LimitState:SLAB yield-line analysis software launched

LimitState:SLAB represents a breakthrough in structural engineering software. For the first time, the well-known yield-line method for analysis of reinforced concrete slabs has been automated in a truly systematic manner. As a result, engineers can now identify hidden reserves of strength in slabs that cannot easily be identified using other available methods.

The method was launched at an event at the IStructE HQ in London sponsored by both LimitState and the University of Sheffield. Research at the University’s Department of Civil and Structural Engineering was the springboard for the optimisation technology which is the software’s foundation. The event was attended by many professionals from leading consulting firms and there was much debate about the value of applying LimitState:SLAB to many challenging slab analysis problems. We were pleased by the reception given to the product, which should have wide application across the profession. Concrete slab analysis and design is a very common task for engineers, but it is an area that seen little innovation in recent years. We believe LimitState:SLAB represents a real step forward for many practitioners.

Here are three key things structural engineers should know about LimitState:SLAB:

1. More realistic evaluation of slab strength, enabling significant cost savings

The yield-line method is a powerful plastic analysis technique which can provide a more realistic evaluation of the flexural load capacity of a slab. Engineers can use LimitState:SLAB to quickly determine how the slab will perform under different load regimes and with different layouts of reinforcement. In fact it will often show that an existing slab has greater reserves of strength than indicated by other methods.

For existing slabs, this can mean that costly upgrading work is not required, potentially saving the client significant sums. For new structures, LimitState:SLAB can help engineers to design slabs that are thinner, and contain less reinforcement than conventional approaches. This is important, because typically, around 60% of the structural cost of a new building is accounted for by the floor. Furthermore, regular reinforcement arrangements can be adopted, so that this is easier to detail and easier to fix, and hence less costly to construct. In contrast, use of elastic analysis (e.g. elastic FEA) tends to lead to much more costly designs.

2. Quickly calculate the load capacity and critical failure mechanism for any slab geometry

LimitState:SLAB systematically identifies the critical yield-line pattern from vast numbers of possible alternatives (yield-lines are fractures in the slab, where the reinforcing bars have yielded). Never before has the yield-line method been so fast to apply; LimitState:SLAB is the only available tool to have systematically automated the process. The breakthrough, and the key technological innovation in LimitState:SLAB, is to use Discontinuity Layout Optimization (DLO). DLO is a plastic limit analysis procedure, underpinned by rigorous theory published in the Proceedings of the Royal Society, and already applied to other engineering applications. As well as using DLO to identify the critical yield-line pattern from vast numbers of alternatives, LimitState:SLAB also allows the critical failure mechanism to be animated to aid interpretation.

3. Fast, flexible modelling to enable quick analysis and decision-making

Engineers can easily analyse how slabs will perform in different scenarios. It is straightforward to try different layouts, different arrangements of bars, different support locations, and different locations of holes in the structure. For both refurbishment and new-build projects, LimitState:SLAB can help engineers develop appropriate engineering solutions. Users of the software can therefore potentially gain a significant competitive advantage. Slab problems are quick to set up and solve in the software. A slab geometry can be defined by importing from a CAD file, or by drawing on the screen. It is then easy to edit the model geometry, and to specify loading, material properties and boundary conditions. Slab models can be easily modified and ‘what if’ scenarios explored. Once the analysis has been performed, users can view an animation of the critical failure mechanism, aiding understanding of the predicted mode of response.

Concrete slabs are one of the most important areas of work for structural engineers because they are found in almost every project and are a vital determinant of cost, safety and design. Yet all too often, it is hard to radically improve slab design, or make truly insightful decisions in refurbishment projects. We think LimitState:SLAB can help engineers do both, with its unique automation of the yield-line method. Do please download the trial version and let us know what you think.