Experimental results show that beam-column joints have a considerable effect on the seismic behavior of precast concrete buildings and the most damages are in this area. Local retrofitting precast concrete beam-column joints with self-centering friction dampers is an effective method for seismic strengthening in the exterior and interior beam-column joints. This study evaluated the seismic performance of retrofitted precast concrete beam-column joints using self-centering friction damper. For this goal, a nonlinear model is proposed to simulate the cycle behavior of the retrofitted joints models in OpenSees software framework that are calibrated by experimental specimens. Then, the efficiency of using self-centering friction damper on the seismic behavior of the precast building damaged during the Bojnord earthquake 13 May 2017 in Iran (M_W 5.4), is investigated. The results show the capability of the self-centering friction damper in enhancing the energy dissipation, stiffness and strength of the precast concrete beam-column joints. Also, the incremental dynamic analysis (IDA) approach was used to determine the fragility curves of the retrofitted precast building. The results show that the haunches retrofitting method increases the mean acceleration values for all damage limit states remarkably.

This study was determined the impact of recycled coarse aggregate content (0%, 50%, and 100%), waste fiber length (12, 19, and 30 mm), volume fraction of waste fibers (0.08%, 0.12%, and 0.16%), slenderness ratio (2, 5, and 8), and eccentricity (0, 30, and 60 mm) on the bearing capacity of concrete columns. The results indicated that the cracking load and ultimate bearing capacity of waste fiber recycled concrete (WFRC) column decrease as the replacement rate of recycled aggregates increases, and initially increase before decreasing with the increase in both the length and content of waste fibers. The highest bearing capacity is achieved when the waste fiber length is 19 mm with a content of 0.12%. The waste fibers exhibit superior bond strength with the concrete matrix and effective load transfer, which inhibit the development the cracks during the loading process and improve the bearing capacity of the specimens. Additionally, the experimental results of WFRC were compared with the theoretical values calculated according to the "Code for Design of Concrete Structures" GB50010-2010, the ratios of the calculated value to the experimental value in the range of 0.81-1.10. The feasibility and safety of the related properties of the WFRC column according to the results calculated by the standard GB50010-2010. The standard GB50010-2010 can guide the application design of WFRC compression members in practical engineering.

Several problems result from concrete in hot weather, especially excessive water evaporation rate at early age, which induces plastic shrinkage, then results in cracks and mechanical characteristics of concrete will reduce. It is primoradial to know in advance concrete behavior at this critical type. Therefore, simulating the behavior of concrete in the short term in hot weather will allow us to predict these problems, especially plastic shrinkage. This study aims to determine of normal concrete (w/c = 0.35 , Portland cement with limestone NA 442, calcareous crushed sand ) at an early age, precisely in the first 24 hours of a mini-slab (27 × 21 × 1.5 cm³) under a hot simulated weather (temperature 55℃, air velocity 2.1 m/s and relative humidity 13%) by experimental study and numeric simulation, which consists of the simulation of the experimental study using COMSOL software. The results showed that the temperature and humidity distribution are different along the mini-slab; also, the numerical simulation results converge to the experimental results. The numerical simulation allowed us to know the exact time the beginning of cracking.

The study presents a review on hybrid Extreme Learning Machine (ELM)-based soft-computing methodology for computing the compressive strength of self-compacting concretes (SCC). Due to its advantages of better quality and aesthetic, as well as suitability for addition of supplementary environment-friendly cement substitutes, SCCs have gathered enormous attention in construction engineering. While the strength prediction of SCCs remains problematic due to constraints like complex constitution, ML-based methodologies have received enormous attention in the field. The application of hybrid ELM models is novel in the field of SCCs, though it has been proved to be a robust alternative to traditional methods in many other fields of engineering. The study develops three hybrid ELM models by integrating three efficient optimization algorithms to the ELM algorithm, namely Particle Swarm Optimization (PSO), Improved firefly algorithm (IFF) and Equilibrium Optimizer (EO). The results report that ELM-EO (R² = 0.916, RMSE = 0.065) is the best performing model in comparative analysis and outperforms the traditional ELM model. The results of the study are compared from the previous studies in literature and the ELM-EO model is concluded as best among them. The proposed methodology provides a robust and efficient alternative for SCC strength prediction, offering potential for practical implementation in the construction industry.

After reading, handling, teaching, and inspecting ACI-318 and EC-2 design codes provisions, which related to the ductility of reinforced concrete structures, should further investigated due to their significance to the safety issues. Therefore, adoption of ductility by current and previous ACI codes are studied and compared with Euro code and two proposed models. Results found that the maximum permissible tensile steel ratio reached 6.7% at concrete strength 82.6 MPa and at low steel grade, the ratio rises as concrete strength increases, resulting in a high level of reinforcement congestion. Furthermore, there is a weakness in the design of double-reinforced beams (with compression reinforcement): ductility can be attained by increasing the tensile steel with a proportional increase in the compression steel, without restricting the amount of steel used, causing unreasonable results. In addition, the item that provides the minimum required steel ratio has a conflict with a previous item from the same section, which requires revision.