Nonlinear formulation based on FEM,Mazars damage criterion and Fick’s law applied to failure assessment of reinforced concrete structures subjected to chloride ingress and reinforcements corrosion

Structural durability is an important design criterion, which must be assessed for every type of structure. In this regard, especial attention must be addressed to the durability of reinforced concrete (RC) structures. When RC structures are located in aggressive environments, its durability is strongly reduced by physical/chemical/mechanical processes that trigger the corrosion of reinforcements. Among these processes, the diffusion of chlorides is recognized as one of major responsible of corrosion phenomenon start. To accurate modelling the corrosion of reinforcements and to assess the durability of RC structures, a mechanical model that accounts realistically for both concrete and steel mechanical behaviour must be considered. In this context, this study presents a numerical nonlinear formulation based on the finite element method applied to structural analysis of RC structures subjected to chloride penetration and reinforcements corrosion. The physical nonlinearity of concrete is described by Mazars damage model whereas for reinforcements elastoplastic criteria are adopted. The steel loss along time due to corrosion is modelled using an empirical approach presented in literature and the chloride concentration growth along structural cover is represented by Fick’s law. The proposed model is applied to analysis of bended structures. The results obtained by the proposed numerical approach are compared to responses available in literature in order to illustrate the evolution of structural resistant load after corrosion start.     

Creep of UHPC in tension and compression: Effect of thermal treatment

Steel fiber-reinforced ultra-high performance concrete (UHPC) is of increasing interest for use in precast prestressed concrete highway bridge girders due to its superior durability and the potential for reducing or eliminating shear reinforcement, due to the presence of steel fibers. However, the contributions of creep, and especially tensile creep, to long-term performance must be better understood to develop appropriate design specifications. Due to practical considerations, it is also of interest to investigate the influence of varying thermal treatment, including temperatures lower than those recommended by the manufacturer (i.e. 90 °C), on the creep of UHPC. In this 1-year study, the effects of three different thermal treatment regimes on tensile and compressive creep performance of UHPC are examined, with complementary characterization by nanoindentation and scanning electron microscopy. Results show that UHPC creeps phenomenologically differently in tension and compression. Both thermal treatments examined resulted in similar tensile creep behavior, suggesting that a lower temperature applied over a longer period could effectively cure UHPC. For the non-thermally cured UHPC, a 10 μm wide region observed at the fiber/matrix interface was characterized by reductions in elastic modulus as well as greater porosity and microcracking than the bulk paste. It is suggested that the quality of the fiber/matrix interface is a major contributor to the measured increased creep of non-thermally treated UHPC as compared to UHPC treated at 60 °C or 90 °C.     

混凝土框架顶层加建钢结构概念设计探讨

随着人们审美的提升，对建筑的要求不止是安全耐用，还要求达到最大程度的美观。而在原有结构上通过钢结构来实现这种美观，已有很多应用。本文主要对混凝土框架顶层钢结构进行了分析，阐述了设计中需要注意的概念设计。     

Mechanistic procedure for parameter determination of multiplicative decomposition based constitutive models

By exploiting the Clausius–Planck local energy dissipation inequality, a large strain, three-dimensional constitutive model has been developed for the monotonic and cyclic response prediction of various asphaltic materials. The model consists of a Zener non-linear, visco-elastic component acting in series with a stress dependent viscous component. A novel computational scheme has been developed for solution of the coupled system of equations expressing the interdependent response of these two in series components. An explicit, mechanistic, parameter determination procedure is presented for the laboratory determination of all necessary model parameters. Examples of model parameter determination and utilisation for prediction of the response of a recycled asphalt mix and a stone mastic asphalt mix are presented.     

泵送混凝土离心工艺优化的研究

通过泵送混凝土离心工艺优化试验,研究离心各级工艺参数对掌握管桩内部结构成型质量,改善混凝土分层现象,提高管桩成桩质量的重要作用。通过研究管桩实际生产过程,探讨泵送混凝土离心工艺优化研究的思路与方法。     

混凝土冻融环境下累积损失模型的确定

应用累积损失理论,以混凝土在受冻时期性能指标的劣化过程发生的两个阶段为基础,初步建立了阶段Ⅰ和阶段Ⅱ时的混凝土在冻融循环条件下的损伤累积模型,为今后冻融环境下的混凝土耐久性研究提供参考。     

混凝土叠合箱网梁楼盖施工技术分析

混凝土叠合箱网梁楼盖是一种特殊的密肋梁楼盖，由预制叠合箱和现浇网（肋）梁组合而成，特点是底部平整、节约耗材和大空腔网梁构造受力等。笔者结合实际经验，在本文中简单地分析了叠合箱网梁楼盖技术。     

苏丹北科尔多凡州混凝土强度推定公式建立

本文通过搜集工程实例中混凝土早期强度数据,根据对数据的分析整理,利用回归法建立苏丹北科尔多凡州地区的早期普通混凝土强度推定公式,结果表明该推定公式能够较好的满足《早期推定混凝土强度试验方法标准》(JGJ/T15-2008)中规定的要求。在工程实践中,能较好的推测混凝土的28d强度。     

二段转化炉内部耐火衬里局部修复和更换

介绍二段转化炉内部下锥段的耐火衬里和拱砖损坏情况,以及衬里局部修复、拱砖更换的施工过程和管理经验。