薄壁U形外包钢再生混合梁受弯性能试验研究

Flexural tests on thin-walled U-shaped steel beams filled with demolished concrete blocks and fresh concrete

对8个含有废弃混凝土块体的薄壁U形外包钢再生混合梁及4个全现浇组合梁进行受弯试验,研究废弃混凝土块体取代率、U形外包钢壁厚、梁底纵筋配筋率等参数对试件受弯性能的影响,给出试件受弯承载力的简便计算式,在总用钢量基本一致的情况下对比薄壁U形外包钢再生混合梁和常规钢筋混凝土梁的受弯承载能力.结果表明：废弃混凝土块体取代率在0～40％之间变化对薄壁U形外包钢再生混合梁的初始刚度、延性、受弯承载力、U形外包钢与内部混凝土之间的相对滑移、应变发展特征无明显影响;为提高薄壁U形外包钢再生混合梁的受弯承载力,增配梁底纵筋比增加外包钢壁厚更为经济有效,同时梁底纵筋还使试件的屈服前刚度有所提高;梁底配置纵向钢筋可显著减小U形外包钢与混凝土之间的相对滑移,此时梁端截面为相对滑移最小截面;根据塑性理论给出的计算式可较好地预测薄壁U形外包钢再生混合梁的受弯承载力,在总用钢量基本相同的情况下该类构件具有与常规钢筋混凝土梁几乎相当的受弯承载力.

Eight thin-walled U-shaped steel beams filled with demolished concrete blocks （DCBs） and fresh concrete （FC） , and four thin-walled U-shaped steel beams filled with FC alone were tested under sagging bending, and the influences of some parameters （i. e. , replacement ratio of DCBs, thickness of U-shaped steel, and longitudinal reinforcement ratio） on flexural behaviors of the specimens were investigated. Simple calculation formula for flexural capacity of the specimens was applied, and a comparison between the flexural capacity of the specimens and that of conventional reinforced concrete （RC） beams with identical total steel weight was conducted. It is found that： the influences of the replacement ratio of DCBs within a range of 0-40% on initial stiffness, ductility, flexural capacity, relative slip between U-shaped steel and concrete, and strain developing of the specimens are very limited; in comparison with the increasing of the thickness of the U-shaped steel, the adding of longitudinal bars is a more effective way to improve the flexural capacity of the thin-walled U-shaped steel beams filled with DCBs ＆ FC, and the longitudinal bars is of help to enlarge the pre-yielding stiffness of the specimens to some extent; the relative slip between U-shaped steel and concrete can be reduced significantly by adding longitudinal bars at the bottom of the beams, and in this case the beam＇ s end section is the cross section with minimum slip ; a simple formula derived from the plastic theory can be used to predict the flexural capacity of the thin-walled U-shaped steel beams filled with DCBs and FC, and the flexural capacity of these beams is almost the same as that of the conventional RC beams with identical total steel weight.