Concrete Structures
COVER SHEET
Kajewski, Stephen (2005) Multilevel Formwork Load Distribution with Posttensioned
Slabs. Journal of Construction Engineering and Management 131(2):pp. 203-210
Copyright 2005 American Society of Civil Engineers
Accessed from: https://eprints.qut.edu.au/secure/00003700/01/CO-2003022775_Manuscript.pdf
Multi-Level Formwork Load Distribution with Post-Tensioned Slabs
By Dr Stephen L Kajewski1
Abstract: Formwork and the associated shoring represent a significant proportion of the costs associated with the construction of multi-level concrete structures. To minimize these costs, a limited number of formwork and shoring sets are recycled up the structure as construction progresses, eliminating the need for a new set of formwork and shoring with each new slab. When a slab is post-tensioned using draped tendons, slab lift occurs as a portion of the slab self-weight is balanced. The formwork and shores supporting that slab are unloaded by an amount equivalent to the load balanced by the post-tensioning. This produces a load distribution through the structure that is inherently different from that of a conventionally reinforced slab. This paper presents two design methods suitable for modeling the multi-level formwork process for post-tensioned slabs: a modification to the simplified analysis method and a finite element model – both techniques will be of immediate use by industry practitioners and of interest to researchers examining the load distribution phenomenon. The paper also summarizes the findings of one of only a few research projects (Kajewski, 1997, 1998) in which actual shore loads were monitored during the construction of a multi-level post-tensioned building, which is used to validate the proposed design models.
1
A/Head, School of Construction Management & Property, Queensland University of Technology, GPO Box 2434,
Brisbane, Queensland, 4001, Australia. Phone: +61 7 3864 2676, Fax: +61 7 3864 1170, email:
Kajewski, Stephen (2005) Multilevel Formwork Load Distribution with Posttensioned
Slabs. Journal of Construction Engineering and Management 131(2):pp. 203-210
Copyright 2005 American Society of Civil Engineers
Accessed from: https://eprints.qut.edu.au/secure/00003700/01/CO-2003022775_Manuscript.pdf
Multi-Level Formwork Load Distribution with Post-Tensioned Slabs
By Dr Stephen L Kajewski1
Abstract: Formwork and the associated shoring represent a significant proportion of the costs associated with the construction of multi-level concrete structures. To minimize these costs, a limited number of formwork and shoring sets are recycled up the structure as construction progresses, eliminating the need for a new set of formwork and shoring with each new slab. When a slab is post-tensioned using draped tendons, slab lift occurs as a portion of the slab self-weight is balanced. The formwork and shores supporting that slab are unloaded by an amount equivalent to the load balanced by the post-tensioning. This produces a load distribution through the structure that is inherently different from that of a conventionally reinforced slab. This paper presents two design methods suitable for modeling the multi-level formwork process for post-tensioned slabs: a modification to the simplified analysis method and a finite element model – both techniques will be of immediate use by industry practitioners and of interest to researchers examining the load distribution phenomenon. The paper also summarizes the findings of one of only a few research projects (Kajewski, 1997, 1998) in which actual shore loads were monitored during the construction of a multi-level post-tensioned building, which is used to validate the proposed design models.
1
A/Head, School of Construction Management & Property, Queensland University of Technology, GPO Box 2434,
Brisbane, Queensland, 4001, Australia. Phone: +61 7 3864 2676, Fax: +61 7 3864 1170, email:
References: Aguinaga-Zapata, M. and Bazant, Z. (1986). “Creep Deflections in Slab Buildings and Forces in Shores during Construction” El-Shahhat, A. and Chen, W. (1992). “Improved Analysis of Shore-Slab Interaction”. ACI Structural Journal, 89(5), 528-537. El-Shahhat, A., Rosowsky, D. and Chen, W. (1993). “Construction Safety of Multistorey Concrete Buildings”. ACI Structural Journal, 90(4), 335-341. Grundy, P. and Kabaila, A. (1963). “Construction Loads on Slabs with Shored Formwork in Multistorey Buildings”, ACI Journal, 60(12), 1729-1738. Kajewski, S., Brameld, G. Thambiratnam, D. and Hampson, K. (1997). “Experimental Investigation into the Effects of Post-Tensioning on Multi-Level Formwork Load Distribution”, Physical Infrastructure Centre Research Report 97-6, Liu, X. and Chen, W. (1987). “Effect of Creep on load Distribution in Multistorey Reinforced Concrete Buildings During Construction”, ACI Structural Journal, vol Liu, X., Chen, W., and Bowman, M. (1985). “Construction load Analysis for Concrete Structures”, ASCE Journal of Structural Engineering, 111(5), 1019-1036. McAdam, P. (1989). “Modeling the Multi-Storey Formwork Process”, PhD thesis, University of Queensland, Brisbane. McAdam, P. and Behan, J. (1988). “Modeling Time Dependent Deformations in reinforced Concrete Flexural Members”, Department of Civil Engineering Research Report CE86, University of Queensland, Brisbane. Mosallam, K, and Chen, W. (1992). “Construction Load Distribution for Laterally Braced Formwork”, ACI Structural Journal, 89(4), 415-424. Stivaros, P. and Halvorsen, G. (1992). “Construction Load Analysis of Slabs and Shores using Microcomputers”, Concrete International, August, 27-32.