Braced Frame Baseplate Connection

[txeng91]

I am designing a 4-part milti-story steel frame with composite deck, buildings range from 3-5 stories, largest columns are W14x120. The lateral bracing mainly consists of chevron frames, using base plates recessed 8" into concrete at the foundation. The foundation is a one-way slab over a 6' deep crawl space supported on concrete beams spanning between concrete columns, which are supported on pile caps supported on auger cast piers. The slabs are 8"-10" thick so the anchors will be cast in at the same elevation as the beam/slab joint. When sizing the anchors for base plates at braced frames, concrete breakout is an obviously an issue as their is a high amount of shear. Is it acceptable to set these anchors in in a concrete beam (probably 32"-48" wide) and negate the shear breakout by using hairpins that hook around the exterior anchors (see attached sketch)? I'm also hooking the concrete column reinforcement into the slab for tension reinforcement. I know this conforms to ACI 318 Appendix D, but am a little uneasy about it since I haven't been able to find much information on this topic and I have only seen hairpins used on metal buildings. Without using shear reinforcement, very large concrete column capitals would be required and that is not really an option since some of the braced frames are located about 1' off of expansion joints.

 

[DaveAtkins]

I think you are OK as long as the reinforcing is properly developed, and near the top of the beam, so that the horizontal reaction from the braced frame is transferred into the beam.

You must also deal with the vertical (uplift) reaction, of course.

DaveAtkins