Southern West Virginia residents experienced three separate flooding events from storms on April 3, April 8 and July 10 of 2015. Many residences were damaged and over 300 private water crossings were reported damaged or completely destroyed due to powerful floodwaters and heavy floating debris. In Lincoln County alone, where the pilot project was performed, over 80 residences experienced bridge or culvert destruction. Without aid, many of these families may never have the ability to safely access their houses.
Members at the monthly WV VOAD meeting in Charleston, WV on August 18, 2015 requested the development of a guideline for the design and construction of private bridges to replace the private water crossings that were destroyed by the flooding. The WV VOAD Bridge Committee was formed as a result to oversee this effort. This guideline was developed with the input of local, state, and federal agencies and advisors. The participants of the WV VOAD Bridge Committee, Bridge Committee Partners and Bridge Committee Advisors are listed in the appendices. This guideline has already been used and will continue to be used to design and construct private brides as part of WV VOAD’s “Resiliently Bridging the Gap” project.
2. PROJECT OWNERSHIP AND REGULATORY CONDITIONS
2.1 The bridges to be replaced are all on private land and privately owned by individuals.
2.2 The County Floodplain and Building Permits Manager shall be responsible to ensure that all
studies and conditions required by local, state and federal agencies have been satisfied
before issuing a building permit. These include the following:
1. US Army Corps of Engineers (USACOE) Nationwide Permits:
NWP 3 Maintenance
NWP 13 Bank Stabilization
NWP 14 Linear Transportation Projects (Bridges)
2. WV Division of Natural Resources (WVDNR)- Endangered Species
3. WV Division of Natural Resources (WVDNR)- Land and Streams
4. WV Department of Highways (WVDOH) – Encroachment Permit (Driveway Permit)
5. WV State Historic Preservation Office (WVSHPO) review
6. County Building Permit
2.3 It appears that most of the bridges to be replaced are located in FEMA Zone A
(Approximated Zones) or FEMA Zone X (outside the 100 year flood zone) flood zones. Most
of the bridges are also from top of bank to top of bank, such that the structures are
completely outside the waterway and therefore do not require USACOE permits.
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3. LIABILITY
3.1 The Property Owner shall assume all liability for the bridge. A Hold Harmless Agreement to
this effect, drafted by WV VOAD Legal Aid, shall be signed by the Property Owner before
the commencement of any work.
3.2 The Hold Harmless Agreement shall hold harmless the Agency or Entity performing or
assisting the construction of the bridge, WV VOAD, Local County Commissions and their
employees, and any sub-contractors hired to do specialty work for the job.
3.3 The Home and Property Owner shall be given and shall sign a document spelling out the
maintenance requirements for the bridge. This document shall include spelling out the
weight capacity limitations and responsibilities to make public notice of those weight
limitations.
4. PROJECT CONTEXT
The majority of the destroyed private bridges were situated in a manner that created
obstructions to the stream channel. The bridge superstructures were either below the flood
water elevation and were therefore overtopped and/or the abutments were built
protruding into the stream channel, restricting its natural width.
Bridge superstructures should ideally be reconstructed above the flood water elevation. For
many of the sites this document addresses, however, it is topographically impractical to
achieve this since the bridge location itself is below the flood water elevation. In some cases
the abutments of the bridges are directly adjacent to the highway right-of-way (generally
15ft from the center of the road in the project area) and ramping up to a higher elevation
is not possible.
Economic resources in this area are severely limited. The poor state of construction of most
of the bridges attests to the fact that the owners had limited economic means for design
and construction. State and federal assistance is either unavailable or very limited for
private bridges. A State of Emergency was declared for the storm events described in the
introduction. Individual Assistance was requested for each event but denied by FEMA. As
an economically depressed area, the private landowners have very limited economic means
to assist in the reconstruction.
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5. PROJECT INTENT
Due to their location, it is inevitable that bridges in this area will be overtopped by flood
waters caused by severe storms within their expected lifetimes. As such, they will be subject
to destructive forces. It is important to note that the proposed bridge replacement designs
are not guaranteed to withstand these severe storms since that would make their
construction cost prohibitive. The intent of the bridge replacement program is to provide
structures that are as resilient as possible given the limited economic resources available.
Resiliency is aimed for by utilizing the following design principles:
1. Design shall seek to avoid impeding the natural flow of the water. New abutments
shall be located outside of the stream channel so as to minimize interference with
the natural stream bed and to maintain the overall integrity of the waterway. Several
of the existing damaged bridges have piers located in the stream bed that appear to
be stable and in good condition. In these cases, the piers may be reutilized if they are
stabilized or reinforced where necessary.
2. Bridge superstructure elevations shall be established with as much clearance above
the floodwater elevation as possible. This, in conjunction with installing abutments
outside of the stream channel, will generally result in longer bridge spans than the
bridges that are being replaced.
3. Design of bridge abutments shall be to minimize the likelihood that they shall be
undermined or damaged by erosion and scour.
4. Bank stabilization shall be provided with riprap and/or gabions so as to minimize
erosion and scouring.
6. CODE AND DESIGN CRITERIA
All of the bridges to be replaced are privately owned. Due to this, design and construction
is not required to conform to The American Association of State Highway and
Transportation Officials (AASHTO) or Federal Highway Administration (FHWA)
specifications. Building to AASHTO specifications would be cost prohibitive. Bridges also do
not fall under the International Residential Code (IRC) for private dwellings. Instead,
structural design criteria were developed to meet the loading conditions of vehicle sizes
expected to cross the private bridges while still keeping the construction economically
feasible. These guidelines were developed utilizing information from the following sources:
The International Residential Code (IRC) 2012
FEMA P-778 Private Water Crossings, June 2009
Private Water Crossing #2 DR-4219-WV
AASHTO “Guide Specifications for Design of Pedestrian Bridges” 1997
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AASHTO “Standard Specifications for Highway Bridges” 17th Edition
7. TECHNICAL AND COST CONSIDERATIONS
Due to the limited economic resources and anticipated construction by individuals and not-
for- profit agencies who may have limited technical experience in bridge building, the
following shall be considered in the design of the bridge:
1. The bridge construction shall be as economical as feasible.
2. Construction techniques shall be as simple as feasible so as to minimize skilled
construction supervision needs.
3. Semi-skilled volunteer-friendly construction methods shall be maximized.
4. Heavy and expensive construction equipment shall be minimized.
5. Design details shall aim to minimize the need for bridge maintenance.
8. DESIGN LOADS
The following design loads are intended for bridges that shall carry pedestrians and a low
volume of private passenger vehicles and heavy-duty pickups, but are not designed or
intended to carry typical highway traffic.
8.1 Pedestrian Live Loading
40 pounds per square foot (psf) on bridge walking area.
Commentary: The AASHTO “Guide Specifications for Design of Pedestrian Bridges” 1997
section 1.2.1.1 specifies a uniform pedestrian loading of 85psf. It is unlikely that a private
bridge will be subjected to this loading. The IRC2012 specifies 40psf live load for residential
areas.
8.2 Vehicle Size and Weight Class
7.5 ton vehicle loading. One vehicle maximum capacity. A single vehicle shall be placed to produce the maximum load effects. The vehicle live load shall not be placed in combination with the pedestrian live load.
Commentary: The weights of the vehicles most likely to cross these private bridges are listed
as follows:
Small pickup or minivan ≈ 6,000 pounds
Heavy duty pickup ≈ 12,000 pounds
Rescue vehicle (i.e. ambulance) ≈ 13,000 pounds
Moderate sized machinery (e.g. small backhoe) ≈ 15,000 pounds
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Discussion with the Duval Fire Department concluded that in most cases, the bridges need
not be designed for fire trucks (H20 loading category) since they stay on the main road and
will not access private driveways due to unknown conditions. Designing for the H5 loading
category (capacity of 5 tons, or 10,000 pounds) is not sufficient, but designing for the next
loading category up (H10, which has a capacity of 10 tons, or 20,000 pounds) is not
necessary and cost prohibitive. As such, a 7.5 ton (15,000 pound) loading capacity was
chosen.
8.3 Wind Loading
50 pounds per square foot (psf) applied to the projected vertical area of the bridge.
Commentary: As per AASHTO “Guide Specifications for Design of Pedestrian Bridges” 1997
section 1.2.2. In general, this wind load is less than the anticipated transverse water loading
so it does not govern the design.
8.4 Transverse Water Loading
For many of the bridges it is highly probable that the flood waters will overtop the superstructure, subjecting it to pressure from the flowing water and resulting drift buildup. To account for this the bridges shall be designed to withstand a transverse pressure of 280psf applied to the superstructure in a uniform distribution. This corresponds to a stream velocity of 10mph and a drift buildup against a square-edged superstructure. Commentary: As per AASHTO Standard Specifications for Highway Bridges 3.18.1.1
8.5 Uplift Loading
Provision shall be made for adequate attachment of the superstructure to the substructure. Commentary: As per AASHTO Standard Specifications for Highway Bridges 3.17.1
8.6 Curb Loading
250 pounds per linear foot of curb, applied at the top of the curb. Commentary: This is one-half of the loading given in AASHTO “Standard Specifications for Highway Bridges” 3.14.2.1. Due to the location of the bridges at driveway entrances, maximum speeds of 15mph are expected, resulting in greatly reduced impact loads.
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9. DESIGN DETAILS
9.1 Deflection
Allowable live load deflection shall not exceed either of the following:
1. Allowable live load deflection shall not exceed l/360, where l is the length of the
bridge span for pedestrian loading and H5 (5 ton) loading.
2. Allowable live load deflection shall not exceed l/240 for a vehicle weighing 7.5 tons.
Commentary: The AASHTO “Standard Specifications for Highway Bridges” 10.6.2 states that
spans preferably should be designed so that the live load deflection shall not exceed l/800.
The deflection limits specified in the AASHTO specification are not mandatory, only
recommended criteria that are up to the judgment of the engineer. The AASHTO “Guide
Specifications for Design of Pedestrian Bridges” 1997 section 1.3.1 specifies a deflection
limit of l/500 for pedestrian load. Since the deflection criterion is what in many cases
controls the size and therefore the cost of the beams, allowing a more liberal deflection
criterion results in significant cost savings. The IRC specifies an allowable live load deflection
not to exceed l/360 for floor beams and not to exceed l/240 for “all other structural
members”.
9.2 Vibrations
Vibration analysis shall not be considered. Due to the location of the bridges at driveway
entrances, maximum speeds of 15mph are expected, limiting excessive vibrations.
9.3 Bridge Deck Width
The total clear width of the bridge deck shall be 10 feet.
Commentary: AASHTO “Guide Specifications for Design of Pedestrian Bridges” 1997 section
1.2.1.2 specifies a clear deck width of 6 feet to 10 feet for a H5 Truck and a clear deck width
over 10 feet for an H10 Truck. Increasing the deck width increases cost.
9.4 Curbs
A bridge curb shall be installed. The height of the bridge curb above the roadway shall be
not less than 8 inches and preferably not more than 10 inches.
Commentary: Curb height complies with AASHTO “Standard Specifications for Highway
Bridges” 2.2.5
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9.5 Signage
A marker guide post will be installed at each of the four corners of the bridge
superstructure. One of the posts facing the highway will include the maximum vehicle
loading limitation.
9.6 Bridge Approach Ramp
The approach ramps to the bridge shall be surfaced with compacted crusher run material.
10. BRIDGE PLANS
Plans shall be developed for each bridge site for permitting and construction purposes. Each
plan will include the following:
1. Cover Page with site location map
2. Bridge Elevation
3. Superstructure
4. Decking
5. Abutments
6. Specifications
7. Material Estimate
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11. APPENDICES
A.1 WV VOAD BRIDGE COMMITTEE MEMBER LIST
A.2 BRIDGE COMMITTEE PARTNERS
A.3 BRIDGE COMMITTEE ADVISORS
B.1 BRIDGE TYPES
B.2 ABUTMENT TYPES
B.3 DECK TYPES
B.4 EXAMPLE SET OF PLANS
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A.1: WV VOAD BRIDGE COMMITTEE MEMBER LIST
Jenny Gannaway: WV VOAD Jim Ditzler: United Church of Christ Barbara Chalfaut: Presbytery of WV Jack Cobb: American Baptist Men Byron Boggs: Southern Baptist Men Dale Peercy (NVOAD): Lutheran Disaster Response Jeff Allen: Council of Churches Jason Yancey (NVOAD): Operation Hope MDS personnel: Kevin King, Larry Stoner and Rodney Burkholder Johann Zimmermann, PE
A.2: BRIDGE COMMITTEE PARTNERS
Michelle Breeland: FEMA Marlyn Lynch: WV-DHSEM State IA Officer Kevin Sneed: State Flood Plain Manager County Flood Plain and Building Permits Managers:
Rick Helton - Lincoln County Amanda Starr - Mingo County Greg Lay - Boone County Ray Perry - Logan County Randy Fry - Wayne County
Annette Taylor - Nicholas County Dan Riley - McDowell County Duval Fire Department: Wendy Beaver
A.3: BRIDGE COMMITTEE ADVISORS
Jimmy Wriston: WVDOT PE, Engineering Advisor Randy Campbell: United States Army Corp of Engineers (USACE)
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B.1: BRIDGE TYPES
Numerous types of structures are available for bridging the water ways. Each location lends
itself to different options at different costs and levels of complexity. The range of options
includes the following:
1. Culverts: These shall only be used for crossing drainage ditches and small waterways
due to their potential to restrict the stream flow.
2. Low water crossings: These shall be avoided due to impassable conditions during
inclement weather.
3. Poured-in-place concrete: These will in general be too expensive.
4. Precast concrete bridges: These will in general be too expensive.
5. Prestressed concrete plank: These may be an economic alternative for shorter spans,
but are not available in the project region.
6. Steel truss: These may be the only option for larger spans, but their cost is beyond
the economic constraints of this project.
7. Laminated timber superstructures: These may be economically and technically
suitable in some situations.
8. Steel beam: From field observations of existing bridges that have withstood flooding
in the project region, this option most economically meets the design criteria for
most sites.
For this project, a bridge with a steel beam superstructure is the most economically and
technically viable option. Typical bridge plans for these are given in the appendices.
B.2: ABUTMENT TYPES
Abutments shall be located outside the stream channel, if possible, so that they do not
impede the flow of the stream. They shall also be protected against erosion and scour.
Along with deck failures, failure of footings that were not supported on bedrock was
observed as the main cause of past bridge failures. Flood events cause unstable soils and
siltation of stream beds which in turn leads to severe erosion. Without extensive erosion
protection, culverts are prone to failure as well. After constructing several bridges using
this guideline document it has been decided that all footings for the new bridges of this
project shall rest on micropiles driven to refusal, which is usually bedrock. This bedrock is
usually encountered four to fifteen feet below the stream bed. Four inch-diameter steel
micropiles can be vibrated through river jack with the weight of a backhoe bucket to the
depth of about four feet. Below that depth, a driver attachment on a 1,500 pound breaker-
hammer shall be used as an economical pile-driver.
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The micropiles support a concrete footing. To avoid dewatering costs, excavation for the
footing shall be kept at or above the water table. This footing shall support one of the
following:
A. The footing shall be installed at an elevation such that the deck beams rest directly
on the pile cap.
B. The footing shall be installed at the water level with a reinforced masonry abutment
wall built up to the elevation needed for the installation of the deck beams. A
reinforced concrete wall may also be used but may be more expensive due to the
costs of labor and concrete pumping equipment needed to pump concrete across
the stream.
C. Concrete piers shall be built on the footing instead of a wall with either a steel or
concrete crossbeam on top to support the deck beams. However, steel crossbeams
shall be avoided if they will be in ground-contact beneath the bridge, which will
likely lead to corrosion. In addition, reinforced concrete beams were found to be
too labor- and time-intensive. It shall be noted that these options are no longer
being used for this project.
Grade beam footings built on top of gabion walls may be used where a retaining wall
structure is needed and where gabions are needed anyway for erosion control structures.
Large concrete abutments with footings in structurally sound soils well below the scour line
or on bedrock and with wing walls to redirect water flow, typical of highway bridges, would
be ideal but are beyond the economic constraints of this project.
The “Typical Bridge Plans” in the appendices show option A and B above. A grade beam on
a gabion wall is also included as a visual aid even though that option was no used for the
bridge design shown in the “Typical Bridge Plans”.
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B.3: DECK TYPES
Cast-in-place concrete, laminated pressure-treated lumber, and locally-sourced white oak planking were considered as options for the bridge decking. All are economically feasible.
Due to the limited amount of time volunteer groups have for installing the bridges, the forming, pouring, and removing of forms required for a cast-in-place concrete deck is difficult to schedule. As such, this option was deemed impractical.
Pressure-treated decks made of nail-laminated 2x4’s (vertically oriented) are easily installed by volunteers. Field observations of this type of bridge deck in the project area have shown that they will last 20 to 30 years. The bridges already constructed using this guideline documents have used this decking option exclusively with great success.
White oak decking is durable and is frequently used for private bridges in this area. Although it has yet to be used on any of the bridges already constructed using this guideline document, it remains a viable option.
B.4: TYPICAL BRIDGE PLANS
1. Cover Page2. Bridge Elevation3. Superstructure4. Decking5.1 House Side Abutment 5.2 Road Side Abutment 5.3 Gabion Abutment Alternative 6. Specifications7. Material Estimate
GENERAL NOTES:1. These specifications are for the design of a residential bridge
to replace or to repair an existing bridge that is on private landand that is privately owned.
2. The County Floodplain and Building Permits Manager shall beresponsible to ensure that all studies and conditions requiredby local, state and federal agencies have been satisfied beforeissuing a building permit. These include the following:
2.1. US Army Corps of Engineers (USACOE) Nationwidepermits
2.2. WV Division of Natural Resources Wildlife Resources(WVDNR)- Endangered Species
2.3. WV Division of Natural Resources Wildlife Resources(WVDNR)- Land and Streams
2.4. WVDOH - Driveway Permit2.5. State Historic Preservation Officer2.6. County Building Permit
3. Structural Loads:- Pedestrian Live Load = 40psf- Vehicle loading = 7.5 ton, one vehicle only. Vehicle loading
not in combination with the pedestrian live load.- Wind load = 50psf on projected vertical area of the
superstructure.- Transverse water loading = 280psf on vertical area of the
superstructure below flood elevation.- Curb loading = 250plf applied to the top of curb.
4. Live Load Deflections:- ≤ 1/360 of the length of the span for pedestrian and H5
loading.- ≤ 1/240 of the length of the span for vehicle weighing 7.5
tons.5. The Contractor is responsible for contacting Miss Utility before
commencing any excavation activities and for coordinatingwork with all necessary utility companies.
6. Contractor is responsible for all job site safety, all temporarysupport and shoring, and shall adhere to all OSHArequirements.
7. Contractor shall confirm all dimensions and conditions. Anydiscrepancies found between the drawings and specificationsand site conditions or any inconsistencies in drawings orspecifications shall be immediately reported to the engineer.Any work done before the engineer is consulted shall be doneat the contractor's risk.
8. Details shown in one place shall apply in all equivalent similarlocations unless specifically called out otherwise.
ABUTMENTS:Footings shall meet one of the following three requirements:1. When bedrock is encountered footings shall bear directly on
bedrock.2. If bedrock is not encountered and pile driving equipment is
available, micropile footings shall be used. Micropiles shall bedriven to bedrock or until refusal.
3. If bedrock is not encountered and pile driving equipment isunavailable, the bottom of the footing shall be a minimum ofone foot below the stream bed elevation or as deep aspossible using the available excavation and dewateringequipment. Pipe piers shall be embedded to a minimum of 4feet below the footer to further anchor the footing.
EARTHWORK:1. Backfilling of abutments and approach ramps shall be with
stone or shale, mechanically compacted with jumping jacktamper. Backfill around the abutments shall be contoured at amaximum slope of 1.5horizontal to 1vertical.
2. Backfill behind the superstructure backwall plank shall be withcrusher run gravel and shall be compacted with a jumping jacktamper.
3. Rip rap stone shall be placed to protect the abutments and theapproach ramps. A minimum 30ft length of riprap bankprotection shall be placed centered on the bridge. Minimumthickness of the riprap layer shall be 2 times the maximumstone diameter, but not less than 6 inches. Rip rap shall beplaced over landscape fabric and shall be placed to top heightof approach ramps.
4. Gabion baskets shall be 11 gage galvanized wire filled with 4"to 8" diameter stone.
5. Seed and mulch all disturbed areas within 14 days ofdisturbance.
CONCRETE:1. All concrete and reinforcing work shall comply with ACI 318
"Standard Building Code Requirements for ReinforcedConcrete".
2. Concrete for footings and abutments shall develop 4000psiminimum 28-day strength, have 3/4 inch maximum aggregatesize, maximum water-cement ratio of 0.49, and a maximumslump of 6 inches.
3. Concrete for all but the footings shall be consolidated bymechanical vibration.
4. Cure concrete at air temperatures of 40º F to 90ºF and followprocedures for cold weather concreting, ACI 306.
5. Reinforcement shall be provided with the following minimumconcrete cover:- Cast against earth - 3 inches.- Primary reinforcement and stirrups - 1.5 inches
6. Rebar shall be provided with the following lap splice lengths:- #5 rebar - 30 inches
7. Reinforcing steel to meet ASTM Specifications A-615, grade 60.
MASONRY:1. All masonry work shall conform to the latest edition of ACI
"Building Code Requirements for Masonry Structures" (ACI530) and ACI “Specification for Masonry Structures" (530.1).
2. Hollow concrete masonry units shall be medium weight units,conforming to ASTM C55 or ASTM C90. Masonry units shallhave a minimum net area compressive strength of 2,150psiwith Type "N" mortar, for a net area compressive strength ofmasonry of f'm = 1500psi.
3.Mortar shall be Type “S”.4. Bond beam and vertical cell grouting shall be with 3000psiconcrete grout, ½” max size aggregate, and shall beconsolidated by mechanical vibration.
5.When the ambient air temperature is less than 40 °F,implement cold weather procedures as per ACI530.1, article1.8C.
METALS:1. All structural steel shall be designed, fabricated and erected in
accordance with the latest specifications of the AmericanInstitute of Steel Construction (AISC).
2. Structural steel:- Structural W-shapes: ASTM A992 Grade 50- Channels, Angles and plates: ASTM A36- Pipe: ASTM A53 Gr.B- High Strength Bolts: ASTM A325- Common Bolts: ASTM A307- Anchor Bolts: F1554 Gr 36
3. Weld electrodes shall be class E70XX.4. All steel shall be painted with rust inhibitive “Noxyde” paint
unless hot dipped galvanized.
WOOD DECKING:1. All lumber shall either be Southern Pine treated for ground
contact or white oak.2. All fasteners used for wood shall be hot-dipped galvanized.
BRIDGE OWNER MAINTENANCE REQUIREMENTS:The following maintenance shall be required of the owner of thebridge:1. The maximum vehicle weight limit of 7.5 tons shall be
maintained.2. No more than one vehicle shall be on the bridge at any one
time.3. Maintain a bridge marker guidepost at each corner of the
bridge as well as signage for weight limit.4. Wood decking and curb shall be repaired or replaced if it
becomes loose, deteriorated or damaged in any way.5. Debris buildup shall be removed and the stream bed around
and under the bridge shall be maintained clean ofobstructions.
6. Erosion after a flood shall be repaired immediately to maintainprotection of the abutments, adjacent embankment andapproach ramp to its as-built profile.
