HW4 (Due April 25) CIVL 3131 Problem 1:
A simply supported built-up I-section beam of 28 ft span carries a concentrated load P at mid-span.
The load is 20% dead load and 80% live load. Determine the maximum service load P that can be
permitted to be carried. The beam is laterally braced at the two supports as well as the mid-span.
Live load deflection may not exceed L/360 (not an AISC Specification requirement). ¾ x 12 ½ x 30 Problem 2:
- The two-span continuous girder shown below is subjected to the following unfactored loads:
PDL = 45 kips (dead)
PLL = 30 kips (live)
- For this problem, there is no live load reduction, but do consider “pattern loading” such that the
member demands are maximized (two primary cases considering: positive moment in a span and
negative moment at the center support).
- Consider self-weight of the member in the design, but self-weight need not be considered when
calculating Cb.
- No deflection check is required.
- Lateral bracing is provided at the load and support points.
- Analysis may be conducted using tabulated solutions (such as Table 3-23 in the AISC Manual) or using
computer tools (such as MASTAN2). If a computer program is used, do not submit many pages of output, but
clearly summarize the key results. a) Select the lightest W section (A992 steel) for the given loading. (Design tables in AISC Steel Construction
Manual may be used to make your selection, but clearly document your procedures and present calculations
that verify the design strength values from the table.) b) For the critical loading case(s) that account for pattern loading, plot factored shear force and bending moment
diagram
c) Calculate (do not refer to a table) the design shear strength and show that it is adequate. Problem 3:
A two-span beam has a large live load (PL = 100 kips, unfactored) that can be placed anywhere
between A and D. Since the dead load (beam self-weight) is small compared to the live load, it will
be neglected in this problem. The beam has a hinge at C, is oriented for strong-axis bending and
has both flanges laterally braced at A, B, C and D.
a) Identify two locations where PL should be placed to maximize moment demand. For each load
location, determine the (Mmax, Lb, cb) combination that will be used for design.
b) Choose the lightest W section (A992), Fy = 50 ksi) for the flexural demands from a). Check for
shear. Problem 4:
A critical stage of construction is shown in the
photo. The contractor will need to temporarily
place a 40 kip load on top of one of the beams
at mid-span. These beams are pin-connected
to the cantilevered girders. Choose the lightest
A992 Gr 50 steel section to support this
construction load. There is no deflection criteria.
Ignore beam self-weight for this problem. Show
all check!

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