All-glass entrance pavillion for an office building in Madrid

SI: Challenging Glass paper
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Abstract

The iconic Torre Europa building in Madrid is currently under refurbishment. The envisaged works include the construction of a new entrance hall composed of two structural glass façades and a steel canopy above them. This paper focuses on the design and construction of the two structural glass façades, which are connected together at an angle of 100\(^{\circ }\). These are made up of a number of laminated glass panels standing on the ground floor slab and stabilised by vertical glass fins. The connection between the cladding panels and the fins is resolved with embedded metal connectors. The top end of the fins is connected to an horizontal glass beam that extends along the two façades, thus forming an L-shape with both ends fixed to the primary structure of the building. This beam is a critical structural element that carries 50% of the wind load applied to the façades and may be also exposed to some vertical load such as snow.

Keywords

Structural glass Embedded metal connectors Spring supports Structural silicone 

1 Introduction

Torre Europa is a 120 m tall office building designed by the Spanish architect Miguel Oriol and located at the very centre of the business district of Madrid (Spain). It was built in the early 1980’s and after more than 30 years in service it is currently under refurbishment. The works, which are scheduled to be completed in the first half of 2018, include the construction of a new entrance hall designed by CallisonRTKL in collaboration with the structural engineers LKS, CHC and the façade consultants ENAR. The specialist contractor in charge of the final design and construction is Bellapart.

The entrance hall is a \(10 \times 10 \times 12\) m cubic volume attached to the façade of the building (Fig. 1). It is composed of two independent structures: a steel and glass canopy that acts as a roof for the hall and extends far beyond it, and two self-supporting structural glass façades connected together at an angle of 100\(^{\circ }\).

This paper focuses on the design and construction of the two glass façades. These are composed of a number of load-carrying glass panels and beams joined together with a combination of bolted connections, embedded metal inserts and structural silicone bonds. Once connected, these elements form an assembly that can bear the applied loads and transfer them to the primary structure of the building.
Fig. 1

Virtual view of the new entrance hall and canopy (courtesy of CallisonRTKL)

The design of the façades was based on the principles of predictability and redundancy. The first concept was incorporated with the definition of clear load paths for the transmission of horizontal and vertical forces from the cladding panels to the building structure. This provides certainty in the loads used for designing the different components and connections, which is essential in this type of structures due to the fragile nature of glass.

On the other hand, redundancy provides safety in the event of failure of any structural glass component. In this project, the effects of breakage of a single glass ply were alleviated with the use of laminated glass and a proper analysis of this accidental scenario. Moreover, the glass components at ground level were protected against severe accidents that might lead to their complete failure (e.g. traffic accidents, vandalism, etc.) with the installation of bollards and a pool of water in front of the most exposed area of the hall.

2 Main components and connections

Figure 2 identifies the glass components that make up the façades of the entrance hall: Cladding panels, glass fins and horizontal glass beam.
Fig. 2

Main components of the glass façades

The cladding panels are \(12 + 15 + 12\) mm low iron glass laminates with 1.52 mm Sentryglas interlayers. The external 12 mm glass plies are heat strengthened whereas the inner 15 mm ply is fully tempered with Heat Soak Test (HST). These panels, with a typical size of 3038 \(\times \) 9750 mm (b \(\times \) h), stand on the ground floor slab and are stabilised by vertical glass fins.

The bottom edge of the cladding panels is connected to the concrete slab by means of a stainless steel channel in which they are inserted. The weight of these panels is supported by two spring supports embedded in the channel that will be further discussed below. In-plane shear forces are taken by a structural silicone bond between the channel and glass.

Along their vertical edges, the cladding panels are point fixed to the typical glass fins with four clamped connections spaced 2280 mm (Fig. 3). Each of these connections is composed of a 400 \(\times \) 50 mm titanium insert embedded in the fin and two similar inserts embedded in the cladding panels at either side of the joint. The connection is achieved with four small clamp plates hidden in the joint which are bolted to the fin and inserted in a groove machined in the cladding inserts. These provide an effective load transfer in out-of-plane direction. In addition, nylon pads are located in the gap between the clamp fixing and the cladding panels to prevent any lateral displacement of the fins.
Fig. 3

a Typical panel-to-fin connection and b temporary half connection during installation

On the other hand, every cladding panel is connected to their adjacent ones with a 50 \(\times \) 30 mm structural silicone joint along its vertical edges and to the top beam with a 40 \(\times \) 20 mm joint. A two component silicone type Dow Corning 993 was used in both cases.

The vertical fins are 4 \(\times \) 12 mm laminates made up of low iron heat strengthened glass with 1.52 mm Sentryglas interlayers. They are used to transfer wind loads from the cladding panels to the ground floor slab and the horizontal glass beam at the top of the façade. The glass fins are aligned with the vertical joints between cladding panels and have a typical depth of 600 mm and a total height of 9750 mm approximately. Additionally, there are two special fins located at the SE and NW corners of the hall, with a depth of 1200 mm approximately, which are also used as lateral cladding panels at the insets adjacent to the interfaces with the building façade.
Fig. 4

Connection between the fin and the horizontal glass beam

The typical fins are connected to the horizontal glass beam at their top end with a hybrid connection composed of bolts and a titanium insert. At their bottom end, the fins are fixed to the ground floor slab by means of a stainless steel socket and a perimetral structural silicone bond. The weight of the fin and any other vertical loads are supported by a single spring support located at the midpoint of its bottom edge.

Flexural and lateral torsional buckling of the typical fins are prevented thanks to the restriction to the lateral displacement of the outer edge of glass provided by the clamped connections of the cladding panels. These connections reduce the buckling length of the compression fibre of the fin when the façade is subject to vertical loads and wind pressure, and they still have a small stabilising effect under wind suction as discussed in Torres et al. (2017).

The top connection deserves some further discussion. Figure 4 shows a vertical section of this connection in which its different components can be identified. Basically, this connection is composed of an embedded titanium insert in the top edge of the fin to which a 25 mm thick stainless steel plate is bolted. The horizontal glass beam leans on this plate and is clamped by a second 10 mm thick stainless steel plate. The two plates are connected by three bolts through holes on glass, which are filled with Hilti HIT-HY 270 mortar. Obviously, adequate spacers were installed in all interfaces between glass and metal.

The thickness of these plates, their size (850 \(\times \) 150 mm) and the length they cantilever from the fin were engineered so that they provide a good rotational constraint to the beam while at the same time minimising local stress concentrations on glass.

However, the embedded metal inserts in the fin cannot withstand the permanent moment caused by the eccentricity between the centres of gravity of the horizontal glass beam and the fin (see Sect. 6). This fact led to the installation of four pins connecting the insert with the external glass plies of the fin through adequate mortar sleeves.
Fig. 5

Connection of the top glass beam to the primary structure of the building

The special 1200 mm deep fins are connected to the top glass beam in a direction perpendicular to the plane of the façade using a pair of titanium inserts equipped with a pin-and-groove detail that prevents the generation of forces in unwanted directions. Vertical forces such as dead and snow loads are transmitted from the top glass beam to the special fins with two nylon pads. The silicone joint between the special fins and the horizontal beam has no structural role.

At their bottom end, the special fins are also fixed by insertion in a stainless steel socket and with a perimetral structural silicone bond. Due to their significant depth these fins rest on two spring supports, in a similar manner as the cladding panels.

Flexural and lateral torsional buckling in the special fins are prevented by connecting their external and internal vertical edges to the adjacent cladding panel and to the frame of the adjacent smoke vent column, respectively. These connections were made with a continuous structural silicone bond.

Finally, the horizontal glass beam located at the top of the façade has a depth of 1340 mm and is composed of two glass panels positioned forming an angle of 100\(^{\circ }\) and connected together in an articulated manner. These panels are 3 \(\times \) 12 mm laminates made up of low iron fully tempered glass with HST, with 1.52 mm Sentryglas interlayers.

At the SE and NW ends of the façade, the horizontal glass beam is pinned to two special steel brackets fixed to the primary structure of the building (Fig. 5). These connections are implemented on the glass side with a 1260 mm long stainless steel channel bolted to glass by means of ten stainless steel pins with cast bushings of injectable mortar type Hilti HIT-HY 270. On the building side, the special brackets are box beams in steel grade S355 cantilevering from a bespoke steel tube that folds one of the external concrete columns of the building and transfers the load to a strong concrete beam at level 2 and to the floor slab of level 3. A soft spacer was installed between the bespoke tube and the building column to avoid any load transfer to it.

The design of the horizontal glass beam required detailed finite element modelling to investigate both stresses at connections and buckling. The latter was assessed by analysing different load cases in which the beam is subject to in-plane (wind) and out-of-plane (dead, snow) loads, together with geometrical imperfections based on its first linear buckling modes. Moreover, the effect of vertical displacements in the glass fins caused by the deformation of the ground floor slab and/or the spring supports was investigated by applying prescribed displacements to the supports of the model.

3 Load paths

The idea behind the design of the glass façades was to establish clear load paths for the transfer of permanent and climatic loads from the cladding panels to the building structure.

All vertical loads are transferred to the ground floor slab. Both the cladding panels and the glass fins rest directly on this slab, whereas the horizontal glass beam transfers its self weight and any snow load on it to the fins, and from these to the ground.

Wind loads are transferred from the cladding panels to the fins by means of the clamping system hidden in the vertical joints that connects these only in out-of-plane direction. The fins are fixed on their bottom end to the ground floor slab and on their top end to the horizontal glass beam. Therefore, approximately half the wind load is transferred by the fins directly to the ground, whereas the other half is transferred to the top beam.

As noted above, the horizontal glass beam is composed of two glass panels connected at an angle of 100\(^{\circ }\). The beam panel above the loaded façade receives an in-plane load from the fins and transfers it to the pinned connections at both ends. One end is directly connected to the building structure whereas the other end is connected to the second beam panel that transfers the load by tension or compression to the building.

This structure is very sensitive to any relative displacements of the supports at ground level. The height of the cladding panels amplifies these relative displacements causing a significant distortion of the vertical glass joints that may lead to collisions between glass panels and compromise the connections between panels and fins.

In order to avoid this, all façade joints were sealed with a two-component structural silicone type Dow Corning 993. Spring supports were also installed under the cladding panels and the fins at ground level to alleviate the effect of the flexibility of the ground floor slab. The combined effect of the silicone bonds and the spring supports prevents excessive distortions in the vertical glass joints and guarantees the integrity of the structure under all envisaged load cases.

4 Door area

The North façade incorporates two revolving doors measuring 2.7 m in diameter and 5.5 m in height, together with two adjacent emergency exits (Fig. 6).
Fig. 6

North façade elevation and vertical section

The revolving doors are self-supporting. Thus, there is no load transmission between these and the glazed façades of the hall. All loads applied on the doors are transferred directly to their fixings on the ground.

The lack of connection between the revolving doors and the façade forces the two cladding panels above the doors to be supported without any contact with these. The problem was resolved by supporting their weight on one side with a special façade panel located between the doors (ref. G7) and on the other side with two vertical columns made up of a 120 \(\times \) 80 mm solid rectangular profile in stainless steel grade 1.4401. At its bottom end, the G7 glass column is inserted in a stainless steel channel and the vertical loads carried by it are transferred to the ground floor slab by means of a Hilti HIT-HY 270 resin pad.

Compression buckling in the G7 panel is prevented by connecting it to the glass fin located immediately behind it by means of five point fixings spaced 1140 mm in height and composed of a bolted connection through drills in the G7 panel and the corresponding titanium inserts embedded in the fin. These connections also allow the G7 panel to provide lateral stabilisation to the fin. The relative vertical displacements between the G7 panel and the fin are released.

At the other side of the revolving doors, the vertical stainless steel columns are strongly fixed to the perimetral frames of the emergency doors, which are composed of an 80 \(\times \) 80 mm square solid profile in stainless steel grade 1.4401. Both the columns and the door frames are connected to the adjacent glass panels and fins at the same heights and with the same clamp detail used in the rest of the façade.

The 120 \(\times \) 80 mm columns are connected to the ground floor slab in an articulated manner whereas at the other side of the emergency doors, the 80x80 mm mullion is connected to the ground with a vertical spring support.

The lintel of the emergency door frame supports the weight of the cladding panel above with two Hilti HIT-HY 270 resin pads, while at the same time being bolted to this panel by means of two titanium inserts embedded in the bottom edge of glass. This bolted connection allows the emergency door frame and the glass panel above it to form a structural unit (virtual panel) in order to provide some in-plane bracing to the façade.
Fig. 7

Spring supports

5 Deformability of the ground floor slab

One of the major difficulties found during the design of the façades was the lack of knowledge on the structural behaviour of the composite steel and concrete slab on which the façades were to be installed. In fact, it was known that the structure of the entrance area had suffered significant design changes during construction in the 1980’s that had not been properly recorded in the available drawings.

Test pits shed light on the composition of the existing structure in this area, although a number of unknowns still remained. This led to a reinforcement of the ground floor slab and the underground structure of the building based on a conservative assumption of its strength and stiffness.

Another difficulty was the lack of information on the construction sequence that would be followed by the main contractor, particularly related with the replacement of the ground floor pavement which had a significant weight of 4 kN/m\(^{2}\).

The possibility of having to install the façades after removal of the old pavement but before the installation of the new one, combined with the unknown stiffness of the supporting structure, led to the application of several conservative considerations during the design of the façades. Using ballast to compensate for the weight of the pavement during installation was inconvenient due to the access difficulties it implied in an already narrow space with load restrictions that did not allow the use of certain elevation machinery.

Therefore, the steel structure of the ground floor slab including the envisaged reinforcements was incorporated in the finite element model of the façades. The contribution of concrete was disregarded as the connection between steel and concrete was not clear. This led to a conservative model in which the supporting structure was more flexible than expected, as confirmed by field measurements later on.

Based on this model, the glass façades were analysed and designed for two extreme scenarios: min. and max. deformation of the supporting structure. In the first scenario, all load combinations were analysed assuming that the façades were built replacing the pavement and without any live load on the ground floor slab. In the second scenario, these were analysed considering that the façades were installed after removing the old pavement but before installing of the new one, and a live load of 5 kN/m\(^{2}\) was applied on the ground floor slab.

These conservative assumptions led to significant deformations in some areas of the already reinforced slab. These could not be accomodated by the façades, which are specially sensitive to ground floor deflections due to the size of the cladding panels.

In order to solve this problem, spring supports were installed under all cladding panels and vertical fins (Fig. 7). These consist in two columns of Belleville washers embedded in the floor channel, holding a steel plate on which the glass panels rest by means of a pad of injectable mortar type Hilti HIT-HY 270.

Although the elastic supports could only carry compression loads, it was possible to find a spring stiffness that could accomodate the expected slab deflections without detachment of any glass panel from its support pads for all load combinations in Ultimate Limit State, while at the same time controlling the deformation of the vertical joints between panels to guarantee the durability of the structural silicone bonds.
Fig. 8

Typical metal insert. In green, delaminated surfaces considered in ULS

6 Design of embedded metal connectors

A number of glass connections in the façades, including the typical connection between cladding panels and glass fins, were designed with metal parts embedded in the glass laminates. In this case, a laminate with a minimum of three glass plies is necessary, with the central ply having a notch that accomodates the metal insert. The bond is provided by the interlayer adhering to both glass and metal during the lamination process. Therefore, the interlayer must have sufficient strength and good affinity with metals, which makes it a perfect application for a ionomer interlayer like SentryGlas.

Besides the obvious visual advantages of these connections, arising from the transparency of the adhesive and unobtrusiveness of the metal parts, their mechanical behaviour is quite complex even under the simplest loading conditions such as a pull-out force.

As discussed in Santarsiero and Louter (2013), a pull-out force on the metal insert is transferred to glass by shear on the lateral surfaces, shear on the top and bottom surfaces and tension on the front surface (Fig. 8). The distribution of the force between these mechanisms depends on their relative stiffnesses. At room temperature and under short term loads, the displacement of the interlayer on the front surface in a direction perpendicular to the force is significantly restrained by the adjacent interlayers and glass panels. This fact, combined with a relatively high Poisson ratio, leads to the force being mainly transmitted by the front surface to the inner glass ply. This mechanism also exists at higher temperatures and for longer load durations, but it is less significant due to the lower lateral constraint provided by a softer interlayer.

In addition to the stresses produced by the applied forces, there may be some residual stresses as a result of the lamination process. The difference in the thermal expansion coefficient and the specific heat between glass and metal produces some differential displacements during the cooling phase of the autoclave cycle. To the authors’ knowledge, a quantification of this effect is not yet available in the literature. However, it is well known that metals with physical properties quite similar to glass (titanium alloys) are easier to laminate than, for instance, typical stainless steel grades.

The combination of relatively high stresses in the frontal bond resulting from external forces and some unknown residual stresses may produce delamination in this area. In fact, the region more prone to delaminate is the curved transition between the frontal and the top/bottom surfaces, which is subject to a combination of tensile and shear forces. Delaminations in these areas appearing spontaneously during the first week after lamination have been observed occasionally.

The numerical prediction of the strength of embedded laminated connections is an active field of research. The recent publication of the excellent Ph.D. thesis of Santarsiero (2015) and some related scientific publications (Santarsiero and Louter 2013, 2015, 2016; Santarsiero et al. 2016, 2017) has shed some light on this issue. However, the results shown in these publications cannot be directly used for design for the following reasons:
  • All results are based on average values obtained from testing. Average strengths are totally correct in a scientific work but cannot be used for design.

  • All tests are performed on glass-to-stainless steel connections. Thus, lab test results in these publications need to be cross checked if other metals (e.g. titanium alloys) are used, although important differences in bond strength are not expected.

  • A method to account for the simultaneous application of tensile and shear stresses, together with the existance of both deviatoric and volumetric stresses is proposed in the thesis. This method needs to be further checked with physical tests before being applied for design.

  • A quantification of the residual stresses resulting from the lamination process and their relaxation with time and temperature is still an open field for research.

Given the current state of knowledge, the following principles were used to design the adhesive bonds in this project:
  • The embedded adhesive connections were used to transfer short term loads exclusively.

  • The design strength of the bond in pure tension and pure shear was determined by testing for the intended temperatures and load durations. The design strength is the characteristic strength as per Eurocode 0 (5%-percentile of the distribution of strengths with 75% confidence) divided by a material factor obtained from IStructE (1999).

    The following interaction expression was obtained from Peters et al. (2007) and adapted to this application. Note that it ignores the existance of hydrostatic stresses.
    $$\begin{aligned} U=\left[ {\left( {\frac{\sigma _{t,Ed} }{\sigma _{t,Rd} }} \right) ^{2}+\left( {\frac{\tau _{Ed} }{\tau _{Rd} }} \right) ^{2}} \right] ^{1/2}\le 1 \end{aligned}$$
  • The embedded connection was analysed in Ultimate Limit State (ULS) with sufficiently accurate finite element models considering the front, top and bottom surfaces, together with a 10 mm strip on the lateral surfaces, to be completely delaminated (Fig. 8). In addition, a 5 mm strip on the lateral surface adjacent to the outer edge was not considered to participate in the force transfer as adhesion may be affected by environmental influences, as shown in Gallizia et al. (2014) . Therefore, only the central part of the lateral surfaces was considered to participate in the force transfer in ULS.

  • Numerical results were cross checked with some physical tests of the final connections.

With regard to glass design, the scenario in which no delaminations existed in ULS was also considered for the determination of the maximum stresses in the central glass plies. At the same time, the scenario of maximum delamination as noted above was considered for the design of the outer glass plies.
Obviously, stresses on glass arising from bending of the panel (in addition to pull out forces) should also be taken into account. These were relevant in the glass fins where metal inserts were located on the tensile fibre under wind suction and the notches created to accomodate the insert produced significant stress concentrations.
Fig. 9

Deflections on a 3 \(\times \) 10 m cladding panel and detail of interlayer stresses

It is interesting to note that in the cladding panels it was possible to take advantage of the metal inserts to help alleviating stress concentrations. These panels, with a size of 3 \(\times \) 10 m approximately, are fixed continuously along their bottom edge and at four points along their vertical edges by means of titanium inserts connected to the internal glass fins. Only out-of-plane wind loads are transferred through the inserts by means of a clamping system.

Significant stress concentrations were found on glass and on the interlayer near the top and bottom edges of the titanium insert. These are due to the high curvature of the panel around point fixings combined with the sudden stiffness change at the transition between glass and metal. Stresses could be significantly alleviated by extending the height of the inserts from the initial 240 mm up to 400 mm in order to locate the transition from metal to glass in an area of small curvature, as shown in Fig. 9.

7 Design of structural silicone joints

The façades make extensive use of structural silicone bonds in glass joints to prevent the distortion of the façade under small relative displacements of the supporting structure, and to provide some cross-bracing.

In order to properly capture the stresses and strains in each structural silicone joint, these were included in the global structural model by means of a series of beam elements connecting the glass panels together at constant distances in the range of 100–200 mm (Fig. 10).
Fig. 10

Modelling of the structural silicone joints

The stiffness of each silicone joint was studied using finite element models that take into account the actual geometry of the bond and the nonlinear behaviour of the specific silicone product for the range of strains under consideration.

The reader is warned against using certain silicone stiffnesses published by silicone manufacturers which may correspond to tensile tests on dumbell specimens or to small joints with aspect ratios of about 1:2, typically found in curtain walling applications. Deeper joints may show significatly higher stiffnesses, specially in tension and compression, and possibly higher stresses than those expected if the above values were used.

In the current project, two-dimensional plane strain finite element analyses were performed for each joint geometry considering the hyperelastic material model of the sealant, which was supplied by the silicone manufacturer. Tension, compression and out-of-plane shear were analysed at different levels of stress within the acceptable range. In this case, the stiffness of the joint under in-plane shear was assumed to be similar to that of out-of-plane shear, although a more accurate approach would require an independent determination of the in-plane shear stiffness by finite element analysis in 3D.
Fig. 11

Stiffness of a 50 \(\times \) 30 mm silicone butt joint in shear

Figure 11 shows the results of such analysis for a typical 50 \(\times \) 30 mm joint subject to out-of-plane shear. Note that the response in the considered range of forces/displacements is almost perfectly linear, thus a single value of effective shear modulus could be found. Linearity was slightly worse in tension and compression.

The design strength of each structural silicone bond was obtained from the European Technical Assessment (ETA) of the product. However, the values shown in the ETA are normally affected by a safety coefficient of 6 that is intended to be used in combination with the simplified methods of analysis shown in ETAG 002 (2012). For more accurate analysis methods such as the one discussed in this paper, the use of lower safety coefficients is possible. In this project, a safety coefficient of 4 was used, as recommended in Dow Corning (2015).

Finally, it was necessary to take into account the interaction of axial and shear stresses. Sandberg and Ahlborn (1989) suggested an elliptical interaction for silicone joints under short-term loads. Currently, silicone manufacturers can provide slightly modified expressions that improve the accuracy of the former and take into account the concurrent application of short- and long-term loads.

8 Construction

The installation of the glass façades was governed by the small space available on site and the load restrictions on the ground floor slab that significantly limited the types of elevation equipment being used. Moreover, the steel canopy including the roof glazing and the vertical smoke vents underneath were already present by the time of the façade installation. These prevented the use certain types of cranes and suckers for the assembly of the large façade panels. A description of the construction sequence that was designed to overcome these difficulties follows.

Prior to the installation of any façade component, the ground floor slab was modified in order to accomodate the revolving doors, etc. It was also reinforced to resist the new loading conditions with the intended deflections and according to current construction codes. The reinforcements consisted a number of steel beams located under the ground floor slab and connected to the embedded steel beams of the slab at specific positions. The installation of these beams was possible thanks to the significant height between levels 0 and − 1.

The reinforcement beams were connected to some existing concrete columns and to four new steel columns that transferred part of the vertical load to the floor slab of level − 1, which was also reinforced in some areas.

After that, the stainless steel channels supporting the cladding panels and the fins were installed at ground level. The steel brackets connecting the top glass beam to the building structure at levels \(+\) 2 and \(+\) 3 were also installed in their intended position, together with the columns of smoke vents located at the NW and SE corners of the hall.

The first glass component to be erected were the glass fins, fixed in position with the aid of temporary steel supports. These were special brackets that clamped the top end of the fins and connected them to the canopy structure and an horizontal beam at mid height of the fins to prevent flexural and lateral torsional buckling during construction.

Once all fins were properly positioned and fixed, the horizontal glass beam was installed. The two glass panels forming this beam were connected together and also to the special end brackets fixed to the building structure.
Fig. 12

Installation of a cladding panel

The cladding panels were then installed by inserting them in the bottom channel with a slight outward inclination and tilting them inwards (Fig. 12). Once in position they were connected to the fins by means of clamps that were bolted to the titanium inserts of the fins through the vertical glass joints and then rotated 90\(^{{\circ }}\) to clamp the metal inserts of the cladding panels.

The cladding was installed sequentially from the SE corner to the NW corner. This allowed the progressive removal of some of the temporary fixings of the fins in a manner that was compatible with their stability.

Finally, the installation concluded with the application and curing of the structural silicone joints, the removal of the remaining temporary elements, and the installation of the revolving and emergency doors (Fig. 13).
Fig. 13

The glass façades almost finished

9 Conclusions

This work has described the main structural glass components that make up the façades of the new entrance hall to the Torre Europa building: cladding panels, vertical glass fins and horizontal glass beam. The load paths and the load transfer mechanisms between these elements and to the primary structure of the building are also discussed for both the typical façade and the door area. This leads to a brief description of the strength and stability checks required for the design of the glass fins and beam, together with a more detailed description of the most important connections between these elements.

The second part of the paper focuses on the main difficulties found during the design of the façades: the excessive deformability of the ground floor slab and the need of slab reinforcements and spring supports, and the insufficient guidance for the design of embedded laminated connections available in the literature. With regard to the latter, further research is necessary to provide practitioners with accurate information and reliable design methods for this type of connections.

Finally, the paper ends up with a brief description of the main problems encountered during installation and an overview of the construction sequence followed to overcome these difficulties.

For more than 30 years, Torre Europa has been a landmark in the skyline of Madrid. The current refurbishment is aimed at providing a more modern atmosphere to a building that was showing the effects of time. In this context, the new super-transparent façades of the entrance hall will help to emphasize its modern appearance, contributing to the success of the tower in the following decades.

Notes

Compliance with ethical standards

Conflict of interest

The authors are employed by the company Bellapart s.a.u. The authors declare that they have no other conflicts of interest.

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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.BellapartLes PresesSpain

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