bridge standards update
TRANSCRIPT
Bridge Standards Update
John M. Holt, P.E.
Texas
of TransportationDepartment
Transportation Short Course
October 2011
Outline
• Precast Caps • Piles and Trestle Bents • Sidewalks/Medians on Bridge Decks • U-Beams • Parallel Wingwalls, PW • Crash Tests and Rails
Precast Caps • Issued PBC-RC in April 2011
– Standard to be included with all standard bents with round columns
• Precasting caps is a Contractor option – Intended for “Standard Bents”, not necessarily
custom bents that look like standard bents – No minimum number of bents per bridge
specified—let the Contractor decide the most cost-effective option.
Precast Caps Caney Creek Bridge SH 198, Henderson
County
Precast Caps
Precast Caps • PBC-P in final review (Standard with Piles)
– When made available, it is to be included with all standard trestle bents with either Concrete or Steel HP piles
• Allows precast caps as a Contractor option – No minimum number of bents per bridge
specified—let the Contractor decide the most cost-effective option
Precast Caps
• PBC-P
Pockets in bottom of cap to receive concrete piles, then grouted
Steel H-piles are welded to embedded steel plates
Precast Caps • Will there be a standard for abutments? Not
planning on developing one • The PBC standards can be modified to cover
precast abutment caps
Piles and Trestle Bents • New HP Sections on Trestle Bent Standards
– HP18 x 135 is steel option to 20” Concrete Piles – HP16 x 101 is contractor option for HP14 x 117
– Only producer of these new HP sections is
Nucor-Yamato – Dimensions are in ASTM A6
Piles and Trestle Bents • Revised Pile Embedment in Caps/Footings
– NEW: 18” Min Embed for 20” and 24” Concrete Piles
– 12” Min Embed for 18” and smaller piles
• All Trestle Bent standards refer the user to the FD standard for pile embedment (with exceptions)
• CP Standard is revised
Piles and Trestle Bents • On all Trestle Bent Standards
– New restriction on unequal span lengths: • Shorter span must be at least 80 percent of the
longer span
• Piles are best suited for low-moment demand conditions and that means reasonably balanced span lengths
Sidewalks/Medians on Bridge Decks
• Drawing is in final review stage • Option to have a drain thru the sidewalk,
using slip-resistant steel deck plate
U-Beams • Revisions prompted by 2 research projects:
– Project 5834, Study of Elastomeric Bearings for Superelevated U-Beam Bridges, complete, Research Supervisor: Dr. Charles Newhouse, Texas Tech
– Project 5831, Bursting and Shear Behavior of
Prestressed Concrete Beams with End Blocks, on-going, Research Supervisor: Dr. Oguzhan Bayrak, UT-Austin
U-Beams • Observations from Bearing Project:
– Superelevation should be considered in bearing design
• There is an eccentric reaction on bearing, producing a transverse moment
• Strain is strain—consider transverse strain together with longitudinal strain
– Significant slip can occur with 6 % and greater superelevations
U-Beams • Draft UBEB Revisions:
– Beveled sole plates required when bearing pad taper report has taper over 5 percent OR when the span has a superelevation over 5 percent.
– Required bevel = the taper listed on the bearing taper report
– Smaller plan dimensions for U40 bearings – 8 x 0.25” layers, resulting in 2.75” overall bearing
height – Recommend not using U-beams for bridges with
superelevations above 6 %
U-Beams • Observations from Shear & End Block
Project: – U-beam ends could benefit with more
reinforcement across the web - bottom flange interface
– Thicker webs and/or thicker end blocks would also be beneficial
U-Beams • U-beam revisions:
– Additional reinforcement in end regions – End block length increased 12”
• Tested and they work
U-Beams
CUT
End-region bottomflange-to-web interface
reinforcement, 𝜌𝑖𝑛𝑡 = 1%
A
B
Square end block length: 2'-6" to 3'-0"
Square end block length: 1'-6" to 2'-0"
R-bar
R-bar
L-bars
End-region bottomflange-to-web interface reinforcement, 𝜌𝑖𝑛𝑡 = 4%
End block vertical
reinforcement (V- and F-bars)
Culvert Parallel Wingwalls • Change to top of wall geometry suggested to
us by Paris District to mitigate erosion at wing ends
1V:6H Slope at Wing Ends
Not used when railings are on top of wingwalls
Crash Tests and Rails
SSTR Retrofit to 6” Thick Pan Form Overhang, MASH TL-3, Pickup
Can a barrier rail be retrofit to the
longest and thinnest pan form overhang at slab edge?
Conventional wisdom said no
SSTR Retrofit to 6” Thick Pan Form Overhang, MASH TL-3, Pickup
Two #8 dowels at
joints
Retrofit SSTR, MASH TL-3
Aftermath
SSTR, MASH TL-4, Single Unit Truck
What is the Minimum Rail Height for the MASH Single Unit Truck?
MASH Single Unit Truck rolls over
32” tall barriers
SSTR, MASH TL-4,
Aftermath
T223 with Shallow Anchorage Embedment, MASH TL-3, Pickup
Can we anchor a concrete rail only
within the 5” CIP slab on Box Beams and Slab Beams?
LRFD Spec requires 8.3” min for No. 5 Gr 60 bar, 90-deg hook,
uncoated
31” Guardrail & Bridge Rails
• 31” guardrail implementation will trigger the retirement of our remaining 27” tall rails: T101, T101RC, T1-101R, and T6
• Unsuccessful crash test for a replacement to the T101 and T1-101R
• Currently working on curb mount retrofit, T131RC
• May need an exception for T101RC installations
T131, MASH TL-3, Pickup
The T131 represents a “replacement” to the T101 and T1-
101R
T8, NCHRP 350 TL-3, Pickup
The T8 was an attempt to have a high speed version of T6
T101, MASH TL-3, Pickup
This is a 3rd high speed test with a rail having steel posts bolted
directly to the overhang
Summary
Passing a high speed crash test with a rail having posts bolted directly to the deck is elusive
A low speed, all-steel rail, bolted directly to an overhang might be
possible
No More T101 and T6? • Recommend using the T1W
– Very open for both view and hydraulics – Modular design—good for installation and
maintenance – Concrete curb:
• Great for strengthening the deck edge and limiting deck runoff
• Not so good for pushing snow off deck edge – Yes, it can be retrofitted to a bridge
T1W Rail
Photos courtesy of Kerrville AO
Bridge Railing Manual • A revised Bridge Railing Manual should be
available soon • Delays are from waiting on crash test
results, implementation of MASH, etc.
