Showing 13–24 of 563 results
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
Modeling of welded angle connections in fire
In this paper, the bرایگان!
In this paper, the behavior of welded angle connections is studied at elevated temperatures using ABAQUS finite element software. In this study, steel members and connection components are considered to behave nonlinearly; the degradation of steel properties with increasing temperature is considered according to EC3 recommendations. The results of finite element and experimental tests conducted on welded angle connections in furnace fire conditions are compared, and the obtained failure modes and moment-rotation-temperature characteristics are in good agreement with those associated with experimental tests. Temperature loading similar to real fire condition is applied to each specimen to study the behavior of these connections in fire condition and the stiffness change with temperature increase under real fire condition is studied. The numerical results show that, in addition to material properties and connection geometry, the applied moments and temperature have significant effects on the stiffness of this kind of steel connection
Near-source ground motions effect on seismic reliability of reinforced concrete framed buildings
Near-Source ground mرایگان!
Near-Source ground motions have characteristics like pulse-like feature which make them distinctive from ordinary records. This paper discusses near-source ground motions effect on seismic reliability of reinforced concrete framed buildings. Since there are significant uncertainties in capacity of structural members and seismic excitations, reliability analysis can be an efficient method for assessing the seismic performance of a structural system. In this study the reliability evaluation is carried out by response analysis. Nonlinear dynamic analysis is used for assessment of structural seismic demands. Two sets of ordinary and near- source records are selected for focusing on comparison of near source ground motion effects with ordinary ones. A vector-valued intensity measure (IM) is adopted for applying the ground motions, which takes into account the spectral shape. Four example buildings with different heights are analyzed through three-dimensional nonlinear time history method, and capacity curves are obtained by incremental dynamic analysis (IDA). The P-Delta effect was considered in nonlinear analysis. In considering the effect of added shear walls on structural seismic reliability in near-source ground motions, the example buildings had two different kind of lateral load resisting systems, moment resisting frame system (MRF) and dual system consisting of moment resisting frames and shear walls. These approaches lead to a more general conclusion about the probability of failure of reinforced concrete framed buildings in near-source ground motions in comparison with ordinary ground motions. The results show that the added shear walls have a little effect on seismic reliability of high-rise reinforced concrete framed buildings subjected to near-source ground motions, but the added shear walls are relatively more beneficial for low-rise buildings against near-source ground motions.
NUMERICAL INVESTIGATION ON FAILURE MECHANISM OF SLENDER STRUCTURAL WALLS
The overall behavior...رایگان!
The overall behavior of the slender structural wall is determined by the behavior of the plastic hinge region at the wall base. A slender structural wall subject to a lateral load is damaged at the wall base. The failure of a slender structural wall with confined end-zones is caused by the crushing of the confined concrete, crushing of the unconfined concrete, fracture and buckling of the flexural re-bars, and fracture of the lateral re-bars. In this study, the crushing of the confined concrete and crushing of the unconfined concrete are investigated by section analysis. Moreover, the slender structural walls have flexural behavior and the behavior of bending members can be explained by moment– curvature relation. The moment-curvature relation for a section is determined using an analysis procedure that satisfies the requirements of strain compatibility, equilibrium of forces, and the stress-strain relations. The proposed moment-curvature relation is extended well into failure stage. Finally, correlation studies between analytical and experimental results are conducted with the objective to establish the validity of the proposed procedure. The occurrence of each failure modes depends on the quantity of confinement reinforcement, the depth of compressive zone, the depth of confined zone and properties of concrete and steel
Numerical investigation on shear strengthening of RC beams using Near Surface Mounted (NSM) FRP
A recent and promisiرایگان!
A recent and promising method for shear strengthening of reinforced concrete (RC) members is the use of near-surface mounted (NSM) fiber- reinforced polymer (FRP) reinforcement. So far, numerical studies concerning the NSM FRP strengthening method have been rather limited. Moreover, virtually no comprehensive analytical research is available on the behavior of shear-strengthened beams considering NSM FRP. This paper illustrates a numerical research program on shear strengthening of RC beams with NSM reinforcement, aimed to investigate individual parameters effecting numerical analysis and capture the effect of important issues. The proposed numerical analysis is validated against published experimental results. Maximum load bearing capacity of proposed numerical models was shown very good conformity to experimental results. As a result, the behavior of the FRP systems predicted by the analytical modeling was slightly stiffer than the values recorded experimentally; probable differences in stiffness are discussed in this study. In general, comparison between the numerical predictions and test results shows desirable agreement