Title:
Deflection Control of Concrete Slabs Longitudinally Reinforced with ASTM A1035/A1035M-07 Steel
Author(s):
Admasu S. Desalegne and Adam S. Lubell
Publication:
Structural Journal
Volume:
109
Issue:
6
Appears on pages(s):
867-878
Keywords:
cracking; deflection; high-performance reinforcement; one-way slabs; reinforced concrete; stiffness
DOI:
10.14359/51684130
Date:
11/1/2012
Abstract:
The ACI 318-08 design code for reinforced concrete construction provides both an implicit check of slab deflection control based on minimum member thickness and a direct computation method for deflection. Similar provisions are given in the ACI ITG-6 design guide (ACI ITG-6R-10) for members reinforced with high-performance ASTM A1035/A1035M-07 steel. This paper reports an analytical study that compared the maximum span-depth ratios from the implicit deflection provisions with corresponding ratios determined from direct deflection calculations. Emphasis was placed on deflection control at the serviceability limit state (SLS) for one-way slabs longitudinally reinforced with ASTM A1035/ A1035M-07 steel where the nominal steel stress at the ultimate limit state (ULS) ranged from 60 to 120 ksi (414 to 828 MPa). The results indicate that the maximum span-depth ratio should decrease as the span length increases, as the design load increases, as the concrete strength decreases, or as the maximum permissible deflection decreases. The maximum span-depth ratio can be increased as the longitudinal reinforcement ratio is increased beyond that required to satisfy the flexural demand. These relationships with the maximum span-depth ratio were all nonlinear in nature and were of similar shape for all nominal reinforcement stress magnitudes considered. Furthermore, these relationships were similar when ULS flexural design was completed using either the simplified or general flexural design models provided in the ACI ITG-6R-10 guidelines. The study recommends that direct deflection calculations should be used for the design of all slabs and proposes graphical design aids for use in initial thickness selection.