Redundant and Robust Structures by Joint Ductility

Transcription

1 COST ACTION TU0601 Robustness of Structures Workshop Zürich 04./05. February 2008 Redundant and Robust Structures by Joint Ductility, Lars Rölle

2 Contents 1 - Objectives of the RFCS-project ROBUSTNESS 2 - Different strategies to achieve robustness 3 - Simulation of the event loss of a column 4 - Composite joint tests under biaxial loading 5 - Ductile joints for redundant frame structures ard.de]

3 Objectives of the RFCS-project ROBUSTNESS - Prevent progressive collapse caused by local damage - Create redundant frame structures allowing for moment and force redistribution by developing new ductile joints solutions N P N N N N N

4 RFCS - research project Robust structures by joint ductility Partners: Universität of Stuttgart Institute of Structural Design (Coordinator), Germany Universitéde Liège - Département de mécanique des matériaux et structures, Belgium Universität Stuttgart PROFILARBED-Research - Product Department, Luxembourg PSP Technologien GmbH, Germany Università degli Studi di Trento - Dipartimento di Ingegneria Meccanica e Strutturale Laboratorio Prove Materiali e Strutture, Italy

5 Different strategies to achieve robustness - Direct Design Methods: Specific local resistance providing specific local resistance to key-elements

6 Different strategies to achieve robustness - Direct Design Methods: Alternate load path method strengthening of one/more floors redistribution of loading by joints with sufficient ductile behaviour

7 Simulation of the event Loss of a column 4,0 m 4,0 m [Substructure tests in Liège within RFCS-project Robustness ]

8 q serv Simulation of the event Loss of a column Load path example: Stage I - service condition - M M M + j,u M + j,u N j,u N N j,u N M - j,u M - j,u

9 q serv Simulation of the event Loss of a column Load path example: Stage II - column failure - M M M + j,u M + j,u M - j,u N j,u N Column failure M - j,u N j,u N

10 q serv Simulation of the event Loss of a column Load path example: Stage III - membrane effect - N j,u N j,u M M M + j,u M + j,u M - j,u N j,u N Column failure M - j,u N j,u N

11 Simulation of the event Loss of a column Ductile joints with membrane forces allow for redistribution inner joint Simulation of the event loss of a column at a composite substructure edge joint [Substructure tests in Liége within RFCS-project Robustness ]

12 Joint properties Composite joint tests under biaxial loading tension zone without studs A B A B section B-B (at column) section A-A (in span)

13 Test procedure Composite joint tests under biaxial loading load step 1 load step 2

14 Test setup Composite joint tests under biaxial loading vertical jack horizontal support horizontal jack Vertical support Vertical support

15 M [knm] Test results Composite joints under biaxial loading M-phi-curve 1 0,8 0,6 0,4 0, ,2-0,4-0,6-0,8-1 phi[mrad] Joint Rotation V1 Joint Rotation V2 Joint Rotation V3 Joint Rotation V4 Joint Rotation V5 Moment [knm] M-N-interaction Normal Force [kn] V1 V2 V3 V4 V5 hogging moment sagging moment Joints have been able to follow the whole M-N-curve from pure bending state to pure tension state due to sufficient ductility

16 Transferability of the results to larger profiles in test in reality results transferable? IPE 140 IPE 500 Influence of size? What have to be taken into account for larger profiles?

17 Former tests on composite joints by Martin Schäfer (2003) L 0 L 0 L 0 = length of the tension zone without fix action by studs Aim of these tests on composite joints: developement of a tension bar in the concrete slab to improve rotation capacity

18 Former tests on composite joints by Martin Schäfer (2003) One of the tests showed that although the ductility criterion acc. EC3 part 1-8 was not violated a premature brittle bolt failure occured: the tension bar (in the concrete slab) could not be activated totally limited ductility of the joint

19 Ductile joints for redundant frame structures u Reinforcement u Endplate Tension components of the pure steel joint have to have a certain ductility: to ensure a complete activation of the component RFT to ensure highly ductile joint behaviour Special focus on the arrangement & adjustment of the single components

20 Additional tests on pure steel joints within RFCS-project Robustness M Aim of the steel joint tests - investigation on: - membrane effects in the endplate underestimation of EP bearing capacity - influence of the bolt arrangement bearing capacity + ductility

21 Parameter variation S1-S6 Steel joint tests S1 S4 S5 S6 390 mm 100 mm 340 mm 150 mm 290 mm 200 mm t = mm t = 12 mm t = 12 mm

22 Test Results: 1 0,8 M u /M u,s1 0,6 0,4 Steel joint tests Influence of the bolt arrangement 0, Rotation Φ [mrad] S1 S5 S6

23 Comparison of the deformations: Steel joint tests validation of the numerical model by the experimental results

24 Influence of the bolt arrangement - vertical distance SP11 SP12 SP z Moment [knm] Steel joint tests Sp 11 m SP 12 SP Rotation Φ [mrad] decrease of the inner lever arm z decrease of M j increase of the vertical distance m 2 between bolts and beam flange increase of ductility

25 Influence of the bolt arrangement - horizontal distance - SP11 SP21 m SP31 Steel joint tests Moment [knm] Sp 11 SP 21 SP Rotation Φ [mrad] increase of m decrease of effective length and M j increase of the horizontal distance between bolts and beam web increase of ductility

26 Findings of steel joint tests Membrane effects in the endplate were clearly identified: cause over-strength effects in the endplate (leads to additional stress of the bolts) ductility criterion acc. EC3 part 1-8 does not sufficiently ensure highly ductile joint behaviour By change of the bolt arrangement: ductility has been clearly increased by only moderate drop of the bearing capacity ductile and sufficiently strong partial-strength (composite) joints may be designed

27 Conclusions Composite joints with realistic profiles may also reach high rotation capacity (> 100 mrad) - depending on the ductility of the single components and their adjustment in these ductile joints membrane forces may be activated for redistribution of forces partial-strength joints with ductile design are applicable to create redundant structures

28 Acknowlegdement The work presented here is carried out, as a joint research project with a financial grant from the Research Fund for Coal and Steel (RFCS) of the European Community. The authors are grateful for the support!

29 Thank you very much for your attention Universität Stuttgart Institute of Structural Design Fields: steel, timber and composite structures Dipl.-Ing. Lars Rölle Pfaffenwaldring Stuttgart Germany Robustness phone faxsmile sekretariat@ke.uni-stuttgart.de [Ice Stadium Bad Feuerwehr Berchtesgaden]