• Structural Engineering and Mechanics
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• v.42 no.1
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• pp.73-93
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• 2012

With an active structural involvement in spiral case structure (SCS) that is always the design and research focus of hydroelectric power plant (HPP), the compressible membrane sandwiched between steel spiral case and surrounding reinforced concrete was often assumed to be linear elastic material in conventional design analysis of SCS. Unfortunately considerable previous studies have proved that the foam material serving as membrane exhibits essentially nonlinear mechanical behavior. In order to clarify the effect of membrane (foam) material's nonlinear stress-strain behavior on SCS, this work performed a case study on SCS with a compressible membrane using the ABAQUS code after a sound calibration of the employed constitutive model describing foam material. In view of the successful capture of fitted stress-strain curve of test by the FEM program, we recommend an application and dissemination of the simulation technique employed in this work for membrane material description to structural designers of SCS. Even more important, the case study argues that taking into account the nonlinear stress-strain response of membrane material in loading process is definitely essential. However, we hold it unnecessary to consider the membrane material's hysteresis and additionally, employment of nonlinear elastic model for membrane material description is adequate to the structural design of SCS. Understanding and accepting these concepts will help to analyze and predict the structural performance of SCS more accurately in design effort.

• Computers and Concrete
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• v.20 no.4
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• pp.381-389
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• 2017

The various types of structural materials that are available in the construction industry nowadays make it necessary to predict their stress-strain behavior. Geopolymer are alternatives for ordinary Portland cement concrete that are made from pozzolans activation. Due to relatively new material, many mechanical specifications of geopolymer are still not yet discovered. In this study, stress-strain behavior has been provided from experiments for unconfined geopolymers. Modulus of Elasticity and stress-strain behavior are critical requirements at analysis process and knowing complete stress-strain curve facilitates structural behavior assessment at nonlinear analysis for structures that have built with geopolymers. This study intends to investigate stress-strain behavior and modulus of elasticity from experimental data that belongs for geopolymers varying in fineness and mix design and curing method. For the sake of behavior determination, 54 types of geopolymer are used. Similar mix proportions are used for samples productions that have different fineness and curing approach. The results indicated that the compressive strength ranges between 7.7 MPa and 43.9 MPa at the age of 28 days curing.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.781-791
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• 2023

Lateral pressure plays a significant role in the stress-strain relationship of compressed concrete. Concrete's internal cracking resistance, ultimate strain, and axial strength are improved by confinement. This phenomenon influences the nonlinear behavior of reinforced concrete columns. Utilizing behavior factors to predict the nonlinear seismic responses of structures is prevalent in seismic codes, and this factor plays a vital role in the seismic responses of structures. This study aims to evaluate the confining action on the behavior factor of reinforced concrete moment resisting frames (RCMRFs) with shear walls (SWRCMRFs). To this end, a diverse range of mid-rise SW-RCMRFs was initially designed based on the Iranian national building code criteria. Second, the stress-strain curve of each element was modeled twice, both with and without the confinement phenomenon. Each frame was then subjected to pushover analysis. Finally, the analytical behavior factors of these frames were computed and compared to the Iranian seismic code behavior factor. The results demonstrate that confining action increased the behavior factors of SW-RCMRFs by 7-12%.

• Computers and Concrete
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• v.1 no.1
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• pp.77-98
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• 2004

This paper presents a numerical model for simulating the nonlinear response of reinforced concrete (RC) shear walls subject to cyclic loadings. The material behavior of cracked concrete is described by an orthotropic constitutive relation with tension-stiffening and compression softening effects defining equivalent uniaxial stress-strain relation in the axes of orthotropy. Especially in making analytical predictions for inelastic behaviors of RC walls under reversed cyclic loading, some influencing factors inducing the material nonlinearities have been considered. A simple hysteretic stress-strain relation of concrete, which crosses the tension-compression region, is defined. Modification of the hysteretic stress-strain relation of steel is also introduced to reflect a pinching effect depending on the shear span ratio and to represent an average stress distribution in a cracked RC element, respectively. To assess the applicability of the constitutive model for RC element, analytical results are compared with idealized shear panel and shear wall test results under monotonic and cyclic shear loadings.

• Journal of Biosystems Engineering
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• v.17 no.3
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• pp.260-271
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• 1992

Fruits are generally subjected to mechanical forces during harvesting, handling, and transportation that may cause damage in the form of bruises, punctures, and cracks. In order to prevent damage, and insure better quality fruits for consumers, it is very essential to study physical properties of these materials. The studies were conducted to examine the effect of storage period, storage condition, and other factors, such as loading rate and initial strain, on the stress relaxation behavior of the fruit flesh, and develop nonlinear viscoelastic models to represent its stress relaxation behavior. The following results were obtained from the study : 1. Since the viscoelastic behavior of the fruits flesh was nonlinear, the behavior was satisfactorily modelled as follows ; $${\delta}({\varepsilon},\;t)={\varepsilon}^A[B\;{\exp}(-Ct)+D\;{\exp}(-Ft)+G(-Ht)]$$ But, for the every strain applied, the stress relaxation behavior of the fruit flesh, such as apple and pear, could be well described by the Generalized Maxwell model, respectively. 2. The effect of loading rate on the stress relaxation behavior was remarkable. The higher loading rate resulted in the higher initial stress, and the faster stress relaxation. 3. The higher initial strain resulted in the higher initial stress, and stress relaxed at the large initial strain was also much higher than at the small initial strain. 4. Stress relaxation rate and quantity stored in the fruits at the low temperature storage were much higher than those at the normal temperature storage in the same storage period. Also, in all fruits tested, the longer storage period was the more relaxation rate and quantity were shown. These trends in the normal temperature condition was the more significant than in the low temperature condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5C
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• pp.183-190
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• 2009

It is necessary to predict the deformation and stresses on soils to establish the nonlinear stress-strain relationship of geomaterials at various strain levels. Especially, a need exists to establish the pre-failure nonlinear characteristic of cemented granular geomaterials used in road constructions. In this paper, therefore, conventional granular soils were mixed with various cementing materials, such as cement and fly ash from coal combustion by-products. Then, the normalized nonlinear behavior of cemented geomaterials was assessed using unconfined compression test. In addition, various constitutive models of soils were evaluated for estimating pre-failure non-linear behavior of cemented geomaterials from the test results.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.2
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• pp.59-68
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• 2018

This study compares true stress-true strain curves obtained by tensile tests of various piping materials with bi-linear stress-strain approximation suggested in the JSME Code Case(CC) Draft, a guideline for piping seismic inelastic response analysis. Based on the comparisons, the reliability of the bi-linear approximation is evaluated. It is found that bi-linear stress-strain curve of TP316 stainless steel is in good agreement with its true stress-true strain curve. However, Bi-linear stress-strain curves of TP304 stainless steel and carbon steels determined by the approximation cannot appropriately estimate their stress-strain behavior. Accordingly new bi-linear approximations for carbon steels and low-alloy steels are proposed. The proposed bi-linear approximations for carbon and low-alloy steels, which include the temperature effect on strength and hardening of material, estimate their stress-strain behavior reasonably well.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.95-100
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• 1999

A FEA(finite element analysis model) was proposed to study stress and strain distributions in thick composites with fiber waviness and initial curvature under flexural loading. Three types of model with initial curvature were considered in this study: flat, concave and concave models. In the analysis, both material and geometrical nonlinearities were incorporated. Four point flexural tests were conducted on the flat specimens to obtain the flexural behavior of thick composites experimentally. It was concluded that the predictions from the models were in good agreement with the experimental results. It was shown that the stress and strain distributions as well as nonlinear flexural behaviors of thick composites were significantly affected by the fiber waviness and initial curvature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1569-1580
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• 2001

A new nonlinear near-wall turbulence model is developed to predict turbulent flow and heat transfer in strongly nonequilibrium flows. The k-$\varepsilon$-f$\sub$${\mu}$/, model of Park and Sung$\^$(1)/ is extended to a nonlinear formulation. The stress-strain relationship is the thrid-order in the mean velocity gradients. The strain dependent coefficients are obatined from the realizability constraints and the singular behavior at large strains. An improved explicit heat flux model is proposed with the aid of Cayley-Hamilton theorem. This new model includes the quadratic effects of flow deformations. The near-wall asymptotic behavior is incorporated by modifying the f$\sub$λ/ function. The model performance is shown to be satisfactory.

• Transactions of Materials Processing
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• v.22 no.4
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• pp.216-222
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• 2013

Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].