One general approach, endless possibilities

Significance 

Bridges are structures often constructed for the main purpose of offering transit between two locations separated by a geological feature. Several types of bridges are available and selection of the type of bridge depends on numerous factors such as economy, design feasibility and existing geological layout. Cable-stayed type is suitable for bridges having medium to long span range. However, due to low inherent damping and flexibility, stay cables on cable-stayed bridges are susceptible to dynamic excitations. In the past, either aerodynamic countermeasures or mechanical solutions have been developed to mitigate excessive cable vibrations, the latter of which mainly includes the attachment of an external damper to the vulnerable cable to increase its damping or using cross-tie(s) to connect the vulnerable cable to its neighbouring ones to improve its in-plane stiffness. However, the effectiveness of the damper solution is limited by the damper installation location, whereas cross-tie cannot help to directly dissipate system energy. Combination of these two solutions gives rise to the hybrid system which offers better control on cable vibration. Unfortunately, little has been published with regard to the dynamic response of such hybrid systems. Worse off, much of the little that is published is not applicable to a generalized case since it was developed for a hybrid system with specific layout.

Recently, Professor Shaohong Cheng and Dr. Faouzi Ghrib at University of Windsor in Canada, in collaboration with Dr. Javaid Ahmad at National University of Computer and Emerging Sciences in Pakistan, developed a generalized approach for formulating an analytical model of hybrid systems which will allow the development of an analytical model of a complex hybrid system based on a relatively simple parent system. The researchers expected that their proposed model would greatly save modelling effort and provide a convenient and useful tool for evaluating and comparing the effectiveness of different hybrid system layouts in the preliminary design stage. Their work is currently published in the research journal, Journal of Engineering Mechanics.

In brief, the research method employed commenced with the consideration of a typical basic hybrid system consisting of a vulnerable cable connected to a neighbouring cable by a transverse linear flexible cross-tie and equipped with a linear viscous damper close to one supporting end. Next, the researchers assessed and validated the proposed model by verifying it using a number of cable systems with various configurations, already analytically derived in literature. Lastly, the developed system was applied to a more intricate system comprising of two damped main cables interconnected with a cross-tie extended to and anchored on the ground or the bridge deck.

The authors observed that the proposed approach was a reliable tool and it allowed for straightforward formulation of an analytical model of a complex hybrid system from a simpler parent system. In addition, they noted that their system resulted in faster modelling hence much time saving. They also found out that the quicker modelling allowed for more evaluation and comparison of the effectiveness of several hybrid systems with different layouts during the preliminary design stage.

In a nutshell, the study presented the derivation of a generalized approach to formulating analytical models of hybrid systems used for bridge stay cable vibration control. In general, the results obtained from application of the developed approach showed that if an additional connector was to be placed at the existing nodal point of a main cable in the parent system, it would only affect the global modes of the parent system, leaving the local modes unchanged. Altogether, the researchers showed that if the cross-tie is not located at the nodal point of the main cables, it is beneficial to increase its flexibility to suppress the local modes.

Sutong bridge-Advances in Engineering- Hybrid Cable Networks
Sutong bridge: the second longest span cable-stayed bridge in the world.

About the author

Dr. Javaid Ahmad is an Associate Professor and the head of Civil Engineering Department at FAST National University of Computer and Emerging Sciences Lahore, Pakistan. He has thirty years of engineering experience in industry and academia. In addition to his academic activities, he is a peace activist and engaged in multiple local committees.

Dr. Ahmad received his undergraduate civil engineering education in 1989 from University of Engineering and Technology, Lahore Pakistan. He then worked for public sector for almost 9 years where he was responsible for the execution of civil engineering projects. All these projects were funded by Asian Development Bank (ADB) and World Bank (WB). In 1998, he acquired his post-graduate diploma in Information Technology (IT) from ITI Toronto, Canada and worked as a senior engineer/developer at Radix Controls Inc. Canada. He received his MENG, MSc and PhD degrees from the University of Windsor, Canada in 2009, 2012 and 2016, respectively. His research work for MSc and PhD was specific to explore various strategies for mitigating the vibrations of stay cables on cable-stayed bridges.

Currently, Dr. Ahmad is working as the head of Civil Engineering Department at one of the prestigious university in Pakistan. While known for his qualitative research work, Dr. Ahmad is a passionate educator who keeps an excellent teaching record. During his stay at FAST – NUCES, he made tremendous efforts to launch PhD program in civil engineering and offered new courses (like Forensic Engineering), both for undergraduate and graduate programs, that fulfils the emerging need of local industry.

As a HoD civil engineering, he supports and facilitates research opportunities, and established a departmental body to focus on research and publication. His fields of interest are vibration control, system control and health monitoring and forensic engineering. He currently teaches Mechanics of Materials, Structural Engineering, Advanced Structural Analysis, Earthquake Engineering, Design of FRP Composite Structures and Forensic Engineering to graduate and undergraduate students.

About the author

Dr. Shaohong Cheng is a Professor in the Department of Civil and Environmental Engineering at the University of Windsor, Windsor, Ontario, Canada. She is a Professional Engineer of Ontario, a member of the American Society of Civil Engineers, the American Association for Wind Engineering, and the International Association for Bridge and Structural Engineering.

Dr. Cheng received her Ph.D. degree in Structural Engineering from Carleton University in Canada in 2000, studying wind-induced response of long-span bridges. She then worked as a post-doctoral research fellow at the University of Ottawa, during which she was in charge of an NSERC CRD research project in collaboration with the National Research Council Canada, the RWDI Inc., and the US Federal Highway Administration, and conducted extensive wind tunnel studies to investigate some newly identified wind-induced vibration problem of bridge stay cables. After working for eight months as a senior consulting engineer in a private company specialized in wind, she joined the Faculty of Engineering at the University of Windsor in 2005.

Dr. Cheng is the founder of the Boundary Layer Wind Tunnel Laboratory at the University of Windsor. She conducts research and supervises students in a broad range of projects, mainly in the areas of bluff body aerodynamics, fluid-structure interaction, vibration control and concrete technology. In recent years, her research is focused on Wind-induced response of structures, in particular, the bridge stay cables; Mitigating excessive stay cable vibrations using external dampers, cross-ties and hybrid systems; Mechanisms associated with dry inclined cable galloping and high-speed vortex excitation; Enhancing the aerodynamic stability of a new small ducted-fan type VTOL UAV model for precision agriculture; Evaluating the design wind load for building guardrail systems; Simulating atmospheric boundary layer effect in the wind tunnel; Shear strengthening of prestressed precast concrete hollow core slabs using carbon fibre reinforced polymer.

About the author

Faouzi Ghrib has a wide interest in solid mechanics and structural modelling. His main area of research is in the realm of mixed experimental-numerical simulations with particular emphasis on using image processing techniques and finite element in modelling concrete structures. He then ventured into the area of cable vibration with Dr. Shaohong Cheng, specifically, he is interested in developing analysis tools to enhance the understanding of cable dynamics. Dr. Ghrib is also working on the rehabilitation of concrete structures damaged by corrosion using composite materials。

Reference

Javaid Ahmad, Shaohong Cheng, Faouzi Ghrib. Generalized Approach for the Formulation of Analytical Model of Hybrid Cable Networks. Journal of Engineering Mechanics, 2018, volume 144(6): 04018035.

Go To Journal of Engineering Mechanics

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