Henk studied Civil Engineering at TU Delft from 1958 to 1963, while also teaching as a special assistant at the Hogere Technische School (higher technical school, or HTS) in The Hague.

‘I was already a qualified concrete constructor, but I had never had the opportunity to continue my studies. Going to a university and moving into student housing was simply not an option in our family with seven children in post-war Utrecht. So, when I entered TU Delft at the age of 28, I was highly motivated. This is why I was able to succeed in the programme, even in combination with a full-time job.’

Special assistent

At that time, there was a major shortage of lecturers in higher education. Henk was given the opportunity to become a ‘special assistant’ at the HTS in The Hague. ‘Because lecturers were expected to teach 17 classroom hours per week, I was able to attend the most important lectures as well’, he explains. ‘I was in a group of forty HTS staffers who also wanted to attend TU Delft. That was great. We earned high marks and progressed rapidly, because we were so motivated.’ Henk has many pleasant memories from that time. ‘For my part, after the HTS and the jobs I had already had, I was ready to dive in deep. The mathematics and mechanics courses were particularly well taught.’ He has high praise for Professors Bouma and Vreedenburgh (Applied Mechanics).

Concrete structures

In 1963, under the supervision of Professors Couperus, Haas, and Vreedenburgh, Henk completed his degree in railways, concrete construction and applied mechanics, with three sub-topics. He designed a monorail for The Hague, performed the calculations for the butterfly roof of the old Central Station in Rotterdam and investigated the ‘Brazilian split test’. ‘Because concrete is brittle, it does not absorb tensile stress well’, he explains. ‘The tensile strength of concrete can be assessed by performing the split test on concrete cubes or cylinders. The tensile strength can be derived from the failure load. There is also a way to visualise this.’ Using the rigid-plate analogy, the tensions in the surface can be converted into bending perpendicular to that surface.

Henk then made a perspex model (see photograph).

‘The perspex takes on a forced bending. In the analogy, the tensile stress occurring across the full height means that the upward curvature should be visible’, he adds. ‘No one believed that at first. If you lay a bar on the model, however, you will indeed be able to see the upward curvature in the reflection on the perspex.’ This makes the split tension (i.e. the tensile stress) visible. This model brought him considerable praise and yielded him 20% of the credits necessary to graduate. 

Plate program

Henk then started working for the Grabowsky & Poort engineering firm.

Many floors are designed in reinforced concrete. ‘Because it was not possible to model this properly at the time, floors were fabricated a bit too thick and with too much reinforcement. It was therefore an economic issue’, he explains. ‘For the purposes of calculation, floors were treated as beams, which could be calculated properly. Because floors work in two directions and involve torsion, however, they call for another type of calculation. This does complicate the mathematics somewhat.’

Even when still attending Professor Vreedenburgh’s lectures, Henk had the notion that differential calculation ought to offer a solution in this regard. This would require computers, however, and in 1964 those were only in the very early stages. With the help of several colleagues, Henk developed the ‘plate program’, the first computer software for calculating floors. It would remain in use for 25 years, as it was ‘custom designed’ for concrete constructors. It was also sold to Switzerland.

From engineering firm to the national government

After twelve years of having his own engineering firm in Rotterdam, he became the Director of Construction for the Government Buildings Agency. Under his leadership, the microwave-link tower at the Waalhaven harbour was raised to a height of 175 metres, with a 30-metre steel antenna mast on top.

He then had the opportunity to conduct an interesting experiment with the microwave-link tower in Hoorn. ‘We fastened a cable on top of the concrete tower and used a lorry to pull it out of balance and make it oscillate.’ A measurement device in the tower and in the pile foundation was used to ensure that the experiment was very well documented. ‘It is interesting to see that if it is pulled to one side, flaws will eventually cause it to sway transversely as well. Students have written theses and even doctoral dissertations on these data.’

TU Delft as a central theme

Throughout all of those years, TU Delft remained a central theme in his working life. Van Roosmalen gave lectures there, developed and taught postgraduate classes and, in the late 1990s, was a guest lecturer for three years in the faculty of Architecture and the Built Environment. ‘I taught them to improve their calculation’, he recounts. ‘One semester, my students and I designed a Zeppelin hall on Malieveld during a contest, which we also won.’ It was therefore not surprising that one of his daughters was inspired to choose TU Delft as well. In 1996, she graduated with a degree in Industrial Design.

Henk still attends his class reunions every year. ‘Last year, it was our 50th! Unfortunately, attendance keeps decreasing each year.’

Keep stimulating the brain

‘I continue to challenge myself. For this reason, I am a member of several associations, including Sociëteit de Witte and Diligentia, the Royal Physics Society. I enjoy attending and giving lectures in these clubs, and I write reports for friends who are unable to attend. I’ve also occasionally sent a report to the professor who gave the lecture. Their reaction? “I wish my students would write reports like that.” That’s nice, isn’t it?’