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

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

NCHRP Project 12-103 202 7 Spot Checking of Secondary Bridge Types (Task 2.4) As an extension of the primary study discussed in Sections 5 and 6, a secondary group of structures were evaluated (or “spot checked”) to identify any differences in either observed trends or levels of tolerable support movement by examining the governing bridge configuration parameters. The bridge types that were incorporated in this study (referred herein as “secondary” bridge types) include: • Closed Steel Box Girders Bridges • Open Steel Box Girder Bridges (Tub Girder Bridges) • Cast-in-Place Concrete Multi-Cell Box Girder Bridges (CIP Multi-Cell) The analyses for the three bridge types listed above are discussed and the results are presented in Sections 7.1 and 7.2. Additional bridge types were considered, but these bridge types were deemed by the Research Team and Project Panel to require no explicit spot checking. The additional bridge types that were considered for the secondary study but ultimately deemed not to require spot-checking were: • Timber Bridges • Cast-in-Place Concrete Tee Beam Bridges • Various Precast Concrete Bridges including: • Precast Concrete Channel Sections with Shear Keys • Precast Concrete Double Tee Sections with Shear Keys • Precast Concrete Tee Sections with Shear Keys First, since the bridge types listed above are not used in continuous bridges, the most stringent support movement cases are not relevant to these bridge types. Moreover, for timber bridges, given that these bridges are constructed of wood beams, the stiffness-to-strength ratio will be less than the primary bridges, and thus they will be more tolerant to support movements. For Cast-in-Place Concrete Tee Beam Bridges, given that these bridges are not PS, their stiffness-to-strength ratio will be less than the PS concrete bridges examined in Task 2.2, and thus they will be more tolerant of support movements. Lastly, for the Various Precast Concrete Bridges, the form of these bridges (i.e. multi-girder) is very similar to the bridges examined in detail in Task 2.2 (see Section 6) and thus the behavior should be quite similar.

NCHRP Project 12-103 203 7.1 Approach to Modeling, Simulation, and Evaluation of Secondary Bridges All of the models were built manually because the construction of these models differs from the multi- girder models used for steel and PS. As detailed in the Phase I report, full shell models were used instead of a beam/shell composition (element-level model). Dead load and support movements were simulated in a similar fashion as they were for the primary bridges. Live load was simulated using Strand7s built in Load Influence Solver, which determines the influence that a point load or series of point loads has on a response at a specified location. In Strand7, Response Variables (RVs) are assigned to elements at locations where a maximum response (shear force, bending moment, etc.) is desired. Based on the findings of Task 2.3, RVs were placed over all support locations to maximize flexure and shear, and in the mid span regions to maximize flexure. Load paths are defined for each loading scenario and the Load Influence Solver is used to determine the loading configuration that gives the maximum response at the location of each response variable. The load influence solver effectively transforms moving loads into equivalent static loads that develop the ultimate response for the corresponding response variable. Final analysis is conducted using the static loading conditions identified by the load influence solver. In order to expedite the analysis/results extraction for the spot checking bridges, only responses in the exterior, first interior, and center interior girders (if applicable) were considered. Shear response was extracted from the shell elements of the webs over each support, while bending moments were extracted from both the positive and negative moment regions. With a cross section comprised entirely of shell elements, the sum of the responses of every shell element in the top flange, web, and bottom flange must be considered. Bending moments and axial forces were extracted from the top and bottom flanges. The total moment from those elements was calculated using Equation 7-1, where P is the axial force in each flange, y is the moment arm from the centroid of each flange shell element to the centroid of the cross section, and M22 is the bending moment in each shell element. Equation 7-1 - Equation for calculating total moment in the flanges. ܯ்௢௧௔௟_ி௟௔௡௚௘௦ =෍ܲ ∗ ݕ +෍ܯଶଶ Shell elements, in general, provide resistance to in-plane bending moment through a variation in axial stress. Thus, the axial force in each shell element of the web is extracted and the product of the axial force times the moment arm to the centroid of the cross-section was summed for each element of the web in order to obtain the total moment in the web. Equation 7-2 gives the calculation for total moment

NCHRP Project 12-103 204 in the webs. The total cross-section moment was calculated as the sum of the total moment in the flanges and the total moment in the web. Equation 7-2 - Equation for calculating the total moment in the webs. ࡹࢀ࢕࢚ࢇ࢒_ࢃࢋ࢈ =෍ࡼ ∗ ࢟ Tolerable support movement was calculated in the same fashion as it was for the primary study. For Open and Closed Steel Girders, tolerable support movement was evaluated for the Strength I Limit State (flexure and shear) and the Service II limit state. Capacities for each limit state were calculated per AASHTO LRFD Design Specifications during the design performed by UD Team (see Section 7.2). CIP Multi-Cell bridges were evaluated for the Strength I Limit State (flexure and shear) as well as the Service I/III limit states (compression/tension). For CIP Multi-Cell, the capacities for the Strength I limit state were taken as the demands calculated using the SLG model divided by the appropriate resistance factor, represented in Equation 7-3. Equation 7-3 - Calculation of nominal moment capacity for CIP Multi-Cell. ࡹ࢔ = ࡹ࢛ ࣐࢘ Assigning the capacity in this fashion assumes the most conservative value of the capacity, i.e., a capacity that provides a SLG rating of 1.0. For the Service I and III limit states, the capacity in regions of positive bending was limited by tension in the bottom flange as defined by AASHTO LRFD Specifications. The capacity in regions of negative bending was limited by compression in the bottom flange as defined by AASHTO LRFD Specifications. Service I and III limits of capacity are represented in Equation 7-4 and Equation 7-5, respectively. Equation 7-4 - Service I compressive capacity at full pre-stressing after losses. ࡲ࢔ = ૙. ૟ ∗ ࢌᇱࢉ − ࢌ࢖࢙ Equation 7-5 - Service III tensile capacity at full pre-stressing after losses. ࡲ࢔ = ૟ ∗ ඥࢌ′ࢉ

NCHRP Project 12-103 205 7.2 Closed and Open Steel Boxes Steel box girders provide several advantages over I-section girders. These advantages include span range, torsional resistance, and stiffness among others. Steel box girders can also be more economical than I-section girders in long span applications. While box girders can be used in short span applications, these are typically for aesthetic purposes or constructability considerations (steel Design Handbook). Due to the design constraints of steel box girder bridges (e.g. a minimum girder depth of 5ft to allow for inspection), the use of box girders in shorter span applications can be less efficient than I-section girders, effectively leading to “over-designed” superstructures. This was evident in the evaluation of shorter span closed and open steel bridges for LD and TD support movement. Closed and open steel bridges will more commonly have spans lengths residing at the upper bound of the limits proposed for this study (greater than 100ft). Despite this fact, designs were developed within the bounds of span length set for this study. The UD team produced three designs each of Closed and Open Steel Boxes. Span length and girder spacing were varied between the designs based on the findings of the primary study. These bridges were modeled by the Research Team and evaluated using the same approach employed for the primary study. Table 7-1 and Table 7-2 summarize the Closed and Open Steel Box Girder designs, respectively. Table 7-1 - Design summaries for Closed Steel bridges. Closed Steel 1 Closed Steel 2 Closed Steel 3 No. of Spans 2 2 2 Span Length, [ft] 60 150 150 Roadway Width, [ft] 40 40 40 Total Width, [ft] 43 43 43 Deck Thickness, [in] 9 9 9 Haunch Thickness, [in] 3.5 3.5 3.5 No. of Girders 3 4 4 Girder Spacing, [ft] 16.5 10.167 10.333 Top Flange Width, [in] 24 55.825 48 Top Flange Thickness, [in] 1 2.375 2 Bottom Flange Width, [in] 24 55.825 48 Bottom Flange Thickness, [in] 1 2.375 2 Depth of Web(s), [in] 60 72 60 Thickness of Web(s), [in] 0.5 0.625 0.5 Steel Modulous, [ksi] 29000 29000 29000 Deck Concrete Strength, [psi] 4000 4000 4000

NCHRP Project 12-103 206 Table 7-2 - Design summaries for Open Steel bridges. Open Steel 1 Open Steel 2 Open Steel 3 No. of Spans 2 2 2 Span Length, [ft] 60 60 150 Roadway Width, [ft] 40 40 40 Total Width, [ft] 43 43 43 Deck Thickness, [in] 9 9 9 Haunch Thickness, [in] 3.5 3.5 3.5 No. of Girders 2 3 2 Girder Spacing, [ft] 24 14 24 Top Flange Width(s), [in] 18 12 18 Top Flange Thickness(s), [in] 1 0.75 1.75 Bottom Flange Width, [in] 102 54 102 Bottom Flange Thickness, [in] 1 0.75 1.75 Depth of Web(s), [in] 60 48 72 Thickness of Web(s), [in] 0.625 0.5 0.625 Steel Modulus, [ksi] 29000 29000 29000 Deck Concrete Strength, [psi] 4000 4000 4000 Table 7-3 through Table 7-6 summarize the tolerable movement results for the closed and open steel box bridges. Closed steel box girders exhibited very high levels of tolerable support movement for the flexure related limits (Strength I Flexure and Service II). It would appear that lower tolerance is associated with larger spans; however, this is not necessarily the case as the shorted spans only exhibit higher tolerance because they were over-designed (due to the minimum 5 ft. depth). The Strength I Shear limit controlled for all three closed steel bridges. Tolerance of open steel bridges was found to be controlled by the flexure limits (Strength I and Service II) for shorter spans. In contrast, it appears that as open steel spans get longer, Strength I Shear controls tolerance. Table 7-3 - Tolerable LD support movements occurring at the abutment. Strength I Flexure Strength I Shear Service II Closed Steel 1 > 30 in. 10.9 in. > 30 in. Closed Steel 2 28.1 in. > 30 in. > 30 in. Closed Steel 3 30.2 in. 4.0 in. > 30 in. Open Steel 1 6.3 in. 7.3 in. 7.5 in. Open Steel 2 6.3 in. 14.3 in. 7.5 in. Open Steel 3 > 30 in. 5.4 in. 27.7 in.

NCHRP Project 12-103 207 Table 7-4 - Tolerable TD support movement occurring at the abutment. Strength I Flexure Strength I Shear Service II Closed Steel 1 > 30 7.0 in. > 30 in. Closed Steel 2 17.8 in. 22.1 in. 23.7 in. Closed Steel 3 29.8 in. 4.7 in. > 30 in. Open Steel 1 4.5 in. 5.7 in. 5.4 in. Open Steel 2 2.7 in. 14.8 in. 3.2 in. Open Steel 3 21.8 in. 3.1 in. 18.6 in. Table 7-5 - Tolerable LD support movement occurring at the pier. Strength I Flexure Strength I Shear Service II Closed Steel 1 26.9 in. 8.9 in. 9.7 in. Closed Steel 2 27.6 in. > 30 in. > 30 in. Closed Steel 3 > 30 in. 26.9 in. > 31 in. Open Steel 1 9.6 in. 7.7 in. 11.4 in. Open Steel 2 7.0 in. 8.2 in. 14.2 in. Open Steel 3 > 30 in. > 30 in. > 30 in. Table 7-6 - Tolerable TD support movement occurring at the pier. Strength I Flexure Strength I Shear Service II Closed Steel 1 26.5 in. 8.2 in. 8.6 in. Closed Steel 2 > 30 in. > 30 in. > 30 in. Closed Steel 3 > 30 in. > 30 in. > 30 in. Open Steel 1 10.3 in. 8.0 in. 8.2 in. Open Steel 2 7.5 in. 8.5 in. 10.0 in. Open Steel 3 > 30 in. 26.8 in. > 30 in. These results were compared to those obtained in the primary study for an “equivalent” steel multi- girder bridge. The multi-girder bridge was equivalent (to within a few feet) for span length, and bridge width, and had little or no skew (less than 5⁰). Closed and open steel bridges displayed much higher (20% or more) Strength I Flexure and Service II tolerance compared to their multi-girder equivalent. However, this was not the case for Strength I Shear. For this limit state, closed and open steel bridges displayed lower (approximately 10%) Strength I Shear tolerance. These results suggest that closed and open steel box bridges behave like steel multi-girder bridges for a support movement under the

NCHRP Project 12-103 208 Strength I Flexure and Service II limit state, thus the observations made for multi-girder bridges may also apply. For the Strength I Shear limit state, more refined evaluation may be required. 7.3 Pre-Stressed Concrete Boxes Given the similarity of the structural response associated with CIP Multi-Cell and numerous other types of PS concrete boxes including: PS Concrete Boxes with an Integral Concrete Deck; Precast Solid, Voided, or Cellular Concrete Boxes with an Integral Concrete Deck; Precast Solid, Voided or Cellular Concrete Boxes with Shear Keys with Cast-in-Place Concrete Overlay; and Open Precast Concrete Boxes, the Research Team grouped these bridge types into a single category (PS Concrete Boxes). PS concrete boxes have a large span range, typically between 100ft and 250ft (Figure 7-1). According to the FHWA Post-Tensioned Box Girder Design Manual (2016), the lower end of this range typically represents simply supported bridges, while the upper end represents continuous span bridges. Figure 7-1 - Applicable span lengths for PS concrete bridges (FHWA 2015). The larger span lengths at the upper bound of the span range for CIP Multi-Cell bridges are out of the bounds of span length proposed for this study. Despite this fact, designs were developed within the bounds of span length set for this study. The UD team produced three CIP Multi-Cell bridge designs. Span length and web spacing were varied between the designs based on the findings of the primary study (web spacing was equated to girder spacing). These bridges were modeled by the Research Team and evaluated using the same approach employed for the primary study. Table X summarizes the three CIP Multi-Cell designs.

NCHRP Project 12-103 209 Table 7-7 - Design summaries for CIP Multi-Cell bridges. CIP #1 CIP #2 CIP #3 No. of Spans 2 2 2 Span Length, [ft] 50 50 100 Roadway Width, [ft] 44 44 44 Total Width, [ft] 47.167 47.167 47.167 No. of Cells 6 4 4 No. of Webs 7 5 5 Web Spacing, [ft] 7 12.9 9.75 Web Thickness, [in] 12 12 12 Top Flange Thickness, [in] 8 8 8 Bottom Flange Thickness, [in] 7 7 7 Total Depth, [in] 52 52 69 Concrete Strength, [psi] 4500 4500 4500 Table 7-8 through Table 7-11 summarize the tolerable support movement results for CIP Multi-Cell bridges. Rather high tolerable LD movements were observed for the Strength I Shear limit state. It also appears that lower tolerance is associated with shorter spans. Service III always controls for tension in the girder due to support movements occurring at the pier (just as it did for multi-girder PS concrete bridges). When compared to their multi-girder equivalent, CIP Multi-Cell Box bridges performed quite similarly if not better, exhibiting higher tolerance for the Strength I and Service I limit states (on the order of 5% or greater). For Service III, CIP Multi-Cell exhibited very low tolerance to movements occurring at the pier. This is consistent with what was found for their multi-girder equivalent. Table 7-8 - Tolerable LD support movement occurring at the abutment. Strength I Flexure Strength I Shear Service I CIP Multi-Cell 1 4.1 in. 18.9 in. 5.8 in. CIP Multi-Cell 2 4.4 in. > 30 in. 6.2 in. CIP Multi-Cell 3 > 30 in. > 30 in. 11.7 in. Table 7-9 - Tolerable TD support movement occurring at the abutment. Strength I Flexure Strength I Shear Service I CIP Multi-Cell 1 7.4 in. 16.5 in. 6.7 in. CIP Multi-Cell 2 6.7 in. 18.5 in. 6.5 in. CIP Multi-Cell 3 > 30 in. > 30 in. 13.3 in.