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Investigation into the Structural Performance of Engineered Wood I-Joists with Web Openings

   School of Computing, Engineering & the Built Environment

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  Dr A Khokhar  No more applications being accepted  Funded PhD Project (Students Worldwide)

About the Project

Description of the Project

Wood I-joists are engineered wood products that fabricated with solid or engineered wood flanges connected to the wood-based web member such as Oriented Strand Board (OSB). These I-joists provide improved structural and dimensional stability compared to traditional solid timber joists and widely used in residential and commercial construction. One of the major considerations of any construction is the service access throughout the structures. Therefore, frequent holes and cuts (openings) are made in the web members for the service conduits and ducts during construction without considering the structural integrity of the joists. However, this procedure modifies the strength and stiffness of the web and may reduce the load carrying capacity of the I-joists. Limited published research has reported that web openings have substantial influence on structural performance of I-joists [1–3]. Researchers [1,4,5] found that the effects of the web openings depend on their size and location, the shape and the frequency within a joist. I-joists with web openings must satisfy the ultimate and serviceability limit state design criteria [6]. Yet, there is no proper design methodology available that takes account of I-joists using service access holes and there is an urgent need to address this. This is what the proposed research will address.

Aim and objectives

This research will be conducted in collaboration with James Jones and Sons timber industry. The aim is to conduct a research investigation to evaluate the influence of geometrical configurations and numerical orders of web openings on the strength and stiffness of I-joists. The other purpose is to develop design approaches that can assess satisfactory ultimate and serviceability performance of I-joists with web openings.

Methodology and the outcome

To achieve the research aims, both laboratory-oriented experimental and finite element (FE) based studies will be conducted. At first, a parametric study through FE models will be carried out and the influence of shapes (eg circular, rectangular and square) and their sizes will be evaluated. Location of openings (mid-span or at near the supports) and their number within a joist, as well as the interaction distance between two adjacent holes will be examined. The FE modelling results will assist in optimising the best possible opening configurations, as well as developing the detailed experimental programme. In the experimental study, three and four-point bending tests will be conducted on I-joists with and without optimised openings and their stiffness and strength will be obtained. In addition, the failure mechanism will also be analysed to understand further about the effects of web openings. The results from the FE and experimental works will be used to develop mechanics and numerical based approaches that can be used in predictive models to determine the structural performance of I joists with web openings under ultimate and serviceability limit state design criteria. This research will provide a deep understanding of the presence of web openings and their effects on the strength and stiffness of I-joists. The outcome from this work will provide general guidelines for facilitating web holes during construction phase. This study could be a valuable contribution in timber structures, especially for industry and for design codes. 

Perspective applicants are encouraged to contact the Supervisor before submitting their applications. Applications should make it clear the project you are applying for and the name of the supervisors. 

Academic qualifications

A first degree (at least a 2.1) ideally in Civil Engineering or Masters in Civil/Mechanical Engineering with a good fundamental knowledge of Finite Element (FE)/Numerical Analysis.

English language requirement

IELTS score must be at least 6.5 (with not less than 6.0 in each of the four components). Other, equivalent qualifications will be accepted. Full details of the University’s policy are available online.

Essential attributes

  • Experience of fundamental experimental work
  • Competent in structural analysis and structural mechanics
  • Knowledge of timber as an engineering material
  • Good written and oral communication skills
  • Strong motivation, with evidence of independent research skills relevant to the project
  • Good time management

Desirable attributes

  • Knowledge of FE Modelling 

For informal enquiries about this PhD project, please contact Dr Aamir Khokhar, Email: [Email Address Removed]

Funding Notes

Payment of the Home/International level of full-time fees for three academic years, plus 36 monthly stipend payments at the prevailing rate set by the UK Research Councils, currently £17,668 for the academic year 2022/23.


1] Pirzada GB, Chui YH, Lai S. Predicting Strength of Wood I-Joist with a Circular Web Hole. Journal of Structural Engineering 2008;134:1229–34.
[2] Islam MS, Shahnewaz Md, Alam MS. Structural capacity of timber I-joist with flange notch: Experimental evaluation. Constr Build Mater 2015;79:290–300.
[3] Zhang S, Zhou J, Chui YH. Simultaneous evaluation of bending and shear stiffness of wood I-joists by transverse vibration tests. Eng Struct 2021;243:112643.
[4] Afzal MT, Lai S, Chui YH, Pirzada G. Experimental evaluation of wood I-joists with web holes. For Prod J 2006;56:26–30.
[5] Zhu EC, Guan ZW, Pope DJ, Rodd PD. Effect of Openings on Oriented Strand Board Webbed Wood I-Joists. Journal of Structural Engineering 2007;133:145–9.
[6] British Standard. BS EN 1995-1-1:2004+A2:2014. Eurocode 5: Design of timber structures. Part 1-1: General — Common rules and rules for buildings. London: 2014.
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