Laboratory for Resilient Steel and Smart Structures

Introduction

  • Background

Civil engineering structures are now faced with increasing risks from natural or man-made hazards, such as earthquakes, wind, fire, explosion, and impact actions. The collapse of engineering structures will cause severe casualties and property losses to the society. It is of great significance to enhance the reliability and safety of the structure in hazards.

However, for some survived buildings with severe damages (usually with storey drift over 0.5%), the repair costs are so high that it is always more economical to demolish them [1]. It is reported by the ASCE Infrastructure Report Card that the cost for rehabilitation for civil engineering structures in the USA is estimated to be US$123 billion [2]. Moreover, even if the damaged buildings can be repaired, the downtime of the building function will cause significant indirect losses to the whole community. These consequences are not consistent with the sustainability guidelines proposed by ASCE that when optimizing the structure, not only the structural effects and responses to loads should be considered, but also the responses to and interaction with the surrounding environment and ecosystems [3]. It seems that the traditional survival-based safety design concept now has far fallen behind the sustainability requirements. Therefore, improving the resilience of engineering structures after hazards and minimizing its impact on the community are important parts to guarantee the sustainable development of the society.

In some third- and fourth-tier cities in mainland of China, there are still many low-rise and middle-rise residential buildings. The construction of these buildings often costs about 10-20 years of the household income. After hazards, the repair cost of the damaged buildings will exert huge economic pressure on the residents. Recognizing this, RSSsL will be committed to developing basic theories and application technologies on smart structures, by using material-based technology, innovative connections and components, or novel structural system, to enhance the resilience of steel structures subject to various hazards. By alleviating disaster damages and avoiding large residual drifts, the cost of the following repair work for the damaged structures can be significantly reduced, which can further promote the sustainable development of the society.

  • Objective

RSSsL aims to conduct advanced studies on the resilience of steel and smart structures subject to extreme actions. These include but not limited to earthquake, wind, fire, explosion, and impact that may significantly affect the robustness and structural integrity of steel structures. By conducting experimental studies, theoretical studies, and advanced numerical analyses, RSSsL will propose resilient-based design guidelines and recommendations for the profession. Cost-effective structural and smart elements and system will also be promoted in practical engineering. The final goal of RSSsL is to promote resilient steel structures design with the adoption of smart materials to alleviate the damage of buildings due to extreme actions. In particular, the advanced technologies developed will be applied to strengthen existing low-rise and middle-rise building structures subject to seismic action. The work of RSSsL will contribute to the sustainable development and construction to enhance the suitability of the society.

Research Team of the Lab

  • Laboratory-in-charge
Prof Michael CH YAM
  • Members
Prof K F Chung
Dr Tak-Man Chan
Dr Fang Cheng (Associate Prof, Tongji University)
Dr Ke Ke (Associate Professor, Chongqing University)
  • Collaborators
Prof Zhou Xu-Hong (Professor, Chongqing University)
Dr Ran FENG (Harbin Institute of Technology)
Dr Zhang Jing-Zhou (Postdoc, PolyU)
Dr Wang Jun-Jie (Postdoc, PolyU)

Venue: ZB207 at Block Z

Lab details

The RSSsL is equipped with state-of-the-art testing facilities to conduct full-scale tests of structural connections, elements, and systems subject to various types of loadings due to the hazards. Advanced numerical and computations techniques are also employed to complement the experimental results and enhance the understanding of the structural performance and behaviour of structural elements and systems to achieve structural resilience.

Research areas of the laboratory includes:

  • Use of smart materials in earthquake resistant structures.
We performed an experimental study of the cyclic performance of extended end-plate connections connected using SMA bolts instead of normal high strength bolts in the connections. The basic concept is to concentrate the earthquake-induced deformation into the connection, such that a ‘superelastic’ hinge can be formed via the elongation of the SMA bolts. Eight full-scale tests were conducted including seven extended end-plate connections with SMA bolts and one conventional extended end-plate connection with normal high strength bolts. The SMA connection specimens were shown to have excellent recentring abilities and moderate energy dissipation capability with an equivalent viscous damping up to 17.5%. The stiffness and strength of these connections mainly fell into the semi-rigid and partial-strength categories, respectively. The ductility, which was governed by SMA bolt rupture, was found to be dependent on the net threaded-to-shank area ratio of the bolts, where a lower ratio led to earlier bolt fracture over the net threaded cross-section. On the other hand, the conventional extended end-plate connection with High Strength bolts was shown to have good energy dissipation capability and ductility but with considerable permanent deformation. To enable a further understanding of the SMA connections, preliminary numerical models were established and validated by the test results.

References

  • Fang, C., Yam, M.C., Lam, A.C. and Xie, L., 2014. Cyclic performance of extended end-plate connections equipped with shape memory alloy bolts. Journal of Constructional Steel Research, 94, pp.122-136. https://doi.org/10.1016/j.jcsr.2013.11.008

 

  • Application of energy dissipation bay for resilient-based design of steel frames
To achieve a delicate balance between self-centring behaviour and energy dissipation, it was proposed to develop the damage-control steel frame equipped with shape memory alloy (SMA) connections and ductile links showing the partially self-centring behaviour. This paper examined the inelastic seismic demand of the novel structure, and the emphasis was given to the spectral energy factor of the system subjected to near-field earthquake motions. Based on single-degree-of-freedom (SDF) systems representing the novel structure and a near-field earthquake database, nonlinear spectral analyses were performed considering a wide range of structural period and hysteretic parameters, and more than 25 million energy factors were obtained. The probabilistic characteristics of the energy factors were examined in detail. The analysis database confirmed that the energy factors were sensitive to structural period and hysteretic parameters. In addition, a right-skewed distribution feature of the energy factors was observed. Thus, a spectral energy factor model for damage-control steel frames equipped with SMA connections and ductile links was developed using the lognormal distribution model. Nonlinear regression analyses were conducted to develop a series of prediction equations. The good agreement between the histograms of the energy factor and predictions by the regression equations confirmed the adequacy of the proposed model. The proposed model was eventually applied to evaluating the damage-control behaviour of a prototype structure under near-field earthquake motions, and the sufficiency of the model for assessing the structural damage-control behaviour from a statistic perspective was confirmed.

References

  • Zhou, X., Zhang, H., Ke, K., Guo, L. and Yam, M.C., 2021. Damage-control steel frames equipped with SMA connections and ductile links subjected to near-field earthquake motions: A spectral energy factor model. Engineering Structures, 239, p.112301.https://doi.org/10.1016/j.engstruct.2021.112301

 

  • Applications of shape memory alloys energy dissipation elements in earthquake resilient structures
We developed a prototype of self-centring energy-dissipative rocking (SC-EDR) column system to enhance the self-centring capability of the EDR column by introducing a set of shape memory alloy (SMA) tension braces. The seismic responses such as load carrying capacities, stress distributions, base rocking behaviour, source of residual deformation, and energy dissipation are primarily investigated.
  • Seismic behaviour of HSS frames
A primary investigation on the cyclic plastic behaviour of high strength steel (HSS) Q690 is conducted, which is a foundation for the seismic behaviour of HSS frames. The cylic plastic response of HSS Q690 is examined under several cyclic loading protocols, including constant strain amplitude (CSA) loading protocols, variable strain amplitude (VSA) loading protocols, and random loading protocols. Cyclic softening phenomenon is observed from the test results, which could be critical for the seismic behaviour of HSS frames. Besides, the cyclic plasticity of Q690 is proved to be plastic strain amplitude independent. We also develop a constitutive model to characterize the cyclic plastic response of Q690. The simulation results are almost identical to the test results (relative error is less than 5%), which indicates the excellent performance of the proposed model.

References

  • Zhou, X., Zhang, H., Ke, K., Guo, L. and Yam, M.C., 2021. Damage-control steel frames equipped with SMA connections and ductile links subjected to near-field earthquake motions: A spectral energy factor model. Engineering Structures, 239, p.112301.https://doi.org/10.1016/j.engstruct.2021.112301

Expected deliverables

  • High quality journal and conference paper publications.
  • Design guidelines and recommendations.
  • Research seminar presentations.
  • Patents.
  • Training of PhD students and research personnel.

About Us

CNERCEstablishment of the Chinese National Engineering Research Centre for Steel Construction (Hong Kong Branch) at The Hong Kong Polytechnic University (PolyU) was approved by the State Ministry of Science and Technology (MOST), People’s Republic of China on 12th October 2015.

Contact Information

Address:
Chinese National Engineering Research Center for Steel Construction (Hong Kong Branch)
The Hong Kong Polytechnic University, Phase 8,
Hung Hom, Kowloon, Hong Kong.

Phone: (852) 3400-8451

Email: cnerc.steel@polyu.edu.hk