21 Where:
s is the cavity space.
k5 is determined in the Table B.3 in Annex B of the standard.
According to these factors, the external loads applied to the glass units, by means of the internal pressure, is distributed according to Table 3-2.
Table 3-2: Load partition for external loads.
Load Partition of load carried by
pane 1 Partition of load carried by pane 2
External load Fd,1 acting on
pane 1 F , = (δ + φ ∙ δ ) ∙ F , F , = (1 − φ) ∙ δ ∙ F , External load Fd,2 acting on
pane 2 F , = (1 − φ) ∙ δ ∙ F , F , = (φ ∙ δ + δ ) ∙ F ,
The internal loads given by the isochore pressure are reduced according to the rigidity of the panes, described by the insulating factor (ϕ). With this, the loads are distributed according to Table 3-3.
Table 3-3: Isochore pressure on each pane of the IGUs.
Load carried by pane 1 Load carried by pane 2
−ϕ ∙ p ϕ ∙ p
It’s also important to notice that the climatic action in an IGUs results from the combination of external and internal pressures applied on the glass. Therefore, the elements must be checked according to the load imposed to each one.
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characterized by a lateral deflection and torsional deformation along the length of the beam. When the element surpasses the limit of lateral torsional buckling, it becomes unstable and can no longer support the applied loads, resulting in collapse.
The critical moment of rectangular cross-section associated to this effect is defined by the CEN/TS 19100:3. This property is influenced by several factors, such as the shape and size of the section, the material properties of the interlayer.
It is important to note that, as mentioned in Chapter 2.8, this standard is a preliminary version of the ongoing Eurocode, and it lacks information for the design of beams subjected to this effect. In particular, the document does not fully explain the meaning of symbols and terms that are crucial for the computation of the critical moment.
The technical document stats that the value for the critical moment (Mcrl,LT) can be obtain by:
M , = C ∙π ∙ E ∙ I ,
L ∙ (C ∙ z ) +G ∙ , ∙ L
π ∙ E ∙ I, + C ∙ z (3.11)
Where:
C1, C2 are factors that consider the bending moment diagram.
E is the Young’s modulus of glass.
Iz,eff is the effective moment of inertia about the minor axis.
LLT is the buckling length.
L is not defined in the standard.
zp is not defined in the standard.
G is the shear modulus of glass.
Also in the computations for Iz,eff and It,eff, the document does not specify the meaning of symbol and term crucial for the computations need to obtain the value of the critical moment.
TIMBER AS A STRUCTURAL MATERIAL
Wood is a natural organic material that has been used for several centuries in construction. Through many countries it is adopted as a primarily building material, due to its relatively management and production. Also, due to the advanced research and improving technology, it is possible to considered that the behaviour material is well known.
Because it is a natural material, its properties are variable and sensitive to the environmental conditions.
It also presents different capacities according to the direction of the grain: it presents a high strength and stiffness parallel to the grain, but low properties perpendicular to the grain [19].
Timber can be used in several forms, but the most current ones are hard wood and laminated. Hardwood, as it is sourced from natural environments, can present certain defects or weaknesses that can negatively impact its structural performance. By cutting the hardwood into layers and gluing them together, these defects can be eliminated, and the resulting laminated glue wood is stronger and more stable. The use
23 of laminated wood has allowed the construction of elements of large dimension and with curvilinear forms, greatly expanding the field of application of wood as a structural material.
Eurocode 5 is a standard that stets several guidelines for designing and constructing timber structures in Europe. It covers a set of technical principles of hard wood, glulam and laminated softwood timber – that is the option chosen for this work. Laminated softwood presents better characteristics then hard wood, in terms of load-bearing capacity, structural integrity and durability.
In the specific case of this work, some of the elements are subjected to compression. The verification for the elements that the standard suggests takes into account the effects of deflection and is given by:
σ, ,
k , ∙ f, , ≤ 1 (3.12)
Where:
σc,0,d is the design compressive stress along the grain.
kc,z is the instability factor.
fc,0,d is the design compressive strength along the grain.
However, other elements are subjected to both compression or traction and bending. The difference between the previous verification and this also accounts the buckling effects, by adding another term to the equation. So, the verification becomes:
σ, , k , ∙ f , ,
+ σ , , k ∙ f , ,
≤ 1 (3.13)
Where:
σm,d is the design bending strength.
kcrit is the factor used for lateral buckling.
fm,d is the design bending strength.
Another verification worth to mention because it is also going to be used, is the crushing effect upon elements that are in an angle towards the beam element. This is given by:
, , ≤ , ,
, ,
, ∙ , , ∙ + (3.14)
Where:
fc,90,d is the design compressive strength perpendicular to the grain.
kc,90 is the factor that takes into account the load configuration, the possibility of splitting and the degree of compressive deformation.
α is the angle of the applied load.
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CASE STUDY
Any intervention on an existing building must be inserted in the context of the building characteristics. This chapter provides the reader with the necessary data about the building and the structure that’s going to be added.
INTRODUCTION
When planning an intervention on a building, it is crucial to have a meticulous knowledge of its features and conservation state. This assessment is known as inspection, and it involves examining the construction to gather information. It is essential for comprehending the construction behaviour, evaluating the causes of damage, and estimating the interventions required, i.e., to produce a diagnosis.
Thus, the data obtained during the inspection serves as the foundation for the diagnosis, i.e., provides the information required to make a precise diagnosis. As previously stated, inspection is the process of gathering information such as historical, photographic, geometrical, material, and damage details. This can be achieved through visual inspection, measurements, testing, or consultation of documents and people. The goal is to identify the global characteristics of the building.
Diagnosis, on the other hand, serve the collected data to determine the building's safety and integrity.
This includes evaluating the cause of eventual existing problems/ damage as well as determining the best course of action for addressing the identified problems.
This chapter aims to present this methodological process. Section 4.2 provides a description of historical data and materials. The inspection results, as well as the damage assessment, are presented in section 4.3. Finally, section 4.4 describes the aim and characteristics of the new structure that is developed in this thesis.
HISTORICAL DATA
Understanding the history of a building is a key factor when thinking to intervene, since it gives important context on how it was designed and used, helping on future decisions. It may also orient the intervention to specific legal aspects or recommendations, as those related to heritage protection.
Regarding the structure itself, by knowing the time in which the building was built can provide information about the materials or techniques that were used. This can give also information about the type of expected damage in comparison to other buildings of the same time period. It also puts into context its cultural importance, identifying elements that are important to maintain or even rehabilitate.
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Concerning the building of this work, the year of construction is uncertain, but it is known that it ended in 1800. At the time, a widow named Brites Maria Felizarda ordered the construction, since she was looking for a building that could house, not only her family, but also the family's gold and silver business.
So, adopting the Neoclassical style – which was very popular at the time – a three-story high building, with a factory behind it, was built. The dimensions were influenced by the depth of the terrain, which forced the façade to align with the street and conditioned the surroundings. As a result, the sides of the house are left with just enough space to fit the stairs that led to the factory, making workers walk around the main residence to get to it. As shown in Figure 4-1, this factory is installed on the first floor, with a wall that divides the two spaces to create privacy to the family. This detail created one of the most striking features of the building – a U-shaped part, which has a higher height then the rest of the constructions, and a factory area that runs along the entire length of the garden in the background.
Figure 4-1: The building in 1800. On the left, a map of 1893 with the location marked in red. On the right, the wall that separated the main house and the factory19.
Throughout the years that the family lived in the building the spaces were used for a variety of purposes.
The main entrance was on the ground floor, and it was identical to the one that exists today. This entrance welcomed carriages that entered the building for a variety of purposes and were kept on the background patio. For this reason, the surrounding rooms were used for storage facilities. The first floor was reserved for the family, while the second was reserved for house servants and maids. As previously stated, the factory was located behind and had no interior connection to the main building [20].
The family lived in the building for about fifty years, but by the end of the 19th century the Portuguese economy had changed dramatically. As a result, the company went bankrupt, and they were forced to move. Fortunately for them, the Royal Family was looking for an official residence in Porto, as they had none close to the city. So, in 1850, the family sold the house to King D. Pedro V.
The building suffered changes with their arrival, but as far as it is known it was only on the use of the rooms. The left side of the middle floor was destined for the king and the queen, and contained their rooms and closets, a salon to receive guests and the throne room. The right side was for the ministers and other members of the state, and in the middle the dining room and the kitchen. The top floor was designed to receive the lower members of the royalty and the attic became the residence for the maids and servants. The use given to the factory facilities is uncertain. However, it is known that the royal family frequently used the garden [21].
19 Figure from: M. A. Macedo, ‘Intervenção no Património Construído: O Caso do Museu Nacional Soares dos Reis’, 2013.
27 Because this was not the permanent residence of the royal family, the building was occasionally occupied, which became worse after the establishment of the Republic and the exile of the last king, D.
Manuel II. So, in 1915 the building was donated to Santa Casa da Misericordia, to establish a children's hospital. However, this never happened, and the building stayed empty [20].
The National Museum Soares dos Reis already existed in another building in the city, but it needed expansion and better conditions. So, the Portuguese State started negotiations to acquire the building and install the museum in there. Following this, the building was bought and placed in the public domain in 1937 [22].
The process of adapting the building to its new use began around this time, with significant changes to its appearance and structure due to its poor conditions. Regarding the main façade, the five gates that composed it were reduced to just one, becoming the main entrance for visitors (see Figure 4-2). The entrance on the left side, destined at the beginning for the works of the factory, was also changed and retracted from the alignment with the street.
Figure 4-2: Façade of the building before the works (left figure) and after the works (right figure)20.
The section of the building that housed the factory facilities was also modified and converted into galleries. The roof was customized to include skylights to enable natural light in and illuminate the various art works on display. The rooms were also altered, and many corridors were demolished to make way for larger rooms and exhibit areas. This intervention ended in 1942, year that also hosted the first exhibition in the museum.
During almost all the 20th century the museum operated without any notable intervention and became the oldest public museum in Portugal. However, in 1992 the museum was subjected to an important intervention by the known Portuguese architect Fernando Távora, that involved a thorough investigation and analysis. These works, which represent the most recent ones on the building, ended in 2001 and are examined in detail in section 4.2.1 [22].
Figure 4-3 summarizes the relevant historical data of the museum.
20 Picture from: M. A. Macedo, ‘Intervenção no Património Construído: O Caso do Museu Nacional Soares dos Reis’, 2013.
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Figure 4-3: History timeline of the Museu Nacional Soares dos Reis21.
21 Scheme made by the author.
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