International Journal of Advanced Structural Engineering
Volume:12 Issue: 4, Winter 2023

Since cementitious materials are brittle, they are prone to cracking. Cracks could be healed via autogenous methods namely healing microcapsules.The objective of this study was twofold. First, microencapsulation of isophorone diisocyanate (IPDI) as a catalyst-free healing agent. Second, evaluation of microcapsules effect on promotion of cementitious materials healing capability. PU prepolymer was synthesized and smoth spherical microcapsules of IPDI with average diameter of 48-62 μm were produced successfully. The microcapsules shell wall thickness varied linearly with microcapsule diameter and so, the shell wall thickness to diameter ratio was constant (~0.04).The microcapsules weight loss in a 6 months period was ~12.47% under ambient conditions. The mortars containg 3% of their cement weight IPDI microcapsules, had up to 74% recovery rate of compressive strength while this rate for control mortars (with no microcapsule) were less than 50%.EDS analysis of healed mortars, showed noticable amount of carbon in the areas of ruptured microcapsules and healed cracks, confirming that healing process had been precisely accomplished according to the theory of self healing assumed.Samples containig micocapsules had higher initial compressive strength in comparison with control ones, indicating that there had been an undesired rupture of portion of microcapsules during prepartion and molding of specimens. This demonstrated need of more studies and work on mechanical properties of microcapsules specially stiffness of those used in cementitious composites.

The lateral bracing frames are one of the common and earthquake-resistant systems. These frames were originally used to withstand wind forces, and were later developed to withstand lateral forces caused by earthquakes. One of the most important lateral bracing systems are eccentric braced frames (EBF). In this investigation, the behavior of eccentrically braced frames with Interchangeable link beam has been studied. Unlike other past researches, in addition to paying attention to the proper function of the fuse in the structure, the researchers have put the simplicity of its construction and easy replacement on the agenda. In this system, the link beam is connected to the out-of-link beam using a pin connection, so that it can be easily interchanged while exhibiting a fully shear behavior. In order to achieve the desired results, eccentric frame design has been done by ETABS software and analysis by ABAQUS software. The results of the research show that the use of pinned link beam, in addition to its impressive performance against lateral force, due to its simple interchangeability, the reconstruction time of the structure after the earthquake has been greatly reduced and the structure can be restored in the shortest possible time to the usable state.

Since the analysis of underground structures in seismic conditions was more based on non-linear terrestrial environment and linear structure, regarding nonlinear behavior of soil and tunnel against earthquake was of paramount significance in order to achieve real responses in practice. The use of polypropylene fibers in concrete materials can help improve the performance of concrete members. In this regard, after verifying the behavioral model of fiber-reinforced concrete seen in the structure of the tunnel and using an article by Conforti et al., the nonlinear seismic analysis of the ground and the structure of the water transmission tunnel of Amirkabir Dam to Tehran refinery no. 6 was performed by a time-history method and through ABAQUS software and concrete damage plasticity model for concrete lining and mohr-coloumb model for host soil of tunnel. Simulations were performed for the fibers with percentages of 0, 0.7, 1 and 1.5. Then, compressive and tensile stresses, compressive and tensile strains, and compressive and tensile failures were obtained while tunnel lining in the mentioned conditions. Since then, normal and shear stresses and normal and shear displacements of the longitudinal joints of the tunnel were examined. Finally, this paper studied the analytical relationships that existed in the ACI 544.7R-16 regulations and the moment-force diagram for the different percentages of fibers for the joint with the maximum normal stress under earthquake records were compared.

Engineering structures are subjected to different loads during their lifetime, which may cause damage or secondary loading effects. Among loading effects on structures, explosion and earthquake may also cause fire. A damaged structure can experience a different response under fire loading in comparison to the intact structure. In addition to strength loss, damaged reinforced concrete (RC) frames may be exposed to cracking and spalling of concrete cover at various damage levels. These phenomena affect heat transfer in the structural section. In this study, Markov probability chain analysis is used to determine the probability of the occurrence of first failure in a 7-story RC frame damaged at different levels is evaluated under fire loading. The time of the first failure in structural elements is also calculated and presented for each damage level. The results show that increased damage levels in RC frame results in a greater probability of failure and reduced time of failure under fire loading scenario. The failure probability was found as zero at damage indices of 0, 0.1 and 0.2, with non-zero probabilities for greater damage indices. The framework developed in this paper outlines the performance assessment procedure for a damaged structure that is later exposed to fire loading.

This paper presents an economical optimization for cost and weight of reinforcement cantilever concrete retaining walls using Cuckoo Optimization Algorithm (COA). The proposed optimization algorithm is inspired from the life of a bird family called cuckoo. The capability of this algorithm is compared with other optimization methods available in the literature including ant colony optimization (ACO), bacterial foraging optimization algorithm (BFOA), particle swarm optimization (PSO), accelerated particle swarm optimization (APSO), firefly algorithm (FA), and cuckoo search (CS). A computer program has been developed by using the COA method for optimizing retaining walls. Five types of retaining walls were considered and sensitivity analyses were performed to find out the role of important parameters such including stem height, surcharge, backfill slope, and backfill unit weight and friction angle. Also, Coulomb and Rankine methods are used to estimate lateral earth pressures. The results show that the COA can minimize retaining walls from both cost and weight viewpoints. In addition, the COA can achieve to better results than ACO, BFOA, PSO, APSO, FA, and CS. The performed sensitivity analysis illustrates that with increasing surcharge and stem height, the cost and weight of wall increase. Also, the cost and weight objective functions decrease with increasing the soil unit weight. In addition, the Coulomb method gives lower cost and weight quantities than the Rankine method.

The current study set to investigate the seismic performance of the steel moment-resisting frames equipped with multi-level pipe dampers considering the connection flexibility in the model. Initially, the behavior model of the damper, connections, and steel columns are presented and calibrated based on the experimental results. Then, three steel moment-resisting frames having 4, 8, and 12 stories with poor lateral strength were modeled in the OpenSees software, while the flexibility of the beam-column connection was taken into account. The structural models were then subjected to the one-direction lateral load and evaluated using the nonlinear static analysis. The results revealed that the rehabilitation of steel moment-resisting frames using the multi-level pipe dampers significantly led to enhanced load bearing capacity of frames compared to the corresponding control frame. The maximum load bearing capacity increase was 57%, 56%, and 60% in the 4-, 8-, and 12-story frames, respectively. The ultimate deformation capacity increased as well, while the yield displacement of frames decreased. The maximum increase on the ultimate ductility of strengthened frames was 43%, 34%, and 33% in the 4-, 8-, and 12-story frames, respectively. The findings can be considered as a criterion to compare the performance of this type of damper with the conventional control structures.