São Gabriel and São Rafael Buildings, LisbonJúlio Appleton, Prot.,A2P Consult,Lda, Lisbon,Portugal,João Almeida, Prot.,JSJ,Lda, Lisbon,Portugal,Tiago Abecassis, Eng.,

Talprojecto,Lda, Lisbon,Portugal

Introduction

The São Gabriel and São Rafael hous-ing towers with 25 upper storeys werebuilt in Lisbon in "Parque das Nações",the former Expo 98 site, and are inte-grated into the Vasco da Gama Com-mercial Complexo The names of thetowers are those of two of the shipsused by Vasco da Gama in the discov-eries of the 15th century. The structureof the transition fIoor looks like thehull of a ship and at the top a sail witha steel triangulated structure is used asa lighting-rod.

Description of the Buildings

The buildings inc1ude 5 undergroundfIoors and 25 upper storeys and reach atotal height of 120 m above groundleveI (Figs. 1, 2). The upper buildingstructure is composed of steel beamscomposite with concrete fIoor slabssupported by steel columns. Resistanceto horizontal wind loads and seismiceffects is performed by two concreteshear wall cores that surround the liftsand stairs. About 11,0 m above ground

Fig. 1: Elevatian af twin tawers

80 Structures in Portugal

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Fig.2: São Gabriel and São Rafael Towers

leveI there is a load transition fIoor, alarge prestressed concrete grid-slab thatspans between the shear wall cores.The bases of the steel columns arefixed to the upper surface of that slab.

The 0,11 m thick concrete fIoor slabworks together with the steel beams;H-sections with a depth of 160 mmspaced 2,10 m apart. The beams aresupported at the columns, typicallyspaced at 6,30 m, by I-sections that arewelded to the steel columns and have a

120,00m

variable depth from 0,24 m at thecolumn face to 0,16 m at a distance of1,00 m from the column. The H-beamsare bolted to these cantilevered I-beams.The steel columns have either a hollowcircular section, with a diameter of273 mm, or an H-section (Figs. 3, 4).

The transition grid-slab that supportsthe steel columns, at leveI 21,40 m, hasan ellipsoidal shape. It is composed ofprestressed concrete longitudinal beamsof variable depths from 1,30m to 5,60 m

Fig. 3: Steel structure of upper floors duringconstruction

Fig. 4: Composite steel-conc.rete structurewith fire protection surfacing

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3,878 2,35 3,95 6,00I I I I .

6,00 .3,65 .2,75

Fig. 5: Plan and longitudinal section of the prestressed concrete transition grid-slab

with a width of 1,20m and transversebeams 1,00 m wide also with variableheights. This grid-slab also inc1udes anupper slab and a curved lower slab andis supported only by the two centralconcrete cores which are spaced 25,20 mapart (Fig. 5).

The central core has a main role; to re-sist the earthquakes, wind loads andtransfer the verticalloads of the upperfloors to the foundations. The rein-forced concrete walls have a variablethickness of 0,25 m at the top to 0,40 mat the base. Their foundations are pre-stressed concrete footings 1,00 m wideand 33,00 m long with a depth of 1,30 mto 2,50 m. The use of a prestressed slabavoided reinforcement congestions andallowed for more uniform stresses inthe soil (Fig. 6).

The five underground floors are solidreinforced concrete slabs, 0,27 m deep,spanning 8,00 m to 9,30 m and have0,40 m thick column heads. These slabsare supported at the retaining walls,0,60 m thick, the reinforced concretecentral cores and the interior columns.

Design of the Structure

The structural design inc1uded a3-D finite element model of the wholestructure. A commercially availablecomputer program was used in this lin-ear model and the slabs were modelledby shell elements, the beams and

columns by linear elements and theshear walls of the central core and ofthe underground retaining walls weremodelled by plate elements.

For the design of the composite floorstructures computer models of a gridwith linear finite elements were used.Each grid had continuous orthotropicmain beams, crossing over the steelcolumns and secondary beams, typical-ly 2,10 m spaced, simply supported onthe main beams.

For the design of the transition grid-slab and the footing slab of the founda-tion other finite element analyses wereperformed.

The first modes of vibration have fre-quencies of 0,5 Hz in the longitudinaldirection and 0,61 Hz in the transversedirection. The maximum inter-storeydrift for the earthquake action is0,76 cm, less than the maximum rec-ommended value of 1,5 cm of Euro-code 8.

For a wind speed of 55 kmlh (on theaverage only 1,8 days per year has awind speed greater than this value) thedisplacement at the top of the buildingis 2,73 mm and for a wind speed of96 kmlh the top displacement is 8,20mm.

For the transition grid-slab the pre-stressing was applied in stages follow-ing the construction of the tower, inheight. The composite steel floors weredesigned according to the Eurocode 4.

Structural Engineering International 2/2005

Fig. 6: Cross-section of the prestressed foundation slab of the main central cores

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A concrete C 30/37 (characteristicstrength: 30 MPa cylinder, 37 MPa cube)was used in general and a concreteC 40/50 was used in floors at levels 9 mand 20,40 m. The steel of Europeangrade A 500 NR and A 1860 with acharacteristic tensile strength of 500 MPaand 1860 MPa respectively were usedin the reinforcement of concrete ele-ments and structural steel of Europeangrade Fe 360 and Fe 500 with a charac-teristic tensile strength of 235 MPa and355 MPa respectively were used forthe floorbeams and columns.

Conclusions

The twin towers São Gabriel and SãoRafael are interesting high~qualitybuildings and have been an economicsuccess. The structural design concepthas proven to be adequate. The use ofa composite steel-concrete floor sys-tem reduced the building's dead weightand allowed for the construction toprogress more rapidly than with a stan-dard reinforced concrete structure.The use of prestressing in the transi-tion grid-slab was unavoidable and theuse of prestressing in the footing slabimproved the quality and the economyof the structure and avoided the diffi-culties in properly placing concrete inextremely dense areas of reinforce-ment.

SEI Data Block

Structural Design:JSJ, Lda, Lisbon, Portugal

! A2P, Lda, Lisbon, PortugalTalprojecto, Lda, Lisbon, Portugal

São Gabriel BuildingOwner:

Praedium, SA, Lisbon, PortugalContractors:

Engil, SA, Oeiras, PortugalContacto, SA, Porto, Portugal

São Rafael BuildingOwner:

Ferrovial Imobiliária, SA, Lisbon,PortugalContractors:

Ferrovial, SA, Lisbon, Portugal

Structures in Portugal 81