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Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2020, Vol. 14 Issue (3) : 664-674     https://doi.org/10.1007/s11709-020-0620-9
RESEARCH ARTICLE
Influence of loading ratio on flat slab connections at elevated temperature: A numerical study
Rwayda Kh. S. AL-HAMD1,2(), Martin GILLIE3, Safaa Adnan MOHAMAD4, Lee S. CUNNINGHAM1
1. Mechanical, Aerospace and Civil Engineering Department, School of Engineering, The University of Manchester, Manchester M13 9PL, UK
2. Prosthetics and Orthotics Engineering Department, College of Engineering, Al-Nahrain University, Baghdad 10011, Iraq
3. Department of Mechanical and Construction Engineering, Northumbria University, Newcastle, NE1 8ST, UK
4. Department of Highway and Transportation Engineering, Al-Mustansiriyah University, Baghdad 10011, Iraq
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Abstract

For reinforced concrete members subjected to high temperature, the degree of in-service loading, commonly expressed as the loading ratio, can be highly influential on the structural behavior. In particular, the loading ratio may be pivotal in relation to the phenomenon of load-induced thermal strain. Despite its potentially pivotal role, to date, the influence of the loading ratio on both material and structural behavior has not been explored in detail. In practice, real structures experience variation in imposed loading during their service life and it is important to understand the likely response at elevated temperatures across the loading envelope. In this paper, the effect of the loading ratio is numerically investigated at both material and structural level using a validated finite element model. The model incorporates a proposed constitutive model accounting for load-induced thermal strain and this is shown to outperform the existing Eurocode 2 model in terms of accuracy. Using the validated model, the specific case of flats slabs and the associated connections to supporting columns at various loading ratios are explored. For the cases examined, a marked difference in the structural behavior including displacement direction was captured from low to high loading ratios consistent with experimental observations.

Keywords concrete      finite elements      fire      load-induced thermal strain      punching shear     
Corresponding Author(s): Rwayda Kh. S. AL-HAMD,Safaa Adnan MOHAMAD   
Just Accepted Date: 21 April 2020   Online First Date: 25 May 2020    Issue Date: 13 July 2020
 Cite this article:   
Rwayda Kh. S. AL-HAMD,Martin GILLIE,Safaa Adnan MOHAMAD, et al. Influence of loading ratio on flat slab connections at elevated temperature: A numerical study[J]. Front. Struct. Civ. Eng., 2020, 14(3): 664-674.
 URL:  
http://journal.hep.com.cn/fsce/EN/10.1007/s11709-020-0620-9
http://journal.hep.com.cn/fsce/EN/Y2020/V14/I3/664
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Rwayda Kh. S. AL-HAMD
Martin GILLIE
Safaa Adnan MOHAMAD
Lee S. CUNNINGHAM
Fig.1  Conceptual drawing for punching shear test set-up and the importance of the heating side.
Fig.2  The load deflection profile for specimens for (a) A, B, and (b) C, adapted from Refs. [1,2]
Fig.3  Typical LITS behavior expressed as a function of temperature for different load levels, adapted from Ref. [12].
Fig.4  Stress-strain behaviour of concrete at various temperatures according to EC2 (solid lines) and EC2 plus LITS (dashed 29 lines) (adapted from Ref. [9]).
Fig.5  Temperature-time data through the depth of the slab (adapted from Ref. [9] under Creative Commons License).
Fig.6  Deflection-time response of Smith’s slab, together with numerical predictions for the EC2 model (with LITS being incorporated implicitly) and Al-Hamd’s model (with LITS).
Fig.7  Mesh sensitivity study showing the deflection-time response for different mesh sizes against experimental results.
Fig.8  Deflection response against the time continues heating scenario.
Fig.9  Conceptual diagram for the cube under the combined heating and loading scenario.
Fig.10  Deflection-time response for different LRs at the center of a standard cube (the solid lines represent the EC2 model and the dashed lines represent the Al-Hamd’s model).
Fig.11  Deflection-time response for different LRs at the center of the slab.
Fig.12  Cracking pattern at the stage of anticipated failure for slab S75 with loading ratio: (a) LR 25%; (b) LR 50%; (c) LR 70%; (d) LR 80%.
Fig.13  Failure envelopes along with the failure profiles for different LRs.
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