Nell’s Woodland Foundation | Serena Sturm Architects, LTD

Nell’s Woodland – North Bridge

The Site – A 60-acre Nature Preserve

The Nell’s Woodland Foundation is an organization that promotes a connectedness to nature and provides programs that support stewardship in the areas of ecology, wellness, and the arts. The backdrop to their work is a 60-acres nature preserve in Ottawa, IL and gives them a platform to connect to the community through providing recreational access to nature and a backdrop for their educational and stewardship program.

Design Team for a New Bridge

The Foundation recently added a new pedestrian bridge that spans a ravine within the nature preserve. Civiltech provided structural engineering design services in support of the project’s design team Serena Sturm Architects, LTD and Carsello Engineering, Inc.

Designed to Blend with Nature

The approximately 150-ft long, 4-span bridge is designed with a reverse curve layout. The curved bridge plan gives it a meandering path in harmony with the natural surroundings and allows for changing views while traversing the bridge. Also, the bridge features a trellis spine along the center of the bridge that is indicative of the mature trees and wooded setting. IPE planks give the bridge decking a natural wood finish.

Engineering the Curved Superstructure

The bridge was designed in accordance with AASHTO’s LRFD Guide Specifications for the Design of Pedestrian Bridges and was modelled in 3D in STAAD.Pro. The superstructure consists of 2 horizontally curved steel W27x146 beams which are supported on 2 abutments and 3 steel HSS square tubes all founded on spread footings.

Challenges of the Curvature

A significant structural engineering challenge was controlling deflections and ensuring the stability of the curved superstructure. Individually the I-beams are not very torsionally resistant. Therefore, stout I sections connected together with numerous diaphragms were utilized to control deflections and resist torsion.