Computational analysis of reinforced concrete structures subjected to fire using a multilayered finite element formulation

Fire is a critical risk in reinforced concrete (RC) structures and appropriate structural resistance against it has to be ensured. In this contribution, an approach using corotational layered beam finite elements is employed in which the cross-section temperature is derived from a low-cost closed form model, as opposed to the more commonly used fully computational thermal analysis. The effect of geometrical and material nonlinearities (constitutive behavior fitted to experimental data for concrete and steel), material degradation as a function of temperature rise, and the contributions of thermal, transient, and creep strains are incorporated in the structural analysis. The computational results are favorably compared to experimental data from the literature for an RC beam and for a larger RC frame. Taking benefit of the layered beam formulation offering local insight into the cross-sectional and material behavior, the relationship between the structural degradation and data extracted from the cross-sectional behavior is successfully established. Noteworthy originalities of the contribution are the use of ultimate strain and its evolution as a function of temperature for both materials and the explanation of the observed structural response in fire conditions from cross-sectional data.

Investigation of the influence of elasticity modulus variation in the ice beam bending model

В работе исследуется влияние неравномерности распределения модуля Юнга в ледяной клавише при ее взаимодействии с наклонным сооружением. Неоднородности в модели отдельно рассматриваются по длине и толщине клавиши. Изменение модуля Юнга по толщине происходит, как правило, в связи с температурным градиентом. При этом лед рассматривается как слоистая балка, в каждом слое которой физико-механические свойства остаются постоянными. При изменении модуля Юнга по длине клавиши рассматривается как простая линейная зависимость, так и представление его как случайной величины. Проведено сравнение результирующих параметров разрушения балки при перечисленных постановках задачи. При помощи статистического моделирования получены кривые, определяющие при различных величинах разброса модуля Юнга границы интервала, в которые значения точек разлома попадают с вероятностью 95% The paper investigates the influence of uneven distribution of Young's modulus in an ice beam during its interaction with an inclined structure. Inhomogeneities in the model considered separately along the length and along the height. The change in Young's modulus along the width occurs in connection with the temperature gradient, when viewed as a layered beam. In each layer of the beam, the physical and mechanical properties of ice remain constant. When Young's modulus is changing along the beam length, its representation is considered as a random variable. The comparison is made of the values of the system parameters with and without taking into account inhomogeneities in the model along the length and width. The study involved a series of numerical experiments to determine the dependence of the standard deviation value of Young's modulus and the interval boundaries in which the values of the breaking point falls with a probability of 95%.

Residual Flexural Performance of Epoxy Polymer Concrete under Hygrothermal Conditions and Ultraviolet Aging

Epoxy polymer concrete (EPC) has found increasing applications in infrastructure as a rising candidate among civil engineering materials. In most of its service environments, EPC is inevitably exposed to severe weather conditions, e.g., violent changes in temperature, rain, and ultraviolet (UV) radiation. In this paper, we designed an accelerated aging test for EPC, which includes periodic variation of temperature and water spray, as well as intensive UV-light irradiation, imitating the outdoor environment in South China. The experimental results show that the flexural performance of EPC is found deteriorate with the aging time. An aging process equivalent to four years (UV radiation dose) results in up to 8.4% reduction of flexural strength. To explore the mechanisms of observed performance degradation, the EPC specimen in the four-point-bending test is considered as a layered beam. The analysis indicates that the loss of flexural load-carrying capacity of an aged EPC beam is dominated by the reduction of mechanical properties of the surface layer. The mechanical properties of the surface layer are closely associated with the aging of epoxy mortar, which can be approximated as a reciprocal function of the aging time. By introducing damage to the surface layer into the layered beam, the proposed model demonstrates a good ability to predict the residual flexural strength of EPC during the aging process