The traditional connections and reinforcement details of precast RC frames are complex and cause difficulty in construction. Ultra-high-performance concrete (UHPC) exhibits outstanding compressive strength and bond strength with rebars and strands; thus, the usage of UHPC in the joint core area will reduce the amount of transverse reinforcement and shorten the anchoring length of beam rebars as well as strands significantly. Moreover, the lap splice connections of precast columns can be placed in the UHPC joint zone and the construction process will be simplified. This paper presented a novel joint consisting of a precast pretensioned prestressed concrete beam, an ordinary precast reinforced concrete (RC) column, and a UHPC joint zone. To study the seismic performance of the proposed joints, six novel interior joints and one monolithic RC joint were tested under low-cyclic loads. Variables such as the axial force, the compressive strength of UHPC, the stirrup ratio were considered in the tests. The test results indicate that the proposed joints exhibit comparable seismic performance of the monolithic RC joint. An anchorage length of 40 times the strands-diameter and a lap splice length of 16 times the rebar-diameter are adequate for prestressed strands and precast column rebars, respectively. A minimum column depth is suggested as 13 times the diameter of the beam-top continuous rebars passing through the joint. In addition, a nine-time rebar diameter is sufficient for the anchorage of beam bottom rebars. The shear strength of UHPC in the joint core area is suggested as 0.8 times the square root of the UHPC compressive strength.

Prestressed steel reinforced concrete (PSRC) beam members have the advantages of both ordinary prestressed concrete and SRC members and are usually applied to the structures with large span or heavy load. They are often designed to crack under service load. In this paper, the service-load behavior is studied based on the experimental results of four unbonded PSRC frame beam specimens. The cracking behavior, deflection, and strains in tensile reinforcement during service-load stage are described in detail. A computer program for a simple macroelement analysis approach, based on conventional matrix-displacement method, is written to predict the response of unbonded PSRC frame beam members under service load. The calculation results by this method agree well with the observed experimental results.Moreover, an approach based on two enacted Chinese codes, one for ordinary concrete members (GB50010-2010) and another for steel-concrete composite members (JGJ138-2001), is provided to calculate the short-term maximum crack width of PSRC beam members. By comparing with the test results, it implies that this approach can be applied to the evaluation of short-term maximum crack width. KEYWORDS design equations, macroelement analysis method, prestressed steel reinforced concrete, serviceload behavior, short-term maximum crack width, unbonded tendons | INTRODUCTIONRecent years, there is a significant growth in the number of high-rise buildings. The most usually used structural systems for high-rise buildings are diagrid, outrigger, and conventional tubular systems. [1][2][3][4] Compared with conventional tubular system, diagrid and outrigger systems are more advanced and effective. The diagonal elements in diagrid system can carry both vertical and lateral loads, which provide significant bending and shear rigidity. Additionally, the bending moment and story drift of outrigger system will be lower than tubular system. [5,6] As for the level of structural member, a high-rise building usually consists of steel, reinforced concrete (RC), and steel-concrete composite members. Within them, the steel RC (SRC) column or beam members are widely used. The behaviors of SRC members have been already extensively investigated. [7][8][9][10][11][12] Results show that SRC members possess high strength, good ductility, and high stiffness. However, for the transfer story of high-rise buildings with large span or heavy load, the calculated crack width under service load often exceeds the design limit. Therefore, the prestressed SRC (PSRC) structure has been put forward. The application of prestress tendons can effectively improve the serviceability of SRC beam members. [13] Besides the transfer story, PSRC beam members are also often used in structures, like bridge, stadium, and industrial factory.There have been already some experimental and analytical investigations on the PSRC members in the past years. Fu et al. tested seven PSRC simply supported beam specimens to study the flexural behavior and finally provided a method to calculate the fl...

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