Frame and Form

Following the series of short articles on wood structural performances,we present this bird observatory on the river Ebro. Unlike other observatories such usGraswarder, this viewpoint is not erected as a tower but it adapts to the rugged terrain on the banks of the river Ebro in bold extending cantilever.

Past spring the Ebro River saw a new structure approaching its waters. This bird observatory located in the city of Logroño has the visual power of one of the most daring structural forms, the cantilever.

As urban experience of closeness to nature, the observatory uses wood as a perfect structural material. Once again, the excellent strength-to-weight ratio and the possibility of prefabrication put this material as the right choice in a work of this type.

View of the observatory from the riverbank - ©2009 Luis Prieto

The draft of this work was proposed as a conceptual exercise for fourth-year students' project of the School of Art and Architecture of the Universidad Europea de Madrid, and promoted by their teachers Jose Luis Esteban Penelas and Manuel Fonseca Gallego . The great reception from the students and the high level of the proposals led to the development of the work presented here today.

Front view of the Observatory - ©2009 Luis Prieto

In the words of the principal author of the proposal, Professor Manuel Fonseca Gallego:

“The fundamental concept is to consider the item as a box girder bounded by four planes, the lower horizontal and the other comprised of ruled surfaces. The composition of these planes is set of wooden planks arranged irregularly, partially covering the surface as ‘bandages', so that we are immersed in the dream world of nests and recreate that unreal atmosphere with its play of lights and shadows.”

Inside the Observatory - ©2009 Luis Prieto

In order to reach a vantage point, structure ‘flies’ some 11 meters above the steep river bank to reach the vertical of the shore. The viewpoint is materialized by a 3D structure composed of 4 flatlattices giving the irregular course of its quasi-organic variation. We highlight several key aspects of the structure:

1. Cross section decreases as it approaches the end of the bracket logically following the law of effort or need for strength that is maximal at the entrance and zero at the tip.

Height variation in the bracket - ©2009 Luis Prieto

2. By intentional irregularity of the geometry of the structure and arrangement of plank wrap (nonstructural) in apparent disorder, it is achieved a suitable ‘camouflage’ with the natural environment, justifying the added complexity to the design and construction, since each metallic joint and every element of wood had to be design uniquely.

Interior view, detail of the unions - ©2009 Luis Prieto

3. The hidden side of this structure, and probably the most important, is the foundation and support system. A micropiles system linked to a solid concrete slab ensures that the reactions transmitted by the two support lines are splited in the ground safely. The support reflect the strong momentum from the fixed tipper through a major pair of vertical reactions as indicated in the following sketch. There has been arranged 4 metal hinges, two per line bearing line, to ensure the transmission of pull and compression of the system.

Structure sketch, reactions and foundation - ©2009 Madergia + Frame and Form

The assembly of the entire observatory has been conducted on site. According to the authors, the procedure was quick, clean and efficient, placing it after a crane lift in its final place. In closing, I recommend this video where you can see the lifting and positioning of the structure in minutes.

Meta-Information:

Diagrams of stresses and strains provided by Madergia, engineer responsible for the calculation of the wooden structure.

Diagram efforts under overload - ©2009 Madergia

3D drawings and diagrams of the structure provided by the team responsible for the work.

Mounting type knot - ©2009

Plan Plan - ©2009

Reasoning and ideas behind the conception of this work in the author's words:

“Observation is a conscious process in which we use our senses to acquire information. According to the constructivist learning, observe is not absorbing information like a sponge absorbs water, but a task of selecting, influenced by our expectations and prior knowledge. If you ask a physicist and an artist to look at the sky at once, observe the two different things. The physician will talk about the process of star formation, time and space, while an artist think of the shape and color of clouds, and visual images that inspire you. "
"The idea of holding an ornithological observatory, a piece as unique and eminently in an urban landscape so well established, part of the developer proposed several locations within an area of outstanding beauty. After carefully reviewing photographic frames, was chosen the most suitable location we thought, among other reasons, because it is a strategic point for the detailed observation of large numbers of migratory birds without altering their natural habitat. Only remains located between two magnificent tree specimens to ensure that the volume is fully integrated built in the riverside vegetation itself as an element. The choice of material for its implementation was apparent. The wooden construction was the most interesting component.”

Description and cutting of elements and materials according to the team responsible for the work:

“The main structure (four girders, diagonals and sleepers) is made with pine plywood, GL28c strength class, from sustainably managed forests certified PEFC. The battens and boards are implemented with pine Class C24. All wood is treated in an autoclave with the product Celure AC-800 to a risk class III.
The structural form produces 40 singular knots with different encounter angles, resolved through joints and fasteners hot galvanized steel then painted. dacromet screws with outdoor treatment.
The four support points of the structure are solved with real joints on two pile caps, beams joined by centering, with micropiles of 200 mm 8 meters deep.
The floor consists of a wooden ties on which support pine tables 200 ×40 mm treated the same way, being spaced 1 cm. Inside the observatory will be placed in the same way, relying on the joists of the structure.
Wrap the outside with boards of 200 × 20mm randomly arranged in apparent disorder, allowing for a focused and sectioned view of the different stretches of the river and decreasing section as advanced to the final point. Whether this element as the rail demanded a fine interior woodwork, something unusual for a company assembling wooden structures but that did not involve additional difficulty.”

Technical Work:

Promoter: Ebro Hydrographic Confederation
Author of project: Fonseca Manuel Gallego
Engineering Solutions specializes in wood: Madergia
Project Date: June 2008
Date of completion of work: April 2009
Budget controlled: 117.822,20 €
Photography: Luis Prieto Saenz de Tejada