钢筋混凝土井字梁是从钢筋混凝土双向板演变而来的一种结构形式。双向板是受弯构件,当板很厚时,板的下部受拉区的混凝土一般都不考虑它的抗拉作用,受拉主要要靠下部钢筋承担。因此,在双向板的跨度较大时,为了减轻板的自重,我们可以把板的下部受拉区的混凝土挖掉一部分,让受拉钢筋适 Reinforced concrete cross-beam is a two-way plate from the evolution of a structural form. Two-way plate is a flexural member, when the plate is very thick, the lower part of the slab of the concrete slab generally do not consider its role in tension, mainly by pulling the lower part of the steel bear. Therefore, when the span of the two-way slab is large, in order to reduce the self-weight of the slab, we can dug a part of the concrete in the lower slab of the slab so that the tensile strength of the slab