portal frame

Topics: Steel, Reinforced concrete, Structural engineering Pages: 22 (3542 words) Published: April 14, 2014
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Jun Kawaguchi, Shosuke Morino, Toshikazu Sugimoto and Junya Shirai Department of Architecture, Mie University
1515 Kamihama-cho, Tsu-shi, Mie, 514-8507 JAPAN
T: 81-59-231-9450; F: 81-59-231-9452; E: jkawa@arch.mie-u.ac.jp

In order to clarify the elasto-plastic behavior of the frame consisting of concrete-filled steel tube (CFT) columns and H-shaped steel beams under seismic loading, portal frame specimens were tested under constant vertical loads on columns and alternately repeated horizontal load. Experimental parameters were: axial load ratio (0.15, 0.3 and 0.5) and width-to-thickness ratio (21,39 and 54). Ds factors which are the factor used in the seismic design practice in Japan, were calculated from the load-deflection curves of all specimens. It was observed that all specimens showed fairly stable hysteresis loops, and the earthquake resistant capacity of a CFT frame was better than a similar steel frame.

CFT frames consist of concrete-filled steel tubular (CFT) columns and pure steel beams. They have become very popular these days, since it has been verified by many investigations since the 1970's that CFT columns have more benefit compared with ordinary steel columns, that is, CFT columns have more load carrying capacity than hollow steel tubular columns due to the interactive effects between steel and concrete; the confining effect of the steel tube on the concrete, and the restraining effect of filled-concrete on the local buckling of the steel tube. However, only a few frame tests have been done which include Matsui's portal frames (1) and CFT threedimensional subassemblages (2) and portal frames (3) tested by first two authors. Test results of portal frames were presented in the Conference on Composite Construction II. This paper presents the results of a additional frame tests, together with the results of analysis, and discusses the structural characteristic factor.

Shape and Dimensions of Specimens
Figure 1 shows the shape and dimensions of a specimen, which consists of CFT columns (125x125xtc) and a built-up H-shaped steel beam. A total of ten specimens were prepared with three different width-to-thickness ratio of the column tubes. The beam was connected by welding to the columns with through-type diaphragms which had holes for concrete casting. The thickness of the diaphragm plate was the same as that of the beam flange. All specimens were designed to yield in column first, and the beam was designed to behave elastically until the end of the test. Column tubes were 725

Composite Construction in Steel and Concrete IV

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connected to the diaphragm plates by butt welding except for the specimens with D/t = 21, in which fillet welding was accidentally used. At the column base, the column tube was inserted into a base stub of an H-150x260x12x16, and fillet welding was used at the connection between the column tube and upper and lower flanges of the base stub, as shown in Figure 1. Details were shown in Ref. (3). Table 1 shows the measured dimensions of the specimens.

The column tubes of the specimens with D/t = 21 and 39 were cold formed square sections made of STKR400 grade steel as per Japanese Industrial Standards, and the beams were of SS400 grade steel. The column tubes of the specimens with D/t = 54 were made by seaming two cold formed channels of SS400 grade steel by butt welding. The mechanical properties of the steel and concrete, obtained from the coupon and cylinder tests, are also shown in Table 1.

D/t =...

References: Structural Steel Conference, Vol. 2, pp. 169-181, 1986.
Concrete II, pp. 726-741, 1992, Potosi, U.S.A..
4) Structural Requirements for Building Construction, The Building Center of Japan,
5) AIJ Standard for Structural Calculation of Steel Reinforced Concrete Structures,
Architectural Institute of Japan, 1987.
of The International Conference on Structural Stability and Design, pp. 295-300,
1995, Sydney, Australia.
7) The Building Standard Law of Japan, The Building Center of Japan, 1986.
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