ARCH 264/564 Structural Elements

Assignment #1

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Issued Jan. 31, 2008.
Due: Feb. 7, 2008

solutions

Analyze a 4-story 50-foot high rectangular building in Portland, ME for various loads. Assume 55' x 120' overall plan dimensions, with a 15-foot wide lateral-force-resisting truss on each end wall. Story heights above grade are as follows: 1st floor at grade; 2nd floor +15.0 feet; 3rd floor +30 feet; 4th floor +40 feet; and roof at +50 feet.

Assume residential occupancy with L = 40 psf; LR = 30 psf; S = 50 psf; and a dead load, D, consisting of floor slabs only (6"-thick reinforced concrete @ 150 pcf). Remember to consider live load reduction.

building geometry

  1. Find the governing design load on a typical interior 3rd-floor column, assuming a 30' x 30' column grid (I realize that this is not consistent with the sketch: even so, just assume 30 x 30 = 900 sq.ft. of tributary area per floor for the column), and:

    a) allowable stress design, steel columns;

    b) allowable stress design, wood columns (include duration of load calculations);

    c) strength design (LRFD), reinforced concrete columns;

  2. Find and sketch the distribution of wind loads (external design pressures) on the windward and leeward surfaces of the building, assuming a wind direction as shown in the sketch above. Assume exposure "B" with Kt = I = Kd = 1.0.

  3. Find and sketch the distribution of earthquake forces on the building, assuming ground acceleration in the direction shown in the sketch above. Assume that the lateral force resisting system consists of a "special steel concentrically braced frame." As before, I = 1.0. Assume that the building site is characterized by "soft soil" conditions (site class "E").

  4. Statics review: For the determinate lateral-force-resisting trusses shown in the sketch above, find the maximum tensile force based on the distribution of seismic forces found above. Only include the seismic loads in the calculations, and assume allowable stress design (i.e., do not use any load factors). Note that the seismic story forces should be divided in two, with each half assigned to one of the trusses. Also note that the truss should be assumed to be supported at grade by a hinge and a roller. The seismic loads are transferred through the floor beams to the truss nodes at each floor and roof level.

    See Structural Elements text for statics review (p.22 for truss analysis method) or, for more detail, see: free truss chapter [PDF] from McGraw-Hill.

  5. Optional: e-mail me a www.youTube URL for use during class breaks.

© 2008 Jonathan Ochshorn. First posted 21 January 2008. Last updated: 06 February 2008