Neno Torić

Creep-free fire analysis of steel structures with Eurocode 3 material model

Purpose This paper aims to propose a methodology to remove inherent implicit creep from the Eurocode 3 material model for steel and to present a creep-free analysis on simply supported steel members. Design/methodology/approach Most of the available material models of steel are based on transient coupon tests, which inherently include creep strain associated with particular heating rates and load ratios. Findings The creep-free analysis aims to reveal the influence of implicit creep by investigating the behaviour of simply supported steel beams and columns exposed to various heating regimes. The paper further evaluates the implicit consideration of creep in the Eurocode 3 steel material model. Originality/value A modified Eurocode 3 carbon steel material model for creep-free analysis is proposed for general structural fire engineering analysis.

Modelling of the Influence of Creep Strains on the Fire Response of Stationary Heated Steel Members

The paper presents an application of a newly developed implicit procedure for including steel creep strain into structural fire analysis through modelling a series of stationary fire tests. An implicit modelling procedure is incorporated into customized structural fire analysis software. Four stationary fire tests on simply supported, steel members were modelled using strain modified stress-strain curves. Strain modified curve was obtained by adding the creep strain directly into the steel stationary stress-strain material curve. The proposed implicit procedure in this manner attempts to create an equivalent transient stress-strain curve from the provided stationary stress-strain curve. The proposed implicit procedure was able to provide satisfactory prediction of member deflections in the temperature region of 400-700°C.

Reduction of Postfire Properties of High-Strength Concrete

This paper presents an experimental study of behaviour of high-strength concrete at high temperature. Reduction of the mechanical properties of concrete was determined starting from the period when the concrete specimens were heated to the maximum temperature and cooled down to ambient temperature and the additional 96 hours after the initial cooling of the specimens. The study includes determination of compressive strength, dynamic and secant modulus of elasticity, and stress-strain curves of concrete specimens when exposed to temperature level up to 600°C. The study results were compared with those obtained from other studies, EN 1994-1-2 and EN 1992-1-2. Tests point to the fact that compressive strength of concrete continues to reduce rapidly 96 hours after cooling of the specimens to ambient temperature; therefore indicating that the mechanical properties of concrete have substantial reduction after being exposed to high temperature. The study of the dynamic and secant modulus of elasticity shows that both of the properties are reduced but remain constant during the period of 96 hours after cooling. The level of postfire reduction of compressive strength of the analyzed concrete is substantial and could significantly affect the postfire load bearing capacity of a structure.

Modelling of Steel Creep at High Temperatures Using an Implicit Creep Model

The paper presents the numerical procedure for modelling the behaviour of steel structures at high temperatures using a newly developed implicit creep model. This implicit creep model uses the calculated creep strains to modify the material stress-strain curves, thus implicitly taking into account the effect of the developed creep strain. The newly calculated stress-strain curves are modified by stretching the initial temperature-dependent stress-strain curves using the calculated values of the creep strain which depend on the level of temperature and stress that the section of structure is being exposed to during fire. The implicit numerical procedure has been implemented in a previously developed numerical model for predicting the behaviour of structures under fire. In order to test the validity of the newly developed implicit creep model, an in-house fire experiment was performed. Results of the experiment have shown a good agreement with the model predictions indicating the validity of the developed implicit numerical procedure.

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

COMPARATIVE ANALYSIS OF STEEL AND ALUMINUM STRUCTURES

This study examined steel and aluminum variants of modern exhibition structures in which the main design requirements includelow weight (increased span/depth ratio, transportation, and construction) and durability (resistance to corrosion). This included a design situation in which the structural application of aluminum alloys provided an extremely convenient and practical solution. Viability of an aluminum structure depends on several factors and requires a detailed analysis. The overall conclusion of the study indicated that aluminum can be used as a structural material and as a viable alternative to steel for Croatian snow and wind load values and evidently in cases in which positive properties of aluminum are required for structural design. Furthermore, a structural fire analysis was conducted for an aluminum variant structure by using a zone model for realistic fire analysis. The results suggested that passive fire protection for the main structural members was not required in the event of a real fire with duration of 60 min.