An analytical model that incorporates time-dependent effects (creep and shrinkage) was developed to predict the long-term deflection of cracked reinforced concrete beams under sustained loading. The deflection model includes both bending and shear effects. Correspondingly, experimental studies were conducted to verify the analytical model. Eight specimens were precracked with a diagonal crack width of 0.2-0.3mm and tested under sustained loading for three months. It was found that the contribution of shear effect to long-term deflection is significant. The predicted deflections including both bending and shear deformations agree very well with experimental measurements. In addition, formulas for calculating creep coefficients from strain increments were derived that provide an approach to calibrating the code specifications. The effects of different creep coefficients on the prediction of time-dependent deformations were discussed.

Compared with simply supported beams, continuous steel-concrete composite beams have many advantages such as higher span/depth ratio, less deflection, and higher fundamental frequency of vibration due to its higher stiffness. However, in negative bending regions near interior supports, tension in concrete is unfavorable and a complicated issue, which deserves a special study. In this paper, a mechanics model based on elastic theory was established to investigate the stiffness of composite beams in negative bending regions by considering slips at the steel beam-concrete slab interface and concrete-reinforcement interface. In order to validate this approach, a test of three composite beams with profiled sheeting under negative bending was conducted. Meanwhile, a three-dimensional nonlinear finite element (FE) analysis was conducted to investigate the general behavior of the tested specimens. In addition, a comparative analysis between results derived from the analytical model, laboratory test, and FE analysis was performed. The results show that slip always exists for composite beams under negative bending even with complete shear connection (full composite action) between the steel and concrete components. The slip effect results in an additional curvature of beam bending and reduces the section stiffness by 10-20% compared with that of a beam without any slip in serviceability condition. This reduction should be considered in designing process especially for cantilever beams. Formulae under other loading cases and boundary conditions were also proposed. The results can serve as a basis for further study on stiffness of continuous steel-concrete composite beams and can directly be used for the deflection calculation of cantilever beams.

Static loading tests were conducted on 16 steel-concrete composite beams and two steel beams to investigate shear resisting mechanisms and the strength of composite beams. The main experimental parameters were the shear span aspect ratio of the simply supported beams, and the width and thickness of the concrete flanges. Based on strain measurements, stress in the steel beam was analyzed using theories of elasticity and plasticity, and the vertical shear that the steel beam resisted was calculated. The shear resistance of the concrete flange was then obtained by subtracting the steel shear contribution from the total load applied. It was found that the concrete flange could sustain 33-56% of the total ultimate shear applied to the composite beam specimens, contrary to the typical assumption of neglecting the concrete shear contribution in most design codes and specifications. A shear strength equation that considers the shear contributions of both the steel beam and the concrete flange is proposed.

对钢-混凝土组合梁的长期变形问题进行了分析和讨论。指出我国现行（钢结构设计规范）关于组台梁长期变形的计算值偏小。并建立了组合梁的长期剐度计算公式。反映了混凝土徐变系数大小的影响。同时还考虑了混凝土收缩对变形的影响。公式意义明确。形式简单，应用方便。

本文结合某会展中心的大跨楼盖结构设计，介绍了大跨交叉钢-混凝土组合梁系楼盖的主要设计思路及构造方法，并介绍了复杂节点的构造措施。通过跨高比、用钢量等技术指标说明应用大跨交叉钢-混凝土组合梁系楼盖具有显著的技术经济效益。工程实践表明，这种大跨楼盖结构应用前景广阔。