Ground-borne noise and vibration transmitted from subway networks to multi-storey reinforced concrete buildings

During the operation of urban subway rail transit systems, vibrations are generated that transmitted through the soil, induce vibrations in nearby buildings. The transmission of ground-borne vibrations from subway rail transit systems in a building is governed by the soil-foundation interaction, the reduction of vibration level between floors, and the amplication due to resonances of building elements. These are influenced by the type of the building, its construction materials, the foundation soil, and the frequency content of the excitation. A methodology is proposed for the determination of the sound vibration along the height of the building for a specic construction type, demonstrating how the attenuation and amplication parameters can be calculated. For this particular building type, a notable amplication of the vibration due to floor and other structural resonances was found, whereas the vibration and hence the radiated noise levels are similar from the first floor up. An overall building amplication factor is proposed, taking into account all the above mentioned transmission mechanisms. First published online 04 September 201

Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

The first author would like to acknowledge the financial support from the European Union under the FP7 COFUND Marie Curie Action. N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 n. 279985 BIHSNAM, ERC PoC 2015 n. 693670 SILKENE), and by the EU under the FET Graphene Flagship (WP 14 “Polymer nano-composites” n. 696656)

Structural impact response for assessing railway vibration induced on buildings

Over the syears, the rapid growth in railway infrastructure has led to numerous environmental challenges. One such significant issue, particularly in urban areas, is ground-borne vibration. A common source of ground-borne vibration is caused by local defects (e.g. rail joints, switches, turnouts, etc.) that generate large amplitude excitations at isolated locations. Modelling these excitation sources is particularly challenging and requires the use of complex and extensive computational efforts. For some situations, the use of experiments and measured data offers a rapid way to estimate the effect of such defects and to evaluate the railway vibration levels using a scoping approach. In this paper, the problem of railway-induced ground vibrations is presented along with experimental studies to assess the ground vibration and ground borne noise levels, with a particular focus on the structural response of sensitive buildings. The behaviour of particular building foundations is evaluated through experimental data collected in Brussels Region, by presenting the expected frequency responses for various types of buildings, taking into account both the soil-structure interaction and the tramway track response. A second study is dedicated to the Athens metro, where transmissibility functions are used to analyse the effect of various Athenian building face to metro network trough comprehensive measurement campaigns. This allows the verification of appropriate vibration mitigation measures. These benchmark applications based on experimental results have been proved to be efficient to treat a complex problem encountered in practice in urban areas, where the urban rail network interacts with important local defects and where the rise of railway ground vibration problems has clearly been identified

Statistical Validation of a Rocking Numerical Model

Validation of numerical models is a paramount task for the design of structures and introduction of new construction solutions in practice. Up to now, rocking structures have been considered unpredictable, hampering their use in practice. Using a recently proposed statistical validation method, this paper claims that rocking motion can be predicted. Herein, a simple 3D wobbling rocking model is statistically validated against multiple shake table tests. Both numerical and experimental seismic response are clustered in six bins, sorted according the excitation type and intensity, and their cumulative distribution functions and median response are compared. The paper shows that, even though the numerical model does not account for sliding and twisting of the columns, it still represents well the statistics of the horizontal displacement of the rocking system. Only in 1 out of the 6 cases the numerical model fails to predict well the statistics of the tested rocking system. Thus, as structures are usually designed for set ground of motions and not individual ground motions, the paper claims that the statistical validation is sufficient and appropriate for validation of rocking models

Shaking table tests of a resilient bridge system with precast reinforced concrete columns equipped with springs

This paper presents the shake table test results of a novel system for the design of precast reinforced concrete bridges. The specimen comprises a slab and four precast columns. The connections are dry and the columns are connected to the slab by an ungrouted tendon. One of the tendon ends is anchored above the slab, in series with a stack of washer springs, while the other end is anchored at the bottom of the column. The addition of such a flexible restraining system increases the stability of the system, while keeping it relatively flexible allowing it to experience negative post-uplift stiffness. It is a form of seismic isolation. Anchoring the tendon within the column, caps the design moment of the foundation, and reduces its size. One hundred and eighty-one shake table tests were performed. The first 180 caused negligible damage to the specimen, mainly abrasion at the perimeter of the column top ends. Hence, the system proved resilient. The 181st excitation caused collapse, because the tendons unexpectedly failed at a load less than 50% of their capacity (provided by the manufacturer), due to the failure of their end socket. This highlights the importance of properly designing the tendons. The tests were used to statistically validate a rigid body model. The model performed reasonably well never underestimating the median displacement response of the center of mass of the slab by more than 30%. However, the model cannot predict the torsion rotation of the slab that was observed in the tests and is due to imperfections.ISSN:0098-8847ISSN:1096-984

Shaking table tests of a re-usable, sustainable, and resilient bridge system with rocking columns

This paper presents the results of shaking table tests of a system exhibiting negative stiffness. As the system uses dry connections, it is suitable for precast construction, and it can be easily disassembled and re-used. The specimen was composed of four restrained rocking columns and a slab. The reinforced concrete columns were protected by steel jackets at both ends and restrained by an ungrouted tendon in series with disc springs. The tendons were anchored at the bottom of the columns and above the slab. The intention of the design concept is to reduce the size of pile foundations, which, in conventional bridges, can comprise a large portion of the total reinforced concrete of the project and is often governed by seismic loading. Hence it saves material and is a contribution towards sustainable design. The system was simultaneously excited in the longitudinal, transversal, and vertical directions by 181 scaled real seismic records. During the tests, it could be observed that the columns not only rocked, but also twisted and slid. The only damage noticed during the first 180 excitations was abrasion on the edges of the steel jackets. The last excitation (#181), however, caused collapse. The tendons unexpectedly failed at a load less than 50% of their capacity (provided by the manufacturer), due to failure of their end socket. This failure highlights the importance of the tendons for the stability of the system at large displacements. The response of the system is discussed in detail presenting the main characteristics of the system

Σεισμική Μόνωση Προκατασκευασμένων Λικνιζόμενων Γεφυρών με Τένοντες και Ελατήρια: Δοκιμές Σεισμικής Τράπεζας

Παρουσιάζονται οι πειραματικές δοκιμές σε σεισμική τράπεζα ενός λικνιζόμενου συστήματος αρνητικής δυσκαμψίας. Το σύστημα αποτελείται από 4 λικνιζόμενα προκατασκευασμένα υποστυλώματα που στηρίζουν μια πλάκα. Ελεύθεροι τένοντες σε σειρά με κωνικά ελατήρια συνδέουν τα μέλη. Μεταλλικοί μανδύες συνδέουν και προστατεύουν τα άκρα των υποστυλωμάτων. Το δοκίμιο αποτελεί παράδειγμα σχεδιασμού προκατασκευασμένης λικνιζόμενης γέφυρας. Το ανασήκωμα των υποστυλωμάτων δρα ως σεισμική μόνωση και περιορίζει τη ροπή σχεδιασμού του θεμελίου. Το σύστημα υπεβλήθη σε 181 διεγέρσεις. Η μόνη βλάβη που προξένησαν οι 180 διεγέρσεις ήταν μια μικρή απόξεση των χαλύβδινων μανδυών. Το σύστημα κατέρρευσε κατά την τελευταία διέγερση, λόγω της απροσδόκητης αστοχίας του τένοντα σε φορτίο που αντιστοιχεί στη μισή αντοχή σχεδιασμού