“L”形槽不出筋叠合板承载性能足尺试验研究
刘威 , 郭小农 , 文艺 , 王兵 , 周森 , 徐军 , 戴靠山
工程科学与技术 ›› 2025, Vol. 57 ›› Issue (06) : 213 -221.
“L”形槽不出筋叠合板承载性能足尺试验研究
Experimental Study on Bearing Capacity of Full-scale Composite Slabs with L-shaped Rabbet
针对传统叠合板外伸钢筋严重影响施工质量和效率的问题,提出“L”形不出筋叠合板端部设计新方法,该方法采用预设“L”形槽孔来放置板边、板间的连接钢筋,避免了板端出筋,具有制作、储运、施工方便等优势,可大幅提高施工效率。为探究该“L”形槽端部设计方法对板梁连接处的整体性以及对叠合板承载性能的影响,本研究采用堆载的方式对6个带端梁的足尺楼板试件进行了静载试验,其中,3个“L”形槽不出筋叠合板、2个传统叠合板以及1个同尺寸现浇整板。采用应变采集仪、高精度位移计和裂缝观测仪获得了试件关键部位的试验数据,如端部“L”形钢筋、传统叠合板端部伸出钢筋的应变,叠合板跨中挠度,跨中裂缝宽度、间距等并进行了分析。结果表明:“L”形槽配合“L”形筋的结构设计可起到与传统纵向钢筋一致的连接效果,其“L”形钢筋弯折与“L”形槽相互作用限制了板端部钢筋的滑移,虽然“L”形钢筋长度较短,较传统伸出钢筋与后浇混凝土黏结强度也略低,其仍然能有效传递荷载;新型端部构造对板的跨中承载力影响微小,“L”形槽不出筋叠合板与传统叠合板的力学性能总体相近,满足正常使用极限状态和承载能力极限状态性能要求。通过试验初步验证了“L”形槽不出筋叠合板构造设计的可行性。
Objective Traditional composite slabs require protruding reinforcement bars in the prefabricated base plate during production to ensure the integrity of the interface between joints and beam-panel connections. However, these protruding bars hinder the handling and stacking of components, adversely affecting on-site construction and component quality. Therefore, this study proposes a construction method for composite slabs with an L-shaped rabbet that eliminates the need for protruding reinforcement bars. Methods This study conducted static loading tests on six full-scale floor slab specimens with end beams to investigate the effect of the L-shaped rabbet end design method on the integrity of beam-panel connections and the bearing capacity of composite slabs. The specimens consisted of three composite slabs with L-shaped rabbets (design method one), two traditional composite slabs, and one cast-in-place solid slab with the same dimensions. The L-shaped rabbet composite slabs served as the experimental group, while the remaining slabs were designed traditionally and served as control groups 1 and 2, respectively. The study compared the load-bearing capacity and crack resistance of the new slabs. The loading was applied by stacking weights, with each weight block weighing 1 ton (900 kg). Each floor slab accommodated up to nine weight blocks in a single layer. The loading sequence followed a centrally symmetrical pattern to ensure even stress distribution during testing. The measurement parameters during the test included: 1) the number of weight blocks applied; 2) vertical displacement at the mid-span and on the upper part of beams, and horizontal displacement at the lower part of beams; 3) strain of reinforcing bars under stress; and 4) crack width at the mid-span and at the interface between the slab and beams. Strain gauges were attached to the reinforcing bars on the upper and lower surfaces of the composite slabs. Displacement meters were installed at the slab ends, mid-span, along the beam edges, and at the top. Crack depth and width were observed using a crack depth-width gauge under various loading conditions. Instruments such as strain acquisition devices, high-precision displacement meters, and crack observation tools were utilized to collect data from critical areas of the specimens. These included strain on L-shaped reinforcement at the ends, strain on protruding reinforcement at the ends of traditional composite slabs, deflection at the mid-span of composite slabs, and crack widths and spacings at the mid-span. These data provided a detailed basis for analyzing the overall performance of the floor slabs and the local performance of steel and concrete components. Results and Discussions Upon analyzing the experimental results, the study evaluated the number, spacing, and width of mid-span cracks, as well as the width of end cracks, as observation indicators. The crack development process in each group of slabs was similar. Cracks initially appeared at the locations of maximum bending moments at the slab ends and mid-span. As the load increased, both the number and width of mid-span cracks increased continuously, with smaller crack spacing and transversely extending cracks, exhibiting typical flexural failure characteristics. Regarding the number of cracks, the new slabs had an average of 13.3 mid-span cracks, close to the 14 cracks observed in traditional slabs. In terms of crack spacing, the average spacing for the new slabs was 10.96 cm compared to 9.275 cm for the traditional slabs, indicating a small difference. This finding indicated that, compared to traditional slabs, the new end construction did not reduce the bearing capacity at the mid-span. Regarding crack width at the slab ends, under a uniformly distributed load of 27.9 kN/m2, the end crack width at each sampling point indicated that the new slabs exhibited similar crack widths to traditional slabs and performed significantly better than the cast-in-place slabs. This similarity was evident from the crack width data and the consistent changes in the curve slopes between the two slab types, confirming that the L-shaped rabbet end design provided comparable overall integrity at the beam-panel connections to that of the traditional protruding reinforcement method in composite slabs. Regarding deflection, the mid-span deflection was considered the representative value. The development of deflection in the new slabs was similar to that of the traditional slabs. The rate of deflection increase in the new slabs was slightly lower than that in traditional slabs, and the deflection at the limit state of bearing capacity was also lower, while the cast-in-place slab demonstrated the lowest stiffness. Based on a comprehensive analysis of deflection and cracking behavior, the end construction with L-shaped reinforcement did not significantly affect the bending stiffness at the mid-span of composite slabs. Regarding strain, similar to traditional reinforcement, the L-shaped reinforcement experienced minimal compressive stress during normal use, particularly before concrete cracking, and contributed little to the bending capacity at the member ends. As the height of the compressed zone decreased, the L-shaped reinforcement at the ends began to bear tensile stress. In the later stages of loading, both the L-shaped reinforcement in the new slabs and the protruding reinforcement in traditional slabs yielded, fully utilizing the load-bearing capacity of the reinforcement. The design of the L-shaped rabbet compensated for the potential reduction in bond strength caused by the shorter length of the L-shaped reinforcement. Conclusions The width and distribution of end cracks in the new slabs are highly similar to those in traditional slabs and significantly better than those in cast-in-place slabs using the L-shaped rabbet during the loading process. This finding indicates that the L-shaped end design method provides sufficient reliability in beam-panel connections. The L-shaped bend restricts relative slippage between the reinforcement and the concrete, ensuring a stable connection between the slab end and the main beam. It compensates for the potentially low bond strength caused by the shorter length of the L-shaped reinforcement, enhancing structural safety. The load-bearing capacity of the new slabs did not significantly decrease and was equivalent or nearly equivalent to that of traditional protruding reinforcement composite slabs, satisfying the requirements for normal service limit state and ultimate limit state conditions. This preliminary validation confirms the feasibility of the L-shaped rabbet design for composite slabs without protruding reinforcement at the ends.
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