Shoring and Reshoring for Multistory Concrete Buildings-Shoring and Reshoring for Multistory Concrete Buildings Formwork economy and safety must go together (PDF)

Shoring and Reshoring for Multistory Concrete Buildings Formwork economy and safety must go together (PDF)

Pdf Summary

The enclosed document explores the complexities involved in determining safe and economical construction schedules for shoring and reshoring in multistory concrete buildings, drawing on insights from the ACI Committee 347 guide. Reshoring involves using temporary supports to uphold the loads from fresh concrete slabs above floors that remain under construction. The guide provides methods to determine whether two or three levels of reshoring are sufficient and advises on safe formwork removal.<br /><br />Formwork economy in multistory buildings requires the rapid stripping and reuse of forms while ensuring the supporting floors are sufficiently strong to handle the imposed loads. Shores support the loads above, while reshores shift these loads across multiple floors to prevent overloading and possible structural failures like slab deflection or even progressive collapse.<br /><br />The document discusses fundamental assumptions and methods for calculating the construction loads outlined in the seminal work by Grundy and Kabaila. These include idealized assumptions such as elastic deformation of concrete slabs and infinitely stiff shores. However, it cautions against assuming infinite stiffness, especially in compressible systems, as this can lead to inaccuracies in load distribution.<br /><br />It emphasizes the importance of engineering analysis in developing shoring schedules, considering construction load distribution, early-age load-carrying capacity, strength requirements, and serviceability requirements. Critical among these is the early-age slab's tensile strength related to various construction factors, which can significantly affect long-term deflections and cracking.<br /><br />Two construction scenarios are explored in the ACI guide: one for two-way flat plate buildings and another for post-tensioned multistory constructions. The guide provides a detailed load distribution analysis and the impact of changing variables like curing temperatures, construction cycles, and reshoring levels on construction slab loads.<br /><br />The key takeaway from the document is that both safety and economy in construction schedules hinge on informed and coordinated decisions between contractors and engineers — leveraging the insights from the ACI guide to optimize for formwork removal safety and constructive efficiency.

Keywords

multistory buildings

shoring

reshoring

ACI Committee 347

formwork removal

construction loads

tensile strength

load distribution

post-tensioned constructions

construction schedules