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From page 217... ... 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. Read the entire page →
From page 218... ... 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. Read the entire page →
From page 219... ... 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. Read the entire page →
From page 220... ... NCHRP Project 12-103 220 TD Support Movement at Abutment* Read the entire page →
From page 221... ... NCHRP Project 12-103 221 Service II 0% 0% - TD Support Movement at Pier* Read the entire page →
From page 222... ... NCHRP Project 12-103 222 at Pier inability of SLG model to properly account for dead load distribution of highlyskewed bridges Strength I Shear 7% 0% - Service II 3% 6% - TD Support Movement at Pier* Read the entire page →
From page 223... ... 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. Read the entire page →
From page 224... ... 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* Read the entire page →
From page 225... ... 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 * Read the entire page →
From page 226... ... 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. Read the entire page →
From page 227... ... 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.) Read the entire page →
From page 228... ... 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 = ૚. Read the entire page →
From page 229... ... 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. Read the entire page →
From page 230... ... 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. Read the entire page →
From page 231... ... 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. Read the entire page →
From page 232... ... 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. Read the entire page →
From page 233... ... 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) Read the entire page →
From page 234... ... 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. Read the entire page →

From page 217...

... 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.