Journal of Rehabilitation in Civil Engineering
Volume:10 Issue: 3, Summer 2022

Cumulated damages caused by the past earthquakes lead to structural damage. Ensuring the safety of individuals – especially in highly populated buildings – and the continuity of immediate occupancy in consecutive earthquakes with short periods is an important matter to consider in seismic design codes. The use of strategies, such as identifying damage sensitive stories, can help ensure the safety of such buildings. This paper identifies damage sensitive stories for reinforced concrete (RC) and steel frames based on damage distribution caused by critical mainshock-aftershocks. In this regard, short, medium and relatively tall steel and RC frames with 3 and 5, 7, 10, 12 and 15 stories are analyzed under single and successive scenarios in the OpenSees software. Damage distribution of frames show that the upper stories in frames with low and medium height and middle stories toward higher stories in relatively tall frames are damage sensitive stories. Also, when tested against successive shocks, the initially-damaged steel frames experienced more destruction than RC frames. In severe conditions, the increased damages of steel frames were about 57%, 94%, 42%, 33% and 84% more than those of the RC frames. Moreover, steel frames with 15 stories were better able to sustain additional damages than RC frames (by about 1.84 times).

Terrorist explosion attacks have increased in recent years. Hand bombs are one of the means for terrorist operations because of their dangerous progressive damages. In this paper, a full coupled numerical method is adopted to study the dynamic response of a metro tunnel in the sandy loam. The numerical model is developed using LS-DYNA and will be able to present a realistic behavior for the physics of this phenomenon. In the current study, the ALE method has been used. The air, explosive charge, and soil are considered as ALE’s parts; while, the structure of the tunnel has Lagrangian mesh. Two paths have been studied in the longitudinal and the circular directions for assessing tunnel lining safety. In the free-field state, the accuracy of the model is verified by comparing the peak pressure and acceleration in the soil with the empirical predictions available in the literature. The safety assessment has been done according to explosion vibration criteria. The tunnel would not be safe, as per the PPV standard, under the condition of w=500kg and R=4m. Tunnel crowns are the most vulnerable areas while the peak particle velocity is 19cm/s with maximum permanent vertical deformation.

Detection of damages in structures during their service life is of vital importance and under attention of researchers. In this paper, it is attempted to identify damages in prestressed concrete slabs using vibration responses obtained from modal testing in the time domain. For this purpose, first some damage scenarios with various geometric shapes and at different locations of numerical models, corresponding to a prestressed concrete slab, were created. Next, the impact hammer force in the modal test was simulated and the accelerations time histories at different degrees of freedom corresponding to the numerical models per two states of damaged and undamaged structure were selected as the inputs for a number of damage indices to identify the damage locations. Some of these damage scenarios have been located at the middle of prestressed concrete slabs and some at the corners. The proposed damage indices in this research are obtained based on the area under the diagram of acceleration time histories, maximum and also the area under diagram of detail coefficients of the wavelet transform using the three wavelet families of Daubechies, Biorthogonal and Reverse Biorthogonal. The results showed that using damage index obtained from the area under diagram of detail coefficients of wavelet transform with the mother wavelet db2 could detect the damage scenarios at the middle and corners of the slab with a well precision. Furthermore, the damage scenarios at the corners of numerical models could be detected properly by using the mother wavelet rbio2.2 in the proposed damage index.

In this study, the progressive collapse of reinforced concrete structures due to vehicle collision to the columns of the ground floor was modeled and examined. For this purpose, a four-story reinforced concrete building with the intermediate moment frame system was designed using ETABS software followed by the simulation of impact loading by SAP2000 software. Performing non-linear time history dynamic analysis, the critical forces required to the column failure were determined via trial and error by considering different live load contribution. Then, the corresponding critical velocities for 4, 8, and 12 ton vehicles were determined. Finally, the progressive collapse of the building was examined by the sudden removal of the column. The results showed that by increasing the percentage of live load contribution, the force and critical velocity for the instability and damage of the column will decrease. Furthermore, comparing the perimeter and corner columns showed that the corner columns are the most critical columns for occurrence of the progressive collapse. In addition, during the assessment of the progressive collapse, it was found that the number of damaged springs in the corner column removal scenario is less than that of the perimeter column removal scenario.

Two numerical methods are proposed for dynamic analysis of single-degree-of-freedom systems. Basics of dynamics and elementary tools from numerical calculus are employed to formulate the methods. The energy conservation principles triggered the basic idea of the first method, so-called energy-based method (EBM). It is devised for dynamic analysis of linear damped system whose damping ratio is greater than 1%. The second method uses function approximation theory and integration scheme, and called simplified integration method (SIM). Several numerical examples are investigated through SIM. A detailed comparison is made between the proposed methods and the conventional ones. The results show that the proposed methods can estimate the dynamic response of linear damped systems with high accuracy. In the first example, the peak displacement is obtained 6.8747 cm and 6.8290 cm which closely approximate the highly exact response of Duhamel integral. Results show that Newmark-β method is the fastest one whose run-time is 0.0019 sec. EBM and SIM computational times are 0.0722 sec and 0.0021sec, respectively. SIM gives more accurate estimate and convergence rate than Newmark-β method. The difference of peak displacement obtained from two methods is almost less than 1%. Thus, SIM reliably estimates the dynamic response of systems with less computational cost.

Using the recycled materials, such as waste concrete aggregates can be considered as a suitable solution for resolving environmental issues. The recycled coarse aggregates (RCA) can be utilized effectively in manufacturing structural concretes. Due to hardness and errors of direct tensile and splitting tensile tests, double -punch test (DPT) can be regarded as a reliable test method for evaluation of tensile strength in concrete specimens. In this study, application of DPT was investigated as a less known test method for RCA concretes considering different effective factors, such as water–to-cement ratio (0.4, 0.5, and 0.6), maximum nominal size of RCA (10 and 19 mm), curing conditions (wet and dry), and replacement level of RCA (0, 50, and 100%) and the results were validated by direct tensile and splitting tensile test results. A statistical analysis was performed to indicate significance of each variable in DPT results of RCA concretes. Also, compressive strength and modulus of elasticity were assessed and their relationships with tensile strength of the specimens were studied. The maximum RCA size, replacement level of RCA, and mechanical properties were diminished in mixtures by increasing water-to-cement ratio. Generally, DPT results showed remarkable proximity to direct tensile test results with a slight increase. In wet curing condition, mean values of splitting tensile, DPT, and direct tensile tests in the specimens containing 19mm of RCA were 11.61, 10.06, and 9.44% higher than those containing 10mm of RCA, respectively. Moreover, results of statistical analysis showed that the studied factors had significant effects on the results and they must be regarded in evaluation of DPT.

Using shell foundations as well as their benefits in the case of improved bearing capacity is investigated these days, especially strip folded shape. Because of more contact in soil, these type of shells have more bearing capacity than shallow foundations. In this research the behaviour of Strip Inverted Folded Plate Shell Foundation is studied on sandy soil. The elastic perfectly plastic numerical analyses and experimental tests are analysed and compared with shallow foundation. The effect of adding edge, variation in width and shell angle are considered. More than 45 geometrical shells models have been selected for research and the results are compared with common strip foundation in same width. Digital stress transducers are used for integrity of stresses and numerical model verification. The results indicate that adding edge with the same width and decreasing the B/D ratio in shell strip foundation improves the bearing capacity. Also when an edge on the toe of the foundation equivalent to the embedment depth is used the bearing capacity is improved in the range of 3-50%. Variation in shell angle with the same width results in increasing the bearing capacity up to two times. Finally, it is recommended to use a shell strip foundation with of 45º to 60º and with an edge equal to embedment depth.

In structural analysis and design, there are always uncertainties in determining loads and capacities. Structural reliability quantitatively considered uncertainties in analysis and design procedure. One of the well-known criteria to assess structural reliability is the Total Reliability Index (TRI) of structures. Yielding Displacement (YD) is an important component for calculations of TRI. Due to the changes in the analysis method, input type, normalization procedure, and the definition of target displacement, there are uncertainties in YD calculation. In structural reliability studies, both loads and resistance parameters are modeled as random variables. Therefore, the YD can be considered as a random variable. This study utilizes incremental dynamic analysis (IDA) to calculate TRI in mid-rise reinforced concrete moment resistant frames with intermediate ductility. The effect of uncertainty caused by YD is calculated based on pushover dynamic analysis. The reliability indices for the six structures of 3, 5, and 8 stories and three and five-span reinforced concrete moment frames show that the uncertainty caused by the YD reduces the TRI, but does not affect the seismic performance of the structure, significantly.

Concrete resistance to chloride ion penetration is an important parameter against the corrosion of rebars. The rapid chloride permeability test has already been used to predict UHPC’s resistance at ages up to 28 days under different curing regimes. However, the simple and non-destructive surface electrical resistivity (ER) method, standard specimens, for longer than 28 days and the effects of sulphate and chloride have seldom been considered in UHPC. Here, the ER and compressive strength (CS) tests were performed on 45 UHPC cylindrical specimen with a diameter of 10 cm and a height of 20 cm cured in water,10% magnesium sulphate and 3.5% sodium chloride solutions for 7, 14, 28, 56 and 90 days. The ER, CS and density increase with age. However, concerning the reduction in ER, the chloride environment was more damaging than the sulphate one. In addition, sulphate had a more destructive effect than chloride on the 90-day CS, so that 3.5% sodium chloride and 10% magnesium sulphate solutions resulted in a decrease after 90 days of 8.73% and 25.5% compared to the control sample, respectively. Furthermore, the curing process affected density’s evolution. Chloride ion penetration was negligible in the specimens cured in water and very low in those cured in the sodium chloride and magnesium sulphate solutions. The results were interpreted by XRD, EDS and SEM. A correlation between ER and CS is proposed.