1,720,971 research outputs found
Vulnerability and retrofitting of torsionally deformable RC buildings: A case study
Full text linkThe paper presents the seismic vulnerability assessment and the subsequent retrofitting strategies of a reinforced concrete (RC) strategic building in Italy. At time of design, the erection site was not classified as a seismic area. With a structural layout widely spread in non-seismic zones and for buildings designed with obsolete seismic codes, the framed system was designed for gravity loads only, with an eccentric lift core and moment-resisting frames aligned in one direction. The structural seismic capacity is impaired by torsional deformability and the possible appearance of both brittle collapse mechanisms and pounding phenomena with an adjacent building, while the seismic demand is governed by the classification of “strategic building”. Two retrofitting strategies are here analysed, under the constraints of eliminating the torsional deformability and minimizing the interruption of normal activities in the building. The results highlight the advantages and disadvantages of the two strategies and the most important features of the structural response, providing indications for further actions. The adoption of a design spectrum reduced by a 0.6 factor, roughly equivalent to that for an ordinary building, extends the relevance of the work well beyond the case stud
Field-testing and serviceability assessment of a lively footbridge
Full text linkFollowing a previous work, the paper describes the serviceability assessment of a footbridge over the Lambro River near Milano ( Italy), based on the comparative analysis of on-field tests and of the outcome of the Hyvoss guidelines. The 3-span footbridge, for a bicyclepedestrian mixed use, is 107 m long, 4.4 m wide and roughly symmetric about both mid-span and the longitudinal axis. A reinforced concrete (RC) deck is supported by a steel structure: two longitudinal welded I-profiles, braced in their lower part, support the transverse beams that, in turn, support the RC deck. Ambient vibration tests identified the footbridge modal properties, detecting the fundamental bending mode, with the maximum amplitude recorded at mid-span, at 1.75 Hz, well within the critical range of excitation from walking pedestrians. Hence, a series of forced vibration tests was subsequently performed, involving single pedestrians or groups of up to 12 people. Sensors, located as in AVTs, recorded footbridge acceleration, both horizontal and vertical. In all the tests, pedestrians walked in resonance conditions with the first mode frequency along straight trajectories. To excite further the first mode, their spatial configurations were symmetric about the longitudinal axis of the bridge. Difference among tests concerns not only the number of test subjects (TSs), but also their spatial configuration and/or the TSs involved in each test. The comparison among tests sharing similar spatial configurations, with TSs either in a row or in a column, allows a serviceability assessment directly from the experimental footbridge response. The numerical analyses are based on a FE model previously developed, showing an excellent reproduction of the first bending mode, but a poor simulation of the second torsional mode. The outcome of the analyses performed according to HiVoSS guideline is in good agreement with the experimental results, in spite of the very low crowd density of the on-field tests and the unsatisfactory reproduction of the torsional mode within the FE model
Research advancement on Submerged Floating Tunnels: Recent activity at DICA-Politecnico di Milano
No full textA few topics, selected from the recent research activities performed at DICA on Submerged Floating Tunnels (SFTs), are presented concerning load modelling, design procedures and dynamic interaction with travelling vehicles. The prototype structure at study, a design proposal for the Messina Strait crossing, is composed of two single tubes independently anchored to the seabed. A model for generating seaquake effects taking into account the variability of the seabed ground motion over the length-scale of a few kilometers is described. A semi-analytical procedure is proposed to perform a preliminary design, without using a complete finite element model. The bridge-vehicle dynamic interaction is analyzed, to assess the serviceability conditions under the transit of heavy vehicles and high- and medium-speed trains. The research effort aims to the development of a complete analysis and simulation toolbox for the design of SFTs in medium-to-high seadepth
Numerical iterative analysis for vehicle-bridge dynamic interaction
No full textabstract in: D. Bismor, M.I. Michalczyk, M. Pawelczyk, J. Ciešlik eds., “The Sixteenth International Congress on Sound and Vibration, Krakow, Poland, 5-9 July, 2009, Program and Book of abstracts”, pag. 108, ISBN 978-83-60716-72-
Iterative Solution Methods for Coupled Vehicle-Structure Systems
No full textSommario su libro p 485-486. Allegata memoria su CD (stessi autori, stesso titolo) di 10 pagin
Measuring the dynamic response of a lively footbridge to ambient and walking excitation
No full textThe paper presents selected results of a first experimental campaign on a footbridge over-passing the Lambro River near Milano (Italy). The 3-span footbridge, for a bicycle-pedestrian mixed use, has a reinforced concrete deck supported by a steel structure. The footbridge, 107 m long and with a constant width of 4.4m, is roughly symmetric about both mid-span and the longitudinal axis. As a part of proof tests performed in March 2016, ambient vibration tests identified the footbridge modal properties, detecting at 1.75 Hz the fundamental bending mode with the maximum amplitude recorded at mid-span, a finding confirmed by an ANSYS FE model of the footbridge. A series of forced vibration tests, performed in July 2017, investigated the response of the bridge under different loading conditions. Groups of pedestrians, in number of 1, 2, 3, 4, 6, 8 and 12, crossed the bridge, walking with a step frequency as close as possible to the first fundamental frequency. Different spatial configurations were explored for each number of pedestrians, investigating the spread in data related to different walking people/groups and their formation. Pedestrians followed straight trajectories and their spatial configuration was symmetric about the longitudinal axis of the bridge; single pedestrians walked along the footbridge axis. This paper focuses on a few results related to: (a) single pedestrians; (b) groups of multiple pedestrians in the same configuration, a longitudinal row; (c) 12 pedestrians in different spatial configurations. Experimental results highlight the effect of both intra-subject and inter-subject variability and the influence of spatial configuration on the maximum measured acceleration. The bridge performance is discussed by comparison between experimental results and limit values of the vertical acceleration according to HiVoSS guideline
FE modelling of the Streicker footbridge
No full textThe Streicker footbridge was completed in 2010 at the Princeton University Campus, over the Washington Road. It is about 104 m long and consists of a central main span supported by a steel arch and four lateral approaching legs. The deck is a post-tensioned high-performance concrete girder. Steel columns with “Y” shape support four lateral legs that connect the bridge to the lateral bearings on the ground and the whole system results a slender varying cross section main girder. The original shape in the horizontal plane provides horizontal stability to the footbridge despite the intrinsic slenderness of the steel supporting columns. Vertical stability is provided also by the arch in the central main-span and by the supporting columns under the legs. Cross section width increases from the midpoint of the main span to the connections with the legs and then remains constant up to the ground bearings. This work is focused on the development of a finite element analysis of the footbridge at different levels of refinement from the essential implementation of beam elements to more refined FE solutions for the prestressed concrete deck. The models are identified with respect to the available operational modal parameters. This deck discretization could further allow simulating the motion of a running/walking pedestrian along different trajectories
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