Bhavna
Sharma, M.Sc. and Kent A. Harries, Ph.D., FACI, P.Eng.
Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh PA 15261
Steel framed parking structures, in general, where introduced in the literature in the 1960’s (Sontag 1970; “New” 1974). Frequent references and case studies appear in the literature through today: in North America, typically appearing in Modern Steel Construction; in Europe, in Acier-Stahl-Steel; and elsewhere including a number of references in the South African Journal Steel Construction. In addition to Design Guide 18, AISC promulgates Innovative Solution in Steel: Open Deck Parking Structures (Troup and Cross 2003). Available references in the literature primarily address precast concrete decks on steel frames (e.g.: Simon 2001; Englot and Davidson 2001).
Cast-in-place post-tensioned concrete slabs on steel girders are an attractive alternative for parking structures. The use of post-tensioned slabs permits somewhat longer spans to be achieved but primarily enhances the durability of the slab system, affecting superior crack control. Investigation of the effects of the post-tensioning stress on the composite behavior of the beams has been explored but not published. Current practice, as promulgated in AISC Design Guide 18, Steel Framed Open-Deck Parking Deck Structures (Churches et al. 2003) assumes that the composite beams experience a small amount of compressive stress from the post-tensioning of the slab along the length of the beam. Design Guide 18 notes that unpublished testing by Mulach Steel Corporation demonstrated a stress increase of 3% in the composite beams under dead load conditions.
Bakota (1988) explores the design of a post-tensioned parking deck and analyzes the effects of post-tension stresses on the composite beam. The author notes various design criteria for a post-tensioned deck and that an effective posttension stress of 100 psi in the transverse shrinkage and temperature direction reduces the effects of the post tensioning parallel to the beam. Bakota presents equations to determine the long-term stresses and deflections. He concludes that the post-tension forces in the deck create long-term beam and slab stresses due to differential volume changes.
This report summarizes a program of monitoring the during- and post-construction behavior of a steel-framed open parking deck having a cast-in-place post-tensioned concrete slab. Monitoring was carried out over two months beginning following steel erection and ending approximately three weeks following completion of the structure. Data was acquired at a variety of stages through the construction process. Additionally, two live load tests were conducted. The objective of this field study was to quantitatively assess the effect that slab post-tensioning forces have on their supporting steel members.
References
Aalami, B.O. (2004) Prestressing Losses and Elongation Calculations, ADAPT, T9-04, September 2004 (revised October 2004), 16 pp.
Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh PA 15261
Steel framed parking structures, in general, where introduced in the literature in the 1960’s (Sontag 1970; “New” 1974). Frequent references and case studies appear in the literature through today: in North America, typically appearing in Modern Steel Construction; in Europe, in Acier-Stahl-Steel; and elsewhere including a number of references in the South African Journal Steel Construction. In addition to Design Guide 18, AISC promulgates Innovative Solution in Steel: Open Deck Parking Structures (Troup and Cross 2003). Available references in the literature primarily address precast concrete decks on steel frames (e.g.: Simon 2001; Englot and Davidson 2001).
Cast-in-place post-tensioned concrete slabs on steel girders are an attractive alternative for parking structures. The use of post-tensioned slabs permits somewhat longer spans to be achieved but primarily enhances the durability of the slab system, affecting superior crack control. Investigation of the effects of the post-tensioning stress on the composite behavior of the beams has been explored but not published. Current practice, as promulgated in AISC Design Guide 18, Steel Framed Open-Deck Parking Deck Structures (Churches et al. 2003) assumes that the composite beams experience a small amount of compressive stress from the post-tensioning of the slab along the length of the beam. Design Guide 18 notes that unpublished testing by Mulach Steel Corporation demonstrated a stress increase of 3% in the composite beams under dead load conditions.
Bakota (1988) explores the design of a post-tensioned parking deck and analyzes the effects of post-tension stresses on the composite beam. The author notes various design criteria for a post-tensioned deck and that an effective posttension stress of 100 psi in the transverse shrinkage and temperature direction reduces the effects of the post tensioning parallel to the beam. Bakota presents equations to determine the long-term stresses and deflections. He concludes that the post-tension forces in the deck create long-term beam and slab stresses due to differential volume changes.
This report summarizes a program of monitoring the during- and post-construction behavior of a steel-framed open parking deck having a cast-in-place post-tensioned concrete slab. Monitoring was carried out over two months beginning following steel erection and ending approximately three weeks following completion of the structure. Data was acquired at a variety of stages through the construction process. Additionally, two live load tests were conducted. The objective of this field study was to quantitatively assess the effect that slab post-tensioning forces have on their supporting steel members.
References
Aalami, B.O. (2004) Prestressing Losses and Elongation Calculations, ADAPT, T9-04, September 2004 (revised October 2004), 16 pp.
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Concrete Institute (ACI) (2005) ACI
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J.F. (1988) Parking Structure with a Post-tensioned Deck. Engineering
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Churches
C.H., Troup, E.W.J. and Angeloff, C. (2003) Steel Framed Open-Deck Parking
Structures, Steel Design Guide 18, American Institute of Steel
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Englot,
J.M and Davidson, R.I.,
(2001) Steel Framed Parking Garages Take Off at JFK and Newark International
Airports, Modern Steel
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[A]
New Structural System for Parking Decks (1974) Modern Steel Construction,
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Poole T.S. (2004) Curing of Portland Cement
Concrete Pavements, Volume II Final Report. FHWA-HRT-05-038.
Poole T.S. (2005) Guide for Curing of Portland
Cement Concrete Pavements. FHWA-RD-02-099.
Simon,
A.H. (2001) Unique Steel Framed Solution to Parking, Modern Steel
Construction, Vol. 44, No. 4, April 2001, 3 pp.
Sontag,
H. (1970) Steel Multi-Storey Garages, Acier-Stahl-Steel, Vol. 35, No.
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Troup,
E. and Cross, J. (2003) Innovative Solutions in Steel: Open-Deck Parking
Structures, American Institute of Steel Construction (AISC), 29 pp.
Young,
C.S. and Budnyas, R.G. (2002) Roark’s Formulas for Stress and Strain, 7th
edition, McGraw Hill.
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