Damage mechanism for high strength steel part frame without diaphragm

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1 High Performance Structure and Materials V 33 Damage mechanism for high strength steel part frame without diaphragm Y. Kimura & T. shihara Building Research nstitute, Tohoku Universit, Japan Abstract Recentl, the high tension steel with thield stress of 8 kn/mm was developed, and the loading test of the structural members with this steel has been confirmed. t is shown that the ratio between ultimate strength and ield strength is almost unit, so that the members with this steel have quite small ductilit. When rigid moment resisting frames with high tension steel are subjected to seismic force, the fracture at the ends of beam ma occur and it causes the strength of frames to decrease. On the other hand, the semi-rigid moment resisting frames without diaphragm with high tension steel can absorb the seismic energ at the beam-to-column connections due to its plate bending deformation. This stud performs ccle loading experiments to high tension steel part frames, and compares the initial rigidit and thield strength of part frames without diaphragm with that of part frames with diaphragm. n addition, these experimental results are compared with the approximation of the reference. Kewords: high strength steel, fracture, plate bending deformation, ultimate strength, diaphragmless. ntroduction The new steel named H-SA7 has been developed to decrease the allo element and to establish the streamlined process of heat treating in the project in Japan during and 8. n the view of cost, it is better than the steel used with 8N/mm. The main seismic frame with this new high strength steel has the possibilit to keep elastic and the onl damper becomes plastic, even though it is subjected to a large earthquake. On the other hand, it is shown that this new high strength steel has smaller fracture capacit and lower fatigue performance than the used steel of SS and SM9 with ultimate stress of N/mm WT Transactions on The Built Environment, Vol, WT Press SSN (on-line) doi:.95/hpsm3

2 3 High Performance Structure and Materials V 9N/mm (e.g. Shioaku et al. [] and Tanaka et al. [ ]), so that it needs to decrease the weld area to prevent fracture at the weld. When the high strength steel is applied to the main moment resisting frame without diaphragm, the frame ma keep elastic during large earthquake. n this paper, the cclic tests for the part frame model with the difference of width and thickness of columns are performed to clarif the initial stiffness and ielding strength. When the column joint stiffness is high, the initial stiffness becomes high. The fracture near the weld area ma occur as soon as the frame becomes plastic. On the other hand, when the column flexural stiffness is small, the initial stiffness and maximum strength become low and the fracture ma not occur at the joint. The joint without diaphragm is investigated to be able to be applied to the main steel frames with high strength steel. The approximations for the initial stiffness and ield strength, maximum strength are suggested to be applicable to the estimation of the experimental results. Cclic loading test for part frame of beam and column. Guideline of cclic loading test Figure shows the set up for the part frames of beam and column. The boundar conditions of beam and column are pinned, and the cclic horizontal load is applied b 5kN oil jack. unit OL JACK 8.3 lb=396 H-5x5x6x9 PN BOX-5x5 t c = lc=33 Figure : Test setup. As shown in Table, there are 6 specimens of part frames with high strength steel. The specimen of No. has the diaphragm, and the others have no diaphragm. The specimens from No. to No.6 are different from the section of the column. The ratio of column moment capacit, Mpc, to beam moment capacit, Mpb from No. to No.6 is the range from.8 to.. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

3 High Performance Structure and Materials V Table : Specimens. Beam H H H H H H No. No. No.3 No. No.5 No.6 35 Column Diaphragm Yes No No No No No Figure shows the cclic loading procedure. n this procedure, the increment of the displacement at allowable bending moment of H-shaped beam, F, is adopted, and after that, the increment of the displacement at ield bending moment capacit of H-shaped beam,, is used. (=9%) (= (=.5%) (=3%) F (=.5%) - F - (=6%).8%) - Figure : サイクル - - Cclic loading procedure. Figure 3 shows the specimen of No., and the strain gauges are also installed on the flange and web of H-shaped beam and box column to investigate the local buckling of flange and web for H-shaped beam and the local plate deformation of beam-to-column connections A Figure 3: B' 6 75 B B-B' Section A' A-A' Section Specimen of No. with strain gages. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

4 36 High Performance Structure and Materials V Figure shows the stress and strain curves for the high strength steel plates b tension test. Thield stress of each plate is about 735 8N/mm, and the ultimate stress is about 8 86N/mm. (N/mm) 8 9mm 6 mm E st u E ( kn/mm) (kn/mm) (N/mm) (N/mm) 6mm mm mm mm mm 6mm Figure : Material propert of high strength steel plate.. Results of cclic loading test Figure 5 shows the hsteretic curves for specimens of No. No.6. P and are thield bending moment, M, divided b the length of the beam, and the horizontal displacement of the beam at the top. epf or ep means the load when the value at an strain gage reaches the strain corresponding to the allowable stress or thield stress, respectivel. The approximation formula of thield strength for part frame without diaphragm with SS or SM9 is suggested such as Equation () b (Akiama et al. [6]). P.38 c tc B tc tr B tc b B tc b () where B or b is the width of column or beam flange, and tc or tr is the column thickness or the weld thickness of the beam flange. c is thield stress of the column flange. Black triangle in the diagram indicates the point of /.5 of the initial stiffness, which is recognized as thield strength of the specimens defined b (Akiama et al. [6]). The maximum load for No. with diaphragm exceeds thield strength of the beam, and the strength suddenl drops below. of thield strength, P at of /. The cause of this strength deterioration is the fracture of the beam flange near the weld to the column flange. On the other hand, the maximum loads for No. ~ No.6 without diaphragm are lower than that for No., because of the local bending deformation of the column flange plate due to the bending moment of the beam. n all of specimens without diaphragm, No.3 with narrow column WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

5 37 High Performance Structure and Materials V P/P P/P max epf /P P /P P /lb ( -) P/P P P /P P /P Eq.() /l b ( -) - (a) No. - (b) No. P/P max max.5 P P /P ep /P P - Eq.() l b ( -) - - (c) No.3 P/P.5 P/P.5 P max P /P ep /P - - (d) No. P max -.5 Eq.() /l b ( -) max P /P P /P - Eq.() /lb ( -) - - (e) No.5 Figure 5: P /P P /P Eq.() /lb ( -) - - (f) No.6 Load-displacement curve for specimens. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

6 38 High Performance Structure and Materials V flange and No.6 with thick column flange has highest strength, and No. with wide column flange and No.5 with thin column flange has the highest ductilit at the maximum load. The strength of all specimens without diaphragm decreases slowl. Figure 6 shows the strain distribution on the column flange below beam flange such as the right diagram in Figure 3. For No. with diaphragm, the value of strain is almost equal to, because the diaphragm carries the axial force of the beam flange to the column as the shear force (e.g. Suzuki et al. [5]). For No. No.6 without diaphragm, the bending strain occurs on the column flange and strain values decrease near the column flange edge % 3%.5% before fracture.5.5.8%.5%.5% 6% 9% 3% (a) No %.5% 3% (b) No % 6% 9%.5.8%.5%.5% 6% 3% 9% (c) No (d) No. Figure 6:.8%.5%.5% 6% 3%.8% 3%.5%.5% (e) No.5 (f) No.6 Strain distribution on column flange below beam flange. The strain value for No.3 and No.6 is smaller than the others, because the fracture b the tensile beam flanges earl occurs. The strain value for No. is highest in all specimens, because the bending stiffness of the column flange for No. is higher than the others except the specimens with fracture and its beamto-column joint carries larger bending moment of the beam. Figure 7 shows the collapse mechanism of the specimens. t is shown that for No., the fracture of the web of H-shaped beam occurs as soon as the fracture of the tensile flange. On the other hand, for No., No. and No.5, the column flanges are shown to be drawn b the tensile beam flanges, and for No.3 and No.6, in addition to drawing of beam tensile flanges, the fracture near the weld of the flange and web occurs due to a higher rotational stiffness at the connection between the beam and the column than those of No., No. and No.5. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

High Performance Structure and Materials V (a) No. (b) No. (c) No.3 (d) No. (e) No.5 (f) No.

3 Estimation of part frame with high strength steel without diaphragm Figure 8 compare the initial

Equation () is shown in the following. 3.5.7 b d t f B tc K 73E B tc b t c.

d is the depth of the beam web and is the thickness of the beam flange.

f K/K is equal to, it means that the beam-to-column joint becomes rigid.

7 High Performance Structure and Materials V (a) No. (b) No. (c) No.3 (d) No. (e) No.5 (f) No.6 Figure 7: Collapse mechanism of specimens Estimation of part frame with high strength steel without diaphragm Figure 8 compare the initial stiffness between the experimental results and Equation () suggested b (Akiama et al. [6]). Equation () is shown in the following b d t f B tc K 73E B tc b t c.5 () where E is the Young s modulus, is tc3/. d is the depth of the beam web and is the thickness of the beam flange. K/K of the vertical axis is the elastic stiffness of H-shaped beam as the cantilever. f K/K is equal to, it means that the beam-to-column joint becomes rigid. The values of the experimental results are distributed in.3.7, so that all specimens without diaphragm are recognized as semi-rigid. Equation () can be applied in less than about.7 of K/K, so that the initial stiffness calculated b Equation () is almost same as the experimental results except No.6. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

8 35 High Performance Structure and Materials V K/K [experiemtal results].8 Range applied b Eq. ().6.. Figure 8: clces + :fracture after drawing :drawing K/K[Equation ()] Comparison initial stiffness between experimental results and Equation (). Figure 9(a) compares thield strength between the experimental results and Equation () suggested b (Akiama et al. [6]), and Equation (3) is the approximation based on Equation () from the experimental results as the following. P.5 c tc B tc (3) tr B tc b B tc b P is thield strength of H-shaped beam as the cantilever. Regardless of the collapse mechanism, the solid line b Equation () is higher than the experimental results, and the broken line b Equation (3) is almost same as the results. Because thielding strength is calculated b general ield method of SS or SM9 and the stiffness of high strength steel after ielding is lower than SS or SM9. Figure 9(b) compares the strength at first ielding between the experimental results and Equation () suggested b (Akiama et al. [6]), and Equation () is the approximation based on Equation () from the experimental results as the following. e P.35 c tc B tc tr B tc b B tc b () PF or ep means the load when the value at an strain gage reaches the strain corresponding to the allowable stress or thield stress, respectivel as shown in Figure 5. The solid line drawn b Equation () is higher than the experimental results, and the broken line drawn b Equation () corresponds to the lower bound. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

9 High Performance Structure and Materials V P /P, P /P P/P [Experimental Results]. Ccle P/P [Equation ()] (a) ield strength Figure 9: P : Column Yielding [Experimental Results].8. : Beam Yielding.8 P : fracture after drawing : drawing P /P, P /P.. [Equation ()] (b) local ield strength Comparison of strength between experimental results and Equations () and (3). 3 Conclusions ) For the part frame model with high strength steel without diaphragm, the initial stiffness and ield strength are lower than those for the part frame model with diaphragm. The initial stiffness and thield strength without diaphragm are % 6% of those with diaphragm, respectivel. ) There are two kinds of collapse mechanism for the model without diaphragm. One of them is the drawing of column flange b beam flange for the wide column flange or thin column flange, and the other is the fracture after the drawing for the narrow column flange or thick column flange. 3) The model with diaphragm reaches the maximum strength due to fracture, and the strength decreases rapidl. On the other hand, the model without diaphragm increases its strength after drawing of column flange b beam flange, and has the high plastic deformation capacit. ) The initial stiffness for the frame model without diaphragm is estimated with Equation (), thield strength for high strength steel is estimated with Equation (3) based on Equation () for the normal steel such as SS or SM9, because the stiffness of high strength steel after ielding is lower than SS or SM9. Acknowledgement This work was carried out under the general technolog development project, Development of Performance Assessment Methods for nnovative Structures Appling Advanced Structural Materials b the Ministr of Land, nfrastructure, Transport and Tourism, Japan. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

10 35 High Performance Structure and Materials V Reference [] Shioaku, T. Yoshida, Y. Sakiama, T. and Fukuda, T., Mechanical Properties of 8 N/mm Class High Strength Steel, Summaries of Technical Papers of Annual Meeting, AJ, C-, pp. 63, 8. [] Tanaka, N. Kaneko, T. Takenaka, H. and Sasaki, S., Elasto-Plastic Behavior of Circular-Column-to-H-shaped-Beam Connections Emploing Super High Strength Steel: Part ~ Part 3, Summaries of Technical Papers of Annual Meeting, AJ, C-, pp , 7. [3] Tanaka, N. Kaneko, T. Suzui, Y. T. Takenaka, H. and Sasaki, S., ElastoPlastic Behavior of Circular-Column-to-H-shaped-Beam Connections Emploing Super High Strength Steel: Part ~ Part 6, Summaries of Technical Papers of Annual Meeting, AJ, C-, pp. 9-, 8. [] Tanaka, N. Suzuki, Y. T. Takenaka, H. and Sasaki, S., Elasto-Plastic Behavior of Circular-Column-to-H-shaped-Beam Connections Emploing Super High Strength Steel: Part 7 ~ Part 9, Summaries of Technical Papers of Annual Meeting, AJ, C-, pp , 9. [5] Suzuki, T. karashi, K. Azuma, T. and Yoshinari, Y., A Stud on Collapse Mode and Plastic Deformation Capacit of High Strength Steel Beam Connected to Box Column, Journal of Structural Construction Engineering, AJ, 57, pp. 33-, 993. [6] Akiama, H. Oh, S. Otake, F. Fukuda, K. and Yamada S., General Moment-Rotation Characteristics of Beam-to-RHS Column Connections without Diaphragms, Journal of Structural Construction Engineering, AJ, 8, pp. 3-, 996. WT Transactions on The Built Environment, Vol, WT Press SSN (on-line)

Mechanical behavior and design method of weld-free steel structure with knee brace damper using square tube column

Mechanical behavior and design method of weld-free steel structure with knee brace damper using square tube column D. Kawai Osaka Institute of Technology, Osaka, Japan Y. Koetaka & K. Suita Kyoto University,