Pedestrian Bridge Misconceptions
With an increased emphasis in the US on multi-modal transportation and awareness of public health, there is more funding available for projects that include sidewalks or multi-use trails. Not surprisingly, HR Green has designed a number of projects requiring pedestrian bridges to carry sidewalks and trails over roadways and creeks. As we gain experience with these types of projects, we have learned valuable lessons and identified common misconceptions regarding pedestrian bridges.
The codes governing the design include AASHTO LRFD Bridge Design Specifications as well as additional guidance available in the AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges. The methods and loads required to complete a pedestrian bridge design is the same as a roadway bridge. The only difference is the magnitudes of the loads are less for the pedestrian bridge.
A second common misconception is that a prefabricated truss superstructure is always the most cost-effective option. In reality we have found that this is often not the case. A simple, traditional beam bridge with a cast-in-place concrete deck is often more economical. Depending on location and bridge length needs. The cost to design and construct the bridge abutments and piers can be identical for either option. Furthermore, the bridge owner may save on consultant design costs with prefabricated structures, the cost of designing the superstructure is factored into to cost to supply the bridge.
In order to clarify any misunderstandings as early as possible, at HR Green we like to kick-off the design process by having a coordination meeting with the key stakeholders. This helps to identify the needs and requirements of the pedestrian bridge and overall project.
Following are some examples of key issues we like to address at this meeting:
- Aesthetics – color, shape, style, corridor themes, lighting, signing/logos, etc.
- Bridge Width – the clear distance between railings
- Pedestrian Railing Height – can range from 3.5-feet to 8-feet
- Vertical Clearance under bridge – by code, pedestrian bridges require greater clearance than roadway bridges
- Bridge Opening Width – clear zone requirements
Based on the wants and needs determined in this meeting, various structural and aesthetic alternatives can be investigated. For each alternative, conceptual opinions of probable cost can be developed and a conceptual design can be recommended. The two most common superstructure types that we find to be viable are the prefabricated truss and a prestressed I-beam bridge.
At most locations, the costs are similar with both options. However, the look is very different. We work with the bridge owner to provide a structure that meets their need, with the look they want, at a cost they expect.
To learn more about how HR Green can help assess your pedestrian bridge needs, please contact Dave Maxwell at firstname.lastname@example.org