On modal analysis of laminated glass: Usability of simplified methods and Enhanced Effective Thickness

Fasan

2019

Applied Sciences

The vibration performance of pedestrian structures attracts the attention of several studies, especially with respect to unfavorable operational conditions or possible damage scenarios. Given a pedestrian system, specific vibration comfort levels must be satisfied in addition to basic safety requirements, depending on the class of use, the structural typology and the materials. To this aim, guideline documents of the literature offer simplified single-degree-of-freedom (SDOF) approaches to estimate the maximum expected vibrations and to verify the required comfort limits. Most of these documents, however, are specifically calibrated for specific scenarios/structural typologies. Dedicated methods of design and analysis, in this regard, may be required for structural glass pedestrian systems, due to their intrinsic features (small thickness-to-size ratios, high flexibility, type and number of supports, live-to-dead load ratios, use of materials that are susceptible to mechanical degradation with time/temperature/humidity, etc.). Careful consideration could be then needed not only at the design stage, but also during the service life of a given glass walkway. In this paper, the dynamic performance of an in-service glass walkway is taken into account and explored via field vibration experiments. A set of walking configurations of technical interest is considered, involving 20 volunteers and several movement features. The vibration comfort of the structure is then assessed based on experimental estimates and existing guideline documents. The intrinsic uncertainties and limits of simplified approaches of literature are discussed, with respect to the performance of the examined glass walkway. In conclusion, the test predictions are also used to derive “perception index” data and scales that could support a reliable vibration comfort assessment of in-service pedestrian glass structures.

Section: Vibration Analysis and Human-structure Interaction (Hsi) Phementioning

confidence: 99%

Section: Vibration Analysis and Human-structure Interaction (Hsi) Phementioning

confidence: 99%

Reliability of Field Experiments, Analytical Methods and Pedestrian’s Perception Scales for the Vibration Serviceability Assessment of an In-Service Glass Walkway

Fasan

2019

Applied Sciences

“…While Z and H can be rationally estimated, and the fundamental period T 1 of the full building can be calculated based on approximate formulations, the reliable estimation of T a can represent a severe challenge for designers. It was shown for example in [33][34][35] that-even for simple independent glass elements with a beam behaviour-the local detailing of restraints can have marked effects on the vibration period T a (and also damping capacity). When more detailed calculations are available, the use of maximum R a values from Figure 5a could result in extremely conservative assumptions, thus in over-design of glass members.…”

Section: Design Seismic Force and Q-behaviour Factormentioning

confidence: 99%

Safety Issues in the Seismic Design of Secondary Frameless Glass Structures

Amadio

Noè

2019

Safety

Glass is largely used in buildings, in the form of an innovative and versatile material. Both for novel and existing constructions, secondary glass systems are frequently realized to interact with primary components of different materials. In most cases, the structural challenge deriving from the intrinsic brittleness and vulnerability of glass is efficiently controlled via laminated (LG) multi-layer sections. However, further potential risks for people should be properly minimized, like for example, in the presence of extreme loads. This is the case of seismic regions, where dedicated calculation methods are required to accommodate displacement and resistance demands, but design specifications are rarely provided by existing standards for earthquake resistant buildings. Even more attention is needed for frameless glass systems in which the bracing members (i.e., continuous frames, cable-nets, etc.,) are reduced to a minimum, in favour of metal point connections (i.e., bolts and mechanical fixings, friction clamps, etc.). This paper aims at discussing the current design requirements for the seismic performance assessment of these relatively simple but challenging structural solutions, with careful consideration for the Italian scenario, where a practical support for design can be found in the CNR-DT 210/2013 technical document. Based on a case-study system, major issues, open questions and uncertainties or critical aspects for the seismic analysis and design of secondary frameless glass assemblies are thus emphasized.

“…While the research community is spending efforts for the refinement or development of analytical/graphical design procedures that are able to capture the limit states of interest for design, the actual dynamic behaviour of even simple laminated glass elements is often described by means of While the research community is spending efforts for the refinement or development of analytical/graphical design procedures that are able to capture the limit states of interest for design, the actual dynamic behaviour of even simple laminated glass elements is often described by means of approximate methods/working assumptions [17]. Such a strategy can be beneficial at the preliminary design stage.…”

Section: Introductionmentioning

confidence: 99%

“…To this aim, classical analytical methods are first recalled in Section 2, so as to introduce the literature concept of "adjusted dynamic" effective thickness for LG beams [17]. Hence, preliminary analytical calculations are carried out on a wide set of LG beams, giving evidence of the expected sensitivity of frequency estimates to some variations in the LG beam composition and/or geometrical configuration.…”

Section: Introductionmentioning

confidence: 99%

Issues on the Vibration Analysis of In-Service Laminated Glass Structures: Analytical, Experimental and Numerical Investigations on Delaminated Beams

2019

Applied Sciences

Load-bearing laminated glass (LG) elements take the form of simple members in buildings (i.e., columns, beams, and plates) or realize stand-alone assemblies, where glass and other traditional constructional materials can interact. Among several relevant aspects, the dynamic response of LG structures requires dedicated methods of analysis, towards the fulfilment of safe design purposes. A combination of multiple aspects must be taken into account for dynamic calculations of even simple LG elements when compared to static conditions, first of all the sensitivity of common interlayers to the imposed vibration frequency. The challenge is even more complex for the vibration serviceability assessment of in-service LG structures, where the degradation of materials and possible delamination effects could manifest, hence resulting in structural performances that can markedly differ from early-design conditions. Major uncertainties can be associated to the actual mechanical characterization of materials in use (especially the viscoelastic interlayers), as well as the contribution of restraints (as compared to ideal boundaries) and the possible degradation of the bonding layers (i.e., delaminations). All of these aspects are examined in the paper, with the support of extended analytical calculations, on-site experimental measurements, and parametric Finite Element (FE) numerical analyses. When compared to literature efforts accounting for ideal boundaries only, an analytical formulation is proposed to include the effects of flexible restraints in the dynamic performance of general (double) LG beams. Special care is also spent for the presence of possible delaminations, including size and position effects. In the latter case, existing formulations for composite laminates are preliminarily adapted to LG beams. Their reliability and accuracy is assessed with the support of test predictions and parametric FE simulations.