ACI-SP-204-2001.pdf
DESIGN AND CONSTRUCTION PRACTICES TO MITIGATE CRACKING EDITOR: EDWARD G. NAW CO-EDITORS: F L O W G. BARTH ROBERT J. FROSCH Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Design and Construction Practices to Mitigate Cracking Editor Edward G. Nawy Co-Editors Florian G. Barth Robert J. Frosch o international SP-204 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- DISCUSSION of individual papers in this symposium may be submitted in accordance with general requirements of the AC1 Publication Policy to AC1 headquarters at the address given below. Closing date for submission of discussion is December 2001. All discussion approved by the Technical Activities Committee along with closing remarks by the authors will be published in the MarcWApril 2002 issue of either AC1 Structural Journal or AC1 Materials I Journal depending on the subject emphasis of the individual paper. i The Institute is not responsible for the statements or opinions expressed in its publications. Institute publications are not able to, nor intended to, supplant individual training, responsibility, or judgment of the user, or the supplier, of the information presented. The papers in this volume have been reviewed under Institute publication procedures by individuals expert in the subject areas of the papers. Copyright O 2001 AMERICAN CONCRETE INSTITUTE P.O. Box 9094 Farmington Hills, Michigan 48333-9094 All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or 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. The photos on the front and back covers are courtesy of Edward G. Nawy, Distinguished Professor of Civil Engineering at Rutgers University, New Brunswick, New Jersey. Printed in the United States of America Editorial production: Bonnie L. Gold Library of Congress catalog card number: 2001093041 ISBN: 0-8703 1-043-7 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Correct design of concrete structural systems requires consideration of serviceability requirements, as determined by crack-control measures. Higher- strength reinforcement, higher-strength concrete, more slender concrete elements, use of a host of admixtures, and emerging construction techniques have increased the need for serious consideration of crack mitigation and crack control in concrete structural systems. This volume is derived from a national symposium of the American Concrete Institute sponsored by AC1 Committee 224, Cracking. The majority of the papers were presented in two highly attended technical sessions in San Diego, CA, entitled “Design and Construction Practices to Mitigate Cracking.” The first session was chaired by Edward G. Nawy, and the second session was jointly chaired by Grant T. Halverson and Harvey H. Haynes. The topics in this volume encompass a wide range of subjects, including a detailed summary of worldwide provisions for crack control in reinforced and prestressed concrete beams; two- way slabs and circular tanks, together with the latest Eurocode provisions, including design examples; early-age thermal cracking; diagonal cracking, including seismically induced diagonal cracks; crack mitigation effects of shrinkage reducing admixtures fibers; repair of cracks; cracking in water- retaining structures; and an overview of the cracking developed in the 1999 earthquake in Turkey. This special publication also includes a list of references at the end of each paper, which can be helpful to design engineers and constructors. All papers presented in this publication were reviewed by recognized experts in accordance with the AC1 review procedures. Each paper had a minimum of two reviewers. It is hoped that designers, constructors, and codifying bodies will be able to draw on the vast material presented in this volume along with the recently revised and updated AC1 224 committee report “Control of Cracking in Concrete Structures,” in improving the long-term cracking behavior and performance of concrete-constructed facilities. Edward G. Nawy Editor and Founding Chairman, AC1 Committee 224 Florian G. Barth Co-editor and Current Chairman, AC1 Committee 224 Robert J. Frosch Co-editor and Secretary, AC1 Committee 224 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- . Preface 111 Design for Crack Control in Reinforced and Prestressed Concrete Beams, Two-way Slabs and Circular Tanks-A State-of-the-Art by E. G. Nawy . 1 Early-Age Thermal Cracking in Laser-Screeded Concrete Slabs by H. Haynes . 43 Crack Control Provisions in the New Eurocode for the Design of Concrete Structures by A. W. Beeby . 57 Diagonal Cracking and Diagonal Crack Control in Structural Concrete by P. Adebar 85 Positive Moment Cracking in Diaphragms of Simple-Span Prestressed Girders Made Continuous by A. Mirmiran, S. Kulkami, R. Miller, M. Hastak, B. Shahrooz, and R. Castrodale 117 Flexural Crack Control in Reinforced Concrete by R. J. Frosch . 135 Crack Mitigation Effects of Shrinkage Reducing Admixtures by A. Bentur, N. S. Berke, M. P. Dallaire, and T. A. Duming . 155 Use of Fibers for Plastic Shrinkage Crack Reduction in Concrete by P. Balaguru . 171 Mitigation of Seismic Induced Diagonal Cracks in Concrete Columns by External Prestressing by M. Saatcioglu . 195 Improving Watertightness of Reinforced Concrete Structures with Shrinkage-Reducing Admixtures by J .K .Buffenbarger, C. K. Nmai, and M. A. Miltenberger . 217 What is the Crack Width in Concrete Structures to Prevent Leakage? by L. G. Mrazek 237 V Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Cracks-Concrete Repairs Life Threatening Wounds by A. M.Vaysburd, R. W. Poston, and J. E. McDonald . 249 Cracking in Concrete Structures During the August 17, 1999 Earthquake in Turkey by M. Saatcioglu . 261 VI Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- SP 204-1 Design for Crack Control in Reinforced and Prestressed Concrete Beams, Two-way Slabs and Circular Tanks - A State-of-t he- Art by E. G. Nawy Syiiopsis: This paper presents the state-of-the art in the evaluation of the flexural crack width development and crack control of flexural cracks in reinforced and prestressed concrete structures. It is based on extensive research over the past five decades in the United States and overseas in the area of macro-cracking in reinforced and prestressed concrete elements. Mitigation and control of cracking has become essential in order to maintain the integrity and aesthetics of concrete structures and their long-term durability performance. The trend is stronger than ever towards better utilization of concrete strength, use of higher strength concretes in the range of 12,000-20,000 psi and higher compressive strength, more prestressed concretes and increased uses of limit failure theories - all these trends require closer control of serviceability requirements of cracking and deflection behavior. The paper discusses and presents common expressions for the mitigation and control of cracking in reinforced concrete beams and thick one-way slabs, prestressed, pretensioned and post-tensioned flanged beams, reinforced concrete two-way action structural floor dahs and plates, and large diameter circular tanks. In addition, recommendations are given for the maximum tolerable flexural crack widths in concrete elements based on the cumulative experience of many investigators over the past five decades. The expressions include the AC1 318-99 crack control provisions in reinforced concrete beams and one-way slabs, and the Concrete Euro Code 1999 for the design of concrete buildings. Kevwords: beams; concrete; concrete strength; crack control; cracking; crack width; environment; equations for reinforced and prestressed beams; Eurocode; flexural crack width; long-term cracking; tanks; tolerable crack widths; two-way action structural slabs 1 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- 2 Nawy Edward G. Nawy, FACI, is Professor of Civil Engineering, Rutgers University, and holds the distinguished professor rank. Active in AC1 since 1949, Professor Nawy is the founding chairman and a current member of AC1 Committee 224 on Cracking; past chairman of AC1 Committee 435 on Deflection of Concrete Building Structures; member of AC1 Committee 340, Design Aids for AC1 318 Building Code; member of Joint ASCE-AC1 Committee 421 on Design of Reinforced Concrete Slabs. Professor Nawy has published in excess of 160 papers and is the author four major textbooks and one handbook: SIMPLIFIED REINFORCED CONCRETE ( 1987); REINFORCED CONCREZE -A fbndamental Approach (4'h Ed., 2000) and translated into several languages; PRESTRESSED CONCRETE - A Fundamental Approach (3d Ed., 2000); FUNDAMENTALS OF HIGH PERFORMANCE CONCRETE (2“ Ed., 2001); and CONCRETE CONSUCTION ENGINEERING HAWBOOK (i998), as well as chapters in several handbooks. He holds several honors including the AC1 Chapter Activities Award, the Henry L. Kennedy Award and the Concrete Research Council's Robert Philleo Award, was m'ce president of the ACI New Jersey Chapter, served two term on the Rutgers Univers the effective concrete area in tension, and the center-to-center spacing of reinforcement, including bonded tendons, is limited to 8 in. (200 mm). Flexural cracking in reinforced concrete slabs is controlled by limiting the center- to-center spacing of bars in each direction to the lesser of 2.5 times the thickness of slab or 20 in (500 mm). In fully prestressed slabs, similar to beams, the maximum tensile stress in the concrete due to short-term service loads is limited to 3 fi. For partially prestressed slabs, the incremental steel stress should not exceed 22 ksi (1 50 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Design and Construction Practices to Mitigate Cracking 11 m a ) and the center-to-center spacing of reinforcement including bonded tendons, is not to exceed 20 in. (500 mm). It should be noted that the extensive Nawy demonstrated that the maximum crack spacing in two-way reinforced concrete slabs should not exceed 12 in. (300 mm), otherwise yield line wide cracks would be prematurely generated. Hence, the AC1 318 Code limits the maximum spacing to twice the slab thickness. FLEXURAL CRACKTNG AND CRACK CONTROL IN PRESTRESSED PRETENSIONED AND POST-TENSIONED BEAMS The increased use of partial prestressing, allowing limited tensile stresses in the concrete under service and overload conditions while allowing non-prestressed steel to carry the tensile stresses, is becoming prevalent due to practicality and economy. Consequently, an evaluation of the flexural crack widths and spacing and control of their development become essential. Work in this area is relatively limited because of the various factors affecting crack width development in prestressed concrete. However, experimental investigations support the hypothesis that the major controlling parameter is the reinforcement stress change beyond the decompression stage. Nawy, et al, have undertaken extensive research since the 1960's on the cracking behavior of prestressed pretensioned and post-tensioned beams and slabs because of the great vulnerability of the highly stressed prestressing steel to corrosion and other environmental effects and the resulting premature loss of prestress.'0*'' Serviceability behavior under service and overload conditions can be controlled by the design engineer through the application of the criteria presented in this section. A. Mathematical Model Formulation for Serviceability Evaluation 1. Crack Spacing Primary cracks form in the region of maximum bending moment when the external load reaches the cracking load. As loading is increased, additional cracks will form and the number of cracks will be stabilized when the stress in the concrete no longer Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/17/2007 07:55:07 MDTNo reproduction or networking permitted without license from IHS -,-,- 12 Nawy exceeds its tensile strength at further locations regardless of load increase. This condition is important as it essentially produces the absolute minimum crack spacing which can occur at high steel stresses, to be termed the stabilized minimum crack spacing, The maximum possible crack spacing under this stabilized condition is twice the minimum, to be termed the stabilized maximum crack spacing. Hence, the stabilized mean crack spacing, acs , is evaluated as the mean value of the two extremes. The total tensile force T in Fig. 3 transferred from the steel to the concrete over the stabilized mean crack spacing can be defined as where Y = c1= T = a s p Co (94 a factor reflecting the distribution of bond stress maximum bond stress which is a function of Co = sum of reinforcing elements circumferences The resistance R of the concrete area in tension this is the direction for
