Civil Engineering Infrastructures Journal
Year:2010 | Volume:44 | Issue:3|Papers Count:15

In this research, materially nonlinear dynamic analysis of concrete arch dam using Concrete Elasto-Plastic models is attempted. At first, common models for nonlinear analysis of massive plain concrete structures are investigated and finally concrete material model of Wiliam–Warnke (five parameters version) for tensional and compression failure is selected. This model is used versus other usual models such as Mohr-Coulomb and Drucker-Prager models for analysis of Morrow Point concrete arch dam under an intensive ground motion of order of 1.0g for the peak ground acceleration. A suitable algorithm for stress integration and conversion of engineering stresses to objective ones is proposed. This stress calculation is particularly desired in large deformations analysis. Fluid-structure interaction is also considered including water compressibility and reservoir bottom absorption. Staggered approach is used for coupled-fluid structure solutions. Although the foundation is considered as rigid. It is demonstrated that usual nonlinear plastic models such as Mohr-Columb and Drucker – Prager models unlike special concrete models are not capable to capture real behavior of such concrete structure. It is suggested that special concrete models such as William–Warnke must be used for the plastic nonlinear analysis of concrete arch dam.

A correct estimation of the sediment transport rate and the amount of sedimentation is among the important and effective factors to be considered in the design of ports and coastal structures. Although many research efforts are now conducted on the influencing parameters of the sediment transport to quantify the transport rate, the approximate and relatively simple formulas are still routinely used. CERC and Kamphuis are among the well-known formulas for the calculation of the potential longshore sediment transport (LST) rate. However, the accuracy of predictions of transport rates, based on the applications of these formulas at different locations of the world, has not been similar. In present paper, using a limited number of data related to local waves and characteristics of grain size distributions, the longshore sediment transport rates at some of the southern coastlines of Iran have been calculated and the results have been compared with the actual sediment impoundments at breakwaters and groins. The volumes of sedimentation are derived from the comparisons of hydrographic surveys. Verification of these formulas at southern coasts of the country reveals the higher accuracy of Kamphuis formula in comparison to CERC formula. A relationship was also presented for the calculation of K parameter of CERC formula as a function of the surf similarity parameter.

This paper investigates the damage pattern of reinforced concrete beams using flexibility matrices. The flexibility matrices were calculated from experimental modal data which were obtained by performing static and dynamic tests on concrete beam specimens. The variations of flexibility matrices were determined using a proposed method based on the Ritz vectors. This method characterizes the damage areas by a parabolic shaped crack zone in the middle part of the beams. The parabolic zone builds up as the damages develop and reduces after CFRP strengthening. The proposed method based on the Ritz vectors agrees well with the methods that detect the stiffness reduction due to bending cracks. By employing this model, the loss of stiffness along the length of beam specimens was estimated in the mathematical framework.

Dam break flood on a mobile bed is simulated using a two dimensional numerical model. The governing equations are solved in the framework of the finite volume method. In order to achieve a second order method both in time and space, the Mac Cormack predictor corrector scheme is used. To overcome the problem of unphysical oscillations the component-wise TVD technique is implemented which is a simple TVD method because it is not necessary to use the Jacobian matrix and its eigenvalues. In the study of mobile bed hydraulics it is necessary to pay due attention to the strong interaction between water and sediment and morphological river changes. Thus the conservation laws are solved in a coupled manner, i. e. the transport equations for water and sediment are solved simultaneously. The model has been verified by its application for different test cases and the results are satisfactory.

The design of concrete arch dams is usually based on linear analyses. However, results of such analyses are not (at least locally) realistic. In order to overcome this shortcoming, different approaches may be utilized. One approach is application of elasto– plastic behavior for foundation and abutments materials. This paper studies the effect of application of the Mohr-Coulomb elasto­ plastic model for foundation on the stresses and displacements of concrete arch dams. For this purpose, displacements and stress distributions are compared for two different approaches against each other. These two cases are relying on elastic and elasto-plastic modeling of foundation rock medium. Furthermore, a parametric study is subsequently carried out in the nonlinear approach which includes parameters such as cohesion, friction angle and dilation angle. The analyses are carried out by utilizing ABAQUS general purpose finite element program. It should be mentioned that the Karun 3 double curvature concrete arch dam is utilized in the present study.

Imperfect elements having initial curvature are usually used in construction and erection of the structures. In this paper, the explicit stiffness matrix for imperfect element is derived. The nonlinear tangent stiffness matrix of the beam-column subjected to the axial force, nodal moments and the lateral uniformly distributed load is calculated. Based on this matrix, advanced analysis of the plane steel frame is performed. Both tensile and compressive axial loads are also taken into account by one formula. By using the proposed stiffness matrix, the load-displacement curve is compared with the accurate plastic region methods, and in the most cases, good agreement is found. Comparing the obtained results with other references shows the accuracy and capabilities of the new formulation in evaluation of the steel frame load capacity having inelastic second-order behavior.

Passive control methods, by reducing seismic demand and increasing ductility, can reduce magnitude of seismic damage. One of the most effective passive control methods is vertical shear link or shear panel system (SPS), in which vertical shear link pieces are installed between node of chevron braces and the flange of floor beam. In designing this system, the vertical link beam first yields and dissipates seismic energy, and the remaining elements would stay elastic. Unlike eccentrically braced frames, EBFs, these pieces are not embedded in floor and can be exchanged easily with least effort and less cost after earthquakes. In this paper, five tests were conducted on five specimens of steel braced frames having vertical shear links in different lengths and sections. The results of tests show that the overall performance of these pieces is convincing. In all specimens, shear distortion in vertical shear links varied between 0.128 and 0.156 rad before failure. All specimens had stable hysteretic curves and showed good energy dissipation. Also other structural elements like beams, columns and braces remained elastic. Averages ratios of equivalent viscous damping in specimens varied between 26.7 and 30.6%. In all specimens that had one or more stiffeners (except SPS1 where its weld failed) ductility coefficients reached about 7. Also response modification factors of specimens varied between 7.15 and 10.65 (while 7.15 belonged to SPS1 and response modification factors of other specimens were in range of 8.97 to 10.65 and had more compatibility and less dispersion). Overall, performances of vertical shear links regarding energy dissipation and ductility increase were satisfactory based on experimental results.

The usual finite element methods reduce the infinite number of degree of freedom (D. O. F. ) of system to a model with a limited number of D. O. F. while capturing the significant physical behavior. Base relation methods reduce number of D. O. F. in new coordinate. One of the base relation methods is gained from Ritz-Wilson vectors which is much better than the conventional base relation methods and eigen value methods in a lot of cases because of simpler and dependence on dynamic load. Also to be costly in large system calculations and to ignore loading parameter can be mentioned as the disadvantages of eigen vectors. Fewer number of required Ritz vectors in comparison with eigen values and considering place distribution of external loading and dominant frequency content of loading has pushed the researchers into applying Ritz vectors. Base alteration methods in nonlinear problems are not usually much applicable due to frequent matrix change of system. Generalized one dimensional subspace method presents an appropriate solution for geometric nonlinearity problems by means of Ritz-Wilson technique. In this article generalized one dimensional subspace method is combined with mode-acceleration technique in order to analyze nonlinear dynamic problems. Based on inside error component and generalized one dimensional subspace method, a modified criterion using mode-acceleration technique in order to update required base vectors for stiffness changes in nonlinear dynamic analysis is proposed. The results indicate that the accuracy and speed of the modified method are appropriate.

Tabarak-Abad dam is a clay core, earth-rock fill dam with the height of 74 m above its rocky foundation. The dam with the crest length of 193.5 m is located on the Tabarak-Abad River at north east of IRAN. Construction of the dam began on January 2003 and completed on October 2004. The dam is extensively instrumented to provide data required for monitoring. The paper will describe the instrumentation system installed in the dam body with back analyses and monitoring the water pressure, earth pressure and deformation.

In this paper, the influence of the axial force on the bending behavior of the extended end plate moment connection is investigated. First, finite element analysis was done on two different shape connections without considering the axial force. This analysis elucidates that results from finite element model has a very suitable correlation with predicted values obtained from yield line theory to anticipate end plate yielding. These two models include both thick and intermediate end plate behavior and they are designed with strong column, strong beam and weak connection design philosophy. Then the influence of axial force (tension and compression) on bending behavior of the specified connections was analyzed by finite element method. In the cases of tensile axial force loading, the decrease in bending moment was observed and on the other hand in some cases of compressive axial force loading, the no-prognosticated failure mode was clarified. Finally, it revealed that the presence of axial force on the beam, obviously affects the connection response.

Recently, scientists developed the seismic rehabilitation of structures and their points of view were changed from strength to the performance of structures. Nonlinear Static Procedure (NSP) or pushover analysis is a new method that is chosen for its speed and simplicity in calculations. “Seismic Rehabilitation Code” & FEMA356 considered this method. Result of this analysis is a target displacement that is the base of the performance of the structures. Exact recognition of this displacement could develop the workability of pushover analysis. Although Nonlinear Dynamic Analysis can exactly apply the seismic ground motions, it consumes time, costs very high and is more difficult than other methods. So it is not applicable as much as NSP. A Coefficient used in NSP for determining the target displacement (C2, Stiffness and Strength Degradations coefficient) is applicable for correcting the errors due to eliminating the stiffness and strength degradations in hysteretic-cycles. In this study, three concrete frames with shear walls have been analyzed by several accelerations. After comparing pushover analysis with dynamic analysis, calculated C2 was comprised with values in rehabilitation codes.

A search of the literature reveals that the studies related to the effects of the degree of bolt tightness on the behaviour of the joints and consequently on the response of the space structures are rather limited. The experimental study of the effects of the bolt tightness on the rigidity of the structures of the compression members of the space structures is the objective of the present research. In order to study of the effect of bolt tightness on the rigidity of the space structures, several experiments were carried out on 10 meters by 10 meters MERO type double layer grids. The grids were assembled with different degrees of tightness of the bolts and a concentrated load was applied at the central node of upper layer of the grids and deflections of a number of bottom layer nodes were measured. The studies has indicated that the degree of bolt tightness has a significant effect on the rigidity of the space structures. In this paper, Different aspect of the bolt tightness on the behaviour of space structures has been considered and some recommendations have been presented in the context of the design assisted by testing.

Many of the structural fractures are happen as the result of ruptures of the constituent materials. The beginning of these ruptures coincides with the cracks and causes serious threats to the structure’s behavior. Therefore, many studies have been carried out on methods of identification and indication of the cracks. In this article, at first the dynamic transient analysis is performed with finite element software (ANSYS) on the structure. Then acceleration time history have been decomposed to the component of wavelet packet using software (MATLAB), then the energy rate index are calculated for each of signals, which illustrated with WPERI. The results show that these Indexes are sensitive and exact indicators for identification of crack.

Distinct target of this paper is development of ' Implicit Discrete Element Method (DEM) ' in three dimensions for estimating the ultimate bearing capacity of shallow foundations on layered (non­ homogeneous) soils consisting of sand overlying sand or clay overlying sand and vice versa with different shear resisting parameters. In this method, shear resisting parameters and density of each layer is used separately for that layer and involves in calculating internal and external forces. Comparisons are made with classical methods where ever applicable.