ARCH 463/563 - ASSIGNMENT 3 - BEAMS (FLEXURE!)

DO INDIVIDUALLY

DUE: 11/7/2011


1.    Given: 8 ft tall basement wall, 6 in. thick (6.0 in.), d = 4.0 in. from soil face to center of rebar, equivalent fluid soil pressure 100 pcf (psf/ft).  Find: reasonable V.S. spacing of the following rebar sizes:

    a)    # 3
    b)    # 4
    c)    # 5

Concrete strength, fc' = 3000 psi; Grade steel, fy = 60,000 psi.

NOTE: try solving this by brute `trial and error' ... picking a bar size and spacing ... probably your first guess(es) will be off, but you can wiggle in pretty quickly.  For example, if your strength ends up 3 times the load, then decrease your spacing by a factor of 3, and try again.  And, once you get a good spacing with, say, # 4, a good spacing for # 5 would be about a_s #5 / a_s #4 as much.


2.    Concrete roof slab 6 in. thick to span 10 ft (simple span) and carry 100 psf Snow load plus its own weight.  Reinforcement will be centered 5 in. from top surface.  Calculate a reasonable rebar spacing for # 5 bars (but not to exceed 18 in. o.c.).

Check (also):

a)    min. reinforcement (0.0033)
b)    max. reinf. (limit to 0.016)
c)    deflection (using Table 9.5(a) of ACI 318)

NOTE: ... if you are comfi with the trial and error approach of the first problem - now try the more direct approach we talked about in class yesterday (11/4) ... setting the Mu equal to the phi Mn and solving (more) directly for the required steel.

FOR THE SECOND PROBLEM USE fy = 60,000 psi and f'c = 3000 psi.

Baby!