Mason UK meets stringent specification with proactive engineering Park Modern is a residential development with luxury apartments, exceptional facilities, and views across Hyde Park. Due to the proximity of the structure to the London Underground, extensive vibration control was required. This article describes how vibration control specialist Mason UK tackled these challenges and delivered a challenging specification. Park Modern includes 57 high-end apartments, with prices for these apartments ranging from £2 million for a one bedroom to £60 million for a striking nine-bedroom penthouse. The development also includes a wellbeing floor, with a residents-only spa, treatment rooms and private healthcare, a 25-metre swimming pool, a gymnasium, and a 16-seat cinema that residents can reserve for private use. For contractor Ant Yapi, this was their sixth project in the UK and their largest to date. The building rises nine levels above the ground with the majority of apartments overlooking Hyde Park. The design and building project required extensive ground retaining structures in close proximity to the London Underground Central Line to support the open excavation to 20 metres below ground level for the lowermost basement level. In addition to the facilities listed above, such as the swimming pool and gymnasium, the basement levels also contain plant areas. Enter Hoare Lea With the London Underground Central Line so close to the basement, vibration from the tube would be easily transmitted into the building’s structure, causing unacceptable noise within. Martin McNulty, a vibration consultant with Hoare Lea, provided the specification to guide the contractor and meet the client’s requirements. In addition to comprehensive site surveys, Hoare Lea carried out a number of computer simulations to predict the vibration levels at the basement level and throughout the development. The results confirmed high levels of vibration would be present in the primary structure. McNulty recalled that ‘‘a view was taken to ensure a premium-quality approach throughout all noise sensitive spaces, including the basements. In this scheme, sensitive spaces were not confined to above ground residential spaces, as is common, but also below ground in amenity and health care zones. This presented a challenge, as a one size fits all approach for building with significant basement zones is difficult.’’ Ultimately, this required a two-stage approach, controlling both groundborne vibration, comprising building isolation to mitigate dwellings at Level 1 and above, and a box-in-box strategy for the floors below. Box-in-box solutions would be required at all basement floors down to the lowest floor of development. Further, the client’s aspiration was that certain noise-sensitive spaces below ground were subject to the same performance standards as those above ground. This was particularly challenging as proximity to the tube tunnels meant vibration levels below ground were far in excess to those which would be above ground. ‘‘To meet this challenge, we developed a high performing box in box system and also insisted upon the contractor testing at key points throughout construction to ensure the designs were optimal. This also had the added benefit of permitting some value engineering opportunities to benefit the client,’’ explained McNulty. To deliver the specification, Ant Yapi turned to vibration control specialists Mason UK. ‘‘We needed Mason both for the structural isolation of the entire building, and for box-in-box isolation at the basement level,’’ explained Baris Bayraktar, Construction Manager at Ant Yapi. Ant Yapi also brought on board another acoustic consultant, Cahill Design Consultants (CDC), to ensure that Hoare Lea’s recommendations were implemented on site. The isolation line As depicted in Figure 1, the isolation line for the project ran horizontally across level one, while dipping down the two elevator cores to the bottom of the basement (B3). This is standard when providing structural isolation for a building with elevators, as cutting through building cores or reacting ground bearing pressures compromises acoustic performance.  This method meant the elevator cores at the bottom of B3, along with the entire building from level one upwards, were isolated on a system of 8Hz rubber bearings. ‘‘I had previously been involved in projects where bearings were used for seismic activity, so I was familiar with the theory. However, this was the first time I had worked on a project where they were required for acoustics,’’ recalled Bayraktyar. In total there were approximately 350 vertical load bearings, ranging in size from 130x130x95mm thick to 460x460x95mm thick to suit the various loads.  The implementation of this design interrupted the vibration transmission path from that generated by tube trains into the building’s structure, where it could manifest as noise disturbance in the apartments above. However, with the bearings in place there was a need to provide lateral restraint. Columns and building cores provide extensive lateral restraint and prevent a building swaying under wind loading. However, measures have to be implemented, both to provide lateral restraint but also to ensure that the acoustic performance of the bearings is not compromised. For this project, this was achieved through the use of a system of shear pins. These are simple, inexpensive and acoustically excellent as they do not engage unless wind loads are present. Furthermore, the introduction of bearings required working closely with the structural engineers at AKT. Adding bearings to a building effectively introduces movable connections which would otherwise be rigid. It was essential that Mason provided preliminary bearing designs well before ground was broken to AKT so the structural model could be updated, and loads redistributed. Charlie Ashton, a structural engineer with AKT, described a ‘‘long winded, iterative approach,’’ involving lots of coordination between AKT’s engineers and Adam Fox, Director at Mason UK. A key part of Ashton’s job was updating the finite elements model to incorporate Mason’s bearings. After the model had been run (a process that typically would take twelve hours) it would usually require Mason to make changes to the system of bearings in light of fresh calculations about loads. ‘‘Every time you run the model, you get a different set of reactions,’’ explained Ashton. ‘‘In addition to calculations about what load a bearing can handle, you also have to