AISC
Effect of Stiffener Weld Detail on Cyclic Performance of End-Plate Moment Connections
- Primary Investigator(s): Ryan T. Stevens, Matthew R. Eatherton, Thomas M. Murray
- Institution: Virginia Polytechnic Institute and State University
- Year Completed: 2020
- Report Number: AISC-FRR-2020-01
Executive Summary
There are currently two types of special moment frame (SMF) stiffened end-plate connections allowed in AISC 358-16: four-bolt extended stiffened (4ES), and eight-bolt extended stiffened (8ES) (AISC 2016a). Most of the specimens used for the qualification testing of the two configurations were fabricated using A36 beam and stiffener steel or A572 Gr. 50 beam and A36 stiffener plate steel. Recently, qualification testing was attempted for a new 12 bolt, stiffened end-plate configuration using built-up 24 in. and 44 in. deep beams. The beam webs and end-plates were A572 Gr. 55 steel while the beam flanges were A529 Gr. 55 steel. Four qualification tests were not successful because of brittle fracture of a beam flange prior to completion of the AISC 341-16 (AISC 2016b) loading protocol. Because of this unexpected failure mode, two tests each using the 4ES and 8ES end-plate configurations and A992 hot-rolled beams with A572 Gr. 50 stiffener material were conducted. Of particular interest was the effect of the weld configuration at the toe of the stiffeners. A complete description the testing program and results is the subject of this report.
The testing program was conducted with four specimens, two having W24×76 beams with 4ES configurations and two with W36×150 beams having 8ES configurations. A cyclic displacement protocol was applied to the specimen in accordance with special moment frame (SMF) qualification testing in AISC 341-16. One each of the 4ES and 8ES connection specimens had the stiffener-to-beam flange weld wrapped around the toe of the stiffener while the other two specimens had welds on the sides of the stiffener only.
All four specimens passed SMF qualification per AISC 341-16 by surviving cycles up to 4% story drift while retaining 80% of the nominal plastic moment at the face of the column. The 4ES and 8ES specimens with welds only on the sides of the stiffener survived 10 cycles and 1 cycle at 5% story drift, respectively, before the flange experienced full fracture. Specimens with the stiffener-to-beam flange weld wrapped around the toe experienced flange fracture one cycle sooner.
These tests showed that 4ES and 8ES connections with A992 rolled beams and A572 Grade 50 stiffener material designed and detailed according to AISC 358-16 are capable of reaching SMF qualification and are appropriate for use in special moment resisting frames. It is recommended to have the weld from the stiffener to the beam flange on the sides only (not wrapped around the toe of the stiffener) because those specimens exhibited more deformation capacity. However, connections with weld wrapped around the toe of the stiffener also satisfied SMF qualification.