Sandwich wall panel use in the United States dates to the 1960s when the use of precast/prestressed concrete became commercially available throughout the country. Initial panel designs were non-composite that used a thick structural wythe and a thinner architectural wythe. The structural wythe was sometimes hollow-core slabs, double tees, or single tees.
Initial composite panels utilized solid areas of concrete to create the stiffness for the load transfer. These solid zones created issues with thermal bridging between the inner and outer wythes. With the advent of new wythe connectors, the solid zones were able to be eliminated while allowing for thinner flat wythes on both sides of the insulation. In the late 1980s, non-composite wall panels were developed using non-metallic ties. These ties significantly increased the thermal efficiency of the sandwich wall panel but utilized a non-composite design, which has significant downsides to project costs and logistics. Carbon-fiber grid was introduced into the sandwich panel market in 2003, by a national partnership of several leading precast concrete manufacturers to provide the first fully composite sandwich wall panel that still meets, or exceeds, today’s ASHRAE 90.1 standard. Figure 2 shows a typical section for a fully composite carbon-fiber wythe connection system.
When beginning to design a composite sandwich wall panel, there are several key criteria that should be considered, including:
Fully composite sandwich wall panel designs have a wide range of aesthetic capabilities, from a basic as-cast gray concrete finish, to embedded terra cotta panels, to digital imaged patterns using technologies such as graphic concrete which allows digitally printed images to be transferred into panel surfaces using high-resolution retarder images. Figure 3 shows the level of detail available using graphic-concrete technology. From the composite perspective, with a focus on weight, it is important to consider any variances in wythe thickness due to reveals or form liner that may impact the structural capacity of the section and may require thickening, or added weight, to meet the structural requirements.
R-value requirements of building façades have continued to increase since the first significant code change in 1986 due to the impacts of the United States oil embargo. Since then, thermal efficiency criteria have continued to increase as awareness around the impacts of energy consumption increases. The latest developments in ASHRAE 90.1, including continuous insulation or edge-to-edge insulation, and a variety of climate zone criteria are easily navigated via the wide range of design options using a carbon-fiber-reinforced fully composite sandwich panel design.
In composite sandwich wall panels, using more insulation can result in the reduction of panel weight, environmental impact, and reduced manufacturing costs through labor. Due to these factors, many precasters prefer to use an expanded polystyrene (EPS) insulation, which has an approximate R-value of four per in. of thickness. Table 1 outlines multiple insulation types, with an incremental insulation thickness to provide an R-16 sandwich panel. The increasing thickness of insulation in a lower-R-value product offsets concrete use in a fully composite sandwich panel design. A typical data-center panel that would be 30 ft. tall by 10 ft. wide, or 300 sq. ft., could recognize a reduction of panel weight of 3,875 lb using EPS in lieu of polyisocyanurate (polyiso) when maintaining the same overall panel thickness. In a 600-panel project, that adds up to a total weight reduction of 2.9 million pounds of concrete.
Reductions in worker hours are also recognized using EPS foam in lieu of XPS or polyiso, as the beaded surface of the foam and carbon-
fiber-grid wythe connectors provide the necessary shear transfer for composite design. XPS designs require the surface of the insulation to be roughened and often require an increased quantity of carbon-fiber wythe connectors. Figure 4 demonstrates manually roughened XPS insulation with carbon grid, and Figure 5 is standard “non-roughened” EPS foam being installed.
If you have any questions on sandwich panel house. We will give the professional answers to your questions.
For more information plastic litter bin manufacturer, please get in touch with us!