ALGOR FEA AND MECHANICAL EVENT SIMULATION SOFTWARE HELPS TO IMPROVE PRODUCT COMPETITIVENESS AND REDUCE MANUFACTURING COSTS

Engineers at West Coast Engineering, Ltd. (WCE), Canada抯 largest steel and aluminum pole manufacturer, optimized the design of two types of transmission poles and components using Finite Element Analysis and Mechanical Event Simulation software from ALGOR, Inc. The poles were part of a 138kV-transmission line, shown here, which was installed by engineering consulting firm Ian Hayward International, Ltd. for an Alberta-based chemical company.

Transmission poles, such as those seen along most urban freeways, often seem to be immovable by the forces of wind, ice and the pure weight of power or telecommunication lines. Manufacturers like West Coast Engineering Group (WCE), British Columbia, Canada, design all types of poles to withstand these predictable sources of loading as well as unpredictable sources, like the impact of a vehicle at a pole抯 base.

Not only are the structures seemingly immovable, they also can be massive, measuring up to several meters in diameter and rising dozens of meters above the landscape. Conducting physical prototype tests to verify the designs of such large structures can be time consuming and expensive. To eliminate these costs, shorten times-to-market and improve the overall quality of the designs, engineers at WCE, Canada抯 largest aluminum and steel pole manufacturer, rely on Finite Element Analysis (FEA) and Mechanical Event Simulation (MES) software from ALGOR, Inc., based in Pittsburgh, Pennsylvania, USA.

Recently, WCE designed and manufactured poles for a 138kV-transmission line, which was installed by engineering consulting firm Ian Hayward International, Ltd., Vancouver, Canada, for an Alberta-based chemical company. WCE Senior Design Engineer Ioan Giosan conducted ALGOR structural analyses on two types of transmission poles, base plates and phase connections to assess the stress distribution and deformation under extreme loading conditions. Then he expanded his study to include a dynamic impact MES of a head-on vehicle collision with a transmission pole. By incorporating ALGOR FEA into his design process, Giosan reduced the prototype testing needed and eliminated a costly, unnecessary manufacturing process. WCE was able to pass these savings on to its clients.

Measuring Up to Design Standards
WCE manufactures tubular, multi-sided and tapered structures for applications, such as light poles, highway signage, telecommunications antennas, ornamental poles and transmission/distribution structures, according to General Manager Ted Brockman, who oversaw the engineering and manufacturing for the Ian Hayward International, Ltd. project.

"This project required poles to support transmission lines from the chemical company抯 co-generator power plant to the nearby electricity grid of a power company," explains Brockman. "West Coast Engineering designed the poles based on the loadings provided by Ian Hayward International, Ltd. The finite element method was used to optimize the insulator attachment bracket and the pole base plate. A buckling finite element analysis with ALGOR software was done to check the pole shaft for buckling."

The project required two types of transmission poles, dead end and tangent. Each pole type used for the project was tapered and 12-sided; however, the placement, phase connection points and dimensions differ. Dead end poles are used either at the termination or at a right angle bend of a transmission line, which is then fastened to the pole at insulator connector points. The dead end poles measure 1.04m in diameter at the base and .320m at the top, stand 25.5m tall and weigh 5647kg (including the base plate).

Tangent pole structures, used when the line is running straight, feature insulator brackets set perpendicular to the pole. The tangent poles have a 0.68m base diameter and a .30mm top diameter, stand 25.5m tall and weigh 2145 kg (including the base plate). The dead end pole required a larger diameter to handle the higher loads associated with its position at the end or corner of the transmission line.

Giosan began his structural analyses by analyzing both pole shafts under ultimate loading, which was calculated by Ian Hayward International, Ltd. using standard industry calculations. Giosan modeled the basic pole shafts using 3-D plate elements in Superdraw III, ALGOR抯 single user interface for FEA and precision finite element model-building tool. Then he supplied the necessary plate element data, including plate thickness, for the models. Giosan specified the material properties for G40.21-450WT steel, which were obtained from the steel manufacturer.

For the tangent pole, static forces in the X and Z directions were applied at the ends of eight simplified insulator brackets to represent both the weight of the lines and dynamic loading due to wind and ice. For the dead end structure, Giosan applied static forces in the X and Y directions where the insulator connectors would have been attached. Giosan fully fixed the models at the base where the pole shaft and base plate meet.

"I was concerned about the performance of the pole shafts under ultimate loading for this analysis," Giosan says. "I conducted many more detailed analyses of the connectors and base plates after I confirmed that the basic structure would adequately handle the required loading."

WCE Senior Design Engineer Ioan Giosan performed ALGOR structural analyses on the tangent and dead end pole shafts to determine the stresses and deformation under ultimate loading conditions, which were determined by Ian Hayward International. The results of the tangent pole analysis are shown here. Overall, the pole shafts performed well under the loading. Maximum stresses occurred several inches above the base of the shaft, which Giosan attributes to the presence of a stronger weld connection at the base.

Giosan performed linear static stress analyses on the models and used the von Mises stress criteria for ductile materials to assess the stress results in Superview, ALGOR抯 built-in visualization program.

"The analysis results matched very closely with our calculations performed using conventional design methods," Giosan says. "The maximum stresses were located on the pole shafts slightly above the welded connections between the base plates and shafts for the models. We expected this due to the added strength of the welded connection. The maximum stresses were within the allowable range for the materials used."

Next, Giosan performed detailed structural analyses of the base plates with welded connections to the shafts. Not only did these analyses confirm that the base plate designs were adequate, they also dispelled a theory that plates with drilled anchor bolt holes are stronger than plates with flame-cut holes.

Eliminating a Costly Manufacturing Process
WCE manufactures all of its base plates using a flame-cut process, in which an intense flame shapes the outside of the base plate and burns a large hole into the center of the steel plate. At this point, the process can be continued to burn the anchor bolt holes or the plates can be drilled in a separate process, according to Brockman. Small slots are created from the outside edge of the plate inward to each hole when the flame-cut process is used. When the holes are drilled, no material is lost outside the circumference of the holes.

"In the past, it was widely believed that using the flame-cut process for the bolt holes would weaken the overall base plate structure." explains Brockman. "Ioan was able to disprove this theory by performing FEA with ALGOR. By flame-cutting both the base plates and the bolt holes, we were able to shorten the manufacturing processes for the Ian Hayward International installation and for many other orders."

Giosan created solid models of the dead end base plate with both flame-cut and drilled holes using AutoCAD 14. The models also included 1m sections of the shaft with the welded connections. He transferred the model geometry to ALGOR via IGES files where he created solid FEA meshes made of eight-node brick elements. Solid brick FEA meshes are often more uniform, more accurate and contain fewer elements than solid FEA meshes comprised of tetrahedra. Giosan applied ultimate loading in the Y and Z directions to the tops of the shaft sections. He constrained the models at the circumference of each of the 12 anchor bolt holes.

ALGOR linear static stress analyses were conducted to compare the structural integrity of base plates having drilled anchor bolt holes with those featuring flame-cut bolt holes. When the holes are flame cut, small slots are created from the outside edge of the plate inward to each hole. This was thought to decrease the overall strength of the plate. The ALGOR analyses revealed no significant difference in von Mises stress values (see insets); therefore, WCE was able to eliminate the drilling process and reduce the time and cost of manufacturing the base plates.

Giosan reviewed the von Mises stress results for both models and found no significant differences in the stress levels or deformation between the drilled and flame-cut holes. The maximum stresses appeared at approximately the same area of the shaft as the previous ultimate loading analyses. In addition, the stresses did not exceed the yield stress of the material; therefore, the thickness of the plate was adequate. Based on these analysis results, Giosan conducted a similar analysis on a base plate with flame-cut holes for the tangent pole and found comparable results.

Correlating Analysis Results with Physical Test Results
With the pole shaft and base plate structures verified, Giosan focused his next analysis on the insulator brackets of the tangent structure to optimize its load bearing capability and material thickness. Giosan built an eight-node brick model of the bracket and insulator in ALGOR抯 Superdraw III and used ALGOR抯 automatic mesh enhancement capabilities to create a finer mesh for the bracket.

"An accurate stress plot for the bracket was very important because this area experiences the most loading from the transmission line," explains Giosan. "By creating a finer mesh on these areas, I was able to ensure a high level of accuracy without significantly increasing processing times."

Giosan conducted analyses of the bracket with both vertical and horizontal welding configurations and varying material thicknesses, from 9mm to 16mm. "The vertical weld configuration results showed lower stresses than the horizontal weld," Giosan says. "Under vertical loading, the maximum stress in a 12.7mm plate was well below the yield stress of the material."

Giosan put this ALGOR analysis to the test. WCE created a load test structure, consisting of a full-size bracket welded on a shaft with geometrical and structural dimensions that correspond to the top connection of the tangent pole. The insulator was simulated using a 12.7mm-thick flange and a 127mm O.D. pipe with the length and orientation to match the required dimensions. The end of the pipe was gradually loaded while engineers checked the bracket, shaft and welded connection for plastic deformation.

"No cracking occurred in the bracket or shaft. We found that the analysis results closely approximated the actual stress concentrations and deflections at the bracket attachment point," says Giosan. For the first load case, the ALGOR stress analysis predicted a deflection of .06861m. The physical test results indicated a .07000m deflection.

"Overall, the ALGOR analysis results used to optimize the pole designs and simulate the physical loading tests corresponded very closely to the results obtained using conventional design methods. This comparison gave us a high level of confidence that the models functioned properly and the results are accurate," continues Giosan. "We concluded that the pole designs met the load capacity specifications and required no full-scale loading test."

With the predictable loading capacity requirements confirmed for his designs, Giosan expanded his study to include a simulation of the impact loading that can result from a head-on vehicle collision. "The goal of the ALGOR MES was to check the maximum deformation of the pole shaft and learn how stresses that result from a sudden impact force should be distributed throughout the base plate," says Giosan.

Creating a Virtual Laboratory for Future Engineering
Giosan used the finite element model of the dead end, flame-cut base plate as the basis for the impact MES. He removed the static loading that had been applied previously because MES does not require dynamic loading inputs. Instead, he modeled a simplified car using ALGOR抯 proprietary kinematic element technology. Kinematic elements behave dynamically like regular, flexible elements and can transmit forces; however, stresses are not calculated for these elements so processing times for large solid models are reduced. Giosan chose kinematic elements for the car and flexible elements for the pole model because he was concerned only with obtaining stress and deformation results for the pole.

Giosan added contact elements between the front end of the car and the pole. These elements enabled the software to simulate the complete interaction of the car and the pole, including the transfer of inertia from one object to the other. After the geometry was completed, Giosan specified the global parameters of the event, including the duration and an acceleration load curve for the car.

Giosan conducted an ALGOR Mechanical Event Simulation of a car impacting the base of a dead end pole. The Mechanical Event Simulation calculated the motion of the car, buckling that resulted from the impact and stresses at each instant in time of the event. The results aided the engineers in determining how the impact stresses were distributed throughout the base plate. The deformation shown here is magnified five times to facilitate viewing.

ALGOR抯 MES software simultaneously calculated the motion of the car, any buckling that might result from the impact and the resulting stresses at each instant in time over the course of the event. "MES produces a virtual picture of what happens in the real world," says Giosan. "The results were very useful in getting a general idea of how stresses were distributed through the base plate."

"By using ALGOR抯 Mechanical Event Simulation software, we have set up a powerful virtual laboratory," continues Giosan. "This is enabling us to change our design procedures to the benefit of our customers. We are creating better locking, more flexible structures, and we have reduced manufacturing costs and improved the competitiveness of our products."

According to Giosan, WCE is continuing its use of ALGOR software in the design of poles and in the development of new pole manufacturing equipment. Currently, he is using MES to simulate and optimize a roll forming process.