International Journal of Advanced Structural Engineering
Volume:12 Issue: 2, Summer 2022

In the current study, granulated blast furnace slag (GBFS) based geopolymer concrete (GPC) was used with 0-2% polyolefin fibers (POFs) and 0-8% Nano silica (NS) to improve its structure. After curing the specimens under dry conditions at a temperature of 60 °C in an oven, they were subjected to Modulus of elasticity and Ultrasonic Pulse Velocity (UPV) tests to evaluate their mechanical properties, as well as Capillary absorption test to assess their durability. all tests were performed at 7 and 90 days of age at ambient temperature (20 ℃). The addition of NS enhanced the whole properties of the GBFS based GPC. Increasing the curing age improved the results of all tests. The results of all tests in GPC showed the superiority of the results over conventional concrete. At 28 days of curing age, the addition of up to 8% NS to the GPC composition improved the modulus of elasticity test results by 14.7%, UPV by 84.88% and capillary water uptake by 64.38%. Addition of up to 2% of POFs to the GPC composition improved the modulus of elasticity by up to 7.21%, capillary water uptake by up to 22.97% and decreased UPV by up to 8.77%. In the following, by conducting the SEM test, a microstructure investigation was carried out on the concrete samples. In addition to their overlapping with each other, the results indicate the GPC superiority over the regular concrete. Besides, it demonstrated the positive influence of NS addition on the concert microstructure.

Base isolation is an appropriate approach to mitigate the seismic hazards. A common type of elastomeric rubber bearing is included rubber pads, intermediate steel plates and steel end plates (anchor plates). The hysteresis behavior of elastomeric rubber bearings is affected by vertical pressure and shape factor. In this study cyclic loading is applied and hysteresis behavior in the first and second cycles is evaluated. Finite element method with ABAQUS software is used and validation analysis was done. The results show that second cycle of force-displacement in the elastomeric rubber bearings is more stable than the first cycle and vertical pressure and shape factor influenced damping and hysteresis behavior. Also, elastomeric rubber bearings with lower shape factor have higher damping in comparison with larger shape factor and increase in vertical load led to increase in the damping. The innovation of this paper is adopted various hysteresis parameters in finite element analysis to achieve closest results in comparison with experimental work.

Behavior factor of the structures is a coefficient that includes the inelastic performance of the structure and indicates the hidden resistance of the structure in the inelastic stage. In most seismic codes, this coefficient is merely dependent on the type of lateral resistance system and is introduced with a fixed number. However, there is a relationship between the behavior factor, ductility (performance level), structural geometric properties, and type of earthquake (near and far). In this paper, a new optimal correlation is attempted to predict the behavior factor (q) of EBF steel frames, under near-fault earthquakes, using Particle Swarm Optimization (PSO) and Simulated Annealing (SA) algorithms. For this purpose, a databank consists of 12960 data created. To establishing different geometrical properties of models, 3-,6-, 9-, 12-, 15, 20- stories steel EBF frames considered with 3 different types of link beam, 3 different types of column stiffness and 3 different types of brace slenderness. Using nonlinear time history under 20 near-fault earthquake, all models analyzed to reach 4 different performance level. data were used as training data of the Artificial Intelligence Models. Results shows the high accuracy of proposed correlation, established by PSO algorithm. The results of the correlation between the studied algorithms show more accuracy in the relations produced than the previous algorithms and confirm the significance of the governing relations.

Lateral bearing systems affect tall structures’ behavior against lateral forces. Shear walls are one of the influential structural members against lateral forces. However, the ends of shear walls undergo severe stress under lateral forces connected to a reinforced concrete shear wall called end shear wall to improve the end structure behavior of the shear walls. Adding the end shear wall by joining the ends of the shear walls strengthened the roof rigidity and decreased the stress intensity at the concrete core end. This study modeled two 30-story concrete structures with frame and reinforced concrete shear walls with and without end shear walls to evaluate the end shear walls’ behavior. First, the structure members were simulated in OpenSees to check the non-linear behavior. Then, the structures were subjected to remote domain records to examine the fragility curves. The results indicated that the end shear wall increased the maximum acceleration at maximum probability in low, medium, severe, and complete collapse states by 50, 28, 27, and 38%, respectively. The fragility curves showed a more appropriate behavior of the 30-story structure with end shear walls in low, medium, high, and complete damage states. This system is more efficient than others since the end shear wall cuts the initial period of the structure in half (from 4 to 2s in a 30-story structure with an end wall). This drastic decrease can add stories to the building. Stairs and elevators can be built into the structure instead of the end shear wall for more flexibility.

Compared to other concrete types, the self-compacting concrete (SCC) offers a higher workability. Accordingly, the SCC performance is highly affected by the ambient temperature and extended transportation time. In previous studies, the effect of constituents on SCC at various time and temperature was only studied after the concrete temperature reached the normal range. Nonetheless, in the present research, it is tried to reduce the negative impacts of changing temperature and time by using cement, limestone powder, and chemical admixtures without considering temperature constraints for concrete. In this research, SCC samples temperature were selected for different seasonal conditions. Therefore, once the concrete temperature reached the ambient temperature, slump flow, T50, VSI, J-ring, and rheology tests were conducted on a total of 21 different concrete mixtures with water to cement ratio of 0.4. According to the results, application of retarding admixture and increased cement dosage contributed to improved workability and rheological behavior. On the other hand, an increase in the limestone powder dosage, rather than cement, was seen to impose a larger contribution to increased passing ability of SCC through rebars, but since the concrete containing limestone powder exhibited larger slump losses, one should increase the dosage of cement or retarding admixture to retain the concrete workability. Generally, it was found that the temperature and concrete mixture composition effectively control performance characteristics of the SCC. Therefore, it is recommended to keep the concrete from being overheated as it can otherwise lead to the acceleration of cement hydration and hence decreased workability.

Providing adequate strength and stiffness is considered a primary principle for structural design. Roof flexural members have a remarkable role to provide lateral and gravity stiffness. A vital issue in the analysis and stiffness assessment is to apply stiffness modification factor for the mentioned members in RC structures so that their impact in gravity and lateral load bearing could be changed. In the present study, to achieve an appropriate coefficient to decrease the stiffness of reinforced concrete slabs under simultaneous gravity and lateral loading, 20 structures from 2 to 20-stories with various roofs including flat slab, beam-column slab, and one-way and two-way waffle slabs were designed and analyzed, and then an equivalent overall coefficient for slabs stiffness decrease was obtained. The results indicate that the coefficient of 0.25 recommended by the building codes for flat slabs is around 60 percent conservative. In other categories of slabs for which the available building codes have not recommended a determined coefficient, the coefficient of 0.45 to 0.5 is achieved based on the analysis of the current study.