Christos Zeris | National Technical University of Athens (original) (raw)

Papers by Christos Zeris

Bulletin of Earthquake Engineering

Over the years a large number of finite element analysis programs have been developed in order to... more Over the years a large number of finite element analysis programs have been developed in order to investigate the behaviour of reinforced concrete (RC) elements and structures. These are based on the use of a wide range of concrete material laws, the majority of which can be classified as empirical, plastic, visco-plastic, damage and hybrid, depending on the theory or combination of theories upon which their analytical formulation is based. The formulation of most, if not all, of these material models relies heavily on a number of empirical parameters, the inclusion of which is essential for defining material behaviour. These parameters are usually linked to post-peak concrete characteristics such as, for example, strain softening, tension stiffening, shear-retention ability, etc, coupled with stress-and/or strainrate sensitivity when high-rate loading problems are considered; their values often vary depending on the type of problem investigated. Three widely used packages, (LS-DYNA, ANSYS and ABAQUS), are adopted in the present work in order to investigate analytically the experimental response of simply supported RC beams under monotonic loading applied at various rates, ranging from static and earthquake to rates encountered in impact and blast problems. A fundamental assumption adopted in the case studies investigated herein, is that for the case of high-rate-loading, concrete constitutive behaviour is essentially independent of the loading rate and that the effect of the latter on structural response can be primarily attributed to inertia forces. The predictions obtained are compared with published experimental data as well as the predictions of a specialized in concrete structures analysis package (RC-FINEL), which, in contrast with the above packages, incorporates a fully brittle material law for the constitutive description of concrete behaviour under triaxial loading. The aim of the present investigation is to explore the generality and applicability of the FE models presently adopted and their ability to yield realistic predictions of structural concrete behaviour.

Journal of Structural Engineering, 2015

Technical Instructions concerning the properties and the use of Self-Compacting Concrete [avail. ... more Technical Instructions concerning the properties and the use of Self-Compacting Concrete [avail. in Greek only].

Aci Structural Journal

The experimental work described herein investigates the applicability of the compressive-force pa... more The experimental work described herein investigates the applicability of the compressive-force path (CFP) method in the repair and/or strengthening of reinforced-concrete (RC) beam-columns, using fiber-reinforced polymer (FRP) sheets. This investigation is based on test results of eight linear members, tested at the Reinforced Concrete Laboratory of the National Technical University of Athens, under different normalized axial load and shear span-to-depth ratios. These specimens had been previously tested and subsequently repaired or strengthened using FRP sheets. For purpose of comparison, either the truss analogy (TA) theory currently adopted, or the CFP method are used for redesign. All specimens are retested under constant axial load and cyclic transverse load, similar to the virgin control specimens. Retest results indicate that, unlike specimens repaired/strengthened by conventional methods that failed early in a brittle manner, all the members repaired by the CFP method reache...

Encyclopedia of Earthquake Engineering, 2014

Το παρόν τεύχος είναι η πέμπτη Τεχνική Οδηγία της Επιτροπής Τεχνολογίας Σκυροδέματος του Συλλόγου... more Το παρόν τεύχος είναι η πέμπτη Τεχνική Οδηγία της Επιτροπής Τεχνολογίας Σκυροδέματος του Συλλόγου Πολιτικών Μηχανικών Ελλάδας. Στην παρούσα έκδοση γίνεται αναφορά στο «Αυτοσυμπυκνούμενο Σκυρόδεμα», μια καινοτομία που μετά την ανάπτυξή της στην Ιαπωνία κατά τη δεκαετία του 1980 έχει πολλάκις χαρακτηριστεί ως επανάσταση στο χώρο των κατασκευών από σκυρόδεμα. Επόμενο είναι λοιπόν το καινοτόμο αυτό προϊόν, μαζί με τις απαιτήσεις που οδήγησαν εξαρχής στην εμφάνισή του, να κερδίζει όλο και περισσότερο έδαφος και στην ελληνική αγορά κι επομένως να προκύπτει η ανάγκη για ενημέρωση των συναδέλφων γύρω από τα ειδικά του χαρακτηριστικά και τις ιδιαιτερότητες της χρήσης του.

Anti-Corrosion Methods and Materials, 2014

Purpose -This paper aims to present results of an experimental investigation on a series of scale... more Purpose -This paper aims to present results of an experimental investigation on a series of scaled reinforced concrete column elements which were subjected to chloride exposure under accelerated conditions under a concurrent service axial load, over a period. In the presence of an axial load, directed microcracks of increasing density and width are introduced in the concrete mass, depending on the axial load level. Such cracks are believed to enhance the intrusion rate of chlorides in the concrete, relative to what is obtained in the normally performed unloaded specimen tests. Design/methodology/approach -Eighteen column specimens were tested over two chloride exposure periods, of duration up to a maximum of six months. Three different service axial load levels were considered, namely, none, 22 per cent and 43 per cent of the normalized axial load capacity of the columns. Findings -The results indicate that the specimens loaded to the higher axial load, which closely resembles actual service situation of such type of elements, exhibited up to ten times faster rates of induced current flow under a constant applied voltage of 500 mV, compared to the unloaded and less loaded specimens. Practical implications -It is proven that the presence of axial load influences the rate of chloride ingress in columns and, therefore, should be taken into account in estimating the concrete cover of such elements in durability design. Originality/value -The influence of axial loading on corrosion rate has not been considered in published experimental and analytical studies of chloride ingression. These studies have typically so far considered the accelerated corrosion of unloaded column specimens.

... steel requirements increase to between 2.00 to 2.70% of the gross section steel ratio. ... Th... more ... steel requirements increase to between 2.00 to 2.70% of the gross section steel ratio. ... The sensitivity of this assumption is currently examined by modelling the columns using refined inelastic ... of 11%), ranging between 195% to 210% and similar sensitivity to frame irregularity. ...

Technical Instructions concerning the structural design, the various different stages of construc... more Technical Instructions concerning the structural design, the various different stages of construction process and the quality control of concrete floors (slabs on ground) [avail. in Greek only].

Bulletin of Earthquake Engineering

Over the years a large number of finite element analysis programs have been developed in order to... more Over the years a large number of finite element analysis programs have been developed in order to investigate the behaviour of reinforced concrete (RC) elements and structures. These are based on the use of a wide range of concrete material laws, the majority of which can be classified as empirical, plastic, visco-plastic, damage and hybrid, depending on the theory or combination of theories upon which their analytical formulation is based. The formulation of most, if not all, of these material models relies heavily on a number of empirical parameters, the inclusion of which is essential for defining material behaviour. These parameters are usually linked to post-peak concrete characteristics such as, for example, strain softening, tension stiffening, shear-retention ability, etc, coupled with stress-and/or strainrate sensitivity when high-rate loading problems are considered; their values often vary depending on the type of problem investigated. Three widely used packages, (LS-DYNA, ANSYS and ABAQUS), are adopted in the present work in order to investigate analytically the experimental response of simply supported RC beams under monotonic loading applied at various rates, ranging from static and earthquake to rates encountered in impact and blast problems. A fundamental assumption adopted in the case studies investigated herein, is that for the case of high-rate-loading, concrete constitutive behaviour is essentially independent of the loading rate and that the effect of the latter on structural response can be primarily attributed to inertia forces. The predictions obtained are compared with published experimental data as well as the predictions of a specialized in concrete structures analysis package (RC-FINEL), which, in contrast with the above packages, incorporates a fully brittle material law for the constitutive description of concrete behaviour under triaxial loading. The aim of the present investigation is to explore the generality and applicability of the FE models presently adopted and their ability to yield realistic predictions of structural concrete behaviour.

Journal of Structural Engineering, 2015

Technical Instructions concerning the properties and the use of Self-Compacting Concrete [avail. ... more Technical Instructions concerning the properties and the use of Self-Compacting Concrete [avail. in Greek only].

Aci Structural Journal

The experimental work described herein investigates the applicability of the compressive-force pa... more The experimental work described herein investigates the applicability of the compressive-force path (CFP) method in the repair and/or strengthening of reinforced-concrete (RC) beam-columns, using fiber-reinforced polymer (FRP) sheets. This investigation is based on test results of eight linear members, tested at the Reinforced Concrete Laboratory of the National Technical University of Athens, under different normalized axial load and shear span-to-depth ratios. These specimens had been previously tested and subsequently repaired or strengthened using FRP sheets. For purpose of comparison, either the truss analogy (TA) theory currently adopted, or the CFP method are used for redesign. All specimens are retested under constant axial load and cyclic transverse load, similar to the virgin control specimens. Retest results indicate that, unlike specimens repaired/strengthened by conventional methods that failed early in a brittle manner, all the members repaired by the CFP method reache...

Encyclopedia of Earthquake Engineering, 2014

Το παρόν τεύχος είναι η πέμπτη Τεχνική Οδηγία της Επιτροπής Τεχνολογίας Σκυροδέματος του Συλλόγου... more Το παρόν τεύχος είναι η πέμπτη Τεχνική Οδηγία της Επιτροπής Τεχνολογίας Σκυροδέματος του Συλλόγου Πολιτικών Μηχανικών Ελλάδας. Στην παρούσα έκδοση γίνεται αναφορά στο «Αυτοσυμπυκνούμενο Σκυρόδεμα», μια καινοτομία που μετά την ανάπτυξή της στην Ιαπωνία κατά τη δεκαετία του 1980 έχει πολλάκις χαρακτηριστεί ως επανάσταση στο χώρο των κατασκευών από σκυρόδεμα. Επόμενο είναι λοιπόν το καινοτόμο αυτό προϊόν, μαζί με τις απαιτήσεις που οδήγησαν εξαρχής στην εμφάνισή του, να κερδίζει όλο και περισσότερο έδαφος και στην ελληνική αγορά κι επομένως να προκύπτει η ανάγκη για ενημέρωση των συναδέλφων γύρω από τα ειδικά του χαρακτηριστικά και τις ιδιαιτερότητες της χρήσης του.

Anti-Corrosion Methods and Materials, 2014

Purpose -This paper aims to present results of an experimental investigation on a series of scale... more Purpose -This paper aims to present results of an experimental investigation on a series of scaled reinforced concrete column elements which were subjected to chloride exposure under accelerated conditions under a concurrent service axial load, over a period. In the presence of an axial load, directed microcracks of increasing density and width are introduced in the concrete mass, depending on the axial load level. Such cracks are believed to enhance the intrusion rate of chlorides in the concrete, relative to what is obtained in the normally performed unloaded specimen tests. Design/methodology/approach -Eighteen column specimens were tested over two chloride exposure periods, of duration up to a maximum of six months. Three different service axial load levels were considered, namely, none, 22 per cent and 43 per cent of the normalized axial load capacity of the columns. Findings -The results indicate that the specimens loaded to the higher axial load, which closely resembles actual service situation of such type of elements, exhibited up to ten times faster rates of induced current flow under a constant applied voltage of 500 mV, compared to the unloaded and less loaded specimens. Practical implications -It is proven that the presence of axial load influences the rate of chloride ingress in columns and, therefore, should be taken into account in estimating the concrete cover of such elements in durability design. Originality/value -The influence of axial loading on corrosion rate has not been considered in published experimental and analytical studies of chloride ingression. These studies have typically so far considered the accelerated corrosion of unloaded column specimens.

... steel requirements increase to between 2.00 to 2.70% of the gross section steel ratio. ... Th... more ... steel requirements increase to between 2.00 to 2.70% of the gross section steel ratio. ... The sensitivity of this assumption is currently examined by modelling the columns using refined inelastic ... of 11%), ranging between 195% to 210% and similar sensitivity to frame irregularity. ...

Technical Instructions concerning the structural design, the various different stages of construc... more Technical Instructions concerning the structural design, the various different stages of construction process and the quality control of concrete floors (slabs on ground) [avail. in Greek only].