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B-1 APPENDIX B DETAILS OF THE EXPERIMENTAL PROGRAM GENERAL nominal capacity of 1.2 Mcr. The cracking moment, Mcr, was calculated using the composite cross section but assuming The experimental program consisted of two parts: con- the entire section was made from slab/diaphragm concrete. nection capacity tests and full-size tests. The design concrete The cracking moment was determined to be 2,950 k-in., so strength for girders was 4,000 psi at release and 5,500 psi at 1.2 Mcr is 3,540 k-in. 28 days. Slabs and diaphragms had design 28-day strengths of The bent-strand connection was made by extending the 4,000 psi Actual concrete strengths are provided in Table B-1. strand extend from the face of the girder and then bending it at All mild reinforcing bars were Grade 60, but the actual yield a 90 angle. To determine the length of strand, the equations strength was 83 ksi. The prestressing strand was Grade 270 developed by Salmons and others (14) were used. These low relaxation. equations provide both an ultimate strength and a working stress. The connection was designed to have an ultimate strength capacity of 1.2 Mcr and a working stress capacity of CONNECTION CAPACITY: Mcr. There are two variables: the area of the strand and length STUB SPECIMEN TESTS of the strand. For the stub specimens, the entire bottom layer Connection Details of six strands was used. This provided an area of 0.918 in2. The original work by Salmons and others allowed for the The stub specimens consisted of two 16-ft-long AASHTO use of horizontal bars attached to the web and perpendicular Type II girders connected by a diaphragm (see Figure B-1). A to the girder (see Chapter 2). If these horizontal bars are not total of six specimens were tested (see Chapter 2 for details). used, the required working stress in the bent strand is given by The original plan was to fabricate six stub girders and to cre- ate the six specimens by using both ends of the stubs. Two fps (req'd) = M stubs would be used to create a specimen for a test, and then Aps jd ps after the test, the stubs would be cut from the diaphragm. The stub girders could then be turned around, and the other ends where used to create a second specimen. This was done for the first M = positive moment, four specimens; however, the last two specimens had the Aps = area of the bent strand crossing the connection joint, girders embedded in the diaphragms, which made cutting them and from the diaphragm impractical. Initially, a total of seven stub jdps = distance between the compressive and tensile girders (six for use plus one spare) were fabricated. To make resultants. the final specimen, an additional stub beam was fabricated and used with the spare stub girder to make Specimen 6. The required embedment length is then found from The stub specimens were designed to simulate an interior girder in a multispan I-girder bridge. This bridge had 50-ft fp = (Le - 8.25 in.)/0.228 < 150 ksi, and spans and used AASHTO Type II girders. The live-load inflec- tion points were approximately 15 ft from the diaphragm, so Le = embedment length (in.). the stub specimens approximated the area between the live- load inflection points. All six specimens used a 10-in. gap Ultimate strength is calculated by between the ends of the girders (see Figure B-1). A 7.5-in.- thick by 8-ft-wide slab was cast on top of the girders. fpu = (Le - 8.25 in.)/0.163, The diaphragms were 8 ft wide. The thickness of the dia- phragms varied from 10 in. to 26 in., depending on whether a = (Aps fpu - As fy )/0.85fc b, the girders were embedded in the diaphragm. Except for Specimen 5, the diaphragms had No. 5 stirrups placed 12 in. Mu = (Aps fpu [dps - a /2] + As fy [d - a /2]), on center with the first stirrup 3 in. from the face of the bot- b = width of compression face (rectangular section tom flange (see Figure B-1). Specimen 5 had two additional assumed), stirrups placed 3 in. on center, just outside of the bottom flange of the girder. fc = compressive strength of concrete, and Two types of positive moment connections were used: bent strand or bent bar. All connections were designed to have a = understrength factor.

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B-2 TABLE B-1 Concrete compressive strength* Concrete Compressive Strength Stub Specimens psi (MPa) Girders 10,500 (73.5) Diaphragm/Slab 1 7,200 (50.4) Diaphragm/Slab 2 8,200 (57.3) Diaphragm/Slab 3 7,500 (52.5) Diaphragm/Slab 4 5,500 (38.4) Diaphragm/Slab 5 5,700 (39.9) Diaphragm/Slab 6 6,400 (44.8) Full-Size Girders 11,500 (80.5) Partial Diaphragm 1 @ 28 Days 5,300 (37.1) Partial Diaphragm 1 @ Test 5,500 (38.5) Slab 1 @ 28 Days 6,550 (45.9) Slab 1 @ Test 6,750 (47.3) Diaphragm/Slab 2 7,100 (49.7) *Strength is at time of test unless noted. (a) It was assumed that the working stress condition controlled and that the connection should be able to develop Mcr at working stress. For six strands, the cracked section has jd = 40 in. with Mcr = 243 k-ft, Le = 26 in. If an Le of 26 in. is then substituted into the ultimate strength equations, the capacity is found to be 315 k-ft, which exceeds 1.2 Mcr = 292 k-ft. For all calculations, the composite cross section is used, but it is assumed to be made entirely of diaphragm concrete. This is consistent with the nor- mal design assumption that failure occurs in the diaphragm concrete. The section is treated as a regular reinforced concrete section and uses 0.9 as the understrength factor. (b) For the bent-bar connection, the composite cross section was designed as a regular reinforced concrete section with an Figure B-2. Stub experimental setup. ultimate capacity of 1.2 Mcr. Using the nominal concrete strength of 4 ksi and 60 ksi for yield of the steel, the section "east" and "west." In Figure B-2, east is foreground. The spec- required five No. 5 bars. imen is held down at the center by a tie down device and is loaded by a yoke system at each end (see Figures B-3 and Experimental Set-Up B-4). Load was applied through two -40 kip hydraulic cylin- ders. Load cells were attached to the rod of each cylinder. Figure B-2 shows the experimental set up. For ease of The system was controlled by servohydraulic valves and an understanding, the ends of the specimen were designated electronic controller. The girders were supported by load cells at the center sup- port placed under the ends of the girders (see Figure B-5). According to data collected in a survey (see Chapter 2), this is the usual method of support. Direct current linear variable differential transformers (DCLVDTs) were attached to the girders and targeted to the diaphragms to measure crack open- ings (see Figure B-5). Crack openings were measured on both sides of the girders and on both faces of the diaphragm--a total of four joints. The DCLVDTs were placed at the mid- height of the top and bottom flanges and at the midheight of the web. Vibrating wire gages were placed in the diaphragm area, as shown in Figure B-6. Vibrating wire strain gages were placed 1.5 in. from the bottom of the diaphragm, at a distance of 3 in. and 12 in. from the outside face of the bottom flange of the girder. Additional external vibrating wire gages were attached to one side of each girder (see Figure B-5). The original idea was to lift both ends of the specimen, Figure B-1. Stub specimen. but this proved to be unstable. The same load effect could

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B-3 Figure B-3. Schematic of loading yoke. be obtained by loading the specimen as a cantilever (see Fig- Next, the specimen was loaded to develop Mcr at the joint ure B-2). One end was loaded while the other remained sta- to simulate the assumed time-dependent and temperature tionary. A load cell placed under the stationary end verified effects. This loading was repeated three times for each end that the loading was correct. by first applying three cycles to one end and then three cycles The specimen was loaded to simulate a condition where the to the other end. time dependent and the temperature effects created a positive After the initial loads had been applied, the load was cycled moment of Mcr, and then traffic loads cycled the moment at to develop moments between Mcr - MLL- and Mcr + MLL+. This the connection above or below Mcr. As a result, a cyclic load- represented an assumed worst-case loading for the connection. ing pattern was developed in which the specimen was loaded The servohydraulic controller applied the load and counted the between Mcr - MLL- and Mcr + MLL+ where MLL- and MLL+ are cycles. The cyclic loading was to last for 1,000,000 cycles or the positive and negative live-load moments at the connec- to failure. The intent was to load the east side and keep the west tion. From analysis, the maximum negative live-load moment side stationary for 100,000 cycles and then switch sides. How- was found to be MLL- = 365 k-ft, and the maximum positive ever, this was only done for Specimens 5 and 6 because they live-load moment was determined to be MLL+ = 90 k-ft. All were the only ones to survive past 100,000 cycles. Load was live-load moment values were at the face of the diaphragm. applied at a rate of 2 hertz as long as the specimen would take Mcr was calculated as 245 k-ft. the load at that rate. As the connection deteriorated, the cycle Prior to the cyclic loading, the specimen was loaded to length had to be slowed down to ensure the correct loads were develop the negative live load moment and then the positive applied; however, this only occurred near failure, and the live-load moment at the joint. This loading was to establish slowest loading rate was 1 hertz. the initial stiffness of connection and was repeated three The cyclic tests were stopped at various intervals, and the times. To ensure consistency, the test was done twice. First specimen was loaded under static loads to Mcr - MLL- and the east end was loaded and the west end was kept station- Mcr + MLL+. Even though only one side was being loaded ary, then the west end was loaded while the east end was kept under cyclic load, the static tests were performed twice, once stationary. on each side. Static tests were to be performed at 5,000;

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B-4 Figure B-4. Loading yoke. 10,000; 15,000; 20,000; 25,000; 30,000; 50,000; 75,000; and spalling off or the specimen pulling out of the diaphragm. At 100,000 cycles (if any test had continued beyond 200,000 this point, the specimen would not hold the required load cycles, static tests would have been conducted every 100,000 under static testing. cycles). The stub girders from Specimens 1 and 3 were reused for Failure of the specimen was accompanied by a catastrophic Specimens 2 and 4. On both Specimens 1 and 3, failure was event such as the concrete on the bottom of the diaphragm accompanied by the concrete spalling off the bottom of the diaphragm, exposing the positive moment bar or strand. This bar or strand could then be cut, if needed (in some cases the bar or strand was already broken). The deck was cut on both sides of the diaphragm, and the girders were removed from DCDT the diaphragm. The stub girders were turned end-for-end and reused in Specimens 2 and 4. DIAPHRAGM FULL-SIZE SPECIMENS GIRDER The full-size specimens were constructed of two 50-ft Type III AASHTO I girders joined with a 10-in. diaphragm. An 8-ft-wide 7.5-in. thick composite concrete deck slab VIBRATING WIRE was cast on top (see Figure B-7). Each end of the girder spec- STRAIN GAGE imens were cast with both bent-bar and extended strands so that either end could be used for either type of connection. When the girders were cast, shrinkage specimens were LOAD CELLS made. One was left with the girder to measure field shrink- age, and the other was used for the standard shrinkage test (AASHTO T160). At 180 days after the girders were fabri- Figure B-5. External instrumentation. cated, the field specimen showed a shrinkage of 710 micro-

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B-5 Figure B-6. Placement of instruments in the diaphragm of the stub specimen. strain and the standard specimen shrank 570 microstrain. cells are very stable and do not drift. Three load cells were Cylinders were cast for creep tests. Two cylinders were used placed under each girder, two at the end near the diaphragm for the standard creep test. At 180 days after the girders were and one at the far end. cast, the average creep coefficient (creep strain/elastic strain) Two vibrating wire strain gages were embedded in each was 2.4. girder at midspan. A vibrating wire strain gage was embed- ded in the slab at midspan directly above the girders (see Fig- ure B-9). A vibrating wire strain gage was also embedded Monitoring Specimen 1 6 in. from the end of each girder, 4 in. from the bottom. Vibrat- Full-size Specimen 1 used a bent-bar connection with the ing wire strain gages and bonded foil strain gages were placed girders not embedded in the diaphragm. The positive moment in the diaphragm, as shown in Figure B-10. Another vibrat- connection was designed as a reinforced concrete section ing wire strain gage was placed 1.5 in. from the bottom of the using the composite cross section and the strength of the dia- diaphragm at a distance of 3 in. from the outside edge of the phragm concrete. As with the stub specimens, the connection girder bottom flange. was designed for a capacity of 1.2 Mcr. Using the design DCLVDTs were installed to measure crack openings. There strengths of the concrete and steel, it was determined that were four joints, one on each side of the girder on each side eight No. 5 bars, in two rows of four, were needed to provide of the diaphragm. Three DCLVDTs were placed on each a capacity of 1.2 Mcr = 500 k-ft (see Figure B-8). The bars joint at 3 in., 23 in., and 42 in. from the bottom of the girder. had standard hooks. The diaphragm was 10-in. wide. The bottom DCLVDTs were placed 1 day after the partial As noted in Chapter 2, a partial diaphragm was cast for Spec- diaphragm was poured by drilling holes in the formwork to imen 1 when the girders were 28 days old. The remainder of the allow the DCLVDTs to be targeted on the diaphragm. These diaphragm and the slab was cast 28 days later. As with the gird- DCLVDTs were removed for a few hours when the forms ers, both field and standard shrinkage specimens were made were removed and then reinstalled. The DCLVDT can never for the slab. At 120 days after the slab was cast, the shrinkage be reinstalled to exactly the same reading as before removal, was approximately 560 microstrain for both specimens. so several data points were taken before and after removal. After the slab was cast, the specimen was monitored for The difference between these two readings was used to cor- approximately 120 days. Girder reactions were monitored by rect future readings. Deflections were monitored by wire six vibrating wire strain gagetype load cells. These load potentiometers placed at midspan of the girders. After the

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B-6 Figure B-7. Full-size composite section. Figure B-8. Full-size bent bar specimen.

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B-7 Figure B-9. Location of vibrating wire gages at midspan. forms were removed, two additional wire potentiometers were Melbourne, Kentucky. The facility is approximately 16 miles attached to the diaphragm. from the University of Cincinnati campus. Because of the The instruments were monitored by an electronic data distance, data was collected every 3 to 4 days. Although the acquisition system, except for the foil gages. The system did computers were furnished with battery backups and surge not have the ability to monitor the foil gages and the foil protectors, there were still occasions in which the research gages tend to drift, so any data obtained would have been team would arrive to collect data and find that one or more of questionable. The gages were read every hour. The tests were the computers had reset and that the data were lost. This is done at an outdoor facility located at Prestress Services in why some gaps appear in the data in Chapter 2. Figure B-10. Location of vibrating wire gages in the full-size specimen diaphragm.

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B-8 After monitoring the first specimen for 120 days after the Testing the Full-Size-Specimens for Continuity slab was cast, the specimen was tested for continuity. These tests are described in a following section. One purpose of the full-size specimens was to determine whether cracking at the diaphragm affected continuity. The plan was to apply the cracking moment to connection and then to apply external loads. Full-Size Specimen 2 In an effort to duplicate the kind of deformation that would occur due to creep and shrinkage of the girders and would Full-size Specimen 2 was a bent-strand connection with crack the diaphragm, a post-tensioning system was used. A the girder ends not embedded in the diaphragm. The strand post-tensioning bar was placed through the bottom flange of length was kept at 26 in. to match the stub girder specimens. the girder, and a post-tensioning force was applied (see Fig- To achieve a capacity of 1.2 Mcr = 500 k-ft, 10 strands were ures B-12 and B-13). This would cause the girders to camber needed (see Figure B-11). The number of strands was deter- up--simulating the formation of additional positive moment. mined from the same equations used for determining strand Note that the post-tensioning bars only went through the capacity for the stub girder specimens. girders and did not go through the diaphragm (i.e., the bar The second full-size specimen was constructed by cut- was dead-ended at the end of the girder where the girder was ting the diaphragm out of the first full-size specimen and attached to the diaphragm). turning the girders end-for-end. When the deck slab was To determine the size and placement of the post-tensioning cast for the first full-size specimen, approximately 12 ft of bar, each span was modeled as a propped cantilever (see slab had not been cast at the end of each girder. When the Figure B-14) with a constant internal moment applied. Note girders were turned end-for-end, there was a gap in the slab that for each 1 k-ft of internal moment, the moment at the over the diaphragm area. When the diaphragm for Speci- connection increases by 1.5 k-ft. To generate the cracking men 2 was cast, a deck slab was cast in this gap to provide moment of 417 k-ft, an internal moment of 278 k-ft was continuity. Reinforcing bars had extended from the end of required. This could be achieved with a 1.375-in.-diameter the existing slab to tie the new slab to the old slab. Full-size Dywidag bar placed as shown in Figure B-12 and tensioned Specimen 2 was not monitored, but was tested for continu- to the maximum allowable force of 160 k. ity when the diaphragm and deck slab were 28 days old. Instru- Four 40-kip-capacity hydraulic cylinders were used to sim- mentation for full-size Specimen 2 was the same as for full- ulate the live load. Two cylinders were placed in each span size Specimen 1. at 22.5 ft from the face of the diaphragm (see Figures B-15 Figure B-11. Full-size bent strand specimen.

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B-9 Figure B-12. Positioning of post-tensioning duct in the full-size specimen. and B-16) because analysis showed that this was the most efficient position for the load. The loading sequence was as follows: 1. Span 1 was loaded, 2. Span 2 was loaded, 3. Span 1 was unloaded, and 4. Span 2 was unloaded. The upward loads created positive moment, and downward loads created negative moment. The general steps of testing for both full-size specimens were as follows: 1. The load was applied such that when both spans were loaded, the negative live-load moment (365 k-ft) was developed at the connection. Figure B-13. End of Specimen 1 showing extended bar, 2. The load was applied such that when both spans were extended strand, and post-tensioning bar. loaded, the positive live-load moment (90 k-ft) was developed at the connection. Figure B-14. Model for developing moment from post-tensioning moment.

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B-10 3. One-quarter of the post tensioning force (40 kips) was applied to the girders; the girders were post-tensioned one at a time. 4. Steps 1 through 3 were repeated until all the post- tensioning force had been applied. 5. When all the required post-tensioning force has been applied, the specimen was loaded to the negative and positive live-load moments. 6. If the girders still appeared to be continuous, the loading system was used to apply additional positive moment until the specimen failed or the system lifted off the supports. This sequence was followed for both full-size specimens. For full-size Specimen 2, additional positive moment was gener- ated by jacking up and shimming the ends of the specimen to Figure B-15. Full-size specimen with loading cylinders. increase the end reaction (see Chapter 2). REFERENCES FOR APPENDIX B 1. Salmons, J.R., and McCrate, T.E. Bond of Untensioned Pre- stress Strand. Interim Report 73-5A, Missouri Cooperative High- way Research Program, Missouri State Highway Department, August 1973. 2. Salmons, J.R., and May, G.W. Strand Reinforcing for End Con- nections of Pretensioned I-Beam Bridges. Interim Report 73-5B, Missouri Cooperative Highway Research Program, Missouri State Highway Department, May 1974. 3. Salmons, J.R. End Connections of Pretensioned I-Beam Bridges. Final Report 73-5C, Missouri Cooperative Highway Research Program, Missouri State Highway Department, Nov 1974. 4. Salmons, J.R. Behavior of Untensioned-Bonded Prestressing Strand. Final Report 77-1, Missouri Cooperative Highway Figure B-16. Overall photograph of the full-size Research Program, Missouri State Highway Department, specimen. June 1980.