Assignment #2
contact | homepage | spring 2008 index for ARCH 264/564 | current index for ARCH 264/564 | homework index | textIssued Feb. 26, 2008.
Due: March 4, 2008
1. Wood column analysis: A first-floor 6x8 Spruce-Pine-Fir South No.1 interior column supports a tributary area of 100 sq.ft. per floor in a residential structure with loads as follows: L = 40 psf (floors only); D = 15 psf (all floors and roof); S = 40 psf (roof only); and LR = 30 psf (roof only). The column has an effective length of 8 feet. Ignore live load reduction for this problem. How many stories tall can this building be, with such a column at the first floor?
2. Wood column design: A triangular (gable) truss is being designed for a single concentrated load of 8,300#. This load consists of snow and dead load, so the duration of load factor, CD = 1.15. The angled top chords consist of double 2x members, braced at the quarter points, so that their effective length can be taken as 1/4 of the distance from point "A" to point "C." Using Douglas Fir South No.2 lumber, and assuming an initial stability adjustment factor, CP = 0.5, design the double 2x members. That is, find the required area based on the assumed adjustment factors; then check (analyze) the capacities of all likely candidates using the actual values of all adjustment factors (CD, CF, CP) to see which one actually works best. Do not try the 2x3.
3. Steel column analysis:
a) Using the steel column analysis tables (A-7.3 or A-7.4) find the capacity of an "extra strong" steel pipe column with a 6" nominal diameter. See Table A-4.8 for section properties (note that the radius of gyration is given directly) and Table A-3.11 for guidance on yield stress (pay attention to note 2). The column is 20 feet high, and is modeled as pin-ended (hinged at both ends).
b) As a check, compute the radius of gyration for the section based on the equation: r = sq.rt.(I / A).
c) Will this column buckle elastically or inelastically?
d) Will a W12x50 be weaker or stronger than the 6"-diamater pipe, given the same effective length and the same yield stress? Base your answer only on a comparison of radius of gyration for the two sections.
4. Steel column design: Design the steel column hidden inside the stone-clad supports for the superstructure of Uris Hall (see various photos below). We'll make some very approximate assumptions* about loads and dimensions: Assume that the load on the tributary area, shown in green on the plan below, is distributed equally to all 8 columns supporting the "Vierendeel" truss on the perimeter of the building (which we assume to be symmetrical); use a live load, L = 50 psf (for 3 floors) and consider live load reduction, a dead load, D = 47 psf (for 3 floors + the roof), and a snow load, S = 35 psf (see Tables A-2.1 - A-2.3 to confirm these loads) to find the governing load combination; assume that the effective length (height) of the column is 10 feet; and assume that the column supports three stories of live and dead load, plus the roof (dead load, and snow or construction live load). The building was constructed in the 1970s, but we will assume A-992 steel. Use design Table A-7.2. Architect: Skidmore, Owings & Merrill LLP.
All photos by J. Ochshorn
* Plan dimensions and column height are based on blind guesses only; I didn't actually go into the building and measure anything.
© 2008 Jonathan Ochshorn. First posted 25 February 2008. Last updated: 25 February 2008