494 About the Project and Study of Post-tensioned Transfer Beams Under the Five-storey Building in the Centre of Warsaw Rafal Szydlowski Cracow University of Technology Cracow, Poland rszydlowski@pk.edu.pl Magdalena Szreniawa TCE Structural Design & Consulting Cracow, Poland magdalena.szreniawa@gmail.com Abstract—Construction of buildings is often associated with creation of the large, free from supports spaces in the lower floors with dense structural system on the upper floors. To transmit the load from the upper floors to the foundation, transfer slabs and beams are constructed. They are heavily loaded, bended and sheared components, which require a significant height of cross-section. The use of prestressing reduces cross-section height of reinforced concrete transfer elements. The Warsaw office and service building completed last year in the part situated above the W-Z route tunnel, contains 6 post- tensioned transfer beams with 1.80×1.60m cross-section and variable span in the supports axes from 23.80 to 28.20m. Beams represent foundation for five storey building. The paper presents basic principles of design, results of deformation of the structure during erection obtained from theoretical FEM model and measured as well as applied technology. Keywords-transfer beam; post-tension; composite cross-section; prestressed slab I. INTRODUCTION During construction of the reinforced concrete buildings, with no possibility of maintaining supports of the higher floors in the lower tier, it is often necessary to transmit loads from the upper floor to the nearest supports through the heavily loaded slab or long-span beams (transfer elements). The problem is mostly caused by a need to locate the large spaces free from supports in the lower floors. Heavily loaded, bended and sheared components of long spans require often a large height of cross-sections. The use of prestressing significantly reduces a height of element cross-section. The prestressing of transfer elements can be performed with straight-line cables at the upper and lower surface of the element respectively, in the span and over the columns. The most effective prestressing is done with curved routes adapted to the diagram of bending moments. In addition to the use of the positive effect of "hanging tendon" for bending such prestressing greatly reduces the shear forces in the vicinity of the supports. Slender elements usually require a strong prestressing with step by step introduction of forces together with the construction of the building. Such solutions have been used successfully in the world for many years. In 1988, in Hong Kong in Pacific Place building, the use of prestressing in quantities of 22kg/m 3 at the slab transfer with thickness of 4.5m, carrying a 52-storey building made it possible to reduce the level of passive reinforcement from 500kg/m 3 in the reinforced concrete version down to 180kg /m 3 in prestressed version [3]. In 1999 in the building of Funchal Crown Plaza Hotel in Portugal six storeys have been placed on the transfer beams with a span of 18m and a height of 2.5m [3]. In later years there have been many similar construction carried out globally. The design problem of transverse slabs have been raised among others in [4]. On the other hand, reference [7] presents a slightly different design solution consisting of two slabs and walls connected into the rigid structure over a large ceremonial hall on the lower floor. In 2014 in a building constructed on Senatorska Street in Warsaw (Fig. 1) 6 transfer beams of cross-section of 1.80×1.60m and with the span in the supports axes from 23.8 to 28.2m have been used. The tunnel of W-Z route was surrounded with 0.8m thick foundation walls. The five storey building was supported by the transfer beams on the foundation walls. II. GEOMETRY OF THE BUILDING, LOAD CHARACTERISTIC, DESIGN ASSUMPTIONS The above indicated building was designed on the projection of elongated rectangle measuring approx. 85×30m. The reinforced concrete tunnel of W-Z route is positioned under the end part of the building (Fig. 2 and 3). Under the whole building two floors of underground garage, which were discontinued by tunnel have been located. Along the tunnel Figure 1. Visualization of the building with transfer beams (source: RKW Rhode Kellermann Wawrowsky Polska Sp. z o.o.). TCE Structural Design & Consulting 4th Annual International Conference on Architecture and Civil Engineering (ACE 2016) 4th Annual International Conference on Architecture and Civil Engineering (ACE 2016) Copyright © GSTF 2016 ISSN 2301-394X doi: 10.5176/2301-394X_ACE16.69 © 2016 GSTF