Evaluating the spread plasticity model of IDARC for inelastic analysis of reinforced concrete frames

Mehdi Izadpanah,AliReza Habibi 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.2

There are two types of nonlinear analysis methods for building frameworks depending on the method of modeling the plastification of members including lumped plasticity and distributed plasticity. The lumped plasticity method assumes that plasticity is concentrated at a zero-length plastic hinge section at the ends of the elements. The distributed plasticity method discretizes the structural members into many line segments, and further subdivides the cross-section of each segment into a number of finite elements. When a reinforced concrete member experiences inelastic deformations, cracks tend to spread form the joint interface resulting in a curvature distribution. The program IDARC includes a spread plasticity formulation to capture the variation of the section flexibility, and combine them to determine the element stiffness matrix. In this formulation, the flexibility distribution in the structural elements is assumed to be the linear. The main objective of this study is to evaluate the accuracy of linear flexibility distribution assumed in the spread inelasticity model. For this purpose, nonlinear analysis of two reinforced concrete frames is carried out and the linear flexibility models used in the elements are compared with the real ones. It is shown that the linear flexibility distribution is incorrect assumption in cases of significant gravity load effects and can be lead to incorrect nonlinear responses in some situations.

Evaluation of moment amplification factors for RCMRFs designed based on Iranian national building code

Habibi, Alireza,Izadpanah, Mehdi,Rohani, Sina Techno-Press 2020 Advances in concrete construction Vol.9 No.1

Geometric nonlinearity can significantly affect load-carrying capacity of slender columns. Dependence of structural stability on columns necessitates the consideration of second-order effects in the design process of columns, appropriately. On the whole, the design codes present a simplified procedure for second order analysis of slender columns. In this approximate method, the end moments of columns resulted from linear analysis (first-order) are multiplied by the recommended moment amplification factors of codes to achieve magnified moments of the second-order analysis. In the other approach, the equilibrium equations are directly solved for the deformed configuration of structure, so the resulting moments and deflections contain the influence of slenderness and increase more rapidly than do loads. The aim of this study is to evaluate the accuracy of moment amplification factors of Iranian national building code whose provisions are similar to the ACI requirement. Herein, finite element method is used to achieve magnified end moments of reinforced concrete moment resisting frames, and the outcomes are compared with the moments acquired based on the proposed approximate method by Iranian national building code. The results show that the approximate method of Iranian code for calculating magnified moments has significant errors for both unbraced and braced columns.

Combination of isogeometric analysis and extended finite element in linear crack analysis

Shojaee, S.,Ghelichi, M.,Izadpanah, E. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.1

This paper intends to present an application of isogeometric analysis in crack problems. An isogeometric formula is developed based on NURBS basis functions - enriched and adopted via X-FEM enrichment functions. The proposed method which is represented by the combination of the two above-mentioned methods, first by using NURBS functions models the geometry exactly and then by defining level set function on domain, identifies available discontinuity in elements. Additional DOFs are allocated to elements containing the crack and X-FEM enrichment functions enrich approximate solution. Moreover, a subelement refinement technique is used to improve the accuracy of integration by the Gauss quadrature rule. Finally, several numerical examples are illustrated to demonstrate the effectiveness, robustness and accuracy of the proposed method during calculation of crack parameters.

An experimental and modeling study of CO₂ solubility in a 2-amino-2-methyl-1-propanol (AMP) + N-methyl-2-pyrrolidone (NMP) solution

Pakzad, Peyman,Mofarahi, Masoud,Izadpanah, Amir Abbas,Afkhamipour, Morteza,Lee, Chang-Ha Elsevier 2018 Chemical engineering science Vol.175 No.-

<P><B>Abstract</B></P> <P>In this study, an experimental setup based on the static-synthetic method was used to measure the new experimental data of CO<SUB>2</SUB> solubility in an aqueous solution of 2-amino-2-methyl-1-propanol (AMP) + N-methyl-2-pyrrolidone (NMP) solution. For the static-synthetic method, the mass balance of compositions and the pressure–volume–temperature conditions were used for measuring the amount of absorbed CO<SUB>2</SUB> by the AMP+NMP solution. The measurements were performed over a temperature range of 313.15–353.15 K, CO<SUB>2</SUB> partial pressure up to 316.7 kPa, and in different concentrations of the AMP+NMP solution. Two models, modified Kent–Eisenberg, and Deshmukh–Mather, based on the empirical correlations and activity-fugacity approach, respectively, were used for the prediction of experimental data. The parameters of the equilibrium constants of the protonation and carbamate reactions for the modified Kent–Eisenberg model and the interaction parameters for Deshmukh–Mather model were obtained. For validation of our setup, a new set of experimental data for the solubility of CO<SUB>2</SUB> in an aqueous solution of AMP, methyldiethanolamine (MDEA) and diethanolamine (DEA) were measured and compared with existing experimental data in the literature, and good results were obtained. The results of the modeling study showed that the Deshmukh–Mather model gave a better prediction of experimental CO<SUB>2</SUB> loadings data than the modified Kent–Eisenberg. Also, the results showed that the solubility of CO<SUB>2</SUB> in an aqueous solution of AMP+NMP increases as the CO<SUB>2</SUB> partial pressure increases while the temperature decreases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New experimental data for CO<SUB>2</SUB> solubility in AMP+NMP+H<SUB>2</SUB>O system was presented. </LI> <LI> Experimental data predicted by modified Kent–Eisenberg and Deshmukh–Mather models. </LI> <LI> Clausius–Clapeyron equation was used for calculation of the absorption heat. </LI> <LI> Deshmukh–Mather model predicted the experimental data with an AARD% of 3.08. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Confinement effect on the behavior factor of dual reinforced concrete moment-resisting systems with shear walls

Alireza Habibi,Mehdi Izadpanah,Yaser Rahmani 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.85 No.6

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%.

Improving the linear flexibility distribution model to simultaneously account for gravity and lateral loads

AliReza Habibi,Mehdi Izadpanah 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.1

There are two methods to model the plastification of members comprising lumped and distributed plasticity. When a reinforced concrete member experiences inelastic deformations, cracks tend to spread from the joint interface resulting in a curvature distribution; therefore, the lumped plasticity methods assuming plasticity is concentrated at a zero-length plastic hinge section at the ends of the elements, cannot model the actual behavior of reinforced concrete members. Some spread plasticity models including uniform, linear and recently power have been developed to take extended inelastic zone into account. In the aforementioned models, the extended inelastic zones in proximity of critical sections assumed close to connections are considered. Although the mentioned assumption is proper for the buildings simply imposed lateral loads, it is not appropriate for the gravity load effects. The gravity load effects can influence the inelastic zones in structural elements; therefore, the plasticity models presenting the flexibility distribution along the member merely based on lateral loads apart from the gravity load effects can bring about incorrect stiffness matrix for structure. In this study, the linear flexibility distribution model is improved to account for the distributed plasticity of members subjected to both gravity and lateral load effects. To do so, a new model in which, each member is taken as one structural element into account is proposed. Some numerical examples from previous studies are assessed and outcomes confirm the accuracy of proposed model. Also comparing the results of the proposed model with other spread plasticity models illustrates glaring error produced due to neglecting the gravity load effects.

Which Patients Are at Higher Risk for Residual Valves After Posterior Urethral Valve Ablation?

Mehdi Shirazi,Mohamadreza Farsiani,Mohammad Natami,Kiomars Izadpanah,Amir Malekahmadi,Abbasali Khakbaz 대한비뇨의학회 2014 Investigative and Clinical Urology Vol.55 No.1

Purpose: To find patients at high risk of obstructive remnant leaflets after valve ablationamong boys with posterior urethral valve (PUV), we evaluated any possible relationshipbetween preoperative findings in our patients and residual obstructive leafletsafter valve ablation. Materials and Methods: We retrospectively reviewed the medical records of 55 patientswith PUV that was treated by the same surgeon between 2008 and 2012. Of these, 37patients (67.3%) had no obstructive remnant leaflets (group A) and 18 patients (32.7%)had obstructive remnant leaflets (group B) in follow-up cystoscopy. Preoperative clinicaland radiological findings were evaluated and compared between the groups. Results: Among all the preoperative data we examined, the analysis revealed that ageat the time of surgery (median age: group A, 15 months; group B, 7 months; p=0.017),echogenicity of kidneys (p<0.05), presence of vesicoureteral reflux (p<0.05), and gradeof reflux (p<0.05) were significantly different between the groups. Method of valveablation, anterior-posterior diameters of the renal pelvis, renal cortical thickness, bladderwall thickening, and scarring on the dimercaptosuccinic acid scan showed no significantdifferences between the two groups. Conclusions: In our patients, younger age at surgery time, hyperechogenicity of renalparenchyma, presence of vesicoureteral reflux, and grade 4 or 5 reflux before surgeryhad a significant relationship with residual valves. More studies may result in enhancedmanagement of patients at high risk of residual valves after PUV ablation, becausethe sooner the obstruction is resolved entirely, the better the outcome.

Practical relations to quantify the amount of damage of SWRCFs using pushover analysis

Habibi, Ali Reza,Samadi, Mohammad,Izadpanah, Mehdi Techno-Press 2020 Advances in concrete construction Vol.10 No.3

Quantifying the amount of damage of structures under earthquakes is an interesting issue that researchers have attended on and have presented some damage indices. Whereas a lot of damage indices have been introduced based on nonlinear dynamic analysis, computational effort, the calculus complicacy and time-consuming of this analysis are the main drawbacks to widespread use of these indices. The objective of this study is to quantify the damage of Shear Wall Reinforced Concrete Frames (SWRCFs) based on pushover analysis as a procedure that can reflect the behavior of structures from elastic to collapse. For this purpose, firstly, several SWRCFs are designed and the capacity spectrum of each one is achieved via pushover analysis. After that, the static damage indices of the designed frames are obtained. Then, nonlinear dynamic analyses are performed on these frames and the Park and Ang damage index as the basis damage criterion is achieved. Afterward, some relations are presented to predict the dynamic damage of these frames via pushover analysis. Eventually, to confirm the validity of the proposed relations, the values of Park and Ang damage index of three new SWRCFs are acquired once utilizing nonlinear dynamic analysis and again applying the introduced relations. Outcomes prove the validity of some presented damage indices.

Constrained and non-constrained aerodynamic optimization using the adjoint equations approach

Mohamad Hamed Hekmat,Masoud Mirzaei,Ehsan Izadpanah 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.9

In this research, the continuous adjoint method is applied to optimize an airfoil in subsonic and transonic flows. An inverse design problem is solved to evaluate the ability of the optimization algorithm and then, two types of optimizations, constrained and non-constrained, are investigated in a drag minimization problem. In the non-constrained drag minimization problem, the optimization is performed in a fixed angle of attack with neither geometric nor aerodynamic constraint, but in the constrained drag minimization problem, the optimization is performed in a fixed lift coefficient. Comparison of the results of these two optimizations shows the effects of the constraint on the optimization trend and the optimized geometry. Moreover, imposing the aerodynamic constraint increased the computational costs of the adjoint method. In constrained and non-constrained drag minimization problems, the surface points are adopted as design variables to show the performance of the adjoint equations approach in problems with numerous design variables.

Combination of isogeometric analysis and extended finite element in linear crack analysis

S. Shojaee,M. Ghelichi,E. Izadpanah 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.1

This paper intends to present an application of isogeometric analysis in crack problems. An isogeometric formula is developed based on NURBS basis functions - enriched and adopted via X-FEM enrichment functions. The proposed method which is represented by the combination of the two abovementioned methods, first by using NURBS functions models the geometry exactly and then by defining level set function on domain, identifies available discontinuity in elements. Additional DOFs are allocated to elements containing the crack and X-FEM enrichment functions enrich approximate solution. Moreover, a subelement refinement technique is used to improve the accuracy of integration by the Gauss quadrature rule. Finally, several numerical examples are illustrated to demonstrate the effectiveness, robustness and accuracy of the proposed method during calculation of crack parameters.