Creating and Renewing Urban Structures 1 Hybrid RC Building Structures with Corrugated Steel Shear Panels Susumu KONO Associate Professor Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected]Susumu Kono, born 1963, received his Ph. D. from the Univ. of Illinois. Yukako ICHIOKA Ph. D. Candidate Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected]Yukako Ichioka, born 1980, received her MA degree from Kyoto University. Yoshihiro OHTA Structural Engineer Takenaka Research & Development Institute, Takenaka Corp., Japan [email protected]Yoshihiro Ohta, born 1965, received his MA degree from Kyoto University. Fumio WATANABE Professor Emeritus Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected]Fumio Watanabe, born 1944, received his Ph. D. from Kyoto University. Summary This research aims to establish an economical seismic response controlling system of RC frames using corrugated steel shear panels (CSSP), which was originally proposed for building structures by Mo and Perng in 2000. The hybrid system with CSSP has large ductility and possibly decreases to construction cost by large amount. The advantage of using CSSP in described from the design view point. Then, the experimental work on two specimens is introduced to show the excellence of CSSP in resisting the seismic force. A stud-type anchorage was employed in two half-scale specimens to fix CSSP to the surrounding RC frame. The degradation of lateral load carrying capacity after the peak load was small compared to reinforced concrete shear walls (RCW) due to stable manner of yielding and buckling of CSSP. The final failure mode of the hybrid system was the tearing of CSSP and the formation of a collapse mechanism of the surrounding reinforced concrete frame. Keywords: Corrugated steel shear panel (CSSP); damage control; shear wall; stud anchorage. 1. Introduction It is a common practice to use reinforced concrete shear walls (RCW) in reinforced concrete structures to maintain high lateral load carrying capacity and stiffness. However, high lateral stiffness with brittle ultimate failure mode of RCW often increases the required lateral load carrying capacity. In order to improve the ductility of reinforced concrete shear walls, some efforts have been made such as using low yield strength reinforcement and introducing slits but the ductility enhancement was not very prominent. Use of steel shear walls in order to increase ductility has some decades of research history. In 1973, Takahashi et al. [1] studied the characteristics of load- deflection relations of flat steel shear panels obtained experimentally and reported the effects of
Transcript
Creating and Renewing Urban Structures 1
Hybrid RC Building Structures with Corrugated Steel Shear Panels Susumu KONO Associate Professor Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected] Susumu Kono, born 1963, received his Ph. D. from the Univ. of Illinois.
Yukako ICHIOKA Ph. D. Candidate Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected] Yukako Ichioka, born 1980, received her MA degree from Kyoto University.
Yoshihiro OHTA Structural Engineer Takenaka Research & Development Institute, Takenaka Corp., Japan [email protected] Yoshihiro Ohta, born 1965, received his MA degree from Kyoto University.
Fumio WATANABE Professor Emeritus Dept. of Architecture Kyoto University Kyoto, JAPAN [email protected] Fumio Watanabe, born 1944, received his Ph. D. from Kyoto University.
Summary This research aims to establish an economical seismic response controlling system of RC frames using corrugated steel shear panels (CSSP), which was originally proposed for building structures by Mo and Perng in 2000. The hybrid system with CSSP has large ductility and possibly decreases to construction cost by large amount. The advantage of using CSSP in described from the design view point. Then, the experimental work on two specimens is introduced to show the excellence of CSSP in resisting the seismic force. A stud-type anchorage was employed in two half-scale specimens to fix CSSP to the surrounding RC frame. The degradation of lateral load carrying capacity after the peak load was small compared to reinforced concrete shear walls (RCW) due to stable manner of yielding and buckling of CSSP. The final failure mode of the hybrid system was the tearing of CSSP and the formation of a collapse mechanism of the surrounding reinforced concrete frame.
1. Introduction It is a common practice to use reinforced concrete shear walls (RCW) in reinforced concrete structures to maintain high lateral load carrying capacity and stiffness. However, high lateral stiffness with brittle ultimate failure mode of RCW often increases the required lateral load carrying capacity. In order to improve the ductility of reinforced concrete shear walls, some efforts have been made such as using low yield strength reinforcement and introducing slits but the ductility enhancement was not very prominent. Use of steel shear walls in order to increase ductility has some decades of research history. In 1973, Takahashi et al. [1] studied the characteristics of load-deflection relations of flat steel shear panels obtained experimentally and reported the effects of
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configuration, width-thickness ratio, stiffeners’ stiffness, etc. on the load-deflection relations. Studies on steel shear walls have been continuing since then [2][3]. However, flat steel shear panels need stiffeners to prevent plate buckling, leading to the increase of self-weight and cost.
In order to solve these problems, corrugated steel shear panels (CSSP) have been used in bridge structures since late 1980s. They weigh less and decease prestressing loss due to their negligible axial stiffness compared to flat steel shear panels reinforced with stiffeners. In 2000, Mo and Perng [4] reported a use of corrugated steel shear panels as a main lateral load carrying component for building structures. They reported that CSSP are effective to delay buckling of shear panels. However, bolt anchorage fastening CSSP to the surrounding RC frame was not very effective and a large slip took place at the interface resulting in pinched hysteresis loops with small energy dissipation. Their test results provided interesting information on the potential capability of CSSP but CSSP has not been used in practice as a main lateral load carrying component. This paper proposes the use of CSSP as shear walls instead of RCW by introducing the experimental work on RC portal frames with CPPS. The stud-type anchorage of CSSP used in bridge girders was employed to fully utilize the shear capacity and stiffness of CSSP. CSSP has larger buckling strength than the flat shear panel due to its configuration, with negligible flexural and axial stiffness. CSSP dissipates much greater energy after the peak load compared to RCW. If CSSP is employed as a main lateral load carrying component in building structures, it is possible to assign vertical load to columns and shear load to corrugated steel shear panels, resulting in a clear design philosophy. In addition, the ductility after shear yielding or even after buckling is excellent and it is possible to decrease the required lateral load carrying capacity.
2. Use of corrugated steel shear panels in design CSSP has many advantages over RCW if it is used as a main lateral load carrying component in building structures as summarized in Table 1. When an RC frame with CSSP is subjected to lateral force, shear deformation dominates. Hence, CSSP deforms in shear and the whole panel evenly dissipate energy after yielding. Energy is dissipated even after the buckling of the panel. CSSP does not exhibit any noticeable damage until the buckling, which takes place at relatively large deformation. Uniform deformation of CSSP causes uniform stress distribution to the surrounding RC frame and damage does not localize in the RC frame either. Since the shear stiffness and
Table 1: Comparison between corrugated steel shear walls and reinforced concrete shear walls
CSSP (Corrugated steel shear panels)
RCW (Reinforced concrete structural walls)
Deformation
Uniform shear deformation is always
dominant
Deformation localizes
if flexure mode is dominant. Weight Light Heavy
Cracking None Possible Energy dissipation Large Low
Creating and Renewing Urban Structures 3
strength of CSSP is about ten times higher than that of RCW and the density is about eight times larger, CSSP tends to weigh less than RCW if two components have equivalent shear stiffness and strength. One of the most attractive advantage of CSSP is its large energy dissipation capability after yielding. The energy dissipation capability does not degrade very much even after buckling.
Large ductility of CSSP produces another advantage in design as schematically shown. In Figure 1, the required shear capacity, Qu, is divided by the elastic design shear force, Qe, for the ordinate. When RCW is incorporated in RC frames, required shear capacity becomes high because of the brittle failure mode of RCW. However, CSSP is incorporated in RC frames, the required shear capacity can be drastically decreased due to its ductility. In the figure, Qu/Qe is required to exceed 0.4 for RC frame with RCW but 0.3 for RC frame with CSSP. The reduced requirement on Qu for RC frame with CSSP decreases the design force on all structural members, leading to large cost saving. Following chapters show experimental works to demonstrate the data supporting interesting features of CSSP explained in this chapter.
3.1 Setup Specimens were made of reinforced concrete portal frame with different anchorage configurations of corrugated steel shear panels. Dimensions of four RC frames are identical as shown in Figure 2 and test variables are shown in Table 2. Two shear panels had flange at the four side and two vertical stiffeners as shown in Figure 3. Thickness of flange and stiffeners were 4.5mm. Mechanical properties of materials are listed in Table 3.
200 300 300
Beamwid th=150
200 150 150 200 200 200
1300
200 20
0 55
045
0
150200
200
130
200 66
66
80
154 104
154
154
Cover20 =
Longitudinal rebar8 D13 (SD345)
Shear rebar3 D6 50 KSPD80
-
- ＠ ( )
Cover20 =
Longitudinal rebar4 D16 (SD345)
Shear rebar2 D6 50 KSPD
-
- ＠ ( 80) (a) Specimen dimensions (b) reinforcement of columns (c) reinforcement of a beam
(d) Dimensions of the corrugated steel shear panel used in the experiment. (e) Specimen A
Figure 2. Dimensions and reinforcement arrangement of specimens (Unit:mm)
1300
550 Line C
430 440 430
12 100@
510
0@
40
4045
40 4045
t 4 5= .
t 4 5= .
St if fner t 4 5 = .
Line C
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550
430 440 430
510
0@
12 100@
40
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40 4045
t 4 5= .
t 4 5= .
St if fner t 4 5 = .
(a) A (Double studs) (b) B (Staggered studs)
Figure 3. Dimensions of shear panels (Unit:mm. Each stud had a 9mm-diameter bolt with a head)
(a) Concrete (b) Steel C om pressivestrength(M Pa)
Tensilestrength(M Pa)
Young'sm odulus(G Pa)
C oncrete 62.0 3.93 29.3
M ortar 63.4 - -
Type
Yieldstrength(M Pa)
Tensilestrength(M Pa)
Young'sm odulus(G Pa)
D6 1099 1207 196
D13 391 551 186
D16 391 569 180C orrugated
panel264 362 191
Flangeplate
282 438 200
Stud 479 512 208
The number of studs of Specimen A was determined based on the following equation.
( ) ( )5 3 5 3 1.0a ap p q q+ ≤ (1)
where p is the design tension force, q is the design shear force, ap is the tensile strength when the stud experiences tension only, aq is the shear strength when the stud experiences shear force only. The tensile strength, ap , is the minimum value of 1) tensile strength due to a cone failure of surrounding concrete, 2) tensile strength due to tensile yielding of the stud, and 3) tensile strength due to bearing failure of concrete. The shear strength, aq , is the minimum value of 1) shear strength due to bearing failure of concrete, and 2) shear strength due to shear yielding of the stud. The design tensile force, p , and the design shear force, q , were obtained from elastic FEM analysis. When the shear panel reached the yield strength, the maximum normal stress was 31.5 N/mm2 and the average shear stress was 160 N/mm2 at the upper edge of the shear panel, which were substituted in p and q . Using of double studs of 9φ at 100 mm spacing, the left side of Eq. (1) became 0.99 and the equation was just satisfied. This determined the number of studs at the upper horizontal joint of Specimen A. The other interfaces were similarly computed. The maximum number of studs in four interfaces was taken after all. The number of studs was simply halved in Specimen B.
500kNhydraulicjack
1000kNhydraulicjack
1000kNhydraulicjack
Loadcell
Loadcell
SouthNorth
Loadcell
Reaction floor
Loading frame
Figure 4. Loading system
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Figure 4 shows the loading system. Constant axial load of 365 kN (Axial load level 0.15) was introduced to each column. Equal magnitude of lateral load was applied to the both ends of the beam by two 1000 kN hydraulic jacks. Two cycles of lateral load was applied at ±150 kN and ±250 kN. Then two cycles of preselected drift was enforced at ±0.1%，±0.2%，±0.4%，±0.6%，±0.8%，±1.0%，±2.0%，±4.0%.
3.2 Test results
3.2.1 Lateral load– drift relations Figure 5 shows the lateral load – drift relations up to R=4.0%. Both specimens showed similarly fat hysteresis loops up to the peak load at which buckling took place. Even after the buckling, the degradation of load carrying capacity was not drastic as RC shear walls failing in shear and reasonable amount of energy was dissipated. Specimen B experienced large degradation of load carrying capacity.
-800
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-5 -4 -3 -2 -1 0 1 2 3 4 5
D rift (%)
Horizontal Load (kN)
experim ent
analysis
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-5 -4 -3 -2 -1 0 1 2 3 4 5
D rift (%)
Horizo
ntal Load (kN
)
experim ent
analysis
(a) A (b) B
Figure 5. Lateral load - drift angle relations and results of pushover analysis
Table 4: Test results
Ry(%)
Q y(kN)
R(%)
Q m ax(kN)
R(%)
Q m ax(kN)
A +0.222 546 0.801 716 -0.759 -720 5.55
B +0.369 614 0.797 702 -0.803 -676 4.10
Yielding lateral loadSpecim en
M axim um lateral load capacityInitial
stiffness
(105 kN/rad)
Positive direction Negative direction
The yielding lateral load, the maximum lateral load carrying capacity and the initial stiffness are summarized in Table 4. The maximum lateral load capacity, Qmax, caused by buckling of the shear panel in positive and negative directions are large for Specimen A than Specimen B and reflects the number of studs. However, the yielding lateral load, Qy, was similar for two specimens although Qy of Specimen B is slightly higher. Drift angles at yielding, Ry, of Specimen A was smaller. This reflects the number of studs but the initial stiffness does not necessarily reflect the number of studs. Drift angles at the maximum capacity were similar for two specimens. Specimens A and B did not show any brittle failure until R=10%. It can be seen that behavior of the hybrid system is greatly affected by the amount of studs and resulting constraint.
Creating and Renewing Urban Structures 7
3.2.2 Lateral load carried by shear panel Lateral load carried by the shear panel is plotted in Figure 6. The shear force carried by shear panel was computed from three Rosetta strain gages on Line C in Figure 3 assuming the plane stress condition and elastic-perfectly plastic yield condition with von Mises yield criteria. Shear force of the shear panel increased rapidly for Specimen A but with slower rate for Specimen B. As the number of studs increased, the shear panel became stiffer and the buckling initiated earlier. The shear panel carried 60% to 70% of the lateral load from the very beginning of the loading till buckling took place at R=1.0%. The computed contribution was expected to be 64% at the ultimate condition by considering the story shear force at the formation of collapse mechanism of the surrounding RC frame and the shear force of the shear panel at yielding.
3.2.3 Lateral load carried by shear panel
Equivalent viscous damping ratio, eqH , is shown in Figure 7. eqH of specimens increased rapidly from R=0.4% at which the shear panel yielded, and large amount of energy was dissipated even after the buckling. Specimen A had larger eqH than Specimen B until yielding. Even after R=1.0%, a large amount of energy was dissipated in both specimens.
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0
50
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0 0.2 0.4 0.6 0.8 1D rift (%)
Shear forc
e o
f shear panel (kN)
specim en A
specim en B
A nalysis (A )
Figure 6. Lateral load carried byCSSP
0
5
10
15
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0 1 2 3 4
D rift (%)
Equivalent damping facto
r heq (%)
S pecim en A
Specim en B
Figure 7. Equivalent viscous damping ratio
Creating and Renewing Urban Structures 9
3.2.4 Numerical Simulation of load –drift relations using a simple frame model Behavior of Specimen A was simulated using a frame analysis program. The analytical model is shown in Figure 8(a). Two columns and a beam were modeled as a single beam-column element with nonlinear rotational spring at both ends. Since the shear panel had shear stiffness without neither axial nor flexural stiffness, it was replaced with a nonlinear spring with an equivalent stiffness in the horizontal direction to the shear stiffness of CSSP.
Figure 8(b) shows the simulation of Specimen A up to R=2%. It also shows that the hysteresis loops were well simulated until R=1.0% at which buckling took place. After buckling, experimental loops became pinched but the analysis does not show this degradation. Figure 8(c) separately shows the contribution of the shear panel and the surrounding RC frame in the analysis.
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Nonlinear springrepresenting shear panel
NonlinearRotationalspring
1500
650
/Q 2
N N
-1000
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-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
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A nalysis
Experim ent
P ushover
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D rift (%)
Shear force (kN)
T otal
R C fram e
S hear panel
(a) frame model (b) Cyclic and pushover Analysis (c) Contribution of the RC frame and shear panel
Figure 8. Shear force - drift angle relations for Specimen A
4. Conclusions A study was conducted on how to use corrugated steel shear panels (CSSP) as a main lateral load carrying component in building structures. The experiment on two RC frames reinforced with CSSP is introduced to demonstrate the advantage of CSSP.
• The revised hybrid system with corrugated steel shear panels excellently behaved as a seismic controlling system with large shear stiffness and shear capacity. In addition, the system showed some increase in shear force after yielding until buckling. The behavior after buckling was ductile and degradation in lateral load carrying capacity was about 20% even at R=5%. The behavior was stable if the number of studs satisfied the Japanese design guidelines (Specimen A). However, even specimens with half number of studs (Specimen B) showed the similar behavior although the stiffness and lateral load carrying capacity was lower.
• Lateral load carrying capacity at the peak was greater and the post-peak degradation in lateral load carrying capacity was less for specimens with the larger number of studs.
• CSSP dissipated large amount of energy after yielding and the dissipation continued even after buckling of shear panel.
5. Acknowledgements A part of this research was financially supported by Japanese Ministry of Land, Infrastructure and Transport (PI, F. Watanabe), Japan Science and Technology Agency in Research for Promoting Technological Seeds (PI, S. Kono), and Structural Engineering Research Center, Tokyo Institute of Technology (PI, Prof Shizuo Hayashi). The authors acknowledge Mr. Y. Kashiwai and Mr. K. Chosa, former students at Kyoto University, for conducting experiments.
6. References [1] Takahashi, Y., Takeda, T., Takemoto, Y. and Takagi, M., “Experimental Study on Thin Steel
shear Walls Particular Steel Bracings under Alternative Horizontal Load,” Preliminary Report of IABSE Symposium, Lisbon, 1973.
[2] Gaccese, V., Elgaaly, M. and Chen, R., “Experimental Study on Thin Steel-Plate Shear Walls under Cyclic Load,” Journal of Structural Engineering, ASCE, Vol. 119(2), pp. 588-605, 1993.
[3] Driver, R G., Kulak, G. L., Kennedy, L. and Elwi, A., ”Cyclic Test of Four-Story Steel Plate Shear Wall,” Journal of Structural Engineering, ASCE, Vol. 124(2), pp. 112-120, 1998.
[4] Mo, Y. L. and Perng, S. F., “Hybrid RC Frame-Steel Wall Systems,” Composite and Hybrid Systems, ACI, SP-196, pp. 189 – 213, 2000.
