Report - District 10 Snowmobile Bridge - February 14, 2011

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100 HUNTER VALLEY ROAD, ORILLIA, ON, L3V 6H2, TEL 705-325-5400, FAX 705-325-8400 FEBRUARY 2011

File: S-11041 February 14, 2011 Parry Sound Snowmobile District 70 Church St. Parry Sound, ON P2A 1Y9 Attention: Bill Park Dear: Bill Re: 110’ Span Bailey Bridge on Snowmobile Trail C in District 10, Township of McDougall Steenhof Building Services Group (SBSG) is pleased to provide a copy of the attached structural review regarding the snowmobile trail bridge located on trail C in district 10 in the Township of McDougall. We would like to thank Bill Park for arranging transportation to site and a representative to assist on site. In the following report you will find our observations and structural assessment of the bridge, abutments, and approach ramps. Steenhof Building Services appreciates the opportunity provided by Parry Sound Snowmobile District to provide the requested engineering services. Should you have any questions, please feel free to contact the undersigned. Sincerely, Jack Steenhof, M.A.Sc., P. Eng. Mark Steenhof, B.Eng., EIT

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110’ SPAN BAILEY BRIDGE ON SNOWMOBILE TRAIL C IN DISTRICT 10 FEBRUARY 2011

Introduction

The Bailey bridge is a portable pre-fabricated truss bridge, designed for use by military engineering units to bridge up to 200 foot (60 metre) gaps. It requires no special tools or heavy equipment for construction, the bridge elements are small enough to be carried in trucks, and the bridge is strong enough to carry tanks. It is considered a great example of military engineering. Bailey bridges are also extensively used in civil engineering construction projects to provide temporary access across canals, rivers, railway lines, etc. A structural assessment of the subject Bailey bridge located on snowmobile Trail C in District 10 (Location Plan 1) is required to confirm that the bridge is able to support the imposed snowmobile, trail groomer, and snow loads. Steenhof Building Services Group was retained by Bill Park of the Parry Sound Snowmobile District to complete the required structural report.

Figure 1: Overall view of subject Bailey bridge on Trail C in District 10.

Background Information

The subject bridge is located on Trail C in District 10 in the Township of McDougall (Location Plan 1) and was placed on site in 1992. A site review was conducted by Jack Steenhof, M.A.Sc., P.Eng. and Mark Steenhof, B.Eng, EIT on Friday January 28th, 2011 to examine and document the bridge, abutment, and approach structures. The review was requested by Bill Park due to visible degradation of the bridge approaches and guards and the age of the structure. Currently the bridge is closed to trail groomers since they were suspected to impose the most severe loads on the structure. Existing structural drawings were not provided by the client for the analysis. During the site visit, detailed measurements, observations, and photos were taken. Figure 2 shows a plan view of the 12 ft wide Bailey bridge that spans 110 ft.

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Location Plan 1: Location of subject Bailey bridge on Trail C in District 10.

Figure 2: Plan view of the subject Bailey bridge.

110 ft Bailey bridge

Bridge location

Hwy. 400

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Purpose The purpose of this structural review is to perform a structural assessment of the subject Bailey bridge. Upon assessment, conclusions and recommendations will be made for maintenance and future use of the structure.

Structural Overview Descriptions of the subject bridge’s major structural components are outlined using schematics and photos documented during the site visit on Friday January 28th, 2011. Panels The main structural members of the bridge are the repetitive vertical panels shown in Figure 3 and 4. Panels are welded steel truss sections 10 feet long, 5 feet 1 inch high, and 6-½ inches wide. The horizontal members of the panel are called chords and are composed of double C-channels. Both chords have male lugs at one end and female lugs at the other. Panels are joined end to end by engaging these lugs and placing panel pins through the holes in the lugs. On the top of the bottom chord are four dowels. The beams that support the bridge deck are clamped to these dowels. The vertical and diagonal web members of the panel are constructed of I-beam segments. The panels observed during the site visit were in good condition with minor rust in some locations. It was also observed that the middle seven panel segments were reinforced with supplemental top and bottom chords (Figure 4). Supplemental top and bottom chords are used to increase the load capacity of Bailey bridges.

Figure 3: Typical Bailey bridge panel.

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Figure 4: Repeating bridge panels on subject bridge.

Panel Pins The panel pin that connects panel sections is 8-5/16 inches long and 1-7/8 inches in diameter and is shown in Figure 5. Four pins are required for connection to adjacent panels. Pins observed on site were in good condition.

Figure 5: Panel pins.

Transom The transom (Figures 6 & 7) is a steel beam that supports the floor system of the bridge. It is 10 inches high by 19 feet 11 inches long. It has a 4-½ inch flange and a 5/16 inch cover plate on each flange.

10 foot panel

Supplemental top and bottom chords

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Figure 6: Transom schematic.

Figure 7: Transoms, sway braces, and stringers on subject bridge .

Transom

Sway brace

Stringers

Decking

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The underside of the transom has six holes into which the panel dowels fit. The transom rests on the lower chord of the panel and is held in place with a transom clamp. The upper side of the transom has six lugs with an additional lug near each end. The stringers and rakers attach to these lugs. Transoms are spaced at 5 feet, one at the middle and one at the end of each panel, to support vehicles of class 70 or less. Transoms were in good shape with minor rust visible in some locations. Sway Brace The sway brace is a 1-1/8 inch steel rod, hinged at the center, and adjusted by a turnbuckle (Figures 7 & 8). At each end is an eye and a chain with a pin attached. This pin is inserted through the eye to the sway brace to the panel. The sway brace is given the proper tension by inserting the tail of an erection wrench in the turnbuckle and screwing it tight. The locknut is then screwed up against the turnbuckle. Two sway braces are required in the lower chord of each bay of the bridge. Sway braces on the subject bridge were heavily rusted as shown in Figure 7.

Figure 8: Sway brace schematic.

Stringers Stringers carry the bridge’s roadway (Figures 7 & 9). Each stringer consists of three 4 inch steel I-beams, 10 feet long, joined by welded braces. There are two types of stringers: plain stringers and button stringers. They are identical except that the latter has 12 buttons which hold the ends of the roadway in place. Each bay of the bridge has six stringers: four plain stringers in the middle and a button stringer on each side. The stringers are positioned by the lugs on the top of the transoms. The majority of stringers were in good condition although several stringers were heavily rusted.

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Figure 9: Stringer schematic.

Decking Bridge decking consists of two layers of 2 inch by 6 inch pressure treated lumber on their flats (Figure 7). Layers were installed perpendicular to each other. The top layer of lumber is a wear deck that can be replaced as necessary. The lower layer of decking was in good condition. The upper layer of decking had signs of wear due to snowmobile traffic.

End Posts End posts, as shown in Figure 10, are used on both ends of each truss of the bridge to take the vertical shear. They are 5 foot 8 inch columns made of two 4-inch channels and plates welded together. There are two types; male and female, having male and female lugs, respectively. These lugs are secured to the end panels of the bridge by panel pins placed through holes in the lugs. End posts have a step to support a transom outside the panel at one end of the bridge. End posts were in good condition with minor rust present.

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Figure 10: End post schematic.

Bearings Steel I-beams support the bridge at each of the ends as show in Figures 11 & 13. Steel bearing plates are provided to distribute the beam load into the wood members below. Bearing plates are secured to abutments using bolted metal straps. The southwest bearing plate (Figure 13) is bent due to shearing of the abutment member below the plate. This has resulted in the bolted metal strap coming loose from the abutment below. Abutments Abutments (Figure 12) that are 14 feet by 14 feet in plan support each end of the subject bridge. Abutments are constructed of 10 inch by 10 inch wood members. Steel cross bracing is provided on three faces to provide restraint against racking. The south abutment appears to have undergone settlement. This has caused an abutment member below the south bearing to shear as shown in Figure 13.

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Figure 11: Bridge bearing supporting subject bridge.

Figure 12: South end abutment supporting subject bridge.

Bearing assembly

South abutment

Steel bracing

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Figure 13: Bridge bearing supporting subject bridge.

Figure 14: South end bridge approach ramp.

Sheared 10”x10” timber

Unfastened metal strap

Bent plate

4”x8” approach timbers

Damaged guard

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Approach Ramps Approach ramps (Figure 14) are located at each end of the bridge and are constructed of 4 inch by 8 inch members on their flats. Due to elevation differences, approach ramps were installed at a steep incline. During the course of the winter season the steep approach is reduced by building up snow with the groomer. Timber approach members appear to be in good condition. Guards Guards constructed of dimensional lumber are located on each side of the north and south approaches. The southeast guard (Figures 14 & 15) appears to have been damaged due to an impact. This has caused the vertical support posts to break as shown in Figure 15. The remaining three guards appear to be in good shape.

Figure 15: Damaged southwest guard.

Bridge Load Capacity and Imposed Loads The main purpose of the bridge structural review was to determine the safe load capacity for the subject snowmobile bridge. The “Bailey Bridge Field Manual No. 5-227”, published by the U.S. Headquarters Department of the Army in 1986, was referenced for original design loads and bridge capacities. Outlined below are our findings. Bridge Classification For military use bridges are classified based on traffic restrictions as shown in Table 1. Higher restrictions on bridge traffic speed and location of vehicle result in heavier vehicles being allowed on the bridges. Snowmobile trail groomers fall within the `normal` classification due to their top speed of 15 mph and the necessity for stopping on the bridge for grooming operations.

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Table 1: Bridge classification.

Bridge Construction, Vehicle Standard Classes, and Single Vehicle Load Capacity The subject Bailey bridge is constructed of single trusses and the trusses are not stacked. As a result, the bridge falls in the SS category for type of construction. As noted earlier, supplemental top and bottom chords have been installed in the middle seven panel segments as reinforcement. Table 2 specifies the highest standard class of vehicle (Figure 16) allowed on a bridge of specified span length. The subject bridge has a span of 110 feet and exceeds the spans for which load ratings are provided in Table 2. Due to the nature of the load (single vehicle on the bridge at any time instant), the load capacity of the bridge for a 110 foot span can be interpolated as done in Figure 17.

Table 2: Bridge classification (with supplementary chords).

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Figure 16: Loads of standard classes of vehicles.

Figure 17: Span vs. weight.

y = -0.275x + 46

0

5

10

15

20

25

30

35

40

0 50 100 150

We

igh

t o

f V

ev

hic

le (

ton

s)

Maximum Span (ft)

Maximum Span vs. Weight of Vehicle

Span vs. Tons

Linear (Span vs. Tons)

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Based on Figure 17, the subject Bailey bridge has the capacity to support a 15.75 ton (14.32 tonnes) vehicle without additional loads (i.e. snow). Bridge Loading Snowmobile bridge loading is specified by the Ministry of Natural Resources (MNR) Snowmobile Bridge Design Guidelines PL 10.08.00 - 1992: Winter:

1. All bridges must support 80% of Ground Snow Load without vehicle load. 2. All bridges 5 feet or more above creek bottom must be provided with a hand railing.

The railing is to be 42 inches high and capable of withstanding 50 lbs/ft horizontal and vertical loads applied simultaneously.

3. Bridges must be designed to carry 50% Ground Snow Load and a lane load of 125 lbs/ft. If the bridge width exceeds 6 feet, the designer must consider the possibility of two lanes of traffic over all or part of the bridge.

4. Bridges must be designed to carry the largest grooming machine expected to be used during the lifetime of the bridge. For bridges more than 6 feet wide, the minimum groomer loading is two 5000 lb loads spaced 10 feet apart. Snowmobile clubs must be aware of bridge capacities when selecting grooming machines.

Summer:

1. Trails with no gravel surface which are only accessible by off-road 4 wheel drive vehicles – a 7500 lb vehicle.

A summary of the groomer and drag weights used in District 10 of McDougall Township are provided in Table 3. Based on these weights, a maximum groomer and drag combination load of 7.45 tons will be imposed on the subject bridge.

Table 3: Groomer and drag weights.

Unit Weight (tons) Weight (tonnes) Mogulmaster 1809 - Drag 1.70 1.55

Tucker Snowcat 2000 - Groomer 5.75 5.23 Bombardier BR180 - Groomer 5.09 4.63

Prinoth Husky - Groomer 5.00 4.55 Bridge Capacity The subject bridge was reviewed under the previously described loads. It was found that the bridge has insufficient load capacity for full snow load without vehicles and for 50% of the snow load with snowmobile loading. As a result, it is required that the snow depth on the bridge be kept to a maximum of 6 inches in depth. This will maintain low enough snow loads to allow the bridge to remain in-service. IT IS REQUIRED THAT THE SNOW ON THE BRIDGE BE KEPT TO A MAXIMUM OF 6 INCHES IN DEPTH.

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Conclusions and Recommendations

Based on the information provided and observations made on site, current and future conclusions and recommendations are provided below: Current Recommendations:

1. Trail groomers and snowmobiles may continue to use the subject bridge for the 2011 winter as long as the snow on the bridge is kept to a maximum of 6 inches in depth.

2. Snow on the bridge shall be cleared to a maximum depth of 6 inches in depth before the groomer is allowed on the bridge.

Required Future Action (Summer 2011):

1. Signage shall be provided that states the bridge’s load capacity of 7.45 tons (6.77 tonnes) and speed limit of 40 km/h (25 mph).

2. The south end of the bridge shall be temporarily shored to allow the crushed timber and bearing plate to be replaced on the southwest corner of the bridge.

3. Sway bars must be cleaned of surface rust and painted with a rust preventing paint. 4. Bearing plate metal strap connectors that have loose bolts shall have new bolts

installed. 5. The guard on the east side of the bridge’s south approach must be repaired to its

original condition. 6. The bridge abutments shall be inspected when they are fully visible to determine their

condition. Current winter conditions prevent a full inspection from being made. 7. The wear deck shall be inspected to determine its condition.

Should you have any questions, please contact the undersigned. Jack Steenhof, M.A.Sc., P.Eng. Mark Steenhof, B.Eng. Principal / Sr. Structural Engineer Engineer-in-Training

Documents

Report - District 10 Snowmobile Bridge - February 14, 2011