In the commercial building industry, z-girts have been used for centuries. Applications include providing lateral support, resisting wind loads, and connecting structural framing to cladding. Due to the increasing concern for thermal efficiency along side 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 differing girts. The alternate z-shaped girt material available include fiber reinforced polymer (FRP) and composite metal hybrid (CMH). These three materials offer several differing structural advantages and disadvantages.
Traditional Steel 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:
- Higher modulus of flexibility compared to FRP
- 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’s exterior. Thermal bridging can cause an overall decreased efficiency, energy loss, increased energy costs, and condensation.
Generic FRP 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 as 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 to it’s 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. Furthermore, making FRP highly customizable with respect to its engineering properties.
Composite Metal Hybrid (CMH) Material
Using a continuous metal insert, 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 system maximizes beneficial properties of both steel and composite materials. Compared to FRP, CMH increases strength and stiffness by 9.5 times, is 2 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 the structural benefits of both steel and FRP material. It is a best practice solution to increasing the energy efficiency of a building and eliminating 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