Shear Strength Capacity of Prestressed Concrete Beam Column Joint Focusing On Tendon Anchorage Location

Fumio Watanabe

Professor, Dept. of Architecture Engineering, Kyoto University, Japan

Minehiro Nishiyama

Associate Professor, Dept. of Urban and Environment Engineering, Kyoto University, Japan

Wei Yue

PhD candidate, Dept. of Architecture Engineering, Kyoto University, Japan

This paper is part of the 13^th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, August 1-6, 2004.

In order to estimate shear strength capacity and overall seismic behavior of prestressed beam-column joint assemblages, seven test units were constructed and tested under earthquake-simulating cyclic loads. The main experimental parameters were location of tendon anchorage, concrete compressive strength and prestressing steel content in the beam section. A reinforced concrete beam-column joint assemblage whose beam section has as large a moment capacity as the prestressed concrete test units was included in the test program. The test units failed in shear and tendon anchorage deteriorated in the joint core. Load carrying capacity, ultimate displacement, hysteretic energy, joint shear distortion were obtained and discussed. The joint shear strength of the test units were compared with those obtained by code specifications, such as the AIJ guidelines and New Zealand concrete design code NZS3101. It should be noted that location of tendon anchorage had a great influence on shear capacity of the joint and load displacement relation of the assemblages. The prestress on the joints was not so effective as the NZS3101 code specifies.

New Zealand concrete design code, NZS3101: 1995 is innovative with respect to prestressed concrete because it specifies the effect of prestress on shear strength capacity of beam-column joints, and it includes other provisions which are not seen in current design codes in other countries. Especially it specifies that tendon anchorages should be placed outside the joint core. Architects generally want to have tendon anchorage inside the joint core, and structural engineers may have misgivings. However, it is not the provision that was proved by experimental results. In addition, the beneficial effect of prestress on shear strength of beam-column joint cores is still controversial.

Yue et al. and Suzuki et al. investigated the effect of location of prestressing tendon anchorage on beam-column joint behavior. The following conclusions are derived from their research works. The maximum load capacity of the specimens with inside anchorage was smaller than those with outside anchorage and the shear distortion was larger. The authors did not mention what kind of failure mode took place in their experimental programs, and joint shear strength was not quantitatively investigated. In this study failure modes as well as shear strength capacity and seismic performance of prestressed beam column joints are examined in detail based on experimental results.

References

Suzuki N. et al., “Experimental Study on Ultimate Strength of Exterior Beam-Column Joint in Prestressed Concrete Frame” proceeding of AIJ Annual Meeting 2003, pp.1009-1014 (in Japanese).

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Architectural Institute of Japan: Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings Based on Inelastic Displacement Concept, 1999.

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Yue W., Hamada Y. and Nishiyama M., “Influences of anchorage position of prestressing steel on joint strength of beam-column joint subassemblage”, proceeding of AIJ Annual Meeting 2001, pp.  927-930 (in Japanese).