Lambros Kotoulas’s research while affiliated with Aristotle University of Thessaloniki and other places

Στην παρούσα εργασία παρουσιάζεται μια μεθοδολογία για την σεισμική αποτίμηση κατασκευών φέρουσας τοιχοποιίας με βάση τις διατάξεις του Κ.Α.Δ.Ε.Τ. μέσα από την μελέτη του Ιερού Ναού Κοιμήσεως της Θεοτόκου στο Καρλόβασι της Σάμου, ο οποίος υπέστη σημαντικές βλάβες κατά τον σεισμό της 30ης Οκτωβρίου του 2020. Τα βασικά σημεία της μεθοδολογίας περιλαμβάνουν την επιλογή της μεθόδου προσομοίωσης και ανάλυσης της κατασκευής σε συνδυασμό με τον τρόπο προσδιορισμού της φέρουσας ικανότητας του δομήματος. Η προσομοίωση της κατασκευής γίνεται με την μέθοδο των πεπερασμένων στοιχείων και ως βασική μέθοδος ανάλυσης για τον καθορισμό των σεισμικών δράσεων επιλέγεται η Ισοδύναμη Στατική Ανάλυση. Οι έλεγχοι επάρκειας αφορούν εκτός επιπέδου δράσεις και πραγματοποιούνται σε όρους παραμορφώσεων σε επίπεδο τοιχοποιίας που διαμορφώνει τις όψεις του ναού. Με συνδυασμό των αποτελεσμάτων των αναλύσεων σε όρους τάσεων και των ελέγχων επάρκειας σε όρους παραμορφώσεων προσδιορίζεται πλήρως η απόκρισή του ναού κατά την ισχυρή σεισμική διέγερση.

Past research of the Laboratory of Experimental Strength of Materials and Structures of Aristotle University of Thessaloniki, Greece, dealt with the development of a new clay unit, vertically perforated, suitable for the construction of reinforced masonry structural members. This novel unit has the proper geometrical and mechanical properties to comply with the existing regulations. At the same time its geometry forms a vertical hole and horizontal prefabricated channels to host reinforcing steel bars. The rest of the vertical holes is filled with expanded polystyrene to improve the overall energy performance of the building. Thus, this unit aims to the integrity of both structural performance and energy efficiency. Experimental measurements have been conducted in reinforced masonry piers under in plane and out of plane seismic type forces. Both unreinforced and reinforced with different reinforcing details were tested. A summary of this experimental campaign is presented here. Following, a two-story building, is investigated based on numerical models with 2D shell elements and equivalent static analysis. The seismic design is conducted according to laboratory measurements. The performance of the structure under seismic loads is discussed taking into consideration the regulations of Eurocode 6 and 8.

This paper presents a proposed method for seismic assessment of masonry heritage structures based on the modern Eurocode 8-Part 3 and Greek Code for Interventions of Masonry Structures regulations. The methodology is presented through the study of a three-story building with stone and brick masonry , floors with metal and timber beams and a timber roof. The main objects of this study include the selection of analysis method combined with the method of evaluating the load-bearing capacity of the structural elements of the building. This process together with the defined Performance Levels-a parameter introduced by the modern codes-is particularly important, as it determines the level of the applied seismic demands. Considering the framework defined by the code regulations, the developed numerical models using Finite Element Method (F.E.M.) are formed with shell and frame elements. The seismic assessment is conducted through Equivalent Static Analysis, calibrated based on Response Spectrum Analysis. Both Load-based and Displacement-based assessments are applied. Displacement-based method allows the nonlinear response of the masonry components, leading to a less conservative evaluation and limiting the extent of the required strengthening schemes. This method could be applied especially in heritage buildings, where extended interventions are not recommended.

This study presents a method for validation of numerical models of stone masonry arch bridges using in-situ and laboratory measurements. These numerical models are utilized in assessing the expected performance of specific case studies of stone masonry bridge structures in Greece towards meeting the demands of extreme events that include design seismic loads. At first, the work focuses on in-situ measurements conducted at selected old stone masonry bridges, using up-to-date system identification techniques, in an effort to quantify their dynamic characteristics in terms of eigen-frequencies, eigen-modes and damping properties. This information provides a basis for realistic numerical simulations towards studying the structural behaviour of such stone masonry bridges and assessing their expected structural behaviour in extreme future seismic events. Selected in-situ measurements are presented together with their use in numerical models of various levels of complexity. Afterwards, a series of experimental tests are presented on bridge materials (stone blocks and mortar) and triplet shear and bending tests. Through the laboratory measurements non-linear constitutive material or interface laws are determined. Thus, the failure criteria of such structures are employed to 3d solid finite element models used for the seismic assessment of masonry bridge structures.

The present study examines the structural assessment of Pashas bridge, located at the Western Makedonia, in Greece. This stone arched bridge, which is declared cultural heritage monument, was built during the end of 17th century and it was destructed during the 2nd civil war, in 1941 by British and New Zealander soldiers aiming to end the German invasion to the South of Greece. It was considered the largest bridge in Macedonia, with a length of more than 100 meters, 6 arches, the biggest one of which was almost 15 meters high. In its current form it is partially collapsed.

The seismic performance of “Greek” churches made by low-strength unreinforced masonry is examined. These structures were damaged during recent strong seismic activity in Greece combined with long term effects from foundation settlement. Measurements from shear-sliding laboratory tests of stone masonry triplets are presented and discussed together with corresponding numerical simulation results in an effort to quantify the in-plane sliding shear failure criterion. The cohesive surface interaction constitutive law was employed in forming realistic limit-state criteria for such weak mortar stone masonry. Next, the performance of specific “Greek” churches is numerically simulated employing simplified dynamic linear elastic analysis and assumed limit-state criteria. This simplified approach yielded realistic predictions of the observed performance. However, the necessity to obtain a comprehensive set of measured strength properties for such type of masonry construction is underlined. From this simplified dynamic linear elastic analysis it can be concluded that the soil-foundation deformability results in a significant increase in the tensile stress demands at critical regions. This conclusion is also in agreement with the observed damage.

Fiber-reinforced polymers (FRP) are rapidly gaining acceptance from the construction sector due to their large effectiveness. They are mainly used as confining reinforcement for concrete columns and as tensile reinforcement for concrete beams, columns and slabs. FRPs are already used to a large extent for applications such as bridges and parking lots, where elevated temperatures are not the main risk. Their increasing use as structural reinforcement is hampered by the concern related to their behavior at elevated temperatures as the relevant research is deficient. Thanks to the significant advantage of FRPs’ mechanical properties, further investigation into the influence of heating on their mechanical behavior may solve many doubts. The present study examines the influence of temperatures, ranging among 50, 100 and 250 °C, on the tensile strength of FRP laminates with carbon fibers (CFRP). In addition, the resistance of CFRP specimens to low-cycle thermal loading at the temperatures of 50, 100 and 250 °C under constant tensile load was investigated. The experiments were carried out in the laboratory of Experimental Strength of Materials and Structures of Aristotle University of Thessaloniki.

The combined seismic and energy retrofit of existing aged buildings represents a topic of importance for the building stock. The current study investigates the out-of-plane performance of a specific type of thermo-insulation scheme with panels attached on the external facades of multistory buildings. The investigation was carried out through flexure tests of prototype masonry specimens. From the comparison of their flexural performance, with or without thermo-insulating attachments, the influence of thermal insulation on the out-of-plane behavior of clay brick masonry is demonstrated. It was found that when the thermo-insulating attachment is in tension from such out-of-plane flexure of the masonry facade it performs in a satisfactory way and gives an increased flexural capacity for the assembly. The thermal insulating panels, although partially debonded from the masonry substrate at a limit-state, do not collapse, even when the masonry panel develops large flexural cracks. This is due to the presence of the used plastic anchors. When the thermo-insulating panel is subjected to compression during such an out-of-plane flexure the resulting increase in the out-of-plane load bearing capacity is relatively small. Based on these observations it can be concluded that such thermo-insulating panels may also lead to a less vulnerable seismic performance than that of the same masonry panel without this type of thermo-insulating attachment. This was also confirmed when the in-plane behavior was considered from a separate investigation already published. The employed numerical modeling was successful in simulating the most important aspects of the out-of-plane response of the tested masonry wallets with or without thermo-insulating attachments. The good agreement with observed performance as well as the general nature of this numerical simulation confirms its validity for further use.

Partial collapse of masonry facades during past strong earthquakes is well documented together with the increased vulnerability due to the presence of thermo-insulation within double wythe masonry. The combined seismic and energy retrofit of existing aged buildings represents a topic of importance for the building stock. The current study investigates the in-plane performance of a specific thermo-insulation scheme with panels attached on the external facades of multistory buildings. Diagonal compression tests of prototype specimens are done to study the influence of thermal insulation on the in-plane behaviour of clay brick masonry panels with or without thermal insulation. It was found that the thermo insulating attachment of the tested type performs in a satisfactory way when subjected to the stress field that arises to these masonry panels when subjected to diagonal compression. The thermo insolating panels, although finally debonded from the masonry substrate, do not collapse, even when the masonry panel develops large diagonal cracks, due to the presence of the used plastic anchors. The presence of such thermo insulating attachments leads to an increase of the in-plane load capacity and to a less brittle behaviour than the one without this thermo-insulation. This may also lead to a less vulnerable seismic performance than that of the same masonry panel without this thermo insulating attachment, although further validation is needed considering also the out-of-plane performance. The employed numerical modeling was successful in simulating the most important aspects of the in-plane response of the tested masonry wallets with or without thermo-insulating attachments. The good agreement with observed performance as well as the general nature of this numerical simulation confirms its validity.