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Capacity design of traditional and innovative ductile connections for earthquake-resistant CLT structures

  • Davide Trutalli
  • Luca Marchi
  • Roberto Scotta
  • Luca PozzaEmail author
Original Research
  • 28 Downloads

Abstract

Traditional connections in earthquake-resistant cross-laminated timber buildings are susceptible of brittle failures, even when buildings are designed and supposed to be ductile. This is mainly due to the large underestimation of the actual strength of the ductile components, with consequent increased strength demand for the brittle parts, which may fail if designed with insufficient overstrength. Recent studies demonstrate that the use of steel connections characterized by a well-defined mechanical behaviour can improve significantly ductility and dissipative capacity of cross-laminated timber structures and the reliability of the capacity design. In this paper, the conceptual model of capacity design is discussed, proposing some modifications to improve its reliability for traditional and high-ductility connections for CLT structures. Results from quasi-static cyclic-loading tests of an innovative ductile bracket are presented and the corresponding overstrength factors are computed using the proposed conceptual method and compared with values available in the literature for traditional connections. Finally, a comparative application of the capacity criteria to the design of the innovative bracket and of a traditional nailed connection is presented and discussed.

Keywords

Capacity design CLT structures Innovative connections Overstrength factor Timber structures 

List of symbols

B

Brittle component (used as subscript)

D

Ductile component (used as subscript)

\({d}_{u}\)

Ultimate displacement

\({d}_{y}\)

Yielding displacement

\({d}_{y,est}\)

Estimated yielding displacement

\({d}_{peak}\)

Displacement corresponding to peak force

\({d}_{target}\)

Target displacement for a ductile element

\({F}_{code}^{-}\)

Characteristic load-bearing capacity estimated according to code

\({F}_{peak}\)

Peak load-bearing capacity obtained by a test

\({F}_{peak}^{-}\)

5th percentile of the peak load-bearing capacity obtained by tests

\({F}_{peak}^{mean}\)

Mean value of the peak load-bearing capacity obtained by tests

\({F}_{peak}^{+}\)

95th percentile of the peak load-bearing capacity obtained by tests

\({F}_{target}\)

Force at target displacement obtained by a test

\({F}_{target}^{-}\)

5th percentile of the force at target displacement obtained by tests

\({F}_{target}^{mean}\)

Mean value of the force at target displacement obtained by tests

\({F}_{target}^{+ }\)

95th percentile of the force at target displacement obtained by tests

\({F}_{u}\)

Ultimate or failure force obtained by a test

\({F}^{1st}\)

Force measured in the first cycle at dtarget from cyclic-loading tests

\({F}^{3rd}\)

Force measured in the third cycle at dtarget from cyclic-loading tests

\({F}^{M}\)

Force measured at dtarget from monotonic test

\({F}_{y}\)

Yielding force obtained by a test

\({F}_{y}^{ - }\)

5th percentile of the yielding force obtained by tests

\({F}_{y}^{mean}\)

Mean value of the yielding force obtained by tests

\({F}_{y}^{ + }\)

95th percentile of the yielding force obtained by tests

\({F}_{d}\)

Design strength

\({F}_{d}^{ - }\)

Lower design load-bearing capacity

\({F}_{d}^{ + }\)

Upper design load-bearing capacity

fax,k

Characteristic withdrawal parameter of a fastener

fh,k

Characteristic embedment strength of a fastener in the timber member

My,Rk

Characteristic yield moment of a fastener

\({k}^{ - }\)

5th percentile of a property obtained by tests

\({k}^{mean}\)

Mean value of a property obtained by tests

\({k}^{ + }\)

95th percentile of a property obtained by tests

kel

Elastic stiffness

kpl

Post-elastic stiffness

\(\upbeta_{Sd}\)

Strength degradation between 1st and 3rd cycle at dtarget, due to cyclic loading

γcyc

Strength degradation between monotonic and cyclic-loading curves at dtarget or dpeak

γan

Analytical overstrength

γsc

Scattering of the target strength or scattering of the peak strength

γRd

Overstrength factor

\({\gamma }_{m}\)

Partial factor for material properties

\(\upgamma_{m}^{ - }\)

Partial factor for material properties in calculating lower design value of the load-bearing capacity according to code

\(\upgamma_{m}^{ + }\)

Partial factor for material properties in calculating upper design value of the target force or the peak force

ρk

Characteristic value of wood density

μ

Ductility

νeq

Equivalent viscous damping

Notes

Acknowledgements

Economical support from “Proof of Concept Network” (PoCN) project, organized and managed by AREA Science Park (Trieste-Italy), financed by MIUR within “Progetti Premiali 2011” action, is acknowledged. Title of the specific project: “foundation system for timber and lightweight structures—ref. UNIPD_03”. Grateful thanks go to the staff of the Mechanical Testing Laboratory of Department ICEA of the University of Padova for their support during experimentation.

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Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  • Davide Trutalli
    • 1
  • Luca Marchi
    • 1
  • Roberto Scotta
    • 1
  • Luca Pozza
    • 2
    Email author
  1. 1.Department of Civil, Environmental and Architectural EngineeringUniversity of PadovaPaduaItaly
  2. 2.Department of Civil, Chemical, Environmental and Materials EngineeringUniversity of BolognaBolognaItaly

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