Moderate ductility of the bracing joints with preloaded bolts


In Europe, concentrically braced frames (CBFs) with double angle bracings are the most frequent lateral-resistant structural systems. Although their standard bolted connections provide economic and robust solutions for the static loading, they are assumed to have almost zero ductility under strong earthquake actions. In order to avoid a brittle failure, the current seismic design requirements of European Code provisions require these joints to have sufficient over-strength, and to remain elastic for the design earthquake. While this is a safe approach for the high seismicity situations, it causes costly solutions for the buildings designed in the low-to-moderate seismicity context. Therefore, mainly for economy reasons, design engineers usually choose standard non-seismic approach (DCL) for the design of CBFs located in low-to-moderate seismic regions. However, such a choice may lead to unsafe solutions, since no effort is paid to control ductility. To combine safety and economy in this context, a new specific method has been studied in the recently concluded EU-RFCS MEAKADO project. To explore the inherent ductility provided by standard double-angle bracing joints with preloaded bolts and respecting new edge-spacing requirements, full scale tests have been performed as a project task. This article analyses the test results, and quantifies the ductility provided by the bolt hole ovalization and the slippage of preloaded bolts of the bracing joints not fulfilling the current over-strength design criteria. The test data has been analysed by means of LVDTs, strain gauges and thermal images. Such ductility and dissipation resources are traditionally not desired from a high seismicity design point of view, but may satisfy the low horizontal shear demand of the buildings designed for the low-to-moderate earthquake zones.

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This article presents the results of full scale tests performed within MEAKADO project coordinated by Prof. Herve Degee, carried out with the financial grant of the Research Program of the Research Fund for Coal and Steel of the European Commission (RFSR-CT-2013-00022). Special thanks to Prof. Carlo Andrea Castiglioni, for his precious comments. Thanks to the manager and technicians of the LPM laboratories of Politecnico di Milano. Marco Cucchi from LPM Politecnico di Milano is also acknowledged for his help in performing thermal camera measurements and the analysis. Assistance from Master thesis students Alberto Volonterio and Umberto Rico during the test implementations is also deeply appreciated.

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Correspondence to Alper Kanyilmaz.

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Kanyilmaz, A. Moderate ductility of the bracing joints with preloaded bolts. Bull Earthquake Eng 16, 503–527 (2018).

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  • Concentrically braced frames
  • Moderate seismicity
  • Joint ductility
  • Double angle bracings
  • Slip resistant joints
  • Preloaded connections
  • Bolted bracing connections
  • Full scale tests