The overwhelming majority of Rishonim who pasken like the Chachamim (see The Overwhelming Majority of Rishonim Maintain Lo Asu Rabbim U’Mevatlei Mechitzta) maintain that a tzuras hapesach would not suffice in a reshus harabbim and that there would be a requirement of delasos. However, it is a matter of debate in the Achronim at what level, me’d’Oraysa or me’d’rabbanan, is the obligation of these delasos.
Many Achronim maintain that me’d’Oraysa, a tzuras hapesach would reclassify a reshus harabbim as a reshus hayachid. Accordingly, the requirement of delasos is only me’d’rabbanan (Rosh Yosef, Shabbos 6b; Shulchan Aruch HaRav, O.C. 364:4; Tzemach Tzedek, Eruvin the end of Perek 5; Aishel Avraham, siman 345; Gaon Yaakov, Eruvin 11a; Yeshuos Malko, O.C. 21; Aruch HaShulchan, O.C. 364:1, and Kaf HaChaim, O.C. 364:12). Since the requirement of delasos is me’d’rabbanan, we can be lenient [safek d’rabbanan l’kulla] and apply any additional heter to remove the requirement of delasos (Kanah V’Kanamon, 5:56; Livush Mordechai, 4:4, and Bais Av, 2:9:3).
Some Achronim state that a tzuras hapesach would not suffice once a street meets all the criteria of a reshus harabbim. Consequently, the requirement of delasos is me’d’Oraysa (Even HaOzer, Eruvin 6a, 22a; Bais Ephraim, O.C. 26, and Chazon Ish, O.C. 74:2-3).
Whether the delasos need to be neulos ba’laila (closed at night) or if reuyos l'hinael (fit to be closed) would suffice is another matter of debate. The Maggid Mishneh (Eruvin 17:10) states that it is dependent on whether or not we pasken asu rabbim u’mevatlei mechitzta. Those who require delasos neulos ba’laila maintain asu rabbim u’mevatlei mechitzta (Rav Yehudah and Rav Yochanan) and those who state that reuyos l'hinael would suffice maintain lo asu rabbim u’mevatlei mechitzta (Chachamim and Rav Elazar). The Bais Ephraim (O.C. 26) asserts that the disagreement is not regarding whether or not we pasken asu rabbim u’mevatlei mechitzta but only if delasos reuyos l'hinael is considered shem daled mechitzos. The opinion that allows delasos reuyos l'hinael to encompass a reshus harabbim maintains that it is regarded as shem daled mechitzos. Those who require delasos neulos ba’laila uphold that delasos reuyos l'hinael are not considered shem daled mechitzos, hence the need for neulos ba’laila.
However, all the Rishonim and Achronim (besides for the Mishkenos Yaakov) would agree that the requirement of delasos according to the Chachamim is only in a situation where a tzuras hapesach is being utilized. On the other hand, where an area is encompassed by mechitzos, there is no question at all that there is no need for delasos to close the pirtzos since the enclosed area is fundamentally a reshus hayachid (Meiri, Eruvin 22b; Tosfos Shabbos; Mayim Rabim, and Bais Meir, O.C. siman 364). Only the Avnei Nezer (O.C. 279:2), necessitates delasos me’d’rabbanan at the pirtzos even in a situation where mechitzos are being utilized. However, since the obligation is only me’d’rabbanan we can be lenient [safek d’rabbanan l’kulla].