Scientia Iranica
Volume:27 Issue: 4, Jul Aug 2020

presented in this paper. The confinement and composite action between the constituent materials result in enhanced compressive strength and ductility of the proposed composite columns compared to traditional reinforced concrete columns. Advantages of FRP products in comparison with other materials include light weight, high specific strength, corrosion resistance, and low maintenance cost. This research showed that pultruded GFRP I-shapes can improve the structural performance of the concrete columns satisfactorily. The effectiveness of discrete and continuous CFRP wrapping arrangements for pultrusion–concrete composite short column subjected to axial compressive loading is assessed in this study. The experimental program is composed of one series of composite columns with discrete wrapping arrangements and one series of full wrapped composite columns. A numerical model was developed to predict the behavior of the FRP-confined composite columns subjected to axial compressive loading. The damage mechanisms of the columns wrapped by the composite layers strongly depend on the chosen materials. The results of finite element models are compared with the data obtained from the carried out experimental program and this comparison showed a good agreement exists between those.

As the concrete material is eliminated from the locations situated around the middle of the cross-sections of bubble decks (BDs), the BD type slabs are lighter than the traditional slabs. In the recent researches, the response modification factor (RMF) is generally determined for the reinforced concrete (RC) structures with the moment-resisting frame (MRF) and dual systems. The dual system comprise mainly the MRF with shear wall (MRFSW), as well as the flat slab having chiefly the BD system. In this paper, the evaluation of values of the RMF of RC structures using BD system are submitted. The obtained results indicate that the lateral strengths of buildings increase by increasing the span length to story height ratio (L/H). Besides, the variations of the span length and the number of the story have more effects than the variation of the usage category buildings on the RMF of structures. Furthermore, the span length has more effect than the number of stories in determining RMF in an MRF. Finally, amongst the building with dual system structures including MRFSW, the low-rise building structures have an RMF equal to 5, and both the mid-rise and high-rise building structures have an RMF of 7.

Funicular shells are thin doubly curved shallow shells which are in compression under dead weight due to their shape. In this study, an analytical approach is employed to consider forced linear vibration of concrete funicular shells with rectangular base under impulse loads based on shallow shells theory. Two boundary conditions simply supported and clamped, both are considered. The solution is obtained by Lagrangian approach. Accuracy of the results has been considered by comparing the results with those of finite element method. The results indicate that under impulse loads, stresses in funicular shells are not only compressive, but also tensile stresses are formed.

Endurance Time (ET) method is a dynamic analysis procedure in which increasing excitations are imposed on structures; these excitations are known as Endurance Time excitation functions (ETEF). This study presents a method to find the optimal objective function for simulating ETEFs which unconstrained optimization problems are. In optimization problems, equations are defined in term of an objective function. In the problem of simulating ETEFs, the objective function can be defined in many different ways regarding considered intensity measures and respective weighting factors. In addition, the type of calculating residuals (absolute way or relative way) diversifies objective function definitions. The proposed method for determining optimal objective function includes quantifying the accuracy of ETEFs in a scalar quantity regardless of their objective functions and introducing an approach to overcome the dependence of results on initial points of optimizations. The proposed method is applied and results are then presented. It is observed that considering only acceleration spectra and calculating residuals in the relative way creates more accurate ETEFs.

Settlement-based designs for foundations, using subgrade reaction modulus (K_s), is an important technique in geotechnical engineering. Plate load test (PLT) is one of the commonly applied methods to directly determine K_s. As the determination of the K_s from PLT—especially at depths—is relatively costly and time-consuming, it is necessary to develop models that can handle simply determinable properties. In the present study, the suitability of the Group Method of Data Handling (GMDH)-type neural network (NN) to estimate the subgrade reaction modulus of clayey soils has been investigated. In order to derive GMDH models, a database containing 123 datasets compiled from geotechnical investigation sites in Qazvin, Iran, has been used. The performance of the GMDH models has been compared with other available correlations for clayey soils, and it has been demonstrated that an improvement in estimating the K_s has been achieved. Finally, a sensitivity analysis has been conducted on the proposed models, showing that the proposed K_s is considerably influenced by changing the LL value.

In this paper, the application of Endurance Time method in seismic analysis of bridges is explained. The Endurance Time method is a novel seismic analysis method based on time history analysis in which a structure is subjected to a predefined intensifying acceleration function. First, six concrete bridges were modeled. Three Endurance Time acceleration functions were applied to the models and the average of the responses were calculated. Next, the time history analysis was conducted using seven real accelerograms scaled using the method recommended by FHWA 2006 to be compatible with the design spectrum of seismic AASHTO guideline for a site with soil type C in Berkeley, California. The average of the responses of these seven analyses is considered as reference. Scaling the mentioned accelerograms over a wide range of hazard levels, Incremental dynamic analysis is performed. Finally, the comparison of the response of ET and time history analysis and also comparison of ETA with IDA curves reveals good agreement. The major advantage of ET method over time history and IDA methods is less computational effort needed for the analysis. This saving in time is resulted due to the possibility of predicting response by fewer analyses despite maintaining the necessary accuracy.

This paper presents the swelling and consolidation characteristics of Lignosulfonate (LS) stabilized expansive clay. Expansive clay samples of Amol city in Iran have been used in this research. Based on Atterberg limits and unconfined compressive strength tests, optimum percentage of LS for treatment of this clay was determined 0.75% by soil dry weight. To investigate swelling and consolidation properties of untreated and LS-treated remoulded samples, one dimensional swell and consolidation tests were conducted on these samples. Test results showed that LS has considerable effect on the consolidation and swelling behavior of the expansive clay. Moreover, the effects of compaction water content change and cyclic wetting and drying on the volume change properties of unstabilized and LS-stabilized samples were investigated. Untreated and LS-treated specimens showed different consolidation behavior to the changes of compaction moisture content due to the altering of soil expansivity category from high to moderate. The SEM images of samples showed that the soil specific area was reduced because of stabilization. This reduction in soil specific area was led to the decrease of affinity of samples to moisture increase, so the volume change of expansive clay was decreased.

In the area of damage detection, there have been many notable methods introduced in the past years. Damage Load Vectors (DLV) is among the most powerful methods, which computes a set of load vectors from variations in flexibility matrices of a frame in the undamaged and damaged conditions. These flexibility matrices are derived from acceleration responses of the frame which can be captured using accelerometers. The DLV method then scrutinizes this shift among the flexibility matrices, which ultimately enables locating the damaged member(s). This study holistically conducted seven experimental tests, with seven damage scenarios of a test frame installed on a semi-harmonic shaking table. The DLV method was subsequently employed to locate the damaged members using recorded frame vibration data obtained from ‘noisy’ accelerometers positioned on the frame at eight predefined locations. The Eigen Realization Algorithm (ERA) alongside Pandy’s recommendations were adapted herein to facilitate generation of accurate flexibility matrices derived from the noisy accelerometers. The outcome is very encouraging with accurate identification of damaged members in all seven damage scenarios without any ‘positive-false’ and ‘negative-false’ findings. Additionally, there is a decrease (from 0.045 to 0.289) in the accuracy of WSI index when the number of damaged members is increased.

Structural collapse is the main concern in the existing structures which are built in the seismic-prone regions. Therefore, the primary goal of the seismic provisions in building codes is to prevent the global collapse. Iran is located in the Alpine-Himalayan belt, and has experienced some of the most destructive earthquakes in the past century. To evaluate the extent to which the Iranian building code provisions meet this objective, the authors have conducted a detailed assessment of collapse risk on a set of moderate moment resisting reinforced concrete (RC) buildings. This study considers P-Delta effects, deterioration in strength and stiffness, and cyclic deterioration in structural components. Structural assessment is performed using OpenSees platform and the multiple-record incremental dynamic analysis (IDA). Results are presented in terms of the IDA capacity curves and the collapse fragility functions at different seismic hazard levels. Results show that probability of instability increases with height of the buildings. Moreover, the collapse confidence level was evaluated considering the available uncertainties. Assuming a minimum confidence level of 90% for the buildings, the collapse prevention limit state under the 2%/50 hazard level is not satisfied for the 9 and 12 story frames, and they need to re-designed.

In this study, effective parameters on polymer concrete (PC) based on epoxy resin such as filler, hardener and solvent are investigated. Rice husk and broom stem ashes as fillers with mixture of 50-50% Acetone-Toluene as solvent in preparation of PC samples were used. According to experimental results, addition of fillers improved compressive, flexural and chemical strengths of the PC samples. In the sample with 18.4% polymer, additional of rice husk ash with ratio of filler-aggregate 0.075, compressive strength improved by 21%. For the sample with broom stem ash ratio of filler-aggregate 0.09, the flexural strength was improved by 27%. In addition, experimental data proved that addition of optimum amount of solvent improved the performance and enhanced the compressive and flexural strengths. But excess amount of solvent may reduce the adhesiveness of the polymer therefore it may have negative impact on PC. The combination of hardener-resin may influence on the strength of PC. Amine type of hardener with low equivalent weight improved 27 and 13% on compressive and flexural strengths. Also elasticity module was increased in compare with the samples having high equivalent weight of amine type hardener.

This research evaluates effects of climatic change on future temperature, precipitation and flow discharge in the Karkheh watershed (a watershed in south west of Iran). For this purpose, it utilizes general circulation models (GCMs) and the non parametric Mann-Kendall (MK) trend test. Considered hydrometric station is the Jelogir station at the upstream of the Karkheh dam. Base time period is 1971-2014 and future time period is 2030- 2073 for prediction of meteorological and hydrometric phenomena in the Jelogir station. For GCM model, the Canadian Climate Change Scenarios Network (CCCSN) database represents data of HadCM3 model for A2 and B2 scenarios. For using in a watershed, this research applies SDSM downscaling model and introduces predicted precipitation and temperature of future time period to IHACRES model for prediction of flow discharge. Also the non parametric Mann-Kendall trend test and the Theil–Sen approach (TSA) estimator distinguishes trend of observed and predicted data. Results of scenarios A2 and B2 have not much difference. Different climatic scenarios show that temperature increases and precipitation and flow discharge decrease, also MK test and TSA estimator represent that slope of their variations will slow down in future and most of changes are related to winter and spring.

Project scheduling in the resource-constrained situation is one of the key issues of project-oriented organizations. The aim of resource-constrained project scheduling problem (RCPSP) is finding a schedule with minimum makespan by considering precedence and resource constraints. RCPSP is a combinatorial optimization problem and belongs to the class of NP-hard problems. The exact methods search the entire search space and are unable to solve large-sized project networks. Thus metaheuristics are used to solve this problem with less computational time. Due to the probabilistic nature of metaheuristics, it is a challenging problem to balance between exploitation and exploration phases. The literature review shows that embedding with chaos improves both the convergence speed and the local optima avoidance of metaheuristics. This paper presents a Chaotic Vibrating Particles System (CVPS) optimization algorithm for solving the RCPSP. Vibrating Particles System (VPS) is a physic inspired metaheuristic which mimics the free vibration of single degree of freedom systems with viscous damping. The performance and applicability of the CVPS is compared with the standard VPS, and five well known algorithms on three benchmark instances of the RCPSPs Experimental studies reveals that the proposed optimization method is a promising alternative to assist project managers in dealing with RCPSP.

In recent years, the construction of high-rise buildings as an urban development strategy has been accepted in many megacities. High-rise buildings have positive, as well as negative impacts on urban environments. Therefore, the environmental impact assessment of high-rise buildings for establishing strategies for sustainable and resilient urban development is essential. In this study, the environmental impact of high-rise buildings with a resilient development mindset is assessed. Resilience mindset provides an approach for including the uncertainties and interdependence of systems and processes for planning new sustainable developments and assessment methods.  The corresponding environmental impact assessment is done by monitoring the structural changes and their impacts on the function of ecosystem and environmental services.  Here, the positive and negative impacts of high-rise buildings are evaluated. Protection of impervious surfaces as a positive and changing the natural pattern of urban wind flow as a negative impact is considered. The transparency of the results and the reduction of uncertainty are the advantages of using the resilience mindset in environmental impact assessment. The results of this study suggest that the resilient development mindset can improve the environmental assessment through the adoption of the appropriate indicators at multiple scales and differentiation between the primary and secondary effects.

An experimental investigation was conducted to improve the limitation of Rice Husk Ash (RHA) blended concrete in terms of durability, by incorporating Re-dispersible Polymer Powder. To examine durability properties of Rice Husk Ash Polymer-Modified Concrete (RHAPMC) matrix, the RHAPMC mix of 1:2:3 proportions was used to prepare the specimens. To prepare Rice Husk Ash-Modified Mix (RHAMM), 10% of RHA was replaced with cement. RHAPMC was made with the inclusion of polymer at the ratio of 1 to 7.5% by the weight of cement. Most common durability related properties, i.e. water absorption, density, water permeability, ultrasonic pulse velocity and compressive strength were experimentally investigated. The results showed a remarkable improvement in durability characteristics in newly developed matrix of rice husk ash polymer modified concrete and could be used as a repair material in aggressive environment.