This two-part paper presents a numerical study on the fire resistance behaviour of pultruded GFRP profiles with square tubular cross-section simultaneously subjected to four-point bending and the standard fire of ISO 834. The first part [1] presented the numerical models and results focused on the most relevant kinematic issues (deflections and strains), while this second part (present paper) reports numerical results associated to the static issues, particularly the evolution of stress distributions and failure initiation with fire exposure time. The paper first presents and discusses the evolution of stress distributions in both longitudinal and transversal directions of an unprotected GFRP beam under one-side fire exposure (reference beam). Next, the influence of using a fire protection system and exposing the beams to fire in three sides is assessed by comparison with the case of reference beam. Additionally, the Tsai-Hill failure (initiation) criterion was used to identify the zones (sections and points) of GFRP beams that are most sensitive to failure due to high temperatures. The numerical results obtained show that (i) longitudinal stresses across the section become highly nonlinear as a result of temperature increase; (ii) shear stress diagram is severely affected by fire exposure in three sides; (iii) transversal stresses are negligible compared to the longitudinal and shear ones; and (iv) the collapse of beams (considering Tsai-Hill failure analysis) occurs due to top flange and web (top part) failure, which generally agrees with experimental observations.
This paper reports on the use of simple kinematic models to simulate the torsion warping restraint and transmission at thin-walled frame joints in the context of beam finite element structural analysis. After reviewing the main concepts involved in the torsional behaviour of thin-walled members, the paper addresses the development of kinematic models aimed at simulating the torsion warping transmission at frame joints connecting two or more non-aligned plain channel (U-section) or I-section members. Finally, numerical results are presented and discussed, in order to illustrate the application and show the capabilities of the above kinematic models, which make it possible to use beam finite element models accounting for the joint torsion warping behaviour. For validation purposes, the beam finite element results obtained are compared with values yielded by rigorous shell finite element analyses.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
This paper presents a numerical study about the thermal behaviour of pultruded GFRP profiles with square tubular cross-section exposed to fire. Two-dimensional and three-dimensional numerical models of previous fire tests of GFRP profiles were developed using the commercial software ANSYS Fluent 14.5. The efficacy of using different fire protection systems (passive and active) and the influence of the number of sides exposed to fire (one or three) in the thermal response of the GFRP profiles was studied. The models developed consider the heat exchanges by means of conduction, internal radiation and convection of the air and/or water enclosed in the cavity of the GFRP tubular profiles. A general good agreement was obtained between numerical temperatures and test data. The results obtained highlight (i) the relative efficiency of the different fire protection systems and (ii) the remarkable influence of exposing GFRP profiles to fire in three sides, and (iii) show the importance of the heat exchanges due to internal radiation and convection inside the cavity of the GFRP cross-section in this type of thermal simulations. The thermal models were further validated through the simulation of previous fire resistance experiments on multicellular slab panels.
In recent years several investigations were performed about the behavior of laminated structural glass elements, namely in terms of their flexural and torsional stiffness, with the lateral-torsional buckling of beams being one of the most relevant and complex topics. Various analytical formulations were proposed to describe the equivalent stiffness of laminated elements; however, none covers more than three layers of glass in a comprehensive and unified manner, and those that exist are not consensual. This work proposes a new formulation, based on sandwich theory, which provides equivalent results to previous formulations in a limited set of conditions, but that is also able to characterize the behavior of simply supported laminated glass columns and beams up to five layers, subjected to compressive axial loads, mid-span loads, uniformly distributed loads, four-point bending, pure bending or torsion. The fundamentals of the formulation presented in this paper allow it to be extended to a larger number of layers and to different load and support conditions. The proposed formulation is assessed by means of a parametric study based on the comparison with numerical results retrieved from finite element simulations, in order to assess the range of validity of each expression. Two analytical approaches for the lateral-torsional buckling problem are studied in detail, with their fundamentals being explained. Another formulation, proposed in Australian Standard AS 1288, is also addressed. An experimental assessment of the work developed is achieved by comparing the results from flexural tests available in the literature with analytical and numerical predictions.
The study of the application of nanotechnology in the construction industry and building structures is one of the most prominent priorities of the research community. The outstanding chemical and physical properties of nanomaterials enable several applications ranging from structural reinforcement to environmental pollution remediation and production of self-cleaning materials. It is known that concrete is the leading material in structural applications, where stiffness, strength and cost play a key role in the high attributes of concrete. This paper reviews the literature on the application of nanotechnology in the construction industry, more particularly in concrete production. The paper first presents general information and definitions of nanotechnology. Then, it focuses on the most effective nanoadditives that readily improve concrete properties, such as (i) nanosilica and silica fume, (ii) nanotitanium dioxide, (iii) iron oxide, (iv) chromium oxide, (v) nanoclay, (vi) CaCO3, (vii) Al2O3, (viii) carbon nanotubes and (ix) graphene oxide. Besides summarising the main nanomaterials used in concrete production as well as the results achieved with each addition, some future potential consequences of nanotechnology development and orientations to explore in construction are discussed.
The elastic local post-buckling behaviour of elliptical tubes under compression is analysed in this paper. A brief outline of the local, distortional and global buckling behaviour of EHS tubes is firstly provided, where it is shown that local buckling modes govern the stability of short to intermediate length tubes while distortional modes control the stability of intermediate length to moderately long tubes and global buckling dominates the behaviour of longer tubes. Following this, an in-depth numerical study employing shell finite element modelling, of the elastic local post-buckling behaviour of compressed elliptical hollow section (EHS) tubes is presented. It is concluded that EHS tubes with a low to moderate aspect ratio can support loads up to their limit loads but are imperfection sensitive (shell-type behaviour), while EHS tubes with a moderate to high aspect ratio can carry loads higher than their limit loads (plate-type behaviour) and are imperfection insensitive. The slope of the ascending post-buckling path increases with the EHS aspect ratio and can reach values up to 40% of the slope of the linear primary path. The bound imperfection amplitude concept, separating the imperfection amplitude ranges where the EHS tube is sensitive and insensitive, is proposed. It is also found that, for increasing EHS aspect ratio, the compressive stresses grow and accumulate near the zones of minimum radius of curvature while the zones of maximum radius of curvature possess an approximately uniform and relatively low compressive stress level. Therefore, it is expected that an approach based on the effective width concept widely used for the evaluation of the strength of flat plates may be adapted to the design of EHS tubes with moderate to high aspect ratios.
This paper reports a detailed investigation concerning the local-plate and distortional elastic postbuckling behaviors of cold-formed steel lipped channel columns with web and flange intermediate stiffeners (the corresponding unstiffened lipped channel column postbuckling behaviors are often used as reference). This investigation relies on results obtained through geometrically nonlinear analyses based on a recently developed and numerically implemented generalized beam theory (GBT) formulation that incorporates (1) conventional (no shear deformation), (2) shear (nonlinear warping), and (3) transverse extension deformation modes. The numerical results shown provide the evolution, along a given local-plate or distortional postbuckling equilibrium path, of the column (1) deformed configuration and (2) relevant displacement profiles and/or stress distributions—mostly for validation purposes, some of them are compared with values yielded by shell finite element analyses performed by means of the code ABAQUS. In order to assess the influence of the member end support conditions, the paper also includes a comparison between the distortional postbuckling behaviors of columns with pinned / free-to-warp and fixed / warping-prevented end sections. Taking full advantage of the GBT unique modal features, all the above results are discussed in great detail and it becomes possible to unveil, explain, and/or shed some new light on several interesting and scarcely known behavioral aspects. In particular, one is able to provide illuminating and structurally (mechanically) meaningful explanations for the qualitative differences exhibited by the local-plate and distortional postbuckling behaviors of plain and stiffened (web and flanges) lipped channel columns.
This paper presents experimental and numerical investigations about the transverse bending and in-plane shear behaviours of pultruded bridge deck panels made of E-glass fiber reinforced polymer (GFRP). The analysed panels have a wide multicellular thin-walled cross-section, with panel-to-panel vertical interlocks (snap-fit) at the lateral edges. The study aimed at understanding and quantifying the structural contribution of the deck panels, in terms of their transverse stiffness and strength properties, w. r.t the load transmission to the lower support girder system along its longitudinal axis (bridge's main axis). Particular focus was given to the influence of the panel-to-panel joining system on the transverse performance of the deck when compared to a continuous panel (i.e. without snap-fit). The effects of complementing the snap-fit connection with two different structural adhesives was also investigated. For all deck configurations tested, the structural response in bending and shear exhibited high post-cracking strength and pseudo-ductility (above 100% and 200% respectively), as a consequence of the redundancy provided by the multi-cellular section. Compared to a continuous deck, the mechanical snap-fit exhibited very high deformability; however, when combined with adhesive bonding, it behaved fairly rigidly. In general, failure occurred in a progressive way (crack initiation and propagation) and the ultimate capacity was governed by the web-flange junctions. The numerical simulations, which were performed with continuum shell finite element (FE) models using Hashin-based damage analysis, provided useful insights about the failure mechanisms. Both bending and in-plane shear responses were simulated with good accuracy, with matrix tension failure governing the load capacity. The low value of the estimated in-plane shear modulus was consistent with the very low interaction degree (3–4%) that was assessed between the panels' flanges under bending, thus highlighting the high flexibility of this bridge deck's multicellular core when subjected to transverse loading.
This paper presents a state-of-the-art report on the use of Generalised Beam Theory (GBT) to assess the buckling behaviour of plane and space thin-walled steel frames. After a very brief overview of the main concepts and procedures involved in performing a GBT buckling analysis, one addresses the development and numerical implementation of a GBT-based beam finite element formulation that is able (i) to unveil local, distortional and global buckling modes, (ii) to handle arbitrary loadings (namely those causing non-uniform member internal force and moment diagrams) and (iii) to incorporate the presence of several frame joint configurations and arbitrary end and/or intermediate support conditions (including those associated with the modelling of bracing systems). In particular, one describes the procedures employed to establish the frame linear and geometric stiffness matrices – special attention is paid to the constraint conditions adopted to ensure the local displacement compatibility at the frame joints. The paper closes with the presentation and discussion of a number of numerical results that make it possible to illustrate the application and show the potential of the GBT-based approach to perform frame buckling analyses – they concern both plane and space frames. In order to validate and assess the numerical efficiency and accuracy of the GBT analyses and results (critical buckling loads and mode shapes), the frames are also rigorously analysed in the commercial code Ansys – both the members and joints are discretised by means of fine shell finite element meshes.
After providing a brief overview of a recently developed and validated elastoplastic post-buckling Generalised Beam Theory (GBT) formulation, the paper presents and discusses illustrative numerical results concerning three tubular members exhibiting bi-linear and non-linear material behaviours. The GBT results consist of equilibrium paths, modal participation diagrams, stress contours, displacement profiles and collapse mechanisms, most of which are compared with values obtained from Abaqus shell finite element analyses. The GBT modal nature makes it possible to (i) acquire in-depth knowledge about the member behavioural mechanics at any given equilibrium state (elastic or elastic-plastic), as well as (ii) evidence the GBT computational efficiency (d.o.f. reduction of over 75%), partly due to the exclusion from the analyses of all deformation modes playing no role in a given member response.
