【作者】 徐勇；

【导师】 史才军；

【作者基本信息】 湖南大学 ， 土木工程， 2023， 硕士

【摘要】 地聚物混凝土是一种新型的绿色低碳建筑材料,更符合当今土木工程绿色发展的需求,且表现出优异的力学性能和耐久性能。但是国内外有关地聚物混凝土的研究主要集中在材料性能层面,为使地聚物混凝土能更广泛的应用于实际工程中,目前国内外学者对地聚物混凝土结构,特别是梁的研究逐渐增多,其中地聚物混凝土梁的抗弯性能受到了重点关注。但目前关于地聚物混凝土梁抗弯性能的研究大多集中在矩形截面梁,缺乏对T形截面梁的研究。相比于矩形截面梁,工程中使用T形截面梁既可节约混凝土、又能减轻自重,且受力性能及抗变形性能更优。因此需对地聚物混凝土T形梁的抗弯性能进行研究。本文共设计与制作了21根地聚物混凝土T形梁和3根普通混凝土T形梁,以混凝土类型、混凝土强度、纵筋配筋率、翼缘宽度、翼缘厚度作为研究变量,对所有T形梁开展四点弯曲试验,测试了承载能力、挠度、纵筋应变和裂缝行为等,得到的主要结论如下:(1)将混凝土强度等级为C30、C50和C70的地聚物混凝土T形梁的抗弯性能与普通混凝土T形梁进行了系统对比。结果表明:相比于普通混凝土T形梁,地聚物混凝土T形梁具有相似的裂缝行为、破坏模式、荷载-跨中挠度关系曲线发展规律、屈服荷载以及极限荷载,但其裂缝发展更快、数量更多、分布散乱,抗弯刚度和开裂荷载较低,屈服和破坏挠度、跨中纵筋应变较大。另外,地聚物混凝土T形梁的弯曲延性明显高于普通混凝土T形梁。(2)系统研究了混凝土强度、纵筋配筋率、翼缘宽度和翼缘厚度对地聚物混凝土T形梁抗弯性能的影响。结果表明:随着地聚物混凝土强度增大,地聚物混凝土T形梁的各项抗弯性能均有不同程度提升,其中开裂荷载和跨中纵筋应变受混凝土强度增大影响显著,而且在不同翼缘尺寸的地聚物混凝土T形梁中,这些影响规律均存在。纵筋直径从12mm增大至20mm,纵筋配筋率从0.72%增大至2.04%,地聚物混凝土T形梁均发生适筋梁破坏,各项抗弯性能均显著提升,就是其弯曲延性会下降,另外,根据我国规范设计的地聚物混凝土少筋T形梁和超筋T形梁也发生了如期的破坏过程。将翼缘宽度从200mm逐步增加到500mm,地聚物混凝土T形梁的抗弯刚度、破坏挠度、屈服荷载、极限荷载、弯曲延性均增大,屈服挠度、跨中纵筋应变均减小,开裂荷载无明显变化,当翼缘宽度与腹板宽度之比超过3.33后,地聚物混凝土T形梁的极限荷载增加很小,且荷载-跨中挠度关系曲线多部分几乎重合,表明越宽的翼缘宽度,也只是靠近腹板的一部分宽度能充分承担荷载,但增加翼缘宽度,弯曲延性会显著增大。增加翼缘厚度对地聚物混凝土T形梁各项抗弯性能的影响与增加翼缘宽度相似,但影响规律受混凝土强度等级影响较大。(3)在本文试验数据的基础上,分析了地聚物混凝土T形梁在正常使用极限状态下的承载能力的主要影响因素,并对现行规范相关内容的适用性进行评估。结果表明:地聚物混凝土T形梁的正常使用极限荷载比普通混凝土T形梁低15.60%-41.18%;地聚物混凝土T形梁的正常使用极限荷载随着混凝土强度、纵筋配筋率、翼缘宽度和翼缘厚度的增大均呈增大趋势;我国规范GB50010-2010的最大裂缝宽度理论计算公式适用地聚物混凝土T形梁,预测其在正常使用极限状态下的承载力时的精度在可接受范围内,美国规范ACI 318-19计算的最大裂缝宽度可靠性较差,预测精度较差。(4)探究了我国规范GB50010-2010和美国规范ACI 318-19中受弯构件的正截面受弯承载力理论计算公式对地聚物混凝土T形梁的适用性,发现我国规范GB50010-2010的预测值与试验值吻合较好,而美国规范ACI 318-19的预测值比试验值偏小一些,我国规范GB50010-2010的正截面受弯承载力公式更适用地聚物混凝土T形梁,但美国规范ACI 318-19的安全储备更高。更多还原

【Abstract】 Geopolymer concrete is a novel and eco-friendly construction material that aligns with the requirements of modern civil engineering for green development.It boasts exceptional mechanical properties and durability.However,research on geopolymer concrete has primarily focused on material performance,and to make it more practical in engineering,studies on geopolymer concrete structures,particularly beams,are gaining momentum.In this regard,the flexural performance of geopolymer concrete beams has garnered attention.Nonetheless,most studies have concentrated on rectangular section beams,with a lack of research on T-beams.T-beams offer advantages over rectangular beams,such as reduced concrete usage,lower self-weight,and better force performance and deformation resistance.Therefore,investigating the flexural performance of T-beams made of geopolymer concrete is essential.This thesis involved the design and fabrication of 21 geopolymer concrete Tbeams and 3 plain concrete T-beams.The T-beams were subjected to four-point bending tests,with concrete type,strength,longitudinal reinforcement rate,flange width,and thickness as research variables.The tests measured the load carrying capacity,deflection,longitudinal reinforcement strain,and crack behavior.The main conclusions obtained were as follows:(1)A systematic comparison was conducted on the flexural properties of geopolymer concrete T-beams with concrete strength classes of C30,C50,and C70,in comparison to plain concrete T-beams.The results indicate that geopolymer concrete T-beams exhibit similar cracking behavior,damage modes,and load-median deflection relationship curves as ordinary concrete T-beams.However,geopolymer concrete Tbeams display faster crack development,a greater number of cracks with a scattered distribution,lower flexural stiffness and cracking loads,and larger yielding and damage deflections and mid-span longitudinal strains.Additionally,geopolymer concrete T-beams demonstrate significantly higher flexural ductility than plain concrete T-beams.(2)This study systematically investigated the impact of concrete strength,longitudinal reinforcement rate,flange width,and flange thickness on the flexural performance of geopolymer concrete T-beams.The results indicate that increasing the strength of geopolymer concrete improves the flexural properties of T-beams to varying degrees,with cracking load and mid-span longitudinal reinforcement strain significantly affected.These patterns were observed across T-beams with different flange sizes.Moderate reinforcement beam damage was observed when longitudinal reinforcement diameter increased from 12 mm to 20 mm,and reinforcement ratio increased from 0.72% to 2.04%.Flange width was found to increase flexural stiffness,damage deflection,yield load,ultimate load,and bending ductility,while reducing yield deflection and spanwise longitudinal bar strain.However,the cracking load did not change significantly.Increasing flange thickness had a similar effect to increasing flange width,with the impact depending on concrete strength grade.When the ratio of flange width to web width exceeded 3.33,the ultimate load increase was minimal,and the load-span deflection relationship curves overlapped in many parts,indicating that only a portion of the flange width near the web could fully bear the load.Increasing flange width significantly improved bending ductility.(3)This thesis analyzes the main factors affecting the load carrying capacity of geopolymer concrete T-beams in the limit state of normal use,based on test data.The study also evaluates the applicability of the relevant contents of the current code.The results indicate that the normal service limit load of geopolymer concrete T-beam is15.60%-41.18% lower than that of ordinary concrete T-beam.However,the normal service limit load of geopolymer concrete T-beam tends to increase with the increase of concrete strength,longitudinal reinforcement ratio,flange width and flange thickness.The theoretical formula of maximum crack width of China’s specification GB50010-2010 is suitable for T-beams of geopolymer concrete and accurately predicts its load bearing capacity in the limit state of normal use.Conversely,the maximum crack width calculated by the American code ACI 318-19 is less reliable and has poor prediction accuracy.(4)The applicability of the theoretical formulae for calculating the flexural bearing capacity of positive section of flexural members in China GB50010-2010 and the American code ACI 318-19 to the T-beam of geopolymer concrete was investigated,and it was found that the predicted value of China GB50010-2010 agreed well with the test value,while the predicted value of the American code ACI 318-19 was a little smaller than the test value.The positive section bending capacity equation of our code GB50010-2010 is more applicable to the geomembrane concrete T-beam,but the safety reserve of American code ACI 318-19 is higher.更多还原