This paper presents a simple analytical method for determining the stress-strain state of reinforced concrete (RC) beams subjected to biaxial bending. A simple supported beam with three input load values applied at two positions is used in this study. The beam cross-section is divided into numerous elements and then the stress-strain state at the centre of these elements is analysed. The material behaviour of concrete and rebar are both simulated using a bilinear model. The results of this method are compared and verified with a three-dimensional finite element approach. The results indicate that the proposed method is easy to implement and its performance is comparable to a numerical simulation method. The stress-strain state, location, and shape of the neutral axis, as well as the shape of the compressive and tensile area can be extracted using the proposed method. This method can also present the position and length of the crack in the cross-section. Moreover, this method ensures accurate evaluation when selecting materials and the initial layout of the rebars. The testing and evaluation of the accuracy of the material selection can be completed by using this proposed method. Also, the method can be applied to RC beams with different cross-sections and complex loading.

Introduction: Climate change (temperature rise and sea level rise) has a considerable influence on the behavior of concrete structures over time. All concrete degradation processes are connected to climate variables and the effects of climate change. The RCP8.5 (Representative Concentration Pathway) scenario, which is part of the report on climate change and level rise scenarios for Vietnam, predicts that the beginning of the 21st century will see an average annual increase in temperature between 0.8 and 1.1°C. In the mid-21st century, the temperature will likely increase by 1.8–2.3°C, with the temperature in the north likely increasing by 2.0–2.3°C and in the south by 1.8–1.9°C. In marine environments, the degradation of concrete structures can occur rapidly due to chloride-induced reinforcement corrosion. Furthermore, sea level rise is going to reduce the distance from the coastline to the structures and lead to increased surface chloride concentration. Methods: The evaluation of chloride penetration was based on the ASTM C1202 test (ASTM, 2012). The cylinder specimens (d = 100 mm, h = 200 mm) used for a rapid chloride penetration test (RCPT) were immersed in water for 28 days in a water-curing tank. Results: This study proposes a predictive model for analyzing the impact of climate change on the service life of concrete structures on Vietnam’s North Central Coast. The corrosion initiation time decreases by 16.5% when the effects of both temperature rise and sea level rise are taken into consideration. When only temperature rise is taken into consideration, the rate of reduction is approximately 9.0%. These results reaffirm that climate change has a significant effect on the corrosion initiation time of concrete structures located in a marine environment.