En el presente trabajo se aborda la tesis “Estudio paramétrico con FEM del refuerzo a punzonamiento de losas de hormigón armado”. Se trata de todo lo relacionado con el fenómeno resistente de punzonamiento en estructuras, especialmente en forjados construidos mediante hormigón armado. Se trata de cuatro apartados bien diferenciados. En este, el primero, se desarrolla la síntesis de la tesis, donde se marcan unos objetivos, seguido de una explicación detallada y descripción de este fenómeno mediante su estado del arte, que abarca el grueso de éste primer apartado, en el cual se describen, entre otros aspectos, las diferentes patologías producidas por el punzonamiento y casos de sucesos catastróficos que provocaron, la historia de los forjados y los principales estudios llevados a cabo sobre este fenómeno, y acabando con las principales resultados y conclusiones de la tesis. Después, el segundo y tercer apartado contienen los artículos publicados y no publicados, respectivamente, por capítulos. Por último, se desarrollan las conclusiones en el último y cuarto apartado.

Abstract A new generation of EN 1992-1-1 (2004) also known as Eurocode 2 is under development and currently there is a set of proposed provisions regarding section 6.4 about punching shear, PT1prEN 1992-1-1(2017). It was of interest to compare the proposal with the current punching shear design provisions. The aim of this master thesis was to compare the punching shear resistance obtained in accordance with both design codes. Furthermore the eect of some parameters on the resistance was to be compared. It was also of interest to evaluate the userfriendliness of the proposal. In order to meet the aim, a case study of a real 　at slab with drop panels was performed together with a parametric study of a pure ctive 　at slab. The parametric study was performed for inner, edge and corner columns in the cases prestressed, without and with shear reinforcement. It was concluded that the distance av from the column axis to the contra 　exural location has a big in　uence on the punching shear resistance. The factor ddg considering concrete type and aggregate properties also has a big impact on the resistance. The simplied estimation of av according to 6.4.3(2) in PT1prEN 1992-1-1 (2017) may be inaccurate in some cases. The length b0 of the control perimeter has a larger eect on the resistance in EN 1992-1-1 (2004) than in PT1prEN 1992-1-1 (2017). In PT1prEN 1992-1-1 (2017), studs located outside the second row has no impact on the resistance. The tensioning force in a prestressed 　at slab has a larger in　uence on the resistance in PT1prEN 1992-1-1 (2017) than in EN 1992-1-1 (2004). Furthermore, the reinforcement ratio is increased by the tendons, and thus aect the resistance in PT1prEN 1992-1-1 (2017). Clearer provisions for the denition of the support strip bs for corners and ends of walls are needed in PT1prEN 1992-1-1 (2017). It may be questionable if the reduction of the perimeter for a large supported area in accordance with 6.4.2(4) in PT1prEN 1992-1-1 (2017) underestimates the resistance v in some cases. Considering the work-load with PT1prEN 1992-1-1 (2017), more parameters are included. However, they may not require that much eort to obtain. Keywords: Punching shear, resistance, concrete, 　at slab, design provisions, Eurocode 2, case study, parametric study, shear reinforcement, prestressed vi

For members and flat slabs without shear reinforcement, the shear and punching shear strength are often the determining design criteria. These failure modes are characterized by a fragile behaviour implying possible partial or total collapse of the structure. Despite extensive research in this field, shear and punching shear in reinforced and prestressed concrete structures, remain complex phenomena so much that the current approach is often empirical or simplified. The ability of Steel Fibre Reinforced Concrete (SFRC) to reduce shear reinforcement in reinforced and prestressed concrete members and slabs,or even eliminate it, is supported by several experimental studies. However its practical application remains marginal mainly due to the lack of standard, procedures and rules adapted to its performance. The stationary processes in precast industry offer optimal possibilities for using high performance cementitious materials such as Self Compacting Concrete (SCC) and High Strength Concrete (HSC). For the author, the combination of High Performance Concrete and steel fibres is the following step in the development and the optimization of this industry. The High Performance Fibre Reinforced Concrete (HPFRC) stands between conventional SFRC and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The HPFRC exhibiting a good strength/cost ratio is, thus, an alternative of UHPFRC for precast elements. The principal aim of this work was to analyse the shear and punching shear behaviour of HPFRC and UHPFRC structures without transversal reinforcement and to propose recommendations and design models adapted for practitioners. Several experimental studies on structural elements, i.e. beams and slabs, were undertaken for this purpose. Firstly, an original experimental campaign was performed on pre-tensioned members in HPFRC. A total number of six shear-critical beams of a 3.6 m span each, and two full scale beams of a 12 m span each, were tested in order to evaluate the shear and flexural strength. The principal parameter between the specimens was the fibres (...)

Neste trabalho analisa-se a resistência à punção e a ductilidade das ligações laje-pilar em doze modelos de lajes-cogumelo de concreto armado, nas quais se efetuam combinações de emprego de concreto de alta resistência, diferentes volumes de fibras de aço e uso de armadura transversal na forma de conectores de aço tipo pino. Todas as lajes são quadradas com 1160 mm de lado e 100 mm de espessura. A armadura de flexão foi composta de barras de aço de 10 mm espaçadas de tal forma a resistir a um momento fletor único em ambas direções. Os conectores, quando utilizados, foram dispostos radialmente e compostos de barras de aço de 6.6 mm soldadas a segmentos de ferro chato nas duas extremidades. Para avaliar a capacidade resistente dos modelos de ligação laje-pilar e observar o ganho de ductilidade que as fibras proporcionam, foram ensaiados segmentos-de-laje, os quais representam uma faixa destes modelos de ligação laje-pilar. Foi utilizado um sistema de ensaio dotado de atuador hidráulico servo-controlado, programado para ensaio com deformação controlada e aquisição contínua dos dados, o que permitiu a avaliação do comportamento pós-pico de resistência e a realização de medições de resistência residual. Várias hipóteses de cálculo foram utilizadas para avaliar a resistência última das ligações laje-pilar. Empregou-se um critério de classificação para caracterizar o tipo de ruptura em: punção ou flexão predominante ou uma combinação de punção-flexão. Constatou-se que o emprego de concreto de alta resistência, juntamente com armadura transversal, aumenta substancialmente a resistência da ligação laje-pilar, e quando combinado com fibras de aço, consegue-se um considerável aumento da ductilidade. / This work analyses the punching shear resistance and ductility of slab-column connections on twelve concrete flat slab models. The model characteristics resulted from combinations of the application of high or ordinary strength concrete, different steel fiber volume fractions and use or not of shear reinforcement. All the slabs are square with 1,160 mm of side and 100 mm of thickness. The main flexural reinforcement was composed of 10 mm steel bars spaced in such a way to resist to the same bending moment in both directions. When used, the shear reinforcement of steel studs were disposed in radial directions and consisted of 6.6 mm steel bars welded to flat steel segments in their ends. To evaluate the resistant capacity of slab-column connection models and to observe the ductility that the fibers provide, they were rehearsed segments-of-slab, which represents a strip of these slab-column connection models. A testing system with a servo-controlled hydraulic jack was used and it was programmed for a controlled deformation test and continuous data acquisition. This method allowed the evaluation of the post-peak strength behavior and the measurement of residual resistance forces. Several calculations hypotheses were used to evaluate the ultimate strength of the slab-column connections. A classification criterium was applied to characterize the failure type as: predominant punching or flexure or a combination of punching-flexure. It was verified that the application of high strength concrete, together with shear reinforcement, increases substantially the slab-column connection strength, and, when combined with steel fibers, a considerable ductility increase is achieved.

When dealing with the separation of materials, the metal shearing process such as punching, is widely used in theindustry due to its time efficient manner. There is however, a need to better understand the process in order toimprove quality of the final product. Working with numerical simulations of themetal shearing process, there aretwo major difficulties. One being the extremely large deformation, the other being material failure. The combinationof these two makes numerical modeling challenging and is the reason for this study.The problem was divided in to two main parts, one where material modeling was studied, the other part focusedon numerical modeling and experiments of the punching process. A material model considering both plasticityandmaterial failure was created for a boron steel material. Plasticity behavior of thematerial was modeled with anelasto-plastic model and a calibratedModifiedMohr-Coulomb (MMC) failure criterion to model the material failure.The resultingMMC-model agreed well with the experiments.Punching experiments with varying clearances were performed on the boron steel. Punch forces and displacementswere continuously sampled throughout the process, and after the punching experiments were finished the punchededge profiles were studied. The multiphysics simulation software LS-DYNA was then utilized, and three dimensionalsimulations of the punching process using the Smoothed Particle Galerkin (SPG)method were performed.Results from the SPG-simulation corresponded very well with the results from punching experiments, and it can beconcluded that the model was able to capture the material behavior of the sheet in a highly detailed level. When thepunched edge profiles from the simulations were compared to the experiments, there was an almost exact match forall the cases studied. The force-displacement behavior of the punch from simulations was in great consistency withexperimental results as well.Itwas also concluded that the combination of a stress state dependent failure criterion together with the SPG-methodshows significant possibilities to cope with three dimensional problems where large deformations in combinationwith difficultmaterial failure occurs. This study focuses on the punching process, but the generality of this novelmodeling technique can be applied to many industrial cases and is a step towards a better and more reliablemodeling of failure in combination with extremely large deformation.

Neste trabalho investiga-se o comportamento resistente de lajes-cogumelo de concreto armado, analisando-se as possibilidades de melhoria de desempenho com relação ao fenômeno de punção, pelo emprego de concreto de alta resistência, pelo reforço com fibras de aço e pelo uso de armaduras transversais de combate à punção, através de ensaios de modelos de lajes-cogumelo quadradas que representam a ligação laje-pilar para o caso do pilar interno. Apresenta-se também uma revisão de conhecimentos sobre as lajes-cogumelo, o seu comportamento estrutural com ênfase no fenômeno da punção, e os principais conceitos sobre os concretos de alta resistência e os compósitos constituídos de matriz de cimento reforçada com fibras. Doze modelos de laje-cogumelo foram ensaiados com diferentes combinações de concreto de alta resistência, concreto de resistência convencional, armadura transversal e volume de fibras (0%, 0,75% e 1,5%). Um acréscimo significativo de resistência à punção foi observado, devido ao uso de concreto de alta resistência e à adição de fibras. A combinação de concreto de alta resistência com 1,5% de volume de fibras e armadura transversal proporcionaram o dobro de aumento na resistência à punção em relação ao modelo de concreto convencional sem armadura transversal e sem adição de fibras. A adição de fibras é a suposta responsável por cerca de 50% de acréscimo de resistência e o aumento da ductilidade. Outras comparações incluindo as previsões teóricas (Texto Base da NB1/94, CEB/90, AGI 318/89 e EUROCODE N.2) são comentadas. / This work investigates the behavior of reinforced concrete flat slabs, analysing the possibility of performance improvement, in relation to punching shear phenomenon, regarding to the use of high strength concrete, the addition of steel fibres and the use of transversal steel reinforcement against punching shear, through tests of flat slab square models that represent the slab-column connection, for the case of an interior column. lt introduce a revision of knowledge of flat slabs, their structural behavior with emphasis on the punching shear phenomenon, and the main concepts about high strength concretes and the composites made of cement matrix reinforced with fibres. Twelve flat slab models were tested in different combinations of high strength concrete, ordinary strength, shear reinforcement and steel fibre volume fraction (0%, 0,75% e 1,5%). A significant increase in the punching shear strength was observed, either due to the use of high strength and the addition of steel fibres. The combination of high strength concrete with 1,5% fibre volume fraction and shear reinforcement provide twice the punching shear resistance of an ordinary concrete strength model without shear reinforcement and without fibre. Fibre addition is supposed to be responsible by about 50% of the resistance improvement and the increase of ductility. Other comparisons including theoretical previsions (Texto Base da NB1/94, CEB/90, ACI 318/89 e EUROCODE N.2) are commented.

Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer. / February 2007

Στόχος της παρούσας διατριβής είναι η διερεύνηση της αποτελεσματικότητας της ενίσχυσης στοιχείων τύπου πλάκας μέσω ενός νέου σύνθετου υλικού. Το νέο αυτό σύνθετο υλικό συντίθενται από ινοπλέγματα δύο διευθύνσεων σε ανόργανη μήτρα. Τα ινοπλέγματα αποτελούνται από ίνες άνθρακα ή ίνες υάλου, ενώ η ανόργανη μήτρα αποτελείται από κονίαμα. Ο όρος που έχει προταθεί από συγγραφείς για το νέο αυτό υλικό είναι Textile Reinforced Concrete, που στην Ελληνική γλώσσα θα μπορούσε να αποδοθεί ως Ινοπλέγματα Ανόργανης Μήτρας (ΙΑΜ). Για τον λόγο αυτό, παρασκευάσθηκαν δοκίμια τύπου πλάκας επί τεσσάρων περιμετρικών δοκών. Συνολικά κατασκευάσθηκαν τέσσερα δοκίμια τύπου πλάκας, εκ των οποίων τρία ενισχύθηκαν μέσω ΙΑΜ και ένα ήταν το δοκίμιο αναφοράς. Τα δύο δοκίμια ενισχύθηκαν με μία και δύο στρώσεις πλεγμάτων συνεχών ινών από άνθρακα, ενώ το τρίτο ενισχύθηκε μέσω εφαρμογής τριών στρώσεων πλεγμάτων συνεχών ινών υάλου. Τονίζεται πως τρεις στρώσεις πλέγματος συνεχών ινών υάλου έχουν ισοδύναμη δυστένεια με μία στρώση πλέγματος συνεχών ινών από άνθρακα. Στο πρώτο κεφάλαιο παρουσιάζονται οι ιδιότητες των ινών και της ανόργανης μήτρας, καθώς επίσης και η μηχανική συμπεριφορά του σύνθετου υλικού. Τέλος, γίνεται μια ανασκόπηση της έρευνας που έχει διεξαχθεί στο Εργαστήριο Μηχανικής και Τεχνολογίας των Υλικών, γύρω από το πεδίο των ενισχύσεων μέσω ΙΑΜ στοιχείων από οπλισμένο σκυρόδεμα. Στο δεύτερο κεφάλαιο συνοψίζονται οι ήδη υπάρχουσες τεχνικές επισκευής και ενίσχυσης πλακών. Επίσης, αναφέρονται παραδείγματα ενισχύσεων στοιχείων τύπου πλάκας από την διεθνή βιβλιογραφία. Στο τρίτο κεφάλαιο περιγράφονται οι εργασίες που πραγματοποιηθήκαν προκειμένου να κατασκευασθούν τα δοκίμια. Το κεφάλαιο αυτό χωρίζεται σε τέσσερις βασικές ενότητες. Στην πρώτη ενότητα παρουσιάζονται οι μηχανικές ιδιότητες των υλικών που χρησιμοποιήθηκαν για την παρασκευή και ενίσχυση των δοκιμίων, καθώς και οι διαδικασίες μέσω των οποίων αυτές διακριβώθηκαν. Στην δεύτερη και τρίτη ενότητα, αναφέρονται οι εργασίες που διενεργήθηκαν κατά την φάση της σκυροδέτησης και της ενίσχυσης αντίστοιχα των δοκιμίων, ενώ στην τέταρτη ενότητα αναλύεται η πειραματική διαδικασία που ακολουθήθηκε. Στο τέταρτο κεφάλαιο παρουσιάζονται τα αποτελέσματα που προέκυψαν από την διεξαγωγή των πειραμάτων. Το κεφάλαιο αυτό χωρίζεται σε τρεις ενότητες. Στην πρώτη ενότητα περιγράφεται η συμπεριφορά κάθε δοκιμίου ξεχωριστά. Στην δεύτερη ενότητα γίνεται σύγκριση των αποτελεσμάτων που εξήχθησαν για όλα τα δοκίμια, ενώ στην τρίτη και τελευταία ενότητα παρουσιάζονται εν συντομία τα βασικότερα συμπεράσματα, που προέκυψαν από την πειραματική διαδικασία. Στο πέμπτο κεφάλαιο, παρουσιάζονται οι βασικές σχέσεις μέσω των οποίων μπορεί να εκτιμηθεί το φορτίο αστοχίας πλακών δύο διευθύνσεων ενισχυμένων μέσω ΙΑΜ. Για τον λόγο αυτό δίνονται προσομοιώματα και σχέσεις, ενώ στην συνέχεια συγκρίνεται το φορτίο αστοχίας εκ των προτεινόμενων σχέσεων με το καταγραφόμενο φορτίο αστοχίας. Το έκτο και τελευταίο κεφάλαιο, παραθέτει συνοπτικά τα βασικότερα αποτελέσματα της παρούσας Διατριβής Διπλώματος Ειδίκευσης. Γενικά η νέα τεχνική ενίσχυσης, είναι ιδιαίτερα αποτελεσματική, αφού αυξάνεται σημαντικά το φορτίο αστοχίας των ενισχυμένων δοκιμίων συγκριτικά με το δοκίμιο αναφοράς. Παράλληλα η συμπεριφορά του πλέγματος είναι άριστη, αφού μέχρι και την στιγμή της αστοχίας δεν παρατηρείται αποκόλλησή του από την επιφάνεια του σκυροδέματος. Αξίζει να σημειωθεί πως η αστοχία των δοκιμίων συνέβη λόγω διάτρησης. Στο τέλος του κεφαλαίου αναφέρονται προτάσεις για μελλοντική έρευνα. / The aim of the present thesis is to investigate the efficiency of a new composite material for the strengthening of two way slabs. This new material is called “Textile Reinforced Concrete - (TRC)”. It comprises textiles, that is fabric meshes made of long woven, knitted or even unwoven fiber rovings in at least two orthogonal directions, impregnated with inorganic binders such as cement based mortars. For the purposes of this study, four specimens of two way slabs were produced. Three of them were strengthened with TRC, and the remaining specimen was kept as control. Two specimens were strengthened with one and two layers of textile respectively, whose yarns consisted of carbon fibers. The third one was strengthened with three layers of textile whose yarns consisted of glass fibers. It is worth mentioning that three layers of textiles with glass fibers, are equivalent in terms of stiffness and strength with one layer of textile with carbon fiber. The first chapter analyses the properties of fibers, yarns, textiles, and those of the inorganic matrix. The principles of the bond behavior are also presented. Moreover, the work done in the area of strengthening of concrete members at the faculty of Civil Engineering of the University of Patras is discussed. The second chapter summarizes the existing techniques of enhancement in strength of two way slabs. The purpose of the third chapter is to describe the course of action towards the construction of the specimens. The test procedure and measurements are also included in this chapter. The results as derived from the testing procedure are discussed in the fourth chapter of this dissertation. Comparisons of the results for each specimen are also drawn. In the fifth chapter, several experimentally and analytically based expressions have been used to evaluate the two-way capacity of slabs. The sixth chapter recapitulates the findings of the present research. It has been generally shown that the suggested technique appears to be effective. Noteworthy is the fact that all specimens experienced punching shear failure.

Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer.

Understanding the bearing response of the footings on layered soils has always been a challenge for researchers. Due to the limitations of analytical and empirical solutions it had been difficult to understand the true bearing behavior. Some researchers have tried solving this problem by numerical analysis and have found some success. In this study the numerical analysis approach has been applied using a commercial tool FLAC (Fast Lagrangian Analysis of Continua) to study the bearing response of surface footings on layered clays. First, small deformation analyses were taken up to study the undrained bearing response of strip and circular footings resting on a horizontally layered strong over a soft clay foundation, and then over soft over strong clay foundation. In the end application of large strain mode of FLAC was explored to investigate the large deformation behavior of the strip footing resting on the surface of a strong over soft clay foundation. All models were run by applying velocity loading and a elastic-perfectly plastic Tresca yield criterion has been used. The results are compared with published Finite Element Method (FEM) results, and with analytical, empirical and semi-empirical solutions. It was found that bearing capacity results from the present small-strain FLAC analyses agree well with the FEM results. However, these results in most of the cases tend to differ (as much as 49% for certain layered clay foundations) from those predicted with analytical, empirical and semi-empirical solutions, mainly due to the assumptions made in these solutions. Since no such assumptions are made in the present FLAC analyses, the results and the methodology of this thesis can be applied to predict the bearing capacity of the practical problems. Application of the large-strain mode of FLAC to study the large deformation of shallow foundations has pointed out a limitation of FLAC in completing such analyses. However, it is observed from the early trends of these analyses that whereas the small deformation analysis may under estimate the ultimate bearing capacity for certain cases of layered foundations where the upper clay is moderately stiffer than the lower clay layer, it might also over predict the ultimate bearing capacity for other cases when the upper clay is very stiff in comparison to the lower clay layer.