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Prevent Over Jacking Girders Using load cells to measure force on beams Recent heavy snows in the Eastern United States will likely require many roofs in the region to be re-supported. Using load cells to measure force on beams in these applications may become more prevalent as engineers look to assure customers that roofs will support future snow loads. When jacking a beam to reinforce a concrete floor or roof structure, it's a common practice to use beam deflection measurements to determine if the beam has been installed properly. On a recent project, a steel erector was asked to apply 18,000 pounds of force to a large girder in order to deflect it 0.71 in. A discrepancy in engineered plans and actual field conditions emerged when the crew was unable to achieve even 0.5 in. deflection after maxing out 20-ton jacks. If force had continued to be applied to the beam, the beam could have become overstressed and damage to it or connections might have occurred. The engineer would not sign off on the project without proof that the beam had been jacked with 18,000 pounds of force. A simple tool provided a solution and prevented detrimental camber or worse. In agricultural applications, cotton bales and feed bags are often measured with strain gauges and load cells. That principle was applied here. By running a current through a piece of metal, resistance changes as the beam is stressed. That change in resistance can be measured to show how many pounds of force the load cell is experiencing. Using off-the-shelf parts, minimal tools, a little electrical ingenuity and an electronic load cell in line with the axis of the jacking, the steel erector was able to measure the force being applied to the beam, providing the information necessary to satisfy the engineer, contractor, and subcontractors, while preventing damage or injury. Best Practices • Depending on your application, use the right type of load cell. A variety of styles exist to measure different factors. • Follow manufacturer's directions for installation. • Use a load cell that has a certificate showing that it has been calibrated to NIST standards. • When choosing your jack, load cell and post members needs to be sized appropriately for the amount of force being applied.
Prevent Over Jacking Girders
Using load cells to measure force on beams Recent heavy snows in the Eastern United States will likely require many roofs in the region to be re-supported. Using load cells to measure force on beams in these applications may become more prevalent as engineers look to assure customers that roofs will support future snow loads. When jacking a beam to reinforce a concrete floor or roof structure, it's a common practice to use beam deflection measurements to determine if the beam has been installed properly. On a recent project, a steel erector was asked to apply 18,000 pounds of force to a large girder in order to deflect it 0.71 in. A discrepancy in engineered plans and actual field conditions emerged when the crew was unable to achieve even 0.5 in. deflection after maxing out 20-ton jacks. If force had continued to be applied to the beam, the beam could have become overstressed and damage to it or connections might have occurred. The engineer would not sign off on the project without proof that the beam had been jacked with 18,000 pounds of force. A simple tool provided a solution and prevented detrimental camber or worse. In agricultural applications, cotton bales and feed bags are often measured with strain gauges and load cells. That principle was applied here. By running a current through a piece of metal, resistance changes as the beam is stressed. That change in resistance can be measured to show how many pounds of force the load cell is experiencing. Using off-the-shelf parts, minimal tools, a little electrical ingenuity and an electronic load cell in line with the axis of the jacking, the steel erector was able to measure the force being applied to the beam, providing the information necessary to satisfy the engineer, contractor, and subcontractors, while preventing damage or injury. Best Practices • Depending on your application, use the right type of load cell. A variety of styles exist to measure different factors. • Follow manufacturer's directions for installation. • Use a load cell that has a certificate showing that it has been calibrated to NIST standards. • When choosing your jack, load cell and post members needs to be sized appropriately for the amount of force being applied.