Cyclic Loading Behavior of Steel Chevron Braced Frames


Abstract eng:
The paper describes an experimental study on the seismic performance of steel concentrically braced frames (CBFs). In Japan, the most common CBF systems place diagonal braces in a chevron (or inverted-“V”) arrangement. Round hollow steel sections (HSS) are popular due to their artistic appeal. While such systems are widely used in commercial buildings, factories, and parking ramps, limited guidance is available in the current code provisions in Japan. Reconnaissance from past earthquakes suggests that these CBFs in Japan are prone to seismic damage. Consequently, three large-scale specimens were tested at Hokkaido University to examine the seismic behavior of chevron CBFs. The specimens placed a pair of braces in a single-bay, single-story moment-resisting frame. The three specimens were identical in dimensions and material selection using a stocky, round-HSS brace with a diameter to-thickness ratio of 18.2. The specimens differed in the design and fabrication of the bracing connections: Two specimens adopted bolted bracing connections that are widely used in Japan, and one specimen adopted a field-welded bracing connection following US recommendations. The specimens were subjected to a cyclic loading protocol based on story-drift ratio that is similar in severity to protocols specified for steel moment-resisting frames. The tests were terminated when one of the two braces fractured or moment-resisting frame distorted severely involving lateral-torsional deformation of the beam and twisting of the column. The test results suggest that chevron CBFs with stocky round-HSS braces and using moment-resisting beam-to-column connections can safely develop large story drifts exceeding 0.03 radians without damage to the bracing connections. Ultimately, severe local buckling in the plastic hinge region led to brace fracture. The force imbalance between the tension and compression braces led to yielding of the beam. Beam deflection forced the braces to deform more in contraction than in elongation: the change in length divided by length of the brace altered between 0.6% in elongation and 3% in contraction. In Specimens 1 and 3, out-of-plane deformation of the braces was accommodated by bending of the gusset plates, which was controlled by design in Specimen 3 but not explicitly intended in Specimen 1. In Specimen 2, the stiffened bracing connection eventually forced twisting of the beam to accommodate brace deformation. All three bracing connections exhibited excellent performance. Although the bolted bracing connections experienced distortion of the splice plates, no bolt slippage was observed. Although the welded bracing connection violated the design requirement for net section fracture, the particular failure mode was not observed in the tests.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2635.:
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