ECC/钢筋混凝土叠合梁正截面受弯承载力试验与理论研究

为了探究ECC/高强钢筋混凝土叠合梁的正截面受弯特征,以及ECC层厚度对叠合梁整体受弯性能的影响,做了两组共5根梁试件的正截面受弯试验。发现与高强钢筋混凝土梁相比,叠合梁的承载力更高,相同荷载下的挠度值和最大裂缝宽度较小。在受弯全过程中其截面应变仍符合平截面假定,钢筋与ECC也可以实现协调变形,说明受拉区使用ECC可以使得高强钢筋的应力得到充分发挥。但ECC层厚度过大可能会使叠合梁发生脆性破坏。进一步地,在此研究的基础上,对已有ECC的本构模型进行简化,忽略其应力强化贡献,并运用叠加原理,提出一种用于计算ECC/钢筋混凝土叠合梁正截面受弯承载力的方法,将计算结果与试验结果及诸多文献结果进行比较,发现吻合度较高。     

塑性铰区采用FRC柱试验研究及正截面承载力分析

采用简化的纤维增强混凝土应力应变关系,根据截面变形的平截面假定和截面力的平衡方程,推导出塑性铰区采用纤维增强混凝土柱在不同极限状态时的曲率。根据各极限状态点曲率,求得截面上各分布力,对截面形心轴取距,到塑性铰区采用FRC柱的开裂、屈服、峰值和极限点的弯矩表达式。与试验结果对比表明,计算值与试验值吻合较好。     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

三连栋日光温室拱式桁架结构静力分析与结构优化

为研究三连栋日光温室的合理性和安全性,通过有限元软件ANSYS对某三连栋日光温室拱式桁架结构进行了三维空间建模,并对该结构在多种荷载组合工况下进行静力分析,探讨了计算方法和结构的优化方法。结果表明：该温室结构吊物拉杆挠度偏大,不能满足设计要求。在原结构的基础上对有竖向拉杆的优化结构进行了计算分析,计算结果与理论值较吻合,且设计安全合理。研究结果为拟建者温室建模和温室结构优化提供参考。     

m法下的双曲线型p-y曲线

工程中基桩大多处于复杂的成层地基中,鲜有位于单一土层中,从宏观角度出发,引入初始地基比例系数,提出了基于m法的双曲线型p-y曲线。某现场7根试桩地基土非线性显著,实测和理论计算的地面处桩身水平位移水平荷载关系曲线均呈良好的二次抛物线关系,且理论与实测曲线吻合良好,验证了本文p-y曲线模型。地基土非线性对桩身最大弯矩、桩侧地基土压力影响显著,不容忽略。工程实际中采用m法计算基桩最大弯矩值偏小,建议乘以1.05~1.25的系数,以计入地基土非线性影响。     

GFRP肋式剪力连接件受力性能对比试验研究

剪力连接件是保证GFRP混凝土组合梁/板中两种不同材料共同工作的重要构造,设计了矩形肋和T形肋两类GFRP肋式剪力连接件,进行了3组共8个GFRP肋式剪力连接件的推出试验,包括：矩形肋开孔、T形肋开孔、T形肋不开孔3组GFRP肋式剪力连接件,得到了其破坏形态、极限承载力、荷载滑移曲线及荷载应变变化规律,重点研究肋内开孔及肋的截面形式对GFRP肋式剪力连接件受力性能的影响。试验结果表明：GFRP肋式剪力连接件的破坏形态均为混凝土劈裂破坏;对比矩形肋开孔试件,T形肋开孔试件强度高、延性好;对比T形肋不开孔试件,T形肋开孔试件强度与延性均能提高。基于试验结果,建立了考虑肋内开孔及肋截面形式影响的GFRP肋式剪力连接件极限承载力计算公式,拟合得到了GFRP肋式剪力连接件的荷载滑移曲线上升段的理论模型,建立了其抗剪刚度计算公式。     

再生混凝土与锈蚀钢筋间的粘结性能试验研究

为了探究再生混凝土结构的耐久性能,对5组不同钢筋锈蚀率(0~9%)的再生混凝土梁式试件进行加载试验。分析不同钢筋锈蚀率对再生混凝土梁式试件的钢筋应变、局部粘结应力、粘结滑移和极限粘结应力的影响。结果表明：钢筋锈蚀率大于3%时试件底部开始有细微锈胀裂缝出现;锈蚀率越大,荷载作用下钢筋应变沿锚固位置的变化曲线越平缓;局部粘结应力沿锚固段呈现出双峰分布,峰值主要集中在加载端和自由端附近;加载端附近位置滑移现象最先发生,远离加载端滑移现象延后;随着钢筋锈蚀率的增大,极限粘结强度先增加后降低,极限荷载下的滑移值增大。     

等截面钢管混凝土格构柱骨架曲线的统一算法

介绍了斜缀管式和平缀管式等截面钢管混凝土格构柱骨架曲线的计算方法并进行评价分析。研究表明,不同缀管布置形式的钢管混凝土格构柱,其抗震性能具有共性。借鉴钢管混凝土单肢柱的计算框架,开展等截面钢管混凝土格构柱骨架曲线的统一算法研究,对弹性刚度、水平峰值荷载、峰值荷载位移、下降段刚度等主要参数的计算方法进行了深入探讨和算例分析,并以干海子大桥格构柱墩为研究对象,采用OpenSEES有限元程序,对骨架曲线算法进行工程实例验证。研究结果表明,计算值与试验值及有限元计算结果均吻合良好。最后提出了适合工程应用的等截面钢管混凝土格构柱骨架曲线的统一简化算法,为钢管混凝土计算理论的进一步完善和规程编撰提供参考。     

Flexural toughness of hybrid fiber reinforced shotcrete

为了研究混杂纤维喷射混凝土的弯曲韧性,采用不同掺量的钢纤维和聚丙烯纤维混杂以及高炉微粉复合超叠加的方法制备600 mm×600 mm×100 mm混杂纤维喷射混凝土方板并置于刚性支撑架上,选用等位移控制对方板进行中心加载。通过生成的荷载挠度曲线及对其进行积分所得的能量吸收值综合评价各组方板的弯曲韧性,同时,通过破坏过程评价各板裂缝控制能力。试验结果表明：掺入1.2%钢纤维和0.11%聚丙烯纤维的喷射板试件的弯曲韧性优于掺入0.8%钢纤维和0.11%聚丙烯纤维的喷射板,其最大峰值荷载提高了18%,板中心挠度至25 mm时的能量吸收值也提高了25.6%;对于仅掺入0.8%单一钢纤维的板,混杂了0.11%聚丙烯纤维后,两种纤维间的正混杂效应使得板中心挠度至25 mm时的能量吸收值提高了28.5%;高炉微粉掺量的增加能提高混杂纤维喷射混凝土板的弯曲韧性;混杂纤维喷射混凝土板均展现出了良好的裂缝控制能力,板整体呈现裂而不断的延性破坏。     

近爆作用下压型钢板组合楼板动力响应及影响因素数值分析

利用有限元软件ANSYS/LS-DYNA,采用流固耦合的计算方法,对压型钢板组合楼板在近爆炸荷载作用下进行了不同工况的数值模拟,得出其受力形态,分析其动力响应及破坏过程,找出影响楼板动力响应的主要因素。数值分析结果表明：适当增加混凝土厚度和提高压型钢板强度,可以显著降低组合楼板的跨中最大位移,提高组合楼板的延性和抗爆性能;组合楼板中钢筋间距的变化,对组合楼板抗爆性能影响较小。     

Experimental Analysis on the Mechanical Properties of Concrete Composite Slabs with Precast Prestressed Rectangular Rib Panels

For the convenience of industrialized production and site operation,specification design of PPCRP (precast prestressed concrete ribbed panels) is discussed. In order to obtain ultimate bearing capacity,bending rigidity and crack resistance,four PPCRP with two types of spans are studied,and the results show that PPCRP can satisfy the requirements of bearing capacity in construction phase and can serve as stay-in place formwork. To verify the mechanical property,shear behavior on contact interface of composite member and moment redistribution factor of continuous composite member,two single-span composite members and one two-span continuous composite member are studied. It is indicated that computational method for bearing capacity of composite member can be the same as cast-in-situ concrete slab. Besides,section strain analysis for composite member in two-loading is conducted,which suggests that thickness of bottom board can be used as calculated height with the consideration of two-loading.     

Experiments on heat loss characteristics in a fully opened cylindrical cavity receiver

The climate has a great impact on highway bridge rubber bearings than on building rubber bearings. In order to study the change of the mechanical properties during the life of the plain chloroprene rubber bearings of highway bridge under freeze-thaw cycle condition, the plain chloroprene rubber bearings were processed 25, 50, 75, 100 times by freeze-thaw cycle in the standard freeze-thaw chamber, then the axial compression tests were carried. The changes of the performance indicators in the bearing capacity , the ultimate compressive strength, vertical stiffness, elastic modulus under different freeze-thaw cycles were analyzed comparatively. The results show that the plain chloroprene rubber bearings are more prone to brittle failure after the freeze-thaw cycle, and the failure phenomena of steel plate exposing or cracks is more serious than the phenomena of the standard specimen. With the increase of the number of freeze-thaw cycle, the ultimate bearing capacity, ultimate compressive strength and compressive elastic modulus of the plain chloroprene rubber bearings decrease. The attenuation formula and decay curve in 50 years of ultimate compressive strength and elastic modulus of compression are analyzed by least square method, the trends of change are both in line with the exponential function. The mechanical properties of plain chloroprene rubber bearings of highway bridge significantly decreased under freeze-thaw cycle condition. therefore, the temperature ranges of plain chloroprene rubber bearings of highway bridge should be strictly controlled, and some suggestions, such as increasing its minimum applicable temperature, usng the natural rubber bearings as much as possible in cold regions, have been given.     

Mechanical Model of Steel Plate Composite Shear Walls

Based on concepts of mechanics, a mechanical model of novel type of steel plate composite shear wall is presented. The novel type of structure is formed by steel plate shear wall and T-shaped solid-web composite columns. Flexural stiffness of steel beams, lateral stiffness of the T-shaped solid-web composite columns, shear stiffness of steel plate composite shear wall and shear stiffness of beam-column connection are taken into account in the mechanical model. And the equivalent damping between steel plate and boundary is considered. Based on the deformation features of structures and the calculation hypothesis, the lateral stiffness model and the energy dissipation model of structures are developed. Meanwhile, the calculation equations of elastic ultimate and plastic ultimate of shear strength of structures are set up. The theoretical analysis results inosculate better with the results of experiment. The comparison between the result calculated from the formula and the experimental result shows that the calculation precision is high enough to meet the demand of theoretical analysis. The difference, including equivalent model, stress states, manufacturing defect and installation error, between the formula and the experiment has been further discussed.     

Effects of Eccentricity on the Ultimate Strength of K joint with Tube gusset Plate Connections

The behavior and strength of tube gusset connections with tube 219×6 and 1/4 annular ribbed plate subjected to eccentric force is investigated. Non dimensionalized ultimate strength interaction relations between the wall moment of tube ,vertical axial force ,and eccentric vertical component force of axial brace force of tube gusset connections with 1/4(1/2) and annular ribbed plate subjected to eccentric force is researched based on the model of equivalent forces of tubular joint. The parameters which influence the ultimate strength of tube gusset joint were analyzed and non dimensionalized ultimate strength interaction relationships were proposed. It is shown that the proposal formula has theoretical and practical significance for design because of comparation with experimentation.     

大豆生育期间抗倒伏性状变化规律的研究

抗倒伏性是大豆高产稳产研究的重要内容。选用黑农37和黑农42两个大豆品种为试验材料,在25万和35万株/hm ²密度条件下,对不同生育时期大豆茎秆的形态指标、茎秆基部挫折力等力学特性进行测定,较系统地研究了大豆生育期间抗倒伏性状变化规律。结果表明,大豆生育期间,随着株高和单株鲜重的变化,植株重力力矩呈单峰曲线变化,R₅-R₆期达到峰值,茎粗和茎秆基部挫折力也呈现相同的变化规律;而抗倒伏系数是大豆茎秆力学特性的综合表现,呈现U型变化,在R₅-R₆期最小,表明该期间最易倒伏;大豆株高、单株鲜重、植株重力力矩与抗倒伏系数呈极显著负相关,大豆茎粗、基部茎秆挫折力、弹性模量与抗倒伏系数呈极显著正相关,表明大豆株高越低、单株鲜重越小、重力力矩越小、茎粗越粗、茎秆挫折力及弹性模量越大,大豆抗倒伏性越强。供试的两种密度条件下,大豆单株鲜重、茎粗、茎秆基部挫折力、重力力矩、抗倒伏系数等性状,35万株/hm ²处理明显低于25万株/hm ²处理,表明随种植密度增加,大豆倒伏风险增大。     

Elastoplastic Bending Buckling of Q420 Eccentric Compression Members with Double-angle Combined Cross-section

The experiments were carried out to investigate the behavior and failure modes of Q420 double-angle combined cross-section members whose specification were L160×12, L160×14, L160×16. The results show that all the members fail with an elastoplastic bending buckling. Based on the improvement of the inverse calculation segment length method and some relevant procedures, the related curves of axial force and moment with different specifications, different slenderness ratios and residual stresses were calculated. The calculation method of in-plane stability and column curves were proposed. The nonlinear power function model is appropriate for such members' moment-rotation relations under equal bending moments.     

高温下钢管约束型钢混凝土柱的受力性能

火灾下无防火保护的结构构件温度会迅速上升,从而造成钢材和混凝土的强度明显下降。为了研究火灾下钢管约束型钢混凝土柱的受力性能,考虑火灾下钢管约束型钢混凝土柱的不均匀温度分布及温度对材料力学性能的影响,提出了火灾下受轴心荷载作用的钢管约束型钢混凝土柱承载力的计算方法。利用有限元软件ABAQUS对提出的计算方法进行了验证,结果吻合较好。进而采用该计算方法对影响高温下承载力的参数进行了分析,研究表明：随着构件截面尺寸的增加以及混凝土强度和钢材强度的提高,构件的承载力逐渐增加,而钢管壁厚的改变对承载力并无太大影响。利用有限元软件ABAQUS分析了荷载比、构件尺寸、钢管壁厚等因素对构件耐火极限的影响,发现耐火极限随着荷载比和钢管壁厚的增加而减小,随着构件尺寸的增加而增大。     

Calculation and Analysis on Critical Moment of Thin-walled Beams under Unequal End Moment

In this paper, comparing the bending-twisting model with the tension-bending one, the critical moment of the thin-walled beams under unequal end moment is derived easily by the improved CDC (column deflection curve) method based on the increment interaction equations of beam-columns.A simplified formula is presented and the calculated results show a good agreement with the numerical ones.