Steel: A History of Strength. A Future of Possibilities. |
| Canada
|
Canadian Institute of Steel Construction |
|
|
|
|
|
|
|
Some Key
Numbers
Completed: 1996
Area: 11,000 ft2
Contributors
Architect: Baird Sampson Neuert Architects Inc.
Engineer: Yolles Partnership Structural Engineers
Owner: Niagara Parks Commission
General Contractor: Robertson Yates Corporation Limited, Hamilton
Steel Fabricator: M&G Steel Ltd., Mississauga
Steel Erector: Spark Steel Erectors Limited, Concord
|
The grounds of the Niagara Parks Botanical Gardens is home to one of North America's largest collection of free flying butterflies.
This year round exhibit showcases a wide variety of butterflies from around the world living in a lush, rain forest-like environment. A 183m network of pathways provides access for the physically challenged throughout the 1,022 square metre conservatory, allowing visitors a rare opportunity to watch numerous species of butterflies floating majestically among nectar producing flowers such as lantanas, pentas, and passion flowers.
The primary structure of the building is steel.
The following is an excerpt from Advantage Steel No. 8, Fall 1997
Soaring butterflies now rival the plunging torrents of water at Niagara Falls, as a tourist attraction. Located 9 km north of the falls, the 1020 m2 Butterfly Conservatory is the focal point of a facility dedicated to the rearing of butterflies and the education and entertainment of the public.
According to Barry Sampson, Baird / Sampson Architects , "the objective inside the conservatory is to achieve a sense of anticipation and wonder for the duration of the visitor's stay". Approximately 2 000 butterflies of over 50 species fly freely in the tropical setting within the conservatory. With a long, plunging waterfall serving as a breathtaking centerpiece, extensive plantings of colourful, nectar producing flowers flourish in the hot (27°C), humid (80%) atmosphere required by the butterflies.
Unique Steel Structure
Exacting architectural and structural engineering requirements for the centerpiece of the Niagara Parks Botanical Gardens were met by means of a unique steel structure. The conservatory is shaped like the chrysalis from which a butterfly emerges. In order to reduce the shading effects caused by the structure and to evoke the tracery of butterfly wings, the structural system was designed to minimize member sizes and to multiply the member frequency. Barry Charnish, Yolles Partnerships Inc., explains that "the choice of the structural system was also influenced by the practicality of the shipping size, the shedding of any moisture from the high humidity and the minimizing of span lengths".
A series of 3-pin 11.5 m high arches located at 9 m centres support gravity loads, as well as resisting the lateral loads in the short axis of the conservatory. The beam portions of the arches are queen post trusses, consisting of a straight top chord (W shapes) and a "double linked" bottom chord (steel rods) about an inverted "V" shaped element, which separates the tension and compression chords. Spanning between the 3-pin arches are W310 roof beams which are oriented obliquely (i.e. not plumb), with their flanges located parallel to the roof to facilitate easy installation of the glazing system. The oblique orientation of the roof beams generates a lateral component of the gravity load which is resisted by double sag rods secured to the ridge at l/3rd span points.
Distinctive columns
Lateral loads acting in the long axis of the conservatory are resisted by a spine of 4 "Y" shaped columns which are connected at their ends to form an extremely stiff frame. The columns are very striking and distinctive.
Two round HSS219X6.4 joined at the base and spaced out at the top support two arms also composed of round HSS. A special plate connection links all members creating in effect a stylized tree. Charnish explains that "the column elements were selected to permit shipping by truck without field splicing". He adds, "the linear frame proved more economical compared to a three dimensional shape which would have limited the number of pieces shipped per truss or required more undesirable field splices". This frame also supports a portion of the gravity load.
A service catwalk in the upper region of the roof provides access to the heating, ventilation, lighting, and misting systems that are required to maintain year round tropical conditions. This catwalk has been configured to converge at each end of the roof structure, thereby eliminating the need for additional cross bracing in the side wall and diaphragm bracing in the roof. Analysis of the structure was assisted by an AutoCAD interface routine with the SAP analysis program. Many elements were designed "by hand" due to the simplicity of the design.
According to Mel Grimes, M & G Steel Ltd., the design required very precise fabrication and erection tolerances throughout, to accommodate the glazing system, which was prefabricated concurrent with steel fabrication. The geometry of the butterfly house is mathematically complex, with a single axis of symmetry running down the central spine. Angelo Paniccia, Spark Steel Erectors Limited says that "this was a pretty complicated job in terms of erection planning and procedure, and experience played a big part in the process". Bolted connections were used throughout most of the structure (95%). A total of about 6 weeks was needed from planning stage to final erection, in early March 1996.
Galvanized and Painted
The strict climate-controlled environment required a unique system of galvanized and painted steel. Field welding was undesirable due to concerns about corrosion resistance and finished appearance. The steel was hot dip galvanized, then sweep cleaned with a non ferrous blasting agent to provide a suitable surface for paint adhesion. The structure was shop primed and field painted with a moisture cured urethane coating. CSA G40.21 300W steel was used for the wide flanges and 350W steel for the round HSS members. About 64 tonnes of steel was used for this project.
With its 5.5 m high stone walls topped with an unusual shaped glass dome composed of 13 wall planes and 8 roof planes, the conservatory is impressive but non-imposing. The reason, according to Sampson, is the structure's relationship to the surrounding topography. The stone-based structure visually links the conservatory with the lime-I stone cliffs of the gorge. The $15 I million facility opened December 14,1996 and the public has respond-I ed with great I enthusiasm. George Bailey, Director of Communications for the Niagara Parks Commission, 9 says that "the conservatory has exceeded our expectations by 40%. After less than 8 months, 1/2 million people have already visited the exhibit. That's an average of 2 200 people per day!".
The Butterfly Conservatory won the 1997 CISC Ontario Region Steel Design Award.
|
|
|