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種別	Paper
主題	DEVELOPMENT LENGTH OF BRAIDED ARAMID TENDONS IN PRETENSIONED BEAMS FIBER
副題
筆頭著者	Toru UTSUNOMIYA（Mitsui Construction Co）
連名者1	Antonio. NANNI（The Pennsylvania State University）
連名者2	Hiroyuki YONEKURA（Mitsui Construction Co）
連名者3	Masaharu TANIGAKI（Mitsui Construction Co）
連名者4
連名者5
キーワード
巻	13
号	1
先頭ページ	969
末尾ページ	974
年度	1991
要旨	INTRODUCTION Development length of prestressing tendons is a fundamental design parameter in pretensioned concrete members. The development length (L_d) is defined as the tendon embedment length necessary to develop the nominal flexural capacity of a member and can be subdivided into transfer length (L_t) and flexural bond length (L_f) as shown in Fig. 1. This figure shows the ideal stress distribution along the tendon of a simply-supported beam subjected to a concentrated load (disregarding self-weight) when flexural and tendon anchorage capacity are reached simultaneously. The stress in the tendon due to the moment distribution is superimposed to the stress due to prestressing. The beam can be divided into cracked region (M>M_cr) and uncracked region (Mcr). The discontinuity in tendon stress at the threshold between the two regions and the different stress gradients result from the substantial difference between cracked and uncracked section moduli (Z_cr and Z_uc) which are for simplicity assumed to be constant. In this figure, tendon stress concentration at the location of cracks is not considered. Tendon anchorage failure conceivably occurs when the bond strength is overcome or splitting crack occurs in the concrete region included between the end of the transfer length and the cross section with M=M_cr. The objective of this experimental study was to determine the value of Ld for braided epoxy-impregnated aramid fiber (AF) tendons of the flexible type. The characteristics of materials and specimens used in this project were reported in a companion paper published in these proceedings. Ref. 1 presents the experimental results and the discussion relative to the determination of transfer length. CONCLUSIONS The experimental determination of development length for pretensioned prestressed concrete beams shows a good performance for epoxy-impregnated aramid fiber tendons of the flexible type. The following conclusions can be drawn: 1. The shortest Ld values are obtained K128 tendon. For K128-type rods, normal strain distribution along the tendon seems to indicate that anchorage failure occurs when the strain gradient in the flexural bond length region approaches the strain gradient measured over the transfer length region. 2. The development length of K64 tendon is longer than that of K128. In particular, the flexural bond length of K64 tendon is long. This may be due to smaller deformations on the K64 tendon surface. 3. The number of AF tendons per member cross-section does not significantly affect development length. 4. As expected from results on transfer length published elsewhere, the development length of conventional steel wire strand is longer than that of aramid fiber tendon of the same diameter. Better anchorage efficiency of AF vs. steel may result from effective AF tendon surface deformation and high Poisson's ratio.
PDFファイル名	013-01-1168.pdf