fib Model Code 2020 Shear and punching provisions, needs for improvements with respect to new and existing structures

Transcription

1 fib Model Code 2020 Shear and punhing provisions, needs for improvements with respet to new and existing strutures Aurelio Muttoni Workshop fib Sao Paulo, Éole Polytehnique Fédérale de Lausanne, Switzerland 0

2 Development of CEB FIP fib Model Codes UNESCO International Code (joint projet CEB + ACI) Several national odes ENV :1991 NBR 6118:1980 EN :2004 NBR 6118:2003, 2014 SIA 262:2003 EN :2023? SIA 262: ?

3 Introdution: shear aand punhing shear 2) shear in slabs (without shear reinforement) 3) punhing 1) shear in girders (with shear reinforement) 2

4 MC2010 for members with shear reinforement (girders): stirrup design q z z otq 3

5 MC2010 for members with shear reinforement (girders): ompression strut strength Strain effet EN :2004: 0.6 NBR 6118:2014: 0.54 MC2010 LoA I: k e = 0.55 Brittleness effet EN :2004: 1-f k /250 NBR 6118:2014: a v2 =1-f k /250 MC2010: h f =(30/f k ) 1/3 1 4

6 Effetive onrete strength in webs EN :2004, Effiieny fator n 1 n f k 250MPa MC 2010, LoA I 30MPa n f k => Larger redution for higher f due to more brittle behaviour 5

7 The levels-of-approximation approah (q min and k ) Assessment of ritial existing strutures, design of speial ases Typial design Preliminary design, non governing failure modes 6

8 The levels-of-approximation approah: shear in girders with transverse reinforement Level I Level II Level III Level IV 7

9 fib MC2020, WP Shear in Beams Topis where there is a need to improve MC2010 (1/3) 1) Provisions regarding yli loading should be improved for the verifiation of olumns and walls subjeted to seismi ations. 2) Improve provisions for points loadings near supports (girders) 3) Combined ations Shear, torsion, bending; interation with torsion in solid setions; shear fores not parallel to the prinipal axes of the ross setions (Bi-axial shear in olumns) 4) Simplified provisions to aount for interation with transversal bending (important for box girders or flanged beams) 8

10 fib MC2020, WP Shear in Beams Topis where there is a need to improve MC2010 (2/3) 5) Shear in members with bent-up-bars and/or plain reinforement 6) Shear in prestressed members with poor longitudinal reinforement at end supports 7) Shear of members where the transverse reinforement is poorly anhored 8) Shear in members where the onstrutive rules are not fulfilled (spaing of the transverse reinforement, or less than minimum shear reinforement for instane) 9) Sustained loading? (a ) Sustained loading ( Rüsh effet ) => a 0.85??? or strength redution fator of 0.85 has another justifiation (NBR 6118:2014 and UK NDP)?? Rüsh, H., Researh toward a general flexural theory for strutural onrete. ACI Journal,

11 fib MC2020, WP Shear in Beams Topis where there is a need to improve MC2010 (3/3) 10) Influene of flanges (onsiderations should be inluded e.g. LoA II or III) 11) Shear fatigue onsiderations 12) Reliability & safety evaluation (TG 3.1): shear resistane funtions 13) Bar utoff effet overestimated? 10

12 fib MC2020, WP Shear in slabs Shear in slabs, or members not requiring shear reinforement 11

13 Provisions for members without shear reinforement: MC 90 and EC2:2004 approah MC 90 and EC2:2004 approah V R, = C b d k r 1/3 f k 1/3 + C p b d s p Prestressing (EC2:2004) Conrete strength Reinforement ratio Size effet Area of ross setion 12

14 One-way shear in MC 2010: MCFT as theoretial basis Level I e x f yd 2E s e f E yd s Level II Strain effet Size effet Sigrist V., Bentz E., Fernández Ruiz M., Foster S., Muttoni A., Bakground to the fib Model Code 2010 shear provisions part I: beams and slabs, Strutural Conrete,

15 One-way shear in NBR 6118:2014 : inspired by MC

16 Development of losed-form equation for the 2 nd generation of EN Fernández Ruiz M., Muttoni A., Sagaseta J., (2015) Shear strength of onrete members without transverse reinforement: A mehanial approah to onsistently aount for size and strain effets, Engineering Strutures 15

17 16 2 1/, v dg R d d f k e s l s R s l s R s l s E s s E v E z a E d b z a d b E d b z a V E A z M r r r e,, 2 1/,, z E a d d f k s l s R dg R r 1/3 3 2, d z a d f E k s dg s l R r dg v R f k d e 1 0.3, 1/3, s dg l R a d f r Development of losed-form equation for the 2 nd generation of EN now replaed by: dg v d d e R f, d/2 a s influene of aggregate size size and slenderness effets ombined V E s s s E s s E v E A z a V E A z M e Muttoni, Fernández Ruiz, Cavagnis, fib Bulletin 2018

18 Development of losed-form equation for the 2 nd generation of EN V 1 Rd, Rd, 100 bw d r l f k d a dg s 1/3 In presene of normal fores, the effetive shear span a s shall be adapted as follows: a s M V E E N V E E d 6 0 N E <0 : ompressive normal fores Muttoni, Fernández Ruiz, Cavagnis, fib Bulletin

19 fib MC2020, WP 2.2.3, Shear in slabs fib MC2010 MC1990 EC2:2023? EC2:2004 V 1 Rd, Rd, 100 bw d r l f k d a dg s 1/3 NBR 6118:2014 ACI 318???? 18

20 fib MC2020, WP Shear in slabs Topis where there is a need to improve MC2010 1) provisions regarding distributed loads 2) aount for variable depth 3) provisions for loadings near supports 4) provisions for points loadings near linear supports 19

21 fib MC2020, WP Punhing Bluhe, Switzerland, 1981 Cagliari, Italy, 2004 Vitoria, Brazil, 2016 Tel Aviv, Israel,

22 fib MC2020, WP Punhing EC2:2004 NBR 6118:

23 fib MC2020, WP Punhing fib MC

24 fib MC2020, WP Punhing fib MC2010 Muttoni A., Fernández Ruiz M., Bentz E., Foster S., Sigrist V., Bakground to fib Model Code 2010 shear provisions part II: punhing shear, Strutural Conrete,

25 Development of losed-form equation for the 2 nd generation of EN k b dg Rd, 100rl fk C a p d C f k 1 k b d 8 b

26 The MC2010 model already suitably addresses needs related to assessment and strengthening a) Influene of slab ontinuity and ompressive membrane ation (important for assessment) hidden safety V R, 1 3 proportion al to r Einpaul J., Fernández Ruiz M., Muttoni A., Influene of moment redistribution and ompressive membrane ation on punhing strength of flat slabs, Engineering Strutures, 2015) Einpaul J., Ospina C. E., Fernández Ruiz M., Muttoni A., Punhing Shear Capaity of Continuous Slabs, ACI, Strutural Journal,

27 The MC2010 model already suitably addresses needs related to assessment and strengthening b) Strengthening Retrofitting using externally bonded FRP s D. M. V. Faria D., Einpaul J., M. P. Ramos A., Fernández Ruiz M., Muttoni A., 2014, On the effiieny of flat slabs strengthening against punhing using externally bonded FRP s, Constrution and Building Materials, 2014 Retrofitting using postinstalled reinforement Fernández Ruiz M., Muttoni A., Kunz J., 2010, Strengthening of flat slabs against punhing shear using post-installed shear reinforement, ACI Strutural Journal 26

28 fib MC2020, WP Punhing and shear in slabs Topis where there is a need to improve MC2010 (1/2) 1) Provisions regarding yli loading (flat slabs subjeted to seismi ations). 2) Shear in slabs with bent-up-bars and/or plain reinforement 3) Shear of slabs where the transverse/longitudinal reinforement is poorly anhored 4) Shear in slabs where the onstrutive rules are not fulfilled (spaing of the transverse reinforement for instane) 5) Influene of ompressive membrane ation (aount for slab ontinuity ) -> expliit formulation 6) Verify/adjust level of safety (parameters to be adjusted aording to a reliability analysis) 7) Better define the aim of LoA I (not a simplified design tool, but a first hek to verify whether shear is a onern) 27

29 fib MC2020, WP Punhing and shear in slabs Topis where there is a need to improve MC2010 (2/2) 8) Simplified expressions / losed-form expressions? 9) Influene of imposed deformations (olumns settlements) 10) Update expressions where reent knowledge indiates a need. For instane: (i) k e for edge and orner olumns; (ii) expression for transverse reinforement based on reent improvements of the mehanial model (footings for instane); (iii) Provisions for integrity reinforement 11) Tailored design methods for strengthening of slabs against punhing 12) Punhing with medium - low slenderness: between 1 and 2 (e.g. pile aps) 13) Redistribution of shear in asymmetrial ases (ψ max versus ψ x and ψ y ) 14) Performane and safety on different LoAA 15) Role of integrity reinforement (although further work is needed) 16) Strutural robustness of flat slab strutures (new & existing strutures) 28

30 fib MC2020, WP Punhing and shear in slabs New Bulletins 1) fib Bulletin on Seismi behaviour of flat slabs 2) fib Bulletin on Strengthening of flat slabs against punhing 3) fib Bulletin on Robustness of flat slabs 4) fib Bulletin on Design and assessment of slabs using linear and nonlinear analysis 29

31 MC > MC2020, Stress distribution in the ompression zones Stress distributions aording to EN :2004 MC 2010 NBR 6118:2014 a f k ENV :1991 (unhanged sine CEB 1964) 30

32 Effetive onrete strength in olumns? f 31

33 Similarities between the effetive onrete strength in webs and in olumns Webs Columns (30/f k ) 1/3 1 1-f k /250 32

34 Comparison between olumns tests and ode alulation EN :2004 Unredued onrete strength in the olumn redued onrete strength in the olumn: (30/f k ) 1/3 1 33

35 Stress distribution in the ompression zones may potentially be simplified a = (30/f k ) 1/3 1 same parabola-retangle distribution (CEB 1964) may be used also for f k > 50 MPa 34