George C. Manos

Numerical investigation of the behaviour of the church of Agia Triada, Drakotrypa, Greece

This paper includes the most important findings of a series of both linear elastic and non-linear analyses focusing on the development of failure developing on the masonry structural elements, identified through different failure criteria, of a post-Byzantine church. The historic monument which was selected for this investigation is the church of Agia Triada, at the District of Karditsa, Greece. The numerical simulation of the behaviour of the structural system for this church includes all parts of the super-structure and load combinations of the gravitational loads and/or earthquake forces. A first objective of this study is to assess the importance of various structural elements, such as the tympana, apses, secondary vaulting and openings in the peripheral walls and the dome. A second objective is to predict the initiation and propagation of failure at various structural elements considering (a) a Mohr-Coulomb failure criterion with a limit on tension strength and (b) three alternative modified Von-Misses failure envelopes. These distinct failure criteria are applied for the same structure and for the same load combinations. The Mohr-Coulomb failure criterion is combined with stress fields as they result from a linear elastic analysis whereas the three alternative modified Von-Misses failure envelopes are incorporated in a non-linear, step-by-step incremental analysis. The initiation and propagation of failure, predicted by all these criteria, and the corresponding failure areas are compared and discussed.

The behavior of masonry assemblages and masonry-infilled R/C frames subjected to combined vertical and cyclic horizontal seismic-type loading

The present systematic study aims to propose valid numerical models that can realistically approximate the shear behavior of masonry assemblages and the hysteretic behavior of masonry infilled reinforced concrete (R/C) frames when they are subjected to combined vertical and horizontal cyclic loads. Successful numerical simulations are developed for the non-linear shear behavior of masonry joints and the non-linear behavior and ultimate strength of relatively weak Greek masonry piers; these are finally used, with the same materials and geometry, as infills in the R/C frames. A valid numerical model is proposed that can capture successfully the various observed non-linear response mechanisms that develop within the masonry infilled R/C frames when they are subjected to combined vertical and cyclic horizontal loads.

Shear Behavior of Rectangular Beams Strengthened with either Carbon or Steel Fiber Reinforced Polymers

The aim of this study is to upgrade the shear capacity of reinforced concrete (R/C) beams strengthened with either Carbon (CFRP) or Steel (SRP) fiber Reinforced Polymers with strips having the form of either closed or open hoop external transverse reinforcement. This investigation also includes the use an anchoring device. Seven prototype specimens in need of shear strength upgrade were tested having a span of 3000mm. The strengthened R/C beams along with a non-strengthened control R/C beams were tested monotonically under four point bending loading conditions. The experimental results indicate that the shear failure of the closed hoop strengthened beams is accompanied with the tensile fracture of the CFRP/SRP strips together with an increase in the shear capacity. A considerable increase in the shear strength was observed when open hoop CFRP/SRP strips with no anchoring were used; however, the debonding of these strips posed a limitation to this upgrade. When these open hoop CFRP/SRP strips were provided with anchoring devices the shear strength of the R/C beams was further increased and the shear failure was accompanied this time by either the fracture of the CFRP/SRP strips or the failure of the anchoring system. In conclusion, a shear strengthening system for R/C beams utilizing open hoop CFRP/SRP strips with properly designed anchoring it is easily applicable, it increases significantly the shear capacity of such R/C beams and it exploits at the same time the high tensile strength of these fiber polymer materials in a cost effective way. An analytical procedure used to predict the shear strength for of such R/C beams yielded good comparison with the measured values.

Numerical simulation of the shear behaviour of reinforced concrete rectangular beam specimens with or without FRP-strip shear reinforcement

The successful validation of a numerical model is presented that can realistically approximate the shear behaviour of reinforced concrete (R/C) rectangular beams strengthened against shear with externally applied open hoop fibre reinforcing polymer (FRP) strips. For this purpose, the measured load-deformation response of ten (10) full-scale R/C beam specimens is utilised. These specimens were loaded monotonically in a four-point bending arrangement up to failure. Open hoop FRP strip shear reinforcement was applied externally to upgrade the shear capacity of eight (8) R/C beam specimens. Four of these specimens had these FRP strips without anchorage, whereas for the other four the FRP strips were attached together with novel anchoring devices. This successful numerical simulation predicts with a very good degree of approximation the observed load-deformation behaviour and the ultimate shear capacity of all these specimens as well as the observed modes of failure including diagonal concrete cracking, debonding of the FRP strips in the case of no anchoring, or the plastification of parts of the anchoring devices plus the adjacent crushing of the concrete.

The Influence of Concrete Surface Preparation when Fiber Reinforced Polymers with Different Anchoring Devices are Being Applied for Strengthening R/C Structural Members

The aim of this study is to investigate the influence of concrete surface preparation when either steel or carbon fiber reinforced polymers (FRP) are applied for strengthening applications of R/C members. The present study also investigates the anchorage or not of the applied FRP strips on the volume of concrete. For this purpose special concrete specimens were fabricated and were used to attach CFRP or SRP strips with or without anchoring and with or without contact surface treatment. The experimental results indicate that the concrete surface preparation is important and results in an increase of the load bearing capacity when the FRP strip is not anchored. When an anchoring device is employed, the concrete surface preparation is of no significance. With a properly designed anchoring device, a significant increase in the bearing capacity was observed and the failure was that of the fracture of the FRP strips for all such specimens. The highest FRP material exploitation was achieved in the specimen that utilises the patented anchoring device together with two layers of SRP strips. Debonding of the FRP strips, or failure of the anchoring device, results as was to be expected, in relatively unsatisfactory FRP material exploitation.

Using virtual reality to teach special populations how to cope in crisis: the case of a virtual earthquake.

The unique characteristics of special populations such as pre-school children and Down syndrome kids in crisis and their distorted self-image were never studied before, because of the difficulty of crisis reproduction. This study proposes a VR setting that tries to model some special populations behaviour in the time of crises and offers them a training scenario. The sample population consisted of 30 pre-school children and 20 children with Down syndrome. The VR setting involved a high-speed PC, a VPL EyePhone 1, a MR toolkit, a vibrations plate, a motion capture system and other sensors. The system measured and modelled the typical behaviour of these special populations in a Virtual Earthquake scenario with sight and sound and calculated a VR anthropomorphic model that reproduced their behaviour and emotional state. Afterwards one group received an emotionally enhanced VR self-image as feedback for their training, one group received a plain VR self-image and another group received verbal instructions. The findings strongly suggest that the training was a lot more biased by the emotionally enhanced VR self-image than the other approaches. These findings could highlight the special role of the self-image to therapy and training and the interesting role of imagination to emotions, motives and learning. Further studies could be done with various scenarios in order to measure the best-biased behaviour and establish the most natural and affective VR model. This presentation is going to highlight the main findings and some theories behind them.

A knowledge-based software for the preliminary design of seismically isolated bridges

Seismic design of isolated bridges involves conceptual, preliminary and detailed structural design. However, despite the variety of commercial software currently available for the analysis and design of such systems, conceptual and preliminary design can prove to be a non-straightforward procedure because of the sensitivity of bridge response on the initial decisions made by the designer of the location, number and characteristics of the bearings placed, as well as on a series of broader criteria such as serviceability, target performance level and cost-effectiveness of the various design alternatives. Given the lack of detailed design guidelines to ensure, at this preliminary stage, compliance with the above requirements, a “trial and error” procedure is typically followed in the design office to decide on the most appropriate design scheme in the number and location of the bearing systems; the latter typically based on engineering judgment to balance performance with cost. To this end, the particular research effort aims to develop a decision-making system for the optimal preliminary design of seismically isolated bridges, assumed to respond as single degree of freedom (SDOF) systems. The proposed decision-making process is based on the current design provisions of Eurocode 8, but is complemented by additional criteria set according to expert judgment, laboratory testing and recent research findings, while using a combined cost/performance criterion to select from a database of bearings available on the international market. Software is also developed for the implementation of the system. The paper concludes with the application, and essentially the validation of the methodology and software developed through more rigorous MDOF numerical analysis for the case of a real bridge.

Field Experiments for Monitoring the Dynamic Soil–Structure–Foundation Response of a Bridge-Pier Model Structure at a Test Site

AbstractSummary results from a series of field experiments at a test site in Greece are presented, involving an in situ instrumented bridge-pier model built on realistic foundation conditions, to study the dynamic behavior of structure-foundation-soil system. It was attempted to link the variation of its dynamic characteristics to certain changes in its structural system, including the development of structural damage. This measured response was next utilized to validate numerical tools capable of predicting influences arising from such structural changes as well as from soil–foundation interaction. This bridge-pier model was supported on soft soil deposits allowing the study of structure–foundation–soil interaction effects during low-to-medium intensity artificial excitations. The in situ experiments provided measurements that were used to verify fundamental analytical solutions for soil–structure interaction. They were also used to validate numerical simulations that were developed to predict the respon...

The Use of Fiber Reinforced Plastic for The Repair and Strengthening of Existing Reinforced Concrete Structural Elements Damaged by Earthquakes

During the last fifty years various parts of the world have been subjected to a number of damaging earthquakes. Greece is one of the countries where such damaging earthquakes oc‐ cur quite frequently ([1]). Some of these earthquakes, not necessarily the most intense, oc‐ curred near urban areas and thus subjected various types of structures to significant earthquake forces leading to damage ([2]). For some of these earthquakes, ground motion acceleration recordings were obtained at distances relatively close to the area of intense shaking, thus providing valuable information for correlating the observed damage with this ground motion recording and its characteristics. Moreover, following the most damaging of these earthquakes, studies were initiated that led to the revision of the provisions of Seismic Codes [3]. The damaged structures included old structural formations, sometimes older than one hundred years, which were not designed for seismic forces. They usually belong to cultural heritage and are under various forms of conservation status that does not allow all types of retrofitting but only retrofitting materials and techniques that are compatible with the existing materials; moreover, the applied retrofitting in these cases must also be reversi‐ ble so that it can be easily removed in case it demonstrates undesirable effects with time. Apart from the cultural heritage structures, the damaged structures also include relatively contemporary structures that are usually less than fifty years old. The vast majority of these structures are multistory reinforced concrete (R/C) buildings. There are other types of struc‐ tures apart from (R/C) buildings, such as structures forming the infrastructure or industrial facilities which can also develop earthquake damage. However, this chapter will be devoted to the usual R/C residential multi-story buildings, the earthquake damage of their structural elements and their strengthening.

THE DYNAMIC AND EARTHQUAKE RESPONSE OF BASILICA CHURCHES IN KEFALONIA, GREECE INCLUDING SOILFOUNDATION DEFORMABILITY AND WALL DETACHMENT.

The dynamic and earthquake behaviour of structural systems representing PostByzantine Christian churches located in Kefalonia-Greece is examined. All these churches are made of stone masonry. They developed damage to their masonry elements due to the amplitude of the gravitational forces acting together with the seismic forces that were generated by the recent 2014earthquake activity, combined with the deformability of the foundation. The numerical results together with assumed strength values are utilized to predict the behaviour of the various masonry parts of these churches in in-plane, shear, and normal stress as well as out-of-plane flexure. Use is made in the numerical simulation of the deformability of the foundation of the results obtained from a specific investigation that dealt in measuring the dynamic characteristics of a bell tower located in Lixouri-Kefalonia-Greece. It is shown that the foundation deformability partly explains the appearance of structural damage. When comparing the numerically predicted regions that reach limit state conditions with actual damage patterns a reasonably good agreement in a qualitative sense can be observed. In addition, the numerical simulation focused in reproducing numerically certain non-linear mechanisms that are typical for this type of structural systems. The numerically predicted non-linear response mechanisms at the corners of the masonry walls as well as at the roof to masonry wall level seem to reproduce in a realistic way the observed damage patterns in these regions.