Title:
External Restraint Factors in Early-Age Massive Foundation Slabs
Author(s):
Barbara Klemczak and Aneta Zmij
Publication:
Structural Journal
Volume:
117
Issue:
2
Appears on pages(s):
45-54
Keywords:
early-age concrete; external restraint factor; foundation slabs; mass concrete
DOI:
10.14359/51721362
Date:
3/2/2020
Abstract:
Massive foundation slabs are one of the structures in which early age effects play a significant role. These effects are mainly related to the exothermic nature of cement hydration and a consequent temperature rise in the structure. The inhomogeneous volume changes have consequences in arising stresses in a concrete foundation slab. Two types of early-age stresses can be distinguished: self-induced stresses caused by the internal restraints,
and restrained stresses resulting from the restraint existing along the contact surface of foundation slab and subsoil. This paper is focused on the distribution and the magnitude of the restrained stresses caused by the restraint between the foundation slab and soil. The results of the study have been expressed by the restraint factor R, defined as a ratio between the real stress generated in the analyzed slabs to the stress generated at full restraint of the slabs. The dependence of the external restraint factor on length/thickness ratio and thickness of the slab, type of subsoil, age of concrete, and presence of slip layers is investigated in the study. The general equations for the R factor, dependent both on length/height ratio (L/H) and thickness of the slabs, are proposed.
Related References:
1. ACI Committee 207, “Report on Thermal and Volume Change Effects on Cracking of Mass Concrete (ACI 207.2R-07),” American Concrete Institute, Farmington Hills, MI, 2007, 28 pp.
2. ACI Committee 209, “Prediction of Creep, Shrinkage, and Temperature Effects in Concrete Structures (ACI 209R-92),” American Concrete Institute, Farmington Hills, MI, 2008, 48 pp.
3. ACI Committee 231, “Report on Early-Age Cracking: Causes, Measurement, and Mitigation (ACI 231R-10),” American Concrete Institute, Farmington Hills, MI, 2010, 50 pp.
4. Bamforth, P. B., “CIRIA C660: Early-Age Thermal Crack Control in Concrete,” CIRIA: Classic House London, UK, 2007, 268 pp.
5. JSCE Guidelines for Concrete No. 15, “Standard Specifications for Concrete Structures,” Japan Society of Civil Engineers, Tokyo, Japan, 2007, 503 pp.
6. JCI, “Guidelines for Control of Cracking of Mass Concrete 2016,” Japan Concrete Institute, Tokyo, Japan, 2017, 302 pp.
7. RILEM TC 119-TCE, “Recommendations of TC 119-TCE: Avoidance of Thermal Cracking in Concrete at Early Ages,” Materials and Structures, V. 30, Oct. 1997, pp. 451-464.
8. Klemczak, B.; Żmij, A.; and Azenha, M., “Numerical Study on Restraints Effects in Massive Foundation Slabs,” Procedia Engineering, V. 193, 2017, pp. 226-233. doi: 10.1016/j.proeng.2017.06.208
9. Klemczak, B., and Knoppik-Wróbel, A., “Early Age Thermal and Shrinkage Cracks in Concrete Structures—Description of the Problem,” Architecture Civil Engineering Environment Journal, V. 4, No. 2, 2011, pp. 35-48.
10. Honorio, T.; Bary, B.; and Benboudjema, F., “Factors Affecting the Thermo-Chemo-Mechanical Behaviour of Massive Concrete Structures at Early-Age,” Materials and Structures, V. 49, No. 8, 2016, pp. 3055-3073. doi: 10.1617/s11527-015-0704-5
11. Honorio, T.; Bary, B.; and Benboudjema, F., “Evaluation of the Contribution of Boundary and Initial Conditions in the Chemo-Thermal Analysis of a Massive Concrete Structure,” Engineering Structures, V. 80, 2014, pp. 173-188. doi: 10.1016/j.engstruct.2014.08.050
12. Azenha, M., and Faria, R., “Temperatures and Stresses due to Cement Hydration on the R/C Foundation of a Wind Tower—A Case Study,” Engineering Structures, V. 30, No. 9, 2008,pp. 2392-2400. doi: 10.1016/j.engstruct.2008.01.018
13. Azenha, M.; Sousa, C.; Faria, R.; and Neves, A., “Thermo-Hygro-Mechanical Modelling of Self-Induced Stresses during the Service Life of RC Structures,” Engineering Structures, V. 33, No. 12, 2011, pp. 3442-3453. doi: 10.1016/j.engstruct.2011.07.008
14. Mihashi, H., and Leite, J. P., “State-of-the-Art Report on Control Cracking in Early Age Concrete,” Journal of Advanced Concrete Technology, V. 2, No. 2, 2004, pp. 141-154. doi: 10.3151/jact.2.141
15. Klemczak, B., and Knoppik-Wróbel, A., “Early Age Thermal and Shrinkage Cracks in Concrete Structures—Influence of Geometry and Dimension of a Structure,” Architecture Civil Engineering Environment Journal, V. 4, No. 3, 2011, pp. 55-70.
16. Klemczak, B., and Knoppik-Wróbel, A., “Reinforced Concrete Tank Walls and Bridge Abutments: Early-Age Behaviour, Analytic Approaches and Numerical Models,” Engineering Structures, V. 84, 2015, pp. 233-251. doi: 10.1016/j.engstruct.2014.11.031
17. Klemczak, B., “Modelling Thermal-Shrinkage Stresses in Early Age Massive Concrete Structures—Comparative Study Of Basic Models,” Archives of Civil and Mechanical Engineering, V. 14, No. 4, 2014, pp. 721-733. doi: 10.1016/j.acme.2014.01.002
18. Knoppik-Wróbel, A., and Klemczak, B., “Degree of Restraint Concept in Analysis of Early-Age Stresses in Concrete Walls,” Engineering Structures, V. 102, 2015, pp. 369-386. doi: 10.1016/j.engstruct.2015.08.025
19. Nilsson, M., “Thermal Cracking of Young Concrete. Partial Coefficients, Restraint Effects and Influence of Casting Joints,” master’s thesis. Luleå University of Technology, Luleå, Sweden, 2003.
20. Nilsson, M., “Restraint Factors and Partial Coefficients for Crack Risk Analyses of Early Age Concrete Structures,” PhD thesis, Luleå University of Technology, Luleå, Sweden, 2007.
21. Larson, M., “Thermal Crack Estimation in Early Age Concrete. Models and Methods for Practical Application,” PhD Thesis, Luleå University of Technology, Luleå, Sweden, 2003.
22. Al-Gburi, M.; Jonasson, J. E.; Yousif, S. T.; and Nilsson, M., “Simplified Methods for Crack Risk Analyses of Early Age Concrete. Part 2: Restraint Factors for Typical Case Wall-on-Slab,” Nordic Concrete Research, V. 46, No. 3, 2012, pp. 39-56.
23. EN 1992-3, “Eurocode 2—Design of Concrete Structures—Part 3: Liquid Retaining and Containment Structures,” European Committee for Standardization, 2008.
24. ATENA, Červenka Consulting, Prague, Czech Republic, http://www.cervenka.cz/. (last accessed Feb. 19, 2020)
25. EN 1992-1-1, “Eurocode 2—Design of Concrete Structures—Part 1-1: General Rules and Rules for Buildings,” European Committee for Standardization, Brussels, Belgium, 2008.