Influence of loading ratio on flat slab connections at elevated temperature: A numerical study

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

References

[1] Kordina K. On the fire behaviour of simply reinforced concrete slabs. Brunswick: Elektronisch veröffentlicht, 1993

[2] Kordina K. On the Fire Behaviour of Reinforced Concrete Flat Slabs. Berlin: Elektronisch veröffentlicht, 1997

[3] Salem H, Issa H, Gheith H, Farahat A. Punching shear strength of reinforced concrete flat slabs subjected to fire on their tension sides. HBRC J, 2012, 8(1): 36–46

[4] Liao J S, Cheng F P, Chen C C. Fire resistance of concrete slabs in punching shear. Journal of Structural Engineering, 2014, 140(1): 04013025

[5] Smith H K M, Stratford T, Bisby L. Deflection response of reinforced concrete slabs tested in punching shear in fire. In: Applications of Structural Fire Engineering, Dubrovnik, 2015

[6] Smith H K M, Stratford T J, Bisby L A. Punching shear of reinforced concrete slabs under fire conditions: Experiment vs. design. In: Proceedings of the First International Conference on Structural Safety under Fire & Blast. Glasgow: ASRANet Ltd., 2015

[7] Smith H K M, Stratford T, Bisby L. The punching shear mechanism in reinforced-concrete slabs under fire conditions. In: Proceeding of PROTECT 2015—Fifth International Workshop on Performance, Protection & Strengthening of Structures under Extreme Loading. East Langsing, Michigan: DEStech Publications, Inc., 2015

[8] Smith H K M. Punching Shear of Flat Reinforced-Concrete Slabs under Fire Conditions. Edinburgh: The University of Edinburgh, 2016

[9] Al-Hamd R K S, Gillie M, Warren H, Torelli G, Stratford T, Wang Y. The effect of load-induced thermal strain on flat slab behaviour at elevated temperatures. Fire Safety Journal, 2018, 97: 12–18

[10] Al-Hamd R K S, Gillie M, Wang Y. Numerical modelling of slab-column concrete connections at elevated temperatures. In: Iabse Symposium—Engineering the Future. Vancouver: ABSE, 2017

[11] EN1992-1-2-2004. Eurocode 2: Design of Concrete Structures-Part 1–2: General Rules-Structural Fire Design. London: the British Standards Institution, 2004

[12] Torelli G, Mandal P, Gillie M, Tran V X. Concrete strains under transient thermal conditions: A state-of-the-art review. Engineering Structures, 2016, 127: 172–188

[13] Andrew H, Buchanan C. Structural Design for Fire Safety. Canterbury: John Wiley & Sons, 2002

[14] Lange D, Jansson R. A comparison of an explicit and an implicit transient strain formulation for concrete in fire. Fire Safety Science, 2014, 11: 572–583

[15] Jansson R, Lange D. The Fire Behaviour of An Inner Lining for Tunnels. Borås: SP Technical Research Institute of Sweden, 2015

[16] Thelandersson B S. Modeling of combined thermal and mechanical action in concrete. Journal of Engineering Mechanics, 1987, 113(6): 893–906

[17] Ring T, Zeiml M, Lackner R, Eberhardsteiner J. Experimental investigation of strain behaviour of heated cement paste and concrete. Strain, 2014, 49(3): 249–256

[18] Ring T, Zeiml M, Lackner R. Underground concrete frame structures subjected to fire loading: Part II—Re-analysis of large-scale fire tests. Engineering Structures, 2012, 58: 188–196

[19] Zhang Y, Zeiml M, Pichler C, Lackner R. Model-based risk assessment of concrete spalling in tunnel linings under fire loading. Engineering Structures, 2014, 77: 207–215

[20] Zhang Y, Zeiml M, Maier M, Yuan Y, Lackner R. Fast assessing spalling risk of tunnel linings under RABT fire: From a coupled thermo-hydro-chemo-mechanical model towards an estimation method. Engineering Structures, 2017, 142: 1–19

[21] Anderberg Y, Thelandersson S. Stress and deformation characteristics of concrete at high temperature: 2. Experimental investigation and material behaviour model. In: Bulletin of Division of Structural Mechanics and Concrete Construction, Bulletin 54. Lund: Lund institute of technology, 1976

[22] Law A. The Assessment and Response of Concrete Structures Subjected to Fire. Edinburgh: The University of Edinburgh, 2010

[23] Rabczuk T, Belytschko T. Cracking particles: A simplified meshfree method for arbitrary evolving cracks. International Journal for Numerical Methods in Engineering, 2004, 61(13): 2316–2343

[24] Rabczuk T, Zi G, Bordas S, Nguyen-Xuan H. A geometrically non-linear three-dimensional cohesive crack method for reinforced concrete structures. Engineering Fracture Mechanics, 2008, 75(6): 4740–4758

[25] Rabczuk T, Zi G, Bordas S, Nguyen-Xuan H. A simple and robust three-dimensional cracking-particle method without enrichment. Computer Methods in Applied Mechanics and Engineering, 2010, 199(37–40): 2437–2455

[26] Rabczuk T, Belytschko T. A three-dimensional large deformation meshfree method for arbitrary evolving cracks. Computer Methods in Applied Mechanics and Engineering, 2007, 196(29–30): 2777–2799

[27] Areias P, Rabczuk T, Camanho P P. Initially rigid cohesive laws and fracture based on edge rotations. Computational Mechanics, 2013, 52(4): 931–947

[28] CEB-FIP. Model Code Design of Concrete Structures MC90. London: Thomas Telford Ltd., 1990

[29] Abdulrahman B Q, Wu Z, Cunningham L S. Experimental and numerical investigation into strengthening flat slabs at corner columns with externally bonded CFRP. Construction & Building Materials, 2017, 139: 132–147

[30] Genikomsou A S, Polak M A. Finite element analysis of punching shear of concrete slabs using damaged plasticity model in ABAQUS. Engineering Structures, 2015, 98: 38–48

[31] Al-Hamd R K S, Gillie M, Cunningham L S, Warren H, Albostami A S. Novel shearhead reinforcement for slab-column connections subject to eccentric load and fire. Archives of Civil and Mechanical Engineering, 2019, 19(2): 503–524

[32] ABAQUS. User’s Manual, Version 6.13. Rhode: Dassault Systémes Simulia Corp., 2013

[33] BS 476-23:1987. Fire tests on building materials and structures. London: British Standards Institution, 1987

[34] CEB-FIP International Federation for Structural Concrete (fib). Structural Concrete: Textbook on Behaviour, Design and Performance: Updated Knowledge of the CEB/FIP Model Code 1990. Lausanne: CEB-FIP International Federation for Structural Concrete (fib), 2009

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