Civil Engineering Infrastructures Journal
Volume:51 Issue: 2, Dec 2018

It is generally accepted that performance-based design has to be reliability-based. Seismic performance evaluation is based on nonlinear dynamics and reliability theory taking into account uncertainties during analysis. Considering the economic importance of jacket type offshore platforms, the present research aims to assess the seismic performance of offshore steel platforms. In this study, three platforms located in the Persian Gulf were modeled using three dimensional structural modeling tools. Each platform was modeled and analyzed using both rigid and pinned connections. Reliability analysis was performed in accordance with Federal Emergency Management Agency (FEMA) guidelines using the results of incremental dynamic analysis for the three platforms. The results showed that platforms possessing rigid connections provide the desired confidence level of FEMA for the performance level of collapse prevention while only one platform with pinned connections was able to provide the desired confidence level.

In this paper a league championship algorithm (LCA) is developed for structural optimization where the optimization variables are of discrete type and the set of the values possibly obtained by each variable is also given. LCA is a relatively new metaheuristic algorithm inspired from sport championship process. In LCA, each individual can choose to approach to or retreat from other individuals in the population. This makes it able to provide a good balance between exploration and exploitation tasks in course of the search. To check the suitability and effectiveness of LCA for structural optimization, five benchmark problems are adopted and the performance of LCA is investigated and deeply compared with other approaches. Numerical results indicate that the proposed LCA method is very promising for solving structural optimization problems with discrete variables.

This study has investigated the creep properties of asphaltic concrete modified with different dosages of waste polyethylene terephthalate (PET) in two different ranges of size. Uniaxial dynamic creep test at 40°C was conducted on the cylindrical specimens of the mixtures. The load was applied in two different frequencies of 0.5 and 5Hz. Creep test results showed that the accumulated strain under dynamic loading increased with increasing PET content, with lower values for the mixtures containing finer PET particles. Moreover, it was found that the accumulated strain under the loading with higher frequency was more than that under lower frequency, with higher sensitivity to frequency for the mixtures containing finer PET. The results of dynamic creep tests were used for determination of the constants of a three stage model. The linear creep slope in the second region of the creep curve and the flow number showed that the increase of PET content and size results in decrease of permanent deformation resistance. However, the mixtures modified with 4% of fine and coarse PET particles had the highest loading cycles at the end of primary creep region, where most of the strain was recoverable.

Run off resulted from rainfall is the main way of receiving water in most parts of the World. Therefore, prediction of runoff volume resulted from rainfall is getting more and more important in control, harvesting and management of surface water. In this research a number of machine learning and data mining methods including support vector machines, regression trees (CART algorithm), model trees (M5 algorithm) and artificial neural networks have been used to simulate rainfall- runoff process in Zayandeh_rood dam basin in Iran. Data used in this research included 9 years of daily precipitation, minimum temperature, maximum temperature, mean temperature, mean relative humidity of daily times 6:30, 12:30 and 18:30 and run off. A number of 3294 lines of data were totally used, and simulations were carried out in two different conditions: without previous run off data as input vectors (M1 condition), and with previous runoff data as input vectors of the models (M2 condition). Results show that machine learning techniques used in this research are not able to present acceptable predictions of runoff in M1 condition (without previous runoff data). However, predictions are considerably improved when previous runoff data are used as input beside other inputs (M2 condition). Between the models used in this research support vector machines (SVM) presented the most accurate results, as the values of RMSE for results presented by SVM, regression tree, model tree and artificial neural network are 2.4, 6.71, 3.2 and 3.04, respectively.

This paper describes a method of performance evaluation and remaining life prediction for an aged reinforced concrete (RC) T-girder bridge by J-BMS RC version via close visual inspection data, and also verifies the assessment results obtained as outputs from the Bridge Rating Expert System (RC-BREX) which is a subsystem of the J-BMS, to evaluate the effectiveness of the system. The Bridge Management System (J-BMS) that was previously developed by the authors, and which is capable of forecasting the deterioration process of existing bridge members, was applied to evaluate the safety indices (soundness score) and remaining life of the target bridge based on these test results. Using these methods, the remaining life of an aged RC-T girder bridge (SK-bridge) can be quantitatively estimated by applying the bridge rating expert (BREX) system, which is a subsystem of the J-BMS RC version that incorporates with the field inspection data. In this study, close visual inspection was carried out on the aged bridge by professional visual inspectors, during which all variations of the inspection results were evaluated using a five-step questionnaire. As a result, it was found that the soundness score (safety index) and remaining life predictions were influenced by the learning (supervised) data selection. Additionally, the predicted remaining lives were verified through concrete core tests extracted from main girders and deck slabs.

One of structural passive control methods is to use Tuned Liquid Damper (TLD). However, because of the nature of the TLD, only one tuning frequency can be created when the water is sloshing. To fix this problem, some installed rotatable baffles can be embedded inside TLD called Variably Baffled TLD (VBTLD) where by changing the angle of the baffles a tuning frequency range is created. This gives the passive control system the capability to be pre-tuned according to the desired frequency. In this paper, the effects of rectangular and cylindrical shapes of container on behavior of VBTLD are studied and numerically validated with experimental results. There are four baffles inside each damper tuned manually in different cases. In numerical investigation, the rectangular TLD created greater returning force than cylindrical TLD in all depth and angle selections. By increasing the baffle angle, from 0 ° to 80 ° at the water depths of 4, 5.2 and 6.4 cm, the control forces are increased 59.8%, 38.4% and 30.2% respectively for rectangular TLD and 58.4%, 50.4% and 46.1% for cylindrical TLD.

Various materials have been utilized for ground improvement techniques based on geoenvironmental compatibility. The application of lime mortar in soil has been catching the attention of researchers and engineers. However, there is a lack of research on the variation of moisture content in soil affecting the mechanical behavior of lime mortar. In this study, large-scale laboratory tests were conducted on approximately thirty specimens to evaluate the size effect on stiffness and load bearing capacity of compacted lime mortar (CLM) columns and clayey soil under different saturation conditions. In addition, approximately forty small-scale laboratory tests were carried out on dry clay, dry CLM column and lime mortar specimens to evaluate the unconfined compressive strength (UCS). According to results, UCS of CLM column under small-scale condition was higher than that of the large-scale. Moreover, high moisture content had a significant influence on the stiffness of improved ground and the bearing capacity of CLM columns. Finally, validation of results indicated that numerical model predictions are in agreement with experimental results.

Nonlinear dynamic analyses are performed to compute the maximum relative input energy per unit mass for 21 multi-degree-of-freedom systems (MDOF) with preselected target fundamental periods of vibration ranging from 0.2 to 4.0 s and 6 target inter-story ductility demands of 1, 2, 3, 4, 6, 8 subjected to 40 the earthquake ground motions. The efficiency of the several intensity measures as an index for damage potential of ground motion in MDOF systems are examined parametrically. To this end, the dispersion of normalized input energy by different intensity measures have been evaluated and compared. Results of this study show that using all intensity measures will result in a significant discrepancy in input energy spectra of MDOF systems, which are in most cases larger than 0.5 and even can take the value of 1.9 for some cases. This signifies that the evaluated intensity measures may not suitable for MDOF systems. A dimensionless intensity measure as a normalized energy index is proposed for MDOF systems subjected to far-fault earthquakes. It was demonstrated that the proposed normalized input energy values have smaller dispersion compared to those of the other indices for MDOF systems with all ranges of period and ductility ratio used.

Installing stone columns in the ground is an effective improvement technique to increase the load bearing capacity and reduce the consolidation settlement of the loose or weak cohesive soils. In addition to the increase in the bearing capacity and reduction in the settlement, stone columns can accelerate the dissipation rate of the excess pore water pressure generated by the surcharge, which expedites the ground improvement procedure. Due to these advantages, this technique has been widely used to improve the mechanical properties of the soft and problematic soils. In this study, the behavior of stone columns in saturated soft grounds are studied using Finite Element (FE) numerical method. For this purpose, a three-dimensional (3D) FE model of the stone column-improved ground is built considering the nonlinear behavior of the soil and stone columns. This model considers the effect of consolidation, and its accuracy is verified using the unit cell concept and the results of a real ground improvement project in Iran. In addition, a parametric study is performed using the verified FE model to investigate the effect of different material and geometric characteristics of the stone columns on the behavior of improved ground. At the end, the efficacy of the stone column method is compared to that of deep soil mixing (DSM) ground improvement technic.

Progressive collapse is defined as the spread of an initial damage from one member to another, leading to extensive partial or total collapse of the structure. In this research, the potential of progressive collapse due to a sudden removal of vertical load-bearing elements in reinforced concrete buildings structures with different floor plans such as geometrical regular and irregular floor plans as well as floor plans with and without torsional irregularity were assessed. The buildings were designed according to ACI 318-14 provisions and Iranian seismic code. The progressive collapse potential of the structures was assessed following of a sudden column or shear wall removal in different locations in their first floor using nonlinear dynamic analysis (NDA). Displacement sensitivity and column sensitivity indexes were utilized to compare different cases of load-bearing element removal in each model. Results indicated that in all geometrical regular floor plan, floor plan with reentrant corner and floor plan with torsional irregularity, the most critical case of column removal was removing columns located in outer corners of the plan. In addition, removing external columns was more critical than internal columns. In buildings with shear walls, removing shear walls led to much more critical scenarios than removing columns. Furthermore, results revealed that buildings with torsional irregularity floor plan, designed according to Iranian seismic code, had a lower potential of progressive collapse rather than those buildings with no irregularity.

Stiffness matrix of the four-node quadrilateral plane stress element is decomposed into normal and shear components. A computer program is developed to obtain the straining modes using adequate and reduced integration. Then a solution for the problem of mixing straining modes is found. Accuracy of the computer program is validated by a closed-form stiffness matrix, derived for the plane rectangular as well as square element. It is shown that method of integration has no effect on the straining modes, but it influences the eigenvalues of the bending modes. This effect is intensified by increasing the element aspect ratio, confirming the occurrence of shear locking.

Semi-buried structures are most commonly used at first line of defense along the border between two countries. This demands investigation of their dynamic behaviour under blast loading. Herein, a semi-buried structure with foam sandwiched walls and buttresses to reduce the effect of blast is analysed. The effect of provision of different configurations of buttresses and foam core between two layers of structural wall subjected to explosive loadings is investigated using ABAQUS/Explicit®. Modelling of semi-buried structure is carried out by employing shell elements and soil is modelled using frequency independent spring-dashpot-mass model. The foam core is modelled using brick elements with reduced integration and volumetric hardening. Effect of strain rate on structural steel is modelled by employing Johnson-Cook (J-C) model. Results indicate that geometry of buttresses and foam core type governs structural response to dynamic loading. It is observed that inner wall of the structure is protected by foam provided in between walls and helps in blast mitigation. Further, it is observed that design of such structures is dependent on the correct identification of buttresses type and isolation of inner wall of structure by provision of energy absorbing materials like foam.