Design and Construction of Precast Bent Caps with Pocket Connections for High Seismic Regions

Report No. CCEER-15-06In conventional cast-in-place reinforced concrete bridge construction, cap beams and their connection to columns are designed to be capacity protected under strong earthquakes. This is because cap beams and their connections maintain structural integrity and are difficult to repair. The same design philosophy is mandatory for precast cap beams that are used in accelerated bridge construction (ABC), particularly in moderate and high seismic zones. One of the key components of ABC is prefabricated reinforced concrete members. The NCHRP report 698 provided a synthesis of different promising ABC connections. Pocket connections were identified as practical means of joining prefabricated columns and pier caps. The AASHTO Scan 11-02 revealed more recent studies about seismic performance of pocket connections. Nevertheless, research was needed to develop practical and reliable cap beam pocket connections ensuring capacity protected behavior. A comprehensive literature search was carried out in the present study to compile and interpret data on seismic performance of cap beams with pocket connections. It was shown through extensive analyses that effects of pocket on the seismic performance of cap beams are negligible for a well-designed cap even under the worst-case scenario in which the concrete within the pocket was excluded from the cap beam section. The reason why precast cap beams with pocket connections yielded in some of the test models was identified as inadequate design rather than the pocket effect. Five practical details for precast pocket bent caps were proposed based on the lessons learned from the aforementioned tasks. Subsequently, constructability of these details was assessed. It was found that the alternative in which fully precast columns are inserted into cap pockets will result in 75% reduction in onsite work. The time saving for other details was 42%. Finally, a design guideline as well as examples were developed to facilitate field deployment of precast bent caps incorporating pocket connections

Design and Construction of Bridge Columns Incorporating Mechanical Bar Splices in Plastic Hinge Zones

Report No. CCEER-15-07Accelerated bridge construction (ABC) relies heavily on prefabricated reinforced concrete members. One method to connect prefabricated columns to footings or cap beams is through the use of mechanical bar splices commonly referred to as couplers. Even though current seismic codes prohibit application of couplers in the plastic hinge area of columns located in moderate and high seismic zones, recent studies have revealed the feasibility of precast columns utilizing couplers in the plastic hinge zones helping expand ABC in this zones. Several types of mechanical bar splices each with a unique performance and anchoring mechanism are available in the U.S. market. Five of these were included in this study: shear screw, headed bar, grouted, threaded, and swaged couplers. A state-of-the-art literature search was conducted to compile and interpret data on the seismic performance of these coupler types as well as columns incorporating these couplers in the plastic hinge zones. Findings were summarized and tabulated. Subsequently, coupler acceptance criteria for seismic applications and acceptance criteria for ductile columns incorporating couplers is plastic hinges were developed. Then the seismic performance of the couplers and the columns was evaluated. It was found that the coupler performance varies for different loading rates and even for the same type of coupler produced by different manufactures. Furthermore, location of the coupler in columns was critical for large size couplers. Special detailing was studied by different researchers to achieve large displacement capacities. Satisfactory performance was usually observed for small size couplers in which their location had insignificant effect on the column seismic behavior. Findings from the literature study as well as the coupler evaluation indicated that a rigorous testing schedule is needed to completely understand the seismic performance of each coupler type and series. Constructability and speed of construction for each coupler type were also studied. It was found that the application of mechanical bar couplers at both ends of precast columns will shorten the construction time by approximately 60% for a three-column bent regardless of the type of the coupler. Since conclusive trends could not be established with limited test data, an extensive parametric study was carried out to investigate coupler effects on the column seismic behavior. A generic stress-strain model was also developed to represent behavior of all types of couplers. It was found that the coupler length, the coupler location, and the rigidity of the coupler significantly affect the displacement ductility capacity of mechanically spliced columns. Furthermore, a simple design equation was developed in which the spliced column displacement ductility capacity can be estimated based on the basic characteristic and geometry of the coupler and the column. Finally, a design guideline as well as examples were developed to facilitate field deployment of precast columns incorporating mechanical bar splices

Next Generation of Bridge Columns for Accelerated Bridge Construction in High Seismic Zones

Report No. CCEER-14-06Accelerated bridge construction (ABC) utilizes advanced planning, new construction techniques, and innovative detailing to facilitate construction. ABC offers many advantages over conventional construction, the most important of which is the reduction of onsite construction time. Even though ABC has been widely used in low seismic regions of the country mostly in superstructure, application of ABC in seismic areas has been limited due to the lack of seismic performance data regarding substructure connections. The main objective of this study was to develop new ABC connections for bridge columns using novel detailing and advanced materials. Three low-damage materials were incorporated: ultra-high performance concrete (UHPC), Nickel-Titanium shape memory alloy (NiTi SMA), and engineered cementitious composite (ECC). Furthermore, two types of mechanical bar splices, grouted coupler and headed bar coupler, were utilized. UHPC-filled duct connections were developed and evaluated through 14 pullout tests. A new detailing was proposed for grouted coupler column end connections to enhance the drift capacity. Three half-scale precast column models were tested under slow reversed cyclic loading, each with a new precast element connection or low-damage plastic hinge. A material model was developed for reinforcing superelastic NiTi SMA bars. Furthermore, new simple methods were developed to account for bond-slip effects and bar debonding effects in analytical models of reinforced concrete members. It was found that bar bond strength in UHPC is eight times higher than that in conventional concrete. UHPC-filled duct connections exhibited no damage even under 12% drift ratio cycles. The displacement capacity and displacement ductility capacity for the grouted coupler column were respectively increased by 47 and 56% compared to grouted coupler column models investigated previously. Longitudinal bar debonding allowed spread of yielding and prevented premature failure of reinforcements in UHPC-filled duct connections and grouted coupler column pedestal. The SMA-reinforced ECC column showed superior seismic performance compared to a conventional column in which the plastic hinge damage was limited to only ECC cover spalling even under 12% drift ratio cycles. The column residual displacements were 79% lower than CIP residual displacements on average due to the superelastic NiTi SMA longitudinal reinforcement, and higher base shear capacity and higher displacement capacity were observed. The analytical modeling methods were simple and sufficiently accurate for general design and analyses of precast components proposed in the present study. The proposed symmetrical material model for reinforcing NiTi superelastic SMA was found to be a viable alternative to the more complex asymmetrical model. Extensive experimental and analytical investigations performed in the present study led to a new generation of ABC bridge columns in which columns can be built in relatively short time but the seismic performance of these columns is equal or better than columns that are built cast-in-place with conventional materials

Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers

One of the important measures of post-earthquake functionality of bridges after a major earthquake is residual displacement. In many recent major earthquakes, large residual displacements resulted in demolition of bridge piers due to the loss of functionality. Replacing the conventional longitudinal steel reinforcement in the plastic hinge regions of bridge piers with super-elastic shape memory alloy (SMA) could significantly reduce residual deformations. In this study, numerical investigations on the performance of SMA-reinforced concrete (RC) bridge bents to monotonic and seismic loadings are presented. Incremental dynamic analyses are conducted to compare the response of SMA RC bents with steel RC bents considering the peak and the residual deformations after seismic events. Numerical study on multiple prototype bridge bents with single and multiple piers reinforced with super-elastic SMA or conventional steel bars in plastic hinge regions is conducted. Effects of replacement of the steel rebar by SMA rebar on the performance of the bridge bents are studied. This paper presents results of the parametrical analyses on the effects of various design and geometric parameters, such as the number and geometry of piers and reinforcement ratio of the RC SMA bridge bents on its performance