Correlations between physical and structural properties of spider silk - Correlaties tussen fysische en structurele eigenschappen van spinnenzijde

Spinnen produceren tot zeven verschillende draden met opmerkelijke mechanische eigenschappen. Als gevolg hiervan is er de laatste jaren veel interesse ontstaan in het ontwerp van deze materialen voor de ontwikkeling van nieuwe proteïne-gebaseerde polymeren. Daarvoor is het vereist om de relaties tussen structuur en eigenschappen te verstaan. De bedoeling van dit doctoraatsonderzoek is om daartoe bij te dragen door het bestuderen van deze relaties voor twee types spinnenzijdes (eizak- en “dragline” spinnenzijde) in vergelijking met zijdes afkomstig van twee rupsen Bombyx mori (of gewone zijde) en Antheraea pernyi (Tussah of wilde zijde). Tijdens dit onderzoek werd vastgesteld dat eizakspinnenzijde een totaal ander mechanisch gedrag vertoont dan de overige zijdes, o.m. de dragline spinnenzijde. Gezien de literatuur zeer beperkt is over dit type spinnenzijde, werd gekozen om de focus dan ook op dit type zijde te leggen. Naast het rek-sterkte gedrag werd ook het visco-elastisch gedrag, meer bepaald het elastisch en kruipgedrag, bestudeerd. De secundaire structuur werd geanalyseerd aan de hand van Fourier-transformatie infraroodspectroscopie (FT-IR) en vastestof nucleaire magnetische resonantie (NMR) spectroscopie. Verder werd ook het thermisch gedrag bestudeerd aan de hand van thermogravimetrie (TGA) en thermische mechanische analyse (TMA). Uit het bekomen structuuronderzoek werd voor eizakspinnenzijde een structureel model afgeleid dat zijn fysische eigenschappen kan verklaren. De structuur van eizakspinnenzijde wordt gedomineerd door een uitgestrekte amorfe faze met verbonden “-turn” structuren. De kristallijne faze is beperkt en bestaat uit korte “-sheet” structuren. Beide fazen zijn verder gegroepeerd tot een niet-fibrillaire kern-mantel structuur

Human-structure interaction effects on the maximum dynamic response based on an equivalent spectral model for pedestrian-induced loading

The paper investigates the effects of the human-structure interaction (HSI) on the dynamic response based on a spectral model for vertical pedestrian-induced forces. The spectral load model proposed in literature can be applied for the vibration serviceability analysis of footbridges subjected to unrestricted pedestrian traffic as well as in crowded conditions, however, in absence of HSI phenomena. To allow for a more accurate prediction of the maximum structural response, the present study in addition accounts for the vertical mechanical interaction between pedestrians, represented by simple lumped parameter models, and the supporting structure. By applying the classic methods of linear random dynamics, the maximum dynamic response is evaluated based on the analytical expression of the spectral model of the loading and the frequency response function (FRF) of the coupled system. The most significant HSI-effect is in the increase of the effective damping ratio of the coupled system that leads to a reduction of the structural response. However, in some cases the effect of the change in the frequency of the coupled system is more significant, whereby this results into a higher structural response when the HSI-effects are accounted for

Serviceability assessment of the Góis footbridge using vibration monitoring

Footbridges are structures that may experience vibration amplification problems caused by pedestrian and/or wind actions. Design codes deal with these phenomena limiting the natural frequencies and the maximum accelerations expected. Aiming at taking into consideration these dynamic phenomena, current procedures to evaluate the structural performance of light-weight bridges based on experimental dynamic analysis are evaluated in this study. To achieve this, the dynamic response of three pedestrians walking, running and jumping was obtained. Maximum comfort limits of dynamic responses were then determined. The results indicate that codes could overestimate the level of vibration in this kind of footbridge(undefined

A simplified method to account for vertical human-structure interaction

This is the final version. Available on open access from Elsevier via the DOI in this recordTo account for vertical human-structure interaction (HSI) in the vibration serviceability analysis, the contact force between the pedestrian and the structure can be modelled as the superposition of the force induced by the pedestrian on a rigid surface and the force resulting from the mechanical interaction between the structure and the human body. For the case of large crowds, this approach leads to (timevariant) models with a very high number of degrees of freedom (DOFs). To simplify analysis, this paper investigates the performance of an equivalent single-degree-of-freedom approach whereby the effect of HSI is translated into an effective natural frequency and modal damping ratio for each mode of the supporting structure. First, the numerical study considers a footbridge structure that is modelled as a simply-supported beam for which only the fundamental vertical bending mode is taken into account. For a relevant range of structure and crowd parameters, the comparison is made between the structural response predicted by the simplified model and the more accurate reference model that accounts for all DOFs of the coupled crowd-structure model. Where the simplified model is found to underestimate the structural response, although to a limited extent, this is compensated for by introducing a correction factor for the effective damping ratio. Second, the performance of the simplified method is evaluated through the application on a real footbridge. The results show that the simplified method allows for a good and mildly conservative estimate of the structural acceleration response that is within 10-20% of the predictions of the reference crowd-structure model.Research Foundation Flanders (FWO

A Robust Methodology for the Reconstruction of the Vertical Pedestrian-Induced Load from the Registered Body Motion

This paper proposes a methodology to reconstruct the vertical GRFs from the registered body motion that is reasonably robust against measurement noise. The vertical GRFs are reconstructed from the experimentally identified time-variant pacing rate and a generalised single-step load model available in the literature. The proposed methodology only requires accurately capturing the body motion within the frequency range 1–10 Hz and does not rely on the exact magnitude of the registered signal. The methodology can therefore also be applied when low-cost sensors are used and to minimize the impact of soft-tissue artefacts. In addition, the proposed procedure can be applied regardless of the position of the sensor on the human body, as long as the recorded body motion allows for identifying the time of a nominally identical event in successive walking cycles. The methodology is illustrated by a numerical example and applied to an experimental dataset where the ground reaction forces and the body motion were registered simultaneously. The results show that the proposed methodology allows for arriving at a good estimate of the vertical ground reaction forces. When the impact of soft-tissue artefacts is low, a comparable estimate can be obtained using Newton’s second law of motion

Advanced Fourier-based Model of Bouncing Loads

This is the author accepted manuscript. The final version is available from Springer via the DOI in this record36th IMAC, A Conference and Exposition on Structural Dynamics 2018Contemporary design guideline pertinent to vibration serviceability of entertaining venues describes bouncing forces as a deterministic and periodic process presentable via Fourier series. However, fitting the Fourier harmonics to a comprehensive database of individual bouncing force records established in this study showed that such a simplification is far too radical, thus leading to a significant loss of information. Building on the conventional Fourier force model, this study makes the harmonics specific to each individual and takes into account imperfections in the bouncing process. The result is a numerical generator of stochastic bouncing force time histories which represent reliably the experimentally recorded bouncing force signals.The authors would like to acknowledge the financial support provided by PRIN 2015-2018 “Identification and monitoring of complex structural systems” and National Natural Science Foundation of China 347 (51478346) and State Key Laboratory for Disaster Reduction of Civil Engineering (SLDRCE14-B-16)

A novel video-vibration monitoring system for walking pattern identification on floors

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordWalking-induced loads on office floors can generate unwanted vibrations. The current multiperson loading models are limited since they do not take into account nondeterministic factors such as pacing rates, walking paths, obstacles in walking paths, busyness of floors, stride lengths, and interactions among the occupants. This study proposes a novel video-vibration monitoring system to investigate the complex human walking patterns on floors. The system is capable of capturing occupant movements on the floor with cameras, and extracting walking trajectories using image processing techniques. To demonstrate its capabilities, the system was installed on a real office floor and resulting trajectories were statistically analyzed to identify the actual walking patterns, paths, pacing rates, and busyness of the floor with respect to time. The correlation between the vibration levels measured by the wireless sensors and the trajectories extracted from the video recordings were also investigated. The results showed that the proposed video-vibration monitoring system has strong potential to be used in training data-driven crowd models, which can be used in future studies to generate realistic multi-person loading scenarios.Qatar National Research Foundatio