双钢筋混凝土梁的受弯试验及裂缝计算

双钢筋系由两根纵向平行的纵筋与之垂直的短横筋按一定间距焊接组成梯格型骨架,采用双钢筋技术,可以改善钢筋混凝土的粘结作用,从而改善钢筋混凝土受弯构件的裂缝分布,减小裂缝宽度,使裂缝开展呈现细而密的特征。然而,目前使用的双钢筋类型主要是由冷拔低碳钢丝或冷轧钢筋制成的双钢筋,这些双钢筋大多用于小跨度的单向板、过梁、楼梯等构件中,而采用大直径热轧带肋三级钢筋制成的双钢筋混凝土构件国内外尚未见有报道。为了充分发挥双钢筋的技术优势,拓宽双钢筋技术的使用范围,对热轧带肋三级钢筋焊制的双钢筋构件作了较全面的分析研究,重点研究了双钢筋受弯构件的裂缝及变形计算,对双钢筋构件的裂缝特征作了较完整的理论分析。通过试验观察和理论分析,并针对热轧带肋三级钢筋制成的双钢筋混凝土构件,提出了裂缝计算的建议公式。并与普通构件对比进行技术经济分析,可取得良好的经济效益。     

Secant stiffnesses for ultimate analysis of strain hardening indeterminate RC structures

This paper presents the iterative use of secant distributions in stiffness analysis to determine ultimate load factors for statically indeterminate concrete structures which strain harden at critical sections. The computational procedure is novel in that it directly seeks the failure state without considering pre-ultimate behaviour, and also in that it permits clear insight into the important effect of the distribution on moments at failure. The procedure iterates until the output moments–in addition to satisfying capacity–give an distribution which returns those very moments on input to the stiffness analysis with the same loads. A flowchart for iterating to these conditions is given, with illustrative examples. Then, removal of higher-order terms from nonlinear distributions is shown algebraically and by stiffness analysis to compromise neither predictive accuracy nor analysis speed in specific cases. Further algebraic analysis of an encastered span with two section stiffnesses shows that, for elastic (e.g. over-reinforced) failure, a unique coincidence exists between the moment diagram and the distribution when turning values of moment occur for any given ratio of the two section stiffnesses. It is concluded that distributions are key to assessing failure states of RC structures.     

Dynamic buckling of thin thermoviscoplastic cylindrical shell under radial impulsive loading

The dynamic plastic buckling of a homogeneous and isotropic thin thermoviscoplastic cylindrical shell loaded radially is studied analytically by analyzing the stability of its stressed/deformed configuration under superimposed infinitesimal perturbations. The wave number of the perturbation that maximizes its initial growth rate is assumed to determine the buckling mode. Cubic algebraic equations are obtained for both the maximum initial growth rate of perturbation and the corresponding wave number. The buckled shape of a cylindrical shell is found to match well with that observed experimentally. The sensitivity of the buckled shape to the impact velocity, the hardening modulus, and the material viscosity has been delineated. For axially restrained shells, it is found that for materials exhibiting strain rate hardening only the maximum initial growth rate of the perturbation and the corresponding wave number vary as and , respectively. For axially unrestrained cylindrical shells made of strain hardening only materials, the maximum initial growth rate of a perturbation and the corresponding wave number vary as and , respectively. Here is the mean value of the generalized stress, ρ the mass density, β the material viscosity, h the shell thickness, and R the mean radius of the shell.     

考虑剪切效应的钢筋混凝土厚板的纵向裂缝研究

试验表明,钢筋混凝土简支厚板在中置集中荷载作用下的双向弯曲很明显.特别是当板的宽跨比较大、集中荷载的面积较小时,其双向作用更为明显.按常规设计,往往只计算Mx方向配筋,而My方向则按构造配筋.因此,工程上经常出现沿板跨度方向的裂缝,即板的纵缝,并且由于My方向配筋过少,板纵向裂缝的宽度远大于横向裂缝的宽度.本文首先对简支厚板在集中荷载下的裂缝形态进行了试验研究,然后,将厚壳单元引入板的有限元分析,进而讨论了钢筋混凝土双向厚板的剪跨比、厚宽比、宽跨比对板横纵向弯矩比值的影响,提出了适用于控制不同厚度的厚板纵缝的纵向弯矩比简化计算公式,为设计提供参考.     

替换空心板的变高度后张预应力T梁设计研究

结合某空心板梁桥的单板受力病害,提出采用一种变高度后张预应力T梁替换空心板的处置设计方案。该结构方案的梁端与原空心板梁高度相等,跨中梁高适当增加,这样可以在不改变原桥面标高的前提下更新桥跨结构。为此,在截面构造上加密了T梁的肋间距(比一般横向装配式T梁的肋间距小),优化了预应力筋布置,并在T梁端部设计了"预埋钢板"和"抗剪钢筋骨架"两种抗剪加强构造,可为同类工程的改造设计提供参考。     

Longitudinal shear test on steel-concrete composite beam with two rows of shear studs

为研究带双排栓钉的组合梁的纵向受剪性能,进行了7个带双排栓钉的钢-混凝土组合梁试件和1个带单排栓钉的钢-混凝土组合梁对比试件的纵向受剪试验。研究栓钉横向或纵向间距、横向配筋率、混凝土强度、栓钉排布方式等因素对带双排栓钉的钢-混凝土组合梁纵向受剪性能和混凝土板破坏形态的影响,并分析了各研究参数对峰值荷载和极限滑移量的影响。结果表明：带双排栓钉的钢-混凝土组合梁试件破坏模式主要表现为“八”字形裂缝的剪切破坏;栓钉横向、纵向间距、混凝土强度以及混凝土板配筋率是影响钢-混凝土组合梁受剪承载力的主要因素;受剪承载力均随着栓钉横向间距、纵向间距、混凝土强度以及混凝土板的横向配筋率的增加而增大。     

钢-混凝土组合梁抗火性能试验研究

对两种组合梁形式:主梁式试件(压型钢板肋平行于钢梁)和次梁式试件(压型钢板肋垂直于钢梁)分别进行了抗火试验。试验中量测了试验炉火升温过程,试件的温度和跨中挠度。通过对试验结果的分析发现:由于混凝土板有明显的阻热作用,组合梁中的混凝土板升温较慢,钢梁升温较快,导致钢梁截面温度分布不均匀;由于高温和外力共同作用下,在梁端发生混凝土抗剪破坏,而栓钉由于受到混凝土的保护,温度较低,栓钉仍能正常发挥抗剪连接作用;跨中挠度达到梁跨的1/30后,变形快速增大,随之在跨中形成一条横向贯穿混凝土楼板的主压溃裂缝,产生塑性铰并形成机构,使简支组合梁产生不适于继续承载的变形,达到破坏。