Zachary B. Haber

Seismic Performance of Precast Columns with Mechanically Spliced Column-Footing Connections

This paper presents the results from a large-scale experimental study that was conducted at the University of Nevada in Reno, NV. Five half-scale bridge column models were constructed and tested under reversed slow cyclic loading. The study focused on developing four new moment connections at column-footing joints for accelerated bridge construction in regions of high seismicity. The new connections were employed in precast columns, each using mechanical splices to create connectivity with reinforcing bars in a cast-in-place footing. Two different mechanical splices were studied: an upset headed coupler and a grout-filled sleeve coupler. Along with the splice type, the location of couplers within the plastic hinge zone was also a test variable. All precast models were designed with the intent to emulate conventional cast-in-place construction and, thus, were compared with a conventional cast-in-place test model. Results indicate the behavior of these new connections was similar to that of conventional cast-in-place construction with respect to key response parameters, although the plastic hinge mechanism could be significantly affected by the couplers.

Behavior and simplified modeling of mechanical reinforcing bar splices

Bridge seismic design codes do not allow mechanical reinforcing bar splices in regions expected to undergo significant inelastic deformations during earthquakes, thus severely limiting precast and innovative bridge column construction that uses such splices. The uniaxial behavior of two commercially available mechanical splices under different loading conditions was investigated experimentally in this study with emphasis on deformation response. Tests were performed with static, dynamic, and cyclic loading. The performance of the splices was satisfactory under all loading conditions in that bar fracture occurred outside the splice. Furthermore, the results revealed the effect of the relatively high stiffness of mechanical couplers. The responses of individual splices were used to interpret data from a series of cyclic tests on half-scale bridge columns employing mechanical splices in plastic hinge zones. Lastly, a simple method was proposed and validated for modeling these devices in reinforced concrete members.

Cyclic Behavior of Precast High-Strength Reinforced Concrete Columns

Double-curvature cyclic tests of large-scale columns were conducted to investigate the seismic performance of precast highstrength reinforced concrete columns. High-strength concrete and high-strength longitudinal and transverse reinforcement were used. The use of grouted coupler splices for the high-strength longitudinal reinforcement in the plastic hinge zone and the use of butt-welded splices for the high-strength transverse reinforcement were examined. Test results showed that precast columns with the grouted coupler splices exhibited comparable seismic performance with monolithic counterparts. The butt-welded splice had a negligible effect on the tensile behavior of the spliced bars. However, precast columns with such welded splices in transverse reinforcement showed smaller ultimate drift capacities than their counterparts with hooked transverse reinforcement. This was due to the reduced resistance of butt-welded transverse reinforcement to buckling of longitudinal reinforcement..

Secondary Anchorage in Post-Tensioned Bridge Systems

Post-tensioning (PT) tendons in segmental bridges are often anchored within the deviator and pier segments. The effectiveness of the PT system is therefore dependent on proper anchorage function. However, anchorage failure may occur due to corrosion of the strand at the anchor head and subsequently cause the PT force to transfer within the pier segment or slacking of the tendon to occur. Following tendon stressing, the anchorage assembly and ducts that house the tendon are filled with grout. These short bonded regions could, in the event of anchorage failure, provide secondary anchorage. This paper presents the results of a full-scale experimental investigation on bonded anchorage tendon pullout. The study focuses on the embedment length required to develop the in-service PT force within the pier segment. Seven, twelve, and nineteen 15 mm (0.6 in.) diameter low-relaxation strand tendons with various bonded lengths were considered.

External Anchorage Failure and Tendon Pull-out Tests on Bridge Piers

Post-tensioning tendons in segmental bridge construction are often only anchored within the deviator and pier segments. The effectiveness of the posttensioning (PT) system is therefore dependent on proper functioning of the anchorages. On August 28, 2000 a routine inspection of the Mid-Bay Bridge (Okaloosa County, Florida) revealed corrosion in numerous PT tendons. Moreover, one of the 19-strand tendons was completely slacked, with later inspection revealing a corrosion-induced failure at the pier anchor location. Anchorage failure caused all PT force to transfer to the steel duct located within the pier segment that in turn slipped and caused the tendon to go completely slack. After the application of PT force, the anchorage assembly and steel pipes that house the tendon are filled with grout. These short grouted regions could, in the event of anchorage failure, provide a secondary anchorage mechanism preventing the scenario mentioned above from occurring. This paper presents the results of a full-scale experimental investigation on anchorage tendon pull-out. The study focuses on the length required to develop the in-service PT force within the pier segment grouted steel tube assembly. Seven, twelve, and nineteen 0.6” diameter strand tendons with various development lengths were considered. Recommendations for pier section pipe detailing and design will be discussed.

GFRP Bridge Deck Systems for Skewed Bridges: An Analytical Investigation on Deck Orientation

Glass fiber reinforced polymer (GFRP) bridge deck systems have been used increasingly for rehabilitation efforts and new construction, particularly for bridge applications requiring high strength, low self-weight, or good fatigue and environmental resistance. GFRP decks are typically constructed by joining pultruded plates and shapes with mechanical fasteners or structural adhesives. This yields a deck system that has one dominant strong direction for flexure. When such a system is installed, the deck panels are placed such that the strong direction is perpendicular to the supporting girders. On skewed bridges this orientation is neither practical nor efficient in terms of construction time. However, orienting the panels at the angle of skew effects behavior of the deck panel in terms of stiffness and how load is distributed to the girders. In this study, the finite element method is used to evaluate the correlation between low profile GFRP deck panel orientation angle and response. Thick shell elements with equivalent elastic stiffness coefficients were calibrated based on previous experimental studies in the principal fiber directions. Five skew angles are considered in the analysis while monitoring the transverse load distribution between girders, mid-span deflections, and principal strains. Practical issues related to the skewed installation will be discussed.