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The seismic vulnerability assessment of existing structures is a well-known challenging task, due to a combination of several aspects. The use of analytical or finite element (FE) numerical models can offer robust support in this analysis but necessitates the accurate calibration of geometrical and mechanical input, with related uncertainties. In this paper, attention is focused on the identification of dynamic parameters, based on modal numerical analysis, of a 50-year-old, reinforced concrete, elevated water tank (EWT) characterised by a reservoir with a truncated cone shape. The structure is located in a high seismic region of northern Italy and presently necessitates retrofit plans to preserve its functionality. Based on the limited available experimental evidence and technical drawings, major efforts are spent for the numerical prediction of fundamental vibration modes and frequencies of the structure, which represent a first key step for seismic analyses, under various water-filling levels. To this aim, four different FE numerical strategies able to include both structural features and possible fluid–structure interaction (FSI) effects are developed. By progressively increasing the computational cost (and expected the accuracy of the solutions), FE models based on added-mass (M0 model), spring-mass (M1-DM or M1-DS models), or acoustic (M2 model) strategies are taken into account and combined with increasing detailing in geometrical description of the structure. Results from parametric modal analyses are discussed for the case-study EWT, in terms of computational cost, possible numerical limitations, accuracy of predicted frequencies/modal shapes, sensitivity to water-filling levels and operational configurations, with the support of several pieces of experimental evidence and consolidated analytical formulations for fundamental frequency estimations.

The use of simplified tools in support of the mechanical performance assessment of pedestrian structures is strongly attractive for designers due to practical efficiency, as well as for researchers in terms of innovation and the assessment of new proposals. On the side of design, the vibration serviceability requires that specific comfort levels for pedestrians are satisfied by taking into account conventional performance indicators and the class of use, or the structural typology for pedestrian systems’ object of analysis. A major issue, in this context, is represented by long-term performance of systems (especially pedestrian) that are based on innovative or sensitive materials and possibly affected by degradation or even damage, and thus potentially unsafe. Consequently, it is clear that, especially for in-service structures, the availability of standardized non-destructive protocols for a reliable (and possibly rapid) structural assessment can represent an efficient support for diagnostics. This perspective paper poses the attention on the residual capacity quantification of laminated glass (LG) pedestrian structures, and on the assessment of experimental and/or numerical tools for their analysis. To this aim, three modular units belonging to two different indoor, in-service pedestrian systems are taken into account like pilot studies. On the practical side, as shown, a primary role is assigned to Operational Modal Analysis (OMA) procedures, which are used on-site, to quantify their structural performance based on vibration response, including damage detection and inverse characterization of materials degradation. As shown, based on earlier detailed validation, it is proven that a rapid structural assessment can be based on a single triaxial Micro Electro-Mechanical System (MEMS) accelerometer, which can be used to derive relevant capacity measures and indicators. To develop possible general recommendations of technical interest for in-service LG pedestrian systems, the so-calculated experimental performance indicators are assessed towards various traditional design procedures and literature approaches of classical use for structural diagnostic purposes, which are presently extended to the structural typology of LG systems.

Bonded-in-Rod (BiR) connections for timber structures are becoming rather popular solution, in place of other traditional fastening techniques. Besides, design rules and recommendations in support of safe and robust verification are still poor in existing standards. As such, the actual mechanical performance and load-bearing capacity – which is severely affected by a multitude of operational parameters – should be possibly addressed with the support of experimental investigations. In this paper, a Cohesive Zone Modelling (CZM) based, Finite Element (FE) numerical investigation is proposed for a total of 144 BiR joints characterized by various geometrical and mechanical properties, including grain orientation (α = 0° or 90°), adhesive type (polyurethane or epoxy glue), diameter (d = 10, 14, 20 mm) and anchorage length of rods (L = 60, 100, 200, 400 mm) is presented. Most importantly, the attention is also focused on the analysis of service class effects / moisture content (9, 18 or 27 %) on the actual residual capacity of the examined joints, which is of paramount importance for safe design applications in timber structures. Based on validation of input model properties to past experimental results, the sensitivity of basic mechanical performance indicators for the examined BiR samples is discussed in the paper.

Mechanical performance assessment of load-bearing elements under ordinary design actions is a priority when material degradation or even severe damage may be experienced. This is especially the case of unconventional constructional materials, or assembled systems like laminated glass (LG) solutions, in which multiple load-bearing components may suffer of different mechanical issues. This turns out in potential risk for customers, and in the need of specific design assumptions to address the problem. For load-bearing elements with direct interaction with final users (as pedestrian systems), a reciprocal modification of mechanical and dynamic parameters should be properly taken into account in the early design process. This paper explores the sensitivity of human-structure interaction effects and performance indicators for LG slab modules subjected to various walking paths of single pedestrians. An extended set of Finite Element (FE) nonlinear dynamic numerical simulations is presented, in which the variation of conventional performance indicators (such as acceleration peaks, deflection, vibration frequency) is investigated for two in-service LG modular units with intact (LGU) or partially fractured (LGF) glass layers. Walking scenarios are described with the support of consolidated deterministic method in use for pedestrian loads, in which walking features do not account for the features of structural background. The comparative analysis of numerical results with earlier experimental outcomes for two reference LG slab modules subjected to random walking conditions shows that time-domain nonlinear simulations with simplified pedestrian loads can efficiently capture some major effects of pedestrians, as well as the presence of damage in glass. At the same time, it is shown that fractured glass layers in LG pedestrian modules can still provide partial post-breakage contribution to the resisting section.

The lateral torsional buckling (LTB) analysis of glass members is a well-known issue, and can be critical for the design of glass fins that are used to brace slab panels or walls and facades . In this paper, the attention is focused on the LTB analysis of glass fins that are restrained to glass wall panels via continuous, flexible joints able to act as lateral restraints (LRs). Under typical wind pressures, the LTB analysis of fins can be critical for overpressure but especially for suction, given that the LR effect at the compressed or tensioned edge largely modifies. Based on literature efforts, closed-form expressions are presented and validated with the support of geometrically simplified but accurate Finite Element (FE) numerical models. The final result is that for a general configuration, the elastic critical buckling moment of LR fins with tensioned edge restrained can be easily predicted. However, a multitude of parameters can affect the expected effect due to LRs. As such, a simplified linearized formulation is proposed to capture the limit conditions for LRs in a given glass geometry. As shown, the formulations can be used also for laminated glass members, as far as the composite section properties are properly take into account. Finally, worked examples are presented to quantify the potential of LRs for LTB verification purposes.

Laminated glass beams without metallic or polymeric reinforcements generally lack post-breakage strength and ductility. This paper aims to perform a comparative study by testing five different fully transparent laminated glass beam designs in order to see how parameters such as the number and thickness of glass sheets (3 x 10 mm or 5 x 6 mm), the interlayer material (PVB Clear or SentryGlas), and the thermal treatment of glass (annealed or heat-strengthened) affect the pre-breakage performance and post-breakage safety. A buckling analysis is also performed using a numerical model with ABAQUS CAE. The study includes a comparison between the results of different experimental mechanical tests on laminated glass beams, including the tests presented in this paper, as well as other tests found in the literature. All designs presented a linear elastic behaviour until initial breakage. The interlayer material mainly affected the crack shape of laminated glass beams. Beams with five sheets of annealed glass had a more progressive breakage, and therefore a safer behaviour, than beams with three sheets of annealed or heat-strengthened glass. The work was partially funded by CRISTEC with CDTI funds (IDI-20160588). The authors at the University of Lleida would like to thank the Catalan Government for the quality accreditation given to their research group GREiA (2017 SGR 1537). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme. The financing support given by the Spanish Ministry of Economy and Competitiveness through the project BIA2014-53774-R is gratefully appreciated. Xavier Centelles would like to thank University of Lleida for his research fellowship and to the University of Oviedo for hosting his secondment during 2019. Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Insulated Glass Units (IGUs) typically consist of two glass layers, either monolithic and/or laminated sections, that mechanically interact via an hermetically-sealed air (or gas) cavity, and a series of linear spacer connections along their edges. In this paper, based on the experimental tests for small-scale IGU joints under pure shear and IGU prototypes in bending discussed in “Part I”, a special care is spent for the Finite Element (FE) numerical characterization and analysis of these composite systems, with a focus on the actual mechanical properties and load-bearing mechanism for the involved components. Major advantage is taken from the full 3D solid geometrical description of the connection components and the gas cavity infill. The actual role of both primary and secondary sealant layers is first assessed. Further support is derived from analytical calculations for the connection efficiency assessment, based on the adaptation of simplified formulations of literature. Finally, a calculation example is proposed to assess the magnitude of load sharing phenomena, based on FE numerical and analytical calculations for selected configurations.

Increasing terrorist attacks towards ordinary or strategic buildings and soft targets represent one of the major impetus to improve existing methods of design for blast-resistant structures. When a building undergoes an extreme dynamic event such as blast or impact, local damage of its key structural components (i.e., the columns) may lead to severe failure and even collapse of the entire building. Consequently, the availability of simplified, time efficient and reliable methods of analysis can be relevant for design. In this paper, H-section steel columns subjected to blast loads are numerically investigated, so as to derive practical formulations for damage evaluation assessment. The strategy is based on parametric Finite Element (FE) models (with up to 5600 configurations), validated towards experiments and, used as an extensive data bank, for further elaboration via Gene Expression Programming. Analytical formulations are in fact proposed for calculating some relevant parameters of design, such as (a) the initial and (b) the residual axial capacity of the examined columns. The collected results show that the proposed formulations can offer a good level of accuracy and high calculation efficiency for blast loaded H-section steel columns. In addition, an expression is proposed to relate the damage index (based residual axial capacity) to the conventional displacement/rotational index. Sensitivity analyses and some calculation examples are finally presented, to further investigate the potential of the approach for design purposes.

Structural glass represents a relatively new solution for constructions, requiring appropriate knowledge, but is largely used for facades , roofs, footbridges , etc. There, composite systems in which multiple glass members can interact with traditional building materials, should offer appropriate fail-safe performances, within the full lifetime. Further efforts are needed for the vulnerability assessment of glazing systems under extreme loads (seismic events, fire, etc.) or severe operational conditions. In this paper, the dynamic characterisation of an existing glass suspension footbridge is presented for a case study structure in Italy. On-site vibration experiments are first discussed, based on Operational Modal Analysis (OMA) techniques, so as to estimate the fundamental parameters of the composite glass footbridge. A Finite Element (FE) numerical study is then carried out, to further assess and explore the structure performance, including a sensitivity investigation. It is shown how the key dynamic parameters can be susceptible to even minor variations of few geometrical/mechanical influencing parameters, or to possible localised damage scenarios, hence affecting the overall composite behaviour of the glazed structure and requiring careful consideration for design and maintenance purposes. Degradation phenomena in the bonding layers, in particular, can severely affect the overall structural estimates and performances. While existing analytical models can provide simplified estimations only, in addition, the actual restraint configuration of all the assembly components should be also properly taken into account for reliable predictions.

This paper reports on the dynamic characterisation of a Reinforced Concrete (RC) stadium grandstand module for the Sporting Stadium in Lisbon. To this aim, a three-dimensional (3D) Finite-Element (FE) numerical model, implemented according to the technical drawings of the structure, is first presented to provide preliminary estimates of the expected modal characteristics for the examined structural system. Ambient vibration tests are then carried out on the same grandstand, and used to extract the natural frequencies and vibration modes of the system, according to conventional state-of-the-art output-only modal parameter identification techniques. A sensitivity investigation and FE model updating study is hence presented for the grandstand, giving evidence of the major influencing parameters and key input data for the numerical fitting of the experimental modal testing results. publishersversion published

Laminated and hybrid glass systems are typically realized by bonding or joining together several structural components and materials. Their structural performance and safe design is hence related to the optimal combination of several parameters, including material properties and degradation, geometrical ratios, connections type and features, etc. This research paper is focused on the numerical assessment of the load bearing performance of full-scale laminated glass (LG) beams with thick embedded connections. There, the structural interaction between multiple glass segments is offered by thick metal inserts, being embedded in the LG sections during the production stage. The overall bending response of such assemblies, given the same glass beam segments, is strictly related to the connection detailing, namely including the number, position, size, etc. of embedded connectors. In this regard, Finite Element numerical models able to properly capture their actual local and global behaviour can represent a robust support for time/cost-consuming full-scale experimental investigations. Refined FE models are hence presented for selected specimen configurations, and validated towards four-point bending experimental tests carried out on LG beams with three different types of embedded connections and available in the literature. In the typical FE model, the geometrical and mechanical properties of the reference specimens are properly taken into account, so to explore both the elastic and post-cracked performance of the LG beams object of study, under specific loading conditions. Comparative results are then critically discussed, giving evidence of major structural performances for the selected configurations, and including a concise parametric study.