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农村建筑中楼面、屋面的钢筋混凝土梁,常采用矩形截面,两端简单地支承在支座上,这就是钢筋混凝土矩形简支梁。针对农村缺乏结构计算力量的情况,为保证结构安全,特根据《钢筋混凝土结构设计规范》TJ10-74中有关公式编制本图表(图1)。其中受弯构件强度设计安全系数≥1.4,受弯构件斜截面受剪强度设计安全系数≥1.55,裂缝宽度≤0.3毫米,挠度≤1/200。构件采用200号混凝土,纵向受拉主筋有Ⅰ级钢及Ⅱ级钢二种。选用Ⅰ级钢时,钢筋末端须加180°弯钩;选用Ⅱ级钢时,不需加弯钩。纵向受拉主筋伸入支座内的锚固长度(从梁下支座的边缘算起),Ⅰ级钢为15d,Ⅱ级钢为10d(d为钢筋直径)。如锚固长度达不到上述规定,应将主筋向上弯起90°角,来满足需要的锚固长度(图2)。③号弯起筋伸入支座的锚固长度分为二种情况:
In reinforced concrete beams in floor and roof of rural buildings, rectangular cross-sections are often used, and the two ends are simply supported on the support. This is the reinforced concrete rectangular simple beam. In view of the lack of structural calculation power in rural areas, in order to ensure structural safety, this chart is prepared according to the relevant formulae in the “Code for Design of Reinforced Concrete Structures” TJ10-74 (Figure 1). The flexural member strength design safety factor ≥ 1.4, the flexural member shear strength shear strength design design safety factor ≥ 1.55, crack width ≤ 0.3 mm, deflection ≤ 1/200. No.200 concrete is adopted for the member, and the longitudinally-stretched main tendons are grade I and grade II steel. When Grade I steel is selected, 180° hooks must be added to the ends of the steel bars; when Grade II steels are used, it is not necessary to add hooks. The anchoring length of the longitudinally drawn main ribs extending into the seat (from the edge of the lower bearing) is 15d for grade I steel and 10d for grade II steel (d is the diameter of the bar). If the anchorage length does not meet the above requirements, the main tendons should be bent upwards by 90° to meet the required anchorage length (Figure 2). The anchorage length of No. 3 bending ribs extending into the bearing is divided into two types: