Note: The pairing of contrasting strains in these small [16-bar] waltzes is very probably the source of the paired 32-bar strains that had become the typical design by the generation of Johann Strauss, jr.
A number of years ago I constructed an informal narrative of formal designs in nineteenth-century dances and related works. In that narrative, the small forms of most dances, including the great majority of Schubert's waltzes, ecossaises, and galops, evolved gradually from 16 bars (8 + 8) to 32 bars by the middle of the century, the work of the second generation Strausses being representative. A parallel history expanded the 8-bar strain (the 8-bar theme of Caplin) to 16 (following the 16-bar period or sentence of Caplin). My history expanded these all still more to "paired 32-bar strains," the paradigm being the first waltz in The Blue Danube (An der schönen blauen Donau, Op. 314 (1867)).
The eight-bar design of the first strain might fit any of Caplin's types, period, sentence, or hybrid. The second eight-bar strain might develop the same material or be strongly contrasting, and the designs thus range from contrasting middle with cadence to a new period or sentence.
As in Caplin's system, the 16-bar theme weakens the final cadence of an eight-bar theme, permitting an expansion through a developmental continuation or through the repetitive consequent. (Note that there is a very close relationship between the 16-bar period and an 8-bar period enclosed in repeat signs.)
The 32-bar theme, then, goes one step further, weakening the final cadence of the 16-bar theme, thus permitting another level of expansion. (As with the 16-bar period, note that there is a very close relationship between the 32-bar period and a 16-bar period enclosed in repeat signs.)
Alas, such neatly reductive histories are almost always too good to be true. The first waltz of The Blue Danube does open with a 32-bar sentence, which is followed by a 16-bar period enclosed in repeat signs. The contrast is strong, including a key change, so that the two strains really sound more like a dance-trio pair -- but Strauss actually repeats the entire pair, so that the overall design is ABAB, and the key sequence D-A-D-A.
None of the other waltzes in The Blue Danube is constructed this way: nos. 2 & 3 are ternary forms whose A & B are both 16-bar themes; no. 4 also has 16-bar strains but both A & B are repeated; and no. 5 is also like no. 1 in that respect but the two strains are "flipped," -- the first is a repeated 16-bar theme, the second a 32-bar period.
If this hints at variety of design in the individual numbers of the Strauss waltzes, that is a much better characterization than my too-clean developmental history. Here a few other examples:
Morgenblätter, Op. 279 (1864): all five waltzes are in dance-trio designs played as ABA. Nos. 1 & 2 are 32 bars in the first strain, 16 in repeat signs in the second. Nos. 3-5 use 16-bar themes in repeat signs for both strains.
Rosen aus dem Süden, Op. 388 (1880): the first waltz is quite close to the first waltz in The Blue Danube, but the first strain is also enclosed in repeat signs; the second waltz relates to the first waltz in The Blue Danube in a different way--again 32 + 16, but the repetition of the second strain is dropped, for an overall ABA design; no. 3 is ABA, with repeat signs for both 16-bar strains; no. 4 (the last in this set) is in effect a 64-bar theme: the final cadence of a 16-bar theme closes normally but the repetition is written out as a reorchestrated tutti whose own final cadence is a PAC in the dominant key, not the tonic, after which what would otherwise have been a second strain rushes in with its own 32-bar sentence (Strauss even tacks on an 8-bar coda extension).
Geschichten aus dem Wienerwald, op. 325 (1868): no. 1 is similar to the last waltz in Op. 388, but the entire 64-bar complex is repeated; no. 2 has two 16 bar strains in repeat signs set out in ABAB format; no. 3 differs only in its ABA format; no. 4 differs in that the repeat of the second strain is written out due to orchestration changes and the format is simply AB; no. 5 is like no. 3.
Final note: these descriptions are based on the piano solo editions (most Strauss waltzes were first published that way). I have not consulted the orchestral scores.
