More reliable responses for time integration analyses

Soroushian, A.,Farjoodi, J. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.16 No.2

One of the most versatile approaches for analyzing the dynamic behavior of structural systems is direct time integration of semi-discrete equations of motion. However responses computed by time integration are generally inexact and hence the corresponding errors would rather be studied in advance. In spite of the various error estimation formulations that exist in the literature, it is accepted practice to repeat the analyses with smaller time steps, followed by a comparison between the results. In this paper, after a review of this simple method and disregarding the round-off errors, a more efficient, reliable and yet simple method for estimating errors and enhancing the accuracy is proposed. The main objectives of this research are more realistic error estimation based on the concept of convergence, approximately controlling the reliability by comparing the actual rate of convergence with the integration method's order of accuracy, and enhancement of reliability by applying Richardson's extrapolation. Starting from the errors at specific time instants, the study is then generalized to cases in which the errors should be estimated and decreased at specific events e.g. peak responses. Numerical study illustrates the efficacy of the proposed method.

More reliabel responses for time integration analyses

A.Soroushian,J.Farjoodi 국제구조공학회 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.16 No.2

Coincidence of calcified carotid atheromatous plaque, osteoporosis, and periodontal bone loss in dental panoramic radiographs

Ramesh, Aruna,Soroushian, Sheila,Ganguly, Rumpa Korean Academy of Oral and Maxillofacial Radiology 2013 Imaging Science in Dentistry Vol.43 No.4

Purpose: This study was performed to assess the correlation of calcified carotid atheromatous plaque (CCAP), the mandibular cortical index, and periodontal bone loss in panoramic radiographs. Materials and Methods: One hundred eighty-five panoramic radiographs with CCAP and 234 without this finding were evaluated by 3 observers for the presence of osseous changes related to osteoporosis and periodontal bone loss. Chi-squared and Mann-Whitney U tests were used to compare the two groups for an association of CCAP with the mandibular cortical index and periodontal bone loss, respectively. Results: There was a statistically significant coincidence of CCAP and osseous changes related to osteopenia/osteoporosis, with a p-value <0.001. There was no statistically significant coincidence of CCAP and periodontal bone loss. When comparing the 2 groups, "With CCAP" and "Without CCAP", there was a statistically significant association with the mean body mass index (BMI), number of remaining teeth, positive history of diabetes mellitus, and vascular accidents. There was no statistically significant association with gender or a history of smoking. Conclusion: This study identified a possible concurrence of CCAP and mandibular cortical changes secondary to osteopenia/osteoporosis in panoramic radiographs. This could demonstrate the important role of dental professionals in screening for these systemic conditions, leading to timely and appropriate referrals resulting in early interventions and thus improving overall health.

Evaluation of the Reinforcement Efficiency of Low-Cost Graphite Nanomaterials in High-Performance Concrete

Peyvandi, Amirpasha,Soroushian, Parviz,Farhadi, Nafiseh,Balachandra, Anagi M. Springer-Verlag 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

Mechanical Properties of Cement Mortar: Development of Structure-Property Relationships

Ghebrab, Tewodros Tekeste,Soroushian, Parviz Korea Concrete Institute 2011 International Journal of Concrete Structures and M Vol.5 No.1

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

Mechanical Properties of Hydrated Cement Paste

Tewodros T. Ghebrab,Parviz Soroushian 한국콘크리트학회 2010 International Journal of Concrete Structures and M Vol.4 No.1

Theoretical models based on modern interpretations of the morphology and interactions of cement hydration products are developed for prediction of the mechanical properties of hydrated cement paste (hcp). The models are based on the emerging nanostructural vision of calcium silicate hydrate (C-S-H) morphology, and account for the intermolecular interactions between nano-scale calcium C-S-H particles. The models also incorporate the effects of capillary porosity and microcracking within hydrated cement paste. The intrinsic modulus of elasticity and tensile strength of hydrated cement paste are determined based on intermolecular interactions between C-S-H nano-particles. Modeling of fracture toughness indicates that frictional pull-out of the micro-scale calcium hydroxide (CH) platelets makes major contributions to the fracture energy of hcp. A tensile strength model was developed for hcp based on the linear elastic fracture mechanics theories. The predicted theoretical models are in reasonable agreements with empirical models developed based on the experimental performance of hcp.

Mechanical Properties of Hydrated Cement Paste: Development of Structure-property Relationships

Ghebrab, Tewodros T.,Soroushian, Parviz Korea Concrete Institute 2010 International Journal of Concrete Structures and M Vol.4 No.1

Theoretical models based on modern interpretations of the morphology and interactions of cement hydration products are developed for prediction of the mechanical properties of hydrated cement paste (hcp). The models are based on the emerging nanostructural vision of calcium silicate hydrate (C-S-H) morphology, and account for the intermolecular interactions between nano-scale calcium C-S-H particles. The models also incorporate the effects of capillary porosity and microcracking within hydrated cement paste. The intrinsic modulus of elasticity and tensile strength of hydrated cement paste are determined based on intermolecular interactions between C-S-H nano-particles. Modeling of fracture toughness indicates that frictional pull-out of the micro-scale calcium hydroxide (CH) platelets makes major contributions to the fracture energy of hcp. A tensile strength model was developed for hcp based on the linear elastic fracture mechanics theories. The predicted theoretical models are in reasonable agreements with empirical models developed based on the experimental performance of hcp.

Coincidence of calcified carotid atheromatous plaque, osteoporosis, and periodontal bone loss in dental panoramic radiographs

Aruna Ramesh,Sheila Soroushian,Rumpa Ganguly 대한영상치의학회 2013 Imaging Science in Dentistry Vol.43 No.4

Purpose: This study was performed to assess the correlation of calcified carotid atheromatous plaque (CCAP), the mandibular cortical index, and periodontal bone loss in panoramic radiographs. Materials and Methods: One hundred eighty-five panoramic radiographs with CCAP and 234 without this finding were evaluated by 3 observers for the presence of osseous changes related to osteoporosis and periodontal bone loss. Chi-squared and Mann-Whitney U tests were used to compare the two groups for an association of CCAP with the mandibular cortical index and periodontal bone loss, respectively. Results: There was a statistically significant coincidence of CCAP and osseous changes related to osteopenia/osteoporosis, with a p-value ⁄0.001. There was no statistically significant coincidence of CCAP and periodontal bone loss. When comparing the 2 groups, “With CCAP” and “Without CCAP”, there was a statistically significant association with the mean body mass index (BMI), number of remaining teeth, positive history of diabetes mellitus, and vascular accidents. There was no statistically significant association with gender or a history of smoking. Conclusion: This study identified a possible concurrence of CCAP and mandibular cortical changes secondary to osteopenia/osteoporosis in panoramic radiographs. This could demonstrate the important role of dental professionals in screening for these systemic conditions, leading to timely and appropriate referrals resulting in early interventions and thus improving overall health.

Mechanical Properties of Cement Mortar

Tewodros Tekeste Ghebrab,Parviz Soroushian 한국콘크리트학회 2011 International Journal of Concrete Structures and M Vol.5 No.1

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin’s bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

Nano-engineered joining employing surface modified graphite nanomaterials

Iman Harsini,Amirpasha Peyvandi,Parviz Soroushian,Anagi M. Balachandra 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.48 No.-

A new joining technique is reviewed where graphite nanomaterials are introduced at the interface to linkthe joining thermoplastic substrates and surfaces via massive interatomic bonds and other interactionsfollowed by microwave irradiation. Replicated tests on the “nano-engineered” joints indicatedimprovement in energy absorption capacity, impact resistance, strength, ductility fatigue resistanceof adhesive bonding as compared to conventional adhesive bonding. The demonstrated increase inmechanical properties, high efficiency in CNT-to-CNT and CNT-to-substrate joining and high level ofreplicability underline the potential for replacement of conventional adhesive bonding techniques withthe technique presented.