Hotel complex "HILTON"

Progresi Limited, Vazha-Pshavela ave.16, 2 fl. Tbilisi,Georgia
(+995 32) 237 10 09 progresi.ltd@gmail.com

Location:  Batumi, Georgia

Architect: RTKL, Architects of Invention
Project development: Engenuiti, Progresi Limited
Chief Architect: Jos Bortsvik
Chief Engineer: Joni Gigineishvili
Finite element analysis: LIRA-SAPR
Building structure: reinforced concrete, steel
Foundation: combined slab and pile foundation
Building regulations: Eurocode
Status: construction completed in 2015

Architectural and planning solutions for the HILTON hotel complex in Batumi were developed by specialised design organisations RTKL and Ramboll. As a basis for solving architectural and volume-planning problems, the design of the complex consisting of two asymmetric different-height towers (H=88m, H=50m) erected on a single foundation was accepted.

After a detailed study of the first version of the hotel complex "HILTON" under construction; and the results of computer modelling, the idea to rework the presented project, keeping its basic concepts has appeared. The main motivation for redesigning the project: the different heights of the towers of the complex cause uneven settlement, which in turn creates serious problems in determining the structural features: the geometric dimensions of the structures were specified using expansion and anti-seismic joints around the entire perimeter of the high-rise buildings. This solution in turn caused certain problems both in the foundation structures and in the reinforcement of load-bearing elements.

The existing architectural and planning solutions, developed by RTKL and Ramboll, were redesigned in creative alliance with Progresi Limited in order to realise the most suitable foundation and construction technology and to take into account the rather difficult construction conditions (the complex is located between the lake and the sea, on weak soils (Fig. 2)). The difficulty of the building foundation was not only in the presence of groundwater and soft-plastic clays and sands at the base of the building [1, 2], but also in the unacceptable structural design of the complex, causing significant distortion. Therefore, instead of the proposed architectural and structural system, an improved frame system was adopted for both the office part of the building and the "residential building", which was agreed with the client after a detailed study.

Consideration of variants of architectural and structural solutions, taking into account static, wind and seismic loads, as well as hydrostatic pressure of water, was carried out on the basis of computer modelling with the use of the software for structural analysis "LIRA-SAPR".

The main attention was focused on the arrangement of foundations on a single base, as well as on the architectural expressiveness of the complex as a whole. At the same time, the harmonious combination of the architectural forms of the complex with the reliability of load-bearing structural elements combined with the minimisation of the cost of the facility under construction remained the decisive factor.

According to the initial (first) version of the architectural part of the project, the structures of the basement floor of the high-rise building and the podium were separated from each other by an anti-seismic joint (Fig. 3, 4).

Based on the consideration of all possible factors and multivariate analysis and on the results of comparison of the variants, it was concluded that instead of seismic joints between the towers, basement part and podium, it is advisable to install an anti-seismic joint only between the high-rise parts of the building and the podium above the basement floors.

At the level of both basement floors, it is preferable to combine the structures into a monolithic horizontal disc in order to create a strong and unified box foundation under the high-rise part of the complex, which significantly improved the structural conditions of the entire complex. In this case, there is a significant increase in the stiffness of basement structures compared to previous solutions, deformation and dynamic parameters are improved, reinforcement of the basement slab and other load-bearing elements of structures is reduced.

Selection of foundation type for the HILTON hotel complex

During the design of the HILTON hotel complex (a complex of multi-storey buildings on a piled base) a characteristic contradiction appeared. On the one hand, the compactness of the building in plan and relatively favourable engineering and geological conditions of the site made it possible to consider a variant of foundation arrangement on a natural base on a continuous monolithic reinforced concrete slab. Under a small layer of technogenic soils (up to 1.5 m thick) to a depth of 10-12 m from the surface lie lacustrine-glacial dusty loam of tight plastic consistency and dense dusty sand underlain by semi-hard moraine loam. On the other hand, calculations of the foundation slab on the base, the operation of which was described by different models (two-parameter model of elastic half-space, three-dimensional elastic-plastic base), showed that when the foundation slab is subjected to loads from towers of different heights, it receives significant non-uniform settlements.

This amount of settlement is allowed by regional geotechnical standards (TSN 50-302-96). However, the resulting unevenness of settlement is 1.5 times higher than the permissible value even for a 1.5-1.75 m thick slab. Thus, the slab foundation option proved to be problematic. Its implementation is possible only if the above-ground structures of the building are able to absorb the forces caused by the resistance to the development of uneven foundation settlement. In other words, a combined building and foundation analysis was required to modify the entire project. The authors of the above-ground structures project, after being convinced that the proposed variant favourably differs from the original one, agreed to change the whole design of the hotel complex.

Pile foundations proved to be an option to ensure the normative unevenness of the building settlement without taking into account the stiffness of the building. A total number of about 200 piles with a length of 18-25m were driven. Obviously, the cost of the pile foundations significantly exceeded the cost of the slab.

As a result, the only feasible option in terms of optimum structural design, as well as strength, stability and reliability with regard to long-term operation is the use of a combined slab-and-pile foundation structure.

Aboveground structure of the building for the HILTON hotel complex

The construction area, according to geological surveys, is located in an 8-point seismic zone. Numerical research was carried out using computer modelling methods using the finite element method [3-5] on the basis of multivariate analysis of existing design solutions, as well as new variants created in order to sel ect the most optimal and acceptable variant both in terms of architectural and planning and structural solutions. The package of artificial accelerograms was generated on the basis of geological and geophysical data of the construction site [6-9]. Computer modelling and analysis of load-bearing structures of the complex as a single spatial system for permanent, temporary and short-term vertical loads, as well as for horizontal seismic and wind effects, taking into account pulsations and accelerations, was performed using the LIRA-FEM software.

Each of the considered models had certain advantages and disadvantages fr om the architectural and planning point of view, but there was no consensus on which of them to favour. According to the first option, when the height difference between the buildings was 5 storeys or more (Fig. 1), significant non-uniform deformations and forces occurred in the foundation structures. Uneven deformations in turn were caused not only by the different heights of the towers, but also by the presence of deformation and anti-seismic joints in the basement slab structures (Figs. 3, 4).

In the final version of architectural and planning solutions, the complex acquired the following dimensions:

• dimensions of the construction site plan of the hotel complex 104x85m;
• height of the hotel tower H=81.835m;
• height of the residential tower H=81.269m;
• height of the podium in the hotel part H=20.485m;
• height of the podium in the residential part H=14.100m.

The spatial computer model and design scheme of the problem is shown in Fig. 6.

Conclusion

On the basis of computer modelling in LIRA-FEM software, taking into account various factors and the results of multivariant design of hotel complex "HILTON" in Batumi, new and more improved architectural and constructive solutions were adopted.

The final spatial solutions adopted to replace the original one, fulfil all regulatory requirements for strength, deformability, stability, construction materials consumption, etc. Based on a detailed analysis of the results obtained from the multi-variant design, an improved product of a more reliable and economical solution to complex structural systems and urban planning problems was obtained:

• based on the results of computer modelling, a final decision was made to replace two towers of different heights with the same height;
• in the final version, the foundation structure is made as a single two-tiered box section over the entire area of the projected building without expansion joints instead of a continuous foundation slab of large thickness and a two-tiered floor basement cut around (around the perimeter of) each tower with anti-seismic joints.

The changes made to the structural part of the project improved not only the strength characteristics of the buildings of the complex, but also favourably influenced the architectural appearance of the complex as a whole.