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13 gation, cap beam dilatation, and overall horizontal specimen ments is presented in Appendix F for SPC1 and in Appen- translation. dix G for SPC2. (These appendixes are provided on the Strain gages were used to measure strains at selected loca- accompanying CD-ROM.) tions in both specimens. These locations included the gird- ers; column spiral reinforcement; column longitudinal rein- forcement; slab reinforcement; and cap beam webs, flanges, 2.5.1 Seismic Test Results diaphragms, and shear studs. General observation of SPC1 revealed that the specimen behaved as expected under lateral loading (i.e., a plastic hinge 2.4.4 Seismic Load Simulation was formed in the column adjacent to the cap beam). The super- structure behaved elastically throughout the entire test, also in To simulate seismic loading of the prototype, the load accordance with the intent of the design. As expected, flexural sequence for both specimens consisted of applying an appro- cracking of the column occurred at loads below the predicted priate column axial load downward to the top of the (inverted) yield of the column longitudinal reinforcement. Defining the column to simulate the prototype gravity effect. While main- displacement ductility, D, as the ratio between the maximum taining the gravity load at a constant level, seismic effects were displacement during a load cycle during the test divided by the simulated by using a cyclic, lateral load with full reversals. displacement required to cause the yield of the column longi- To determine appropriate column axial loading, the expected tudinal reinforcement, concrete spalling at the column-to- shear and moment values for the prototype bridge and the test cap beam connection began to occur at displacement ductility specimens were compared. Based on the results of this = 1.5. At ductility = 4.0, several column longitudinal bars investigation, most of the test of SPC1 was conducted with were visible, with a few showing indications of buckling. At a column axial load of 270 kN (60 kips) to produce a better ductility = 6.0, the three extreme column longitudinal bars prototype/specimen moment comparison, and the axial load on each side of the column fractured, as shown in Figure 7. The was increased to 580 kN (130 kips) in a later stage of cyclic buckling is believed to have been caused by loss of confinement testing to carefully evaluate the shear transfer. The load was because of interaction effects between the steel cap beam and returned to 270 kN (60 kips) for the remainder of the test. In concrete column. The steel flange of the cap beam interrupts the SPC2, a similar pattern was used except an axial load of 220 concrete of the column and represents a discontinuity of the kN (50 kips) was used instead of the 270 kN (60 kips) used in concrete. In addition, the column spiral was terminated at the SPC1. Seismic effects were simulated using a cyclic, lateral flange of the cap beam and was restarted on the other side of load pattern with full reversals as shown in Figure 6. the flange. Each end of the spiral was anchored with an addi- Details of the test fixture and the loading system are presented tional two turns of the spiral as required by current design prac- in Appendix E (provided on the accompanying CD-ROM). tices for concrete members. However, it appears that, because of the discontinuity presented by the steel cap beam flange, this 2.5 TEST RESULTS anchorage is not sufficient. Specimen SPC2 also displayed satisfactory seismic per- A summary of the test results is presented below. A formance, exhibiting the formation of a plastic hinge in the detailed description of the test observations and measure- Force Displacement Control Control 580 kN Axial load 270 kN Lateral load sequence 1.0 y' -y' -1.0 # of Cycles =1 3 3 3 3 3 3 4 steps = 1 = 1.5 = 2 = 3 = 4 = 6 Figure 7. Fracture of column longitudinal bars at = Figure 6. Load sequence selected for simulation of 6.0 1 (SPC1, column tension side while pull direction seismic effects on test specimen SPC1 (1 kN = 0.225 kips). load is being applied).

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14 column adjacent to the cap beam and showing elastic behav- ior of the superstructure. Early stages of the test revealed similar behavior to SPC1. Increased cracking was seen in the slab as could be expected for the more flexible superstructure in SPC2. The primary difference in results in SPC2 was the failure mechanism of the longitudinal bars, which appeared to lose anchorage in the connection region and fractured the mechanical connections. (Mechanical connections were not used in SPC1 because the increased cap beam height in SPC1 provided adequate anchorage length for the longitudinal rein- forcement.) The plastic-hinge region of SPC2 following test- ing is shown in Figure 8. Views of the columns from SPC1 and SPC2 following seismic testing are shown in Figures 9 and 10. Figures 11 and 12 show the experimental load-displacement hysteresis for specimens SPC1 and SPC2, respectively. Both specimens exhibit satisfactory seismic behavior through duc- tility = 4.0 as indicated by the regular shape of the hys- teresis and the gradual degradation of stiffness. In the load- displacement response for SPC1 (Figure 11), the decreased load resistance resulting from the fracture of several of the column longitudinal bars at = 6.0 is indicated by the lower stiffness of the last cycles in Figure 11a. SPC2 also exhibits decreased load resistance at ductility = 6.0 because of the Figure 9. Tension side of the column in the push loading direction after seismic testing (SPC1). fracture of the mechanical anchorage of several of the lon- gitudinal bars as shown in Figure 12a. The predicted load- displacement relationships developed from the grillage analy- ses are also shown in Figures 11b and 12b. The actual column Figure 8. Partial view of column at the completion of behavior is quite consistent with the predicted behavior for seismic testing (SPC2, tension side of the column in the pull the initial load steps. The pull direction response of SPC2 is loading direction). seen to begin to differentiate from the predicted behavior at