This report is in two distinct parts .
Part I is a summary of published studies on slab deflections (3 from Australia, 1 from Scotland, 1 from Sweden, 2 from U.S.). The summary focuses on construction practices and materials quality. Comparison of deflections calculated by various methods with actual long-term deflections is made in some cases.
Part II summarizes several construction problems and material deficiencies which can contribute to large long-term deflections. Focusing on large construction loads, the authors showthat construction loads may be considerably higher than design loads and that high construction loads cause high initial deflections because concrete has a lower modulus of elasticity when loaded at an early age. Furthermore, concrete creeps more when it is loaded at an early age, thereby causing additional high long-term deflections, even when construction loads are sustained only for a few days.
The authors then suggest a method of form removal and reshoring that has proved successful in the New York City area in preventing large slab deflections. Essentially, no more than an 8-foot slab span is left unsupported until a slab is mature.
Keywords: concrete construction; concrete slabs; creep properties; deflection; flat concrete plates; form removal; loads (forces); modulus of elasticity; reinforced concrete; shorinq; shrinkage; two-way slabs.
Table of Contents
FIELD DEFLECTION MEASUREMENTS OF REINFORCED CONCRETE FLAT PLATES,
FLAT SLABS AND BEAMS: A REVIEW OF LITERATURE
Investigation A (Commonwealth Scientific and Industrial Research
Organization, Melbourne, Australia - experimental flat plate structures)
Investigation B (Jenkins, Plowman and Haseltine - Scottish apartment building)
Investigation C (Army Engineer Waterways Experiment Station, Vicksburg, Mississippi - Army barracks flat plate structure)
Investigation D (Taylor, Heiman - five Sydney area buildings)
Investigation E (Chalmers University, Goteborg Sweden - two apartment houses)
Investigation F (Jenkins - Australian flat plate building)
Investigation G (Sbarounis - multistory flat plate building)
FACTORS CONTRIBUTING TO DEFLECTION PROBLEMS IN TWO-WAY
REINFORCED CONCRETE SLABS
Factors Contributing to Slab Deflection Problems
Loads During Construction
Properties of Concrete at Early Ages
Creep of Concrete Loaded at Early Ages
Control of Slab Deflections
Summary and Conclusions