This is a difficult piece to analyze because the sections are rarely divided clearly. Instead, Beethoven uses the end of one phrase to begin another - in a word, ellision. Rather than finishing cadences, the expected resolution of one cadence is the first chord of the next phrase.
In broad terms, this segment is closed, rounded binary form.
The A section begins with an expository double parallel period that lasts for the first 23 measures. The two phrases of each half are asymetric. The first phrase is four measures long and ends with a perfect authentic cadence, and the second phrase, after being extended, is eight measures long and ends with a half cadence.
The first phrase of the second half begins with the first four notes of the main theme, then modulates to F# major. The second phrase finishes six bars later with a perfect authentic cadence in F# major. Because it modulates to F# major, it's closed rather than open (in my opinion).
Then comes the B section, which is comprised of three short expository sections. At first listen, they sound as though they function as transitions or developmental sections, but the material first presented in this section is used again throughout the movement. Also, they lead nowhere and hardly develop the main theme.
The first section lasts from measure 23 to measure 38 and is a double parallel period. The next section lasts until measure 46 and is a period in B major. Then comes the third section which lasts until measure 57 and, through an ellision, is linked to the return of the A section, which is the last four measures of this segment - the rounding begins in measure 57.
Structural phenomena and cadences are far too numerous to explain in any detail.