Title:
An Overview of Flexural Cracking Mitigation in Two-Way Slabs and Plates
Author(s):
Edward G. Nawy
Publication:
Symposium Paper
Volume:
284
Issue:
Appears on pages(s):
1-16
Keywords:
concrete strength, cracking, crack control, crack width, environment, fiber glass plastic bars, green structures, tank walls, two-way slabs
DOI:
10.14359/51683802
Date:
3/1/2012
Abstract:
This paper covers the state of knowledge on the cracking development and mitigation of cracks in two-way action slabs and plates as a measure of the health state of structural floors. In addition, the present trend is to construct green concrete structures for long-term behavior in structural and environmental serviceability performance. As supported two-way concrete slabs are an integral component of most structures, crack control is a major factor in their design.
This subject has been of major interest to the author since the 1960s when extensive research on cracking in two-way action slabs and plates was started at Rutgers University that culminated in tests to failure of in excess of 95 two-way action large scale models of concrete plates accompanied by detailed analysis and development of a hypothesis on how two-way action cracks have been generated. The fracture grid controlled by the spacing of the nodal intersections of the reinforcing bars or wires proved to be the controlling factor in the generation, spacing and width of flexural cracks in two-way action. This work was extended to two-way slab tests and analysis of 12 specimens reinforced with glass fiber reinforced plastic bars. They verified the extension of this work to structural two-way floors reinforced with non-metallic reinforcing bars. The existing literature shows only two or three additional sources of limited work by other investigators and only on small scale reinforced concrete two-way slabs, perhaps due to the high expense and elaborate infrastructure needed for the necessary experimental tests to verify any proposed hypothesis or expressions.
The resulting expression presents the criteria applicable to almost all normal boundary condition for concentrated and uniformly distributed loads in supported two-way slabs. It enables the choice of the size and spacing of the reinforcement that can control the propagation of the crack width, as reported in the first edition in 1972 and the several subsequent editions of ACI 224 Report “Control of Cracking in Concrete Structures.” A modified expression for crack control in walls of liquid retaining tanks is presented as well as a table of tolerable crack widths in concrete structures.