Quiz 1 Distribution

100     
100     
99     
98     
97     
97     
97     89     
97     89     
97     89     
97     89     
96     88     79
95     88     79               
95     88     78               
95     88     78               
94     87     78               
94     87     77               
93     86     77               
93     85     77     69          
93     85     76     68          
93     85     75     68          
92     84     75     68            49     
92     83     74     66            48     
91     82     73     65     57     48     
91     81     73     64     57     42     
91     80     72     64     57     41     
91     80     72     63     55     41     
90     80     70     63     50     40     28     17

Mean: 77.8, Median 81

Quiz 2 Distribution

                78.0                    
                77.0                    
                76.5                    48.5        
                76.0            59.0    48.0        
                76.0            59.0    48.0        
                76.0            58.0    47.0        
                75.5            57.0    47.0        
        86.0    75.5            57.0    46.5        
        84.0    75.0            56.0    46.5        
        84.0    74.0            56.0    45.0        
        82.5    74.0            56.0    45.0    39.0    
        82.5    73.5    65.0    56.0    44.0    37.0    
93.0    82.0    73.0    64.0    52.5    42.0    36.5    28.0
93.0    81.5    72.0    64.0    52.0    42.0    36.0    28.0
92.5    81.0    72.0    63.0    51.0    41.0    34.0    27.0
91.0    81.0    72.0    62.5    51.0    41.0    34.0    24.0
90.5    80.0    71.0    62.0    50.0    41.0    33.0    22.0
90.0    80.0    70.0    61.0    50.0    41.0    32.0    20.0

Problem 1

The most common stumbling points on this problem were parts b) and c), which requred the selectoin of an appropriate free body followed by the application of the equations of statics.

Problem 2

Although the problem did not list I_y for the given section, it did list r_y, which is sufficient to calculate the allowable buckling stress.

Problem 3

The following is an extremely clear solution explaining the steps and logic.

Problem 4

a)

The key point is that the moment strength of a reinforced concrete beam depends on two factors: the strength of the concrete, and the strength of the steel. The strength of the beam is determined by the weaker of these two, and it is much better to have the steel be weaker, since this leads much more ductile failure. The following answer, though not perfect, hits the main point on each part.

The following answer takes a slightly political angle...

b)

c)

Crack control and deflection control are the major benefits. Prestressing does not make a beam stronger.