ACI 347.2R-2017 Guide for Shoring Reshoring of Concrete Multistory Buildings.pdf

1、Guide for Shoring/Reshoring of Concrete Multistory BuildingsReported by ACI Committee 347ACI 347.2R-17First PrintingJanuary 2017ISBN: 978-1-945487-51-4Guide for Shoring/Reshoring of Concrete Multistory BuildingsCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved.

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11、ACI Manual of Concrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis guide presents information and design criteria for shoring/reshoring operations during the construction of reinforced and

12、post-tensioned multistory buildings. Methods for developing safe construction practices, including sequencing and timing, as well as design examples, are provided. It is written for the use of formwork engineer/contractors and engineer/architects.Keywords: construction loads; falsework; form removal

13、; formwork; post-tensioning; reshoring; shoring.CONTENTSCHAPTER 1INTRODUCTION, p. 21.2Scope, p. 2CHAPTER 2NOTATION AND DEFINITIONS, p. 22.1Notation, p. 22.2Definitions, p. 3CHAPTER 3SHORING/RESHORING CONSTRUCTION NEEDS, p. 33.1Use of reshoring, p. 33.2Types of forming systems, p. 3CHAPTER 4CONSTRUCT

14、ION LOADS ON FORMWORK, p. 44.1Construction loads, p. 44.2Load combinations, p. 44.3Typical construction phases, p. 54.4Construction load distribution, p. 64.5Application of the simplified method, p. 64.6Factors affecting the construction load distribution, p. 84.7Post-tensioning load redistribution,

15、 p. 9CHAPTER 5STRENGTH OF CONCRETE SLABS AND FORMWORK, p. 105.1Early-age concrete material strength development, p. 105.2Construction load factors, p. 115.3Early-age strength of concrete slabs, p. 115.4Serviceability of concrete slabs, p. 125.5Strength of formwork, p. 12CHAPTER 6CONSTRUCTION EXAMPLE

16、S, p. 126.1Two-way slab construction, p. 126.2Post-tensioned construction example, p. 18CHAPTER 7REFERENCES, p. 20Authored documents, p. 21Kenneth L. Berndt, Chair Matthew J. Poisel, SecretaryACI 347.2R-17Guide for Shoring/Reshoring of Concrete Multistory BuildingsReported by ACI Committee 347Rodney

17、 D. AdamsMary Bordner-TanckGeorge CharitouEamonn F. ConnollyJames N. Cornell IIJack L. DavidAubrey L. DunhamJeffrey C. ErsonNoel J. GardnerBrian J. GolanowskiTimothy P. HayesGardner P. HorstJeffery C. JackDavid W. JohnstonRoger S. JohnstonRobert G. KentKevin R. KoogleJim E. KretzH. S. LewRobert G. M

18、cCrackenEric S. PetersonSteffen PippigDouglas J. SchoonoverAviad ShapiraJohn M. SimpsonRolf A. SpahrPericles C. StivarosDaniel B. ToonRalph H. TulisACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document

19、is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the st

20、ated principles. The Institute shall not be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mand

21、atory language for incorporation by the Architect/Engineer.ACI 347.2R-17 supersedes ACI 347.2R-05 and was adopted and published January 2017.Copyright 2017, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any means, including the making of c

22、opies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.1CHAPTER 1INTRODUCTIONIn mult

23、istory cast-in-place concrete building construction, freshly cast floors are placed on formwork that is tempo-rarily supported by a system of shores and reshores until the concrete has the ability to be self-supporting. Construction loads imposed by the shoring system can be greater than the permane

24、nt structure service load on a single floor. Construc-tion loads can also be applied in a manner that differs from the design intent of the completed structure. Furthermore, the concrete of the supporting slabs has to attain suffi-cient strength, considering that the capacities of the floors below v

25、ary depending on concrete age, ambient conditions following placement, and the rate of strength development properties of the slabs. As a result, it is critical to determine the early-age load capacity of the floor slabs, including punching shear strength, to avoid the possibility of partial or tota

26、l failure of the structural system. To reduce the construc-tion load on the floor immediately below and distribute it to several lower floors or to the ground, it is necessary to add reshores. Therefore, an engineering analysis that considers both the construction load distribution and the early-age

27、 load-carrying capacity of the concrete slabs should be performed before shoring/reshoring operations begin.Formwork failures and failures caused by improper reshoring or premature removal of supports and inadequate lateral bracing have periodically occurred throughout the history of concrete constr

28、uction. Premature removal of shores and reshores prior to concrete slabs achieving the necessary strength can contribute to construction failures or defects such as permanent deflections (sagging) or cracking in the completed structure in excess of those anticipated by the design. Also, if overloade

29、d prematurely, time-dependent deflections under load (creep) will be larger than predicted by the design and may be more noticeable and objectionable.The schedule and process for removal of forms, shores, and reshores should be based on an analysis of the structural effects. Except for the simplifie

30、d method described in ACI 347R and ACI SP-4, there is no method universally accepted as the proper analysis of the distribution of construction loads to the floor slabs and the shoring system.To ensure structural performance and safety during construction, a thorough understanding of construction lo

31、ads applied to the slabs at early ages is necessary. Equally important is knowledge of the behavior and the strength of early-age concrete members that support their own weight and construction loads.For guidance in formwork operations, the formwork engineer/contractor can refer to several codes, st

32、andards, or guides, including ACI 347R, ACI 318, ACI 301, ACI SP-4, ANSI/ASSE A10.9, OSHA 29 CFR 1926, and ASCE/SEI 37. These documents provide basic guidelines for general formwork operations.Other documents that can provide formwork design requirements or guidelines include state and local buildin

33、g codes, and guidelines prepared by contractors, formwork manufacturers, and other construction agencies governing construction practices.1.2ScopeAlthough the aforementioned documents provide basic guidelines for general formwork operations, there are no codes or standards that provide detailed desi

34、gn and construc-tion requirements specifically for shoring/reshoring opera-tions for multistory reinforced and post-tensioned concrete construction. Investigations for usable procedures to estab-lish safe and cost-effective shoring/reshoring operations have been ongoing for several decades. These in

35、vestigations focus on two major areas: 1) determining the distribution of loads carried by the concrete structure during construc-tion; and 2) estimating the ability of the concrete members to resist construction loads.This guide outlines the importance of appropriate shoring/reshoring design for mu

36、ltistory structures and provides basic requirements for safe construction. ACI SP-4 serves as an expanded commentary to ACI 347R and provides detailed information related to formwork practices, including a discussion of shoring/reshoring procedures and analysis examples. Contract documents or the au

37、thority having juris-diction may require the contractors to supply to the building official, upon request, the structural analysis and concrete strength requirements used in planning and implementing shoring/reshoring operations. Such data and information should be furnished to the engineer/architec

38、t who should evaluate the effects of construction loads on the immediate and long-term deflections. The contractors and formwork designers should acquire an understanding of the construc-tion loads and the structural behavior of the buildings during construction. This understanding enables them to d

39、evelop a rational shoring/reshoring system design that is economical without compromising safety, quality, and serviceability.The objective of this guide is to present practical guide-lines for the design of shoring/reshoring operations. This guide provides tools to design and evaluate construction

40、schedules for shoring/reshoring of multistory reinforced and post-tensioned concrete structures.CHAPTER 2NOTATION AND DEFINITIONS2.1Notationbo= perimeter of critical section for shear in slabs, in. (mm)D = design dead load, lb/ft2(kPa)Dc= construction dead load, lb/ft2(kPa)d = distance from extreme

41、compression fiber to centroid of longitudinal tension reinforcement, in. (mm)Ew= reference design value for modulus of elasticity of wood, psi (MPa)Fc= reference design value for compression parallel to grain of wood, psi (MPa)fc= compressive strength of concrete, psi (MPa)fc = specified compressive

42、 strength of concrete, psi (MPa)K = resulting coefficient of the governing punching shear equations from ACI 318 that is a function of column and slab geometryL = design live load, lb/ft2(kPa)American Concrete Institute Copyrighted Material www.concrete.org2 GUIDE FOR SHORING/RESHORING OF CONCRETE M

43、ULTISTORY BUILDINGS (ACI 347.2R-17)Lc= construction live load, lb/ft2(kPa)n = elevated slab numberR28= nominal flexural strength at 28 days, lb/ft2(kPa)Rc= early-age nominal flexural strength, lb/ft2(kPa)U28= design factored load, lb/ft2(kPa)Uc= construction factored load, lb/ft2(kPa)Vc= nominal she

44、ar strength provided by concrete, lb (N)Vu= factored shear force, lb (N)Vuc= factored construction shear force, lb (N)c= ratio of the early-age concrete compressive strength to 28-day specified strength, c 1.0 = modification factor to reflect the reduced mechan-ical properties of lightweight concret

45、e relative to normalweight concrete of the same compressive strength = strength reduction factor2.2DefinitionsACI provides a comprehensive list of definitions through an online resource, “ACI Concrete Terminology,” https:/www.concrete.org/store/productdetail.aspx?ItemID=CT16. The definitions provide

46、d herein complement that source.backshoresshores placed snugly under a concrete slab or structural member after the original formwork and shores have been removed from a small area without allowing the entire slab or member to deflect or support its own mass or existing construction loads.drop-head

47、shoreshore with a head where part of the head can be lowered to allow removal of horizontal forming components without removing the shore or changing its vertical support for the floor system.engineer/architectengineer, architect, engineering firm, architectural firm, or other agency issuing project

48、 plans and specifications for the permanent structure, administering the work under contract documents, or both.formwork engineer/contractorengineer of the form-work system or contractor in charge of designated aspects of formwork design and formwork operations.preshoresadded shores placed snugly un

49、der selected panels of a deck forming system before any primary (orig-inal) shores are removed.reshoresshores placed snugly under a stripped concrete slab or other structural member after the original forms and shores have been removed from a full bay, requiring the new slab or structural member to deflect and support its own weight and construction loads applied before installation of the reshores.shorevertical or inclined support member or braced frame designed to carry the weight of the formwork, concrete, and construction loads.CHAPTER 3