Tailor Made Concrete Structures – Walraven & Stoelhorst (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8

High Rise Buildings. The challenge of a new field of possibilitiesfor the use of structural concrete

H. Corres, J. Romo & E. RomeroFHECOR Ingenieros Consultores

ABSTRACT: In this paper, the design and construction of several buildings of moderate height (no morethat 250 m) are analyzed. In all these projects structural concrete has been used for different elements:floorings, special steel-concrete composite columns using high performance concrete, Shear walls, stiffeningfloors, etc.

1 INTRODUCTION

During the last decades of the XXth Century and whathas transpired of the XXIst Century, a new and excitingexplosion in the design and construction of High RiseBuildings has taken place. The speed with which the

Figure 1. Views of skyscrapers presently under constructionin Madrid.

height of buildings is growing has greatly increased inthe last decades. While the maximum height attainedduring the XXth Century was of the order of 500 m,during the next years this value is likely to be morethan doubled with credible projects achieving heightsof about 1200 m. Concrete, with its new performancefeatures, presents itself as an ideal material in viewof solving some of the problems of this type of con-structions, especially for medium height structures. fibis about to form a new Task Group in order to bringtogether the experience gathered in the last few yearsand study the new challenges involved in the use ofstructural concrete for this type of structures.

In Madrid, the construction of four towers of about250 m of height designed by Norman Foster, Ribio &Alvarez-Salas, Cesar Pelli and Pei is reaching its con-clusion. In all of them structural concrete in several dif-ferent varieties has been widely used. These varietiesinclude concrete poured on site and prefabricated, nor-mal density concrete of several characteristic strengthsand lightweight concrete, concrete of normal worka-bility conditions and self-compacting, reinforced, pre-stressed, pre and post-tensioned with bounded and un-bounded strands. Finally concrete has also been usedin very different composite steel-concrete elements.

2 USE OF STRUCTURAL CONCRETE INDIFFERENT STRUCTURAL MEMBERS

2.1 Foundations

The foundations of high-rise buildings have gener-ally been solved using structural concrete. The newpossibilities of concrete offer new alternatives. The

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Figure 2. Foundation slabs of the Torre de Cristal (GlassTower) in Madrid.

concreting of members with very dense reinforce-ment can best be solved by the use of self-compactingconcrete. The use of prestressing allows the trans-mission of very large concentrated loads which arepresent in some areas of foundation slabs. Prestress-ing is also used in pile cups of deep foundationswith a large number of piles or very large pilediameters.

2.2 Vertical elements

In most of the towers built in Madrid, compositecolumns of great capacity located at the buildingperimeter have been used.

In the perimeter columns of the Torre de Cristal(Glass Tower), which are working mainly as com-pression members, a composite cross-section witha constant diameter of 0,95 m has been used. Thecolumn is filled with self-compacting C-45 grade con-crete and reinforced with steel profiles of decreasingarea as height increases. In the lower floors, steel pro-files of type HD with HISTAR S 460 steel and varyingthickness of up to 120 mm were used.

Due to the unusually large thickness of the profilesand to the need to speed up constructions, the pro-files are considered solely as compression membersworking by contact. In order to resist tension forcesdue to local bending, only the resistance of ordinaryreinforcement bars was considered.

From the point of view of construction, it becamenecessary to devise a coupling system for the suc-cessive columns fragments which would guaranteeconditions of flatness and perpendicularity in order tominimize the contact problems between two succes-sive column fragments. The steel profiles were builtin fragments spanning three floors and were lifted intoposition with the reinforcement already in place. Selfcompacting concrete was important in order to mini-mize concreting problems, given the great density ofreinforcement and the presence of the steel profile. In

Figure 3. Plan view of the structure of the Torre de Cristalwith a total height of 250,00 m. Cross section of the compos-ite columns.

Figure 4. Assembly of the composite columns of the Torrede Cristal.

this case the required concrete strength was not veryhigh (C-45). In some of the other towers, with com-posite columns but with smaller profiles, the strengthof concrete decreased with height.

The use of composite columns with high strengthconcrete minimizes the effect of the differential verti-cal displacement between the supports and the centralnuclei. Structural steel reduces time dependent strainsof concrete and high strength concrete has per se

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Figure 5. Variation of the concrete strength with the heightof the tower in Torre Espacio [2].

smaller time dependent strains than conventional con-crete. This design therefore results in a reduction ofthe difference in vertical displacements between thecolumns located along the building perimeter and thestiffening nuclei.

2.3 Floors

In the present time, the possible solutions for the floorsare many. In the Madrid towers almost all possibletypes have been used.

In the Sacyr – Vallehermoso tower and the Cajade Madrid tower, one of the more classical systemsinvolving a composite floor deck with light weightconcrete has been used.

In the Torre de Cristal an original system involvinga composite horizontal structure coupled with prefab-ricated hollow-core slabs was designed. This solutionwas adopted because the available elevation meanswere compatible with the placing of the hollow coreslabs and because it was decided that this solutionwould increase construction speed. With this systemone floor could be built within one week.

In the Torre Espacio, the floor structure was solvedusing post-tensioned concrete slabs with unboundedprestressing strands. This solution is specially indi-cated when the shape of the floors cannot be easilysolved using a horizontal steel structure. When usinga prestressed slab system it is very important to solvewell the connection between the support which ismade with a high strength concrete and the slab whoseconcrete strength is lower.

In this case this problem has been solved by usingconfined concrete in slab near the connection with thesupports. In this way the confinement increases theconcrete strength of the slab and makes it compatiblewith the strength of the supports.

Figure 6. Composite steel deck with lightweight concretesolution for the floor structure. Sacyr-Vallehermosotower [2].

Figure 7. Hollow core slab solution for the floor structure.Torre de Cristal.

2.4 Special members

The new architectural demands need structural solu-tions which provide new possibilities for the use ofstructural concrete.

Figure 9 shows the façade of Torre Espacio whosegeometry, as can be seen changes from one floor tothe next. This design requires the building of inclined

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Figure 8. Solution with prestressed slabs,Torre Espacio [2].

Figure 9. Inclination of the façade columns ofTorre Espacioand balancing of horizontal components by means of pre-stressing integrated in the slabs.

façade supports. The variable inclination has beensolved with a change in the inclination of the steelcasing of the columns at the floor levels. The resultinghorizontal force components are transmitted to thefloor structure by prestressing located within the slab.

In this type of buildings, very often in the lowerfloors in which the loads carried by the supports arelarger, it is necessary to provide transition elementsdue to discontinuation of columns. In the case of TorreEspacio this situation is present in the lobby area andhas been solved with a composite truss having a heightequivalent to that of one floor. The upper and lowerchords are composite elements integrated within thefloor slabs. The struts and ties of the web are steelboxes filled with concrete. In the case of the verti-cal struts, subject to compression, the concrete fillinghas the double role of stabilizing the steel plates andincreasing the strength. In the case of the diagonal ties,the composite steel boxes are prestressed in order toincrease their bearing capacity in tension.

In order to increase the efficiency of the verticalwalls in resisting horizontal forces such as those dueto wind actions, the designing of stiffening floors isa common practice. Stiffening floors work togetherwith compressed and decompressing columns forming

Figure 10. Composite prestressed load spanning beams inTorre Espacio [2].

Figure 11. Elements in transition floors used for lateralstiffening [2].

a very efficient stiffening system. These stiffeningmembers are usually located in floors containingbuilding installations and can be prestressed elementssuch as those used in Torre Espacio.

3 FINAL REMARKS

The new possibilities of concrete from the point ofview of strength, technology and construction demanda review of possible applications of this material in allexisting structural typologies and also, of course, inhigh rise buildings.

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The adequate, intelligent and creative use of the newconcretes is widely extending the field of applicationof this material and is opening new design possibilitiesunexplored until now.

BIBLIOGRAPHY

[1] GÓMEZ NAVARRO, M. Proyecto y construcción dedos torres de 235 m de altura en Madrid: Similitudes ydiferencias entre estructura mixta y estructura de

hormigón. XVII Curso Master CEMCO. Jornada J5:ACHE y el hormigón estructural. Instituto EduardoTorroja. Madrid, 15 de junio de 2007.

[2] Gómez Hemoso, J. Proyecto y construcción de edificiosaltos. XVII Curso Master CEMCO. Jornada J5: ACHEy el hormigón estructural. Instituto Eduardo Torroja.Madrid, 15 de junio de 2007.

[3] Romo Martín, J. Cargas horizontales – edificios enaltura. Curso de Especialidad en Cálculo Estructural:Concepción Estructural del Edificio. Máster en Estruc-turas de la Edificación.

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