Bridge Standards Update

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.

• Email – [email protected]

• Or Call

– 512-416-2212

Questions?