Steel is a great building material; everyone knows that. It’s so common that it’s probably taken for granted in many instances. From structure and facades to rebar and fasteners, it’s economical, readily available, highly adaptable, and very strong, so what’s not to like?
Well, if the owner’s use of the building includes testing that is sensitive to magnetic fields, the answer is quite a bit.
Elbit Systems of America in Merrimack, NH engaged Green Leaf to build a tower for the testing of various commercial and defense related devices which contain magnetic compasses; these compasses are high precision instruments which are accurate to within a very small fraction of one degree and rely on the Earth’s unperturbed magnetic field. The tower is intended to provide a high vantage point to perform testing while preserving a magnetically sterile environment in which the accuracy of the magnetic compasses can be preserved.
Summit Engineering of Portsmouth NH was the designer on the project. Their charge – design a tower, including foundations, that had no ferrous steel which if magnetized would interfere with the testing of devices containing magnetic compasses to be performed in the building atop the tower.
Bob Champagne of Summit Engineering noted “the design of a structure comprised exclusively of non-ferrous materials on a limited budget required an innovative approach. We budgeted several options,” he continued, “including (non-magnetic) stainless steel, aluminum, and pressure treated wood framing. Each had their unique design nuances. Stainless steel was determined to be the most expensive solution and was therefore eliminated. That left either wood or aluminum. Though somewhat more expensive than wood, the aluminum option was ultimately chosen for the tower because of its aesthetics and durability. A wooden structure will be positioned on top of the aluminum tower structure and will house occupants who will perform tests on the various devices. The wooden structure is connected exclusively with stainless steel fasteners and the underlying foundation is reinforced with glass fiber reinforced polymer (GFRP) reinforcing; selected because it is more readily available than stainless steel rebar.”
Once the bulk building materials for the project were selected, Green Leaf set our sights on the details. Ties for the GFRP reinforcing couldn’t be traditional steel wire, so plastic zip ties will be used. Adding further complexity, the prospect of constructing a wooden room 25’ atop the tower posed significant challenges. The team determined that building the room and hoisting it into place would mitigate safety concerns as well as expedite the project schedule; as construction of the tower and the room could take place concurrently. Bay State Industrial Welding of Hudson, NH is fabricating the Tower and stairs, and has been a great partner in this process.
As someone who loves building, projects like this one which offer differing challenges and complexities – regardless of their size - always prove to be particularly rewarding for me. This project will be complete in a few weeks. Be on the lookout in early February for photos of this very cool project.