Our company has over 45 years of experience in engineering of steel structures and we have installed buildings around the world. Our superior engineering ensures our customers’ complete satisfaction and the durability of their structures.
The MegaDome truss arches are made from oval tubing, stronger than round tubing. It also provides a wide, flat surface for superior welding and a stronger assembly. Straight bracing joins the top and bottom chord for unparalleled strength.
The bronze-silicon welding we use on our pre-galvanized buildings combines good welding performance and corrosion resistance, without the need to apply zinc paint. The corrosion protection of MegaDome is complete.
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MegaDome Steel Structure

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Steel specifications

Our MegaDome philosophy is to only use high quality structural steel, originating from North American mills. This material must meet and/or exceed our rigid standards, as specified at the time of purchase, in terms of mechanical and chemical properties. This philosophy differs greatly from other manufacturers who elect to use cheaper “commercial steel” which possesses quality characteristics which vary greatly from one lot to the next. In contrast, the consistent quality of the steel used for our MegaDome structures allows our engineers to accurately predict how our designs will react to real world applications, thus ensuring that our buildings meet and exceed the highest standards. The following table outlines the main differences between structural and commercial steel:

  Structural steel Commercial steel
Yield Minimum of 50,000 psi Between 33,000 and 60,000 psi (with no guaranteed consitency from lot to lot)
Steel chemistry Fixed and validated with mill tests for each tube Variable and not validated
Subjected to a quality standard? Yes No
Enables enigneers to accurately predit steel reactions under wind and snow loads? Yes No
  • North American specs

The steel used for our North American customers is high strength, low alloy, structural steel and meets the minimum structural and mechanical properties of ASTM A-500 GR B. It has an ultimate tensile strength of 380 mpa, and a yield strength of 345 mpa.

All of our steel must be new (not recycled), and of minimum Grade 300W, in accordance to CAN/CSA G40.20 and CAN/CSA G40.21 standards.

 


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Galvanization specifications

MegaDome offers two types of galvanization treatments. The choice of treatments will be determined by the projected application for the building, and the level of corrosion protection requested by the client. By definition, all galvanization processes are of the hot dip type. It is important to remember that simply asking for hot dip galvanization will not ensure clients get the protection they require.

Types of galvanization treatments offered by MegaDome:

Pre-galvanized steel

In this instance, the galvanization treatment occurs at the time the tube is roll-formed during production. Referred to as “in-line galvanization” or “pre-galvanization”, this treatment is applied BEFORE any transformation occurs to the tubing. A steel plate goes through a hot molten zinc bath before it is formed and welded into a long, uniform tube. These tubes are then cut and welded at our manufacturing facility to become key components for the next MegaDome building. Welding on MegaDome’s steel frame is of the silicon-bronze type, in order to preserve the pre-galvanization’s corrosion protection properties.

MegaDome pre-galvanized truss
Figure 1 MegaDome pre-galvanized truss arch with silicon-bronze welding

MegaDome uses three different types of pre-galvanized tubing for the components of its structures.

  • Galvalume

Galvalume is steel covered with a zinc-aluminium alloy (45% zinc, 55% aluminium) coating. Weight of the galvanization finish is 150 g/m², or the equivalent of 0.50 oz/foot² (total for both sides). The Galvalume treatment is applied to both sides of the cold formed steel and applied with a precise, hot dipped galvanization process, in accordance to the ASTM A792/A792M-97a Steel Sheet, 55% Aluminum-Zinc Alloy-Coated Hot-Dip Process. A clear protective coating is applied after the treatment to help preserve the finish.

Galvalume has demonstrated a superior resistance to corrosion compared to regular galvanized steel. It is the product favoured by MegaDome for all critical steel components.

  • Gatorshield

Gatorshield steel is only used for MegaDome’s 100 series buildings manufactured with 3’’ X 5 5/16‘’ oval tubing. Its three-layer protection makes it the ultimate choice for superior corrosion protection.

1. Organic clear coat
2. Conversion zinc coat
3. 99,99% pure zinc coat

  • Z600

The protection offered by the Z600 hot dip galvanization process is directly related to the thickness of the zinc coating which is applied. MegaDome only uses the highest caliber treatments, such as the Z600, which provides 600 grams of zinc (minimum) per square meter of corrosion protection. The vast majority of commercially available galvanized tubing typically contains between 90 to 450 grams of zinc.

Corrosion resistance of pre-galvanized steel

Extensive independent testing has been performed to demonstrate the corrosion resistance of our pre-galvanized steel. These lab tests are completed under strict control, using standardized methods. The steel samples are subjected to a salt spray which reproduces, in a controlled and intensive way, the natural progression of red rust on steel.

The following graph shows the number of hours steel samples spent under salt spray conditions before showing the first signs of red rust. Commonly available pre-galvanized steel samples were used for these comparisons.

tableau signesrouille

 

Hot Dip galvanization

In corrosive environments, we highly recommend a hot dip galvanization process, which is applied after welding, to offer complete protection. Since the finished components are completely immersed in a zinc solution, the treatment covers all surfaces, inside and out. Stainless steel hardware can also be supplied to ensure maximum corrosion protection.

Figure2 ArcheMegaDome
Figure 2 MegaDome Hot Dip galvanized (after welding) truss arch

The hot dip galvanization process is performed by Corbec (Montreal), in accordance with the following standards: CSA G164M-92, ASTM A-123, ASTM A-153. Each of MegaDome’s ® steel components are submerged in a boiling zinc solution, guaranteed to provide a minimum of 4 ml of 99.9% pure zinc coverage.


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Truss design

Oval tubing
The MegaDome truss arch is formed by two oval tubes joined by straight bracing. This design offers several advantages :

  • By welding the bracing onto the larger flat surface of the oval tube, the design benefits from a wider contact area over similar welding over a round tube. By selecting the oval tubing, MegaDome can provide superior welding quality and a more solid assembly. Once the fusion between the two components is complete, the welds are much stronger and safer.
  • The oval tubing design allows for superior engineering:
    • Because of its geometry, oval tubes can resist higher compression/flexion forces. According to the CSA S16-09 - Design of steel structures standard, the oval will be able to go into the plastic limits (Class 1 or 2), whereas the equivalent square or rectangular tubing will remain in the elastic limit (Class 3). In summary, manufacturers using round or rectangular (square) tubing for their buildings will need to use more steel than MegaDome to achieve the same wind and snow load specifications.
    • The oval tubing which is used in MegaDome buildings offers a large, smooth surface over which the membrane is tensioned. There are no sharp edges to create stress points on the membrane, thereby eliminating premature wear and contributing to the increased longevity of MegaDome’s membrane.

Straight truss bracing
To join the top and bottom chord of its trusses, MegaDome uses straight bracing made from square or rectangular tubing. Each brace is individually welded onto the flat surface of the oval tube.

  • Using straight bracing is far superior to bent bracing, and contributes to making our trusses stronger. We use straight bracing rather than the bent alternative because each bend creates a weak point in the tube’s overall strength.

Truss section’s end channels
MegaDome uses end channels to cap each section of the truss arch. These channels are designed to connect up to 5 truss sections to create one building arch. Each section is joined to the other using Grade 5 bolts.

The channel design offers several advantages over connections found on other structures.

  • Made from steel plate and u-shaped, the geometry adds to the truss’s overall strength and rigidity.
  • All contact points between the channel and truss sections are welded, contributing to added strength.
  • Capping the end of each truss section solidifies the truss assembly.

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Bracing

MegaDome uses a variety of bracing methods throughout our buildings. We refuse to compromise on quality, and apply the following principles to our designs:

  • When tubes are used as bracing, we limit the length in order to ensure that rigidity and strength is retained when the structure is subjected to compression forces;
  • The membrane which covers our structures is never used as bracing, as is the case for structures using the Keder system. Our MegaDome buildings are engineered and designed to ensure that structural integrity is maintained should damage occur to the membrane.
  • The top and bottom chords of our trusses are braced separately, which solidifies the strength of the building, and provides added resistance to the loads for which it was designed.
  • Whenever MegaDome uses cables, they only act as a retaining device. They are not used to solidify the building but rather are there as an added security feature when the structure is subjected to the loads that it was designed to resist.

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