Glulam structures: some Portuguese case studies

Transcription

1 Glulam structures: some Portuguese case studies Artur O. Feio University Lusíada and University of Minho, Portugal Paulo Cruz University of Minho, Portugal Agostinho Pinto Inwood, Portugal ABSTRACT: Timber is one of the most used materials in specific typologies of roofs and floors (churches, play grounds, bridge building, pools, etc.) in Portugal. The geometry is defined by elements that occupy a limited and well defined part of the tri-dimensional space, with a clear evidence of the hierarchy of the components. Timber elements are often visible, which allows easier conservation, identification of the wood species, characterization of details and evaluation of deterioration. In construction Glulam is used for its strength and character building versatility. It can be produced in individual shapes straight or curved large or small, providing to the building a light and gentle touch. Modern Glulam technique combined with the durability of wood makes Glulam a highly versatile construction material with unique qualities. Complex timber structures, such as those belonging to the roofs of large Glulam structures, are often not easy to understand in a expedite way. This complexity makes the field of Glulam structures not only a challenge but a field much in need of modern research. The objective of this paper is to present some of the Portuguese experience in this field, showing how architectural solutions can be supported by an extensive knowledge about the constituent material from which the structure was made, both from the mechanical point of view and from the physical point of view. A number of case studies will be presented to illustrate common design problems and solutions, as well as the possibilities and limitations of this material. 1 INTRODUCTION Timber, frequently associated with masonry and stone, is the material most uninterruptedly used by mankind. Thus, the heritage of timber structures is immense and several and wideranging structural typologies and functions are assigned to these structures. Timber is also one of the most used materials in specific typologies of roofs and floors (churches, bridge building, pools, etc.) in Portugal. In construction Glulam is used for its strength and character building versatility. It can be produced in individual shapes straight or curved large or small, providing to the building a light and gentle touch. Modern Glulam technique combined with the durability of wood makes Glulam a highly versatile construction material with unique qualities. Complex timber structures, such as those belonging to the roofs of large Glulam structures, are often not easy to understand in a expedite way. This complexity makes the field of Glulam structures not only a challenge but a field much in need of modern research. This paper presents some of the Portuguese experience in this field, showing how architectural solutions can be supported by an extensive knowledge about the constituent material from which the structure was made, both from the mechanical point of view and from the physical

2 point of view. A number of case studies will be presented to illustrate common design problems and solutions, as well as the possibilities and limitations of this material. 2 THE PORTUGUESE TRADITION OF TIMBER CONSTRUCTION There are several relevant time periods concerning the importance of timber in Portuguese traditional construction. The end of the Middle Age was a period of creative energy, where a changing society tried to keep and to revive tradition based on paradoxes and controversy. In this context, religious manifestations and profane events occurred with great apparatus and spectacularity. Timber also played a role in the collective life of medieval societies, in relation with architecture of the buildings needed for the festive events, and also with military constructions associated to the effort that the maritime expansion required, during the XV century. The relevance of carpenters was also stressed during the period of the reconstruction of downtown Lisbon, after the disastrous 1755 earthquake, tsunami and fires. The new constructions were based on a composite timber structure of plummets, crosspieces and diagonal lines, filled with masonry, constituting a three-dimensional frame of very high ductility and with an excellent anti-seismic behaviour. This, so-called Pombalino system, represents a genuine Portuguese structural typology especially conceived to enhance the seismic performance and following the experience in timber construction surviving to the earthquake. Here Pombalino is the term coined after Marquis of Pombal, who was the prime minister in 1755 and took most of the decisions regarding the reconstruction of Lisbon. Figure 1 shows an internal timber wall arrangement example for downtown Lisbon, see Cóias e Silva et al. (2001) for detailed information. Figure 1. Internal timber wall and floor arrangement in a composite timber-masonry wall of the Pombalino system (Feio, 2006). Floors and stairs were frequently made by a system of beams up to 6-7 m of length spaced around 400 mm up to 600 mm. The dimensions varied according with the timber species. For spans larger than 7 m, after the XIXth century and following the development of the iron industry in the industrial revolution, it was common to use steel beams and composite floors as an alternative to the traditional timber solutions. The timber roofs of monumental and historical buildings are probably the most emblematic structural systems and incorporate the larger structural complexity. The multiplicity of joints and constructive solutions found reflect the evolution of techniques and materials in the last 300 years. The most typical timber roof structures in traditional constructions are trusses made of main roof beams, which received the purlins that supported the rafters, which, in turn, received the laths that supported the roofing tiles.

3 3 CASE STUDIES 3.1 Salesiano s Church Estoril, Portugal The origin of the Salesianos s Church dates back to the middle of the 20th century (1948). The original structure of the roof was entirely made of timber, see Figure 2a, and the owner did not want to keep the existing roof structure due to the fact that: (i) previous remedial measures did not provide a real solution, (ii) a change in the interior of the choir was needed taking into account that the choir-organ did not performed well because of the proximity to the ceiling, see Figure 2b. The demand of the owner organist was the real spark to the intervention. (a) (b) Figure 2. Salesiano s Church: (a) view of the roof structure (existing vault), and (b) localization of the choir-organ and its proximity to the ceiling Adopted strategy The exiting timber structure is composed by pine trusses and has a span around 13.5 m, see Figure 10, being composed by: (i) a set of main trusses, spaced 4.20 m; (ii) secondary trusses located only in the area closer to the vault in the altar which does not allow a traditional roof structure using a tie beam, see Figure 3a. The structure was visually inspected and it was possible to verify that the timber is globally in good condition and exhibits no structural damage; however treatment against xylophagous insects was needed, see Figure 3b. A solution has been proposed: to adopt a new timber solution using new curved elements/trusses, see Figure 3c to Figure 3f, supported in a ring concrete beam that will be constructed on the side masonry walls. The steel connections of the new timber structural system are nailed or bolted with steel plates. All steel elements are made using stainless steel type AISI 316. The top ridge tiles are to be placed dry, in order to allow ventilation. The airflow is to be ensured by small plastic tubes located in the bottom part of the roof.

4 (d) (e) (f) Figure 3. Salesiano s Church: (a) to (c) different perspectives of the existing roof structure, (d) to (f) different perspectives of the new roof structure. 3.2 Redondo Coliseum Redondo, Portugal As a result of the recovery of the ancient Simão da Veiga Junior bullring, the now called Redondo Coliseum presents an avant-garde architecture and was designed as multipurpose one, primarily as bullring but it may be used for some sports and cultural events of performances hosting several initiatives and spectacles, see Figure 4f. The Coliseum offers 2000 seats in the stands. To these may be added about 1000 seats in the arena. The ground plan dimension of the Coliseum is 39 m radius. The roof structure of the Coliseum is made from glulam timber lamella mesh circular formed structure supported on a steel structure, see Figure 4a to Figure 4c. The basic net of the timber lamella structure is of glulam conifer wood (GL 28h) elements ranging about 24 m and 29 m long and 210/990 mm cross-section. The joint connections are made with steel cross connectors, which are holding the timber elements on the top and the bottom side. The upper and bottom steel crosses are connected with 2 M-14 presstresed bolts to each timber element in the joint. The construction of the Coliseum, including the roofing, see Figure 4d and Figure 4c, was completely produced and erected in 2,5 month time. The global timber volume, including the timber rafters and arches, is about 215 m 3 and the structural steel is about 7 kg/m 2. (d) (e) (f) Figure 4. Redondo Coliseum: (a) to (f) different phases of the production and construction of the roof structure.

5 3.3 Pools Moreira of Cónegos and Felgueiras Municipal Pools, Portugal According to the initial basic program the Municipal pool in Moreira of Cónegos project foresees the construction of two tanks. The ground plan dimensions of the tanks are 12 m span and 16 m in length and 8 m span and 12 m in length respectively, with a maximum capacity utilization or instantaneous peak of 144 users, see Figure 5a to Figure 5c. The building consists of a nave with approximately 38 x 20 m. The basic structure is based in 6 curved beams of glulam conifer wood (GL 28h) with 20 m long and 210/900 to 1440 mm cross-section. The joint connections are made with steel cross connectors, which are holding the timber elements on the top and the bottom side. The construction of the roof structure, including the roofing, see Figure 5c, was completely produced and erected in 1 month time. The global timber volume, including the timber rafters and curved beams, is about 54 m 3. Figure 5. Municipal Pool, Moreira of Cónegos: (a) to (c) view of the building and roof structure during works. The pool is located in the center of Felgueiras. The structural system consisted in 3 different frames of glulam conifer wood (GL 28h) with variable cross-sections: 8 with 33,4 m long (190/670 to 1450 mm cross-section), one with 29,6 m long (190/670 to 1340 mm cross-section) and one with 24,3 m long (190/670 to 1280 mm cross-section), see Figure 6a to Figure 6c, spaced at 3,1 m. All the joint connections (bolts and plates) are made with steel cross connectors (AISI 316), see Figure 6d. Loadings were taken according to Eurocodes. The construction of the roof structure, including the roofing, see Figure 6e to Figure 6f, was completely produced and erected in 1,5 month time. The global timber volume, including the timber rafters and the main wood frames, is about 160 m 3.

6 (d) (e) (f) Figure 6. Municipal Pool, Felgueiras: (a) to (f) different phases of the production and construction of the structure. 3.4 Pentieiros School, Ponte of Lima, Portugal The National program for the reorganization and rehabilitation of the school network of primary and pre-school education aimed to ensure equal opportunity of access to educational spaces and resources to educational success. Thus, it should therefore give priority to the reorganization of the school network, identifying, in outreach work with local authorities to recover or building schools. The construction of new schools, and its implementation should be viewed in the logic of creating better conditions of comfort and functionality that meet the current demands on the school, understood as a space to host education of students. In this context, were mobilized significant financial resources provided by the National Strategic Reference Framework (NSRF) , in order to enable the fulfillment of this objective of educational policy. The NSRF constitutes the framework for the implementation of the Community's economic and social cohesion in Portugal in The scholar center of Pentieiros is located in Ponte of Lima. The structural system consisted in several curved beams of glulam conifer wood (GL 28h) with m long and 165/476 cross-section, see Figure 7a to Figure 7f, spaced at approximately 4 m. The roofing of the building is based in a conventional roof garden system, see Figure 7a. Besides the decorative benefit, roof plantings provided temperature control, hydrological benefits and architectural enhancement. Loadings and structural dimensions were taken according to Eurocodes. The construction of the roof structure, including the roofing, see Figure 7b to Figure 7d, was completely produced and erected in 2 month time. The global timber volume, including the timber rafters and curved beams, is about 130 m 3.

7 (d) (e) (f) Figure 7. Pentieiros School, Ponte of Lima: (a) the applied roof garden system, (b) to (d) different phases of the production and construction of the structure, (e) detail of the connections, and (f) final view of the structure. 4 CONCLUSIONS A series of case studies depicting the value and importance of timber construction have been presented to showcase modern Glulam intervention cases in Portugal. The combination of knowledge, architecture and structural analysis are key factors to a successful approach. The case studies presented highlight the Portuguese experience in this field, showing how architectural solutions can be supported by an extensive knowledge about the constituent material from which the structure was made, both from the mechanical point of view and from the physical point of view. REFERENCES Cóias e Silva, V.; Lourenço, P.; Ramos. L.; Mesquita, C.; 2001 Accounting for the block effect in structural interventions in Lisbon s old Pombaline downtown buildings. Historical Constructions, P. B. Lourenço, P. Roca (Eds.), Guimarães: pp Feio, A.; 2006 Inspection and Diagnosis of Historical Timber Structures: NDT Correlations and Structural Behaviour. PhD thesis, University of Minho. Caironi, M.; Bonera, L.; 1989 Il legno lamellare il calcolo. Edolo. Nevada, M.; 1999 Diseno Estructural en Madera, AITIM (Asociacion de Investigacion Tecnica de las Industrias de la Madera y el Chorco). KHITARIS SL., Madrid.