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4.9. SR 10-19-1998ITEM 4.9. Howard R, Green Oompany QONSULTING ENGINEERS October 14, 1998 File: 803450J-0060 CONSULTING ENG]NEER~ Formerly MSA Consulting Engineers Honorable Mayor and City Council City of Elk River 13065 Orono Parkway Elk River, MN 55330 RE: TRUNK HIGHWAY 169 PEDESTRIAN BRIDGE Dear Council Members: As you are aware, we have been working on the federal paperwork and beginning the design on the Trunk Highway 169 pedestrian overpass. As we get further into the design, there are a number of issues that we would like to make the City Council aware of, and get some input. Most of these regard the type of construction materials and style of bridges. We have a short videotape (approximately 10 minutes) of several bridges from around the Twin Cities area that we will show at the City Council meeting. Several of the key considerations that we would like some input into are as follows: A. MATERIALS There are basically three materials that a pedestrian bridge can be constructed of. These are steel, concrete, and wood laminate. Generally, steel is the least expensive, with wood laminate the most expensive and concrete somewhere in the middle. B. STYLE OF CONSTRUCTION The look of a bridge is dictated by the design style, pier type, material selection and choice of aesthetic elements. There are several styles of construction including continuous span, through girder, through truss, and pony truss. A brief description of each of these is as follows: Continuous span: This is probably the most common style of pedestrian bridge. This is where the material used for the beams is underneath the floor of the pedestrian bridge, and the handrail and fencing are attached to the floor of the bridge. This type of bridge has the greatest overall height. Through girder: The girders are two L-shaped beams placed to form a U shape. The walkway is within the U. Because of the long spans required to cross a four-lane highway, the beams get quite deep. To reduce the overall height of the bridge, the floor O:~ROJ\803450j\0060~450-0902.oct.doc 1326 Energy Park Drive · St. Paul, MN 55108 ° 612/644-4389 fax 612/644-9446 toll free 888/368-4389 City of Elk River October 14, 1998 Page 2 of the bridge is placed at the bottom of the beams and the beams themselves form the handrail of the bridge. The fencing is then installed on top of the beams. Through truss: A lighter weight bridge can be constructed if a truss is used. In a through truss, the sides and roof of the bridge are used as structural elements of the truss. Effectively, the structure of the bridge surrounds the walkway. Fencing is attached to the interior of the truss. Pony truss: A pony truss is a combination of a through girder and a through truss bridge. Piers, the middle support columns, can vary widely in appearance, and are an important part of the aesthetics of the bridge. The video shows examples of V, open V, T, Y, column and cap, tapered and simulated stone piers. The Pony Truss and Through Truss designs are able to make use of canned bridge quotations. This means that a bridge supplier would furnish specifications and costs based on the required length and height. The pier and abutments would be designed to match the bridge being supplied. This can slightly reduce the design cost. MAINTENANCE Long term maintenance requirements are another element to consider. Steel bridges generally require more maintenance than concrete or wood types. They require painting every 10 - 15 years. The video does show one type of Iow maintenance steel bridge. It uses CorTen steel that is made to rust evenly on the surface to present the rust color and not need painting. While concrete and wood bridges both generally require Iow maintenance, there is a difference in their life spans. Wood bridges can be expected to last 25 to 30 years while concrete and steel structures will last in excess of 50 years. Due to the shorter life span of wood bridges and higher maintenance of painted steel, we recommend the selection of either a concrete or CorTen steel bridge. OTHER DESIGN ELEMENTS Mn/DOT requires bridges over roads to have a fence to prevent items from being dropped from the bridge. The least expensive and most basic approach is to use standard chain link fence. Chain link can also be coated with PVC, which comes in black, green or brown colors. This is a little more expensive, but generally looks nicer. Another option is to construct a wrought iron fence. This will only work with certain bridge designs and is the most expensive of the three fencing options. Lighting is not required by Mn/DOT, but may be desired as it provides an element of safety. There are three main methods used to light a pedestrian bridge. One way is to string lights along the bridge fencing. This would involve a number of Iow power lights. A Howard R, Green Company O:\PROJ\803450j\0060\450-0902.oct.doc CONSULTING ENGINEERS City of Elk River October 14, 1998 Page 3 second method is to have several light poles mounted on the bridge. Another method is to make use of larger light poles along the highway that shine onto the bridge as well as the roadway. Making patterns or coloring concrete is another method of developing aesthetic effects. If any of these additional design elements are too elaborate and expensive, the expense is not covered by Mn/DOT. FINANCING As you are aware, the City received High Priority Project funding for this project. This funding requires a 20% local match. The following shows the budget available for this project. Federal funds available (80%) Required local match (20%) $530,250 $132,550 TOTAL $662,800 Estimated construction costs of different style and material bridges are shown below. These costs are for a basic bridge of each type with standard chain link fencing. Steel Concrete Wood Continuous Span $445,000 $475,000 $480,000 Pony Truss $465,000 -- $500,000 Through Gi~er $480,000 $490,000 $515,000 Through Truss $490,000 --- $530,000 As can be seen from these estimates, it appears that the City can afford any style and material bridge they choose. Again, we suggest either a concrete or CorTen steel bridge. Then some of the excess budget would be available to upgrade the fencing, add lighting, and consider other aesthetic treatments. We are looking for some direction as to how the City Council would like us to proceed on these issues. Sincerely, Howard R. Green Company TJM/st Howard R, Green Company O:~PROJ\803450j\0060\450-0902.oct.doc CONSULTING ENGINEERS