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Towards a rational understanding of shear in beams and slabs (PDF)

No. 85. Towards a rational understanding of shear in beams and slabs. Technical report (338 pages, ISBN 978-2-88394-125-0, May 2018) - PDF format
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Description

FIB BULLETIN NO. 85

Title: Towards a rational understanding of shear in beams and slabs

Category: Technical report

Year: 2018

Pages: 338

Format approx. DIN A4 (210x297 mm)

ISBN: 978-2-88394-125-0

DOI: doi.org/10.35789/fib.BULL.0085

Abstract:

Reliable performance of beams and slabs in shear is essential for the safety and also for the serviceability of reinforced concrete structures. A possible failure in shear is usually a brittle failure, which underlines the importance of the correct specification of the load carrying capacity in shear. The knowledge of performance in shear is steadily developing and it is now obvious that older structures were not always designed in accordance with contemporary requirements. The increasing load – mainly on bridges – requires the assessment of existing structures, often followed by their strengthening. An appropriate understanding of actual performance of concrete structures in shear is therefore of primary interest.

The workshop which was held in Zürich in 2016 brought together a significant number of outstanding specialists working in the field of shear design, who had a chance to exchange their opinions and proposals for improving the current knowledge of shear behaviour in beams and slabs. The specialists came from different parts of the world, which made the workshop general and representative. The workshop was organised by fib Working Party 2.2.1 “Shear in Beams” (convened by O. Bayrak), which is a part of fib Commission 2 "Analysis and Design".

Individual contributions mainly address shear in beams with low transversal reinforcement. It is crucial because many existing structures lack such reinforcement. Different theories, e.g. Critical Shear Crack Theory (CSCT), Modified Compression Field Theory (MCFT), Multi-Action Shear Model (MASM), etc. were presented and compared with procedures used in selected national codes or in the fib Model Code 2010. 

The models for shear design were often based to a great extent on empirical experience. The refined presented models tend to take into account the physical mechanisms in structures more effectively. A brittle behaviour in shear requires not only to check the equilibrium and failure load, but also to follow the progress of failure, including the crack development and propagation, stress redistribution, etc. The significance of the size effect – which causes the nominal strength of a large structure to be smaller than that of a small structure – was pointed out.

Nowadays, the fibre reinforcement is used more than before since it allows significant labour costs savings in the construction industry. The contribution of fibres is suitable for shear transfer. It is very convenient that not only ordinary fibre reinforced elements were addressed but also the UHPFRC beams. The production of this new material is indeed growing, while the development of design recommendations has not been sufficiently fast.

Fatigue resistance of structures with low shear reinforcement is also an important issue, which was also addressed in this bulletin. It cannot be neglected in prestressed bridges, which are exposed to dynamic loads.

A comprehensive understanding of the shear behaviour is necessary. Although many laboratory experiments are carried out, they are suitable only to a limited extent. New testing methods are being developed and show promising results, e.g. digital image correlation. An actual structure performance should rather be tested on a large scale, ideally on real structures under realistic loading conditions.ii 

The papers presented in the bulletin are a basis for the discussion in view of the development of updated design rules for the new fib Model Code (MC2020), which is currently under preparation. fib Bulletins like this one, dealing with shear, help to transfer knowledge from research to design practice. The authors are convinced that it will lead to better new structures design of as well as to savings and to a safety increase in older existing structures, whose future is often decided now. 

Jan L. Vítek

Chair of fib Commission 2 “Analysis and Design”

Download the copyright page (= list of authors) as a PDF file. 

Download the table of contents as a PDF file.

 

0. Survey of participants in the fib Workshop on beam shear - doi.org/10.35789/fib.BULL.0085.Ch00

1. From detailed test observations to mechanical models and simple shear design expressions - doi.org/10.35789/fib.BULL.0085.Ch01

2. Shear transfer actions in reinforced and prestressed concrete beams - doi.org/10.35789/fib.BULL.0085.Ch02

3. Predicting the shear strength of thick slabs - doi.org/10.35789/fib.BULL.0085.Ch03

4. Shear capacity of members without shear reinforcement based on limit analysis - doi.org/10.35789/fib.BULL.0085.Ch04

5. Shear transfer actions of slender members without stirrups - doi.org/10.35789/fib.BULL.0085.Ch05

6. Influence of M/V-combination on the shear behaviour of members without stirrups - doi.org/10.35789/fib.BULL.0085.Ch06

7. Insights from the numerical modelling of reinforced beams under distributed loads - doi.org/10.35789/fib.BULL.0085.Ch07

8. ACI-DAfStb shear databases - doi.org/10.35789/fib.BULL.0085.Ch08

9. Database of shear tests subjected to uniformly distributed loading - doi.org/10.35789/fib.BULL.0085.Ch09

10. Stress fields in concrete teeth and jawbones - doi.org/10.35789/fib.BULL.0085.Ch10

11. Cracking and the shear strength of reinforced concrete - doi.org/10.35789/fib.BULL.0085.Ch11

12. Contribution of the shear transfer actions in short span beams - doi.org/10.35789/fib.BULL.0085.Ch12

13. Shear strength of UHPFRC I-shaped beams without stirrups - doi.org/10.35789/fib.BULL.0085.Ch13

14. Out-of-plane shear strength of steel-concrete sandwich panels - doi.org/10.35789/fib.BULL.0085.Ch14

15. Shear fatigue of prestressed concrete beams - doi.org/10.35789/fib.BULL.0085.Ch15

16. Simplified Multi-Action Shear Model for shear design - doi.org/10.35789/fib.BULL.0085.Ch16

17. Towards a unified approach for shear design of SFRC and UHPFRC girders - doi.org/10.35789/fib.BULL.0085.Ch17

18. Three-parameter kinematic approach for short coupling beams - doi.org/10.35789/fib.BULL.0085.Ch18

19. Biaxial shear in reinforced concrete beams and columns - doi.org/10.35789/fib.BULL.0085.Ch19

20. Future directions for research on shear in structural concrete - doi.org/10.35789/fib.BULL.0085.Ch20

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