Seismic Resilience of Pre-Tensioned Bridge Bents

Transcription

1 Seismic Resilience of Pre-Tensioned Bridge Bents Eric Ramirez Home Institution: University of Texas at El Paso REU Site: University of Nevada, Reno PI: Dr. David Sanders Graduate Student Mentor: Islam Mantawy August 8, 2014

2 Abstract A new bridge system which uses advanced building construction methods, includes pretensioned strands in the columns and uses rocking connections at the ends of the columns has been developed for high seismic performance within the George E. Brown Jr Network for Earthquake Engineering and Simulation (NEES). The new bridge system ultimately decreases construction time, reduces post-earthquake residual displacements, and minimizes earthquake damage. A prototype bridge system with the aforementioned characteristics and modeled to a quarter scale was constructed in collaboration between the University of Nevada, Reno and the University of Washington. The bridge was then tested on shake tables at the University of Nevada, Reno s earthquake engineering laboratory and the data was compared with similar data obtained from shake table tests conducted on a conventionally-built bridge system. The comparisons indicated that the new bridge system induced less damage, provided reduced residual displacements, higher peak displacements at high-amplitude motions and larger drift ratios at high-amplitude motions. A comparison was also made within the new bridge system to assess how displacements and bridge accelerations associated with a ground motion changed after the new bridge system had been induced to higher ground motions and it was found that the bridge system s period changed. The aforementioned findings are preliminary but they indicate the new bridge system provides superior seismic performance. Further work is currently being conducted within NEES to fully assess the new bridge system s seismic resilience. i

3 Contents 1: Introduction : Literature Review : Methods Bridge System Properties Construction of Bridge System Instrumentation Testing Protocol : REU Student Contribution Construction of System Installation of Instrumentation Post-Processing of Shake Table Results Evaluation of Conventional Bridge Shake Table Results : Results Comparisons between New and Conventional Bridge Observed Behavior Comparison Peak Transverse Displacement Comparison Residual Transverse Displacement Comparison Column Longitudinal Reinforcement Strain Comparison Transverse Drift Ratio Comparison : Comparisons within New Bridge Transverse Acceleration Comparisons Transverse Displacement Comparisons : Discussions, Conclusions and Future Work Contact Information Acknowledgements : References Appendix Test Data ii

4 1: Introduction The ability of bridges to be seismically resilient is critical in reducing human losses and mitigating economic damage in the event of an earthquake. Several devastating earthquakes such as the 1994 Northridge California earthquake and the 1995 Kobe, Japan earthquake are notable examples where bridge and other structural damage resulted in human deaths and billions of dollars in damage (Johnson et al., 2008). The aforementioned events have motivated considerable efforts to study the seismic performance of bridges. However, the vast amount of research that has been performed has focused on testing of individual components due to a limitation in facilities that are capable of testing large-scale bridge systems (Johnson et al., 2006). Recently, testing of a large-scale bridge system conducted at the University of Nevada, Reno has significantly increased the amount of quality of data on the performance of bridge systems (Johnson et al., 2008, Kavianipour and Saiidi, 2013; Vosooghi and Buckle, 2013). A conventionally-built two-span bridge system has been tested on shake tables and has demonstrated to provide adequate seismic resilience (Johnson et al., 2008). Research performed through the George E. Brown, Jr. Network for Earthquake Engineering and Simulation (NEES) has resulted in the development of a new precast, two-span bridge bent system that features unbonded pre-tensioned strands in the columns and rocking connection at the ends of the columns (Eberhard et al., 2014). These features ultimately result in a reduction in construction time, a minimization in post-earthquake residual displacements, and a reduction in damage induced by an earthquake (Eberhard et al., 2014). The project, funded though the NEES program and entitled Seismic Resilience of Pre- Tensioned Bridge Bents, tested the new bridge system at the NEES facility at University of Nevada, Reno. The system was tested on shake tables in July 2014 and the data was postprocessed and was compared with the data obtained from a previous shake table test conducted on a three-bent, two-span bridge system that was built using conventional details (Johnson et al., 2006; Johnson et al., 2008). Also, a comparison was made within the new bridge system in order to evaluate how the bridge system responds to a previous equal ground motion after it has been induced to higher ground motions (Mantawy, personal communication, July 2014). 2: Literature Review Previous tests conducted on a conventionally-built bridge system have determined that columns which are designed according to contemporary earthquake design codes perform well (Johnson et al., 2006). Similarly, previous tests conducted on pre-tensioned columns found that this design has reduced residual displacements (Schaefer, 2013). The accelerated bridge construction methods associated with the new system improve the speed of construction, seismic resilience and durability (Eberhard et al., 2014). These findings indicate that a new, rocking, pre-tensioned bridge system should provide superior seismic resilience compared to a conventionally built bridge. The new bridge system will be compared with a similar system that was built using conventional details. Shake table tests conducted on a conventionally-built two-span bridge system with three bents determined that collapse of bridges during earthquakes can be prevented on bridge bents with different column heights (Johnson et al., 2006; Johnson et al., 2008). The large scale study, conducted by Johnson et al (2006)., investigated the response of bridge system irregularities due - 1 -

5 to the differences in column heights. According to Johnson et al., (2006), the study consisted of subjecting a two-span bridge system with three bents to both low-amplitude and high-amplitude earthquake motions. The low amplitude tests consisted of coherent, incoherent, and biaxial motions and were applied so that the maximum estimated bent displacement remained below 50%. No damage was observed on either the columns or superstructure during low-amplitude tests. The high-amplitude tests consisted of coherent and transverse excitations and were applied with the target Peak Ground Acceleration (PGA) intensity increasing from g to 1.66 g. The shake table tests demonstrated that the columns provided adequate performance (Johnson et al., 2006). Some of the conclusions obtained by Johnson et al., (2006), were the following: 1) the bridge superstructure remained rigid throughout the testing, 2) even though the bent with the stiffest column failed when subjected to a 1.66 PGA motion, the remaining two bents withstood a 1.0 PGA motion, 3) for the equivalent rare design earthquakes, the columns were in accordance with the design code life-safety performance objectives for service and damage, and 4) no signs of shear distress were seen when the bridge was considered to have failed which was when the stiffest bent failed in flexure. Table 1 summarizes the damage progression during the high amplitude tests for the west column s top east side at bent 3. It must be noted that the stiffest bent was bent 3 and that failure for the column in bent 3 occurred during test 19 as shown in Table 1. Table 1. Damage progression for bent 3 when induced to high amplitude excitations (Johnson et al., 2006) A new aspect to be tested within the new bridge system is the use of pre-tensioned strands in the columns which are implemented so the columns will return to their original position after an earthquake (Eberhard et al., 2014). Previous research conducted on unbonded prestressed hollow concrete columns found that such designs provide excellent drift ratio capacity with limited permanent displacements (p.5) (Kavianipour, and Saiidi, 2013). Similarly, research on unbonded pre-tensioned columns has found that the re-centering performance of an unbonded pre-tensioned column is superior to that of an unbonded post-tensioned column (Schaefer, 2013). Another new aspect to be tested within the bridge system is the implementation of rocking connections at the ends of the columns to minimize damage to the system (Eberhard et al., 2014)

6 The rocking connection will be achieved by 1) confining the concrete at the interface by a steel jacket (or shoe ), 2) debonding the bars near the interface to avoid bar failure where the system is designed to deform, and 3) including discontinuous bars in the system which will confine deformations at the rocking interface (Eberhard et al., 2014). Previous tests on the new bridge system s subassemblies found that the cyclic performance for the new bridge system were larger than those of a similar conventionally reinforced concrete column connection and also demonstrated that the columns re-centered at larger drift ratios and induced less damage. An integral part of the new system is its reduction of construction time by precasting the beams and columns. Previous research has found that accelerated bridge construction methods such as segmental construction and the precasting of columns save significant time in construction (Kavianipour, and Saiidi, 2013). The new system features columns and beams that are cast offsite and assembled rapidly on site, which not only accelerates construction but improves worker safety and construction quality (Eberhard et al. 2014). Construction is further accelerated by using a wet socket connection between the column and spread footing. This connection features a pre-cast column that has a saw-tooth detail at the exterior of the column base. The purpose of this detail is to facilitate the transfer of forces into the surrounding concrete (Eberhard et al., 2014, p 2). The connection is achieved by placing the pre-cast column into the footing and pouring the concrete in place where no bars cross the interface between the precast column and cast-in-place footing (Eberhard et al., 2014, p 2). In this connection the longitudinal bars are not bent out and are developed by using mechanical anchors within the part of the column that is embedded in the footing (Eberhard et al., 2014, p 2). This design ultimately facilitates transportation, increases safety (no protruding bars), and improves performance (compared with bent-out bars) (Eberhard et al., 2014, p 2). Not only is construction time reduced by using precast members, but according to Kavianipour and Saiidi (2013), precast bents perform similar to cast-in-place bents in terms of capacity and displacement. Previous research conducted on a conventionally-built two-span bridge bent system as well as research on pre-tensioned columns and rapidly constructed bridges indicate that these systems perform well in resisting and mitigating seismic damage (Johnson et al., 2006; Johnson et al., 2008; Schaefer, 2013; Eberhard et al., 2014;). Shake table tests conducted on a conventionallybuilt two-span bridge have demonstrated adequate seismic resilience and unbonded pretensioned columns have been shown to provide superior re-centering and reduced residual displacements (Johnson et al., 2006; Johnson et al., 2008; Schaefer, 2013). Similarly, tests indicate that non-conventionally built bridges have similar seismic resilience compared to conventionally built bridges and also allow for a reduction in construction time (Eberhard et al., 2014). The aforementioned studies indicate that the new, rocking, pre-tensioned bridge system should provide adequate seismic resilience with an additional benefit of a reduction in construction time. 3: Methods 3.1 Bridge System Properties The pre-tensioned bridge test specimen was developed in collaboration between the University of Nevada, Reno and the University of Washington (Eberhard et al., 2014) and was modeled to a quarter scale based on a prototype highway bridge. It consisted of two spans, each measuring 30 ft and included three 2-column bents with varying column heights; bridge bent 1 was located at - 3 -

7 the east exterior of the system and included two 6 ft tall columns, bridge bent 2 was located where both spans met and included two 8 ft tall columns, and bridge bent 3 was located at the west exterior and included two 5 ft tall columns. The columns featured unbonded pre-tensioned strands and the columns were designed to have a similar strength to that of a typical reinforced concrete column (Eberhard et al., 2014, p 4). The columns had an octagonal geometry with a 20 in diameter and a cantilever length of 60 in (Eberhard et al., 2014). The column bases were attached to a spread footing which was rigidly fixed to the shake tables. Cap beams were used to connect the column to the superstructure and the connection featured post-tensioned reinforcement. The superstructure consisted of two spans which were composed of three precast beams. The beams featured post-tensioned reinforcement in both the transverse and longitudinal direction. (I Mantawy, personal communication, June/July 2014) 3.2 Construction of Bridge System The new bridge system incorporated accelerated bridge construction methods and was constructed in collaboration between the University of Nevada, Reno and the University of Washington. The column and cap beams were constructed at the University of Washington and were then shipped to the University of Nevada, Reno where the entire system was assembled. Similarly, the beams were pre-cast. The bridge system followed a similar construction process to that of a non-pre-tensioned bridge that was constructed in Washington State that crossed over Interstate-5 (Khalegi, et al., 2012). The construction process of the bridge in Washington State began by excavating the footing after which the first segment of the precast columns were set in place (the columns were placed in segments to simulate the construction of a larger bridge system). Next, the reinforcement was installed and the footing concrete was cast. Afterwards, the middle and top segments of the columns were installed along with the bracing. Once this was done the precast cap beams were installed. The next process was to grout the joints between the column segments and the column-to-cap-beam which was all done at once. After the grouting was completed the superstructure was placed. This was done by placing the precast girders along with the installation of the girder bracing. Afterwards, the slab reinforcement was installed followed by the casting of the slab. Khaleghi et al. (2012) found that the bridge was built successfully and the construction did not encounter any problems. The process is similar to the one demonstrated in Figure

8 Figure 1 Construction process (Khalegi et al. 2012) 3.3 Instrumentation To evaluate the performance of the bridge, strain gauges, accelerometers, displacement transducers, string potentiometers, and load cells were located throughout the system (I. Mantawy, personal communication, June 2014). The strain gauges were placed to identify when yielding of the column reinforcement occurred with a total of 236 strain gauges being used. Displacement transducers were installed on the columns to measure the curvature for each column. The curvature transducers were placed on the top and bottom of the columns which amounted to 12 transducers for each column. Load cells were also placed on the strands which connected the cap beam and column. The purpose of the load cells was to measure the force in the strands and a total of 23 load cells were used. The displacement of the superstructure was also measured and was done so in the horizontal, longitudinal and vertical direction. This was achieved by installing a total of 25 string potentiometers which were placed throughout the superstructure. Acceleration was also measured in the vertical, transverse, and longitudinal directions and was achieved by installing accelerometers. The accelerometers were placed on the superstructure and amounted to 15. (Thonstad 2014a) 3.4 Testing Protocol The specimen was tested at the NEES shake table facility at University of Nevada, Reno in July The testing protocol for the bridge system involved subjecting the bridge to low-amplitude and high-amplitude motions as well as white noise and square wave motions. The white noise motions consisted of small motions that were applied to determine the bridge system s natural frequency while the square wave motions, which followed the white noise motions, were applied to induce free vibration of the bridge. The low-amplitude tests consisted of coherent, incoherent, biaxial and sinusoidal motions, which were applied to maintain the bridge components in the elastic range while the high-amplitude motions consisted of coherent and sinusoidal motions and were applied to test the performance of the bridge components in the plastic range (T. Thonstad, personal communication, July 2014). The low-amplitude and high-amplitude motions were selected from a previous experiment conducted on a conventionally built bridge which were based on motions recorded from the 1994 North Ridge Earthquake and the 1995 Kobe Earthquake (Thonstad, 2014b). The selected motions from the Northridge Earthquake were based on the recorded motions at the ground stations in Century City Country Club North (CCN090) and Olive View Medical Center (SYL360) while the selected motions from the Kobe Earthquake were based on the recorded motions at Takatori Station (TAK). For each motion, the drift ratios for the new bridge system were obtained by modeling the motions on OpenSees. The drift ratios for the new bridge were then compared with the drift ratios from shake table tests conducted on a conventionally-built bridge system and, in the instances where the drift ratios for - 5 -

9 the new bridge system differed, the motions for the new bridge system were modified in order to obtain similar drift ratios (Thonstad 2014b). Table A1 in Appendix A shows the full motion schedule for both bridges. 4: REU Student Contribution The Research Experience for Undergraduate (REU) student contribution in the project included assistance in the construction of the system, assistance in the installation of the measuring instruments, and the post processing of data related to the transverse displacements, the strains for the longitudinal column reinforcement, the acceleration for the bridge bents, and the drift ratios for each bent. 4.1 Construction of System By the time of the REU student start date of June 2, 2014, all three bents were set in place and the bridge beams had already been cast as shown in Figures 2 and 3, respectively. The first process in the construction of the system included the installation of the transverse post-tension for the bridge beams which made up the superstructure. After this was completed, the superstructure was installed atop of the bents. The superstructure consisted of 2 spans made up of 3 precast beams and was installed by means of a crane. Although not involved in the operation of the crane or installment of the bridge beams, the REU student was present for the installation Figure 4 shows the installation of one span. Afterwards, hydrostone was mixed and poured between the bent caps and the bridge beams in order to obtain a rigid connection which is shown in Figure 5.. Figure 2 Bridge bents set in place Figure 3 Bridge beams - 6 -

10 Figure 4 Placement of bridge beams Figure 5 Pouring of hydrostone The next step was to place grout onto the foundation to distribute the forces on each foundation as shown in Figure 6. This was accomplished by mixing the grout and subsequently pouring the grout into each foundation. The next progression in the construction of the system was to install the longitudinal reinforcement in the bridge beams. This was first accomplished by cutting a total of 21 strands after which 7 of the strands were placed along the longitudinal direction of each beam and were then post-tensioned. The installation of the post-tensioned strands, which were unbonded, is shown in Figure 7. After the bridge deck beams were post-tensioned and had sufficient strength, concrete blocks were placed atop of the bridge deck to simulate the loads that the prototype bridge would incur. For each span, 4 masses of 20 kips each were placed on the superstructure. Once more, the REU student did not install the blocks but aided in installing reinforcement in the blocks which were connected to the superstructure. These masses along with their locations in the bridge are shown in Figure 8 Figure 6 Grout poured into foundation Figure 7 Installation of longitudinal posttensioned reinforcement for bridge superstructure - 7 -

11 Figure 8 Bridge loads Once the masses were placed atop the bridge superstructure, the beams were grouted to the cap beams to obtain a rigid connection. This was accomplished by mixing the grout and subsequently pouring the grout into the hollow section which served as the connection for the cap beams and column and also included the reinforcement. A photograph of the grouting process is shown in Figure 9 and a photograph of the hollow sections where the grout was placed is shown in Figure 10 Figure 9 Grouting of cap beam and column Figure 10 Location of grout 4.2 Installation of Instrumentation The REU student helped install strain gauges, curvature transducers, load cells, and string potentiometers. A total of 236 strain gauges were installed for all 6 columns. Each column included strain gauges which measured the damage progression for the top and bottom of the longitudinal bars, the pre-stressed strands and transverse spirals. Curvature transducers were also installed. As previously stated, the curvature transducers measured the curvature of each column. Each column had 6 curvature transducers located at the column ends. String potentiometers which measured the displacement of the structure in the transverse, longitudinal and vertical direction were installed throughout the bridge superstructure. A total of 25 string potentiometers were used; 5 measuring the transverse displacement, 4 measuring the longitudinal displacement, - 8 -

12 and 16 measuring the vertical displacement. The instruments of concern for the REU student contribution were the string potentiometers which measured the transverse displacements at each bent, the accelerometers which measured the transverse accelerations at each bent, and the strain gauges which measured the strain for the bottom portion of the longitudinal column reinforcement. The string potentiometers which were used for post processing were DT5, DT3, and DT1 which were located at bent 1, bent 2, and bent 3 respectively. Similarly, the accelerometers which were used for post-processing were AT5, AT3, and AT1 which were located at bent 1, bent 2, and bent 3 respectively. The strain gauges which were used for post processing were used for the bottom portion of the column longitudinal bars and their locations are summarized in Table 2 for each respective test while the instrumentation plan for bent 3 is shown schematically in Figure 11. Table 2. Strain Gauge instrument locations used for longitudinal column bars North Column South Column North Column South Column North Column South Column Test 1A Bent 1 Bent 2 Bent 3 1NBSL5-1 1NBSL6-1 2NBSL5-1 2NBSL4-1 3NBSL5-1 3NBSL6-1 1SBSL5-1 1SBSL6-1 2SBSL5-1 2SBSL7-1 3SBSL5-1 3SBSL6-1 Test 14 Bent 1 Bent 2 Bent 3 1NBSL5-1 1NBSL6-1 2NBSL5-1 2NBSL4-1 3NBSL5-1 3NBSL6-1 1SBSL5-1 1SBSL6-1 2SBSL5-1 2SBSL7-1 3SBSL5-1 3SBSL6-1 Test 19 Bent 1 Bent 2 Bent 3 1NBSL5-1 1NBSL6-1 2NBSL5-1 2NBSL4-1 3NBSL5-1 3NBSL6-1 1SBSL5-1 1SBSL6-2 2SBSL5-1 2SBSL4-2 3SBSL5-1 3SBSL

13 Figure 11 Bent 3 strain gauge instrumentation plan (Thonstad 2014a) 4.3 Post-Processing of Shake Table Results The shake table test results that were post processed were the unfiltered data for low-amplitude test 1A, and high amplitude tests, 14, 16, 19 and 20A. The data was not filtered due to time constraints and since the effects of the filter is not high for high-amplitude motions. For tests 1A, 14, and 19 the results that were post-processed were the transverse displacements at each bent, the strains in the bottom section for two longitudinal bars at each column, and the drift ratios at each bent. For tests 16 and 20A, the results that were post-processed were the transverse displacements and the recorded accelerations at each bent. Data was post-processed by correcting the unprocessed data in order to obtain the true results. Regarding the displacements, the unprocessed data was corrected by taking into account the lateral movement of the shake tables which was subtracted from the recorded displacements. After this was done, the displacements were plotted with respect to time and the peak and residual displacements were obtained. Next, the drift ratios were obtained by dividing the corrected displacements at each bent by its respective column height. Regarding the strains in the bottom portion of the column longitudinal reinforcement, the unprocessed data was corrected by subtracting the offset from the remaining recordings obtained from each respective strain gauge. Afterwards, the strains were plotted with respect to time for each column longitudinal bar. The final results that were postprocessed were the recorded accelerations at each bent. This was done by plotting the recorded acceleration with respect to time

14 4.4 Evaluation of Conventional Bridge Shake Table Results The results of a previous test conducted by Johnson et al. (2006) on a conventionally built bridge system were evaluated to compare them with the seismic resilience of the new bridge system. The conventionally-built bridge system had the same configuration as the new bridge system. As such, the transverse displacements and the strains for the longitudinal column reinforcement were evaluated at the same locations for tests 1A, 14, and 19. This was done by plotting the postprocessed data of the previous tests. By doing so the peak displacements and residual displacements were obtained in the transverse direction and the strain histories were obtained for the bottom portion of two longitudinal bars in each of the columns. 5: Results 5.1 Comparisons between New and Conventional Bridge In order to evaluate the seismic resilience of the new bridge, comparisons were made between the results obtained from the new bridge and the results obtained from the conventional bridge. The results that were compared were the observed damage, the peak transverse displacements, the residual transverse displacements, the longitudinal column reinforcement strains, and the drift ratios. The results were compared for tests 1A, 14, and Observed Behavior Comparison Similar to the conventional bridge, the shake table tests demonstrated that the new bridge system did not collapse. The tests also demonstrated that the entire superstructure remained rigid throughout testing and that the bents did not fail. This differs from the conventional bridge, where bent 3 was considered to have failed after test 19 (Johnson et al., 2006). Minor cracking began to be observed in the new bridge after test 9C as shown in Figure 12. However this cracking was expected since the column rocking feature cannot be achieved without this occurring. Therefore these cracks were not considered as damage. For the new bridge, the first significant cracks were observed at bents 1 and 3 during test 14C as shown in Figure 13. This differs from the conventional bridge where cracks began to appear in bent 1 during test 13 (Johnson et al., 2006). Afterwards, more cracks began to appear but column reinforcement was not exposed for any subsequent test. This differs from the conventional bridge where column lateral reinforcement at bents 1 and 3 became exposed during test 17 (Johnson et al., 2006). Figures 14 and 15 show bent 3 damage during test 19 for the new bridge and the conventional bridge, respectively. By viewing both figures it can be noted that the column reinforcement became exposed in the conventional bridge and that it induced higher damage

15 Figure 12 Bent 1 south column damage test Figure 13 Bent 1 south column damage test 14c, 9c, new bridge new bridge Figure 14 Bent 3 north column damage test 19, Figure 15 Bent 3 west column damage test 19, new bridge conventional bridge (Johnson et al., 2006) Peak Transverse Displacement Comparison The peak transverse displacements for both bridge systems are summarized in Table 3. Table 3 demonstrates that for low-amplitude test 1A, the new bridge system had a lower peak displacement at all three bents. Regarding high-amplitude test 14, Table 3 demonstrates that the new bridge had larger displacements at bents 1 and 2. Finally, for high-amplitude test 19, Table 3 shows that the new bridge system demonstrated a larger peak displacement at all three bents. These larger displacements during the high-amplitude tests in the new bridge are due the rocking connections. The transverse displacements history at bent 3 for both systems during highamplitude Test 19 is shown in Figure

16 Displacement (in) Table 3. Peak displacements for new bridge and conventional bridge Peak Displacement (in) New Bridge Conventional Bridge Test 1A (0.08 PGA) Peak Displacement (in) Bent Bent Bent Test 14 (0.25 PGA) Peak Displacement (in) Bent Bent Bent Test 19 (1.66PGA) Peak Displacement (in) Bent Bent Bent Time (s) New Bridge Conventional Bridge Figure 16 Bent 3 transverse displacements, test Residual Transverse Displacement Comparison The residual displacements at bents, 1, 2 and 3 were compared for tests 1A, 14 and 19. The residual displacements at all three bents are shown in Table 4. By viewing Table 4 it can been seen that for low-amplitude test 1A, the new bridge provided reduced residual displacements at bents 1 and 2. Similarly, review of Table 4 demonstrates that for high-amplitude test 14, the new bridge once again provided reduced residual displacements at bents 1 and 3. Regarding highamplitude test 19, Table 4 demonstrates that the new bridge provided reduced residual displacements at bents 1 and 2. The lower amount of residual displacements in the new bridge is due to the unbonded pre-tensioned strands in the columns which have better re-centering capabilities

17 Table 4. Residual displacements for new bridge and conventional bridge Residual Displacements New Bridge Conventional Bridge Test 1A Residual Displacement (in) Bent Bent Bent Test 14 Residual Displacement (in) Bent Bent Bent Test 19 Residual Displacement (in) Bent Bent Bent Column Longitudinal Reinforcement Strain Comparison The column longitudinal reinforcement strains were compared by plotting the strain histories for the longitudinal bars that were located in equivalent positions at both bridge systems. By doing so, the maximum and minimum strains were obtained for both bridge systems. For lowamplitude test 1A, it was shown that the conventional bridge had larger maximum and minimum strains. The only exceptions to this were two strain gauges in the new bridge which were strain gauge 1NBSL5-1 and strain gauge 2NBLS4-1. Strain gauge 1NBSL5-1 had a larger minimum strain while strain gauge 2NBLS4-1 had a larger maximum strain. Regarding high-amplitude test 14, it was shown that the new bridge had larger minimum strains while the conventional bridge had larger maximum strains. Again there were two exceptions to the aforementioned findings which were two strain gauges in the new bridge. These were strain gauge 1SBSL6-1 and strain gauge 3NBSL6-1 which both had lower minimum strains. Test 19 followed a similar pattern compared to test 14 which showed that the new bridge generally had larger minimum strains while the conventional bridge had larger maximum strains. However there were a greater amount of exceptions to this which were six strain gauges in the new bridge. These were strain gauges 1NBSL6-1, 1SBSL5-1, 1SBSL6-2, 3NBSL5-1 and 3SBSL5-1 which all had lower minimum strains and strain gauge 2SBSL4-2 which had a larger maximum strain. Table 5 summarizes the maximum and minimum strains during test 14. The comparisons for the strain gauges during tests 1A and 19 are shown in Appendix Tables A2 and A3, respectively

18 Table 5. Maximum and minimum strain comparisons, test 14 Strain Gauge Comparison Test 14 New Bridge Conventional Bridge Bent 1 Strain Gauge 1NBSL5-1 Strain Gauge 1WBSL Strain Gauge 1NBSL6-1 Strain Gauge 1WBSL Strain Gauge 1SBSL5-1 Strain Gauge 1EBSL Strain Gauge 1SBSL6-1 Strain Gauge 1EBSL Bent 2 Strain Gauge 2NBSL5-1 Strain Gauge 2WBSL Strain Gauge 2NBSL4-1 Strain Gauge 2WBSL Strain Gauge 2SBSL5-1 Strain Gauge 2EBSL Strain Gauge 2SBSL4-1 Strain Gauge 2EBSL Bent 3 Strain Gauge 3NBSL5-1 Strain Gauge 3WBSL Strain Gauge 3NBSL6-1 Strain Gauge 3WBSL Strain Gauge 3SBSL5-1 Strain Gauge 3EBSL Strain Gauge 3SBSL6-1 Strain Gauge 3EBSL Transverse Drift Ratio Comparison By comparing the transverse drift ratios for tests 1A, 14, and 19 it was shown that during lowamplitude test 1A, the peak drift ratios at all three bents were smaller for the new bridge. By comparing the drift ratios for high-amplitude test 14, it was shown that the peak drift ratio for the new bridge was larger at bents 1 and 2 but was smaller at bent 3. Finally by comparing the peak drift ratios for high amplitude test 19, the new bridge had larger peak drift ratios at all three

19 bents. With regards to test 19, the peak drift ratios for the new bridge during test 19 were 46% larger for bent 1, 60% larger for bent 2, and 60% larger for bent 3. The larger drift ratios in the new bridge are due to the rocking connections. The drift ratio comparisons at bent 3 for tests 1A, 14, and 19 are displayed in Figures 17, 18, and 19, respectively. Table 6 summarizes the peak drift ratios for both bridges during all three tests New Bridge Conventional Bridge Figure 17 Bent 3 drift ratios, test 1a New Bridge Conventional Bridge Figure 18 Bent 3 drift ratios test

20 New Bridge Conventional Bridge Figure 19 Bent 3 drift ratios, test 19 Table 6. Maximum transverse drift ratio comparisons Maximum Drift Ratios (%) New Bridge Conventional Bridge Test 1A Bent Bent Bent Test 14 Bent Bent Bent Test 19 Bent Bent Bent : Comparisons within New Bridge In order to evaluate how the new bridge system responds to a previous equal ground motion after it has been induced to higher ground motions, a comparison was made between motions 16 and 20A. Both motions were high-amplitude motions which were based on recordings obtained from ground station CCN090 and consisted of a PGA of 0.75g. These motions were separated by motions 17, 18 and 19 which all had higher PGA s; motion 17 had a PGA of 1.00g, motion 18 had a PGA of 1.33g, and motion 19 had a PGA of 1.66g. The transverse displacements and transverse accelerations were compared at each bent Transverse Acceleration Comparisons The transverse bridge accelerations were compared for bents 1, 2 and 3 during tests 16 and 20A. The comparisons demonstrated that the recorded bridge accelerations for test 20A were lower at

21 Acceleration (g) Acceleration (g) all three bents than they were for test 16. The acceleration comparisons for bents 1, 2 and 3 are shown in Figures 20, 21 and 22, respectively Time (s) Test 16 Test 20A Figure 20 Bent 1 accelerations Time (s) Test 16 Test 20A Figure 21 Bent 2 accelerations

22 Acceleration (g) Time (s) Test 16 Test 20A Figure 22 Bent 3 accelerations Transverse Displacement Comparisons By comparing the transverse displacements between tests 16 and 20A, it was demonstrated that the peak displacements were larger during test 20A at all three bents. The peak displacement was 45% larger at bent 1, 62% larger at bent 2, and 67% larger at bent 3. The increase in peak displacements was due to bar fractures in the columns during high-amplitude tests These bar fractures changed the dynamic properties of the bridge which allowed for more displacement due to a shift in the bridge period. This shift in the bridge period is also related to the decrease in bridge transverse accelerations seen during test 20A. Table 7 summarizes the peak transverse displacements for all bents and Figure 23 shows the displacement comparisons for bent 3. Table 7. Transverse peak displacements for test 16 and test 20A Transverse Peak Displacements (in) Test 16 Test 20A Bent Bent Bent

23 Displacement (in) Time (s) Test 16 Test 20A Figure 23 Bent 3 displacements 6: Discussions, Conclusions and Future Work To fully assess the new bridge system s seismic resilience, a further and more in depth assessment is currently being conducted. However, the results obtained in this project provide some preliminary conclusions on the new bridge system s seismic resilience. These are as follows: 1) The advanced bridge construction methods associated with the new bridge system were successful in preventing collapse of the system. The superstructure remained rigid throughout testing and the bents did not fail. 2) Compared to the conventional bridge, the new bridge induced less observed damage with no exposure of column reinforcement occurring during any test which was due to the rocking connection 3) Compared to the conventional bridge, the peak transverse displacements for the new bridge system were higher when induced to a high-amplitude ground motions. These larger displacements are due to the rocking connections. 4) The new bridge system demonstrated lower residual displacements during tests 1A, 14 and 19. These reduced residual displacements are due to the unbonded pre-tensioned strands in the columns. 5) For low-amplitude tests, the maximum and minimum strains were generally larger for the conventional bridge. 6) For high-amplitude tests, the maximum strains were generally larger for the conventional bridge while the minimum strains were generally larger for the new bridge. 7) Compared to a conventional bridge, the drift ratios for the new bridge system are smaller at low amplitudes but larger at high amplitudes. This is due to the rocking connections 8) By comparing equal ground motions for the new bridge system which were separated by motions with higher PGA s, it was demonstrated that the accelerations decrease whereas the transverse displacements increase. This was due to the fact that several reinforcement column bars failed during the motions with higher PGA s. This resulted in a change in

24 the dynamic properties of the bridge which allowed for a greater displacement due to a change in the bridge period. Although the aforementioned findings are preliminary, they indicate that the new bridge system s seismic resilience is superior to that of a conventional bridge. Further work is currently being conducted within NEES to fully assess the new bridge system s seismic resilience. 7. Contact Information For further information regarding the project please contact principal investigator Dr. David Sanders (sanders@unr.edu) and graduate student Islam Mantawy (imantawy@unr.edu). For information regarding this paper, please contact REU student Eric Ramirez (edramirez110@gmail.com). 8. Acknowledgements I would like to thank the George E. Brown Network for Earthquake Engineering and Simulation for providing me with this opportunity. I would like to thank Dr. David Sanders for his guidance, graduate student Islam Mantawy for his mentorship, NEES REU coordinators Dr. Thalia Anagnos, Alicia Lyman-Holt, and Rebecca Kloster for their continuous direction and constructive criticism. Thanks also goes to NEES Site Coordinator, Kelly Doyle for arranging all site logistics. I would also like to thank Chad Lyttle and the entire lab staff at UNR s Earthquake Engineering Laboratory for helping me and letting me be involved in the experimental set-up. Additional thanks goes to my virtual peer team members for providing valuable criticism through our online collaboration and to the other two REU students at UNR, Erin Segal and Shirley Tang, for their friendship throughout the summer. The project was funded through the National Science Foundation NEES research program (award # ), NEES REU program (EEC ) and the NEES Operations Cooperative Agreement (CMMI ). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundations. 9: References Eberhard, M., Stanton, J., Sanders, D., Schaefer, J., Kennedy, B., Thonstad, T., Harldsson, O. and Mantawy, I., (2014) Shaking Table Tests on a New Bridge System Designed to Re-Center. Proc. of 10 th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering, Anchorage, AK., July Johnson, N., Ranf R., Saiidi, M., Sanders, D., Eberhard, M, (2008) Seismic Testing of a Two- Span Reinforced Concrete Bridge, Journal of Bridge Engineering, ASCE March/April 2008, pp Johnson, N., Saiidi, M., and Sanders D., (2006) Large-Scale Experimental and Analytical Studies of a Two-Span Reinforced Concrete Bridge System, Center for Civil Engineering Earthquake Research, Department of Civil Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-06-02, March

25 Kavianipour, F. and Saiidi, M.S., (2013) Experimental and Analytical Seismic Studies of a Four- Span Bridge System with Composite Piers, Center for Civil Engineering Earthquake Research, Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-13-17, September 2013 Khaleghi, B., Schultz, E., Seguirant, S., Marsh, L., Haraldsson, O., Eberhard, M., and Stanton., J. (2012). Accelerated Bridge Construction in Washington State PCI Journal, Fall 2012, pp Schaefer, J. (2013) Unbonded Pre-tensioned Bridge Columns with Rocking Detail. M.S. thesis, University of Washington, Seattle WA Thonstad, T (2014) Instrumentation Plan. Seismic Resilience of Pre-Tensioned Bridge Bents, NEES Project Warehouse # Thonstad, T (2014) Phase III Preliminary Results Summary. Seismic Resilience of Pre- Tensioned Bridge Bents NEES Project Warehouse # Vosooghi, A. and Buckle, I.G., (2013) Evaluation of the Performance of a Conventional Four- Span Bridge During Shake Table Tests Center for Civil Engineering Earthquake Research Department of Civil and Environmental Engineering, University of Nevada, Reno, Nevada, Report No. CCEER-13-02, January

26 Appendix Test Data Table A1. Full ground motion schedule and comparisons Test Ranf/Johnson (RC) New Bridge Significance Motion PGA Motion PGA WN001A SQ001A WN001B SQ00IB NS White Noise NS Square Wave EW White Noise EW Square Wave 1 Low Level CCN CCN A Coherent Motion CCN CCN CCN /0.08/0.07 2A Incoherent CCN /0.15/ Motion CCN /0.08/0.03 3A CCN /0.15/0.07 WN0304A SQ0304A WN0304B SQ0304A NS White Noise NS Square Wave EW White Noise EW Square Wave 4 CCN /0.18/0.18 CCN /0.18/ Incoherent CCN /0.07/0.18 CCN /0.07/ Motion CCN /0.18/0.07 CCN /0.18/ CCN NS White Noise NS Square Wave EW White Noise EW Square Wave WN0709A SQ0709B WN0709B SQ0709B 9A Biaxial CCN090/CCN CCN090/CCN Motion 9B CCN090/CCN CCN090/CCN Centrifuge CCN /0.06/ Motion CCN /0.05/0.09 WN1112A SQ1112A WN1112B SQ1112B 12 High Level CCN090 NS White Noise NS Square Wave EW White Noise EW Square Wave 0.08 CCN Coherent CCN CCN Motion CCN CCN S1 T0.25sec 0.05 Sinusodial S2 T0.25sec 0.10 Motion S3 T0.25sec C Biaxial Motion CCN090/CCN S4 Sinusodial T0.3sec 0.15 S5 Motion T0.3sec 0.10 WN1415A SQ1415A NS White Noise NS Square Wave

27 14B1 High Level SYL B2 Coherent Motion SYL C (HLCM) TAK WN1415B SQ1415B 15 High Level CCN090 NS White Noise NS Square Wave 0.50 CCN Coherent CCN CCN Motion CCN CCN WN1718 SQ HLCM CCN090 NS White Noise NS Square Wave 1.33 CCN WN1819 SQ HLCM CCN090 NS White Noise NS Square Wave 1.66 CCN WN1920 SQ A HLCM CCN090 NS White Noise NS Square Wave 1.00 CCN B HLCM SYL WN2021 SQ A HLCM CCN090 NS White Noise NS Square Wave 1.00 TAK B HLCM TAK C HLCM TAK WN022 SQ022 NS White Noise NS Square Wave

28 Table A2. Maximum and minimum strain gauge comparisons, test 1a Strain Gauge Comparison Test 1A New Bridge Conventional Bridge Bent 1 Strain Gauge 1NBSL5-1 Strain Gauge 1WBSL Strain Gauge 1NBSL6-1 Strain Gauge 1WBSL Strain Gauge 1SBSL5-1 Strain Gauge 1EBSL Strain Gauge 1SBSL6-1 Strain Gauge 1EBSL Bent 2 Strain Gauge 2NBSL5-1 Strain Gauge 2WBSL Strain Gauge 2NBSL4-1 Strain Gauge 2WBSL Strain Gauge 2SBSL5-1 Strain Gauge 2EBSL Strain Gauge 2SBSL7-1 Strain Gauge 2EBSL Bent 3 Strain Gauge 3NBSL5-1 Strain Gauge 3WBSL Strain Gauge 3NBSL6-1 Strain Gauge 3WBSL Strain Gauge 3SBSL5-1 Strain Gauge 3EBSL Strain Gauge 3SBSL6-1 Strain Gauge 3EBSL

29 Table A3. Maximum and minimum strain gauge comparisons, test 19 Strain Gauge Comparison Test 19 New Bridge Conventional Bridge Bent 1 Strain Gauge 1NBSL5-1 Strain Gauge 1WBSL Strain Gauge 1NBSL6-1 Strain Gauge 1WBSL Strain Gauge 1SBSL5-1 Strain Gauge 1EBSL Strain Gauge 1SBSL6-2 Strain Gauge 1EBSL Bent 2 Strain Gauge 2NBSL5-1 Strain Gauge 2WBSL Strain Gauge 2NBSL4-1 Strain Gauge 2WBSL Strain Gauge 2SBSL5-1 Strain Gauge 2EBSL Strain Gauge 2SBSL4-2 Strain Gauge 2EBSL Bent 3 Strain Gauge 3NBSL5-1 Strain Gauge 3WBSL Strain Gauge 3NBSL6-1 Strain Gauge 3WBSL Strain Gauge 3SBSL5-1 Strain Gauge 3EBSL Strain Gauge 3SBSL6-2 Strain Gauge 3EBSL