Assessing the accuracy of RC design code predictions through the use of artificial neural networks

Abstract In light of recently published work highlighting the incompatibility between the concepts underlying current code specifications and fundamental concrete properties, the work presented herein focuses on assessing the ability of the methods adopted by some of the most widely used codes of practice for the design of reinforced concrete structures to provide predictions concerning load-carrying capacity in agreement with their experimentally established counterparts. A comparative study is carried out between the available experimental data and the predictions obtained from (1) the design codes considered, (2) a published alternative method (the compressive force path method), the development of which is based on assumptions different (if not contradictory) to those adopted by the available design codes, as well as (3) artificial neural networks that have been calibrated based on the available test data (the later data are presented herein in the form of a database). The comparative study reveals that the predictions of the artificial neural networks provide a close fit to the available experimental data. In addition, the predictions of the alternative assessment method are often closer to the available test data compared to their counterparts provided by the design codes considered. This highlights the urgent need to re-assess the assumptions upon which the development of the design codes is based and identify the reasons that trigger the observed divergence between their predictions and the experimentally established values. Finally, it is demonstrated that reducing the incompatibility between the concepts underlying the development of the design methods and the fundamental material properties of concrete improves the effectiveness of these methods to a degree that calibration may eventually become unnecessary

Application of strut-and-tie models for assessing RC half-joints not complying with current code specifications

The work described is concerned with an investigation of the effectiveness of the use of strut-and-tie models for the structural assessment of half joints. Such elements form a part of many existing bridges which, although not complying with current code specifications, have not as yet displayed any significant signs of distress in spite of the increase in traffic volume and loads over the years. The work is based on a comparative study of the predicted and experimentally established values of load-carrying capacity and location and causes of failure of half-jointed beams with reinforcement layouts that replicate those found in structures designed in accordance with previous code specifications. The results obtained show significant shortcomings of the assessment method as this is found not only to underestimate load-carrying capacity by a margin ranging between 40 % and 65 %, but also to often fail to identify the location and causes of failure. Therefore, there is a need for an alternative assessment method that will be based on concepts capable of both providing a realistic description of structural-concrete behaviour and identifying the causes of failure leading to the loss of load-carrying capacity

Application of strut-and-tie models for assessing RC half-joints not complying with current code specifications

The work described is concerned with an investigation of the effectiveness of the use of strut-and-tie models for the structural assessment of half joints. Such elements form a part of many existing bridges which, although not complying with current code specifications, have not as yet displayed any significant signs of distress in spite of the increase in traffic volume and loads over the years. The work is based on a comparative study of the predicted and experimentally established values of load-carrying capacity and location and causes of failure of half-jointed beams with reinforcement layouts that replicate those found in structures designed in accordance with previous code specifications. The results obtained show significant shortcomings of the assessment method as this is found not only to underestimate load-carrying capacity by a margin ranging between 40 % and 65 %, but also to often fail to identify the location and causes of failure. Therefore, there is a need for an alternative assessment method that will be based on concepts capable of both providing a realistic description of structural-concrete behaviour and identifying the causes of failure leading to the loss of load-carrying capacity

Behaviour of reinforced concrete beam-molumn joints under cyclic loading

523 σ.Στόχος της Διδακτορικής Διατριβής είναι η ανάπτυξη μιας νέας μεθοδολογίας σχεδιασμού εξωτερικών κόμβων δοκών-υποστυλωμάτων από Ο.Σ. η οποία βασίζεται στην ύπαρξη ενός μηχανισμού αντίστασης, αυτή του διαγώνιου θλιπτήρα, για την παραλαβή και μεταφορά των δυνάμεων μέσα στον κόμβο. Για το σκοπό αυτό πραγματοποιήθηκαν δυο σειρές πειραμάτων σε στοιχεία εξωτερικών κόμβων από Ο.Σ. φυσικής κλίμακας υπό τη δράση στατικής -μονότονης και ανακυκλιζόμενης- φόρτισης. Μέσω της πρώτης σειράς πειραμάτων διερευνήθηκε η εγκυρότητα των κανονιστικών διατάξεων για το σχεδιασμό εξωτερικών κόμβων και από τα αποτελέσματα των πειραμάτων κρίθηκε αναγκαία η ανάπτυξη μιας νέας μεθοδολογίας σχεδιασμού. Στη δεύτερη σειρά πειραμάτων διερευνήθηκε η εγκυρότητα της προτεινόμενης μεθοδολογίας σχεδιασμού και στη συνέχεια τα αποτελέαματα της διερεύνησης αυτής επιβεβαιώθηκαν μέσω μιας συγκριτικής μελέτης των προβλέψεων της προτεινόμενης μεθόδου με δημοσιευμένα πειραματικά αποτελέσματα που προέκυψαν από δοκιμές άλλων ερευνητών σε ένα ευρύ φάσμα δοκιμίων εξωτερικών κόμβων υπό ανακυκλιζόμενη φόρτιση.The main scope of this thesis is the development of a new method for the seismic design of external beam-column joints by considering that the load transferred from the linear elements to the joint is predominantly resisted by a diagonal strut mechanism. For this purpose two test series are carried out on full-size beam column joint sub-assemblages which are subjected to cyclic loading. The first test series is concerned with the investigation of the validity of the current code provisions for the earthquake design of RC external beam-column joints; from the results obtained, it became clear that there is an urgent need for the development of a new method for the earthquake-resistance design of RC external beam-column joints. The second test series investigates the validity of the proposed method, with further evidence for the verification of the proposed design method being obtained from a comparative study of the method’s predictions with already published experimental information on the behaviour of a wide range of exterior beam-column joints sub-assemblanges under cyclic loadinΓρηγορία Μ. Κοτσωβο