Bridge Module (2)

Project Preparation and AdministrationBridge Module

Why are bridges part of this training? Big cost. Long Process Design is complicated Tough Decisions

R1 Trails Project Preparation

But they are Fun!

Proud crew!

Trails do nothing more than connect the Bridges!

R1 Trails Project Preparation

Training Focus Bridge Design Process Decisions to be

made. How to make those decisions!

R1 Trails Project Preparation

Training Focus Northern Region Standard Trail Bridge Plans

Intended uses Limitations, Inappropriate Uses Costs Maintenance

Wilderness Bridges Helicopter Usage Preservative Treatments If there is time NP Wilderness Bridge Project Presentation

R1 Trails Project Preparation

Authorities All Decisions Line Office Approval of Bridge Design Director of Engineering Unless using

Regional Standard Trail Bridge Designs Forest Engineer.

All Trail Bridges need to be designed!R1 Trails Project Preparation

Bridge in Bob Marshall Wilderness

Authorities Design Resources Available. Forest Engineer Regional Bridge Group

John Kattell David Scovell

Our job is to provide technical assistance to Forest personnel and complete and/or approve all bridge designs.

R1 Trails Project Preparation

Bridge Design ProcessFunction (To bridge or not? Replace or remove?) Project Scope** Who is User? ROS? TMO? Force Account/Contract?

**Contact FE and /or RO during Project Scope

Location/Survey Where is best spot? Many decisions. Preliminary Design Project Funding and Scope finalized.

Plans, Specs, Estimates.

Final Design Construction COR

R1 Trails Project Preparation

Project Initiation and Scope Function To Bridge or Not to

Bridge? Replace or remove? Preliminary Engineering needed?

Factors? TMO & ROS User Safety Resource Protection Others?

Albino Trail Bridge Site - GalR1 Trails Project Preparation

Funding Feasibility Aesthetics Wilderness

Bridge Design Process In general, more complicated than road bridges. Why? Defining the User Location Access Wilderness Size?

R1 Trails Project Preparation

Bridge Design Process Dome Mtn. On Ktn. 24-foot span Wilderness 6-mile from TH but

4000 ft elevation gain. Force Account Dangerous work.

R1 Trails Project Preparation

Bridge Design Process Iron Springs on D-P 50-foot span Easy access Total cost -

Maah-Taah-Hey Trail

~$35,000 Contract

R1 Trails Project Preparation

Project Initiation and ScopeDefine the User (TMO & ROS)Pedestrians Stock ATVs Bicycles Administration vehicles Outfitters / other permittees User affects size, design

and cost. Bridge many times limits the user!

R1 Trails Project Preparation

Project Initiation and Scope Force Account or Contract? (Effects designdecisions!)

Design (in house or A/E) Complexity of bridge project. Availability of Forest or RO Engineers Funding Typically, R1 designs are done in house. Construction Safety Force Account capability, skill level, and availability. Complexity of bridge. Funding Pros and Cons

R1 Trails Project Preparation

Force Account or Contract?Goat Creek on NP Remote site required packing all materials. Simple construction NP has trained Crews. Force Account

R1 Trails Project Preparation

Force Account or Contract?Yellow Mule on Gallatin Bridge part of a larger trail construction project. Short distance from trailhead. Complicated construction Contract

R1 Trails Project Preparation

Force Account or Contract?Mystic on Custer Site at trailhead. Working over large water penstock and tracks. Needed large equipment Contract

R1 Trails Project Preparation

Project Initiation and Scope Summary Function (To bridge or not to bridge) Define Users. Force Account versus Contract Funding. Project a go or no go? May need some preliminary engineering

this early.

Who makes these decisions?R1 Trails Project Preparation

Location / Survey Location Narrowest spot? Not necessarily Stable stream reach. Where users want it! Good trail

Survey - Varies Simple small creek

Profile of trail and stream with few xsections. Sketches Complex

approaches for user(function for hikers vs stock vs snomobiles vs ATVs)

Full site survey of area. Geotechnical (drilling) In general, experienced

bridge engineer may get by with less.

R1 Trails Project Preparation

Location / SurveyHolter Cut on Btr. No survey done.

R1 Trails Project Preparation

Location / SurveyLittle Salmon on Flathead in Bob Marshall. Full site survey completed. Needed for hydraulic analysis.

R1 Trails Project Preparation

Preliminary DesignDetermine Span Height Width Bridge Type Foundations FA or Contract Cost

FactorsCrossing and height Flood waters, Clearance User Span, location, aesthetics Site geology See earlier slide All of the above.

R1 Trails Project Preparation

Preliminary DesignTwo biggest problems in R1

Bridges too short.Abutments scour and fail Resource damage

R1 Trails Project Preparation

Preliminary DesignBridges are too low!

R1 Trails Project Preparation

Preliminary Design Sill-Thru Configuration Little work in water. Hydraulically efficient. (less susceptible to scour). More $ in superstructure, less in abutments. No wingwalls needed.

R1 Trails Project Preparation

Preliminary Design Vertical Wall Configuration More work in water. Hydraulically less efficient. (more susceptible to scour). Less $ in superstructure, more in abutments. Need wingwalls

R1 Trails Project Preparation

Preliminary Design Span Length Field Estimate (Rule of Thumb) typical spill-thru bridge.

BH

Span Length (L)

Estimated Span Length (L) = BW + 3 x BH BW Channel bottom width BH Bridge height from channel bottom to trail tread.

R1 Trails Project Preparation

Preliminary Design Span Length Field estimate must be verified on paper. Do not undersize. Better to spend more on span than abutments. Evaluate existing bridge (did it function OK) Iterative process with what? Bridge height What controls bridge height?

R1 Trails Project Preparation

Preliminary Design What controls bridge height? Trail height Bridge structure

depth Rule of thumb 1/20 x span Clearance for debris

Minimum 2 feet above high water (100 yr flood) to bottom of bridge.

Little Salmon on Flathead

R1 Trails Project Preparation

Preliminary Design Span Length Vertical Wall abutment

BH

Span Length (L)

Span Length = Bankfull +. Must be able to pass

flood without damage to bridge or stream. Footings must be below stream bed as minimum unless on bedrock.R1 Trails Project Preparation

Preliminary DesignFactors for Bridge Width - Users - Railing

Bridge w/o railing

R1 Trails Project Preparation

Preliminary DesignVariable widths Single log 14 Stock w/railing 8 Snowmobile 16+ Manual guidance but can be anything.

Bridge with railingR1 Trails Project Preparation

Preliminary Design Bridge Types Single Log Timber stringer Glu-lam stringer Truss Suspension Packable

FactorsSpan Access Aesthetics Materials

R1 Trails Project Preparation

Preliminary Design Foundations Spread footings Gabions Geocell Walls

Factors Site geology Site materials Access Scour Potential

Generally we use spill-thru configuration with timber sill on gabion or geocell.

R1 Trails Project Preparation

Preliminary Design Costs Very difficult to estimate. No rules of thumb. Procedure Take off and price materials (variable) Crew up labor. $2500/day for crew of 4 with misc.tools/equipment Or use Davis Bacon rates

Estimate Equipment needed (cranes, backhoe, helicopter)

R1 Trails Project Preparation

Preliminary Design Costs - continued Materials Sawn Timber GL timber Bolts/hardware Concrete Reinforcing Steel Gabions Geocell Geocell fillR1 Trails Project Preparation

$1350/mfbf $2500/mfbf $3.00/lbs. $600 - $1000/cy $1.25/lb $125/cy $15/cy $25-$75/cy

Preliminary Design Costs - continued Equipment Excavator Backhoe Dump Truck Crane (Light) Crane (medium) Helicopters Packing$130/hr $80/hr $75/hr $350/hr $650/hr See later slides

$225/mule trip (180 lbs per mule)

R1 Trails Project Preparation

Preliminary Design

Typical work items to accomplish for labor. Project Management Mobilization Excavation Build Abutments Install Superstructure Build Approach walls Build Approach fills

Less Common Work Items Helicopter use. Packing Materials Supply Camp Install Falsework.

R1 Trails Project Preparation

Preliminary Design Nail Lam built 15 years ago. Replace with glulam stringer bridge. On sills. Wilderness Use Helicopter to fly in stringers. Estimate based on Contract Construction Flood Creek Custer

R1 Trails Project Preparation

R1 Trails Project Preparation

Preliminary DesignWhose Responsibility / Authority for preliminary decisions?

Forest! However, Engineering must assist! Why? Call FE and or RO during Project Scope for assistance with alternatives and options. Meet with Rec staff and Ranger to discuss preliminary design options and alternatives.

R1 Trails Project Preparation

Preliminary Design At this point Re-evaluate Project Scope! Re-evaluate Funding!

Why? Many times each site has