Laminated Beam Spanning Garage is Dangerously Undersized, Causing the Floors Above to Slope GENERAL INFORMATION Date of Site Inspections: August12, 1998 Location: Matthews, NC Prepared for: Dr. James Warren | Top | Table of Contents | BACKGROUND At your request, we performed a structural investigation at the above referenced address on July 25, 29, and August 2. You were present during the inspections on July 25 and August 2. John Holton of Holton Construction Company assisted us on July 29. The purpose of the investigation was to determine how much and where the floor slopes, what is causing the problem, and how to correct it. During our field inspection, we observed the garage, first floor, second floor, and attic areas. Our inspection did not involve any intrusive work, except for the removal of acoustical ceiling tiles in the garage. For purposes of the discussion below, all directions are in relation to a person facing the front of the house. | Top | Table of Contents | DESCRIPTION The house is an 8-year old two story wood-framed structure with brick veneer cladding and a hip roof. It has a floor area of approximately 2500 sq. ft., not including the garage, and is about 38' wide by 44' long. The house is on a sloping lot. This provides space for a two-car garage and small basement area under the left rear section of the house. There is a crawl space under the front section. The garage and basement areas have an 8' high concrete block foundation, and the crawl space has a pier and curtain wall type foundation. The floors on the left rear side of the house (all levels) are primarily supported by a 5.25"" x 18"" laminated girder that spans 22.5' across the garage. The laminated girder supports 12"" pre-engineered truss joists spaced at 2'- 0"" on center. The laminated girder runs from front to back, and the truss joists run from left to right. We did not determine whether the second floor is supported with similar truss joists, because this would have involved removing the ceiling in the family room. We assume that the joist framing is the same. The attic floor is framed with standard wood joists spanning between the second floor partition walls. The joists run from left to right on the ends of the attic and from front to back in the center of the attic. Much of the roof weight is carried by interior struts that bear on the wall between the stairway hall and sitting room. The right side of the attic is the only part that is used for storage. The wall between the stairway hall and family room (directly below the wall between the stairway hall and sitting room) is supported with a 1.75"" x 12"" laminated beam that bears on the 5.25"" x 18"" laminated girder. This beam has considerable weight on it because it supports the walls on the first and second floors, part of the attic floor, and a large part of the roof. | Top | Table of Contents | OBSERVATIONS The first floor area at the juncture of the family room, stairway hall, master bedroom, and master bathroom slopes downward from surrounding floor areas. The drop is sharpest in the stairway hall, where the difference in elevation is about 1-?"" in 8'. The second floor slopes similarly. The National Association of Home Builders performance standard for levelness of wood floors is º"" in 32"" and ?"" in 20', whichever is less. The slope in your floors greatly exceeds this standard. The primary cause of the problem is sag (deflection) in the 5.25"" x 18"" laminated girder that spans across the garage. Sag in the 1.75"" x 12"" laminated beam that frames into the girder also contributes to the slope. These structural members deflected because they are not of the proper size for the imposed loads. The 18"" laminated girder spans 22.5'. According to our calculations, it supports a uniform load of 1600 lbs. per ft. and a concentrated load of 6,000 lbs. at the 12"" laminated beam connection. The total load on the beam is 42,000 lbs. The 12"" laminated beam spans 15'. It supports a uniform load of 800 lbs. per foot. The total load on this beam is 12,000 lbs. The above loading is based on minimum design loads in the North Carolina Residential Building Code. Using the above loads, our calculations indicate that the 18"" girder will deflect about 2.2"" when fully loaded. The Code allows a maximum deflection .67"" at the center of the span. The maximum deflection occurs where the 12"" laminated beam bears on the girder. Our measurements indicate that the girder is presently deflecting about 1.5"", more than twice the allowable deflection of .67"". Our calculations indicate that the 12"" beam will sag about 1.8"" when fully loaded. We did not measure the actual deflection. The Code allows a maximum deflection of .50"". Our calculations indicate that the allowable bending stresses and shear stresses are also grossly exceeded in these beams. While the floor slope is an aesthetic matter, overstressing is a safety and property damage concern. Properly designed beams should have a safety factor of at least 2.0. There is no margin of safety in these beams. | Top | Table of Contents | RECOMMENDATIONS The 18"" girder should be jacked up until it is level and a steel pipe column installed at the center of the span. Our calculations indicate that the vertical reaction at the new post will be 27,000 lbs. under full load conditions. A 4"" diameter standard steel pipe column is required to support this load. Assuming that the presumptive load bearing capacity of the soil is 2000 pounds per sq. foot, a 44"" x 44"" x 12"" concrete footing is required under the post. The footing should be allowed to cure for 7 days before any load is placed on it. When the girder is jacked up, the 12"" truss joists will be subjected to high reaction forces where they bear on the girder. The truss joists are apt to crush unless the bearing points are strengthened. According to the manufacturerís specifications, the maximum reaction force that this type of joist can withstand is 2385 lbs. We estimate that each joist will be subjected to force of 4800 lbs. (2 x 1600 x 1.50) during the jacking operation. Squash blocks must installed along the entire length of the girder at the bearing points to prevent the joists from being crushed. No jacking should be attempted until all the blocking is in place. The estimated reaction force on each of the second floor truss joists during jacking is 2550 lbs. (2 x 850 x 1.50). Since the joists can withstand 2385 lbs. of force, blocking is probably not required on this level. However, to be on the safe side, some of the joists near the stairway hall wall should be exposed so that they can be monitored during the jacking operation. If signs of distress appear, it will be necessary to block all the second floor truss joists, as well. The joists are apt to crush suddenly with little warning, so prudence should govern the decision to install or not to install blocking. The 12"" beam should be jacked up along with the 18"" girder to minimize the bearing stress at its supports. The 12"" beam does not have enough bearing length on the 18"" girder. According to our measurements, the present bearing length is only 1.25"". The Building Code requires a minimum bearing length of 3"". The 18"" girder should be widened at the support to provide 3"" of solid bearing. After the 12"" beam is jacked into position, a 3"" diameter standard steel pipe column should be installed at the center of the span. The column requires a 24"" x 24"" x 10"" footing. The footing should be allowed to cure for 7 days before any load is placed on it. If it is not practical to install a column under the beam, the beam can be reinforced with º"" steel flitch plates on each side of the beam. The flitch plates should be same depth as the beam and the same length. The flitch plates should be bolted to the beam with two rows of 5/8"" diameter machine bolts, staggered, at 12"" on center. It is anticipated that some cracks will occur in walls and ceilings during the jacking operation. Also, some of the door frames may become mis-aligned. You should have an understanding with the contractor that does the work that he will repair any damage to the floors, walls, doors, ceilings, and other building components that occurs as a result of the jacking. Because of the difficult nature of this work and the risk of damage to your house, we recommend that you employ a contractor who has experience in doing this type of work. Let us know if you need help in this regard. | Top | Table of Contents | William A. Stanton, P.E. | Top | Table of Contents | | Structural Inspections | Residential & Commercial Services |