Iranian Journal of Science and Technology Transactions of Civil Engineering
Volume:38 Issue: 1, 2014

In this article, a model of anisotropic damage coupled to plasticity based on thermodynamics framework is proposed. This model is introduced to describe the plastic and damage behavior of metals adequately. According to the elastic energy equivalence hypothesis between the undamaged material and the damaged material, the constitutive equations for the material in damaged configuration are written. The damaged material is modeled using the constitutive laws of the undamaged material in which the stresses in undamaged configuration are mapped by the stresses in damaged configuration. The damage is proposed through a damage mechanics framework, and the material degradation is determined by utilizing an anisotropic damage measure. In developing constitutive model, a plastic yield surface is used to demonstrate the onset of plasticity, and a damage surface is used to demonstrate the onset of damage. The plastic relationships have been written in undamaged configuration, and by using relationships between damaged and undamaged configurations, plastic equations are extended to damaged configuration. Numerical simulations of the elastoplastic deformation behavior of hydrostatic stress sensitive metals demonstrate the efficiency of the formulation, and also show the physical effects of parameters of the model. In order to achieve an equilibrated global solution, a nonlinear finite element program that employs a Newton Raphson iteration procedure is applied. Finally, the numerical results of some examples are validated with the existing experimental measurements.

Seismic performance evaluation of arch dams under different environmental conditions is vital for the structural safety of the existing dams. In the present paper, effects of the reservoir water in four different levels are investigated on the seismic performance of an arch dam. Dynamic equilibrium equations of the dam-reservoir-massless foundation coupled system are solved by Newmark’s time integration algorithm. Several three-component ground motions, obtained from deterministic hazard analysis of the dam site, are used for excitation of the finite element model.Seismic performance evaluation is utilized considering parameters such as crest displacement, demand capacity ratio, cumulative inelastic duration and extension of the overstressed areas on upstream and downstream faces obtained from linear elastic analyses. It is found that dewatering the reservoir leads to extension of the overstressed areas on both upstream and downstream faces and increases structural operating risk. In such a case, detailed nonlinear analyses, including joint and material nonlinearities, are required for more realistic results on crack propagation.

This paper reports the results of experimental, analytical and numerical studies on the effect of spacers on the behaviour and ultimate capacity of intermediate length Cold formed steel (CFS) open section column. A channel section is considered. Totally, four columns were experimented with hinged-hinged end condition. The section properties and selection of column length were obtained by performing elastic buckling analysis using CUFSM software. Finite Element models incorporating the geometric, material non linearities and initial geometric imperfection of the specimens were developed by using ANSYS and its accuracy was verified using the experimental results. Following the verification, a finite element parametric study was carried out by varying the depth and number of spacers. Experimental and numerical strength of open sections were compared with the predicted resistance by DSM – AISI S100:2007, AS/NZS: 4600- 2005, Eurocode 3 and IS: 801-1975. Effects of spacers on the ultimate load capacity of the column have been examined. The results are presented in the form of design charts. It is concluded that depth and number of spacers have significant influence on the behaviour and strength of the columns. Based on the nonlinear regression analysis the design equation was proposed for the selected section.

Maximum deflection in a beam is a design criteria and occurs generally at or close to the mid-span. A methodology has been developed for continuous composite beams to predict the inelastic mid-span deflections, d i (considering the cracking of concrete) from the elastic mid-span deflections, d e (neglecting the cracking of concrete). Nine significant structural parameters have been identified that govern the change in mid-span deflections. Six neural networks have been presented to cover the entire practical range of the beams. The proposed neural networks have been validated for a number of beams with different number of spans and the errors are small for practical purposes. The methodology enables rapid estimation of inelastic deflections in continuous composite beams and requires a computational effort that is a fraction of that required for the conventional iterative or incremental analysis. The methodology can easily be extended for large composite building frames where a huge savings in computational effort would result.

This paper presents the experimental investigations of the resistance of geopolymer mortar slabs to impact loading. For this, specimens of size 230mmx230mmx25mm with 4 layers of chicken mesh 2 layers of rectangular weld mesh and combination of single layer of weld mesh and four layers of chicken mesh were cast and subjected to impact loading by drop weight test.The results obtained show that the addition of the above mesh reinforcement has increased the impact residual strength ratio of geopolymer ferrocement by 4-28 that of the reference plain ferrocement mortar slab. The combination of 1 layer of weldmesh and 4 layers of chicken mesh of geopolymer ferrocement specimens show the best performance in the test, i.e. energy absorbed, residual impact strength ratio (Irs).It was concluded that the increase in volume fraction of reinforcement Vr, increases the energy absorption and also residual impact strength ratio of geopolymer ferrocement than that of ferrocement specimens.

Castellated beam is formed by modifying a standard rolled beam through creating a regular pattern of holes in the web. The main goal of manufacturing these beams is to increase the moment of inertia and section modulus, which results in greater strength and rigidity. In this study, the charged system search algorithm is used for obtaining the solution of the design problem. Here, castellated beams with hexagonal and circular openings are considered as design problems. The minimum cost is taken as the design objective function. The design methods used in this study are consistent with BS5950 part 1 and 3 and Euro code 3. A number of design examples are considered to demonstrate the efficiency of the presented algorithm. It is observed that optimization results obtained by the ECSS algorithm for three castellated beams with hexagonal openings have less cost in comparison to the cellular beams. Also, the results of these examples illustrate the capability of the ECSS algorithm in finding the optimum solution in less number of iterations.

In reinforced concrete design an important consideration that can be added to the requirements of strength and serviceability is ductility. This consideration is of importance to determine the amount of redistribution of moment that is possible in limited state design. Also, it is of importance in seismic design because to survive a severe earthquake, a structure should be capable of absorbing and dissipating energy by post-elastic deformations. To have an idea about the energy dissipation and ductility, it is essential to conduct impact test. An attempt is made in this paper to cast and test the cylindrical specimens made of Plain Cement Concrete (PCC) and Waste Tyre Rubber Aggregate Concrete (WTRAC) for impact loads with a steel ball drop weight.The test results show that the WTRAC with 6% replacement of both fine and coarse aggregate with rubber aggregates considerably improves the impact resistance and ductility characteristics. Regression model has been developed to estimate the impact strength for WTRAC specimen.

Earth retaining structures are referred to those structures which can control backfill heights that are just about to slide. Some examples of these structures are gravity and cantilever retaining walls. The cantilever retaining walls were utilized after the introduction of the reinforced-concrete construction technique. In the previous studies, the optimization of the retaining walls has been accomplished by quasi-static methods; however, in this paper a pseudodynamic approach is utilized. The advantage of the pseudo-dynamic analysis is that the phase difference effects and time can be entered in the design of retaining walls as the dynamic characteristics of the earthquake loading. Here, by optimizing a cantilever retaining wall via a recently developed method, so-called Ray Optimization, the design controlling parameters are investigated. Ray Optimization method is a multi-agent optimization method which is inspired from the concept of light refraction. In this method by moving the agents to new positions, the optimal solution is found.

In many developing countries, crushed rock is employed as a base course material for road pavement. Since crushed rock is required in large quantities, its shortages coupled with fuel price hike are having the effect of pushing up highway construction cost. In addition, the production of crushed rock involves drilling, blasting, crushing and road haulage, all of which create dust which is detrimental to the environment. Although lateritic soil is obtainable in many areas, it is too brittle and thus not suitable as road base course material. This paper presents the idea of adding cement to stabilize the lateritic aggregate. It compares the strength characteristics of cement-enhanced lateritic soil against those of crushed rock, and at the same time discusses their microstructure which was investigated using an X-ray diffraction machine (XRD) and a Scanning Electron Microscope (SEM). Mineralogical influences and the mechanism of soil-cement reaction of stabilized soils were also studied. Strength of the materials was measured using the unconfined compressive strength (UCS) and California Bearing Ratio (CBR) methods. The UCS and CBR tests indicated that when cement is added to lateritic soil at only 3% by weight, the resulting laterite-cement mixture exhibited a compressive strength as high as that of crushed rock. This shows that cement-enhanced lateritic soils are a viable substitute for crushed rock for road pavement construction.

This paper developed a new elastoplastic model for coarse-grained soils. Plastic potential surface was established by solving a differential dilatancy equation, which is obtained via the triaxial test results. This model obeys a non-associated flow rule; therefore, the yield surface is not consistent with the plastic potential surface. Expression of the yield surface was established similar to the plastic potential surface, but its shape is influenced not only by the stress ratio η, but the mean stress p. A unified hardening parameter that is independent of stress path is adopted, so that negative dilatancy and positive dilatancy properties of coarse-grained soils could both be described. In this research, elastoplastic formula of the proposed model is deduced. This model was also evaluated with several groups of test results under different stress paths (i.e. conventional triaxial tests, constant mean stress test and constant stress ratio test, etc.). Results showed that model predictions agree well with the test results.

Iran is a large producer of agricultural products. Irrigation water resources are limited and the water use efficiency is low. The micro irrigation system (MIS) is a versatile management tool that can increase water productivity. Although micro irrigation has a lot of advantages, some of its disadvantages are its difficult and time-consuming design. Economical analysis of the design is one of the main factors that should be considered. This study introduces a model developed in Visual Basic called Micro Irrigation Design Software (MIDS). The software can design a MIS for various crops, climate, and topographic conditions. It calculates the primary design parameters such as ETo, ETC, irrigation water depth, wetting pattern and leaching fraction. This software determines suitable arrangements of pipes, pipe length and diameter, emitters, hydraulic parameters design, and head loss. The manifolds and main pipes could be designed as monodiameter and telescopic, and the optimized size is reported to the user. The focus of this software is on economic analysis in accordance with electricity price, energy consumption use and initial and operation projects costs. To examine the software accuracy, some executed projects (manually designed) in Fars province were rechecked considering electricity energy price in Iran. Results showed that the Software was able to provide more reliable design parameters, also with electricity price build-up to more than a certain limit, It would be possible to increase the pipeline diameters to a certain extent with a better economic result during the project lifetime.

The main objective of this study was to identify the operating conditions which influence Ni(II) adsorption onto pre-treated walnut shell. For this purpose, in the first step, a series of experiments were planned according to a full 24 factorial experimental design. The factors investigated here were solution pH, adsorbent dose, the initial concentration of nickel, and temperature. The results predicted using the factorial regression model showed high values of regression coefficient (R2=99.55%), indicating good agreement with the experimental data. It was observed that the main effect of all the factors, besides the interaction of pH and metal concentration, were significant within a 95% confidence level, while for the conditions tested in this study, the pH of the solution was the most influential parameter in the removal of nickel.In the second stage, univariate studies were conducted to validate the results obtained in the first part and also to find the conditions that would give the highest removal of nickel from aqueous solutions. The univariate experimental results provided evidence supporting the sorption data obtained in the factorial design phase of this study. Under the optimal conditions obtained, the nickel ion adsorption equilibrium could be satisfactorily described by the Langmuir isotherm model. The maximum pre-treated walnut shell adsorption capacity for Ni(II) was 8.57 mg/g. The kinetics of Ni(II) adsorption onto pre-treated walnut shell followed the pseudo second order model.