Seismic assessment and retrofitting of existing structures

Εισαγωγή Η μέθοδος της Δομικής Αποτίμησης (Structural Assessment) με εφαρμογή Συντελεστών Δομικής Υποβάθμισης, είναι μια υβριδική διαδικασία μέσα από την οποία ο μηχανικός μπορεί να αποδώσει τη δομική υποβάθμιση μιας κατασκευής σε ειδικές περιπτώσεις δομικών φθορών και βλαβών (όπως αυτή της διάβρωσης των οπλισμών), οι οποίες δεν καλύπτονται από τα εθνικά κανονιστικά κείμενα. Ο Κανονισμός Επεμβάσεων προβλέπει τη διαδικασία υπολογισμού των μηχανικών ιδιοτήτων των υλικών καθώς και τον υπολογισμό των αντιστάσεων R των διατομών. Το κανονιστικό πλαίσιο του ΚΑΝ.ΕΠΕ καθώς και του Ευρωκώδικα 8 μέρος 3, δεν περιλαμβάνει σχέσεις αποτίμησης της δομικής υποβάθμισης των βλαμμένων στοιχείων σε φθορές όπως η διάβρωση των οπλισμών, απομίξεις και κενά στο σκυρόδεμα, τοπικές κακοτεχνίες και χαμηλές αντοχές του σκυροδέματος τοπικά στα δομικά στοιχεία. Προκύπτει η ανάγκη ανάπτυξης μιας προσέγγισης μέσα από την οποία θα ποσοτικοποιηθεί η δομική υποβάθμιση υφιστάμενων κατασκευών που παρουσιάζουν βλάβες δομικές και μη δομικές, ως ένας συντελεστής (r eff :συντελεστής δομικής υποβάθμισης), ο οποίος θα πολλαπλασιάζεται με την αντίστοιχη υπολογιζόμενη αντοχή – αντίσταση R των δομικών στοιχείων χωρίς βλάβες. Η μεθοδολογία που προτείνεται αποτελεί περαιτέρω ανάπτυξη της πρότασης Coronelli (2007) [1], σύμφωνα με την οποία γίνεται η αξιολόγηση προκαθορισμένων βλαβών (Defect List) [2, 3] ως προς τη βαρύτητα, την ένταση και τις επιπτώσεις της βλάβης στη κατασκευή. Υπολογίζεται ο συντελεστής δομικής υποβάθμισης r eff , εφαρμόζοντας απευθείας τα ευρήματα 11 συνολικά προκαθορισμένων εργαστηριακών ή επιτόπου μετρήσεων για τη κατάταξη της βαρύτητας της βλάβης (Διάβρωση) σε μια κλίμακα από το ένα μέχρι το τέσσερα (1-4, Πίνακας 5) [3]. Η μεθοδολογία εφαρμόζεται σε υφιστάμενο κτίριο της δεκαετίας του 1960. Τα αποτελέσματα της μεθόδου συγκρίνονται με αντίστοιχες εξειδικευμένες αναλύσεις βλαμμένων δομικών στοιχείων. Ιστορικό Κτιρίου Το Υφιστάμενο Κτίριο βρίσκεται στο κέντρο της Λάρισας. Αποτελείται από 4 ορόφους με υπόγειο και ισόγειο, καθώς και μια αυθαίρετη απόληξη κλιμακοστασίου. Η κατασκευή του κτιρίου έγινε τη περίοδο 1964 – 1969 με εγκεκριμένη άδεια το 1964 η οποία προέβλεπε μελλοντική προσθήκη ορόφου. Η κατηγορία του σκυροδέματος βάσει μελέτης είναι Β160 και του χαλαρού οπλισμού StI. Γεωμετρικά Δεδομένα Κτιρίου (as built) Η γεωμετρική αποτύπωση του σκελετού του κτιρίου έγινε με γεωδαιτικό σταθμό (Total Station) Leica υψηλής ακρίβειας. Η αποτύπωση του κτιρίου έγινε εφόσον ολοκληρώθηκαν όλες οι εργασίες καθαίρεσης των υφιστάμενων τοιχοπληρώσεων, επιχρισμάτων και των επικαλύψεων των δαπέδων. Τα γεωμετρικά δεδομένα αφορούν μόνο το σκελετό του κτιρίου (Διαστάσεις – Ίδια βάρη). Από τη σύγκριση με τις διαθέσιμες τελικές κατόψεις προκύπτει ότι ο υφιστάμενος φορέας δεν παρουσιάζει αποκλίσεις από την αρχική μελέτη ως προς τις διαστάσεις κυρίως των κατακόρυφων δομικών στοιχείων καθώς και τη τοποθέτηση τους στη κάτοψη.

The main objective of the present study is the assessment and retrofit of an existing road bridge that is located in Cyprus over the river Kouris. In particular the study concerns in a road bridge with seven spans of 10.5 m + 5 * 12.6 m + 10.5 m, a cross section width of 7.10 m and a 5 m piers height that was constructed in the early 50's. The structural system of the bridge comprises of cast in situ reinforced concrete T-beams and slab deck that is simply supported on masonry piers. According to the new urban plan to design the bridge should now accommodate two lanes per direction, a pedestrian walkway and a cycling lane with total cross section width of new deck 15.60 m. The deck of the bridge widened using for aesthetic reasons the same cross section type and the new T-Beams and slab deck connected monolithically to the existing one. The existing part of the deck was strengthened with reinforced concrete jacketing due to inadequacy in shear resistance. Major challenge of the project posed the existing masonry pier layout that was insufficient to carry the new design seismic forces. New piers, founded on piles, were designed adjacent to the existing piers in order to support the new widened part of the bridge, and also to bear all the horizontal loads arising from the masses of the total deck. Sliding bearings (free movement) placed in the part of the bridge over the existing piers and elastomeric bearings with movement only in the longitudinal direction placed in the new piers.

The seismic sequence which hit the Northern Italian territory in 2012 produced extensive damage to reinforced concrete (RC) precast buildings typically adopted as industrial facilities. The considered
damaged buildings are constituted by one-storey precast structures with RC columns connected to the ground by means of isolated socket foundations. The roof structural layout is composed of pre-stressed RC beams supporting pre-stressed RC floor elements, both designed as simply supported beams. The observed
damage pattern, already highlighted in previous earthquakes, is mainly related to insufficient connection strength and ductility or to the absence of mechanical devices, being the connections designed neglecting seismic loads or neglecting displacement and rotation compatibility between adjacent elements.
Following the vulnerabilities emerged in past seismic events, the paper investigates the seismic performance of industrial facilities typical of the Italian territory. The European building code seismic assessment methodologies are presented and discussed, as well as the retrofit interventions required to achieve an appropriate level of seismic capacity. The assessment procedure and retrofit solutions are applied to a selected case study.

The main objective of the present study is the assessment and retrofit of an existing road bridge that is located in Cyprus over the river Kouris. In particular the study concerns in a road bridge with seven spans of 10.5 m + 5 * 12.6 m + 10.5 m, a cross section width of 7.10 m and a 5 m piers height that was constructed in the early 50's. The structural system of the bridge comprises of cast in situ reinforced concrete T-beams and slab deck that is simply supported on masonry piers. According to the new urban plan to design the bridge should now accommodate two lanes per direction, a pedestrian walkway and a cycling lane with total cross section width of new deck 15.60 m. The deck of the bridge widened using for aesthetic reasons the same cross section type and the new T-Beams and slab deck connected monolithically to the existing one. The existing part of the deck was strengthened with reinforced concrete jacketing due to inadequacy in shear resistance. Major challenge of the project posed the existing masonry pier layout that was insufficient to carry the new design seismic forces. New piers, founded on piles, were designed adjacent to the existing piers in order to support the new widened part of the bridge, and also to bear all the horizontal loads arising from the masses of the total deck. Sliding bearings (free movement) placed in the part of the bridge over the existing piers and elastomeric bearings with movement only in the longitudinal direction placed in the new piers.

A quite general base connection modeling capable of accurately representing material and geometrical nonlinear behavior of the base plate and arbitrary nonlinear contact with concrete foundation has been demonstrated and its implementation in a finite element nonlinear seismic analysis is presented. A time domain finite element methodology for nonlinear dynamic analysis problem that accounts for base connection lift-off and the inelastic behavior of anchor bolts through an incremental-iterative procedure is developed. A representative problem of cable-stayed bridges tower subjected to strong ground motion is analyzed. The maximum bearing stress on the concrete foundation as well as the tension force per anchor bolt that necessary to design the anchorage system is computed.

The main objective of the present study is the assessment and retrofit of an existing road bridge that is located in Cyprus over the river Kouris. In particular the study concerns in a road bridge with seven spans of 10.5 m + 5 * 12.6 m + 10.5 m, a cross section width of 7.10 m and a 5 m piers height that was constructed in the early 50's. The structural system of the bridge comprises of cast in situ reinforced concrete T-beams and slab deck that is simply supported on masonry piers. According to the new urban plan to design the bridge should now accommodate two lanes per direction, a pedestrian walkway and a cycling lane with total cross section width of new deck 15.60 m. The deck of the bridge widened using for aesthetic reasons the same cross section type and the new T-Beams and slab deck connected monolithically to the existing one. The existing part of the deck was strengthened with reinforced concrete jacketing due to inadequacy in shear resistance. Major challenge of the project posed the existing masonry pier layout that was insufficient to carry the new design seismic forces. New piers, founded on piles, were designed adjacent to the existing piers in order to support the new widened part of the bridge, and also to bear all the horizontal loads arising from the masses of the total deck. Sliding bearings (free movement) placed in the part of the bridge over the existing piers and elastomeric bearings with movement only in the longitudinal direction placed in the new piers.

την Τρίτη 31/05/2016 διοργανώνουμε μια ημερίδα με τίτλο “Αντισεισμικός σχεδιασμός και ενισχύσεις των κατασκευών 2016”

Εδώ μπορείτε να δείτε αναλυτικά το πρόγραμμα και να εγγραφείτε για την βεβαίωση συμμετοχής
http://retrofit.teipir.gr/?page_id=3230

Seismic damage in frame structures often localizes in areas of stiffness deficiency such as soft-storeys. A common remedy in such situations is the addition of stiffness in the structure to limit drift demands thereby controlling the extent of damage. From among the available alternatives, addition of masonry infills is a low-cost, easily replaceable in the event of damage alternative that combines the advantage of not burdening the foundation with excessive flexural strength demands as would occur in the case of infill R.C. structural walls. To facilitate the design of such retrofit solutions, practical design charts have been derived in the paper, linking drift demand to the area ratios of infills in the critical floor of the structure; the number of floors and the strength characteristics of the infills are parameters of the charts. Using the charts dimensioning masonry infills in existing reinforced concrete structures is controlled by performance criteria such as target distributions of interstorey drift demand, a target estimate of the fundamental period as required by the designer, and a limit on acceptable displacement ductility for the retrofitted structure. Application of the retrofit design through infills is demonstrated on example case studies. Behavioral mechanisms mobilized by masonry infills in successful retrofits are shown to emulate confined masonry behaviour. It is also shown that despite their brittleness, well connected infills can successfully mitigate the occurrence of catastrophic damage by diverting damage
localization from the vulnerable regions of the building.