building structures in the equivalent nonlinear static procedures is Modal Pushover Analysis developed by Chopra and Goel (2002). For evaluation of effect of number of contributed modes on the accuracy of MPA procedure, 22 vertically irregular 5-story steel moment resisting frames are considered that each irregular frame is designed to represent low and high values of response reduction factor (R). Many nonlinear time histories and static pushover analyses are performed and the results of nonlinear static analyses are compared with the results for nonlinear dynamic analyses to evaluate the accuracy and conservatism of MPA for predicting target displacement, base shear, and story drifts.
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
Flexibility based method for the extent of damage in degrading bridge structures after in-service loading
This paper presents ...رایگان!
This paper presents a method to identify damage in bridge structures based on the flexibility matrices in the modal strain space. In the tudy by the Ritz vectors extracted from flexibility matrix, the damage is identified. The localization approach is applied to low levels of damage on the prestressed concrete girder of simply supported bridge, with a focus on using a small number of sensors and only the fundamental mode of vibration. The validity of the method is also demonstrated using experimental modal data of a plate girder from I-40 Bridge over the Rio Grande. The predictions were found to closely match the actual response of the bridges. The proposed method can detect the damage in bridge structures using a limited number of sensors and vibration modes
Foundation size effect on modulus of sub grade reaction on Sandy soils
Winkler model is one...رایگان!
Winkler model is one of the most popular models in determining the modulus of sub grade reaction. In this model, the sub grade soil is assumed to behave like infinite number of linear elastic springs. The stiffness of these springs is named as the modulus of sub grade reaction. This modulus is dependant to some parameters like soil type, size, shape, depth and type of foundation. The direct method for estimating the modulus of sub grade reaction is plate load test that is done with 30-100 cm diameter circular plate or equivalent rectangular plate. Afterward, we have to extrapolate the test value for exact foundation. In the practical design procedure, Terzaghi’s equation is usually used to determine the modulus of sub grade reaction for exact foundation, but there are some uncertainties in utilizing such equation. In this paper the size effect of foundation on sandy sub grade with use of finite element software (Plaxis 8.2) is proposed to investigate the validation of Terzaghi’s formula on determination of sub grade reaction modulus. Also the comparison between Vesic’s equation, Terzaghi’s one and obtained results are presented
INFLUENCE OF FIBER REINFORCEMENT ON TRIAXIAL SHEAR BEHAVIOR OF CEMENTED SANDY SOILS
A number of triaxialرایگان!
A number of triaxial tests were conducted for evaluation of randomly distributed fiber reinforcement effects on the behavior of cemented sand. Cemented samples were prepared by addition of Portland cement up to 3% by weight and were cured for about seven days after mixture. Polypropylene fibers with a length of 12 mm were added and mixed in three different weight percentages of 0%, 0.5%, 1%. Specimens were compacted in relative densities of 50% and 70%. Consolidated drained compression triaxial tests were performed under confinements of 100, 300 and 00 kPa. Tests results indicated that addition of polypropylene fiber to cemented sandy soils increases peak and residual strength. However, ultimate dilation decreases with enhancement of fiber content in cemented soil
Influence of the Type of Bracing System on Dynamic Response of Steel Frames
This paper presentsرایگان!
This paper presents an overview of comparing the dynamic response of steel braced frames subjected to seismic loadings. To perform this study, four types of bracing systems including X-bracing, Diagonal bracing, chevron-inverted V and chevron-inverted V type EBF, with 3, 6, 9 and 12- story frames are modeled and designed in accordance with AISC-ASD 89 code. To compare the dynamic characteristics of considered structural systems, nonlinear static analysis was conducted. The parameters which are evaluated and compared in these models are consisted of economical viewpoint with evaluating the weight of the structures based on steel used, the maximum roof displacement, behavior factor, ductility and the energy absorption. Results indicate that response modification factors (R) have different values depending on the brace configuration type and the building height. However, EBFs possess the highest amount of R factors, it seems in order to obtain the light weight structure, as well as the high energy absorption capacity, the best solution among compared bracing systems, is to apply the Inverted-chevron V bracing systems in steel frames. Obtained results are presented in relative diagrams and tables.
Investigation of the Rockfill Materials Properties Based on the Confining Pressure Effect and the Rock Type
Rockfill materials hرایگان!
Rockfill materials have been widely utilized in large structures as well as rockfill breakwaters and rockfill dams construction. Design procedure of such structures requires a rather precise estimation of geomechanical properties of such materials and hence, such properties are often evaluated with great difficulty. In this research, one of the important parameters commonly used in elasto-plastic constitutive model, namely dilation angle, is investigated by studying triaxial test results on five rockfill materials