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D-day landing craft tank proudly displayed, with Hillcrest Structural and Tekla Structures

D-Day landing craft tank displayed under steelwork cantilevered roof canopy

With a cantilevered roof canopy set to form an integral part of the new resting place for a unique piece of D-Day history, Hillcrest Structural employed Tekla Structures’ 3D model environment to help design, detail, fabricate and erect the steel support structure.

Measuring 59 metres long, LCT 7074 is the last-surviving Second World War, D-Day Landing Craft Tank, used to carry 10 tanks to Normandy for D-Day. As part of a conservation project by The National Museum of the Royal Navy and The D-Day Story, the tank has been restored to her 1944 configuration and is to be showcased as part of the newly-opened D-Day Story museum in Portsmouth, offering a unique visitor experience. 

Designed by Pritchard Architecture and Mann Williams, the outdoor display will provide public access to all suitable areas of the craft, while also protecting it from the external elements, featuring a wave-like canopy roof. 

Side view of wave-like canopy roof

Hillcrest Structural, the specialist steelwork contractor, was appointed by Ascia Construction to produce a fully-coordinated 3D model of the primary steelwork canopy structure, design and detail the steel to steel connections and fabricate and erect the new roof structure directly over the proposed resting position of LCT 7074. 

Speaking about the project, Jamie Green, Managing Director at Hillcrest Structural said: The roof canopy frame consisted of 12 bespoke fabricated steel columns, each standing at 12 metres tall and, in turn, supporting primary fabricated tapered rafters and tapered rear cantilevered arms. To achieve the architect’s wave-like visual aesthetic, our team had to ensure the critical setting out points matched the design teams’ requirements, resulting in each set of front and rear arms being set at varying levels and differing rotations to one another. Finally, to the front and rear elevations, curved perimeter CHS members fit between the arms and there was to be a full roof bracing system to provide stability to the frame.

Tekla Structures 3D model of the primary steelwork canopy structure

Having been a user of Tekla software since the early 2000’s, Hillcrest Structural once again chose to use Tekla Structures for all modelling and detailing aspects of the project. 

Jamie continued: Tekla Structures is truly at the core of our business from a technological standpoint, enabling us to create and manage structural objects in a digital, 3D environment, from conception through to site planning and logistics. 

As well as enabling us to model and achieve the proposed wave-like form, Tekla Structure’s 3D environment was also invaluable in aiding our consideration of and integration with other disciplines on the project. An example of this is the structure’s electrical services and rainwater drainage system, which were both to be welded to the inside of our fabricated steel mast columns in order to preserve the desired streamlined aesthetic. 

Tekla Structures 3D model showing MEP services in the steel columns

The pipework was all rather complex, consisting of tight curves and a junction box where all pipes converged. After being provided with a basic hand-drawn sketch outlining the design intent for the pipework, it was vital that we were able to translate this 2D information into our model, so that we could accurately visualise both the MEP services and our steel columns in the same digital environment. Fortunately, through Tekla’s powerful modelling capabilities, the wide array of view and selection filtering options available and various built-in tools, such as ‘Cut Object by Part’, we were able to model both the MEP and structural steel elements, ensuring the overall design was constructible.

Another example of design integration on the project was regarding the roof canopy itself. To support the fabric sail membrane, Hillcrest Structural had to detail small RSA cleats at close centres on the underside of the primary roof steelwork.

Jamie explained: In order to ensure a smooth transition between design and on-site installation, it was important that we were able to fully coordinate our model with that of the contractor responsible for the design of the sail membrane. As a result of Tekla’s open BIM approach, we were able to use the 3D CAD model supplied by the contractor to coordinate our design and positioning of the RSA cleats. 

Crane positioning columns and cantilevered arms into place

Accurately detailing connections, such as these RSA cleats and other steel-to-steel joints, presented a particular challenge on the project, as Jamie commented:

Considering the time-consuming nature of modelling all the various complex and unique connections and welds, Tekla Structure’s intelligent tools and functionalities were invaluable in helping us to ensure that we were able to deliver the steelwork on schedule. The wave-like formation of the structure was especially challenging, with the frequent geometry changes meaning that each rafter and rear arm splice position and cut angle was variable, presenting us with a potentially complex process of positioning the splices. 

Tekla Structures model view from side showing wave-like formation of structure

However, by using Tekla Structures ‘Copy to Another Plane’ function, once the main connections were in place for one set of the columns and rafters we were able to simply copy the pre-detailed connections and welds to all of the other bays, while simultaneously maintaining the correct position and splay angles in relation to the primary elements. This resulted in a far quicker and more efficient process, saving time and ensuring high levels of accuracy. 

With this idea of speed and efficiency in mind, Tekla does also offer various industry-standard connection macros. However, due to the unique nature of the architectural design on this project, several bespoke connections were required, particularly for connecting the plan brace members. Fortunately, as a result of the software’s intelligent flexibility, we were able to create our own custom components within Tekla Structures and add them to our BIM object library, for use throughout the detailing stage. 

Tekla Structures model of complex steel connections

Given the complex cantilevered form and unique shape of the roof structure, being able to detail, visualise and review the structural steelwork and its connections and welds in the context of a 3D environment was hugely beneficial for Hillcrest Structural, as Jamie explained:

Working in 3D provided us with levels of detail and insight that 2D simply could not offer. We were able to pan around the completed model and check for any design issues or visual imperfections, particularly regarding the exposed steel elements, before we moved on to the fabrication stage. To demonstrate the value of this ability in practice, when examining the proposed splay cut to each of the roof’s four corner steel tubes in a 2D format, no issue was detected. However, once these same cuts were viewed in 3D, it was clear that they were incorrect. This enabled us to rectify the issue prior to fabrication, avoiding potentially significant delays to site operations. 

Tekla Structures model view of splay cut to the roof’s corner steel tubes

Once the model was fully completed, Hillcrest Structural were able to run a final clash check, with the software automatically reviewing the model and highlighting any potential clashes between the primary steel elements and the connections, providing both Hillcrest and its client with added assurance that the design was correct and constructible. 

End view of Tekla Structures model showing column with MEP with tapered rafters and tapered rear cantilevered arms

As well as Tekla Structures, Hillcrest Structural also employed Trimble Connect, the cloud-based collaboration tool, and Microsoft’s HoloLens technology at other stages of the project’s construction sequence. 

As a business, we find the HoloLens mixed reality technology invaluable, helping to improve visualisation for all involved on a project and assisting us in making key decisions regarding the detailing and installation sequences. Here, we used the technology at various stages of the project, helping us to plan the assembly process in a safe and efficient way and also allowing us to check the suitability of connection details in terms of bolt and welding access. It essentially offered us a digital rehearsal of the installation works, before we got on to site.  

Trimble Connect was similarly used to ensure a smooth process on site, with the relevant information, such as GA drawings, loading lists and assembly drawings, extracted from the model and uploaded onto Trimble Connect. Hillcrest Structural’s site team were then able to instantly access this electronic information via their tablets and laptops, helping them to efficiently resolve any queries or issues encountered on site. 

Construction of curved perimeter CHS members between the arms

Speaking about the appointment, Jamie concluded: All of us at Hillcrest Structural were delighted to be involved with this project and for the opportunity to contribute to the public display of such a significant piece of history. Through the combination of our skilled team and the intelligent tools and modelling power within Tekla Structures, we were able to deliver the structural steelwork and its connections on time, to a high degree of accuracy and ensure fulfilment of the client’s design brief. Quite simply, this would not have been the case should 3D modelling software not have been utilised, with the drawing time likely to have been severely extended as a result.

Completed roof structure directly over 59 metres long D-Day Landing Craft Tank, LCT 7074

Installation of the structural steelwork was completed in June 2020, with the D-Day Story’s LCT 7074 exhibition set to be open to the public later this year. 

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