What will happen if I apply 220 dc voltage to a 220 ac load?
An incandescent bulb will do fine. The 220 V AC is the RMS value, for Root Mean Square. The sine's amplitude will be \$\sqrt{2}\$ higher than that, or 310 V. But the RMS value tells you what equivalent DC voltage you would need to get the same power, so that's exactly what you need. The bulb will use the same power and light as bright under 220 V AC as DC.  

Switching on an incandescent bulb may cause a large current peak: the cold resistance is only about a tenth of what it is when the lamp is lit, and when the voltage applied is high at that time the lamp may break. You may have noticed that if a bulb breaks it always does when switching on. So at AC worst case is when you switch on at the peak of the sine, at 310 V. But there will be lots of cases when the voltage is lower when switching on, even zero if you just happen to switch on during a zero-crossing of the sine. In fact that's the best thing to do for the bulb's longevity.  

At DC you don't have this; anytime you switch it on it will be 220 V. Not as bad as 310 V, but you can't use zero-crossing switching either.

about RMS
Why do we use RMS value instead of just the average? The average of a sine is just zero, so that doesn't help at all. If we want to know how much power a voltage generates in a load we have to use the power equation  

\$ P = V \times I = \dfrac{V^2}{R} \$  

It's the second form we're interested in. Power is proportional to voltage squared, that's what the "S" in RMS comes from, we square the voltage.  



The blue sine is our AC voltage, 1 V peak. The purple curve is that voltage squared, and the yellowish is the average of that, or mean: the "M" in RMS. It's precisely 0.5 V\$^2\$. It has still the dimension of voltage squared, so to get to a voltage quantity we take the square root of that, that's \$\frac{\sqrt{2}}{2}\$ V. The "R" in RMS. So RMS spelled out in full means: "the square root of the average of the voltage squared".  

This shows that the amplitude (1 V) is \$\sqrt{2}\$ higher than the RMS value. That's where the 310 V comes from: 220 V \$\times \sqrt{2}\$ = 310 V.