Why trench drains fail - Part 1
Trench drains are meant to be a long term investment that provides years of drainage service life. Unfortunately, all to often we see trench drain failures in a relatively short time period because the wrong products were installed. A properly designed trench drain will last for 25-50 years or longer. Poorly selected trench drains often fail in 2-5 years or even sooner.
We are going to start this series talking about the top edge of the trench drain. This edge receives traffic and is responsible for supporting the trench drain grate. This is one of the most overlooked parts of a trench drain. On the DuraTrench system this is called the frame, but with many systems this can be an integral part of the trench drain body. This frame is responsible for supporting the loading that the grating takes and transferring it to the surrounding concrete. If the material or design of this portion of the drain is not correct for the loading it cannot transfer this load to the surrounding concrete.
There are four factors that determine the load transfer ability of the trench drain frame: The frame material, the frame gauge or thickness, the bearing area, and the anchoring of the frame. Note that the frame must be sufficient in ALL of these categories to transfer the load. If any one of these areas is a weakness then the frame will fail and consequently the entire drain system will fail prematurely.
Let's start with the frame material. If the frame material can take the design load and not fail then it will pass this test. (Use this link to learn more about common load classes). Note that some materials such as plastics can initially take more load than later on in their life due to environmental decay. Sunlight and weather exposure tend to make plastics more brittle over time causing them to fracture easier as they age. Metals not properly protected can corrode over time causing them to lose their strength. Choose a material with proper compressive and tensile strengths and one that can handle the environment over time.
Next the frame thickness. No matter what the material, if the gauge is too think it will fail. The thinner the material the weaker and more flexible it becomes. You can choose a material with very high strength, but if it is not sufficiently thick it can still bend and or break. This is true of all materials including plastics and metals. Thickness typically costs money but will usually reduce lifetime costs.
Bearing area is the next trait that should be considered. Assuming the material has not failed and it is sufficiently thick to not bend or break then any loading will be transferred to the back side of the frame to the supporting concrete. If it is resting on a large enough area then the load will pass out of the system and into the surrounding concrete. This load transfer area is called the bearing area. The loading transferred on this bearing area cannot exceed the strength of the concrete.
Finally, the frame must stay firmly anchored into the concrete. With traffic moving over the frame there are torque and lateral loads that are placed on the frame. To resist these loads anchors are placed on the frame. The larger, longer, and thicker the anchors are the better equipped they are to handle larger dynamic loads. When a system does not have anchors the frame can come loose from the surrounding concrete and cause channel wall or concrete failures.
Before specifying or purchasing a trench drain system be sure to properly evaluate the frame to ensure it can transfer the loading to the surrounding concrete. If you do this you can expect a long life from the trench drain system's frame. Learn more about specifying trench drain components here!