Don't be deflected

Deflections should always be considered in the design of slabs, in order to meet serviceability criteria applicable to concrete floor systems. While there are several ways to determine and calculate slab deflections, Tekla Structural Designer is arguably the most capable software solution available. Kenny Arnott, Principal Structural Consultant at Trimble Solutions (UK) Ltd explains why here.

There can be many requirements to consider when assessing deflections of concrete floors: the deflection (slope) of a slab should not be noticeable by occupants and deflections should not cause damage to attached partitions, cladding and other critical non-structural elements. The most basic requirements are stipulated in design codes, but quite often more onerous project specific limits will apply.

'Flat slabs' (concrete slabs supported directly by columns/walls without the stiffening effect of beams) offer the greatest concern and challenges in this area. Although buildings have been constructed using flat slabs and columns for many years, serviceability compliance (deflections) was traditionally assessed by hand, without the aid of computers. However, this traditional method relied heavily on regularity, standard conditions and limits to keep design complexity to a minimum. As structures became more individual - and complex - more innovative solutions were required to perform the necessary analysis.

Therefore, a growing choice of specialist slab design software became available to help engineers analyse and calculate deflections more easily. Despite this being good news for engineers, it did mean that a variety of different software solutions would have to be purchased to fulfil these requirements. This in turn meant engineers could end up creating separate analysis/design models in multiple software packages for one project. Any changes, such as column size/position adjustments, would need to be separately applied to keep them in sync with the project's master model. Indeed, as you can imagine, this could become a very time-consuming and potentially error prone task.

As such, Trimble invested a lot of time in developing Tekla Structural Designer to modernise the way engineers calculated slab deflections. This revolutionary software gives engineers the power to analyse and design buildings efficiently and profitably.

Fully automated structural design software, packed with many unique features for optimised concrete and steel design, Tekla Structural Designer helps engineering businesses to win more work and maximise profits. In terms of calculating slab deflections, Tekla Structural Designer follows the guidance in the Concrete Society's Technical Report 58, which advises on interpretation of Eurocode 2. It utilises iterative crack section analysis of a sequentially loaded slab/structure to not only accurately estimate the whole life deflection, but also deflection at various construction load stages of the engineer's choice. All of the different idealisations can then be simultaneously viewed in one model, at one time to ensure optimal design time and ease of use.

The results of this complex analysis are visualised as contours of total deflection at any load stage, differential deflection between any two stages, effective reinforcement and slab stiffness. Our unique check lines feature enables rapid pass/fail recognition of whatever total or differential deflection limits the engineer deems suitable, which can then be reported on at the touch of a button.

Perhaps the most remarkable aspect of this is the shear speed in which Tekla Structural Designer is able to handle such a complex task. By being so quick to produce results, engineers are granted much greater freedom to make changes and re-run the program to ensure the overall design is as optimal as possible.

Tekla Structural Designer has completely modernised the way in which people are designing concrete and steel structures; it is a practical and painless process.

Stuart Vaughan, Director of Wentworth House Partnership, said: "We have been using Tekla Structural Designer for around five years now, as it allows us to model complex geometry, saving valuable time on site and producing a more accurate analysis when compared to using a 2D method. We have also recently combined Tekla Structural Designer with Tekla Structures to enable us to produce coordinated construction information and fabrication drawings."