Understanding Overhead Crane Deflection and Criteria
In general, the literal definition of deviation is "deviation from a specified route." This may mean that something has gone off track due to a U-turn or off-track. For bridge cranes, this definition is converted to the relative vertical or horizontal displacement of the components or parts of the bridge crane. So how does this affect the design of the crane, and how are the vertical and horizontal deflection calculated? Moreover, what are the differences in organizational norms between different cranes and different associations? Let us explain.
Vertical Deflection Standard The vertical deflection standard is the maximum (vertical) deflection ratio allowed by the lifting equipment. Vertical deflection is different from horizontal deflection, but closed-track bridge cranes take both into account. Vertical deflection will affect any part of the crane standing vertically, including masts, columns, walls, etc. Most systems are manufactured to approximate deflection because manufacturers cannot control standard variations in installation, foundation stiffness, or thickness tolerances of pipes, pipes, steel plates, and metal plates. This means that some changes above or below the deflection defined by the manufacturer should be considered normal. Having said that, when the bridge crane is installed in accordance with the standard installation manual and maintained in accordance with the manufacturer's installation and maintenance manual, you can ensure the safety of the elevator product and its ability to handle the selected rated capacity and performance standards.
When measuring the deflection of the safety standard, the deflection is measured at 100% capacity instead of 125% capacity. According to the ANSI standard (ANSI/ASME B30. Different types of cranes have different deflection values, depending on the total length, span or range of the crane. For workstation (closed track) bridge cranes, the vertical deflection value is less than that of heavier bridge cranes. The deflection limit of the closed-track workstation bridge crane is L/450. The letter "L" literally represents the length or span of the crane. In other words, to determine the deflection of your workstation bridge crane, you must first know its span or length. This equation is always in inches. That's because if your deflection is higher than the measured value in inches, then you are in big trouble. The deflection should be small. To measure deflection, use the deflection limit defined for that type of crane and divide that number by the length (or span) of the specific system. If your bridge is 34 feet long, you will divide by the manufacturer-defined deflection limit (L/450 for workstation overhead cranes). The deflection of the 34-foot bridge on the workstation bridge crane can be determined by first changing the unit of measurement from feet to inches. A 34-foot bridge is 408 inches long (feet x 12 = inches). Divide 408 inches by the specified deflection limit (L/450) of the enclosed overhead crane. This will make your deflection less than one inch (0.9 inches). Use the same method to determine the deflection of other overhead crane systems. The standards are the same, but the terminology and deflection limits vary from system to system. For example, when determining the deflection of a work station (closed track) bridge crane, we will use the deflection limit of L/450, as described above. However, when determining the deflection of the gantry crane, the deflection of the steel gantry is limited to L/600, and the deflection of the aluminum gantry is limited to L/450. Compared with aluminum, steel almost always has a slightly higher deflection limit because of its rigidity.
To determine the deflection of an all-steel gantry with a span (beam length) of 25 feet, you will follow the same formula we used to determine the deflection of a workstation bridge crane, using only the deflection limits of a steel gantry crane. To do this, we must first change the unit of measurement to inches. A span of 25 feet (multiplied by 12) is 300 inches. Next, we will determine the deflection by dividing the gantry span (in inches) by the deflection limit specified by the manufacturer. For Spanco, this number is, as mentioned above, L/600. A gantry crane with a span of 300 inches has a half inch (0.5 inch) of deflection. In order to determine the deflection of the jib crane, the formula remains the same, but the terminology may vary from system to system, and the deflection limits are again different. Some manufacturers refer to the length or span of the jib as the "range." This is why you may see the deflection limit of jib cranes using the letter "R" instead of the letter "L". It depends on your manufacturer. However, to determine your deflection, remember that "R" only stands for "arrival" and "L" stands for "length". In this case, it doesn't matter whether it refers to range, span, or length. The deflection equation remains unchanged. When determining the deflection of a cantilever crane, the type of cantilever in question is also an important factor. At Spanco, we have five different jib crane series, each with several installation types that affect deflection limits. For example, the deflection limit of our 100 series free-standing jib crane is L/150 (also known as R/150). This figure is the same as our 200 series mast jib cranes and 300 series wall-mounted jib cranes. However, the deflection limit of our 400 series articulated jib crane is L/200 (or R/200), while the deflection limit of our 500 series workstation cantilever crane is L/150 or L/225, depending on the crane’s deflection limit. Run mode installation. For stand-alone workstation jib cranes, there is a lower deflection limit. But for our 501 series wall-mounted cantilever workstation cantilever crane, due to its wall-mounted type, we use a higher deflection limit L/225. For the 501 series wall-mounted workstation cantilever crane, the deflection of the 12-foot span crane can be calculated similarly to the above system. First, we need to change the unit of measurement to inches. In this case, a span (or range) of 12 feet is equivalent to 144 inches.
If we divide 144 inches by the deflection limit of 225, we get a deflection slightly greater than half an inch (0.64 inch). Horizontal deflection standard The horizontal deflection standard is the maximum deflection ratio allowed by the bridge crane or runway. Unlike vertical deflection, horizontal deflection affects crane components that run horizontally. The closed track system takes this into consideration, including workstation bridge cranes and workstation booms. The maximum lateral deflection of runways and cranes designed by most manufacturers is L/400. In this case, "L" refers to the span of the bridge crane from the runway support center. Divide this number by the deflection limit of 400. For example, to determine the deflection of a ceiling-mounted workstation bridge crane with a bridge length of 40 feet, we must first convert the unit of measurement to inches. A span of 40 feet is equivalent to 480 inches. If you divide 480 inches by the specified deflection limit of 400, the horizontal deflection for that particular crane is 1.2 inches. Rigidity requirements It is important for manufacturers to comply with theoretical considerations and perform various checks on their systems, such as stress analysis and horizontal and vertical deflection analysis of bridges, beams, masts, columns and other components. These systems should prove to be in line with the theory, and their static structural response must maintain the response of the original crane structure to pass these tests. According to the rigidity requirements stipulated by OSHA and ANSI, the following maximum crane beam deflection is usually not exceeded to avoid adverse dynamic effects and ensure the function of the crane: Vertical deflection is defined as the maximum allowable value of the deflection ratio allowed by the hoisting device. For bridge cranes, this value is usually L/700.
For workstation bridge cranes, this value is small (L/450) because the enclosed track is lighter. The horizontal deflection is the maximum deflection ratio allowed by the bridge crane or runway. For ordinary bridge cranes, the value is usually L/600. For workstation bridge cranes, the value is small (L/400). In the absence of more detailed calculations, it is acceptable to assume that the top flange resists the entire horizontal force. The rigidity requirement for horizontal deflection is essential to prevent the crane from slanting. Vertical deflection is usually limited to a value not greater than 25 mm to prevent excessive vibration caused by crane operation and crane travel. Test requirements According to OSHA and ASME, crane load testing is usually specified as 125% of the crane's rated capacity. However, neither of these two standards specify acceptable tolerances for numbers above or below 125%. ASME B30.2 actually refers to a number in its interpretation of the load test, which indicates that the tolerance of the test load weight is 0%/-4%. In practice, this indicates that the weight of the test load is between 120% and 125% of the rated crane capacity (ie: 125% -125% x 0.04 = 120%).
In addition, any bridge crane that has undergone major modifications or installed after January 1999 must undergo a load test before being put into use. The deflection test defined by OSHA and ASME recommends that the deflection of the structure must be measured under a load of 100% of the rated capacity and must not exceed the allowable deflection specified by the applicable design standard (deflection limit, as listed above). OSHA and ASME also stipulate that during these load tests, the load must pass the full length of the bridge and tramway, and only runway components that successfully pass the load test can be put into use. If you have any questions about the deflection or deflection limits outlined in this blog, please feel free to leave a comment below. To ensure that your deflection value is calculated correctly,