AN ANISOTROPIC DAMAGE MODEL FOR METALS BASED ON IRREVERSIBLE THERMODYNAMICS FRAMEWORK
text
article
2014
eng
In this article, a model of anisotropic damage coupled to plasticity based onthermodynamics framework is proposed. This model is introduced to describe the plastic anddamage behavior of metals adequately. According to the elastic energy equivalence hypothesisbetween the undamaged material and the damaged material, the constitutive equations for thematerial in damaged configuration are written. The damaged material is modeled using theconstitutive laws of the undamaged material in which the stresses in undamaged configuration aremapped by the stresses in damaged configuration. The damage is proposed through a damagemechanics framework, and the material degradation is determined by utilizing an anisotropicdamage measure. In developing constitutive model, a plastic yield surface is used to demonstratethe 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 usingrelationships between damaged and undamaged configurations, plastic equations are extended todamaged configuration.Numerical simulations of the elastoplastic deformation behavior of hydrostatic stresssensitive metals demonstrate the efficiency of the formulation, and also show the physical effectsof parameters of the model. In order to achieve an equilibrated global solution, a nonlinear finiteelement program that employs a Newton Raphson iteration procedure is applied. Finally, thenumerical results of some examples are validated with the existing experimental measurements.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
157
173
https://ijstc.shirazu.ac.ir/article_1861_5086bc8bed124bca870c5f5e4c8624dd.pdf
dx.doi.org/10.22099/ijstc.2014.1861
STRUCTURAL SAFETY OF HIGH ARCH DAMS WITH VARIABLE WATER LEVELS BASED ON SEISMIC PERFORMANCE EVALUATION
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article
2014
eng
Seismic performance evaluation of arch dams under different environmental conditionsis vital for the structural safety of the existing dams. In the present paper, effects of the reservoirwater in four different levels are investigated on the seismic performance of an arch dam. Dynamicequilibrium equations of the dam-reservoir-massless foundation coupled system are solved byNewmark’s time integration algorithm. Several three-component ground motions, obtained fromdeterministic 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 onupstream and downstream faces obtained from linear elastic analyses. It is found that dewateringthe reservoir leads to extension of the overstressed areas on both upstream and downstream facesand increases structural operating risk. In such a case, detailed nonlinear analyses, including jointand material nonlinearities, are required for more realistic results on crack propagation.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
175
190
https://ijstc.shirazu.ac.ir/article_1862_4f699246f1a05752a368b2512ee11fec.pdf
dx.doi.org/10.22099/ijstc.2014.1862
STUDY ON THE EFFECT OF SPACERS ON THE ULTIMATE CAPACITY OF INTERMEDIATE LENGTH THIN WALLED SECTION UNDER COMPRESSION
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article
2014
eng
This paper reports the results of experimental, analytical and numerical studies on theeffect 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 wereexperimented with hinged-hinged end condition. The section properties and selection of columnlength were obtained by performing elastic buckling analysis using CUFSM software. FiniteElement models incorporating the geometric, material non linearities and initial geometricimperfection of the specimens were developed by using ANSYS and its accuracy was verifiedusing the experimental results. Following the verification, a finite element parametric study wascarried out by varying the depth and number of spacers. Experimental and numerical strength ofopen 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 thecolumn have been examined. The results are presented in the form of design charts. It is concludedthat depth and number of spacers have significant influence on the behaviour and strength of thecolumns. Based on the nonlinear regression analysis the design equation was proposed for theselected section.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
191
204
https://ijstc.shirazu.ac.ir/article_1863_e16fc189512fa66834b0670038afaa2d.pdf
dx.doi.org/10.22099/ijstc.2014.1863
NEURAL NETWORKS FOR DEFLECTIONS IN CONTINUOUS COMPOSITE BEAMS CONSIDERING CONCRETE CRACKING
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article
2014
eng
Maximum deflection in a beam is a design criteria and occurs generally at or close tothe mid-span. A methodology has been developed for continuous composite beams to predict theinelastic mid-span deflections, d i (considering the cracking of concrete) from the elastic mid-spandeflections, d e (neglecting the cracking of concrete). Nine significant structural parameters havebeen identified that govern the change in mid-span deflections. Six neural networks have beenpresented to cover the entire practical range of the beams. The proposed neural networks havebeen validated for a number of beams with different number of spans and the errors are small forpractical purposes. The methodology enables rapid estimation of inelastic deflections incontinuous composite beams and requires a computational effort that is a fraction of that requiredfor the conventional iterative or incremental analysis. The methodology can easily be extended forlarge composite building frames where a huge savings in computational effort would result.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
205
221
https://ijstc.shirazu.ac.ir/article_1864_f197957e888bdce23c766f5631aa1be8.pdf
dx.doi.org/10.22099/ijstc.2014.1864
BEHAVIOUR OF GEOPOLYMER FERROCEMENT SLABS SUBJECTED TO IMPACT
text
article
2014
eng
This paper presents the experimental investigations of the resistance of geopolymermortar slabs to impact loading. For this, specimens of size 230mmx230mmx25mm with 4 layersof chicken mesh 2 layers of rectangular weld mesh and combination of single layer of weld meshand 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 theimpact residual strength ratio of geopolymer ferrocement by 4-28 that of the reference plainferrocement mortar slab. The combination of 1 layer of weldmesh and 4 layers of chicken mesh ofgeopolymer 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 ofreinforcement Vr, increases the energy absorption and also residual impact strength ratio ofgeopolymer ferrocement than that of ferrocement specimens.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
223
233
https://ijstc.shirazu.ac.ir/article_1865_10e0d2b6dbe0b78ab737f7acb372642b.pdf
dx.doi.org/10.22099/ijstc.2014.1865
COST OPTIMIZATION OF CASTELLATED BEAMS USING CHARGED SYSTEM SEARCH ALGORITHM
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article
2014
eng
Castellated beam is formed by modifying a standard rolled beam through creating aregular pattern of holes in the web. The main goal of manufacturing these beams is to increase themoment 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. Theminimum cost is taken as the design objective function. The design methods used in this study areconsistent with BS5950 part 1 and 3 and Euro code 3. A number of design examples areconsidered to demonstrate the efficiency of the presented algorithm. It is observed thatoptimization results obtained by the ECSS algorithm for three castellated beams with hexagonalopenings have less cost in comparison to the cellular beams. Also, the results of these examplesillustrate the capability of the ECSS algorithm in finding the optimum solution in less number ofiterations.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
235
249
https://ijstc.shirazu.ac.ir/article_1866_2e8b3fddd29084ce37647b183f696135.pdf
dx.doi.org/10.22099/ijstc.2014.1866
EXPERIMENTAL BEHAVIOUR OF WASTE TYRE RUBBER AGGREGATE CONCRETE UNDER IMPACT LOADING
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article
2014
eng
In reinforced concrete design an important consideration that can be added to therequirements of strength and serviceability is ductility. This consideration is of importance todetermine the amount of redistribution of moment that is possible in limited state design. Also, itis of importance in seismic design because to survive a severe earthquake, a structure should becapable of absorbing and dissipating energy by post-elastic deformations. To have an idea aboutthe energy dissipation and ductility, it is essential to conduct impact test. An attempt is made inthis paper to cast and test the cylindrical specimens made of Plain Cement Concrete (PCC) andWaste 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 aggregatewith rubber aggregates considerably improves the impact resistance and ductility characteristics.Regression model has been developed to estimate the impact strength for WTRAC specimen.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
251
259
https://ijstc.shirazu.ac.ir/article_1867_2993bc91429fcd2b273a69fc06061e75.pdf
dx.doi.org/10.22099/ijstc.2014.1867
OPTIMAL DESIGN OF CANTILEVER RETAINING WALLS USING RAY OPTIMIZATION METHOD
text
article
2014
eng
Earth retaining structures are referred to those structures which can control backfillheights that are just about to slide. Some examples of these structures are gravity and cantileverretaining walls. The cantilever retaining walls were utilized after the introduction of thereinforced-concrete construction technique. In the previous studies, the optimization of theretaining walls has been accomplished by quasi-static methods; however, in this paper a pseudodynamicapproach is utilized. The advantage of the pseudo-dynamic analysis is that the phasedifference effects and time can be entered in the design of retaining walls as the dynamiccharacteristics of the earthquake loading. Here, by optimizing a cantilever retaining wall via arecently developed method, so-called Ray Optimization, the design controlling parameters areinvestigated. Ray Optimization method is a multi-agent optimization method which is inspiredfrom the concept of light refraction. In this method by moving the agents to new positions, theoptimal solution is found.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
261
274
https://ijstc.shirazu.ac.ir/article_1868_5a381ccb37b587b39fbd5483262295a1.pdf
dx.doi.org/10.22099/ijstc.2014.1868
FEASIBILITY OF LATERITE-CEMENT MIXTURE AS PAVEMENT BASE COURSE AGGREGATE
text
article
2014
eng
In many developing countries, crushed rock is employed as a base course material forroad pavement. Since crushed rock is required in large quantities, its shortages coupled with fuelprice hike are having the effect of pushing up highway construction cost. In addition, theproduction of crushed rock involves drilling, blasting, crushing and road haulage, all of whichcreate dust which is detrimental to the environment. Although lateritic soil is obtainable in manyareas, it is too brittle and thus not suitable as road base course material. This paper presents theidea of adding cement to stabilize the lateritic aggregate. It compares the strength characteristics ofcement-enhanced lateritic soil against those of crushed rock, and at the same time discusses theirmicrostructure which was investigated using an X-ray diffraction machine (XRD) and a ScanningElectron Microscope (SEM). Mineralogical influences and the mechanism of soil-cement reactionof stabilized soils were also studied. Strength of the materials was measured using the unconfinedcompressive strength (UCS) and California Bearing Ratio (CBR) methods. The UCS and CBRtests indicated that when cement is added to lateritic soil at only 3% by weight, the resultinglaterite-cement mixture exhibited a compressive strength as high as that of crushed rock. Thisshows that cement-enhanced lateritic soils are a viable substitute for crushed rock for roadpavement construction.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
275
284
https://ijstc.shirazu.ac.ir/article_1869_c80dfff2848c728a29aa17d5204d6d3f.pdf
dx.doi.org/10.22099/ijstc.2014.1869
AN ELASTOPLASTIC CONSTITUTIVE MODEL FOR COARSE-GRAINED SOILS
text
article
2014
eng
This paper developed a new elastoplastic model for coarse-grained soils. Plasticpotential surface was established by solving a differential dilatancy equation, which is obtained viathe triaxial test results. This model obeys a non-associated flow rule; therefore, the yield surface isnot consistent with the plastic potential surface. Expression of the yield surface was establishedsimilar to the plastic potential surface, but its shape is influenced not only by the stress ratio η, butthe mean stress p . A unified hardening parameter that is independent of stress path is adopted, sothat negative dilatancy and positive dilatancy properties of coarse-grained soils could both bedescribed. In this research, elastoplastic formula of the proposed model is deduced. This modelwas also evaluated with several groups of test results under different stress paths (i.e. conventionaltriaxial tests, constant mean stress test and constant stress ratio test, etc.). Results showed thatmodel predictions agree well with the test results.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
285
296
https://ijstc.shirazu.ac.ir/article_1870_de51ae6693efe5ca65ea5569f1f6f4cd.pdf
dx.doi.org/10.22099/ijstc.2014.1870
DEVELOPMENT OF MICRO IRRIGATION DESIGN SOFTWARE (MIDS) TO OPTIMIZE TOTAL PROJECT COST AND HYDRAULIC PARAMETERS
text
article
2014
eng
Iran is a large producer of agricultural products. Irrigation water resources are limitedand the water use efficiency is low. The micro irrigation system (MIS) is a versatile managementtool that can increase water productivity. Although micro irrigation has a lot of advantages, someof its disadvantages are its difficult and time-consuming design. Economical analysis of the designis one of the main factors that should be considered. This study introduces a model developed inVisual Basic called Micro Irrigation Design Software (MIDS). The software can design a MIS forvarious crops, climate, and topographic conditions. It calculates the primary design parameterssuch as ETo, ETC, irrigation water depth, wetting pattern and leaching fraction. This softwaredetermines suitable arrangements of pipes, pipe length and diameter, emitters, hydraulicparameters design, and head loss. The manifolds and main pipes could be designed as monodiameterand telescopic, and the optimized size is reported to the user. The focus of this software ison economic analysis in accordance with electricity price, energy consumption use and initial andoperation projects costs. To examine the software accuracy, some executed projects (manuallydesigned) in Fars province were rechecked considering electricity energy price in Iran. Resultsshowed that the Software was able to provide more reliable design parameters, also with electricityprice build-up to more than a certain limit, It would be possible to increase the pipeline diametersto a certain extent with a better economic result during the project lifetime.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
297
307
https://ijstc.shirazu.ac.ir/article_1871_78b760cb3d49a25739b93286a825122e.pdf
dx.doi.org/10.22099/ijstc.2014.1871
INVESTIGATION OF FACTORS AFFECTING REMOVAL OF NICKEL BY PRE-TREATED WALNUT SHELLS USING FACTORIAL DESIGN AND UNIVARIATE STUDIES
text
article
2014
eng
The main objective of this study was to identify the operating conditions whichinfluence Ni(II) adsorption onto pre-treated walnut shell. For this purpose, in the first step, a seriesof experiments were planned according to a full 24 factorial experimental design. The factorsinvestigated here were solution pH, adsorbent dose, the initial concentration of nickel, andtemperature. The results predicted using the factorial regression model showed high values ofregression coefficient (R2=99.55%), indicating good agreement with the experimental data. It wasobserved that the main effect of all the factors, besides the interaction of pH and metalconcentration, were significant within a 95% confidence level, while for the conditions tested inthis 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 thefirst part and also to find the conditions that would give the highest removal of nickel fromaqueous solutions. The univariate experimental results provided evidence supporting the sorptiondata obtained in the factorial design phase of this study. Under the optimal conditions obtained, thenickel ion adsorption equilibrium could be satisfactorily described by the Langmuir isothermmodel. The maximum pre-treated walnut shell adsorption capacity for Ni(II) was 8.57 mg/g. Thekinetics of Ni(II) adsorption onto pre-treated walnut shell followed the pseudo second-ordermodel.
Iranian Journal of Science and Technology Transactions of Civil Engineering
Shiraz University
2228-6160
38
v.
C1+
no.
2014
309
324
https://ijstc.shirazu.ac.ir/article_1872_86e82d033345734099e2049d0f150afc.pdf
dx.doi.org/10.22099/ijstc.2014.1872