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HomeMy WebLinkAboutEngineer Report 06.11.2020Studio M Engineers. LLC Structural Engineering Consultants Innov atíon By P er ceptí on www.mbengineering.elementfx.com studiom.engineer@gmail.com June ll,2020 Re: Lot 7 Native Springs To Whom It May Concern: As requested by my client, Mr. Mike Ruiz, my office was asked to inspect the residence at the address above in an effort confirm that the project was structurally constructed according to the structural plan set by Westar Engineering dated January 8, 2018. In addition to a general walkthrough inspection I was asked to address a gable end truss located on the north side of the garage. The truss is identifîed as truss type B-GAB on the attached truss layout by Trusfab of New Castle, Colorado. PROJECT DESCRIPTION: Lot 7 (aka 19 Native Springs Drive) is a ranch style residential structure with a squÍìre footage listed on Sheet 2 of the architectural set as 4,251square foot. The foundation is a cast in place concrete system over a strip footing layout. Walls are between 8 and 12 inches thick and are reported as extending down below the 36 inch frost requirement of Garfield County. The main level floor is cast in place concrete slab on grade, with an anticipated thickness of 4 inches. IValls are light framed wood consffuction (2x6 exterior, 2x4 interior non load bearing typically). The roof is primarily prefabricated wood truss by a company from New Castle by the name of Trusfab. The truss shop drawings are attached for reference. The entry foyer is a clerestory configuration with a2xl0 rafter roof. Rafters are typically spaced at 24 inches on center. OBSERVATIONS: Framing anomalies that need to be changed or repaired are as follows: The west facing kitchen wall is framed with a hinge, meaning the studs to not extend to a point of bracing. Typically gable end studs are framed to the lookouts or ceiling, or a gable end truss is provided. The studs will require a l, vz" wide light guage Simpson strap installed on their interior, natrow edge. Straps shall be a Simpson MSTA36 and shall occur on at least 4 studs within the entire wall. Straps shall center at the plate /gable wall intersection, o a z5o Tripp Drive a Rifle a Colorado a 81650 .97o-366-869o . Lot 7 Native Springs Page Two o The south facing living room window is at least 12 foot in width. It is currently supported by a double trimmer single kind stud arrangement. The king stud is undersized and cannot $uppoft the 115 mph 3 second ultiinate wind load required by Garfield County. There is no column configuration specification on the original structural drawing set. The opening needs a single 5.Vz'o LVL king stud added to each end to satisfy the design wind load requirement. There is an elcctrical line in the way of inserting the stud straight in. The line should be backed out of the box and installed through pre-drilled holes in the new king studs.o There is no foundation or footing at the dividing line between Pantry and Dining Room (reference Sheet 2 of the architectural drawings). The current framing configuration has a trþle 2x10 beam supported by a built up 2x column. The column lands on a 4 inch thick slab with no footing support. The original structural drawing does not specify a header in this location. The header needs to span 17 foot, from one foundation element to the next. The appropriate header would be a triple 16 inch lvl fastened with 4 rows of 16d nails at a spacing of 12 inches on center. The multi ply beam fastening detail is attached for reference (clarification 6a). The beam needs to be installed as close to the ffusses as possible, ideally right against the bottom of the trusses so that the top edge of the beam is braced against compressive buckling of the top edge. LVL specifications are found on clarification 5.4.o The end reaction for this same beam is nearly 10,000lbs. The support column at each end needs to be a built up (nailed) 4-2x6 Hem Fir No. 2 post or better. The column needs to be fastened off to adjacent framing, since it cannot bç secured through the exterior sheathing because exterior finishes are already installed. Blocking needs to be provided at truss ends to prevent them from rolling.¡ The 2x10 rafters in the great room ceiling were framed without hangers. They appear to be toe nailed into the primary glue lam central ridge beam. The rafters need a positive fastening system. The anticipated rafter reaction is 470lbs per rafter end. The rafters can be secured to the ridge beam with a pair of Simpson LS90light guage clips (715 lb capacity per clip). There was no clip or hanger specification found on the original structural drawings.o The gable end walls at the clerestory of the entry foyer extend over 20 foot in height from the slab to the underside of the lookouts above. The distance is so far that the contractor could not find 2x6 studs that could go the entire height. As a result the studs were lapped (i.e. non continuous) and nailed off. The lap creates a hinge in the wall that is susceptible to failure from a design wind load event normal to the wall. The condition exists on both the south facing and north facing clerestory wall. During my on site meeting I briefly discussed the possibility of strapping the wall interior to bridge the hinge anomalies. After I was able to run a detailed calculation and analysis it is clear that the strap solution will not be sufficient. The wall will either need to be reconstructed with proper full height 1.55E LSL 2x6 stud framing (16 inches on center) or reinforced with a "stiffbacK' element that provides rigidity, especially at the wall midpoint, where deflections will currently exceed the limits required in Table R301.7 of the 2015 IRC. 25o Tripp Drive a Rífle a Colorado o 8t65o .97o-366-869o . Lot 7 Native Springs Page Three The stiffback option seems to more practical because of the fact that the exterior of the wall is already finished. a a The 3-7 . r/d" LYL stiffback and corresponding fasteners shall be as depicted in the attached clarification 3.4. The detail applies to both clerestory walls at the entry (north and south). The truss type A1 is missing the permanent bracing identified on the truss shop drawings. The bracing needs to be 'diagonaled' to either the roof or ceiling to prevent a simultaneous truss web buckling phenomenon associated with the fact that a bank of brace truss webs with a single brace is physically not considered o'stâble". Diagonals should occur at each end of the run of trusses, and no more than 20 foot on center. Diagonals can be 2x6's extending no more than 6 foot. The diagonal essentially laps the bracing member identified on truss piece drawing al and extends down to a wood cleat installed on either the ceiling or roof structure. The truss identified as truss type B-GAB on the north side of the garage is a gable end truss that is intended to have full bearing support along its bottom chord. As built, the truss is situated a few inches north of the 2x6 bearing wall that forms the northern boundary of the garage. The ffuss can be replicated by framing a series of 2x6 studs ftnee wall) extending from the northern wall of the garage to the underside of a sloping double top plate that is fastened to blocking extending between the northern and southern adjacent roof truss. Refer to clarification 1A for a visual depiction of this scenario. The project was not designed to resist lateral loads, as is indicated by the lack of any specification regarding any type of prescriptive bracing or shear wall detail. There are no hold down brackets or starps, special nailing specifications, braced wall line identifications, or braced panel identifications etc. The lack of a lateral system design is most apparent at the garage, where the ratio of wall to opening is l:4. Table R602.10.5 requires a 54 inch CS-WP (continually sheathed wall panel) when the panel is adjacent a 9 foot door opening. The cuffent wall panel is between 2 foot and 2' -6 inch in width. The code allows for the use of a more heavily reinforced panel, known as an "alternate braced wall panel" (ABIV). This panel needs to be at least 32 inches in width. Construction methods are outlined in section R602.10.6 of the code, and graphically summarized in the attached clarification 2.4. Alternate Braced Wall Panel Locations are indicated on clarification 4.4. Existing panel nailing can be considered adequate so long as the walls are spray foam insulated. It is my experience that lateral rigidity from spray foam applications in 2x wood framed walls is significant. The heavy timbers from the accessory roofs that pocket into the 2x6 extenor wall framing need to be attached so they don't uplift or pull out. The cunent attachment is insufficient (a couple toenail 16d nails). Side lap the members with a2x6 cleat and stitch into the existing framing with a series of r/¿" dia. X 3.W'wood screws (6 screws per member end minimum). a a o a 25o Tripp Drive a Rifle Colorado a 8165o .97o-366-8690 . Lot 7 Native Springs Page Four LIMITATIONS: r The areas that I observed were readily accessible using conventional means of access and observation. Likewise, framing and structural system deficiencies that were hidden behind finishes or obstructed from readily available points of visible access may exist, and would similarly invalidate the conclusions in this report. Such anomalies should be reported as they are discovered. o The foundation could not be inspected primarily because it was concealed from view by slab and dirt. o The purposed of this inspection and letter was to find and address framing insufficiencies. Verification that as built conditions are in general compliance with the permitted documents is ultimately the responsibility of the Garfield County Building Department. r Unless indicated otherwise, my conrments or lack thereof, do not indicate an approval of existing structural systems. o No warranty is either implied or expressed. o The following services are beyond scope architecture, site plans, energy studies, building component assembly descriptions, land surveying, civil, geotechnical, electrical, mechanical, heating ventilating and air conditioning plumbing, site grading, or acoustical engineering, architectural issues including, but not limited to, site location, access, egress, zoning conformanceo stairs, guardrails, waterproofing, insulation, architectural plans, elevations, sections, and schedules. This concludes this repotr. Please contact my office with any questions or cornments. Sincerely, W/ç*r, Michael J. Baca, PE NCEES Principal, Studio M Engineers LLC Enclosures: 8.5x1I Clarifications lA to 44. Trusfab Truss Layout and Piece Drawings a z5o Trípp Drive a Rifle a Colorado a 8t65o .970-366-869o .