Review of

D.T. Dekker, S. Hakimi, Shell structures, Report for course CT3280 Shell Roofs, Delft University of Technology, Department of Civil Engineering and Geosciences, 2024, online: phoogenboom.nl/B&B_schaal_report_4.pdf

by dr.ir. P.C.J. Hoogenboom, Delft, 20 February 2024

 1. The report structure is a bit confusing. The headings of the chapters do not explain their contents well. For example, "Experiments" is clearer than "Results". The report should have an abstract. The report should have a preface. The report should have a literature list. Good English, Few language errors. Handed in on time (31 Jan. 2024).

 2. The introduction is incomplete. It does not say that the model represents a large shell roof. Moreover, it is does not read well. A good introduction starts with a problem or opportunity, then states the objective or research question, then explains the approach ...

 3. Figure 1 needs a reference to the person who made this picture. This is plagiarism, unless you made the picture yourself. People got into big trouble for plagiarism, for example prof. Diekstra, Leiden University.  

 4. Page 6. What is the height (sagitta) of the shell?

 5. Beautiful design. Large curvature. The dome design is spherical, while in the physical model the laths have a parabolic shape. How did this happen? What are the consequences?

 6. Page 8. This is indeed a representative model. However, the 0.41 kN/m buckling line load falls out of the sky. How is it computed? This cannot be checked. Computations need to be checkable. How does the buckling mode look? What is the total load [kN] on the shell?

 7. Page 9. What is the load for which the stresses were computed? 

 8. What is the deflection of the shell?

 9. Page 10 and 11. This hand calculation is reproducible. But it would be easier for the checker, if the calculations are presented as in comment 11 below.

10. Page 11. If the buckling shape were computed with SCIA, the buckling length could have been seen in the plot.

11. Page 11. moment of inertia of a lath ... I = 1/12 x b x h^2 = 1/12 x 10 x 5^3 = 104 mm4
             normal force in a lath ........ Ncr = pi^2 x EI / l^2 = 3.14^2 x 9000 x 104 / 350^2 = 75 N
             distributed load on a lath .... q = Ncr/a = 75/370 = 0.20 N/mm = 0.20 kN/m
             total load on the shell ....... R = q x length_of_all_laths = 0.20 x 12.56 = 2.5 kN = 250 kg
             About the same result as in the report.
             Isn't the above calculation much easier to check than the one in the report?
             
12. Page 13. Last sentence. The number 2.29 kN is surely wrong. It should be 1.93 kN, shouldn't it? But you submitted a prediction of 1.96 kN. Why the difference?

13. The construction process is not described! Is this a secret? We do not have secrets in science. How were the laths curved this much? How were they attached to each other? How were they attached to the foundation? And lots of photos please. Others should be able to reproduce your shell model from the report.

14. The load distribution system is not described. How was it made? Are there photos?

15. A photo of the point load would have been useful. The results need to be reproducible.

16. Excellent load-displacement curve. Good recording job.

17. Solid description of the point load failure. Good photo too.

18. Good ideas on building the real shell roof. Actually, the stress of bending a 4 mm thick lath to a radius of 370 mm is the same as bending a 400 mm thick beam to a radius of 37 000 mm.

19. Plagiarism: Figure 11 needs a reference. 

20. How large can we build this roof?
    5.09 / 0.58 = 8.8 kN/m2 
    0.00314 / 0.58 = 0.0054 kN/m2
    8.8 / 2 = x 0.0054 + 1 => x = 630 Essentially the same as in the report.

21. Page 21. Discussion. Many interesting facts and photos are given here that should be in a chapter Building or in the chapter Experiment. Not just the design was solid, the shell had been built exceptionally well.

22. It seems that you have been adding more and more to the end of the report, while you should have improved the beginning of the report.

23. Page 26. The objective here is different from the objective in the introduction. They should be the same. 

24. The conclusions are true and interesting. Indeed, you made an exceptional shell roof. My complements. Nonetheless, the conclusions could be less lyrical and more business-like.