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Seismic Responses of SCBF with In-Plane Buckling Braces
Date Issued
2010
Date
2010
Author(s)
Ao, Wai-Hang
Abstract
Under the strong earthquake, special concentrically braced frames (SCBF) dissipate seismic input energy through cyclic tension yielding and compression buckling of braces. Tradition brace-to-gusset connection design allows the braces to buckle out-of-plane. As observed in the previous tests, the out-of-plane deformation can be greater than 40cm. Thus, the buckling of braces is likely to injure the near-by occupants and cause severe damage on the partition walls covering the braces. The use of knife plate in the brace end connections can transfer the brace buckling direction from out-of-plane to in-plane.
In this research, a total of five 3026mm long H175×175×7.5×11mm, A36 grade wide flange braces are tested in NCREE using the MATS facility. All knife and gusset plates are A572 GR 50. The key differences of the specimens are the shape, thickness of the knife plates and the brace-to-knife plate connection details where a net brace section near the knife plate connection was created or avoided. The Balance Method proposed by others was used in the design of the brace end connection details. All specimens were designed to allow the knife plate to deform using a linear clearance of three times the knife plate thickness. Test results suggest that the cyclic performance of five specimens is similar, all developed the design tensile and compressive strengths of the brace, sustained the peak strains of about +2.5% in tension and –2.0% in compression. All specimens failed due to the fracture of the brace at the mid-span where severe local buckling had occurred. Analytical results indicate that cyclic response of the specimens can be well simulated using the bi-liner soild elements and the ABAQUS model.
Comparing the fabrication cost and the constructability, Type TH connection has been chosen for the brace end connections in the specimen design of a 3-story SCBF. The existing 3-story moment resisting frame has been used with buckling or buckling-restrained braces several times in NCREE. In order to estimate the demands on the horizontal actuators and the vertical anchorage during the pseudo dynamic tests of the 3-story SCBF to be conducted in the future, OpenSEES program and scaled LA03 ground motion records were used.
Based on the analyses, it is concluded in this research that the size of the six braces be reduced from H175×175×7.5×11mm to H150×150×7×10mm due to the limits in the existing laboratory condition. In this manner, it is anticipated that under the 10/50 hazard level earthquake, the peak inter-story drift will reach 3.6%, 2.8% and 0.7% radians in the first, second and third stories, respectively.
In this research, a total of five 3026mm long H175×175×7.5×11mm, A36 grade wide flange braces are tested in NCREE using the MATS facility. All knife and gusset plates are A572 GR 50. The key differences of the specimens are the shape, thickness of the knife plates and the brace-to-knife plate connection details where a net brace section near the knife plate connection was created or avoided. The Balance Method proposed by others was used in the design of the brace end connection details. All specimens were designed to allow the knife plate to deform using a linear clearance of three times the knife plate thickness. Test results suggest that the cyclic performance of five specimens is similar, all developed the design tensile and compressive strengths of the brace, sustained the peak strains of about +2.5% in tension and –2.0% in compression. All specimens failed due to the fracture of the brace at the mid-span where severe local buckling had occurred. Analytical results indicate that cyclic response of the specimens can be well simulated using the bi-liner soild elements and the ABAQUS model.
Comparing the fabrication cost and the constructability, Type TH connection has been chosen for the brace end connections in the specimen design of a 3-story SCBF. The existing 3-story moment resisting frame has been used with buckling or buckling-restrained braces several times in NCREE. In order to estimate the demands on the horizontal actuators and the vertical anchorage during the pseudo dynamic tests of the 3-story SCBF to be conducted in the future, OpenSEES program and scaled LA03 ground motion records were used.
Based on the analyses, it is concluded in this research that the size of the six braces be reduced from H175×175×7.5×11mm to H150×150×7×10mm due to the limits in the existing laboratory condition. In this manner, it is anticipated that under the 10/50 hazard level earthquake, the peak inter-story drift will reach 3.6%, 2.8% and 0.7% radians in the first, second and third stories, respectively.
Subjects
concentrically braced frame
brace in-plane buckling
knife plate
pseudo dynamic test
Type
thesis
File(s)
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Name
ntu-99-R97521214-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):7323c3d27d7e688750a991a44a9169ba