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HomeMy WebLinkAboutEngineer Report 07.23.2013Studio M Engineers. LLC Structural Engineering Consultants I nnov atí on By P er ceptí o n www.m bengineering.elementfx.com micbaca@yahoo.com JuIy 23,2013 Mitch Hyra 12613 Mile Road Garfield County, Colorado Re: Shop at 12613 Mile Road To Whom it May Concern, As requested by Mitch Hyra, my office was asked to inspect the thickened edge concrete slab on grade at a 1,472 square foot residential work shop located in the 3 Mile drainage. south of the City of Glenwood Springs. My inspection oıcurred the afternoon of July 19th at4pm. 1261 3 Mile Road is the address of the property. The shop is located at 39 degrees, 30 minutes 25.07 seconds north by 107 degrees 20 minutes 7.28 seconds west at an elevation of 6,510 feet. The shop is built on a steep East facing slope. Based on conversations with Mr. Hyra the shop has been under construction since the Spring of 2010. It is my understanding that the slab was poured on November 28,2OIl and remained uncovered for approximately 8 months. STRUCTURAL DESCRIPTION: The shop is located in a cut on the hill side. Soil retaining is provided on the North and West by an 8'-8" CMU (concrete masonry) wall. The other walls are conventional light frame wood construction. The foundation is a thickened edge reinforced concrete slab that extends 4" outboard of the building shell. I understand that portions of the slab were thickened to a depth of 8 to 12 inches at interior columns, beam end reactions, pilasters, and slab perimeter. The slab and footings were poured monolithically as shown in Figure R403.1(1) of the IRC. The unheated shop is covered by a three tiered roof system with rafters spanning East- West. The East and Iù/est roofs are at the same elevation, with the center tier roof extending an additional4'-0" upward. Two garage doors face south, towards the road that accesses the site. Roof structure consists of three steel beams with a center column support at each ofthe three beam lines. The three beam lines are located at the approximate quarter points of the building and span in the North South direction. . 3o8 N. Hyland Park Dr. . Glenwood Springs . Colorado . 8t6ot . 97o-366-869o 1261 3 MiIe Road Page Two The structure was partially backfilled on the north (hill) side at the time of my inspection. A nearly vertical embankment existed directly adjacent to the building on the north elevation. ANTICIPATED STRUCTURAL LOADING: The slab can be expected to support loads based on the current load requirements of Garfield County and the 2009IRC. These loads are as follows: Loads Directly On Slab: Passenger Vehicle Garage: 50 PSF, or 2000 lb vehicular point load per the IRC. Loads Indirectly On Slab: The perimeter walls are anticipated to translate shear and bending stresses into the slab. The edge acts as the footing element for the retaining walls. These loads are a result of the following: o Snow Load o Roof and wall material self weight (dead loads). o Lateral loading from Soil Surcharge, Seismic Events and Wind. There was no soils report available at the time of my inspection. OBSERVATIONS: Two interior slab drains exist,located at the south of the two parking bays. The slab in these areas slopes minimally towards the drains. Elsewhere, the slab is approximately level. Slab elevations were measured around the interior perimeter and at the three steel columns. The relative slab elevations included in the survey were found to be within one half inch. Cracks were observed at several locations. The cracks were coincidental with the thickened edges of the 16" square footing located below some of the interior steel columns. The East bay contained a vehicle parked on a large area mat. The mat was not removed during the inspection. No reinforcement was visible at the time of the inspection. Seven undated construction drawings (sheets 1 to 7 from a set of 10 pages) were available for review. It is our understanding that several as-built portions of the thickened edge slab were not depicted in the drawing (i.e. thickened edges below the steel beam ends on the South). A portion of the slab had been uncovered a utility line, confirming a thickness of 12 inches. CONCLUSIONS: The concrete slab at the shop addition of 12613 Mile Road is part of a structure that is still under construction. The slab has not experienced a design level event. . 3o8 N. Hyland Park Dr. . Glenwood Springs . Colorado . 8t6ot . 97o-366-869o 1261 3 Mile Road Page Three Slab Levelness: The measured levelness of the slab was within the construction tolerances I would anticipate for a structure of this size and use, although these tolerances are considered as part of the construction phase, prior to any significant design load event. Slab Serviceability: The monolithic concrete pour (no separation of slab and footings) despite being a detail in the actual IRC code, will lead to visible cracking that is the result of a rigid and brittle construction element (concrete) transitioning from a location of high stiffness (footing) to little stiffness (approx. four times less) in the slab. These cracks will be exacerbated by gravity loading effects and any lateral transitioning ofthe supports of the steel beams once the walls and beams experience a design level event. Anticipate Backfill Effects on Slab: The introduction of backfill on the North wall combined with a design level lateral event (most likely seasonally saturated high density fill) against the'West and North walls may have a substantial impact on the performance ofthe 4" thick concrete slab on grade and its associated thickened edge footing. This impact may affect other structural systems that are beyond the scope of this report. Frost Depth: The bottom of the slab edge on the East and South is shallower than the typical 36" frost protection requirement of Garfield County and the requirements of R403.1.4.1. There is no horizontal foam insulation in conformance with IRC Section R403.3.1. or figure R403.3 (3). Frost heave effects would include seasonal vertical differential movement. It is my experience that water saturation and soil type are large determinants of frost heave. Based on the level survey taken during the inspection, frost heave has caused negligible movement to date. RECOMMENDATIONS: I would recommend an aggressive site drainage plan complete with compacted soil cap, steeply sloping swales, gravel backfill, weep holes and proper lifts of compaction in an effort to keep water away from the walls. Roof gutters with controlled discharge lines would be an asset. Specifications regarding an aggressive drainage plan are beyond the scope ofthis report. Slab Serviceability: The slab can be anticipated to continue cracking along the boundary between thick and thin slab areas. Cracks should be periodically monitored for moisture intrusion. Vertical separation of slab edges at a crack should raise concern. Cracks may be controlled by saw cutting control joints (I. Il4 deep x 1/8" wide) at these transition locations, although the existing cracks running directly parallel to the existing control joints are indicative that this method of remediation may have little effect. Retaining Wall Monitoring and Anticipated Movements: I would recommend that the retaining walls be monitored for plumbness and bowing, both horizontally and vertically. Monitoring should include the pilasters and wall. , 3o8 N. Hyland Park Dr. . Glenwood Springs . Colorado . 8t6ol . 97o-366-869o 1261 3 Mile Road Page Four Failure of the slab at the retaining wall interface would be recognized by cracks parallel to the wall, first on the underside of the slab, and finally on the top surface. The slab edges at these cracks would be charactenzedby an abrupt change in elevation, and an over rotation of the top of masonry piers and/or walls towards the building interior. Anticipated deflection of a properly designed and constructed foundation system loaded by the conditions found at 12613 Mile Road is beyond the scope of this report. Per the ASCE 7-10 Table 12.I2-I, allowable story drift at the top of wall should not exceed'77o of the wall height, or in this case three quarters of an inch. Horizontal and vertical bowing between masonry pilasters should not exceed IJlzO (L = length of wall) per IRC Table R301.7. Another alternative to the monitoring solution would be to calculate the capacity and verify code compliance of the foundation walVslab interface system with the anticipated loads. Analysis would include strength and serviceability checks and is beyond the scope of this report. Soil design parameters from a qualified Geotechnical Engineer would ensure an accurate analysis. It should be noted that the reinforcement was not inspected prior to grouting and concrete pouring and that such analysis would be based on an "assumed-as-reported" reinforcement condition. Frost Effects: The foundation frost effects can be remediated. I would recommend the previously mentioned IRC reference as the most prominent solution in areas without existing exterior slabs. Keeping moisture away from the slab base will help minimize heave. Areas already covered by driveway slabs (South) may be shielded in part by the exterior concrete slab on grade. LIMITATIONS: The slab on grade with thickened edges that I observed was readily accessible using conventional means of access and observation. My site observation and report does not: o Include numerical analysis of the existing CMU retaining walls and pilasters, slab on grade, thickened edge slab, reinforcement or any associated components or reinforcement.¡ Predict that the gravity or lateral systems (framing and foundation) of any and all structural, waterproofing or drainage materials, components and systems will perform satisfactorily following my inspection. o Warranty or approve (express or implied) the existing work or the means and methods used to arrive at the current as-built condition nor any other aspect of construction.o Warranty or approve (express or implied) the plan specifications that were available for my review at the time of inspection. o Imply that the monitoring of the masonry walls and pilasters will identify a problem prior to sudden failure. The as-built reinforcement and grouted conditions of the walls and slab are unknown and unverified. Stability analysis was beyond the scope of this report. Investigation and inspection of the walls was also beyond the requested scope. , 3o8 N. Hyland Park Dr. . Glenwood Springs . Colorado . 8t6ol . 97o-366-869o I261 3 Mile Road Page Five The purpose of the site visit was observation of the thickened edge concrete slab on grade only. The site visit does not relieve the contractor of his responsibilities for performing the work in accordance with the submitted permit drawings and building code specifications. This concludes this report. Please contact my office with any questions or comments. Sincerely, %il C Michael J. Baca, P.8., NCEES Principle Design Engineer cc:mitch(âpeakdesi e4. org r Jo8 N. Hyland Park Dr. . Glenwood Springs . Colorado . 8t6ot . 97o-366-869o