2008 Ballot Items 69-73

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2008 AASHTO BRIDGE COMMITTEE AGENDA ITEM: 69 (REVISION 1)

SUBJECT: LRFD Bridge Design Specifications: Section 3, Article 3.14 (WAI 26)

TECHNICAL COMMITTEE: T-5 Loads

REVISION ADDITION NEW DOCUMENT

DESIGN SPEC CONSTRUCTION SPEC MOVABLE SPEC

LRFR MANUAL OTHER

DATE PREPARED: 1/25/08

DATE REVISED: 5/22/08

AGENDA ITEM:

Item #1

Revise the 2nd

paragraph of Article C3.14.1 as follows:

The requirements herein have been adapted from the AASHTO Guide Specifications and Commentary for

Vessel Collision Design of Highway Bridges (1991) using the Method II risk acceptance alternative, and modified

for the LRFD Edition (2008). The 1991 Guide Specifications required the use of a single vessel length overall (LOA)

selected in accordance with the Method I criteria for use in estimating the geometric probability and impact speed to

represent all vessel classifications. This was a conservative simplification applied to reduce the amount of effort

required in the analysis. With the introduction of personal computers and programming, the simplification can be

lifted and AF can be quickly obtained for each design vessel, which was originally envisioned. The end result is a

more accurate model for the vessel collision study as well as more informative conclusions about the vessel fleet and

associated probabilities of collision.

Item #2

Revise the 1st

paragraph in Article 3.14.5 as follows:

3.14.5 Annual Frequency of Collapse

The annual frequency of a bridge component collapse shall be taken as:

( ) ( ) ( ) ( ) AF = N PA PG PC (PF) (3.14.5-1)

where:

AF = annual frequency of bridge component collapse due to vessel collision

N = the annual number of vessels, classified by type, size, and loading condition, that utilize the channel

PA = the probability of vessel aberrancy

PG = the geometric probability of a collision between an aberrant vessel and a bridge pier or span

PC = the probability of bridge collapse due to a collision with an aberrant vessel

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PF = adjustment factor to account for potential protection of the piers from vessel collision due to upstream or

down stream land masses, or other structures, that block the vessel

AFshall be computed for each bridge component and vessel classification. The annual frequency of collapse for thetotal bridge shall be taken as the sum of all component AFs.

Revise the 3rd

paragraph as follows:

For regular typical bridges, the maximum annual frequency of collapse, AF, for the total bridge, shall be taken as

0.001.

Item #3

Add Article 3.14.5.5 as follows:

3.14.5.5 Protection Factor

The protection factor, PF, shall be computed as:

PF= 1 (% Protection Provided/100) (3.14.5.5-1)

If no protection of the pier exists, then PF=1.0. If the pier is 100% protected, then PF=0.0. If the pier protection (for

example a dolphin system) provides 70% protection, then PFwould be equal to 0.3. Values for PFmay vary from pier

to pier and may vary depending on the direction of the vessel traffic (i.e., vessel traffic moving inbound versus traffic

moving outbound).

Item #4

Add Commentary to Article 3.14.5.5 as follows:

C3.14.5.5

The purpose of the protection factor, PF, is to adjust the annual frequency of collapse, AF, for full or partial protection

of selected bridge piers from vessel collisions such as:

dolphins, islands, etc.

existing site conditions such as a parallel bridge protecting a bridge from impacts in one direction

a feature of the waterway (such as a peninsula extending out on one side of the bridge) that may block vessels

from hitting bridge piers

a wharf structure near the bridge that may block vessels from a certain direction.

The recommended procedure for estimating values for PF is shown in Figure C3.14.5.5-1 that illustrates a simple

model developed to estimate the effectiveness of dolphin protection on a bridge pier.

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Figure C3.14.5.5-1. Illustrative Model of the Protection Factor (PF) of Dolphin Protection

Around a Bridge Pier.

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Item #5

Add as paragraph 3 to the Commentary of Article 3.14.5.2.3 as follows:

Following the terrorist attacks upon the U.S. on September 11, 2001, the U.S. Coast Guard has required that all

foreign ships entering the U.S. waterway system to be equipped with a variety of advanced electronic navigation

aids and tracking systems. These requirements do not extend to domestic barge tows on the inland waterway

system. An argument could be put forth that the use of such advanced navigation aids may reduce the risk of vessel

collision with bridges and should be accounted for in the computation of the probability of aberrancy (PA). At

present however, no studies have been performed to analyze and document the potential reduction in PA due to

such electronic aids-to-navigation. If a case can be made at a particular waterway and bridge site that improved

electronic navigation aids would reduce PA, then such a factor could be used in the equation provided that it is

approved by the Owner.

As an example, such a reduction was recently used in the design of a new cable-stayed bridge in Argentina. The

thought process proceeded as follows: 1) approximately 60-90% of all accidents are caused by pilot error (a valueof 70% was chosen for the analysis); 2) the bridge Owner firmly believed that improvements to electronic

navigation would result in a decrease in the rate of pilot error however there were no studies or data to support

this beliefor what the reduction should be; 3) though no actual data existed, the Designer believed, and the Owner

agreed, that the pilot error rate could conservatively be reduced by 30% due to the electronic aids; therefore a

factor of 0.3 x 0.7 = 0.21 was used to model the reduction in the ship accident rate by about 20% for the risk

analysis.

It is anticipated that future research will provide a better understanding of the probability of aberrancy and how to

accurately estimate its value. The implementation of advanced vessel traffic control systems using automated

surveillance and warning technology should significantly reduce the probability of aberrancy in navigable

waterways.

Item #6

Revise ninth paragraph of Commentary to Article 3.14.1 as follows:

The water level and the loading conditions of vessels influence the location on the pier where vessel impact loads

are applied, and the susceptibility of the superstructure to vessel hits. In addition, the The water depth plays a

critical role in the accessibility of vessels to piers and spans outside the navigation channel. In waterways with large

water stage fluctuations, the water level used can have a significant effect on the structural requirements for the pier

and/or pier protection design. The water depth at the pier should not include short-term scour. In addition, the

water depth should not just be evaluated at the specific pier location itself, but also at locations upstream and

downstream of the pier which may be shallower and would potentially block certain deeper draft vessels from

hitting the pier. In waterways with large water stage fluctuations, the water level used can have a significant effect

on the structural requirements for the pier and/or pier protection design.

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Item #7

Add after existing Commentary to Article 3.14.1:

Unless otherwise indicated in these Specifications an evaluation of the following two vessel collision events

combined with scour conditions are recommended:

1. A drifting empty barge breaking loose from its' moorings and striking the bridge. The vessel impact loads

should be combined with one-half of the predicted long term scour plus one-half of the predicted short term

scour. The flow rate, water level and short term scour depth are those associated with the Design Flood for

Bridge Scour (100-year flood event).

2. A ship or barge tow striking the bridge while transiting the navigation channel under typical waterway

conditions. The vessel impact loads should be combined with the effects of one-half of the long term scour and

no short term scour. The flow rate and water level should be taken as the yearly mean conditions.

OTHER AFFECTED ARTICLES:

None

BACKGROUND:

None

ANTICIPATED EFFECT ON BRIDGES:None

REFERENCES:

None

OTHER:

None

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2007 AASHTO BRIDGE COMMITTEE AGENDA ITEM: 70

SUBJECT: LRFD Bridge Design Specifications: Section 1, Various Articles (WAI 27)



DESIGN SP EC CONSTRUCTION SPEC MOVABLE SPEC

LRFR MANUAL OTHER


DATE REVISED:

AGENDA ITEM:

Item #1

Delete the Commentary to Article 1.1, 1st paragraph.

Horizontally curved concrete girders are not fully covered and were not part of the calibration data base.

Item #2

Revise Article 1.3.2.1 as follows:

1.3.2 LIMIT STATES

1.3.2.1 General

i = load modifier: a factor rela ting t o

ductility, redundancy, and operational classification

importance

I = a factor relating to operational

classification importance as specified in Article 1.3.5

C1.3.2.1

Eq. 1 is the basis of LRFD methodology.

Assigning resistance factor = 1.0 to all nonstrength

limit states is a default, and may be over-ridden by

provisions in other Sections temporary measure;

development work is in progress.

Ductility, redundancy, and operational classification

importance are considered in the load modifier .

significant aspects affecting the margin of safety of

bridges. Whereas the first two directly relate to physical

strength, the last concerns the consequences of the bridge

being out of service. The grouping of these aspects on the

load side of Eq. 1 is, therefore, arbitrary. However, it

constitutes a first effort at codification. In the absence ofmore precise information, each effect, except that for

fatigue and fracture, is estimated as 5 percent,

accumulated geometrically, a clearly subjective approach.

With time, improved quantification of ductility,

redundancy, and operational classification importance,

and their interaction with and system reliability synergy,

may be attained, possibly leading to a rearrangement of

Eq. 1, in which these effects may appear on either side of

the equation or on both sides. NCHRP Project 12-36 is

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currently addressing the issue of redundancy.

The influence of on the girder reliability index, ,

can be estimated by observing its effect on the minimum

values of calculated in a database of girder-type

bridges. Cellular structures and foundations were not a

part of the database; only individual member reliability

was considered. For discussion purposes, the girder

bridge data used in the calibration of these Specifications

was modified by multiplying the total factored loads by

= 0.95, 1.0, 1.05, and 1.10. The resulting minimum

values of for 95 combinations of span, spacing, and

type of construction were determined to be approximately

3.0, 3.5, 3.8, and 4.0, respectively. In other words, using

an > 1.0 relates to a higher than 3.5.

A further approximate representation of the effect of values can be obtained by considering the percent of

random normal data less than or equal to the mean value

plus , where is a multiplier, and is the standard

deviation of the data. If is taken as 3.0, 3.5, 3.8, and 4.0,

the percent of values less than or equal to the mean value

plus would be about 99.865 percent, 99.977 percent,

99.993 percent, and 99.997 percent, respectively.

Item #3

Revise as follows:

1.3.3 Ductility

The structural system of a bridge shall be

proportioned and detailed to ensure the development of

significant and visible inelastic deformations at thestrength and extreme event limit states before failure.

It may be assumed that the requirements for ductility

are satisfied for a concrete structure in which the

resistance of a connection is not less than 1.3 times the

maximum force effect imposed on the connection by the

inelastic action of the adjacent components.

Energy-dissipating devices may be accepted as means

of providing ductility. Energy-dissapating devices may be

substituted for conventional ductile earthquake resisting

systems and the associated methodology addressed in

these Specifications or the AASHTO Guide Specifications

or Seismic Design of Bridges.

For the strength limit state:

D 1.05 for nonductile components and connections

= 1.00 for conventional designs and details

complying with these Specifications

0.95 for components and connections for which

additional ductility-enhancing measures have

been specified beyond those required by these

Specifications.

Formatted: Bullets and Numbering

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For all other limit states:

D = 1.00

Item #4

Revise as follows:

1.3.4 Redundancy

Multiple-load-path and continuous structures should

be used unless there are compelling reasons not to use

them.

Main elements and components whose failure is

expected to cause the collapse of the bridge shall bedesignated as failure-critical and the associated structural

system as nonredundant. Alternatively, failure-critical

members in tension may be designated fracture -critical.

Those elements and components whose failure is not

expected to cause collapse of the bridge shall be

designated as nonfailure-critical and the associated

structural system as redundant.


R > 1.05 for nonredundant members

= 1.00 for conventional levels of redundancy,

foundation elements where already accounts

for redundancy as specified in Section 10.5

0.95 for exceptional levels of redundancy beyond

girder continuity and a torsionally-closed cross-

section.


R = 1.00

C1.3.4

For each load combination and limit state under

consideration, member redundancy classification

(redundant or nonredundant) should be based upon the

member contribution to the bridge safety. Several

redundancy measures have been proposed (Frangopol and Nakib 1991 ).

Single-cell boxes and single-column bents may be

considered nonredundant at the Owners discretion. For

prestressed concrete boxes, the number of tendons in each

web should be taken into consideration. For steel cross-

sections and fracture-critical considerations, see Section 6.

The Guide Manual for Condition Evaluation and Load

and Resistance Factor Rating (LRFR) of Highway Bridges

(2003 w/05 Interims) defines bridge redundancy as the

capability of a bridge structural system to carry loads after

damage to or the failure of one or more of its members.

System factors are provided for post-tensioned segmental

concrete box girder bridges in Appendix E of the Guide

Manual.

System reliability encompasses redundancy by

considering the system of interconnected components andmembers. Rupture or yielding of an individual component

may or may not mean collapse or failure of the whole

structure or system (Nowak 2000). Reliability indices for

entire systems are a subject of ongoing research and are

anticipated to encompass ductility, redundancy, and

member correlation.

Item #5

Revise as follows:

1.3.5 Operational Importance Classification

This article shall apply to the strength and extremeevent limit states only.

The Owner may declare a bridge or any structural

component and connection thereof to be of operational

priority importance.


I 1.05 for important critical/essential bridges

= 1.00 for typical bridges

C1.3.5

Such classification should be done by personnelresponsible for the affected transportation network and

knowledgeable of its operational needs. The definition of

operational priority may differ from Owner to Owner and

network t o network. should be based on social/survival

and/or security/defense requirements. The commentary to

Article 3.10.3 provides some guidance on selecting

importance categories as they relate to design for

earthquakes. This information can be generalized for other

situations Guidelines for classifying critical/essential

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0.95 for relatively less important bridges

classified by the Owner.


I = 1.00

bridges are as follows:

Bridges that are required to be open to all traffic

once inspected after the design event and are

usable by emergency vehicles and for security,

defense, economical, or secondary life safety

purposes immediately after the design event.

Bridges that should, as a minimum, be open to

emergency vehicles and for security, defense, or

economical purposes after the design event, and

open to all traffic within days after that event.

Bridges that are formally designated as critical

for a defined local emergency plan.

Owner-classified bridges may use a value for < 1.0

based on ADTT, span length, available detour length,

or other rationale to use less stringent criteria.

Three levels of importance are specified in

Article 3.10.3 with respect to seismic design:

critical, essential, and other. For the purposes of

this article, bridges classified as critical or

essential in Article 3.10.3 should be considered of

operational importance.

Revise 1.2 Definitions as follows:

Load ModifierA factor accounting for ductility, redundancy, and the operational importance classification of

the bridge.

Revise 1.3, 4.3, 6.3 Notation; Eq. C4.6.7.2.1-1 as follows:i = load modifier: a factor relating to ductility, redundancy, and operational classification importance

Revise 2.7.1 as follows:

An assessment of the importance priority of a bridge.

For bridges deemed critical/essential important.

Revise C2.7.1 as follows:

there are no uniform procedures for accessing the importance priority of a bridge.

procedures to access bridge importance priority .

The procedures established for accessing bridge importance priority


These criteria should take into account importance priority of the structure.

Revise C2.7.2 as follows:

The level of the threat and of the operational importance classification bridge.Approximate methods should be used for low-force, low-importance bridges, while more sophisticated analyses

important priority bridges.

Revise Article 3.10.5 (see 08 Interims) as follows:

3.10.5 Importance Categories Operational Classification

For the purposes of Article 3.10one of three operational importance categories

Revise header in Tables 3.10.5-1

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Importance Operational Category

Revise header in 3.10.5-2 as follows:

All Importance Categories All Operational Categories


The Owner shall establish and/or approve the bridge operational importance classification.

Revise Article 3.14.3 as follows:

3.14.3 Operational Classification Importance Categories

For the purpose of Article 3.14, an operational importance classification, either critical/essential or typical

regular, shall be.

Revise the Commentary to Article 3.14.3 as follows:

This Article implies that a critical critical/essential bridge may be damaged to an extent acceptable to the Owner, asspecified in Article 3.14.2, but should not collapse and should remain serviceable, even though repairs are needed.

Revise Article 3.14.4 as follows:

The design vessels shall be selected on the basis of the bridge operational importance classification.

Revise Article 3.14.5, paragraphs 2 and 3, as follows:

For critical critical/essential bridges, the maximum annual frequency of collapse, AF, for the whole bridge, shall be

taken as 0.0001.

For regular typical bridges, the maximum annual frequency of collapse, AF, for the total bridge, shall be taken as

0.001.

In Appendix B3, revise the 2nd and 3rd bullets as follows:

For bridges in Zones 3 and 4 with operational importance classification of.

In C4.1, revise as follows:

size, complexity, and priority importance of the structure.

Revise 4.7.2.2.1 as follows:

For important critical or essential structures.

Revise paragraph 3 in Article 4.7.4.1 as follows:

regardless of their importance operational classification and geometry.

Revise C4.7.4.3.1 as follows:

seismic zone, regularity, and importance operational classification of the bridge.

In Appendix A4 step E3 and Appendix C6 step E3, revise as follows:

Operational Importance Classification

In Appendix A10, sentence prior to Fig. A10.1-1, revise as follows

in the case of important critical/essential bridge sites

In Article 12.5.4, last sentence, revise as follows:

Operational importance classification shall be determined on the basis of.

Item #6

Add the following Reference at the end of Section 1:

Nowak, Andrzej, and Collins, Kevin R. 2000. Reliability of Structures, McGraw-Hill Companies, Inc.

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None

BACKGROUND:

Item #1, C1.1: Not appropriate to single out horizontally curved concrete girders as not being fully covered. The

calibration database didnt include cellular members, either. Furthermore, this statement can make some

engineers hesitant to use the LRFD Specs and instead use the LFD Specs.

Item #2, 1.3.2.1:

Commentary 2nd

par.Sections 5, 6, and 10 also make statements on values for in limit states other than

strength. Better to call = 1.0 a default, and refer to other Sections.

Commentary 3rd par.--The NCHRP 12-36 research was completed, but needs to be revisited before

implementation.

Commentary 4th--par.--Cellular structures have inherently higher reliability indices than those listed here

for single girders, and were not a part of the original database. Foundations were not considered in the

original study.

See sub-item 5, below, concerning operational importance

Item #3, 1.3.3 Ductility:

2nd par.Ductility of concrete components is more a function of the maximum reinforcement and

detailing, and more appropriately addressed in Section 5.

3rd

par.--Not appropriate to use = 0.95 for Strength when only Extreme Event I has considered ductility.

Item #4, 1.3.4 Redundancy:

Failure means reaching the ultimate load-carrying capacity, and not necessarily rupture or collapse.

Perhaps the intended meaning has evolved to fracture-critical since the writing of this provision; the

terminology is now used for steel members, but not concrete members. That concept differs from

redundancy. Single-cell boxes and single-column bents are now addressed in the Commentary.

This reduction for redundancy cannot be taken in addition to other methods of accounting for redundancy.

Girder continuity is not enough of a redundancy to take the 5% reduction.

Commentary, 3rd

paragraph--The changes to LRFR for segmental bridges were developed by FDOT.

Commentary, 4th paragraphSystem reliability is potentially the next generation in structural reliability of

bridges.

Item #5, 1.3.5 Operational Importance

The present terminology can imply that some bridges arent important and could be of concern to those

not familiar with bridge design specifications.

The topic was consciously avoided in the Seismic Guide Specs by developing performance criteria:

Higher levels of performance, such as the operational objective, may be established and authorized by the

bridge owner.

Commentary, 1st parBridge engineers need it in writing that we shouldnt be the ones deeming bridges

as critical/essential, or non-critical/essential! Commentary, 2nd

. parThe reference to Article 3.10.3 must be deleted because it was revised last year to

address a different topic. Now, the Specs merely say (C3.10.1) Bridge Owners may choose to mandate

higher level of performance for special bridges. The Seismic Guide Specs elaborate with the three

proposed bullets.

ANTICIPATED EFFECT ON BRIDGES:

None

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REFERENCES:

Ghosn, M., Moses, F., NCHRP Report 406, Redundancy in Highway Bridge Superstructures, Transportation

Research Board, Washington, DC (1998)

Liu, W.D., Ghosn, M., and Moses, F. NCHRP Report 458, Redundancy in Highway Bridge Substructures,

Transportation Research Board, Washington, DC (2001)

Nowak, Andrzej, and Collins, Kevin R. 2000. Reliability of Structures, McGraw-Hill Companies, Inc.

OTHER:

None

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2008 AASHTO BRIDGE COMMITTEE AGENDA ITEM: 71

SUBJECT: LRFD Bridge Design Specifications Section 2, Article 2.5.1 (WAI 28)




LRFR MANUAL OTHER


DATE REVISED:

AGENDA ITEM:

Revise the Commentary to Article 2.5.1 as follows:

Minimum requirements to ensure the structural safety of bridges as conveyances are included in these

Specifications. The philosophy of achieving adequate structural safety is outlined in Article 1.3. It is recommended

that an approved QC/QA review and checking process be utilized to ensure the design work meet these

Specifications.


None

BACKGROUND:

None


Improved QA/QC

REFERENCES:

California Department of Transportation, internal correspondence

NTSB Safety Recommendation H-08-1, dated 1/15/08

OTHER:

None

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SUBJECT: LRFD Bridge Design Specifications: Section 3, Articles 3.4.1 and 3.7.5, Section

10, Article 10.5.5.3.2 (WAI 29)




LRFR MANUAL OTHER



AGENDA ITEM:

Item #1

Revise Extreme Event I in Article 3.4.1 as follows:

EXTREME EVENT ILoad combination including earthquake. The load factor for live load EQ, shall be

determined on a project-specific basis.

At the end of Article 3.4.1, delete the following existing paragraph:

The load factor for live load in Extreme Event Load Combination I, EQ, shall be determined on a project- specific

basis.

Revise the commentary to Extreme Event I in Article 3.4.1 as follows:

Although this limit state includes water loads, WA, the effects due to WA are considerably less significant than

the effects on the structure stability due to degradation. Therefore, unless specific site conditions dictate

otherwise, local pier scour and contraction scour depths should not be included in the design. However, theeffects due to degradation of the channel should be considered. Live load coinci dent with an earthquake is

discussed elsewhere in this article.

Past editions of the Standard Specifications used EQ = 0.0. This issue is not resolved. The possibility of partial

live load, i.e., EQ < 1.0, with earthquakes should be considered. Application of Turkstras rule for combining

uncorrelated loads indicates that EQ = 0.50 is reasonable for a wide range of values of average daily truck

traffic (ADTT).

At the end of Article C3.4.1, delete the following existing paragraph:

Past editions of the Standard Specifications used EQ = 0.0. This issue is not resolved. The possibility of

partial live load, i.e., EQ < 1.0, with earthquakes should be considered. Application of Turkstras rule for

combining uncorrelated loads indicates that EQ = 0.50 is reasonable for a wide range of values of average daily

truck traffic (ADTT).

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Item #2

Revise Extreme Event II in Article 3.4.1 as follows:

EXTREME EVENT IILoad combination relating to ice load, collision by vessels and vehicles, check floods, and

certain hydraulic events with a reduced live load other than that which is part of the vehicular collision load, CT.

The cases of check floods and hurricanes shall not be combined with CV, CT, or IC.

Revise the commentary to Extreme Event II in Article 3.4.1 as follows:

The recurrence interval of extreme events is thought to exceed the design life.

The joint probability of these events is extremely low, and, therefore, the events are specified to be applied

separately. Under these extreme conditions, the structure is expected to undergo considerable inelastic

deformation by which locked-in force effects due to TU, TG, CR, SH, and SEare expected to be relieved.

The 0.50 live load factor signifies a low probability of the concurrence of the maximum vehicular live load

(other than CT) and the extreme events.

Item #3

Add new commentary opposite Extreme Event I as the 1st

paragraph of the commentary.

The following applies to both Extreme Event I and II:

The recurrence interval of extreme events is thought to exceed the design life.

Although these limit states include water loads, WA, the effects due to WA are considerably less

significant than the effects on the structure stability due to scour. Therefore, unless specific site conditions

dictate otherwise, local pier scour and contraction scour depths should not be included in the design

combined with EQ, IC, CV, or CT. However, the effects due to degradation of the channel should beconsidered. Alternatively, one-half of the total scour may be considered in combination with EQ, IC, CV,

or CT.

The joint probability of these events is extremely low, and, therefore, the events are specified to be

applied separately. Under these extreme conditions, the structure is expected to may undergo considerable

inelastic deformation by which locked-in force effects due to TU, TG, CR, SH, and SEare expected to be

relieved.

Item #4

Revise the 2nd

paragraph of Article 3.7.5 as follows:

The consequences of changes in foundation conditions resulting from the design flood for scour shall beconsidered at strength and service limit states. The consequences of changes in foundation conditions due to scour

resulting from the check flood for bridge scour and from hurricanes shall be considered at the eExtreme eEvent II

lLimit II sStates. The appropriate load combinations are specified in Table 3.4.1.

Item #5

Revise the first paragraph of Article 10.5.5.3.2 as follows:

The foundation shall be designed so that the nominal resistance remaining after the scour resulting from the

check flood (see Article 2.6.4.4.2) provides adequate foundation resistance to support the unfactored Strength Limit

States loads with a resistance factor of 1.0. For uplift resistance of piles and shafts, the resistance factor shall be

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taken as 0.80 or less.

The provisions of Articles 2.6.4.4.2 and 3.7.5 shall apply to the changed foundation conditions resulting from

scour. Resistance factors at the strength limit state shall be taken as specified herein. Resistance factors at the

extreme event shall be taken as 1.0 except for uplift resistance of piles and shafts, the resistance factor shall betaken as 0.80 or less.

Revise the commentary to Article 10.5.5.3.2 as follows:

The axial nominal strength after scour due to the check flood must be greater than the unfactored pile or shaft

load for the Strength Limit State loads. The specified resistance factors should be used provided that the method

used to compute the nominal resistance does not exhibit bias that is unconservative. See Paikowsky et al. (2004)

regarding bias values for pile resistance prediction methods.


None

BACKGROUND:

The current commentary on Extreme Event I applies to both Extreme Events I and II, while the appropriate

commentary for Extreme Event I is elsewhere. Some of the current commentary on Extreme Event II applies to

both Extreme Events I and II. The terminology certain hydraulic events in Extreme Event II is unclear, and

combination with CT or IC is unclear. The items concerning scour were discussed with the Chair and Vice-Chair

of T-15 and concurrence obtained.


None

REFERENCES:

None

OTHER:

None

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SUBJECT: LRFD Bridge Construction Specifications: Section 11, Various Articles

TECHNICAL COMMITTEE: T-4 Construction / T-14 Steel



LRFR MANUAL OTHER



AGENDA ITEM:

SECTION 11 STEEL STRUCTURES

Item #1

Revise Article 11.4.8.1.1 as follows:

11.4.8.1.1 General

All holes for bolts shall be either punched or drilled, except as noted herein. The width of each standard

bolt hole shall be taken as the nominal diameter of the bolt plus 0.0625 in. The standard hole size diameter for

metric bolts M24 and under smaller shall be taken as the nominal diameter of the bolt diameter plus 2 mm. For

metric bolts M27 and over larger, the standard hole size diameter shall be taken as the nominal diameter of the bolt

diameter plus 3 mm.

Except as noted in the articles below, Mmaterial forming parts of a member composed of not more than

five thicknesses of metal may be punched full-size. whenever the thickness of the material is not greater than 0.75

in. (20 mm) for structural steel, 0.625 in. (16 mm) for high strength steel, or 0.5 in. (12 mm) for quenched-and

tempered alloy steel, unless subpunching and reaming are required under Article 11.4.8.5.

When material is thicker than 0.75 in. (20 mm) for structural steel, 0.625 in. (16 mm) for high-strength

steel, or 0.5 in. (12 mm) for quenched-and-tempered alloy-steel, all holes shall either be subdrilled and reamed or

drilled full-size. Also, w When more than five thicknesses of material are joined or, as required by Article 11.4.8.5,

material shall be subdrilled or subpunched and then reamed full-size, or drilled full-size while in assembly.

When required, all holes shall be either subpunched or subdrilled (subdrilled if thickness limitationgoverns) 0.1875 in. (5 mm) smaller and, after assembling, reamed or drilled to full size.

Holes in cross frames, lateral bracing components, and the corresponding holes in connection plates

between girders and cross frames or lateral components may be punched full size. Cross frames and transverse

connection plates designated as main load-carrying members shall not be punched full-sized. Holes in longitudinal

main load-carrying members, transverse floorbeams, and any components designated as fracture critical (FCMs)

shall not be punched full-size.

When shown in the contract documents, enlarged or slotted holes are allowed with high-strength bolts.

With the owners approval, round or slotted holes for non-main members in thin plate may be thermally

cut by plasma, laser, or oxygen-acetylene methods subject to the requirements herein.

Item #2

Revise Article C11.4.8.1.1 as follows:

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C11.4.8.1.1

Previous punching restrictions whenever the thickness of the material was not greater than 0.75 in. (20

mm) for structural steel, 0.625 in. (16 mm) for high strength steel, or 0.5 in. (12 mm) for quenched-and temperedalloy steel, are upper limits but not necessary because the punching equipment may be more restrictive controls

the thickness.

For other dimensional criteria assumed in the design of bolted details, e.g., oversize holes, slotted holes,

edge distances, and end distances, see Article 6.13.2, Bolted Connections, of the AASHTO LRFD Bridge Design

Specifications.

With the owners approval, round or slotted holes for non-main members in thin plate may successfully be

thermally cut by plasma, laser, or oxygen-acetylene means. The maximum surface roughness of ANSI 1000 in.

(25 m) and the conical taper of the hole must be maintained within tolerance. See references AISC Steel

Construction Manual, 13th Edition, Section M2.5; RCSC Specification for Structural Joints Using ASTM A325 or

A490 Bolts, Section 3.3; and NSBA Steel Bridge Fabrication, S2.1.

Item #3

Revise Article 11.4.8.1.2 as follows:

11.4.8.1.2 Punched Holes

The diameter of the die shall not exceed the diameter of the punch by more than 0.0625 in. (1.5 mm). If

any holes must be enlarged to admit the bolts, such holes shall be reamed. Holes must be clean-cut without torn or

ragged edges. The slightly conical hole that naturally results from punching operations shall be considered

acceptable.

Item #4

Revise Article 11.4.8.4 as follows: Revise last sentence.

11.4.8.1.4 Accuracy of Holes

Holes not more than 0.03125 in. (0.8 mm) larger in diameter than the true decimal equivalent of the

nominal diameter that may result from a drill or reamer of the nominal diameter shall be considered acceptable.

The width of slotted holes which are produced by thermal flame cutting or a combination of drilling or punching

and thermal flame cutting should be not more than 0.03125 in. (0.8 mm) greater than the nominal width. The

thermally flame-cut surface shall be ground smooth to obtain a maximum surface roughness of ANSI 1000 in.

(25 m).

Item #5

Revise Article 11.4.8.5 as follows:

11.4.8.5 Preparation of Field Connections

Holes in all field connections and field splices of main member of trusses, arches, continuous-beam spans,

bents, towers (each face), plate girders, and rigid frames shall be subpunched or subdrilled and subsequently

reamed while assembled or drilled full-size through a steel template while assembled. Holes in cross frames, lateral

bracing components, and the corresponding holes in connection plates between girders and cross frames or lateral

components may be punched full size. Cross frames and transverse connection plates designated as main load-

carrying members shall not be punched full-sized. Holes in longitudinal main load-carrying members, transverse

floorbeams, and any components designated as fracture critical (FCMs) shall not be punched full-size. Holes for

field splices of rolled beam stringers continuous over floor beams or cross frames may be drilled full-size

unassembled to a steel template. All holes for floorbeams or cross frames may be drilled full-size unassembled to a

steel template, except that all holes for floor beam and stringer field end connections shall be subpunched and

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reamed while assembled or drilled full-size to a steel template. Reaming or drilling full-size of field-connection

holes through a steel template shall be done after the template has been located with utmost care as to position and

angle and firmly bolted in place. Templates used for reaming matching members or the opposite faces of a single

member shall be exact duplicates. Templates used for connections on like parts or members shall be so accuratelylocated that the parts or members are duplicates and require no match-marking.

For any connection, in lieu of subpunching and reaming or subdrilling and reaming, the Fabricator may, at

the Fabricators option, drill holes full-size with all thicknesses or material assembled in proper position.

Item #6

Revise REFERENCES as follows:

AASHTO. 2005. Standard Specifications for Transportation Materials and Methods of Sampling and Testing,

27th Edition, HM-27, American Association of State Highway and Transportation Officials, Washington, DC.

AISC. 2005. Steel Construction Manual, 13th Edition, American Institute of Steel Construction, Chicago, IL.

Research Council on Structural Connections (RCSC). 2004. Specification for Structural Joints Using ASTM A325

or A490 Bolts. American Institute of Steel Construction, Chicago, IL.

NSBA. 2002. Steel Bridge Fabrication Guide Specifications, S2.1, National Steel Bridge Alliance, Chicago, IL.

See also AASHTO NSBASBF-1 2002. [2nd

edition under review]


LRFD Bridge Design Specifications Article 6.5.4.2, Table 6.6.1.2.3-1, Articles 6.8.2.1, 6.8.3, and 6.13.4.

BACKGROUND:Reference document was prepared by The University of Texas at Austin in cooperation with TxDOT and FHWA

Project title: Performance and Effects of Punched Holes and Cold Bending on Steel Bridge Fabrication


The fabrication specifications for bolt holes in structural steel were updated. Punching requirements are controlled

by the fabricators equipment, not the plate thickness or strength. Thermal-cut holes should be considered by

owners for secondary members of thin plate.

REFERENCES:

Evaluation of Influence of Hole Making Upon the Performance of Structural Steel Plates and Connections,

Brorn, Lubitz, Cekov, Frank, and Keating. 2007 Report FHWA/TX-07/0-4624-1

OTHER:

None

Documents

2008 Ballot Items 69-73