Pushover Analysis of Steel Seismic Resistant Frames with RWS and RBS Connections

The widespread brittle failure of welded beam-to-column connections caused by the 1994 Northridge and 1995 Kobe earthquakes highlighted the need for retrofitting measures effective in reducing the strength demand imposed on connections under cyclic loading. Researchers presented the reduced beam section (RBS) as a viable option to create a weak zone away from the connection, aiding the prevention of brittle failure at the connection weld. More recently, an alternative connection known as a reduced web section (RWS) has been developed as a potential replacement, and initial studies show ideal performance in terms of rotational capacity and ductility. This study performs a series of non-linear static pushover analyses using a modal load case on three steel moment-resisting frames of 4-, 8-, and 16-storeys. The frames are studied with three different connection arrangements; fully fixed moment connections, RBSs and RWSs, in order to compare the differences in capacity curves, inter-storey drifts, and plastic hinge formation. The seismic-resistant connections have been modeled as non-linear hinges in ETABS, and their behavior has been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in an earthquake with ground motions having a 2% probability of being exceeded in 50 years. The study concludes that RWSs perform satisfactorily when compared with frames with fully fixed moment connections in terms of providing consistent inter-storey drifts without drastic changes in drift between adjacent storeys in low- to mid-rise frames, without significantly compromising the overall strength capacity of the frames. The use of RWSs in taller frames causes an increase in inter-storey drifts in the lower storeys, as well as causing a large reduction in strength capacity (33%). Frames with RWSs behave comparably to frames with RBSs and are deemed a suitable replacement

Optimum drilled flange moment resisting connections for seismic regions

Extensive damage in welded unreinforced flange (WUF) connections in previous earthquakes has led to the idea of using reduced beam section (RBS) connections to prevent brittle failure modes in welded joints. Using a similar concept, drilled flange (DF) moment resisting connections are established by a series of holes drilling on the top and the bottom flanges of the beam to create an intentional weak area to shift nonlinear deformations. DF connections are very easy-to-construct and they can also prevent the premature local buckling modes in the reduced section of RBS connections. This study aims to improve the performance of DF connections to make them viable alternatives to RBS connections for ductile steel frames in seismic regions. A wide range of experimentally validated non-linear FE models are used to investigate the effects of different design parameters such as drilled flange hole locations, hole configurations, panel zone shear strength ratio and doubler plate thickness. The results indicate that there is an optimum location and configuration for the drilled flange holes, which can reduce by up to 40% the maximum Equivalent Plastic Strain and Rupture Index of DF connections. It is shown that using strong panel zones can also improve the seismic performance of DF connections by reducing stress concentrations at the CJP groove weld lines. The results of this study are used to develop optimum design solutions for DF connections, which should prove useful in practical applications

A FE parametric study of RWS beam-to-column bolted connections with cellular beams

In recent years, researchers study alternative connection designs for steel seismic-resistant frames by reducing the beam section in different ways including that of creating an opening in its web (RWS connections). A similar design is applied in the fabrication of perforated (i.e. cellular and castellated) beams mostly used to support the service integration, as well as the significant mass reduction in steel frames. This paper presents a comprehensive finite element (FE) analysis of extended end-plate beam-to-column connections, with both single and multiple circular web openings introduced along the length of the beam while subjected to the cyclic loading proposed by the SAC protocol from FEMA 350 (2000). The three-dimensional (3D) FE solid model was validated against FE and experimental results and the chosen configuration was capable of representing the structural behaviour of a partially restrained connection, without the necessity to be idealised as fully fixed. The study focuses in the interaction of such connections and the mobilisation of stresses from the column to the perforated beam. The parameters introduced were the distance from the face of the column, S, and the web opening spacing, So, with closely and widely spaced web openings. It is found that RWS connections with cellular beams behave in a satisfactory manner and provide enhanced performance in terms of the stress distribution when subjected to cyclic loading. The design of partially restrained RWS connections should be primarily based on the distance of the first opening from the face of the column

Unattended ground sensors - applications in security and surveillance

Μεταπτυχιακή Διατριβή που υποβλήθηκε στη σχολή ΣΜΠΔ του Πολ. Κρήτης για την πλήρωση προϋποθέσεων λήψης του Μεταπτυχιακού Διπλώματος Ειδίκευσης.Περίληψη: Από αρχαιοτάτων χρόνων, η επιτήρηση και η ασφάλεια περιοχών, εγκαταστάσεων και συνόρων αποτελούσε πολύ σημαντικό παράγοντα στην ευημερία και την επιβίωση μιας κοινωνίας. Τοποθεσίες οικονομικής και στρατηγικής σημασίας, χωριά, πόλεις – κράτη και στρατόπεδα ήταν ουσιαστικά απαραίτητο να φυλάσσονται με κάποιο τρόπο από όσους τα επιβουλεύονταν. Η ανεπαρκής ασφάλεια ή και έλλειψη πληροφοριών σχετικά με πιθανούς εισβολείς μπορούσε συχνά να έχει καταστροφικές συνέπειες. Τα δεδομένα αυτά δυστυχώς δεν έχουν αλλάξει και είναι έως και σήμερα και θα είναι πιθανότατα για αιώνες ακόμη αναγκαία η επαρκής φύλαξη, επιτήρηση και παροχή πληροφοριών σχετικά με ύποπτες κινήσεις σε περιοχές σημασίας. Το θετικό στοιχείο είναι ότι σε αντίθεση με το παρελθόν, όπου τα μέσα ήταν είτε ανύπαρκτα είτε πρωτόγονα κι ανεπαρκή και ήταν απαραίτητη η ανθρώπινη φυσική παρουσία, πλέον υπάρχουν εξελιγμένες κι αποδοτικές μέθοδοι για την επίτευξη του ανωτέρω σκοπού, με μειωμένο κόστος και απασχόληση ανθρώπινου δυναμικού. Αντικείμενο της παρούσας μεταπτυχιακής διατριβής αποτελεί η κατασκευή και χρήση Αυτόνομων Επίγειων Αισθητήρων. Με τη μέθοδο αυτή, είναι δυνατή η σύνθεση ενός συστήματος δικτύου πολυ-αισθητήρων για την επιτήρηση ολόκληρων περιοχών ή περασμάτων διέλευσης ανθρώπων ή οχημάτων, με πολύ μικρό κόστος. Πρέπει να αναφερθεί ότι η εφαρμογή αυτή χαρακτηρίζεται από ελάχιστες απαιτήσεις σε ανθρώπινο δυναμικό και πρακτικώς μηδαμινή ανάγκη συντήρησης του εξοπλισμού, στις περισσότερες περιπτώσεις. Οι ενεργειακές ανάγκες των υπό εξέταση συστημάτων είναι μικρές κάτι που ευνοεί την εφαρμογή τους σε δύσβατες και απομακρυσμένες περιοχές. Θα γίνει επιπλέον παρουσίαση πρακτικής εφαρμογής των Αυτόνομων Επίγειων Αισθητήρων, με κατασκευή λειτουργικών δειγμάτων και δημιουργία κατάλληλης εφαρμογής για τη διασύνδεση τους με έναν Ηλεκτρονικό Υπολογιστή, για την παρουσίαση των δεδομένων και την διαπίστωση της αποτελεσματικότητάς τους. Τέλος, θα παρατεθούν συμπεράσματα και οι παρατηρήσεις από τη χρήση τους και θα προταθούν τρόποι περεταίρω ανάπτυξής τους και πιο αποτελεσματικής χρήσης τους.Summarization: Since ancient times, surveillance and securing of areas, facilities and borders was a very important factor in the welfare and survival of a society. Locations of high economic and strategic importance, villages, city-states and military camps were essentially required to be guarded in some way, from any hostile force. Insufficient security or lack of information on possible intruders could often have catastrophic consequences. This situation hasn’t changed even nowadays, unfortunately, so adequate security, surveillance and collection of information of suspicious movement in proximity to areas of importance are still necessary today and it will probably be for centuries to come. The good news is that unlike what happened in the past, when the surveillance means were inexistent or primitive and inadequate and human presence was necessary, there are nowadays advanced and effective methods that accomplish the above purpose and they manage that with lower cost and less human resources. The subject of this dissertation is the manufacturing and utilization of Unattended Ground Sensors. By employing this method, the synthesis of a system of a multi-sensors' network becomes possible, for the purpose of surveillance of large areas or human and vehicle passages, with a very low cost. It ought to be mentioned that this application is characterized by minimum requirements in human resources and virtually zero need of equipment maintenance, in most cases. The energy requirement of such a system is also very small, which favors its use in inaccessible or remote areas. Moreover, a practical application of Unattended Ground Sensors will be presented, by building operational sample Sensors and a computer application for their interconnection with a Computer, in order for the data to be visualized and their effectiveness to be proven. Finally, conclusions and comments on their utilization will be presented, as well as ways of further improvement and more effective implementation