Structurally Sound
By Maraliese Beveridge and Kevin Hanna
Photos courtesy of Maser Consulting P.A.
It’s a dreaded scenario: revitalizing an outdoor facility only to have Mother Nature blow through town and damage the updated structure. Although damage may not be apparent on the surface, many parks and recreation agencies have been through the rigors of inspecting structures manually to ensure they withstood hurricane or tornado winds and damage from debris. Thanks to the latest technology, 3-D laser scanning may make the process less arduous and save time and more important--money.
Practical Yet Purposeful
In the densely populated urban city of Elizabeth, N.J., open space is at a premium. In 2010, the city embarked on the revitalization of the Mickey Walker Recreational Facility, a park with an aging pool that was to be transformed into a water-efficient, cost-effective, ADA-accessible, water spray park with seating areas. Designed by Maser Consulting P.A., the spray-park project was to include an open steel shelter where friends and family can sit in the shade but still monitor their children's activities. Another dimension was added when elderly patrons from the adjacent senior center also visited the spray park to sit under the shade structure and watch the children play. This unexpected—yet positive—revelation eventually led to the expansion of the initial building-structure design to approximately double the original size.
The structure was constructed with galvanized steel columns to avoid corrosion along the ground level. The remaining building was constructed of structural steel shapes of varying sizes. All hardware was stainless steel that will provide longevity and minimal maintenance. The roof panels were screwed into tubular steel to avoid screws penetrating the corrugated-steel roof, and a cupola was installed to improve the aesthetics of the overall structure.
Hit By A Hurricane
After the park’s reconstruction was completed in the summer of 2011, the city was subjected to the effects of Hurricane Irene, as well as an earthquake shortly afterwards. Concern for the park—particularly the shade structure—from the effects of the hurricane’s high winds and potential damage from the earthquake prompted the engineers to revisit the park. While confident that the building would withstand the effects of both events without damage, the engineers performed a post-storm structural-building analysis to assess the member stress levels and quantify the effects of the storm and earthquake.
To accomplish this, they implemented the latest technology in 3-D laser scanning. The open design of the structure was the perfect subject for using laser-scanning technology rather than the traditional method of manually gathering existing measurements of a building. The laser scanner records 50,000 independent measurements per second, making it a more accurate means of capturing the structure's physical components, including the various structural steel shapes, sizes, and lengths. Fewer professionals also are required to take the measurements, and data can be gathered in one field visit, thereby eliminating the need for costly return site visits.
Starting The Scan
Engineers utilized on-the-ground 3-D laser scanning in conjunction with STAAD.Pro software to provide a structural analysis based on a real-life representation of the building. The 3-D scanner created aile known as a “point cloud” that was analyzed and imported into CAD software to create 3-D models. The point cloud was reduced into a wireframe (centerline) structural model representing the actual building in true three dimensions. The wireframe model was then imported into structural-engineering software for analysis.
In the analysis performed, the loads represented the peak gust winds experienced from the hurricane, and the earthquake analysis represented the estimated peak seismic magnitude experienced by the building.
Because the building’s original design criteria were based on aesthetics that dictated the nominal structural sizes, the building was known to have a reserve structural capacity. The original structural computer model used to check for building-code compliance was not considered to be highly accurate because some modifications during fabrication and on-site construction altered various structural members’ locations and lengths.
The results indicated that structural members of the building were well within acceptable and safe limits as prescribed by the applicable building code resulting from loads imposed by both natural events. The estimated wind gusts at the park were estimated to be 65 mph, while the earthquake simulated an event that was relatively minor in magnitude by the time the effects of the earthquake reached New Jersey from its epicenter in Virginia.
Additional Applications
The use of this technology has vast applications for the analysis of numerous structural-types systems, including buildings, bridges, towers, etc. However, the technology does have limited applications when working with hidden structural members, as it does not capture information that is not visible to the eye. Therefore, this building proved to be the perfect subject for demonstration using this technology. The economic advantage of using laser scanning is also applicable for numerous other real-world applications requiring accurate 3-D representations, such as highly detailed graphic renderings used for demonstration and presentation purposes in court cases involving forensic-engineering testimony in litigation for failed or collapsed buildings. Its accuracy, combined with savings in manpower, is making this tool a valued option while becoming more and more accepted by today’s professionals.
On opening day, approximately 325 children and parents visited the spray park. Throughout the warm summer months, residents continued to frequent it, including visitors from local city clubs, summer camps, and other community groups that can rest assured the park is safe for use.
Kevin Hanna, P.L.S., Laser Scanning/Surveying; Robert DiBartolo, P.E., P.P., CPM, Structural Engineering/Forensic Engineering; and Gus De Blasio, C.P.S.I, CTE, ISA, CIC, LEED AP, Landscape Architectural/Park Designer contributed to this article.
Maraliese Beveridge is the marketing writer for Maser Consulting P.A., a multi-disciplined engineering firm with a unique balance of public and private sector experience. For additional information, call (877) 627-3772 or visit www.maserconsulting.com.