Ένα από τα θέματα προβληματισμού στη σεισμική μόνωση γεφυρών μέσω δύο μονωτήρων τριβής σε συμμετρική θέση ως προς τον διαμήκη άξονα της γέφυρας είναι ο μηδενισμός του κατακορύφου φορτίου του εφεδράνου/μονωτήρα λόγω της στρεπτικής - περί το διαμήκη άξονα – ταλάντωσης του φορέα καταστρώματος, οπότε η οριζόντια ταλάντωση και η μεταβολή του κατακορύφου φορτίου των μονωτήρων οφείλονται στην απόκριση της γέφυρας κατά την εγκάρσια στον άξονά της διεύθυνση, και το συχνοτικό περιεχόμενο και οι φάσεις της οριζόντιας και της κατακόρυφης ταλάντωσης επηρεάζονται από κοινού από την ελαστική απόκριση του βάθρου και του φορέα καταστρώματος (στρεπτική ταλάντωση περί τον διαμήκη άξονα). Σκοπός της εργασίας είναι να διερευνήσει τη μεταβολή του αξονικού φορτίου στα εφέδρανα σεισμικής μόνωσης τύπου σφαιρικής επιφάνειας ολίσθησης και την πιθανότητα ανασήκωσης του φορέα καταστρώματος. Περιλαμβάνονται στο προσομοίωμα τα βάθρα και ο φορέας με τους κατάλληλους βαθμούς ελευθερίας και ιδιότητες μάζας και δυσκαμψίας. Γίνεται ανάλυση ευαισθησίας σε μία σειρά από παραμέτρους, όπως η δυσκαμψία των εφεδράνων και του βάθρου, ο λόγος μαζών και υψών φορέα καταστρώματος και βάθρου, τα γεωμετρικά χαρακτηριστικά του φορέα καταστρώματος, η θέση των μονωτήρων ως προς το διαμήκη άξονα της γέφυρας και η ένταση της σεισμικής διέγερσης. Διερευνάται η επιρροή των παραμέτρων αυτών στην απόκριση της γέφυρας (μετατόπιση και επιτάχυνση του φορέα καταστρώματος και του βάθρου) και στην οριζόντια δύναμη που αναλαμβάνουν τα εφέδρανα. Το συμπέρασμα είναι ότι ο κίνδυνος ανασήκωσης του φορέα καταστρώματος εξαρτάται μόνον από τα γεωμετρικά χαρακτηριστικά της διατομής του φορέα καταστρώματος και αυξάνεται κατά πολύ για υψίκορμες διατομές. Σε διατομές με ύψος κιβωτίου παρόμοιου μεγέθους με την απόσταση μεταξύ των εφεδράνων στη στήριξη στο βάθρο, έχομε σχεδόν βέβαιη ανασήκωση του φορέα για σεισμική δράση με PGA στο βράχο πάνω από 0.5g, ή πιθανότητα ανασήκωσης 20-35% γιά PGA στο βράχο 0.4g. Οι υπόλοιπες παράμετροι διαδραματίζουν ασήμαντο ρόλο. Πραγματοποιήθηκε πειραματική και αναλυτική έρευνα σεισμικής μόνωσης γέφυρας με ελαστομεταλλικά εφέδρανα με ή χωρίς πυρήνα μολύβδου (περιλαμβανομένων ψευδοδυναμικών δοκιμών σε μεγάλη κλίμακα), με ή χωρίς πρόσθετη απόσβεση. Επιδιώκεται να προσδιοριστεί η σχέση μεταξύ της αύξησης της θεμελιώδους ιδιοπεριόδου του συστήματος και της προσθήκης αυξημένης απόσβεσης στο σύστημα σε γέφυρες με σεισμική μόνωση και τελικώς να γίνουν συστάσεις για σχεδιασμό και προδιαγραφές. Στο δεύτερο σκέλος της παρούσας διατριβής, παρουσιάζεται η αναλυτική έρευνα, η οποία βασίζεται στα αποτελέσματα τις αντίστοιχης πειραματικής. Περιγράφονται και χρησιμοποιούνται γραμμικά και μη γραμμικά αναλυτικά προσομοιώματα. Διερευνώνται οι καταλληλότερες παράμετροι ανάλυσης των προσομοιωμάτων, ώστε τα αποτελέσματα της ανάλυσης να είναι συμβατά κατά το μέγιστο δυνατόν με τα πειραματικά. Οι παράμετροι ανάλυσης συγκρίνονται με αυτές που προτείνονται από τον κατασκευαστή/προμηθευτή. Διερευνάται η καταλληλότητα του εκάστοτε προσομοιώματος για τις διάφορες εφαρμογές και γίνονται συστάσεις για την ευαισθησία του, την αποτελεσματικότητά του και τον τρόπο χρήσης του. Πέρα από την εύρεση και τον σχολιασμό των κατάλληλων παραμέτρων και συστάσεων για την βέλτιστη ανάλυση, ως γενικότερο συμπέρασμα θα μπορούσε να αναφερθεί το ότι μία «ισοδύναμη» ελαστική (γραμμική) ανάλυση, με κατάλληλη επιλογή παραμέτρων, κρίνεται αρκετά αξιόπιστη για ελαστομεταλλικά εφέδρανα. Ακόμα και η έντονη υστερητική συμπεριφορά των ελαστομεταλλικών εφεδράνων με πυρήνα μολύβδου περιγράφεται αξιόπιστα, χωρίς ένα μη-γραμμικό αναλυτικό μοντέλο (Bouc-Wen) να προσφέρει ιδιαίτερα μεγαλύτερη αξιοπιστία. Στην περίπτωση όμως συστήματος μόνωσης με αποσβεστήρα, μία γραμμική ανάλυση αδυνατεί να περιγράψει με τον καλύτερο δυνατό τρόπο την απόκριση του συστήματος, όταν αυτή καθορίζεται κυρίως από τις ιδιότητες του αποσβεστήρα. Στην τελευταία περίπτωση, ένα πιο σύνθετο μη γραμμικό μοντέλο, προσφέρει μεγαλύτερη αξιοπιστία στον μελετητή. / -

Steel orthotropic and reinforced concrete bridge decks experience costly serviceability problems from fatigue and de-icing salts. Pultruded glass fibre reinforced polymer (GFRP) cellular decks show great promise as a means of tackling these concerns. However uptake of GFRP decks is slow, partly due to limited understanding of key structural facets (including fatigue degradation of GFRP decks under repeated tyre loading) of the resulting new bridge forms. This thesis addresses these shortcomings through extensive experimental and finite element studies, including the construction of an 8 m long, 3.65 m wide full-scale laboratory bridge specimen comprising cellular GFRP decking adhesively bonded across three pre-tensioned concrete beams. From the experiments, the mechanics of Plying of the bonded deck-to-beam connections were elucidated and shown to be a potential concern for the concrete near the bond line. Polymer concrete surfacing applied to the deck was observed to significantly reduce the local patch load-induced strains, whilst also altering the contact mechanics between the loader and the flexible decking. FE modelling reliably predicted these experimentally-observed mechanics.

Integral abutment bridges, also known as integral bridges, have become one of the most common types of joint-less bridge construction, certainly over the last three decades. Their principal advantages are derived from the elimination of expansion joints and bearings, making them a very cost-effective system in terms of construction, maintenance, and longevity. The elimination of joints from bridges creates a significant soil-structure interaction behind the abutment and the piles generating an interesting problem since the response of the different elements of the integral bridge are interdependent. This research project used numerical analyses to investigate the complex interactions that exist between the structural components of the stub-type integral abutment bridge and the backfill soil. Where possible, these results were validated with existing field data. A literature review was conducted to gain an insight into the behaviour of integral abutment bridges, particularly the soil-structure interaction of integral bridges. To gain a better understanding of the behaviour of integral abutment bridges and their interaction with the backfill soil adjacent to the abutment and the piles, particularly due to thermally induced movement/loads, a 2D finite element analysis was performed on a typical integral abutment bridge using OASYS GSA and OASYS SAFE. The results from this research are believed to help answer two of the most debated issues with respect to stub-type integral abutment bridge-soil interaction analyses. Firstly, it is clear, and now possible, that a reliably accurate soil profile is used in the analysis/design. The Mohr-Coulomb soil model was found to realistically represent the soil behaviour. Secondly, the research may suggest that cyclic movements / loads may not significantly influence the overall behaviour of integral abutment bridges. In addition, it was found that the development of earth pressure behind the integral abutment is significantly affected by the backfill soil properties and is a function of the integral abutment displacement. Limiting values for the abutment displacement, which induces maximum backfill pressure, have been suggested. The soil separation phenomenon (gapping) was also found to significantly affect the backfill/foundation soil-load relationship behaviour. Implications· of this research for practising engineers and recommendations for future research work are also included.

Masonry arch bridges continue to play an important role in the UK's transport infrastructure, forming a significant proportion of road, rail and waterway crossings. Many of these bridges are relatively old and are still in service in their original configuration. Increasing vehicle loads and speeds have highlighted the need for reliable estimates of both ultimate and serviceability load levels. Most experimental work and assessment methods have so far been carried out under ultimate load. Only limited work has been undertaken to date on serviceability assessment methods, this project therefore aims to develop a systematic method to assess the serviceability load of masonry bridges under a series of different serviceability criteria. A complex spreadsheet was developed as the main analytical tool for the serviceability assessment and was an encastered elastic analysis based on Castigliano's complementary energy method. The geometric data from a large number of real masonry bridges data was gathered and analysed to develop suitable distribution statistics. Three independent serviceability criteria were then developed based on an attempt to replicate, on average, the existing assessment methods. These three criteria are stress, deflection and cracking depth. Finally, a serviceability assessment method system was fully established within the developed spreadsheet.

No description available.

This thesis investigates human-structure interactions between pedestrians and oscillating footbridges via experimental kinematic and kinetic tests. The first aspect was to improve and validate a simple frontal plane gait model, the Inverted Pendulum Model (IPM), based on kinematic and kinetic gait data for stable ground walking. Next, test subjects were recorded while crossing a laterally swaying footbridge in order to examine kinematic and kinetic walking patterns and assess the model's accuracy at predicting unstable gait. Participants were recorded walking over force plates in a gait laboratory so their normal ground forces could be compared to each other and the IPM. High inter-subject variability and low intra-subject variability were observed. The IPM did not reproduce transient components of the ground forces. An analysis of the IPM's inherent assumptions revealed that some were inappropriate. A Modified Inverted Pendulum Model (MIPM) is proposed, eliminating some of the IPM's assumptions. For all samples examined, the correlation between the real ground forces and the MIPM was higher than that of the IPM. Custom-designed force plates were installed into a novel laboratory footbridge rig. The footbridge was excited naturally by the participants' walking and the participants responded naturally to the swaying of the bridge. The participants' step widths could be predicted by the phase of the structure at the previous heel strike. At high structural amplitudes, CoP and ground force patterns were dominated by the motion of the structure. Centre of Mass (CoM) motion was found to be 'fixed-in-space' with patterns dissimilar to those anticipated by the IPM. The MIPM was typically better than the IPM at predicting ground forces on the moving base. Finally, a spherical model was compared to the two-dimensional MIPM. The model exhibited few discrepancies to the spherical kinematic data, but the predicted medial-lateral ground forces were significantly different to the force plate data.

No description available.

The selection process of bridge superstructure construction methods in Egypt currently depends on experts' knowledge, experience and intuition and is not supported by systematic procedures. This means that the decisions made can be sub-optimal, not taking account of all the necessary considerations. Invariably, these are cost, schedule and quality problems. This thesis is concerned with the development of a decision support system that provides a systematic and structured framework to improve the current selection process of bridge superstructure construction methods.

Bridges play an important role as the backbone of a country’s road network system, since they have a major impact on a country’s industrial development. Therefore, a vast amount of public and private capital is invested into bridge construction. For this reason, bridges will continue to be constructed as long as they contribute to both the economic development and the industrial development of a country. Currently, bridges are evolving fast in terms of their size and roles on account of developments inrelevant techniques and the use of advanced computers and information technology (IT). However, bridge monitoring technologies have fallen behind these rapidly advancing bridge construction techniques. Bridge accidents can be directly linked to the indifference of society and slow developments in monitoring systems of the road network system. Consequently, a number of bridge collapse accidents have occurred either directly or indirectly as a result of a lapse in monitoring. These accidents are attributed mainly to construction-oriented policies and the public’s insensitivity to safety. The ultimate goal of the present study is to establish a global navigation satellite system (GNSS)-based bridge health monitoring system (BUMS). The study was implemented under the category of a structuralhealth monitoring (SHM) system. In addition, a variety of experiments were performed and algorithms were applied in the study in order to obtain a more reliable set of results and to achieve safer information delivery and operation of the system. The outcome is the realization of a new' paradigm of a BHMS, which outperforms its present counterpart.

Bridge falsework systems are one of the most common temporary structures used in the construction industry, namely to support the formwork during the construction, rehabilitation or retrofit works of concrete bridges and viaducts. This Thesis presents new results and research that improve the available knowledge about the structural behaviour, reliability, robustness and risk of these structures. The main, internal and external, hazards are identified and detailed, including the procedural, enabling and triggering hazards. The use of reduction factors to determine the values of the applied loads to design bridge falsework, and other temporary structures, is critically analysed and it is recommended not to use them, unless supported by specific site data. The importance of implementing effective quality control, inspection and communication measures to manage human errors during planning, designing and operation is highlighted. From the 192 tests carried out during the experimental campaign, consisting of five different tests using three different joint types, new results are obtained concerning bridge falsework components, namely the bending behaviour and resistance of spigot joints and forkhead joints (falsework to formwork interface) from which no published research was found. Existing joint models are evaluated and improved alternative models are developed. The results of numerical studies of a selected structural system are presented using a novel joint finite element and information gathered from the experimental tests. This new finite element has features that the available elements in ABAQUS® program do not have, specifically the capability of simulating an analytical modelling of the cyclic behaviour of joints with allowance for stiffness and resistance degradation and joint failure. The accuracy and precision of the developed numerical models improves the existing numerical results of full-scale tests of bridge falsework systems, in respect to structural behaviour and resistance. It is recommended that formwork should be explicitly modelled and modelling of spigot joints should follow the model presented in this Thesis. From a sensitivity analysis of the bridge falsework systems to modelling hypothesis, it is found that the most important joints are the beam-to-column joint, followed by the forkhead joint and the spigot joint, with variations of up to 70% between the resistance of the system when the joints are modelled as continuous or as pinned. A key contribution of the Thesis is to introduce a novel risk management methodology based on newly developed robustness and fragility indices. This new methodology is applicable, in principle, to all structural analyses not only those concerning bridge falsework systems. Based on advanced deterministic studies, the main parameters affecting the performance of bridge falsework are identified, analysed and discussed. These studies involved a comprehensive set of external and internal hazards: (i) applied external actions of different nature and (ii) structural configurations to design bridge falsework. It is found that differential ground settlements are a critical action and that stiffer systems are more sensitive. Also, it is highlighted by use of plenty examples that bracing is an essential design requirement. Advanced stochastic investigations are also carried out, in which the key random variables that control the stochastic behaviour of bridge falsework systems are identified, namely joint looseness and initial stiffness after looseness. Possible strategies to increase robustness and decrease fragility are discussed and based on an application example the cost-benefit of alternative solutions is investigated. It is concluded that implementing quality control and quality assurance procedures to bridge falsework elements is an extremely effective and efficient way of reducing existing risks. The information gathered in this Thesis can be used to develop more rational and reliable bridge falsework structures thus safer and more design efficient.