scholarly journals An accurate and computationally efficient three dimensional nonlinear model for the analysis of large-scale RC structures subjected to cyclic and dynamic loading conditions

2019 ◽  
Author(s):  
Χρήστος Μουρλάς
Keyword(s):  
Nonlinear Model ◽  
Large Scale ◽  
Three Dimensional ◽  
Discrete Elements ◽  
Computationally Efficient ◽  
Rc Structures ◽  
Smeared Crack Approach ◽  
Smeared Crack ◽  
Pinching Effect ◽  
Dynamic Loading Conditions

Η προσομοίωση της περίπλοκης συμπεριφοράς του οπλισμένου σκυροδέματος όταν υποβάλλεται σε διαξονική ή τριαξονική ανακυκλική ένταση αποτελεί αντικείμενο έρευνας πολλών ερευνητών τις τελευταίες δεκαετίες. Το σκυρόδεμα είναι ένα ανομοιογενές σύνθετο υλικό όπου παρουσιάζει πολύπλοκη συμπεριφορά η οποία επηρεάζεται από της συνθήκες φόρτισης, την γεωμετρία διατομών και φορέα, ποσοστό οπλισμού και διαδικασία κατασκευής. Τα καταστατικά μοντέλα που έχουν προταθεί στην βιβλιογραφία, εξαρτώνται από ένα σύνολο παραμέτρων με τις οποίες καλύπτουν ένα περιορισμένο φάσμα προβλημάτων-φορέων (δοκούς, στύλους, τοιχία). Το προτεινόμενο καταστατικό μοντέλο περιγράφεται μέσω κατάλληλου αλγοριθμικού σχεδιασμού και βασίζεται στην ψαθυρότητα του υλικού κάνοντας χρήση των καταστατικών σχέσεων που έχουν προκύψει από τριαξονική πειραματική διερεύνηση (Kotsovos and Newman 1977). Ένα βασικό προνόμιο του προτεινόμενου καταστατικού μοντέλου είναι οι καταστατικές σχέσεις εξαρτώνται μόνο από την μονοαξονική αντοχή του σκυροδέματος σε θλίψη fc. Η ρηγμάτωση προσομοιώνεται με την μέθοδο της διανεμημένης ρηγμάτωσης (smeared crack approach). Επιπλέον, ένα νέο κριτήριο κλεισίματος των ρωγμών προτάθηκε το οποίο βοήθησε στην ευστάθεια και ακρίβεια της υπολογιστικής διαδικασίας στην περίπτωση της ανάλυσης υπό οριακή ανακυκλιζόμενη φόρτιση του εξεταζόμενου φορέα. Επιπλέον προτάθηκαν δύο παράμετροι βλάβης οι οποίοι απομειώνουν την συνεισφορά του σκυροδέματος και του οπλισμού λόγω έντονη ρηγμάτωσης και του αριθμού του ανοιγοκλεισίματος των ρωγμών. Με αυτόν τον τρόπο το μοντέλο κατάφερε να προσομοιώσει ακριβέστερα την συμπεριφορά κατασκευών που υπόκεινται σε πολλούς κύκλους φόρτισης καθώς και σε δυναμικές φορτίσεις.Για την αριθμητική προσομοίωση του σκυροδέματος χρησιμοποιήθηκαν τρισδιάστατα 8-κομβικά πεπερασμένα στοιχεία. Παράλληλα οι ράβδοι οπλισμού προσομοιώθηκα ως ενσωματωμένα διακριτά στοιχεία (embedded discrete elements) στο εσωτερικό των 8-κομβικών στοιχείων σκυροδέματος. Για τα στοιχεία του οπλισμού χρησιμοποιήθηκαν τα στοιχεία δοκού με την μέθοδο δυνάμεων (natural beam column flexibility based elements). Επίσης χρησιμοποιήθηκε ένας υβριδικός τρόπος διακριτοποίησης για κατασκευές μεγάλης κλίμακας από οπλισμένο σκυρόδεμα, με τον οποίο το προτεινόμενο τρισδιάστατο λεπτομερές προσομοίωμα χρησιμοποιείται σε περιοχές όπου η συμπεριφορά του υλικού χαρακτηρίζεται ως διατμητική (κόμβοι τοιχία) ενώ οι περιοχές του σκυροδέματος που χαρακτηρίζονται από καμπτική συμπεριφορά (ενδιάμεσα τμήματα δοκών και κολώνων) διακριτοποιούνται με χρήση δομικών στοιχείων δοκού. Με αυτόν τον τρόπο, απομειώνεται σημαντικά το υπολογιστικό κόστος χωρίς σημαντικές επιπτώσεις στην ακρίβεια των αποτελεσμάτων. Το προτεινόμενο μοντέλο χρησιμοποιήθηκε για την ανάλυση φορέων με διαφορετική μηχανική συμπεριφορά όπως τοιχία, δοκούς, κόμβους από οπλισμένο σκυρόδεμα που καταπονούνται σε ανακυκλιζόμενη φόρτιση. Η ανάλυση έδειξε ότι τα αποτελέσματα παρουσιάζουν ικανοποιητική ακρίβεια σε σύγκριση με τα πειραματικά αποτελέσματα χαρακτηριστικά όπως την απομείωση της δυσκαμψίας, της αντοχής και της στένωσης των κύκλων υστέρησης (pinching effect). Το υβριδικό μοντέλο χρησιμοποιήθηκε για την ανάλυση ενός τετραωρόφου κτιρίου από οπλισμένο σκυρόδεμα σε ανακυκλιζόμενη φόρτιση που αναπαριστούσε χαμηλής και υψηλής έντασης σεισμική φόρτιση. Τέλος εξετάστηκαν εναλλακτικοί τρόποι ενίσχυσης του κτιρίου όπου διεξάχθηκε ιδιομορφική ανάλυση για την διερεύνηση της αποδοτικότητας τους.

scholarly journals A Multidimensional and Multiscale Model for Pressure Analysis in a Reservoir-Pipe-Valve System

2018 ◽  
Author(s):  
Feng Jie Zheng ◽  
Fu Zheng Qu ◽  
Xue Guan Song
Keyword(s):  
Pressure Fluctuation ◽  
Large Scale ◽  
Three Dimensional ◽  
Industrial Process ◽  
Multiscale Model ◽  
Computational Time ◽  
Small Scale ◽  
Cfd Model ◽  
Computationally Efficient ◽  
Proposed Model

Reservoir-pipe-valve (RPV) systems are widely used in many industrial process. The pressure in an RPV system plays an important role in the safe operation of the system, especially during the sudden operation such as rapid valve opening/closing. To investigate the pressure especially the pressure fluctuation in an RPV system, a multidimensional and multiscale model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the model, the reservoir is modeled by a zero-dimensional virtual point, the pipe is modeled by a one-dimensional MOC, and the valve is modeled by a three-dimensional CFD model. An interface model is used to connect the multidimensional and multiscale model. Based on the model, a transient simulation of the turbulent flow in an RPV system is conducted, in which not only the pressure fluctuation in the pipe but also the detailed pressure distribution in the valve are obtained. The results show that the proposed model is in good agreement with the full CFD model in both large-scale and small-scale spaces. Moreover, the proposed model is more computationally efficient than the CFD model, which provides a feasibility in the analysis of complex RPV system within an affordable computational time.

scholarly journals A Multidimensional and Multiscale Model for Pressure Analysis in a Reservoir-Pipe-Valve System

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Feng Jie Zheng ◽  
Chao Yong Zong ◽  
William Dempster ◽  
Fu Zheng Qu ◽  
Xue Guan Song
Keyword(s):  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Multiscale Model ◽  
Computational Time ◽  
Small Scale ◽  
Dimensional System ◽  
Cfd Model ◽  
Computationally Efficient ◽  
Proposed Model

Reservoir-pipe-valve (RPV) systems are widely used in many industrial processes. The pressure in an RPV system plays an important role in the safe operation of the system, especially during the sudden operations such as rapid valve opening or closing. To investigate the pressure response, with particular interest in the pressure fluctuations in an RPV system, a multidimensional and multiscale model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the model, the reservoir is modeled as a zero-dimensional virtual point, the pipe is modeled as a one-dimensional system using the MOC, and the valve is modeled using a three-dimensional CFD model. An interface model is used to connect the multidimensional and multiscale model. Based on the model, a transient simulation of the turbulent flow in an RPV system is conducted in which not only the pressure fluctuation in the pipe but also the detailed pressure distribution in the valve is obtained. The results show that the proposed model is in good agreement when compared with a high fidelity CFD model used to represent both large-scale and small-scale spaces. As expected, the proposed model is significantly more computationally efficient than the CFD model. This demonstrates the feasibility of analyzing complex RPV systems within an affordable computational time.

Numerical simulation of the debonding process in pull-out tests of near-surface mounted FRP rod in concrete

2019 ◽  
Vol 37 (3) ◽  
pp. 1109-1130
Author(s):  
Tie-Lin Chen ◽  
Wenbin Tao ◽  
Wenjun Zhu ◽  
Mozhen Zhou
Keyword(s):  
Three Dimensional ◽  
Crack Model ◽  
Bond Failure ◽  
Near Surface ◽  
Content Type ◽  
Rc Structures ◽  
Pull Out ◽  
Smeared Crack ◽  
Near Surface Mounted ◽  
Debonding Process

Purpose Near-surface mounted (NSM) fiber-reinforced polymer (FRP) rod is extensively applied in reinforced concrete (RC) structures. The mechanical performances of NSM FRP-strengthened RC structures depend on the bond behavior between NSM reinforcement and concrete. This behavior is typically studied by performing pull-out tests; however, the failure behavior, which is crucial to the local debonding process, is not yet sufficiently understood. Design/methodology/approach In this study, a three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure process in pull-out tests of NSM FRP rod in concrete. The smeared crack model is used to capture the cohesion failures in the adhesive or concrete. The interfacial constitutive model is applied to simulate the adhesion failures on the FRP-adhesive and concrete-adhesive contact interfaces. Findings The present method is first validated by two simple examples and then applied to a practical NSM FRP system. This work studied in detail the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone. The developed method provides a practical and convenient tool applicable for further investigations on the debonding mechanism for the NSM FRP rod in concrete. Originality/value A three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure in NSM FRP-strengthened RC structures. The smeared crack model and the interfacial constitutive model are introduced to develop a convenient approach to analyze the failures in adhesive, concrete and related interfaces. The developed numerical method is applicable for studying the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone in detail.

scholarly journals Structural geology and geophysics as a support to build a hydrogeologic model of granite rock

Solid Earth ◽  
2016 ◽  
Vol 7 (3) ◽  
pp. 881-895 ◽  
Author(s):  
Lurdes Martinez-Landa ◽  
Jesús Carrera ◽  
Andrés Pérez-Estaún ◽  
Paloma Gómez ◽  
Carmen Bajos
Keyword(s):  
Structural Geology ◽  
Large Scale ◽  
Preferential Flow ◽  
Three Dimensional ◽  
Pumping Test ◽  
Discrete Elements ◽  
Flow Paths ◽  
Preferential Flow Paths

Abstract. A method developed for low-permeability fractured media was applied to understand the hydrogeology of a mine excavated in a granitic pluton. This method includes (1) identifying the main groundwater-conducting features of the medium, such as the mine, dykes, and large fractures, (2) implementing this factors as discrete elements into a three-dimensional numerical model, and (3) calibrating these factors against hydraulic data . A key question is how to identify preferential flow paths in the first step. Here, we propose a combination of several techniques. Structural geology, together with borehole sampling, geophysics, hydrogeochemistry, and local hydraulic tests aided in locating all structures. Integration of these data yielded a conceptual model of the site. A preliminary calibration of the model was performed against short-term (< 1 day) pumping tests, which facilitated the characterization of some of the fractures. The hydraulic properties were then used for other fractures that, according to geophysics and structural geology, belonged to the same families. Model validity was tested by blind prediction of a long-term (4 months) large-scale (1 km) pumping test from the mine, which yielded excellent agreement with the observations. Model results confirmed the sparsely fractured nature of the pluton, which has not been subjected to glacial loading–unloading cycles and whose waters are of Na-HCO3 type.

scholarly journals An Enriched Constitutive Model for Fracture Propagation Analysis Using the Material Point Method

2014 ◽  
Vol 553 ◽  
pp. 731-736 ◽  
Author(s):  
Giang Dinh Nguyen
Keyword(s):  
Large Scale ◽  
Constitutive Models ◽  
Material Point Method ◽  
Fracture Propagation ◽  
Material Point ◽  
Point Method ◽  
Localized Deformation ◽  
New Approach ◽  
Smeared Crack Approach ◽  
Smeared Crack

We develop a novel constitutive modeling approach for the analysis of fracture propagation in quasi-brittle materials using the Material Point Method. The kinematics of constitutive models is enriched with an additional mode of localized deformation to take into account the strain discontinuity once cracking has occurred. The crack details therefore can be stored at material point level and there is no need to enrich the kinematics of finite elements to capture the localization caused by fracturing processes. This enhancement also removes the drawback of classical smeared crack approach in producing unphysical snapping back constitutive responses when the spatial resolution is not fine enough. All these facilitate the implementation of the new approach in the Material Point Method for analysis of large scale problems. Numerical examples of fracture propagation are used to demonstrate the effectiveness and potentials of the new approach.

scholarly journals 3D Fiber-Based Frame Element with Multiaxial Stress Interaction for RC Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Alexander Kagermanov ◽  
Paola Ceresa
Keyword(s):  
Reinforced Concrete ◽  
Three Dimensional ◽  
Beam Theory ◽  
Material Model ◽  
Element Formulation ◽  
Multiaxial Stress ◽  
Rc Structures ◽  
Frame Element ◽  
Out Of Plane ◽  
Smeared Crack

A three-dimensional fiber-based frame element accounting for multiaxial stress conditions in reinforced concrete structures is presented. The element formulation relies on the classical Timoshenko beam theory combined with sectional fiber discretization and a triaxial constitutive model for reinforced concrete consisting of an orthotropic, smeared crack material model based on the fixed crack assumption. Torsional effects are included through the Saint-Venant theory of torsion, which accounts for out-of-plane displacements perpendicular to the cross section due to warping effects. The formulation was implemented into a force-based beam-column element and verified against monotonic and cyclic tests of reinforced concrete columns in biaxial bending, beams in combined flexure-torsion, and flexure-torsion-shear.

scholarly journals Structural geology and geophysics as a key to build a hydrogeologic model of granite rock to support a mine

2016 ◽  
Author(s):  
L. Martinez Landa ◽  
J. Carrera ◽  
A. Perez-Estaún ◽  
P. Gomez ◽  
C. Bajos
Keyword(s):  
Structural Geology ◽  
Large Scale ◽  
Preferential Flow ◽  
Three Dimensional ◽  
Pumping Test ◽  
Discrete Elements ◽  
Flow Paths ◽  
Preferential Flow Paths

Abstract. A methodology developed for low permeability fractured media has been applied to understand the hydrogeology of a mine excavated in a granitic pluton. This methodology consists of (1) identifying the main ground water conducting features of the medium, such as the mine, dykes and large fractures, (2) implementing them as discrete elements into a three-dimensional numerical model, and (3) calibrating them against hydraulic data (Martínez-Landa and Carrera, 2005b). The key question is how to identify preferential flow paths in the first step. Here, we propose a combination of several techniques. Structural geology, together with borehole samples, geophysics, hydrogeochemistry and local hydraulic tests aided in locating all structures. Integrating these data yields a conceptual model of the site. A preliminary calibration of the model was performed against short-term (less than a day) pumping tests, which helped in the characterization of some fractures. Their hydraulic properties were then used for other fractures that, according to geophysics and structural geology, belonged to the same families. Model validity was tested by blind prediction of a long-term (4 months) large-scale (1 km) pumping test from the mine, which yielded an excellent agreement with observations. Model results confirm the sparsely fractured nature of the pluton, which has not been subjected to glacial loading-unloading cycles and whose waters are of Na-HCO3 type.

Sign in / Sign up

Export Citation Format

Share Document