In a perfect world, every roof would only need to support a uniform layer of light snow or a standard metal deck. In the real world of industrial and commercial architecture, however, roof systems are subjected to a chaotic array of “complex loads.” From heavy HVAC units to the unpredictable accumulation of snow, the engineering team at COMSA Steel specializes in designing joists that go beyond the standard load tables to handle these specific architectural challenges.
Modern buildings are machines, and those machines often sit on the roof. Large HVAC units, industrial fans, and refrigeration compressors represent “concentrated point loads.”
If a 5,000-pound AC unit is placed randomly on a standard joist, it can cause local buckling of the chord or failure of a web member. At COMSA Steel, we utilize “header” systems or reinforced “super-joists” to distribute these loads. By knowing the exact “curb” weight and dimensions of your equipment during the design phase, our engineers can reinforce the specific panel points of the joists to ensure the load is transferred safely to the primary framing.
In many climates, the wind doesn’t distribute snow evenly; it blows it against parapet walls or higher roof elevations, creating “drifts.” These drifts can create a load that is three to four times heavier than the “ground snow load” specified in local building codes.
Similarly, if a roof is not perfectly sloped, “rain ponding” can occur. As water accumulates, the joist deflects; as the joist deflects, it holds more water, creating a dangerous cycle of increasing weight.
Industrial facilities often require “collateral loads”—additional weight hanging from the bottom chords of the joists. This includes:
When you specify these requirements to COMSA Steel, we don’t just “guess” the capacity. We engineer the bottom chords with extra tension capacity to ensure that your facility remains flexible for future equipment upgrades without needing expensive structural retrofits.
Sometimes the greatest threat to a roof isn’t weight pushing down—it’s wind pulling up. During a storm, high-velocity winds create a vacuum effect on the roof. Because joists are primarily designed for downward compression, “uplift” can cause the bottom chord (usually a tension member) to suddenly go into compression and buckle. COMSA Steel engineers provide “uplift bridging” and specialized seat attachments to “tie” the building down, ensuring the roof stays attached even in hurricane-force winds.
To handle these complex scenarios, we utilize 3D structural analysis software. This allows us to “stress test” the joist virtually before a single piece of steel is cut. By simulating the exact placement of equipment and the most severe weather patterns, we ensure that every COMSA Steel component is a custom-fit solution for your specific site conditions.
