Bridge Superstructure Tolerance to Total and Differential Foundation Movements (2018)

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NCHRP Project 12-103 217 10 Conclusions & Recommendations This section summarizes the general conclusions that were made in the respective sections for steel and PS concrete bridges. 10.1 Tolerable Support Movements for Multi-Girder Bridges Superstructure tolerance to LD and TD support movements is a complex problem that depends not only on bridge configuration but on the level of conservativism inherent in a specific bridge design, the type and location of support movement, and the limit state being evaluated. Through this research several mechanisms were identified as influencing the tolerance to support movement for multi-girder bridges. First, the AASHTO LRFD live load distribution factors used within the common SLG model contain some inherent conservatism, particularly for bridges with smaller girder spacing. That is, for smaller values of girder spacing, the live load distribution is over-estimated by the SLG model. These distribution factors become more accurate with larger girder spacing. As a result, additional capacity is available for certain bridge configurations (bridges with smaller girder spacing) to accommodate support movements. However, for PS concrete bridges, while this conservatism still exists, it is over-shadowed by another mechanism. Contrary to steel girders, stiffness is decoupled from capacity for PS concrete girders, and as a result concrete girders with larger girder spacing can be more flexible compared to steel and thus can exhibit higher tolerance to support movements. Second, the common tributary width approach to estimating dead load force effects can underestimate the level of these effects for exterior girders. This phenomenon becomes exacerbated in highly-skewed bridges. As a result, these elements may be under-sized for dead load force effects, which can reduce (or completely eliminate) a bridge’s tolerance to support movement. The effect on tolerance due to this mechanism is ultimately a factor of the ability of the superstructure to evenly distribute load to each of the girders. When loading is not evenly distributed, girders will exhibit less tolerance to LD and TD support movements. Third, for elements that are controlled by fatigue limit states (particularly in steel bridges), additional capacity is available in the positive moment regions accommodate support movements (since fatigue is only concerned with cyclic loading). This occurs in the positive moment region of steel multi-girder bridges, but does not influence PS concrete multi-girder bridges. As discussed throughout Sections 5 and 6, the parameters that influence superstructure tolerance to support movements will vary depending on the type and location of support movement. In the study of

NCHRP Project 12-103 218 steel multi-girder bridges, span length, girder spacing, skew, and SD ratio were identified as the most influential parameters for steel bridges. In the study of PS concrete multi-girder bridges, span length, girder spacing, and skew were identified as the most influential parameters for PS concrete bridges. Skew has a significant effect on tolerance for both flexure and shear related limit states. Bridges with larger skew angle were found to be less tolerable to movements occurring at the abutment or at the pier. Specifically, little to no shear tolerance and low flexure tolerance was observed for bridges with higher skew. Additionally, for steel multi-girder bridges only, it was discovered that skew in conjunction with diaphragm configuration (particularly for skews greater than 20⁰) results in low levels of tolerable support movement. The effect of higher skew angle becomes even more unfavorable for TD movements. Span length was found to be most influential for the flexure related limit states, although the influence of span length on Strength I Shear tolerance rises for bridges with lower skew. Girder spacing affects both flexure and shear related limit states. With steel bridges, for the Strength I Shear limit state, greater tolerance was found to be associated with bridges that have larger girder spacing, however, for the Strength I Flexure limit, greater tolerance was found to be associated with smaller girder spacing. This is like due to the conservatism in the live load distribution factors for bridges with smaller girder spacing. In contrast, for PS concrete bridges, greater Strength I Flexure tolerance was found to be associated with larger girder spacing. This is likely be attributed to the decoupling of strength and stiffness experienced by PS concrete girders. SD ratio was found to have an influence on shear tolerance for steel multi-girder bridges. Lower Strength I Shear tolerance was found to be associated with smaller SD ratio (i.e. deeper/stiffer girders). The effects of each of the influential parameters can most likely be attributed to their contribution to the stiffness of the superstructure and its elements. Compared to structures that are more flexible, stiffer bridges will experience greater force effects to dead load, live load, and support movement, and therefore stiffer bridges will exhibit less tolerance to support movement. This was evident in the results of this study. For example, longer span continuous bridges have less flexural stiffness than shorter spans, and thus they displayed higher levels of tolerable support movement. Another example is given for girder spacing of steel bridges; larger girder spacing leads to a larger (and therefore stiffer) girder in order to carry the additional flexure load. The lower flexural tolerance to support movement is further reinforced by the fact that live load distribution factors are less conservative (more accurate) for larger

NCHRP Project 12-103 219 girder spacing. Comparable relationships between the other influential parameters, the stiffness of the superstructure, and ultimately the tolerance to support movements have been made. A summary of the results for steel and PS multi-girder bridges is presented in the following two subsections. 10.1.1 Steel Multi-Girder Bridges The results for steel multi-girder bridges indicated that for bridges with skew angles under 20o the current AASHTO LRFD criterion is appropriate for LD support movements (i.e. when a single support undergoes a uniform vertical translation) with one exception. For 3-span continuous bridges, this criterion was unconservative for approximately 20% of the population studied. If the criterion is reduced from 0.004L to 0.003L and is limited to span length greater than 100 ft. (which is quite common for 3- span continuous bridges) it becomes conservative for the entire population studied. In general, TD support movements (i.e. where a single support undergoes a transverse differential movement across the width of the bridge) produced greater force effects than LD support movements, and thus were associated with smaller tolerable movements. Table 10-1 provides a summary of the results obtained for steel multi-girder bridges for the various support movement locations/types and design limit states studied. Table 10-1 - Summary of results for steel-multi-girder bridges. Continuity Type of Support Movement Limit State Comparison with Current AASHTO Guidance (% Failing) Comparison with Current AASHTO Guidance for Bridges with Skew < 20o (% Failing*) Comments Simple- Span LD Support Movement at Abutment Strength I Flexure 0% 0% - Strength I Shear 0% 0% - Service II 0% 0% -

NCHRP Project 12-103 220 TD Support Movement at Abutment** Strength I Flexure 0% 0% - Strength I Shear 37% 0% Due to stiffness effects of highly-skewed bridges and inability of SLG model to properly account for dead load distribution of skewed bridges Service II 0% 0% - Two-Span Continuous LD Support Movement at Abutment Strength I Flexure 15% 7% Due to the stiffness effects of shorter spans and larger girder spacing Strength I Shear 1% 0% - Service II 1% 0% - TD Support Movement at Abutment** Strength I Flexure 34% 3% Due to stiffness effects of shorter spans, higher skew, and larger girder spacing, and inability of SLG model to properly account for dead load distribution of highly- skewed bridges Strength I Shear 17% 0% Due to stiffness effects of highly-skewed bridges and inability of SLG model to properly account for dead load distribution of skewed bridges Service II 5% 0% - LD Support Movement at Pier Strength I Flexure 0% 0% - Strength I Shear 6% 0% -

NCHRP Project 12-103 221 Service II 0% 0% - TD Support Movement at Pier** Strength I Flexure 5% 0% - Strength I Shear 25% 0% Due to stiffness effects of highly-skewed bridges and inability of SLG model to properly account for dead load distribution of skewed bridges Service II 1% 0% - Three-Span Continuous LD Support Movement at Abutment Strength I Flexure 19% 20% 0.003L for bridges with less than 20o skew and spans longer than 100 ft Strength I Shear 3% 0% - Service II 0% 0% - TD Support Movement at Abutment** Strength I Flexure 22% 13% Due to stiffness effects of shorter spans, higher skew, and larger girder spacing, and inability of SLG model to properly account for dead load distribution of highly- skewed bridges Strength I Shear 11% 0% Due to stiffness effects of highly-skewed bridges and inability of SLG model to properly account for dead load distribution of skewed bridges Service II 1% 0% - LD Support Movement Strength I Flexure 36% 39% Due to stiffness effects of shorter spans and larger girder spacing, and

NCHRP Project 12-103 222 at Pier inability of SLG model to properly account for dead load distribution of highly- skewed bridges Strength I Shear 7% 0% - Service II 3% 6% - TD Support Movement at Pier** Strength I Flexure 39% 30% Due to stiffness effects of shorter spans, higher skew, and larger girder spacing, and inability of SLG model to properly account for dead load distribution of highly- skewed bridges Strength I Shear 17% 0% Due to stiffness effects of highly-skewed bridges and inability of SLG model to properly account for dead load distribution of skewed bridges Service II 4% 0% - * The percentage given is that of the subset of bridges that have skew less than 20⁰. ** Although current AASHTO LRFD guidance is not intended for TD movements, these movements are still considered for comparison purposes. 10.1.2 Pre-Stressed Concrete Multi-Girder Bridges The results for PS concrete multi-girder bridges indicated that this bridge type has relatively little tolerance to support movements (both LD and TD). For these bridges the current AASHTO criterion was unconservative for the entire population studied. This difference between steel and PS concrete bridges was traced to the lack of additional capacity available within the positive moment regions of PS concrete continuous bridges. In the case of steel bridges the fatigue limit state governs these regions and thus provides additional capacity to accommodate support movements. The lack of this mechanism for PS concrete bridges renders them far more sensitive to both LD and TD support movements. As opposed to the angular distortion based criterion currently provided by AASHTO, a uniform level of tolerable support movement (e.g. 0.5 inches) may be most appropriate for PS concrete multi-girder bridges.

NCHRP Project 12-103 223 Table 10-2 provides a summary of the results obtained for PS concrete multi-girder bridges for the various support movement locations/types and design limit states studied. Table 10-2 - Summary of results for steel-multi-girder bridges. Continuity Type of Support Movement Limit State Comparison with Current AASHTO LRFD Guidance (% Failing) Comments Simple- Span LD Support Movement at Abutment Strength I Flexure 0% - Strength I Shear 0% - Service I & III 0% - TD Support Movement at Abutment* Strength I Flexure 6% - Strength I Shear 68% Due to inability of SLG model to properly account for dead load distribution of skewed bridges Service I & III 68% Due to the lack of additional capacity for the Service III limit state Two-Span Continuous LD Support Movement at Abutment Strength I Flexure 3% - Strength I Shear 0% - Service I & III 0% - TD Support Movement at Abutment* Strength I Flexure 1% - Strength I Shear 18% Due to inability of SLG model to properly account for dead load distribution

NCHRP Project 12-103 224 of skewed bridges Service I & III 10% - LD Support Movement at Pier Strength I Flexure 31% Due to increase in positive moment in positive moment region Strength I Shear 10% - Service I & III 100% Due to the lack of additional capacity for the Service III limit state TD Support Movement at Pier* Strength I Flexure 28% Due to increase in positive moment in positive moment region Strength I Shear 56% Due to inability of SLG model to properly account for dead load distribution of skewed bridges Service I & III 100% Due to the lack of additional capacity for the Service III limit state Three-Span Continuous LD Support Movement at Abutment Strength I Flexure 2.5% - Strength I Shear 0% - Service I & III 0% - TD Support Movement at Abutment* Strength I Flexure 1% - Strength I Shear 18% Due to inability of SLG model to properly account for dead load distribution of skewed bridges

NCHRP Project 12-103 225 Service I & III 10% - LD Support Movement at Pier Strength I Flexure 31% Due to increase in positive moment in positive moment region Strength I Shear 10% - Service I & III 100% Due to the lack of additional capacity for the Service III limit state TD Support Movement at Pier* Strength I Flexure 28% Due to increase in positive moment in positive moment region Strength I Shear 56% Due to inability of SLG model to properly account for dead load distribution of skewed bridges Service I & III 100% Due to the lack of additional capacity for the Service III limit state ** Although current AASHTO LRFD guidance is not intended for TD movements, these movements are still considered for comparison purposes. 10.2 Spot Checking of Secondary Bridges In addition to the primary bridge types of steel and PS concrete multi-girder bridges, this research conducted a limited secondary parametric study of three bridge types: open and closed steel box girder bridges, and multi-cell concrete box bridges. The goal of this secondary study was to investigate whether the observations made for the primary bridge types could be extended to these bridges types. The results showed that multi-cell concrete box bridges follow the same trends as their multi-girder counterparts. In the case of steel box girder bridges, the results indicated that for flexural limit states they performed similar to multi-girder bridges. For shear limit states however, they were more sensitive to support movements and had tolerable support movements approximately 10% lower than their multi-girder counterparts.

NCHRP Project 12-103 226 10.3 Functionality Limits on Tolerable Support Movement The recommended tolerable support movement criterion based on ride-ability concerns is provided in Table 10-3. Table 10-3 - Tolerable movement limits for ride quality. Movement Case Limits for Ride Quality For movements occurring at the abutment of simply supported bridges with an approach slab ߜ ܮ௔ + ߜ ܮ௦ < 1 250⁄ For movements occurring at the abutment of continuous bridges with an approach slab ߜ ܮ௔ + 2ߜ ܮ௦ < 1 250⁄ For movements occurring at the pier of multiple- span simply-supported bridges 2ߜ ܮ௦ < 1 250⁄ For movements occurring at the pier of continuous bridges 2ߜ ܮ௦ < 1 250⁄ Where: ߜ = absolute support movement ܮ௔ = length of approach slab ܮ௦ = length of span 10.4 Proposed Expressions for Estimating Tolerable Support Movements Table 10-4 below contains the proposed expressions for estimating maximum tolerable support movements of steel and prestressed concrete multi-girder bridges based on the findings of this report. The coefficients of these expressions have been rounded from those presented in Sections 5 and 6 of this report. It is expected that these expressions with rounded coefficients are better suited for inclusion in the ballot items for the proposed revisions to the AASHTO LRFD Bridge Design Specifications.

NCHRP Project 12-103 227 Table 10-4 - Tolerable movement limits for steel and concrete multi-girder bridges. Type of Superstructure Applicable Cross-Section from Table 4.6.2.2.1-1 Tolerance Estimate (in.) Range of Applicability Concrete Deck, Reinforced Concrete Slab on Steel Beams a (also b and c, however this expression may provide more conservative estimates for these bridge types as these types are typically constructed outside the range of applicability) Strength I & Service II 40ft ≤ L ≤ 160ft 5ft ≤ S ≤ 12ft 0 ≤ Skew ≤ 45° 36ft ≤ Width ≤ 72ft 20 ≤ L/d ≤ 30 Concrete Deck, Reinforced Concrete Slab on Prestressed Concrete Beams k (also d through j, however this expression may provide more conservative estimates for these bridge types as these types are typically constructed outside the range of applicability, or will have a lower cross-sectional stiffness than the bridges studied in the research) Service III 40ft ≤ L ≤ 160ft 5ft ≤ S ≤ 12ft 0 ≤ Skew ≤ 45° 36ft ≤ Width ≤ 72ft 20 ≤ L/d ≤ 30 Strength I Table 10-5 and 10-6 show how the expressions for rideability considerations and the above expressions for Strength and Service limit states are intended to be used for simple-span and multiple-span continuous steel and prestressed concrete multi-girder bridges with span length and girder spacing equal to 150 ft. and 10 ft., respectively, and an approach slab length of 25 ft. ∆ = 0.55 ܮܵ − 2.6 ∆ = 0.0005 ܮ + 0.17 ∆ = 0.13 ܮܵ − 0.17

NCHRP Project 12-103 228 Table 10-5 - Example application of proposed expressions for rideability considerations on a sample bridge with span length of 150 ft., girder spacing of 10 ft., and an approach slab length of 25 ft. Continuity Limits for Ride Quality Simple-Span Referencing Table 10.3, the limits of tolerable support movement for a simple span steel or prestressed concrete multi-girder bridge can be determined by evaluating the following inequalities: For movements occurring at the abutment of a simply supported bridge: ߂ ܮ௔ + ߂ ܮ௦ < 1 250 ⁄ ߂ 25 ∗ 12 + ߂ 150 ∗ 12 < 1 250⁄ ࢤ = ૚. ૙૜ ࢏࢔ࢉࢎࢋ࢙ ∎ For movements occurring at the pier of multiple-span simply-supported bridges: 2߂ ܮ௦ < 1 250 ⁄ 2߂ 150 ∗ 12 < 1 250⁄ ࢤ = ૜. ૟ ࢏࢔ࢉࢎࢋ࢙ ∎ Continuous Referencing Table 10.3, the limits of tolerable support movement for a continuous span steel or prestressed concrete multi-girder bridge can be determined by evaluating the following inequalities: For movements occurring at the abutment of continuous bridges: ߂ ܮ௔ + 2߂ ܮ௦ < 1 250 ⁄ ߂ 25 ∗ 12 + 2߂ 150 ∗ 12 < 1 250⁄ ࢤ = ૙. ૢ ࢏࢔ࢉࢎࢋ࢙ ∎ For movements occurring at the pier of continuous bridges: 2߂ ܮ௦ < 1 250 ⁄ 2߂ 150 ∗ 12 < 1 250⁄ ࢤ = ૜. ૟ ࢏࢔ࢉࢎࢋ࢙ ∎

NCHRP Project 12-103 229 Table 10-6 - Example application of proposed expressions for Strength and Service limits on sample bridge with span length of 150 ft., girder spacing of 10 ft., and an approach slab length of 25 ft. Steel Prestressed Concrete Continuity Strength I & Service II Service III Strength I Simple-Span Rideability concerns will govern allowable levels of tolerable support movement for both steel and prestressed concrete simple-span bridges. See Table 10-5. Continuous ∆ = 0.55 ܮܵ − 2.6 ∆ = 0.0005 ܮ + 0.17 ∆ = 0.13 ܮ ܵ − 0.17 ∆ = 0.55 (150 ∗ 12)(10 ∗ 12) − 2.6 ∆ = 0.0005 (150 ∗ 12) + 0.17 ∆ = 0.13 (150 ∗ 12) (10 ∗ 12) − 0.17 ∆ = ૞. ૟૞ ࢏࢔ࢉࢎࢋ࢙ ∎ ∆ = ૚. ૙ૠ ࢏࢔ࢉࢎࢋ࢙ ∎ ∆ = ૚. ૠૡ ࢏࢔ࢉࢎࢋ࢙ ∎ As stated in the AASHTO LRFD Design Specifications, service-level demands should be used when calculating the expected support movement (i.e. the support movement “demand”). The expressions shown here and in the proposed ballot item provides designers with conservative estimates of the support movement “capacity” (i.e. the support movement that may be accommodated without violating any of the Strength and Service limit states). These expressions were developed using the load and resistance factors associated with the Strength and Service limit states prescribed by the AASHTO LRFD Design Specifications.

NCHRP Project 12-103 230 10.5 Proposed Revisions to AASHTO LRFD Bridge Design Specifications The following is a draft ballot item for the modification of the AAHSTO LRFD to incorporate the results of this study. 2018 AASHTO BRIDGE COMMITTEE AGENDA ITEM: Click here to enter text SUBJECT: LRFD Bridge Design Specifications Article C10.5.2.2 TECHNICAL COMMITTEE: T-15 Substructures and Retaining Walls ☒ REVISION ☐ ADDITION ☐ NEW DOCUMENT ☒ DESIGN SPEC ☐ CONSTRUCTION SPEC ☐ MOVABLE SPEC ☐ MANUAL FOR BRIDGE ☐ SEISMIC GUIDE SPEC ☐ MANUAL BRIDGE ELEMENT INSP EVALUATION ☐ OTHER DATE PREPARED: 12/29/2017 DATE REVISED: Click here to enter a date AGENDA ITEM: Item #1 Revise Article C10.5.2.2 as follows: C10.5.2.2 Experience has shown that bridges can and often do accommodate more support movements and/or rotations than traditionally allowed or anticipated in design. Creep, relaxation, and redistribution of force effects, and additional capacity accommodate these movements. Some studies have been made to synthesize apparent response. These studies indicate that angular distortions between adjacent foundations greater than 0.008 rad. in simple spans and 0.004 rad. in continuous spans should not be permitted in settlement criteria (Moulton et al., 1985; DiMillio, 1982; Barker et al., 1991). Rotation movements should be evaluated at the top of the substructure unit in plan location and at the deck elevation. Previous studies recommended settlement limits based on a factor applied to span length (Moulton et al., 1985; DiMillio, 1982; Barker et al., 1991). Recent work by Romano et al., 2017 developed separate deflection limits for simple span and continuous bridges, and for steel and prestressed concrete multi-girder bridges accounting for the additional capacity present due to conservatism in the distribution factor method. For steel and prestressed concrete simple span bridges, the deflection limit was found to be controlled by rideability considerations. The angular break caused by differential support movements across each adjacent span, or across the approach slab and adjacent span, should be limited to 0.004 radians. This suggested limit for rideability considerations was determined after reviewing the literature of research conducted within the previous two decades on the subject of bridge functionality limitations and rider discomfort (Puppala et al. 2012, Stark et al. 1995, Tan and Duncan 1991, and Wahls 1990). The guidance that follows applies to steel and prestressed concrete multi-girder bridges meeting the criteria for curvature given in Article 4.6.1.2.4b, designed using the distribution factor method, and having skew angles less than 45

NCHRP Project 12-103 231 degrees, span lengths within the range of 40 ft. to 160 ft., girder spacing within the range of 5 ft. to 12 ft., bridge width within the range of 36 ft. to 72 ft., and for steel bridges only, girder depths between L/30 and L/20 (where L is the span length). For continuous steel multi-girder bridges, the deflection limit was found to be influenced by span length as well as girder spacing. The data suggests there exists a strong relationship between steel superstructure tolerance and the ratio of span length to girder spacing. This relationship is represented in the following expression which may be used to calculate inches of tolerable support movement for a continuous steel multi-girder bridge for the Strength I and Service II limit states: ∆ = 0.55 ∗ (ܮ ܵ⁄ ) − 2.6 (C10.5.2.2-1) Where L is the minimum of adjacent span lengths, in inches, S is the girder spacing in inches, and Δ is the maximum tolerable support movement, in inches. For prestressed concrete multi-girder bridges made continuous for live load, the tension stress limit of the Service III limit state was found to control the tolerable support movement. The following expression may be used to calculate the tolerable support movement for a prestressed concrete multi-girder bridge under the Service III limit state: ∆ = 0.0005 ∗ ܮ + 0.17 (C10.5.2.2-2) Where L is the minimum of adjacent span lengths, in inches, and Δ is the maximum tolerable support movement, in inches. If the designer chooses to ignore the Service III limit state for support movements, the tolerable support movement will then be controlled by the Strength I limit state, and may be calculated using the following expression: ∆ = 0.13 ∗ (ܮ ܵ⁄ ) − 0.17 (C10.5.2.2-3) Where L is the minimum of adjacent span lengths, in inches, S is the girder spacing in inches, and Δ is the maximum tolerable support movement, in inches. As indicated in Table 3.4.1-1, the effects of settlement need to be included in the evaluation of several different Load Combinations, including Strength and Service limit states. The Service I Load Combination is used to determine the magnitude of settlement. Other angular distortion limits may be appropriate after consideration of: • cost of mitigation through larger foundations, realignment or surcharge, • rideability, • vertical clearance, • tolerable limits of deformation of other structures associated with a bridge, e.g., approach slabs, wing walls, pavement structures, drainage grades, utilities on the bridge, etc. • roadway drainage, • aesthetics, and • safety. Tolerance of the superstructure to lateral movement will depend on bridge seat or joint widths, bearing type(s), structure type, and load distribution effects. OTHER AFFECTED ARTICLES: None

NCHRP Project 12-103 232 BACKGROUND: NCHRP 12-103 investigated the ability of bridges designed using the distribution factor method to accommodate settlement deformations at abutments and piers. The methodology used was to develop a large number of conforming multi-girder designs in both steel and precast prestressed concrete, simple and continuous, using the distribution factor method that satisfy all of the AASHTO LRFD Bridge Design Specification provisions, and then use refined analysis methods to determine the amount of settlement the designs could accommodate. Pier settlements in continuous spans tend to increase the positive moments in the span, while decreasing the negative moment over supports. Because many steel designs are controlled in the positive moment region by the fatigue limit states, they were found to be very tolerant of this type of movement. Prestressed concrete bridges made continuous for live load were found to be less tolerant of pier settlement, even when accounting for the relieving effects of creep. The strong influence of girder spacing was identified as a key variable in determining the magnitude of settlement that could be accommodated. The revised equation(s) presented herein are more accurate, and less conservative than the previous limits which were given solely as a function of span length. Three graphs are shown, one for steel girders and two for prestressed concrete girders showing Service III and Strength I limits, respectively. Each data point indicates a particular combination of design variables that just meets the limits of the LRFD BDS. Also shown are plots of the deflection limit equations. Steel (All Limit States) Figure 1 – Scatter plot of support movement tolerance for Strength I and Service II limit states for multi-girder continuous steel bridges, with the expression developed for estimating maximum tolerable support movement.

NCHRP Project 12-103 233 Prestressed (Service III) Figure 2 – Scatter plot of support movement tolerance for the Service III limit state for multi-girder continuous (for live load) prestressed concrete bridges, with the expression developed for estimating maximum tolerable support movement. Prestressed (Strength I)

NCHRP Project 12-103 234 Figure 3 – Scatter plot of support movement tolerance for Strength I limit states for multi-girder continuous (for live load) prestressed concrete bridges, with the expression developed for estimating maximum tolerable support movement. ANTICIPATED EFFECT ON BRIDGES: If designers follow the guidance provided to determine allowable settlements, and use that value to determine the most economical foundation type, significant savings are possible. Current practice often involves setting arbitrary, small values of allowable settlement when designing foundations, which results in inefficient design. REFERENCES: Romano, Masceri, Braley, Moon, Mertz, Samtani, and Murphy. Final Report, NCHRP 12-103. 2017 (to be updated when published) OTHER: