If you work as a maintenance engineer in the mining sector in Saskatchewan, then you’ve likely utilized existing structural steel to hoist milling equipment such as pumps, motors, or even mill drums. The lifting anchor points are often weld-on lugs or beam clamps connected to overhead structural steel, and lift is provided by one or a series of manual chain hoists. I understand these sorts of operations occur frequently. I’m writing on this topic to discuss the technical calculations and precautions that should be performed prior to executing these sorts of lifts in the field.
First, one must understand the dead, live and other loads that may be acting on beams. The majority of mill structural steel has reserve moment and shear capacity. Further, the loads on beams may be reduced with clever control of live loads during the time structural steel will be utilized for the lift. When the two factors are considered one may be able to lift thousands of kilograms from a single beam with little or no modification to the structural steel.
It’s important to verify the structural steel grade or yield strength to determine its capacity. For newer structural steel the material grade is often noted on the drawings, but for older steel without good data it would be wise to assume 230MPa yield strength. Also, anything pre-1930 has a good probability of having high carbon content and should not be used for hoisting because of the brittle nature of these older beams.
If you’re using a single point to lift from then you’ll likely be inducing torsion on the beam. If the load is not straight vertical or if the load is eccentric from the beam’s shear centre (for W and S shapes the shear centre is in the same location as the centroid, or dead centre of the beam), then the torsion should be accounted for. For a full and in-depth torsion analysis of open sections (such as W or S shapes) you should consult AISC’s design guide 9. The guide provides a simplified approach that I’ve found quite useful. Effectively, the method includes resolving the eccentric force into two component forces acting through the shear centre and a moment. The moment and lateral force components are resolved into lateral forces acting on each flange. Flange moment is calculated based on distance from the restraint and magnitude of the force. Remember that flange moment or stress may be superimposed on other normal stresses or moments acting through the flange. Another consideration is to ensure there is adequate restraint in the flanges. This may include connecting the most highly loaded flange or both as there is little resistance in beams with typical shear connections. I’ve included a figure below to better illustrate the method.
I hope you’ve found this post useful. If you have any further questions or if there’s a specific problem that you might need help with then please feel free to contact me at firstname.lastname@example.org. We’re always happy to help and look forward to discussing your project with you.
Liability disclaimer: As with all engineering work, if you’re not competent in an area of practice then you should consult a competent professional engineer prior to proceeding with the work.
Kova is an engineering and inspection services provider. We’re local to Saskatchewan with offices in Saskatoon and Regina, and operate in Saskatchewan’s largest economic sectors including mining, oil and gas, forestry, agriculture, construction and fabrication. We specialize in safety, lifting, and industrial equipment design. We pride ourselves in knowing there is no problem that is too technically challenging for us as our expertise and long-term employees are second to none. We provide services in a very timely fashion with personalized service. Our in-house inspection services allow for a complete quality assurance scope for our projects. Kova has permit to practice in nearly all Canadian provinces.
Paul Caughlin, P.Eng., M. Eng., Engineering Manager