1,721,031 research outputs found
Numerical validation of the generalized equivalent spectral model through crowd dynamics simulations
No full textThis paper aims to provide a validation of the Generalized Equivalent Spectral Model of pedestrian-induced loading through numerical simulations of crowd dynamics. Pedestrian flows with varying density are numerically simulated based on the social force model. The instantaneous step frequency of each pedestrian is obtained from his instantaneous velocity. Results obtained from numerical simulations are statistically analyzed to obtain probability density functions of the step frequency. Then, each pedestrian is modelled as a moving harmonic load, whose trajectory and velocity are obtained from crowd simulations. The power spectral density function of the modal force obtained from numerical simulations is then compared with the analytical expression provided by the Generalized Equivalent Spectral Model. Possible modifications of the original formulation are analyzed, in order to fit numerical results
The Structural Effects of Micro-Geometry on Masonry Vaults
Full text linkMasonry vaults are able to withstand their dead load and external forces thanks to their curved surface, therefore geometry plays a major role in their structural behaviour. Besides the well-known effects of the macro-geometry (overall shape and dimensions), micro-geometry (details of the masonry apparatus) is also expected to play a key role. The study seeks to determine the advantages (constructional and structural) that a specific masonry apparatus offered for simple forms like barrel vaults and more complex forms like cross vaults. It is carried out, firstly, through a critical review of the European technical literature concerning vault construction with particular focus on brick laying techniques; then, numerical approach is adopted to scientifically investigate the role of micro-geometry on the static behaviour of barrel and cross vaults subjected to self-weight. Comparison of results allows observing different structural behaviour (displacement field, elastic stiffness, reaction forces) for different brick patterns and provides a scientific validation to some speculations found in historical technical literature
Finite element models of a benchmark footbridge
Full text linkModern footbridges are often lively structures, characterized by natural frequencies that fall in the range of pedestrian activities, such as walking, running, and jumping. Therefore, serviceability assessment under human-induced excitation is crucial both at the design stage and during the footbridge lifetime. This paper presents and validates two different FE models of an existing footbridge with very complex geometry: the Streicker Footbridge at the Princeton University Campus. It represents a benchmark in the field as a testbed for vibration serviceability assessments under pedestrian excitation. The real structure is equipped with strain and temperature sensors that are currently used to collect measurements in both static and dynamic modes for research and educational purposes in Structural Health Monitoring (SHM). Based on detailed drawings of the Streicker Footbridge, a three-dimensional beam-based model was developed to represent the complex behavior of the full-scale benchmark bridge. Subsequently, a more refined discretization of the bridge deck adopting shell elements was inserted. The bridge Finite Element models were validated against available SHM data concerning static and dynamic tests. The relevant ANSYS APDL script files along with an example of pedestrian jumping application are available upon request for further research developments on the relationship between pedestrians and the benchmark footbridge
Numerical modelling of masonry vaults with different brick pattern
No full textMasonry vaults represent one of the most widespread types of horizontal structural elements in historical constructions. Vaults can be built according to different brick pat terns, which, in historical building practices, were generally chosen for technical reasons. Brick pattern is expected to play an important role in the global behaviour of vaulted structures, but, despite the importance of this topic, its role on the mechanical behaviour of vaults has been investigated only by few authors. This study evaluates the influence of the masonry apparatus in barrel and cross vaults subjected to imposed displace.ments. The study is carried out through a numerical approach, considering micro finite element modelling. Results evidence that different brick patterns correspond to different structural stiffness and reaction forces. Moreover, barrel vaults are more sensitive,. than cross vaults to the orientation of the masonry apparatus
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Vibration Serviceability Assessment of a Historic Suspension Footbridge
No full textExperimental and numerical studies for the structural and vibration serviceability assessment of a historic suspension footbridge adopting non-invasive surveys and low-cost equipment are presented. Field surveys have been carried out to determine geometric properties, ambient vibration tests have been performed to estimate the dynamic properties, and the dynamic response of the footbridge under the action of a single crossing pedestrian has been recorded. Based on field surveys, a 3D Finite Element model was built and was then calibrated against ambient vibration test results. The experimentally-measured maximum acceleration under the action of one crossing pedestrian is compared with the ones obtained numerically and analytically. Furthermore, vibration serviceability assessment under multi-pedestrian loading is carried out, adopting the simplified procedure recommended by a recent guideline. Results show that low-cost non-invasive dynamic testing is suitable to correctly identify the footbridge vertical natural frequencies and mode shapes, including higher-order ones, and to draw considerations about the state of degradation of the structure. Moreover, the level of vibration under the action of a single pedestrian can be estimated with sufficient accuracy using a simplified loading model, provided that the modal damping ratio is properly tuned
Seismic assessment of masonry cross vaults through non-linear static analyses
Full text linkMasonry cross vaults are common structural elements in historical buildings. They are largely diffused in all European countries, including those characterized by higher levels of seismicity. Although they have been constructed for centuries, they represent some of the most vulnerable elements of traditional architecture, especially with reference to horizontal loads. The understanding of their behaviour under seismic loading and the definition of their safety are crucial aspects for the accurate assessment of the global health conditions of historical buildings. In the present work, masonry cross vaults are analysed through the Finite Element Method (FEM) and static non-linear analyses are performed considering the effect of different brick pattern. A simplified micro-modelling approach is adopted for the generation of the FEM models and two different brick arrangements are considered, i.e., radial bricks and diagonal bricks, which are the most widespread in European cross vaults. Static non-linear analyses are performed by monotonically incrementing a lateral acceleration until collapse. Results are analysed in terms of maximum load factor, crack pattern and damage mechanisms. The analysis of the results shows that the masonry apparatus strongly influences the vault seismic response both in terms of stiffness and ductility as well as in terms of global capacity
- …
