1、Bulletin ACI-fib symposium proceedingsPunching shear of structural concrete slabs:Honoring Neil M. HawkinsACI-fib International Symposium81ACI SP-315Technical reportProceedings of a symposium held in Philadelphia, PA, USA, on 25 October 2016 Edited by Carlos E. Ospina, Denis Mitchell and Aurelio Mut
2、toniBulletin81Punching shear of structural concrete slabs: Honoring Neil M. HawkinsApril 2017Approval of this bulletin Subject to priorities defined by the technical council and the presidium, the results of the fibs work in comisions and task groups are published in a continuously numbered series o
3、f technical publications called bulletins. The following categories are used. Category Approval by Technical report Task group and the chairpersons of the Comision State-of-the-art report Comision Manual/Guide to god practice/Recomendation Technical council Model code General asembly Any publication
4、 that has not met the above requirements wil be clearly identified as preliminary draft. fib Buletin 81 is published as a technical report and is a colection of contributions to a symposium that was co-sponsored by the fib and the American Concrete Institute (ACI). The authors have presented their i
5、ndividual views. Although these contributions have not been discused in any of the fibs working bodies, the subject mater is highly topical and believed to be of general interest to members of the fib. This buletin is also published as an ACI Symposium Publication, ACI SP-315. Cover images: Saw-cuts
6、 of iner slab-column conections failed in punching. Photographs courtesy of A. Herzog, EPFL Fdration internationale du bton (fib) and American Concrete Institute (ACI), 2017 Although the International Federation for Structural Concrete / Fdration internationale du bton (fib) does its best to ensure
7、that any information given is acurate, no liability or responsibility of any kind, including liability for negligence, is acepted in this respect by the organisation, its members, servants or agents. All rights reserved. No part of this publication may be reproduced, modified, translated, stored in
8、a retrieval system, or transmited in any form or by any meanselectronic, mechanical, photocopying, recording, or otherwisewithout prior writen permision from the fib. ISSN 1562-3610 ISBN 978-2-88394-121-2 Layout by Laura Vidale on behalf of the fib secretariat. Printed by DC Document Competence Cent
9、er Siegmar Kstl e.K., Germany ACI-fib International Symposium Punching shear of structural concrete slabs iii Foreword fib Bulletin 81 deals with punching of slabs, which is a relevant issue in the design of reinforced concrete. Punching is one of the most frequent reasons for failure of concrete st
10、ructures, which underlines the importance of this problem. Flat slabs are used in buildings, bridges and other structures. Punching may result in brittle failure, which requires that special attention be paid to the design of new structures and the assessment of existing ones. Punching and shear cap
11、acity of structures is often evaluated using empirical methods, which does not always provide a sufficient level of safety. This bulletin is a result of an international symposium where experts from fib and ACI met and exchanged their experience. The papers included in this bulletin provide new expe
12、rimental evidence and a comprehensive review of analytical and numerical methods that are used to evaluate the structural performance of slab-column connections. This bulletin provides a review of the performance of slabs under static, dynamic and seismic loading. The individual papers generally sho
13、w the studied phenomena using experiments and analytical evaluation, which makes it possible to compare results obtained according to the European code (EC2), the ACI code and the international code, the fib Model Code for Concrete Structures (MC2010). Particular attention is paid to the so-called s
14、ize effect (i.e. the nominal load carrying capacity of thicker slabs is lower than that of thin slabs). The arrangement of reinforcement is important for the residual strength after a local failure and robustness, which are instrumental to avoid the progressive collapse of the entire structure after
15、 a local failure. It is confirmed that the bottom reinforcement crossing the column is very beneficial to ensure sufficient residual strength and avoid progressive collapse. A paper dealing with the shear capacity of bridge slabs illustrates an extended strip model, which may be used for efficient a
16、ssessment of bridge slabs under concentrated loads. This bulletin also presents new types of shear reinforcements and shows efficiency of distribution of classical shear reinforcing elements like headed studs. Some papers deal with retrofitting and strengthening of existing slabs. Post-installed she
17、ar reinforcing elements may be used for strengthening of existing structures. This bulletin summarizes several phenomena that influence the performance of slabs sensitive to punching. It is a valuable summary of the state-of-the art knowledge for practicing engineers, academics and also for students
18、. It is also important to appreciate that the opinions and experiences of American and European experts are summarised in one publication. Finally, it is necessary to thank all authors, as well as the main organizers of the symposium (A. Muttoni convener of fib WP 2.2.3, and C. E. Ospina and D. Mitc
19、hell representing ACI committee 445) for their editing of this extraordinary document. Last but not least, many thanks to Laura Vidale for the preparation of the bulletin for publication. Jan L. Vtek Chairman of fib Commission 2, Analysis and design ACI-fib International Symposium Punching shear of
20、structural concrete slabs iv Preface fib Bulletin 81 reports the latest information available to researchers and practitioners on the analysis, design and experimental evidence of punching shear of structural concrete slabs. It follows previous efforts by the International Federation for Structural
21、Concrete (fib) and its predecesor the Euro-International Commite for Concrete (CEB), through CEB Bulletin 168, Punching Shear in Reinforced Concrete (1985) and fib Bulletin 12, Punching of structural concrete slabs (2001), and an international symposium sponsored by the punching shear sub-commite of
22、 ACI Commite 445 (Shear and Torsion) and held in Kansas City, Mo., USA, in 2005. This bulletin contains 18 papers that were presented in three sesions as part of an international symposium held in Philadelphia, Pa., USA, on October 25, 2016. The symposium was co-organized by the punching shear sub-c
23、ommite of ACI 445 and by fib Working Party 2.2.3 (Punching and Shear in Slabs) with the objectives of not only diseminating information on this important design subject but also promoting harmonization among the various design theories and treatment of key aspects of punching shear design. The paper
24、s are organized in the same order they were presented in the symposium. The symposium honored Profesor Emeritus Neil M. Hawkins (University of Illinois at Urbana-Champaign, USA), whose contributions through the years in the field of punching shear of structural concrete slabs have been paramount. Th
25、e papers cover key aspects related to punching shear of structural concrete slabs under different loading conditions, the study of size effect on punching capacity of slabs, the effect of slab reinforcement ratio on the response and failure mode of slabs, without and with shear reinforcement, and it
26、s implications for the design and formulation in codes of practice, an examination of different analytical tools to predict the punching shear response of slabs, the study of the post-punching response of concrete slabs, the evaluation of design provisions in modern codes based on recent experimenta
27、l evidence and new punching shear theories, and an overview of the combined efforts undertaken jointly by ACI 445 and fib WP 2.2.3 to generate test result databanks for the evaluation and calibration of punching shear design recommendations in North American and international codes of practice. Sinc
28、ere acknowledgments are extended to al authors, speakers, reviewers, as well as to fib and ACI staff for making the symposium a succes and for their efforts to produce this long-awaited bulletin. Special thanks are due to Laura Vidale for preparing the bulletin for publication. The editors of fib Bu
29、lletin 81: Carlos E. Ospina (chair of ACI 445 Punching Shear Sub-commite) Denis Mitchel (ACI 445) Aurelio Muttoni (chair of fib Working Party 2.2.3) Prof. Emeritus Neil M. Hawkins ACI-fib International Symposium Punching shear of structural concrete slabs v Participants in the 2016 ACI-fib symposium
30、 on punching shear of structural concrete slabs. Standing, L to R: Sagaseta (Surey, UK), Volum (Imperial Colege, UK), Ramos (Nova, Portugal), Fernndez Ruiz (EPFL, Switzerland), Kueres (Aachen, Germany), Genikomsou (Quens, Canada), Walkner (Innsbruck, Austria), Topuzi (Toronto, Canada). Seated, L to
31、R: Lantsoght (Delft, The Netherlands, and Quito, Ecuador), Polak (Waterlo, Canada), Ospina (Houston, USA), Hawkins (U. of Ilinois, USA), Mutoni (EPFL, Switzerland), Mitchel (McGil, Canada), Criswel (Colorado State, USA), Alexander (Edmonton, Canada). Not shown: Baant (Northwestern, USA), Dam (U. of
32、Michigan, USA), Gayed (Calgary, Canada), Hueste (Texas A however, an average shear stress does not model the behavior in a D-region. D-regions are more correctly modeled using strut-and-tie. Column-slab connections exhibit the characteristics of both B- and D-regions. Tests show that radial arching
33、action is an important mechanism of shear transfer between a slab and a column, suggesting that column-slab connections should be considered D-regions. In the circumferential direction, however, column-slab connections behave more like B-regions. This paper provides a brief summary of the mechanics
34、of the strip model and extends the model to account for size effect. It then introduces the concepts of non-proportional loading and shows how these are used to describe the transfer of shear moment at a column-slab connection. 2 Strip model for concentric punching 2.1 Internal load distribution The
35、 Strip Model divides the slab into radial strips and plate quadrants, as shown in Fig. 1. No load can reach the column without passing through one of the radial strips. Within each radial strip shear is carried to the column by arching action. This is visualized as a curved arch, with maximum slope
36、at the face of the column as shown in Fig. 2. The quadrants of two-way slab are fundamentally slender flexural elements, which means shear transfer across the boundary between a strip and its adjacent quadrant of plate is through the two-way plate equivalent of beam action. Figure 1: Geometry of Str
37、ip Model. Consider the compression arch shown in Fig. 2. The compression force in the arch is approximately constant throughout. At the column face, the vertical component of the arch accounts for the shear transferred to the column; the horizontal component provides a flexural compression. Line s o
38、f ze ro sh earDire ctio n o f Re info rc eme ntRadial St ripsColu mnRemote end loca ted at po sitio n o fze ro sh ea rDirection ofReinforcementSha de d reg ion indic ate s rad ial ha lf-strip (Fig. 3)ACI-fib International Symposium Punching shear of structural concrete slabs 3 Figure 2: Beam and arc
39、hing action at column-slab connection. Moving away from the column, the slope of the arch decreases. Vertical equilibrium of the arch requires that there be a transverse stress field. The transverse stress field is internal and is generated by the two-way plate equivalent of beam action shear acting
40、 in a direction perpendicular to the arch. Thus, the model is of the interaction between the slender quadrants of plate and the radial strips acting as deep beams. Figure 3 shows a free body diagram of half of a radial strip. The half-strip is loaded on its side face by a combination of plate bendin
41、g moment, mn, torsional moment, mt, and shear, v. The strip is supported by a vertical reaction, Ps, at the column-supported end and bending moments, Mneg and Mpos, at the column and remote ends of the strip, respectively. Figure 3: Forces on radial half-strip. The internal vertical shear at any poi
42、nt along the side face of a radial strip is a function of the gradients of bending and torsional moments at that point. Alexander and Simmonds (1992) and Afhami et al. (1998) examine the various components of this internal shear in some detail to justify the simplified free body diagrams of radial s
43、trips at ultimate load, shown in Fig. 4. The loading term, w, is the limiting one-way shear that can be carried by the slab. An internal radial strip, such as those shown in Fig. 1, is loaded on two faces; hence the total distributed line load on the strip is 2w. At an edge column, a spandrel strip
44、running parallel to the free edge of the slab would be loaded on only one side and so would be subject to a line load of w. 0 . 5Mpos0 . 5Mn eg0 . 5Psn m nm tvm nC olu mn En dR em ot eEn dqrLACI-fib International Symposium Punching shear of structural concrete slabs 4 Figure 4: Simplified loading on
45、 radial strip. The flexural strength of the radial strip, Ms , is the sum of the negative and positive flexural capacities, Mneg and Mpos, at the ends of the strip. The loaded length of the strip is l and the total load carried by one strip is Ps, termed the nominal capacity of a strip. Equilibrium
46、for an internal radial strip requires that: = (1) = 2 (2) The corresponding equations for a spandrel strip are: = 2 (3) = 2 (4) The total load that can be delivered to the column is simply the summation of the individual strip contributions. = (5) While the load distribution described above is certa
47、inly a simplification of reality, it is nevertheless realistic. The radial strips are parallel to the stiff directions of the reinforcing mat. Alexander et al. (1995) and Afhami et al. (1998) show that bending moment gradients perpendicular to the side faces of radial strips, estimated from strain g
48、auge measurements, account for the measured column reaction over a considerable range of loading. Using non-linear finite elements, Afhami et al. (1998) show that yielding of flexural reinforcement through the column results in a stepped distribution of internal shear along the side face of a radial
49、 strip, consistent with what is shown in Fig. 4. Earlier work (Alexander and Simmonds, 1992) examines a limited data set of 116 concentrically loaded interior column-slab connections from eight sources, six with simply supported edges and two with rotationally restrained edges. The flexural capacities are strictly limited to those of the strip of slab defined by the width of the column. = 2 (6a) LlM posM negP s2wLlM posM negP sw(a) Int eri or St rip(b) Spa ndrel S tri pCol um n E
