somerset county, pa kings bridge rehabilitation · 3/7/2019 · history 1803 “built” date on...
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Kings Bridge Rehabilitation
Somerset County, PA
Somerset County, Pennsylvania
Kings Covered Bridge Rehabilitation
William Collins, RLA Samer Petro, P.E
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Location
Middlecreek Township, Somerset County, Pennsylvania
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History
1803 “Built” date on bridge (incorrect)
mid-1800’s Probable construction period
1906 “Rebuilt” date on bridge - likely
1930’s Bypassed with steel highway bridge
1930’s-2002 Used as a King Family farm building
1996 PA funding for stabilization
Fall 2000 Stabilized in place
2002 Acquired by S. Alleghenies Conservancy
2008 Acquired by Middlecreek Township
2009 Completed – bridge and site
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Superstructure
Multiple Kingpost Truss w/ Retrofitted Tied Arch
Note
bay spacing and
repair rods
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• Retrofitted 1906 with nail-laminated arches creating “Arch-Truss”
• Arches “tied” to bottom chord
Multiple Kingpost Truss with arch added
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Bridge data
Length: 114 feet clear span
Width: 14’-6” out to out
Superstructure form: Multiple Kingpost with
retrofitted arches (1906)
Primary Species: White Oak
Timbers members: hewn, circular, up & down
Substructure: local limestone
Hardware: round nails
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Engineering – DCF Engineering Inc, Cary, NC
Construction – Arnold M. Graton Associates Inc
Stabilization
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Queenpost-tensioned trusses w/ needle beams
Temporary Superstructure
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Interior
Used as a barn after bypass
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Failures
Both lower chords, several posts and tie beams
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Moisture testing
Non-destructive Field Testing
Technical Assistance
USDA Forest Service
Morgantown, WV
Forest Products Laboratory
Madison, WI
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Non-destructive Field Testing
Resistance Drilling Stress Wave Timer
Both chords had relative drilling
resistance below 15%
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Destructive Testing
4-foot lower chord segment
removed for species
analysis by Forest Products
Laboratory
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Mapping
Lower chord segments
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Lower tie beam / tail of truss post
Failure from compression force of truss brace
Lower Chord Failure in both trusses
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Substructure
Horizontal thrust from broken chords, struts ceased to work
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Bed timbers
Note deformation
Retrofitted Struts Typical failure at seats
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Arches
Nail-laminated retrofits
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Arches
Deformation and previous interventions
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Thrust Block at Portal Post
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Bearing
Chord seat at abutment
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Roof assembly
Mortised, pinned, and wedged horizontal X-bracing
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Post - upper tie beam, rafter sill
Cantilevered tie beams failed where leaks occurred
Truss Bracing
water damage
at truss post
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Preservation Philosophy
• Rehabilitate for pedestrian use
• Retain historic fabric as much as possible
• Replace with in-kind materials
• Meet the Secretary’s Standards
Resource eligible
for National
Historic Register
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Structural Analysis
3-D rendering (STAAD Model) – Samer Petro, P.E.
Goal of Analyses: 1. Compare stresses to allowable stresses based on (NDS)
2. Understand arch-truss system
• 3-D Model STAAD
• Provides member forces, moments, and deflections
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Modeling
• Ends of diagonals and ends of posts pinned (free to rotate)
• Chord members and arches continuous
• Multiple kingpost modeled as pinned
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Loads
• Dead loads: approximated by field measurements and
using white oak density of 43 pcf (MOE 1.4M psi)
• Live load: Pedestrian load of 85 psf (AASHTO)
• Snow Load: 35 psf
• Wind Load: 12.5 psf based on wind velocity on 100 mph
(ASCE 7)
• Load Combination: [dead load + wind+live+snow)*0.75]
(ASCE 7)
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Stress Distribution
Arch-Truss
Truss
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Repair / Solutions
Dapped lower chords to permit laminated arches to
extend forces directly into the abutments
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Abutment Repairs
Excavated abutments, buttressed with flowable backfill
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Truss Repairs
Post splices and replacement
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Truss Repairs
Post splice Innovative GFRP
rods embedded in
epoxy
Chord
Traditional white
oak “joggle”
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Engineering Results
• Arches: are structurally dominant
• Trusses: lower chord in tension and max @ mid-span (expected)
• Arch-truss system: maximum compressive forces in arches at ends
• All member stresses well below allowable values
• Deflections due to dead and live loads below AASHTO limits
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Before – stabilized After – restored
Completion
Modjeski Award for Historic Preservation, 2008
Preservation Pennsylvania
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Completion
Before
After
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Budget
$ 90,000 Stabilization - 1996 (Source – PA DCED)
Engineering, construction, funding strategy
$945,000 Rehabilitation
Engineering, construction, environmental
(Sources)
$595,000 FHWA Enhancements
$340,000 FHWA National Covered Bridge
$ 10,000 Rockwood Area Historic Society
$1.035 M TOTAL
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Technical Team
Prime Consultant – Simone Collins Inc.
Structural Engineer – Samer Petro (formerly of Gannett Fleming Inc. now at Herbert Rowland Grubic)
Historic Consultant – Dr. Emory Kemp
Stabilization Engineer – DCF Engineering Inc.
Scientific Investigation – Forest Products Laboratory
Stabilization Contractor – Arnold M. Graton Assoc.
Rehabilitation Contractor – Allegheny Restoration
Surveyor – Paul C. Rizzo Inc.
Permit Assistance - Somerset Conservation District.
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Project Partners
Client – Southern Alleghenies Conservancy
Funding Partner – Federal Highway Administration
Funding Partner – Pennsylvania Commonwealth
(PennDOT and DCNR)
Funding Partner – Rockwood Area Historic Society
Funding Partner – Somerset County
Project Administration – PennDOT
Ultimate Owner – Middlecreek Township
Steward / Donor – King Family
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Contacts
Samer H. Petro, P.E.
Herbert, Rowland & Grubic, Inc.
829 Fairmont Road, Suite 201
Morgantown, WV 26501
304 284 9222
William Collins, RLA
Simone Collins Landscape Architecture
119 East Lafayette Street
Norristown, PA 19401
610 239 7601