Developing durable and functional infrastructure products requires in-depth analysis and experience. It’s all in the detail and depends on cutting-edge technology.
The Structa Group of companies manufactures and supplies a range of infrastructure-related products extending from streetlight poles and electrical distribution support structures to mega water storage tanks.
The Group has a proud history of innovation in these fields, many of them driven by the application of advanced analytical techniques. Examples of these are illustrated here.
As a starting point, some might pose the question: Why is complex and costly analysis required to design and develop seemingly simple structures? The answer lies mainly in product cost minimisation.
Costs of material, processing, transport and erection can be reduced by having optimal designs. Optimal designs in turn can only be achieved if structural loads, responses and failure modes can be accurately predicted.
A prime example lies in the apparently simplistic streetlight pole design. The SANS 10225 code for lighting structures allows the structure to be designed according to a failure envelope consisting of a deflection constraint, as well as ‘ultimate failure’, being the point at which the structure can no longer fulfil its function.
Perfecting the monopole
So how can advanced analysis techniques benefit the simple monopole? The critical load to be considered for such structures is wind loading. Typically, such structures need to survive wind gusts of up to 150km/h.
Wind loading on a structure relates directly to its shape and wind-induced drag. Accurate calculation of such drag factors is therefore of prime importance. Enter “computational fluid dynamics”, a numerical technique used to predict pressure and velocity distribution in airflow around a structure.
This technique has largely replaced wind tunnel technology and, though expensive, is far more cost effective. The flow around an 18-sided high mast light (Figure 1) displays the flow pattern, as well as breakaway vortices that induce vibrations into the pole. Very accurate drag factors can be calculated from the analysis data.
Similarly, flow inside complex pipe sections can be predicted accurately, resulting in better design and pressure-resisting structures. In Figure 2, we illustrate the flow prediction in a complex pipe bifurcation and reduction system and resulting structure.
Finite element analysis
Once loads are accurately predicted, structural response needs to be optimised. Here the finite element method has developed rapidly over the last few decades as the primary tool for calculating structural response.
This is a numerical technique which predicts response by considering the individual, yet linked, response of many sub-parts of a structure (‘elements’) to loading. It is especially the so-called ‘non-linear’ analysis that drives optimisation as it allows accurate prediction of ultimate failure modes.
Illustrated here (figures 3 and 4) are predictions of buckles in folded plate-type lighting masts, as well as failure of typical streetlight poles owing to buckling of inspection opening sidewalls.
Non-linear finite element analysis has also been used successfully to predict stresses and deflections in panel-type water tanks, which – in Structa’s case – is the Prestank product series. This has allowed designers to optimise sealing systems and to define panel weld detail for prolonged fatigue life, as shown in Figure 5.
It is this accurate prediction of ultimate failure modes which allows the designer to optimise structural design, albeit within the limits of design codes.
As with all advanced technology solutions, the proviso is that the technology requires well-trained and experienced engineers to apply and interpret the analyses.
This capability is well entrenched within the Group and spearheaded by the Structa Konsult business unit, which houses a team of a highly qualified experts.
In addition to serving the Group, Structa Konsult provides consulting services and professional advice to external clients. It is also a Group policy to work closely with universities. In this regard, the Structa Group has an extremely fruitful relationship with the Faculty of Engineering at the University of Pretoria.
These partnerships form part of the Group’s relentless commitment to research and development and