Replacing Existing Steel X Bracing on Vaulted Structure

[parris]

Seeking suggestions on the type and method of replacing existing X bracing to allow design/construction under a vaulted structure.

A 1987 72' L x 46' W x 25' H single-story structure sits atop 27 5"x5"x3/16" steel tube columns and a 6'x14'6"x8" concrete block wall. 18 of the columns and 6 feet of block wall are perimeter. The block wall primarily supports a 22' high rocked wall inside the structure. Each column is bolted through a 10"x10"x5/8" baseplate to an independent footing at a different elevation on a 2D-sloping hillside (i.e. South columns range from 10" to 14', North columns range from 13' to 23'). Columns and three places on the conrete block wall are joined by glu-lam woods beams. The structure is adjoined on the North to a vaulted stair/tram enclosure traversing 50 vertical feet to a ground-level entry.

Existing X bracing comprises 2.5"x2.5"x3/16" angle iron welded to 3/8" steel plate welded to column centers. There are five sets of X bracing between perimeter-interior columns and nine sets of X bracing between perimeter columns.

The existing bracing and its method of attachment interfere with the design and attachment of new beams and walls to enclose the space under the existing structure. The walls could be located between columns or just inside columns but for the X bracing config. New beam pockets could be welded at the base of each column but for the X bracing config. At least some and perhaps nearly all of the replacement bracing may be visible through windows so an architecturally appealing style of bracing is desirable. Because of the 2D sloping hill, in order to reasonably maximize enclosed volume, new beams must make vertical jogs.

Welding nine sets of new X bracing to the exterior of perimeter columns before removing the nine sets of existing X bracing is the most obvious thought, except that avoiding/minimizing visible bracing is preferred. Could the wind loads be transferred to the footings or sufficiently absorbed by simply tying the columns together by new beams, trusses, wall sections, etc.? With respect to the design, variable temps on interior and exterior steel could be a concern (could be 20 below outside and 75 inside).

Grateful to receive any suggestions.

 

[SperlingPE]

No mention of location, loads, dimensions between columns, beam connections, etc. Further information is required and review of the structural & architectural plans needed. Consult local engineer.

 

[parris]

SperlingPE:

Thanks for responding.

Sorry for failing to mention it, but I'm not looking for details or analyses; only general concepts to introduce to a local SE, select what appears to be the best concept, model, simulate, approve, and implement it.

The original SE isn't available. The local SE who said he'll get to it when he can fit it in, like the other handful of SEs in the area, primarily does standard lowrise commercial work. His initial comment was that he thought some of the X bracing was overkill in view of the concrete block wall, but I think once he studies the plans he'll back off that because only the tips of three beams rest on or towards one end of the conc. blk. wall.

The location is Rapid City, SD, pop. 60,000. Denver is the nearest metro, 6.5 hour drive away. A friend of mine here represents what seems to me to be an awful lot of engineering professionals for design negligence. Also, through experience hiring other professionals here, I have reason to worry about competence and thoughtfulness so I am trying to become more versed on SE to make sure this doesn't wind up a pile at the bottom of a hill or unnecessarily nasty looking. Statics and Dynamics 15 years ago isn't enough, but its helpful.

Primarily, I don't know the liklihood that tying the columns and beams together with new beams, trusses, wall sections, etc. (e.g. maybe joining each column along its length with welded rectangular wall frames) is enough or whether dedicated bracing will remain necessary. Plus, in order to add the new beams, trusses, wall sections, the existing X bracing will need to come off, so would temporary welded bracing two columns at a time be necessary or ... If dedicated bracing will still be necessary then I'm looking for an economical and architecturally beautiful solution because it would likely be visible from inside and outside.

I imagine there are multiple solutions and that's what I was hoping to hear from those of you who practice in the particular field.

In case added details help with ideas:
Reinforced concrete footings are 4' deep with 10" thick square pads (ranging from 2'6 sq. to 4'6" sq.) topped by 3'2" H x 18" dia. reinf. conc. cylinders. 19 perimeter and 15 interior beams are bolted with two bolts to columns through 1/4" steel U plate beam pockets welded to the top of each column. Each beam pocket joins two or three beams. Half the beams are 5' to 12' and half are 12' to 16' long. Beams are 5" to 7" W x 15" to 18" H glu-lam. Plans note, "Steel ASTM 3000 lb PSI, A615, Grd 40, MSBP 2000 PSF" and minimum design stresses for beams are Fb = 2400 psi, Fv = 165 psi, Fc = 385 psi. The house sits towards the bottom of a 40 degree angle hill rising 350 feet. Winds generally come from the northwest striking the tallest beams first. High winds, fast temp changes, and heavy snow loads are possible here.

I have plenty of detailed pictures/plans if anyone wants to see them.