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9 Cslab = total or resultant compressive force of the slab from Stop, Beam Theory = elastic section modulus for the extreme Equation 1 compression fiber A = area of an equivalent compressive block for simple beam theory This procedure can require an iterative process, unless the tslab = total structural slab thickness values of the maximum compressive stress at the extreme max = maximum compressive stress at the extreme com- compression fiber obtained from the simple beam theory pression fiber of slab (Equation 3) are comparatively close to the extreme fiber min = minimum compressive stress at the bottom of the slab stresses resulting from the finite element analysis. Initially developed with the positive moment region in mind Elastic section properties such as second moment of iner- as shown in Figure 1 and illustrated above, the same princi- tia (Ixx) and elastic section modulus (S) can be determined ples were applied to the negative moment region as shown in using the effective slab width (beff). The maximum compres- Figure 5. Further details of the derivation and resulting expres- sive stress at the extreme compression fiber can be calculated sions for effective width are provided in Appendix C. The by simple beam theory using the total bending moment for new definitions exploit the expressive power afforded by the the specific section obtained from the finite element analysis use of four layers of three-dimensional (3-D) brick finite ele- as shown in Equation 3: ments through the deck thickness and "smeared" modeling of the top and bottom mats of rebar in the deck. M FEM max,BeamTheory = Equation 3 Stop,BeamTheory 2.3 FINITE ELEMENT MODELING where AND VERIFICATION max,Beam Theory = maximum compressive stress at extreme 2.3.1 Finite Element Modeling compression fiber MFEM = bending moment at the specific section A suitable finite element modeling methodology was sys- (Condition #1 holds) tematically established for use during the parametric study. (a) Slab Tensile Stresses (b) Rebar Tensile Stresses (c) Combined Tensile Stresses (d) Detail Figure 5. Effective width for the negative moment section.

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10 This methodology is outlined briefly in this section and doc- The stud shear connector is modeled using a type of con- umented more fully in Appendix D. nector element called a "Flexible Joint Element" or JOINTC element. The JOINTC elements are composed of transla- tional and rotational springs and parallel dashpots in a local, 2.3.1.1 Structural Element Modeling rotational coordinate system. This type of element was used to model the interaction between two nodes that are (almost) Solid (also known as continuum) elements were used in coincident geometrically so that the second node of the joint ABAQUS to model both steel girder and concrete slab in this can displace and rotate slightly with respect to the first node. research. The element type used is a 3-D eight-noded element The JOINTC elements that represent the stud shear connec- with a reduced integration formulation (element C3D8R). tors consist of three nonlinear springs in each of the transla- Reduced integration provides accurate results while signifi- tional coordinate directions. cantly reducing computation time. Steel reinforcing bars in Figure 6 shows the finite element modeling scheme the deck slab are modeled using the *REBAR function as a employed. smeared property in ABAQUS. The rebars in the 3-D con- tinuum elements are thus defined as layers lying in surfaces with respect to the isoparametrically mapped cube of the 2.3.1.2 Material Models 3-D elements. The stiffness of the reinforcement layer is superposed onto the stiffness of the continuum element in Concrete. The concrete model employed in this investiga- which the rebar resides. tion is based on classical 3-D plasticity (ANATECH, 1997). Figure 6. Element modeling scheme employed.

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11 An advanced concrete model called ANAMAT takes into con- A procedure for post-processing was prepared in such a way sideration many critical aspects of concrete material behavior. that all relevant information can be systematically extracted The ANAMAT concrete constitutive model is based on the from a large data file (.dat file from ABAQUS) and post- smearedcracking methodology developed by Rashid (1968) processed in order to achieve the following: and a Drucker-Prager modified J2-plasticity theory. In the ANAMAT concrete model, a crack is a mechanism Comparing FEM and lab experimental results and that transforms the material behavior from isotropic to ortho- Formulating the "Effective Flange Width" criteria. tropic, where the material stiffness normal to the crack sur- face becomes zero while the full stiffness parallel to the crack For extracting the data from the .dat file, FORTRAN 77 is maintained. The cracks can follow independent histories. In routines were developed for the different data groups (i.e., this smeared-crack model, a smooth crack should close and Load vs. Displacement, Load vs. Girder Strain, Load vs. all the material stiffness in the normal direction is recovered. Concrete Strain, and Load vs. Rebar Strains). Given that crack surfaces are typically rough and irregu- Before starting the parametric study, systematic studies lar, ANAMAT takes into consideration the mechanism of were performed to verify the correctness of the behavior of shear transfer in cracked concrete by retaining a reduced the material models, geometric and boundary condition mod- shear modulus in the stress-strain matrix. Tension stiffening eling in both the linear (elastic) and nonlinear (inelastic- of cracked concrete, which is the ability of cracked concrete cracking and crushing) realms of material behavior. Initially, to share the tensile load with the reinforcement, is also con- other researchers' results on steel-concrete composite bridges sidered in the ANAMAT concrete model. The addition of were used for this purpose, as documented in further detail in tension stiffening to the smeared-crack model improves the Appendix D. Appendix D also includes further specifics about numerical stability of the solution. The ANAMAT concrete the material models and other aspects of the finite element for- material model was implemented using the UMAT subrou- mulations and modeling. tine available in the general-purpose finite element program ABAQUS. 2.3.1.4 A Question about Barriers Steel. The steel constitutive model used in the girders is based on the incremental theory of plasticity in which the total plas- Another FEM modeling question that arises regards barri- tic strain is obtained by summing the plastic strain increments. ers that may be cast with the deck. A study of the barrier effect Ordinary reinforcing bars are modeled as elastic-perfectly under the applied load on the exterior girder was divided plastic. A bilinear stress-strain relationship is used. Because into three parts: (1) load-displacement, (2) strain profile, of the monotonic nature of the loading, the reduction in the and (3) effective slab width. The purpose of this study was to yield stress of the steel due to cyclic loading, that is, the evaluate the significance of the barrier on the structural behav- Bauschinger effect, is not considered. ior and to determine whether it can be ignored. Three differ- ent barrier-modeling schemes were considered: Steel-Concrete Interface (Shear Connectors). The shear connection is modeled based on Oehlers and Coughlan (1986), Beam element, which proposed a simple mathematical formulation that incor- Solid element, and porates the beneficial effects of friction. The shear connec- No-barrier. tion is modeled using two orthogonal spring elements to sim- ulate the shear stiffness of stud shear connectors between the steel-concrete interface and the stiffness normal to the inter- A typical "New Jersey Barrier" used in the OPIS software face. A bilinear rigid-elastic relationship is used to model the was used. Section properties of the barrier were computed steel-concrete interfacial behaviors of the composite bridge and used in the finite element modeling. girders, as described further in Appendix G. From this investigation, it was concluded that the barriers in the parametric study cases can be ignored for the follow- ing reasons: 2.3.1.3 Management of the Parametric Study By not considering barriers, shear-lag would be more The pre-processing package called MSC/PATRAN is pronounced. Hence, the effective slab width would be employed with this modeling procedure. Hence, every model smaller, which is more conservative. will have the same level of consistency and accuracy in Practically, barriers are sometimes placed after the con- terms of crete is poured and cured without connecting to the slab or with expansion joints that eliminate full continuity. Node numbering, Therefore, they should not always be considered as struc- Element numbering and orientation, and tural components for design and rating purposes. It is for Reinforcing steel location. these purposes, after all, that effective width will be used.

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12 2.3.2 Verification Based on Experiments 2.3.3.1 Prototype Description by Others The prototype bridge on which the laboratory specimens are The finite element modeling scheme described above was based is a two-span continuous plate-girder bridge with a cast- verified for use in conducting the parametric study by com- in-place reinforced concrete deck. The AASHTO LRFD Bridge paring the results obtained from ABAQUS/ANAMAT with Design Specifications (1998, with Interims through 2001) were those of full-scale and model-scale laboratory experimental used to design the prototype bridge in accordance with the results by others. These included a full-scale concrete deck HL-93 notional live load. Material properties used for the on steel superstructure bridge experiment conducted by the design are shown in Table 2. The bridge is 13.68 m (45 ft) Nebraska Department of Roads (Kathol et al., 1995) and a wide, and each span has a length of 24.4 m (80 ft). As seen in continuous composite beam test conducted at Lehigh Uni- Figure 7, the four girders are spaced at 3.8 m (12 ft, 51/2 in.), versity (Daniels and Fisher, 1967). and there is a deck overhang of 1.14 m (3 ft, 9 in.) at the exte- As documented further in Appendix D, suitable agreement rior girders. An elevation view of a typical girder is illustrated was found between those experiments and the FEM-based in Figure 8, and Figure 9 shows the framing plan. The Tradi- predictions, even well into the nonlinear range of behavior. tional method (Section 5.7.3 of The Code) was used to design the reinforced concrete deck, and the reinforcement details are provided in Figure 10 in addition to Figure 7. Shear studs are used to connect the concrete deck to the steel girders thus form- 2.3.3 Verification Based on Experiments ing an intentionally composite structure. The shear stud pitch by the Authors of the intentionally composite prototype is designed according The literature survey produced little information related to Section 9.7.3 of The Code and is shown in Figure 11. specifically to experimental investigation of the negative This prototype bridge served as the basis for experimental moment regions of multi-girder bridge specimens. Much of studies carried out as part of the NCHRP Project 12-58 effort. The quarter-scale two-span continuous specimen is called the research has focused on composite beams alone and not 4GQTCOM. The two half-scale negative moment region sub- necessarily on bridge superstructure systems. Also, many of assemblage specimens are called 4GHFCOM and 4GHFNON. the bridge experiments encountered in the review focus on In these specimens, instrumentation is placed with a number positive moment region alone or do not provide strain data in of factors considered. Such factors include providing insight the negative moment region. There is little detail to be found regarding specimen behavior and furnishing a practical data in the literature about deck instrumentation methods for those that included instrumentation in the negative moment region. Furthermore, very little presentation of composite behavior TABLE 2 Prototype material properties is not explicitly intentional (i.e., composite behavior in the fy f' c Components negative moment region due to friction and interface bond or in MPa [ksi] in MPa [ksi] due to longitudinal deck rebar anchored at the ends but with- Girder Flanges 345 [50] out shear connectors along the length). This lack of data moti- Web 345 [50] Stiffeners Bearing 345 [50] vates the experimental research discussed in this report, which (transverse) Intermediate 345 [50] is documented more fully in Appendixes E and F. Stud Connector 345 [50] The experiments performed as part of the NCHRP Project Weld *550 [80ksi] 12-58 work provided an additional source of verification data Reinforcement 420 [60ksi] Concrete 28 [4ksi] for the FEM-based parametric study. The specimens built were based on a prototype bridge. *f u No. 16 @ 200mm (7.87in) No. 16 @ 200mm (7.87in) 50mm (2in) Cover No. 16 @ 200mm (7.87in) No. 16 @ 200mm (7.87in) 24mm (0.9in) Cover (8in) 200mm 1140mm 3800mm 3800mm 3800mm 1140mm (45in) (150in) (150in) (150in) (45in) REINFORCEMENT DETAIL Figure 7. Cross section of prototype bridge.

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13 Web 18300mm (720in) 12200mm (480.3in) 18300mm (720in) 16mm (0.63in) x 940mm (37in) 16mm (0.63in) x 16mm (0.63in) x 940mm (37in) 940mm (37in) Top 18300mm (720in) 12200mm (480.3in) 18300mm (720in) Flange 24mm (0.9in) x 340mm (13.4in) 24mm (0.9in) x 24mm (0.9in) x 340mm (13.4in) 400mm (15.7in) 40mm (1.57in) x Cross-frame 168mm (7.1in) Cross-frame Connection Plate Bearing Stiff. Connection Plate (Typical) Each Side (Typical) 20mm (.787in) x 20mm (.787in) x 160mm (6.3in) 160mm (6.3in) Bearing Stiff. Bearing Stiff. Each Side Each Side 3000mm (118.1n) Cross-frame 7200mm 7100mm 7100mm 3000mm 7100mm 7100mm 7200mm Spacing (283.5in) (279.5in) (279.5in) (118.1n) (279.5in) (279.5in) (283.5in) Bottom 18300mm (720in) 12200mm (480.3in) 18300mm (720in) Flange 24mm (0.9in) x 400mm (15.7in) 36mm (1.4in) x 2 4mm (0.9in) x 400mm (15.7in) 400mm (15.7in) 24400mm (960.6in) 24400mm (960.6in) C.L. Span 1 C.L. Span 2 C.L. Bearing Pier Bearing Figure 8. Girder elevation of four-girder prototype. C.L of Girder (Typical) 3@3800mm (150in) Cross-frame (Typical) 3000mm (118.1n) Cross-frame 7200mm 7100mm 7100mm 3000mm 7100mm 7100mm 7200mm Spacing (283.5in) (279.5in) (279.5in) (118.1n) (279.5in) (279.5in) (283.5in) 24400mm (960.6in) 24400mm (960.6in) C.L. Span 1 C.L. Span 2 C.L. Bearing Pier Bearing Figure 9. Framing plan of four-girder prototype.

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14 50mm (2in) No. 16 (#5) @ 200mm (7.87in) (Top) No. 16 (#5) @ 200mm (7.87in) (Bottom) No. 16 (#5) @ 200mm (7.87in) (Top) No. 16 (#5) @ 200mm (7.87in) (Bottom) 24400mm (960.6in) 24400mm (960.6in) C.L. Span 1 S C.L. pan 2 C.L. Bearing Pier Bearing Figure 10. Deck reinforcement plan in prototype. 120mm [4.72in] 100mm [3.94in] 7320mm [288.2in] 2440mm [96.1in] 100mm [3.94in] 280mm [11in] (Sym. about CL Pier) 4880mm [192.1in] 4880mm [192.1in] 80mm [3.15in] 260mm [10.23in] 2440mm [96.1in] 2440mm [96.1in] 2.0L 1.8L 1.6L 1.4L 1.2L 1.0L 0.8L 0.6L 0.4L 0.2L 0.0L (Typ) 24400mm 24400mm [960.6in] [960.6in] C.L. C.L. C.L. Bearing Span 2 Pier Span 1 Bearing Figure 11. Prototype shear stud pitch. set for comparing experimental test results with the FEM ing is 0.95 m (3 ft, 1 in.), transversely connected by cross- analysis. Findings from these studies are described next. frames along the span length. The geometric parameters of the composite specimen are shown in Figures 12 and 13. The specimen was designed to enable study of the behavior 2.3.3.2 Quarter-Scale Specimen within the positive and negative moment regions of continu- and Instrumentation ous span bridge girders. The girders were designed using Grade 345 (50 ksi) steel, with compact flanges to develop full The four-girder, quarter-scale composite I-beam specimen plastic moment capacity and lateral bracing close enough to consists of two continuous 6.1 m (20 ft) spans. Girder spac- avoid lateral buckling. Webs were designed to be compact

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15 G1 G2 G3 G4 East Abutment this observation, a two rear-axle loading configuration was applied to the test specimen. For the service limit state, five loading positions were used to test the positive moment region and eight loading posi- tions were used to test the negative moment region. Positive moment tests were performed at 0.4L and negative moment tests performed at 0.6L. The design truck was located at 0.4L and 0.6L for the positive and negative moment tests, respec- 6.1m (20 ft) tively. For the ultimate loading tests, a re-configuration of the Span 1 design truck was used which allowed loads to be applied over each girder line. For the negative strength test, each girder was 0.7L loaded at 0.6L on Spans 1 and 2 until failure. Strain and deflection measurements were recorded during the testing process. Displacement transducers were used for the deflection measurements along the bridge. Center Abutment 2.3.3.3 Selected Experimental Results from the Quarter-Scale Specimen 1.3L The purpose of the experiments was to establish a basis for Span 2 confidence in the finite element modeling scheme employed in the parametric studies of this research. Two experimental 6.1m (20 ft) loading cases were the focus of the results presented herein for the experiments conducted on the four-girder, quarter- scale, two-span continuous slab-on-girder bridge specimen: The "Positive Service Yield Case," loading one span to just reach yield of the bottom flanges in the positive moment region, and West Abutment The "Negative Strength Case," loading both spans to maximize negative moment at the support and form a Figure 12. Plan view of four-girder specimen. plastic collapse mechanism in the specimen. and unstiffened. Typical cross sections through the positive Positive Service Yield Case Results. Primarily positive and negative moment regions can be seen in Figure 14. moment region results are presented here because the nega- The maximum aggregate size was chosen as 9.5 mm (3/8 in.) tive-moment region subassemblages reported in the follow- to prevent any large voids in the deck. The slab reinforcement ing sections and Appendix F provided much better negative was isotropically laid out in the reinforced concrete deck with moment region data, with strain-gaged longitudinal rebars, a thickness of 50 mm (2 in.) and the double-layers of 4 mm etc. Sufficient agreement was obtained between experimen- (.157 in.) diameter reinforcing steel placed at 50 mm (2 in.) tal results and FEM predictions that the originally planned spacing, transversely and longitudinally. fourth experimental specimen (2GQTCOM) was deleted A modified design truck was recommended for the experi- from the scope of work for this project. mental study. Two different loading conditions were consid- Figure 15 shows the position of loading for the Positive Ser- ered: (1) complete 6-wheel design truck portion of the HL-93 vice Yield Case. Deflections of an exterior (G1) and interior loading and (2) 4-wheel loading representing the two rear (G2) girder were compared with FEM results. Figure 16 com- axles of the design truck. Analysis results using SAP2000 pares recorded deflections of exterior girder G1 and interior show variations less than 1 percent in the high-stress regions girder G2 versus FEM results and line girder (LG) predictions. and less then 10 percent in the low-stress regions. Based on Line girder deflections were computed using predicted values G1 G2 G3 G4 286 mm (11.25 in) 950 mm (37.5 in) 950 mm (37.5 in) 950 mm (37.5 in) 286 mm (11.25 in) Figure 13. Cross-section view of four-girder specimen.

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16 68 mm (2.7 in) 68 mm (2.7 in) 50 mm (2 in) 50 mm (2 in) 12.5 mm (.5 in) 12.5 mm (.5 in) 254 mm (10 in) 260 mm (10.2 in) 4.76 mm (.1875 in) 68 mm (2.7 in) 10 mm (.4 in) 100 mm (4 in) Positive Moment Region Negative Moment Region Figure 14. Typical cross sections in quarter-scale specimen. of beff, which included full width (beff = S) in the positive prevent the bridge from any lift-off that might have otherwise moment region and 0.9 full width (beff = 0.9 S) in the neg- occurred during testing. This clamping process introduced ative moment region. The FEM used the value of the load cell unintended rotational restraint, which affected the deflection of to provide the direct comparison noted earlier. The values G1 (Figure 16) at a distance of 10,800 mm (425 in.) from the having box symbols on the graph correspond to problematic end where a slight reverse in curvature is evident. G2 (Figure gages. Clamps were placed at the end supports of Span 2 to 16) and FEM show a good correlation in Span 1 and 2. The Positive Service Yield Case was designed to capture the elastic response of the experimental model at yield load levels for comparison with FEM. The various comparative plots show reasonable accuracy in the positive moment region. The experimental results (i.e., deflections and strains) were consistent throughout the test. Deflections that exceeded FEM values were accompanied by corresponding high strain val- 0.4L ues. Strains through the depth of the cross section remained plane throughout the test for nearly all the specified locations Span 1 (neglecting problematic gages). The FEM adequately pre- dicted the observed behavior of the experimental specimen throughout the Positive Service Yield Case. Further testing was performed beyond yield and is presented next. Negative Strength Case Results. Figure 17 identifies the Load Location points of load application during the Negative Strength Case. Next, Figure 18 shows values at two loading stages, one at 360kN (81kips) and the other at 453kN (102kips), the maxi- mum loading achieved. Figure 18 compares the experimen- tal and FEM-predicted deflections of G1 and G2. Under both Span 2 loading conditions, the experimental results were consistent with the FEM results. 1.4L G1 G2 G3 G4 The Negative Strength Case showed significant cracking in the negative moment region, as was to be expected with the continuous specimen. Although the results between the FEM and experimental specimen differed slightly, the results were generally consistent and thus verified FEM results for the positive moment region. Discussion of Test Results. These experiments consisted of various serviceability level loads followed by tests to failure. The major cracking occurred in the negative moment region, Figure 15. General layout and load location which was expected and can be seen in Figure 19. The cracks for positive service yield case. shown in Figure 19 carried across the specimen transversely.

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17 Deflection (G2) Distance (in) 0 60 120 180 240 300 360 420 480 10.00 0.39 5. 00 0.20 0. 00 0.00 Deflection (mm) Deflection (in) -5. 00 -0.20 -10.00 -0.39 EXP FEM LG -15.00 zero -0.59 -20.00 -0.79 0 1525 3050 4575 6100 7625 9150 10675 12200 Distance (mm) Figure 16. G1 and G2 deflection for positive yield case. G1 G2 G3 G4 Figure 20 shows the specimen after the testing was com- 0.07L pleted. At 0.6L, after the positive strength case, a significant 0.13L amount of rotation occurred along with a permanent displace- ment confirming a high level of ductile behavior from the specimen. The other service and strength cases demonstrated that the FEM and experimental behavior were consistent and 0.4L accurate in the positive moment region. The experimental behavior was predicted reasonably accurately by FEM. 6.1m (20 ft) Span 1 As mentioned above, a crack check was performed after 0.6L each test, and each crack was outlined and dated. This pro- vided enough information to create the drawings shown in Figures 21 and 22. Many of the gages in the negative moment region on the concrete deck were lost because of severe cracking as shown in Figure 22. 0.9L 0.95L Load Location 1.05L 2.3.3.4 Half-Scale Specimens and Instrumentation Two half-scale bridge specimens were produced based on the negative moment region of the prototype bridge described in Section 2.3.3.1. The specimens represented a portion of the Span 2 prototype that included two of the four girders and ranged 1.4L from 0.70L to 1.3L, where the parameter L represented one span length. Figure 23 illustrates the portion of the proto- 6.1m (20 ft) type that was represented by the specimens. Additional cross- frames are shown within the specimen portion of the bridge at 0.75L and 1.25L. Although these additional cross-frames were not in the prototype, they were required for stability because the specimens were loaded at those locations. Tie-down and loading at 0.75L and 1.25L (respectively) simulated shear forces at the permanent load inflection points of the prototype while the pier of the prototype was directly represented by a *Note: Max load: 453kN (102kips) Span 1 and 2 central support in the specimen at 1.0L. The bridge specimens were composed of two continuous Figure 17. General layout and load location for homogeneous girders 7220 mm (284 in.) long and a 110-mm negative strength case. (4.375-in.) thick reinforced concrete deck. The girders were

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18 Deflection (G1) Distance (in) 0 60 120 180 240 300 360 420 480 40.00 1.57 20.00 0.79 0.00 0.00 Deflection (mm) Deflection (in) -20.00 -0.79 -40.00 -1.57 EXP 453kN (102kips) FEM 453kN (102kips) -60.00 EXP 360kN (81kips) FEM 360kN (81kips) -2.36 -80.00 -3.15 0 1525 3050 4575 6100 7625 9150 10675 12200 Distance (mm) Deflection (G2) Distance (in) 0 60 120 180 240 300 360 420 480 40.00 1.57 20.00 0.79 0.00 0.00 Deflection (mm) Deflection (in) -20.00 -0.79 -40.00 -1.57 EXP 453kN (102kips) FEM 453kN (102kips) -60.00 EXP 360kN (81kips) FEM 360kN (81kips) -2.36 -80.00 -3.15 0 1525 3050 4575 6100 7625 9150 10675 12200 Distance (mm) Figure 18. G1 and G2 deflection for negative strength case. 490 mm (19.25 in.) deep and had a spacing of 1900 mm typically will rely on. Furthermore, the AASHTO LRFD (75 in.), while the overhang was 570 mm (22.5 in.). Cross- Bridge Design Specifications appear to be inconsistent with frames were constructed from L3 3 3/8 stock and welded in regard to composite action in the negative moment region. place in an X configuration. Specimen geometry is depicted in "Article S6.10.7.4.3 states that `Where composite girders are Figures 24 through 27. noncomposite for negative flexure, additional shear connec- The main difference between the two bridge specimens was tors shall be provided in the region of points of permanent load the layout of the shear connectors. Many states use shear con- contraflexure'. However, the commentary to that article states nectors in the negative moment region of composite bridges that `The purpose of the additional connectors is to develop the while for others it is less common. Effective width criteria are reinforcing bars used as part of the negative flexural compos- based on composite behavior. Composite behavior that is ite section.' Is it composite or noncomposite?--the code is unintentional (i.e., which results only from friction and steel- confusing on this point" (Chen et al., 2001). In any event, to-concrete interface bond strength and not the presence of dis- AASHTO LRFD Bridge Design Specifications were used to crete mechanical connectors) is not something that designers design the shear connectors for both specimens.

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19 G1 G2 G3 G4 0.4L Span 1 0.6L 0.8L 0.9L 0.95L Figure 19. Cracking at G3 over the center support. 1.05L 1.2L 1.3L Span 2 1.4L Figure 21. Cracking due to service loading. Figure 20. Final curvature after testing. in concrete as well as on the deck and girders. In addition to direct strain measurements, displacement transducers such as Temposonics, Linear Variable Displacement Transducers The intentionally composite bridge was designated as (LVDTs), and potentiometers were used to measure quanti- 4GHFCOM because it was based on a four-girder prototype at ties such as displacement, slip, plastic hinge rotation, and half scale. Similarly, the noncomposite specimen was desig- smeared values of strain. nated as 4GHFNON. The shear studs used for both specimens The strain gages placed on the rebar included regular and are 10 mm [3/8 in.] in diameter and have a length of 80 mm backup gages placed on both longitudinal layers (top and bot- [3.1 in.]. As shown in Figure 25, studs are placed in two rows tom) of rebar. A significant number of gages were placed at 75 mm [3 in.] in the vicinity of the permanent load inflec- near the pier because one objective of this experiment was to tion point and at 300 mm [12 in.] elsewhere on 4GHFCOM, investigate behavior near the interior support. A denser con- resulting in 128 shear connectors per beam. The `noncom- centration of gages near the pier might be desired but was not posite' specimen, 4GHFNON, has clusters of shear studs in fully provided because of equipment limitations and because the vicinity of the permanent load inflection point to develop protective coating and wires in the vicinity of the gage might longitudinal rebar as The Code specifies. slightly reduce the volume of concrete and, therefore, the Instrumentation was placed not only for the reasons listed amount of concrete in contact with the bars in the immediate above but also to generate data that might be useful in com- vicinity of the gages. This reduction of concrete volume and paring the intentionally composite behavior of specimen contact area was not expected to be significant, however, 4GHFCOM with the behavior of specimen 4GHFCOM, given that the gages were reasonably spaced across the width which was noncomposite but had longitudinal rebar anchored of the deck. A significant number of gages were placed along at the ends. Strain gages were placed on the rebar embedded Girder 1 as well in order to provide information for comparing

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20 G1 G2 G3 G4 6080mm [239.4in] 0.0L 2440mm [96.1in] 0.2L 0.4L Span 1 0.4L 0.6L 0.6L 0.8L 0.9L 0.95L 0.8L 1.05L 14640mm [576.4in] 1.0L 1.2L 1.3L Span 2 1.4L 1.2L 1.4L Specimen Portion 1.6L 1.8L Figure 22. Cracking due to ultimate loading. 2.0L 1140mm the composite action of 4GHFCOM with that of 4GHFNON. [44.9in] In addition to those near the pier, another transverse line of 1140mm 3800mm rebar strain gages was placed along 0.85L. This location was [44.9in] [149.6in] chosen because it was expected to be far enough away from the point of loading (0.75L) such that local effects from the Figure 23. Specimen portion of prototype. loading were not a concern. Other rebar gages were placed to provide data points to plot the strain profile through the com- posite section. Backup gages were provided in case some 2.3.3.5 Selected Experimental Results: gages were damaged during deck casting. The line of backup Half-Scale Specimens gages on Bar 10 was supplied to replace the gages along Bar 8 if the state of stress near the shear studs was complex Figures 28 and 29 show deck cracking results for the enough to corrupt the readings along Bar 8. They also served 0.95 yield case and the post-yield case, respectively. Fig- as backup for other gages in their vicinity. ure 30 shows the force displacement relationships for both Strain gages on the girders and on the concrete deck girder 4GHFCOM and 4GHFNON on the same plot. The load levels line were positioned to give information about the strain pro- used for FEM comparison are also depicted. The 4GHFNON file within a section. These gages corresponded to the rebar specimen deviated from the FEM curve sooner than the gages mentioned earlier for the same purpose. Other concrete 4GHFCOM specimen. This was probably the result of at least deck gages were placed to provide information about the partial loss of composite action. The plots indicate that the strain variation in plan across the width of the deck. forces were similar in the ultimate limit state, thus indicat- Further information about instrumentation is provided in ing that overall behavior of the noncomposite specimen Appendix F. with developed longitudinal rebar was similar to that of the

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21 C.L. Girder 2 Cross-Frame (Typ.) 1900mm [74.8in] C.L. Girder 1 560mm 560mm [22.0in] [22.0in] Cross-Frame Spacing 1525mm 1525mm 1525mm 1525mm [60.0in] [60.0in] [60.0in] [60.0in] 3050mm 3050mm [120.0in] [120.0in] Span 1 Span 2 Point of C.L. Point of Inflection Pier Inflection Figure 24. Specimen framing plan. intentionally composite one. Comparative deflection pro- 1. There is a good correlation between the FEM and line- files shown in Figure 31 generally confirmed this behavior girder (LG) predicted results for much of the experi- as well, although deviation from linear behavior began slightly mental data. Before the specimens' girders buckled, sooner for the noncomposite specimen. their load displacement curves followed very near the The findings from the negative moment region subassem- FEM curve. These specimens were designed to have blage experiments may be summarized as follows: barely compact webs (based on the current 12t-limited Top Flange 6100mm [240.0in] 13mm x 178mm [1/2in x 7in] Web 6100mm [240.0in] 8mm x 457mm [5/16in x 18in] Shear Stud 560mm [22.0in] 6100mm [240.0in] 560mm [22.0in] 2/Row @ 75mm 2/Row @ 300mm [12in] 2/Row @ 75mm [3in] [3in] 25mm x 76mm [1in x 3in] Bearing Stiffener/ Cross-frame Connection Plate 5/16 5/16 5/16 Each Side (Typ.) 560mm 560mm [22.0in] [22.0in] Cross-Frame Spacing 1525mm 1525mm 1525mm 1525mm [60.0in] [60.0in] [60.0in] [60.0in] Bottom Flange 6100mm [240.0in] 19mm x 178mm [3/4in x 7in] 3050mm 3050mm [120.0in] [120.0in] Span 1 Span 2 Point of C.L. Point of Inflection Pier Inflection Figure 25. 4GHFCOM girder elevation.

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22 Top Flange 6100mm [240.0in] 13mm x 178mm [1/2in x 7in] Web 6100mm [240.0in] 8mm x 457mm [5/16in x 18in] Shear Stud 400mm [15.75in] 400mm [15.75in] 400mm [15.75in] 400mm [15.75in] 3/Row @ 57mm 3/Row @ 57mm 3/Row @ 57mm 3/Row @ 57mm [2.25in] [2.25in] [2.25in] [2.25in] 25mm x 76mm [1in x 3in] Bearing Stiffener/ Cross-frame Connection Plate 5/16 5/16 5/16 Each Side (Typ.) 560mm 560mm [22.0in] [22.0in] Cross-Frame Spacing 1525mm 1525mm 1525mm 1525mm [60.0in] [60.0in] [60.0in] [60.0in] Bottom Flange 6100mm [240.0in] 19mm x 178mm [3/4in x 7in] 3050mm 3050mm [120.0in] [120.0in] Span 1 Span 2 Point of C.L. Point of Inflection Pier Inflection Figure 26. 4GHFNON girder elevation. 3040mm [119.8in] 25mm C.L. C.L. [1in] Girder 1 No. 10 @ 75mm [#3 @ 3in] 25mm [1in] Cover Girder 2 Cover (All Layers) 110mm [4.4in] 25mm [1in] Haunch 13mm [1/2in] Cover 570mm 1900mm 570mm [22.5in] [74.8in] [22.5in] Figure 27. Specimen section. definition of effective width) in order to develop a plas- model the geometric nonlinearity of web buckling com- tic hinge and investigate experimentally the cracked- bined with the material nonlinearity of yielding in the deck effective width at plastic hinge conditions. But in FEM model were unsuccessful. Thus, the plotted FEM doing so, it was overlooked that full (not 12t-limited) model results neglected web buckling. Even after buck- effective width would raise the neutral axis, thereby ling, however, the general shape of the load displace- rendering the web noncompact. Such a web would be ment curve mimics the shape of that predicted by FEM expected to buckle before full plastification, which is modeling. It is therefore reasonable to assume that, had precisely what occurred in the experiment. Attempts to the section been fully compact, it might have continued

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23 Cracking From Case Y3 Total Cracking After Case Y3 Figure 28. 4GHFCOM Case Y3 cracking. close to the FEM curve. That it was not compact itself the second specimen did, however, yield reasonable is evidence of full effective width, given that, on the results. This favorable outcome is believed to be due to basis of current AASHTO provisions for effective width, the introduction of epoxy as the protective coating. The it would have been compact. Deflection profiles were general unreliability of deck-related strain gages because also predicted reasonably well by the FEM model up to of deck cracking makes it difficult, if not impossible, to the onset of buckling. extract effective width values directly from experi- 2. Girder strains obtained from the experiment also com- mental results. That most of the other data correlated pared well with FEM-predicted values. There were some well with FEM, however, was considered sufficient to discrepancies near the boundary conditions (i.e., load- conclude that FEM results were reasonable. The reader ing and tie-down points) but this was to be expected. may wish to refer to the dissertation by Chiewanichakorn 3. Strain readings associated with the deck were generally (2005) for more information regarding the validity of unreliable for the composite specimen, and most of them FEM relating to evaluation of composite bridges. were questionable for the noncomposite one as well. 4. The global behavior of the 4GHFNON specimen (non- Unfortunately, deck surface gage results were the most composite but with developed rebar) was similar to that unreliable. Some of the rebar-mounted strain gages on of the 4GHFCOM (intentionally composite) specimen,