Entrant: Light Weight Structures
- Category: 4 ID Number: 4351
- Location: Mooloolaba
- Client: Mooloolaba Bowls Club
- Completion Date: November 2011
- Structural Engineer: Jeremy Hunter
- Specialists: Trevor Scott Building Designer
- Builder: Light Weight Structures
- Fabricator: Stanfast
- Installer: Light Weight Structures
"An elegant project - the best of the bowling club offerings. As well as taking care of core business, the structure lends some design distinction to a town not oversupplied with architectural gems."
APPLICATION OF PROJECT: Bowling Green Canopy
The project covered two bowling greens each measuring 1240 sqmts for a total undercover area of the tensile structure 3253 sqmts. Fabric roofing was the superior choice of roofing material over metal roofing, as fabric offers translucency of natural light during daylight hours and with the use of energy efficient up lights an aesthetically favorable backlit effect at night with the added benefit of shadow free reflected lighting to the bowling arena.
The structural design features leaning arches and valley cables spanning the width of the structure forming a Ridge and Valley canopy. The ends of structure are curved/closed encapsulating artificial nighttime light within the roof canopy minimizing the nighttime light spillage and annoyance to neighboring properties.
Enclosing two bowling greens with one fabric canopy is an innovative design developed by our company.
Unconventionally, the striking beauty of this minimalist structure is held on the underbelly of the fabric canopy. Representing an authentic lightweight structure with a structural steel to surface area ratio of the fabric canopy at 19.4 kilograms per square meter of fabric and spanning a width of 42.8 mts and a length of 76 mts, the structure offers 3,253 sqmts of clear-span space under canopy.
The structure has a maximum height of 9.5mts, decreasing to a height of 3.2 mts along the perimeter. The east and west ends of the structure are designed with curved structural support to add stability to the fabric canopy with a low perimeter beam which provides much-needed protection from the hot summer sun and prevailing weather. Designed into the end perimeter beam is a fall of 0.5 mts from the mid point to the end. This feature assists in water runoff in the perimeter guttering and minimizes the need for downpipes.
On the underside of the canopy large sections of heavy-duty pipe span the project width of 42.8 mts forming six sets of leaning arches. At a height of 9.5 mts, the fabric canopy appears to hug the leaning arch rafters positioned at 12 mt intervals. Adding contrast to the canopy’s form, cables tension the fabric between the leaning arches, creating a series of 1.2-mt deep valleys. This combination of leaning arch and valley cable creates an external ridge and valley effect when viewing the structure from the northern and southern sides.
For night time use, the low perimeter frame encapsulates artificial light, up lighting and illuminating the canopy and reflecting shadow-free lighting down to the playing surface. Energy efficient lights are mounted on slender droppers from the leaning arches to a predetermined distance from the canopy surface to gain maximum reflective light. This feature utilizes the unique reflective nature of a fabric roof canopy. Externally, the eastern and western ends of the structure appear as a dome.
DESIGN / FABRICATION / INSTALLATION BRIEF
The project represents an authentic Light Weight Structure with the ratio of structural steel to surface area of the fabric canopy being 19.4kg per sqmt of fabric.
Creative engineered design meeting a functional and budgetary outcome was the driving force behind the development of the Mooloolaba Bowls Club Wide Span Fabric Structure. The client wanted a shade and weather protection structure covering two bowling greens and allowing for community friendly night time bowling. The client had a fixed budget. Previously, two other Australian bowling clubs, Raymond Terrace Bowls Club NSW (2007) and Pine Rivers Bowls Club Qld (2010) embraced fabric roofing as a solution for weather protection over synthetic bowling greens.
In both instances the two unrelated suppliers covered two greens, utilizing highly similar individual fabric structures to cover each separate green, with conjoined fabric canopies and multiples of center columns dividing the total covered area into two separate spaces. Both structures featured open ends, trussed rafters. With the benefit of hindsight, it was identified these structures were cumbersome, heavy in structural steel, costly and flawed in functional design. Notably during the day the sun and rain poured in the open ends of the structure, while at night the artificial light for night time bowling poured out the ends frustrating neighbouring properties. Additionally, trussed steel rafters used to create strength within a roof frame over a 42.8 mt width provides an inviting home for bugs, birds and dirt build up resulting in high cleaning maintenance costs.
With thoughtful design and engineering an innovative more functional project outcome could be delivered.
When developing the Mooloolaba Bowls Club Structure it was determined the difficulty in engineering the structure lay in developing a means to span the 42.8 mts unsupported. Once the span was achieved the length of 76 mts required to cover two bowling greens was a matter of duplication of the structural elements. There was no need to cover the two bowling greens with two individual structures; the bowling greens could be covered with one large structure offering ambient free span space. Our designer concluded, all these negative factors could be addressed through design and engineering.
Rather than using trussed steel rafters, large diameter high strength pipe sections in a leaning arch configuration would create the required strength to span the 42.8 mt distance. These pipe sections maintain strength but are cost effective as they require minimal labor during fabrication. Valley cables over the top of the fabric canopy deliver both strength and stability to the fabric. In addition, the Valley cables allow for tensioning of the canopy if required after a severe storm event.
Along the 76 mt length of the structure an inverted vee column configuration has been utilized to offer longitudinal stability to the structure. On the eastern and western ends of the structure, straight columns have been utilized for the possible future addition of clear blinds for additional wind and rain protection. Strut members brace the 12 mt perimeter beam span between the inverted vee columns to the leaning arches minimizing deflection introduced into the perimeter beam by the tension of the fabric canopy.
The combination of leaning arches and valley cables resulted in less structural surface for dust, dirt and birds nesting birds to accumulate. Consequently less cleaning maintenance is required to keep the structure looking in optimum condition.
Visually the end result for the Mooloolaba Bowls Club project is dramatic: clean elegant design lines, combined with an undulating fabric line and soaring height creating an open expanse that has transformed the once exposed site into an iconic landmark within the region.
Our design engineer took into consideration the site orientation, prevailing weather direction and site location, 700 meters from the Pacific Ocean when completing structural analysis for the project.
The design wind criteria for the site is Region B, terrain category 2.5 recurrence interval 1/500 design wind speed 51.9mps (strength) in accordance with AS1170.2-2002. The geotechnical report showed that the site consisted of fill and sand. Site-specific foundations had to be developed to overcome the lack of bearing capacity of the site soil.
The site location beside a canal results in a high water table with maximum depth of foundations at 1.6 mts. Large pad foundations utilizing screw piles were designed specifically overcoming the site problems of fill, sand and high water table.
CFD software was used to assist with the design optimization of the fabric canopy. AS1170.2-2002 was used for determining Cp values for the ridge and valley fabric canopy profile.
The project site boundary is a busy aerial road with heavy environmental pollution. Ferrari 1002T2 was chosen due to the fabric’s self-cleaning properties, 15 year warranty, ease of installation and cost effectiveness.
All structural members are grade 350 steel coated with Dulux Weathermax paint system for corrosion protection.
The 3253 sqmt canopy was manufactured in four pieces. The canopy was patterned in accordance with the stretch percentages obtained from biaxial test results of fabric samples taken from the fabric rolls used for the project. Each of the canopies is attached to the perimeter beams and across a leaning arch. The designer had to consider the fabric canopy manufacture and installation when determining each one of the four canopy sizes and the weatherproof attachment method over the three leaning arch members.
To streamline the installation process folding plans were developed for each of the four canopies to ensure the correct method of folding in the fabricators factory. Detailed planning at this stage, assisted the fabric installers and minimized onsite handling of the each canopy.
On site the hold down bolts were installed to a tolerance of 5mm spanning the project site width of 42.8mts and length of 76 mts. The accuracy and positioning of the hold down bolts was achieved by engaging a site surveyor.
COLLABORATION, CONSTRUCTION AND MAINTENANCE
Timeline: A tight timeline governed the project; the client required the full facility to be ready for use by mid December 2011 to capture the Christmas and New Year trade.
Site access was limited therefore the project manager adhered to strict time line coordination of delivery of goods and the various contractors required on site.
During the design phase our designer maintained close co-ordination with the clients architect who was overseeing the future extensions and development of the Mooloolaba Bowls Club, clubhouse building.
To maintain optimum condition of the structural steel (vee columns, perimeter beam and leaning arches) our company has put in place a maintenance program. Completed in 2011 the Ferrari Fabric 1002T2 has performed well, as specified the fabric is self-cleaning during rain periods. There appears no reason to clean the fabric at this stage.
The structure was completed on time and on budget.
The contract was signed 6th June 2011.
Site installation work commenced 15th - 19th August 2011 for foundations.
Steel and Fabric installation from 29th September – 14th November 2011.
The design submitted in this application is a copyright design developed in response to the Mooloolaba Bowls Club tender in May 2011.