CICA Tech Corner The CICA technical committee highlights changes to wind load calculations

CICA WIND GUIDANCE NOTE REVISION

The CICA Technical Committee explains recent changes to wind load calculations.

MOBILE CRANE OPERATIONS ARE SUBJECT

to wind speed limitations during lifting, erection, dismantling, and also when outof-service. Excessive wind forces acting on loads and cranes have led to several serious accidents around the world. If not controlled properly, wind can be a major risk for crane operations.

To provide assistance to mobile crane users, the CICA technical committee developed a guidance note on wind load calculation, six years ago. This guidance note covered the manufacturer’s permissible wind surface area, the calculation of the dynamic wind pressure and the permissible wind speed. Following the calculations in the guidance note, wind effects can be assessed to determine reduced permissible wind speeds based on load surface area in accordance with load charts.

For example: • If the wind surface area of a load is less than the total allowable wind surface area (specified by the crane manufacturer) multiplied by the chart capacity, no further calculations need to be made. • If the wind surface area of a load is greater than total allowable wind surface area, further calculations need to be made to determine the permissible wind speed.

Wind speed on site should be measured and compared with the load chart wind speed or the calculated permissible wind speed, to see if it is safe to operate the crane under the site condition. (It should be noted that the wind speed can vary between ground level and the boom tip or load height. guidance on wind load calculation has The use of anemometers attached to the hoisted load (mass of the load and a pendulum arrangement on a boom the hook) should be used to calculate tip, can be an excellent means to assess the allowable wind surface area. To the conditions.) provide guidance for the Australian crane

When the CICA technical committee industry with the latest industry practice, developed the guidance note six years the CICA technical committee have ago, it was recommended by the decided to revise the CICA wind guidance manufacturers and the industry that note to reflect this change. the crane load chart capacity be used This revision of the guidance note is to calculate the allowable wind surface underway, and we expect to finalise the area, so for that reason, the calculation updated guidance in two months’ time. The CICA technical committee If not controlled properly, wind can be a is currently working with major risk for crane operations. the crane manufacturers to obtain their support for the new guidance. Manufacturer’s recommendations on wind load calculation will be attached in the appendix for reference and CICA are also evaluating the international guidance on this topic, to capture the best industry practices. Calculating wind load impact on crane operation can be complicated and for special cases, the lift designer should seek manufacturer’s instruction on wind load calculation as the crane manufacturers have a better knowledge of the crane limits. formulas used in the guidance note are the new guidance will also consider all based on crane load chart capacity. practices on site for the dogger/rigger

Most of the CICA technical who are controlling the load, for example committee members are heavy lift - topics on tag lines, recommendations planners themselves and they have on assessing forces and rotational effects noticed that over the past few years, acting on a load and load controlling the practice recommended by the crane skills for different load cases will manufacturers and some international be discussed. Other than the calculations, changed. Instead of using the crane Once completed, the guidance note will be chart capacity for the allowable wind available to CICA members, please contact surface area calculation, it is now widely Alice Edwards (projeng@cica.com.au) if you adopted by the crane manufacturers that would like a copy.