Bridges for Service Life Beyond 100 Years: Service Limit State Design (2014) / Chapter Skim
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Pages 14-47
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14 2.1 Approach As part of Phase 1, an assessment of the current state of the art related to service limit states (SLSs) was conducted as follows: • A review of technical literature was conducted and is summarized in Section 2.2.
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15 • Eurocode (EN 1992-2 2005) -- Perform adequately under all expected actions.
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16 4▪ Prestressed concrete -- structural cracks, exposed prestressing tendons, corrosion of tendons in bond zone, loss of camber due to creep or prestress losses; 4▪ Reinforcement -- corrosion; and 4▪ Causes -- temperature fluctuation, chemical attack, moisture absorption, differential foundation movement, design and construction deficiencies, fire. 44 Steel -- corrosion, fatigue cracking, overloads, collision, heat, paint failures; 44 Concrete decks -- cracking, scaling, delamination, spalling, efflorescence, honeycombs, pop-outs, wear, collision damage, abrasion, overload damage, reinforcement corrosion, prestressed concrete deterioration; and 44 Steel decks -- bent, damaged, or missing members; corrosion, fatigue cracks, other stress-related cracks.
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17 of these documents could show a need for additional SLSs that were not approved for funding but may still be worthwhile in the context of this project. However, there is apparently no archive of old research problem statements.
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18 replaceable. Expansion joint manufacturers also provided estimates of service life for their products.
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19 foundations can affect the ride quality, functioning of deck drainage, and the safety of the traveling public, as well as the structural integrity and aesthetics of the bridge. Such movements often lead to costly maintenance and repair measures.
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20 limits may be used when the superstructure is adequately designed for such settlements. The designer shall also check other factors such as rideability and aesthetics.
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21 than simple-span bridges; and there is no defined level of vibration that constitutes being undesirable. The vibration of the bridge is affected by the following quantities: • Bridge flexibility and associated natural frequency.
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22 equations developed by Wright and Walker (1972) or the criteria provided in the CHBDC (2006)
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23 • Barker et al.
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24 44 Natural frequency for simple or equal spans: 2 2 f L E I g wb b b = pi 44 Speed parameter: 2 v f Lb α = 44 Impact factor: DI = a + 0.15 44 Dynamic component of acceleration = a = 2 2 DI fs b) (× δ pi must be less than 100 in./s2 • Barth and Wu (2007)
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25 range for estimating accumulated fatigue damage may be taken as shown by Equation 2.1: (2.1) effective 3 3 i i ∑( )
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26 identified in the research and to determine their uncertainty in terms of bias, mean, and coefficient of variation. The various thresholds were grouped together to make design practical and more rational than the single threshold currently defined.
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27 where A is a constant defined for each detail category, and N is the number of cycles to failure. The current constant, A, is tabulated for each detail category in Table 2.7 for the mean finite-life fatigue resistance.
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28 testing near the threshold is time consuming and costly. Conservative thresholds were estimated graphically by using limited experimental test observations.
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29 n = ratio of modulus of elasticity of steel to concrete (assumed to be 8 in Clark's study) ; h = overall depth of beam/slab (in.)
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30 dc = thickness of concrete cover measured from extreme tension fiber to center of bar or wire located closest thereto, in.; s = maximum spacing of reinforcement (in.) ; as = reinforcement factor; gc = reinforcement coating factor: 1.0 for uncoated reinforcement, 0.5 for epoxy-coated reinforcement, unless test data can justify a higher value; and fs = calculated stress in reinforcement at service load (ksi)
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31 dc = thickness of concrete cover (in.) (for bottom face reinforcement, measured from extreme tension fiber to center of bar, and for skin reinforcement, measured from side face to center of bar)
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32 but not greater than 12 40,000 , fs where cc is the least distance from the surface of reinforcement or prestressing steel to the tension face. If there is only one bar or wire nearest to the extreme tension face, s in Equation 2.19 is the width of the extreme tension face.
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33 Okeil (2006) concluded that Equation 2.23 provides a better estimate of the tensile strength over a wider range of concrete compressive strengths.
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34 some experts opined that a completely crackless concrete member is only better for the specific purpose, but others thought that cracking of prestressed concrete beams is as important as yielding. In 1958, the Tentative Recommendations for Prestressed Concrete proposed by ACI-ASCE Joint Committee 323 suggested that prestressed concrete, before losses due to creep and shrinkage, should meet the following limits (note units in the following provisions are in pounds per square inch for the allowable tensile stress)
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35 Fatigue in Concrete Deck Slabs and Culvert Top Slabs (AASHTO LRFD Article 5.5.3.1) Stresses measured in concrete deck slabs of bridges and top slabs of box culverts in service are far below infinite fatigue life, most probably due to internal arching action.
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36 approximately 1 in. at the midspan of bridges of an approximately 50-ft span.
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37 current demand is higher than that required by the Standard Specifications. Several issues arose regarding retention of, or revisions to, the provisions related to control of permanent deformations; these are discussed in Section 6.4.
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38 execution (construction) of the structure (e.g., inspection during execution)
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39 of construction works or agreed with the client or the national authority. combinaTion of acTions (loaD combinaTions)
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41 determined by reference to past practice. As an example of this process, special consideration was given to the tensile stress limit state in prestressed concrete girders.
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42 is considerably larger than the HL-93 truck alone (i.e., without the uniform distributed load)
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43 The above functional statements are in the context of design working life. The JGS document indicates that the design working life may be determined by considering various factors including life-cycle cost, durability, deterioration, and the functional life of the structure.
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44 Approach A does not require any specified method for performance verification of the structure. It requires, however, that the designer prove the structure satisfies the specified performance requirements with an appropriate level of reliability.
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45 • Additional limit states for connections, expansion joints, and bearings. Despite suggestions for additional limit states, there was a common theme that additional limit states would not have affected or prevented the observed reduced serviceability.
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46 Canadian provinces, the District of Columbia, and many turnpike authorities, bridge authorities, and commissions. The survey included 20 questions covering the following topics: • Modifications to the specification loading (HL-93 loading)
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47 and ranking of existing or promising strategies to quantify the reduction in service life due to deterioration. As there are no quantitative data for ranking and selection of the problematic areas, the R19A research team prioritized the research topics based on the qualitative opinion of experts.
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