Reshoring and Early-Age Building Behavior-Introduction to ACI 347.2R-17, Guide for Shoring-Reshoring of Concrete Multistory Buildings (PDF)

Introduction to ACI 347.2R-17, Guide for Shoring-Reshoring of Concrete Multistory Buildings (PDF)

Pdf Summary

The document is an overview of the ACI 347.2R-17 guide discussing shoring and reshoring in concrete multistory buildings, presented at The Concrete Convention and Exposition. Initially published in 2005 and revised in 2017, the guide accounts for advancements and editorial changes while maintaining most original content. The guide's components are organized into several chapters, including construction needs, loads on formwork, concrete slab strength, and construction examples like two-way slab and post-tensioned construction.<br /><br />The guide provides definitions for key terms: "Reshores" refer to support structures placed after removing original forms in multistory buildings. Other terms like "back shores," "preshores," and "drop-head shores" describe different support methods and configurations used during construction.<br /><br />Significant focus is given to assumptions about the behavior of concrete and supporting shores, citing principles from foundational studies by Grundy and Kabaila (1963), Hurd and Courtois (1986), and subsequent updates in 2014 and 2017. These assumptions include the rigidness and spatial distribution of shores compared to the slabs they're supporting, as well as the equal distribution of loads due to consistent slab stiffness.<br /><br />The guide describes procedures for installing shores and reshores, emphasizing that reshores are placed without initially bearing load. It explains how new slabs eventually support their own weight plus construction loads.<br /><br />Further discussion centers on the concrete’s bending and shear strength as functions of time and temperature. Strength assessments typically rely on cylinder tests, with results indicated in terms of percents of full strength achieved at various ages. Method B and Method C from SP-4 are different approaches to estimating early load capacity relative to the strength percentage, impacting decisions about construction speeds and reshoring needs. Lastly, some assumptions are challenged, suggesting potential variability in stiffness with modern, faster construction cycles.

Keywords

ACI 347.2R-17

shoring

reshoring

multistory buildings

concrete slab strength

formwork loads

construction methods

structural support

load distribution

construction cycles