ACI PRC-435.8-85: Observed Deflections of Reinforced Concrete Slab Systems, and Causes of Large Deflections (Reapproved 1997)

Notes/Preview

Note: 435.8R-85 is Out of Print. However, a PDF version is available.

Description

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.

Document Details

Author: ACI Committee 435

Publication Year: 2002

Pages: 47

ISBN: 9780870315213

Categories: Deflections

Formats: PDF

Table of Contents

Part I

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)

Part II

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

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