In the commercial building industry, Z-girts have been used for centuries. Applications include providing lateral support, resisting wind and dead loads, and connecting structural framing to cladding. Due to the increased concern for thermal efficiency along with advancements in technology and design, we have seen several changes to the materials used in Z-shaped girts.
In addition to traditional steel Z-girts, there are two additional types of girts. The alternate Z-shaped girt material available includes fiber-reinforced polymer (FRP) and composite metal hybrid (CMH). These three materials offer several differing structural advantages and disadvantages.
Traditional Steel Z-Girt Material
Structural steel design practices are routinely done using established uniform codes across the United States and the world. Steel materials have properties that are the same independent of the direction considered. Some advantages of steel structural components are:
- High modulus of elasticity compared to FRP (more resistance to deflection)
- Easier and faster connection using fasteners with durable, large loads
- Better durability, torque retention and pull-out loads when using screws compared to fastening to FRP
However, steel is not thermally efficient and can create a thermal bridge through a building envelope. Thermal bridging can cause an overall decreased efficiency, energy loss, increased energy costs, and condensation.
Generic FRP Z-Girt Material
Fiber-reinforced polymer (FRP) composite design is dependent on manufacturer recommendations. These vary tremendously as different approaches and design methods are adopted by different manufacturers. Such status of FRP design practices is not favorable for advancing the successful use of FRP. This is due to variations in the design practice methods used.
FRP is significantly different from steel, as its materials are, in general, orthotropic, meaning that their engineering properties are different in each of the three space directions (x,y,z). The properties depend on the direction considered and primarily on the amount of glass fibers oriented along the direction under consideration. This makes the analysis of FRP more involved.
The list of what makes FRP complex is dynamic. This is, in part, due to its ability to be customized using different resins, fibers, fillers, color pigments, and the proportions thereof. Each combination of these constituents will compose a different material with unique properties. This makes FRP highly customizable with respect to its engineering properties, providing an increase in flexibility but a more difficult material to structurally analyze.
Composite Metal Hybrid (CMH) Z-Girt Material
Using continuous metal inserts, located in the FRP flange of the cross-linked thermoset Z-profile, the GreenGirt Z-girt leverages a composite metal hybrid (CMH) material selection. This CMH product maximizes beneficial properties of both steel and composite materials. Compared to FRP, CMH increases strength and stiffness by 9.5 times, is typically at least two times better in fastener pull-out, and has greater durability and torque retention.
If proper fasteners are used, CMH material acts as an insulator or barrier, preventing thermal energy from passing through. This can be achieved while still utilizing the advantage and structural benefits of its continuous metal inserts. The GreenGirt Z-girts provide the structural benefits of both steel and FRP material. It is a best practice solution to increase the energy efficiency of a building and eliminate the possibility of thermal bridging because of the material’s unique properties, innovative design, and ease of installation.
|Lighter weight*||Lower transportation costs and faster installation|
|High strength to weight ratio||Structural capacity|
|Higher modulus of elasticity**||Withstands greater stress|
|Improved fastener retention**||Building life product that lasts without fastener pull-through or torque loss|
|Manufacturing process*||Customizable pultrusion process does not depend on natural resource availability|
|Eliminates thermal bridging||Increased thermal efficiency and decreased energy costs|
*compared to steel, **compared to FRP
The choice of Z-girt material comes down to the specific needs and requirements of your project. Steel Z-girts provide a great deal of strength and durability, but do not offer the thermal efficiency benefits of FRP or CMH. FRP Z-girts are lightweight and are corrosion resistant but may not have the same level of strength as steel or CMH. CMH Z-girts provide a good balance between strength, corrosion resistance, and thermal efficiency, making GreenGirt CMH a best practice solution. Ultimately, the pros and cons of each material should be carefully considered.
Contacting an A2P Representative for more information about GreenGirt CMH or SMARTci continuous insulation systems is an excellent way to get the facts you need to make an informed decision. A2P Representatives are knowledgeable and experienced in Z-girt materials and can help answer any questions you may have.
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