Aldina Santiago

A component model for the behaviour of steel joints at elevated temperatures

Abstract Recent experimental evidence has shown that steel joints exhibit a distinct change in their moment–rotation response under increasing temperature. In terms of cold design, the component method is currently the widely accepted procedure for the evaluation of the various design values. It is the purpose of the present paper to extend the component method to the prediction of the response of steel joints under fire loading. Using typical mechanical models consisting of extensional springs and rigid links, whereby the springs exhibit a non-linear force deformation response (here taken as a bi-linear approximation), an analytical procedure is proposed capable of predicting the moment–rotation response under fire conditions that incorporates the variation of yield stress and Young’s modulus of the various components as the temperature increases. An application to a cruciform flush end-plate beam-to-column steel joint is presented and compared to the experimental results obtained under various loading conditions.

Post-limit stiffness and ductility of end-plate beam-to-column steel joints

Abstract A procedure for the evaluation of ductility in steel joints is presented. Using the component method as background, a non-linear analysis for a number of end-plate beam-to-column joints is performed that is capable of identifying the “yield” sequence of the various components and the failure of the joint. Each component is characterised using a bi-linear approximation for the force–displacement relation. Comparing these results with the corresponding experimental results leads to a proposal of the post-limit stiffness of the various components. A component ductility index is proposed for each component as a means of classification with respect to ductility, using the three ductility classes currently proposed in the literature. A joint ductility index is also proposed, which can be used to verify available rotation against the structure required rotation.

Development of an experimental system to apply high rates of loading

Purpose – The purpose of this paper is to develop an experimental system to apply high rates of loading, in order to characterize the behaviour of bolted steel connections subjected to accidental loads, such as impact. The work presented in this paper is part of an ongoing research project at the University of Coimbra IMPACTFIRE PTDC/ECM/110807/2009. Design/methodology/approach – The experimental set-up was designed to test under tension T-stubs and is capable to apply high strain rates. The test rig comprises a series of beams and steel elements placed horizontally, providing resistance and stiffness for the proposed tests. The loading system is operated by high-pressure nitrogen and it comprises three main components: pneumatic reservoir, pneumatic cylinder and a rapidly opening valve, which and allows the instantaneous nitrogen flow from the reservoir to the cylinder. This paper presents a detailed description of the experimental components developed, designed and fabricated at University of Coimbra. F...

Impact Loads in Steel Connections

After attacks on World Trade Center (2001), Madrid (2004), London (2005) and Mumbai (2008), special attention was given to the study of robust structures subjected at different accidental loads, allowing localized failure without being damaged to an extent disproportionate to the original cause. The collapse of the World Trade Center (WTC) showed problems in the design of structural elements: columns collapse, beams buckling and brittle failure of connections. Concerning this last topic, it was realised that the joint structural details plays very significant role behaviour in structures subjected to accidentals loads. The accidental loads may result from an object impact, blast, explosions, earthquake and fire.

MATERIAL MODELLING OF TENSILE STEEL COMPONENT UNDER IMPULSIVE LOADING

Purpose – Characterization and modelling of the material properties, as well as the fracture simulation needed for the numerical analysis of bolted T-stub connection under impulsive loads. The strain rate effects are considered on the material law; fracture simulation is explored following “element deletion” technique for a given level of ductile damage. The paper aims to discuss these issues. Design/methodology/approach – The T-stub model is used in Eurocode 3 – part 1.8 as part of the “component method” for the representation of steel connection’s tension zone and is usually responsible for providing ductility to the connection. Looking forward to establish the “T-stub’s” maximum displacement capacity under impact loading: first, fracture simulation of steel elements is here explored following “element deletion” technique for a given level of ductile damage; second, material softening and triaxial stress state dependency are assessed by finite element analysis of common uniaxial tension tests; and third...

STRUCTURAL ANALYSIS OF A STEEL COLUMN EXPOSED TO A LOCALIZED FIRE

(Received: 13 October 2017; accepted: 14 November 2017) Tonko Faldić University of Split, Faculty of Civil Engineering, Architecture and Geodesy, Master Student Corresponding author: tonko.faldic@gmail.com Helder David Craveiro ISISE University of Coimbra, Faculty of Science and Technology, Department of Civil Engineering, Invited Assistant Professor Aldina Santiago ISISE University of Coimbra, Faculty of Science and Technology, Department of Civil Engineering, Assistant Professor Neno Torić University of Split, Faculty of Civil Engineering, Architecture and Geodesy, Assistant Professor

Composite joints under M-N at elevated temperatures - Experimental investigations and analytical model

The Eurocodes recognise robustness as a way to ensure the structural integrity of a building frame subjected to an unforeseen event and therefore to avoid a so-called “progressive failure” mode in extreme loading situations. However few practical guidelines exist nowadays which would allow a designer to design a structure accordingly. Within the European RFCS ROBUSTFIRE project, the behaviour of steel and composite car parks subjected to localised fire leading to a column loss was investigated. Under such a scenario, the beam-to-column joints play a key role in the global structural response. Indeed, these joints, initially loaded in bending, may be subjected to elevated temperatures and to combined axial load “N” and bending moment “M”. In this paper, a methodology to predict the mechanical response of bolted composite beamto-column joints at elevated temperatures under M-N is presented and validated through comparison to experimental tests conducted at the University of Coimbra.

Axial Force And Deformation Of A Restrained Steel Beam In Fire : Description and validation of a simplified analytical procedure

Structural fire design is exceedingly adopting the performance based approach. There are evidentadvantages of this approach compared to the prescriptive methods from codes. An analytical procedure, ...

Numerical Study of Steel Beams in Sub-frame Assembly Validation of Existing Hand Calculation Procedures

The design methods currently proposed by the codes prescribe the strength assessment of structures to be based on their strength limit state. These design methods can be applied to isolated steel members to determine their design strengthin fire. The real response of a structural member is, however, more complex due to the thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of a structural member at high temperature in a way which includes its interaction with its surroundings. This paper focus on the numerical investigation of steel beams in structural frames connected to concrete filled tubular (CFT) columns through reverse channel connections and comparison to hand calculation procedures. Finite element models (FEM) of the sub-frames were validated against fire tests conducted on sub-frames and then their results were compared to the proposed simplified hand calculation procedures (HCM).

Numerical Behaviour of a Steel Sub-frame System in Fire

Steel framed buildings are generally designed with “simple” shear-resisting connections, and lateral forces are resisted by vertical bracing and shear walls. However, when a beam form part of a complete structure, its behaviour is complex and very much dependant on the restraint at the member ends. In order to capture the beam behaviour during a fire, it is therefore required to take a wonder view and examine the behaviour of a representative sub-structure [1]. Using the data and results from the few available sub-structure fire tests, numerical models were developed and validated to try to explain and predict the behaviour of such systems.