Phase 1 Test Observations 153

During the lateral load testing, the extreme column longitudinal bars in the column began yielding at an average lateral displacement of 0.46 in., which was established based on the measured strains in the extreme column longitudinal reinforcement in the push and pull direction of loading during testing at ±1.0F’y. By combining this information with the

theoretical first yield and idealized yield lateral force resistance, the idealized yield displacement for the test unit was defined as 0.7 in. Consequently, the displacement at each ductility level was obtained as a factor of 0.7 in. Table 6.2 outlines the updated loading protocol during Phase 1 testing.

Whiffle Tree Top Beam

Spacer Blocks

154

Table 6.2: Updated Horizontal Test Protocol for Phase 1 Testing

Cycle Target ∆ (in)

Average Absolute Measured Actuator Force (kips) Number of Cycles ±0.07 F’y ± 0.05 40 1 ±0.17 F’y ± 0.12 80 1 ±0.36 F’y ± 0.25 120 1 ±0.6 F’y ± 0.42 160 1 µΔ = ±1 ± 0.7 210 3 µΔ= ±1.5 ± 1.05 224 3 µΔ= ±2 ± 1.4 233 3 µΔ= ±3 ± 2.1 247 3 µΔ= ±4 ± 2.8 247 3 µΔ= ±6 ± 4.2 253 3 µΔ= ±8 ± 5.6 245 2 µΔ= ±10 ± 7.0 221 1

Under positive moments, cracking between the diaphragm and cap interface did not develop on the underside of the superstructure until a displacement ductility of 1.5 was reached. These cracks were observed in each bay between two girders on the positive moment side and were primarily concentrated near the girders. However, none of the cracks extended along the entire length of the cap. Additionally, cracking was observed at the interface between the bottom flange of each of the girders and the underside of the bent cap under positive moments. On the as-built connection side of the bent cap, the aforementioned girder to cap interface cracks had a width of 0.4 mm at the center girder. Similar cracks were noticed on the improved connection side, when subjected to a positive moment, at a ductility level of 1.5; however, the crack width was only about 0.2 mm at the center girder. At this ductility level, vertical flexural cracking was also noticed along the interface between the web of the girders and the diaphragm on both the improved and as-built connection sides, when each connection was subjected to a positive moment, and extended roughly half way up to the underside of the deck. Finally, significant cracking was observed on the topside of the deck, primarily outside the edge of the diaphragm on the negative moment side of the bent cap. A significant number of the flexural cracks in the deck, which had developed

155

during earlier cycles due to negative moment, had also connected and spread across the entire length of the deck, indicating the engagement of all five girders in resisting the column moment on each side of the bent cap.

At a displacement ductility level of 2, the previously mentioned flexural cracks between the bottom flange of the center girder and the bent cap on the as-built connection side had widened to 0.5 mm, while the same gap on the improved connection side remained at 0.2 mm. The vertical cracks between the webs of the girders and the diaphragm on both sides of the connection extended almost all the way to the underside of the deck. Cracking on top of the deck continued to develop further away from the bent cap and extended across the entire width of the deck. The first signs of crushing and spalling of the concrete at the top and bottom of the column were also noticed.

Between displacement ductility 3 and 8, the majority of the significant changes to the test unit occurred within the column and the deck near the column. A few new cracks developed in the column; however, the primary observation was that the old cracks began to extend and increase in width. The cover concrete at both the top and bottom column ends also began to crush and spall within the plastic hinge regions as the cycles progressed. Incipient buckling to one of the exposed longitudinal column reinforcement bars was observed in the bottom plastic hinge at a ductility level of 8, on the South side of the column. The number of cracks in the deck increased in an evenly distributed manner and spread across the entire width of the superstructure, the majority of which were located between the diaphragm and vertical tie-down locations on each side of the bent cap. No significant changes were observed in either the as-built or the improved connection regions on the underside of the superstructure. Instead, the cracks remained essentially unchanged in regard to both their extension and width.

By the time the test unit had reached a displacement ductility of 10, or a horizontal displacement of 7 in., it was apparent that the column had reached its ultimate capacity. A significant amount of concrete had crushed and spalled off of the column within the top and bottom plastic hinge regions, as shown in Figure 6.14. Several spirals and longitudinal bars were visible and concrete within the column core had crushed. The majority of the longitudinal column bars within the hinge regions had also begun to buckle across the spirals.

156

However, no significant further cracking was observed within the connection region between the girders and the cap or diaphragm, as shown in Figure 6.15. Furthermore, no joint cracking between the column and inverted-T bent cap was observed during the entire test. More flexural cracks along the top of the deck had developed between the diaphragm and hold-down locations, while only a few cracks were observed within the cap region. Some of the cracking in the deck, near the stem on the inverted-T also extended all the way through the deck.

Figure 6.14: A Close-Up View of the Column Performance at +7.0 in. of Lateral Displacement (µ∆=+10)

157

Figure 6.15: Condition of As-Built Center Girder-to-Cap Connection at µ∆=+8