Civil Engineering Infrastructures Journal
Volume:50 Issue: 2, Dec 2017

This study introduces, two models based on Gene Expression Programming (GEP) to predict compressive strength of high strength concrete (HSC). Composition of HSC was assumed simplified, as a mixture of six components (cement, silica fume, super-plastisizer, water, fine aggregate and coarse aggregate). The 28-day compressive strength value was considered the target of the prediction. Data on 159 mixes were taken from various publications. The system was trained based on 80% training pairs chosen randomly from the data set and then tested using remaining 20% samples. Therefore it can be proven and illustrated that the GEP is a strong technique for the prediction of compressive strength amounts of HSC concerning to the outcomes of the training and testing phases compared with experimental outcomes illustrate that the.

Environmental Flow Requirement (EFR) is defined as the flow that is necessary to ensure the existence of habitats in water resources systems. EFR is defined in rivers as flow index commonly. Tennant method is the most popular hydrological method in rivers and based on the historic flow data. The most common method of hydraulic rating method is the wetted perimeter method. Habitat simulation techniques attempt to assess environmental flow requirements on the basis of detailed analyses of the suitability of instream physical habitat. Investigation of the relationship between simple approaches and physical habitat simulation approach and presentation of new recommendations based on the hydraulic and hydrological data can be very useful in estimation of environmental flow in planning phase of river projects. Main objective of present research are modification of Tennant and wetted perimeter methods and providing more reliable recommendations in Simindasht basin in Tehran province which Rainbow Trout is dominant species. Based on the results, in April to September 60% of mean annual flow (MAF) and in October to March 120% of MAF can provide sustainable habitats approximately. Also common wetted perimeter method estimates EFR more than real instream flow need of target species. This method will assess the suitable value for environmental flow on 86% of the maximum wetted perimeter approximately. But based on Physical habitat analysis mean suitable environmental flow will be assess in 63% of the maximum wetted perimeter. Hence modification of wetted perimeter based on physical habitat analysis can reduce instream flow need significantly.

The soil is a heterogeneous and anisotropic medium. Hydraulic conductivity, an intrinsic property of natural alluvial deposits varies both deterministically and randomly in space and has different values in various directions. In the present study, the permeability of natural deposits and its influence on the seepage flow through a natural alluvial deposit is studied. The 2D Finite Difference code, FLAC 5.0, is used for modeling permeability as a random variable with lognormal distribution and correlated structure. Effect of spatially varying permeability on the seepage flow through deposit is investigated for both isotropic and anisotropic conditions. Results show that in isotropic condition, the mean discharge flow rate calculated from stochastic analyses is less than the equivalent deterministic value and this reduction depends on the coefficient of variation, COV of permeability and the correlation length. The directionality of permeability introduced as mechanical anisotropy was also studied along with the heterogeneity. It was found that increasing the anisotropy ratio of permeability leads to the formation of horizontal flow canals and increasing the seepage flow consequently at a constant vertical permeability. Variation of permeability coefficient was found to have almost no impact on mean discharge flow rate for anisotropic fields in comparison to the isotropic condition.

In this paper, a plane quadrilateral element with rotational degrees of freedom is developed. Present formulation is based on a hybrid functional with independent boundary displacement and internal optimum strain field. All the optimality constraints, including being rotational invariant, omitting the parasitic shear error and satisfying Fliepa’s pure bending test, are considered. Moreover, the static equilibrium equations are satisfied in this scheme. Authors’ element has only four nodes and twelve degrees of freedom. For the boundary displacement field, Alman’s second-order displacement function is employed. The validities of the proposed element are demonstrated by eleven numerical examples: thick curved beam, thin cantilever beam, Cooke’s skew beam, thin curved beam, cantilever beam with distortion parameter, high-order patch test, cantilever beam with five and four irregular mesh, Mc Neal’s thin cantilever beam and cantilever shear wall with and without openings. When utilizing the coarse and irregular meshes, numerical tests show the high accuracy, rapid convergence and robustness of the suggested element. Less sensitivity to distortion is another property of the new element.

Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral spreading, this vulnerability is particularly conspicuous due to a loss of strength and stiffness in the liquefied soil. A nonlinear effective stress analysis incorporating an elastoplastic constitutive model based on Finite Difference Method (FLAC2D program) was used to numerically simulate shake table experiment on piles in laterally spreading soils. The soil-pile interaction has been properly considered by using interface elements. The main objective of this paper is to assess the accuracy of a 2D numerical simulation of physical models in predicting the dynamic response of pile foundations and to identify the capability of 2D numerical simulation for 3D effects such as shadow and neighboring effects in pile groups without a pile cap. Results are presented and discussed, in which the obtained response from the simulation is compared to that measured in the test. For the single pile, a fairly good agreement was observed between computed and measured results. It was also found that the shadow and neighboring effects reduced lateral load on the piles by few percent of difference compared with experimental results.

This paper extends the previous work of authors and presents a non-layered Finite Volume formulation for the elasto-plastic analysis of Mindlin-Reissner plates. The incremental algorithm of the elasto-plastic solution procedure is shown in detail. The performance of the formulation is examined by analyzing of plates with different boundary conditions and loading types. The results are illustrated and compared with the predictions of the layered approach. These several comparisons reveal that the non-layered Finite Volume approach can present accurate results with low CPU time usage despite its simplicity of the solution procedure.

Although, experimental studies have reported fracture at the corner of Steel Plate Shear Walls (SPSW), no study has been performed to investigate the crack effect, yet. Therefore, in this paper, the effect of crack at the corner of SPSWs on the seismic behavior of the system was investigated. Two probable cracks, that have been studies at the corner of SPSWs utilizing extended Finite Element method based on cohesive crack approach, are initial horizontal crack and initial vertical crack. Numerical results indicated that small initial crack does not have considerable effect on the seismic behavior of SPSW. In addition, the horizontal crack is more effective than vertical crack. Since SPSWs with long initial horizontal crack are ruptured suddenly, so they could not be utilized as a lateral resisting in seismic zone. Nevertheless, no ruptures occur in SPSWs with vertical cracks. Therefore, SPSWs with horizontal crack must be repaired, but no repairing is needed in SPSWs with initial vertical cracks.

In this study, the application of type-1 and type-2 fuzzy inference system (FIS) in semi-active seismic vibration control of the College Bridge using magnetorheological (MR) dampers is investigated. For this purpose, a detailed 3D finite element model of the bridge fitted with MR dampers is created in OpenSees. The command voltage of MR dampers is determined by employing both types of FISs in Matlab environment and making connection between both software. The results show the higher performance of the type-2 FIS for reducing the undesirable vibrations than that of type-1. This is because of the fact that the type-2 FIS considers interval membership functions for inputs in order to obtain the command voltage of MR dampers. Moreover, type-2 FIS effectively includes the effect of uncertainties and time delay. The results demonstrate that type-2 fuzzy controller is capable of reducing further the maximum displacement, base shear, and moment of the bridge by 24.6, 22.8, and 39.25%, respectively, compared to the type-1 fuzzy controller.

The determination of structural and nonstructural damage under earthquake excitations is usually considered as a key factor in performance-based seismic design (PBSD) methods is In this regard, various damage indices have been developed in recent years to quantitatively estimate structural damage. The aim of this study is to develop a simple method to evaluate performance levels of zipper-braced frame (ZBF) structures by using damage indices based on the results of nonlinear static and dynamic analyses. To this end, 5, 7, 10, 12 and 15 story zipper-braced frames (ZBF) are modeled and undergone to twenty different synthetic ground motion records and their damage values have been computed. In dynamic damage analysis procedure, the performance levels of the ZBF models have been computed based on the FEMA-356 standard. Considering the results of the nonlinear dynamic analyses, the correlation between FEMA-356 performance levels and damage indices has been investigated and some simplified formula is presented. On the other side, in static damage analysis approach, by using pushover analysis the performance points of ZBF models have been estimated based on capacity spectrum method (CSM) provided by ATC-40 standard. Then, the correlation between ATC-40 performance levels and some static damage indices has been investigated and some simple equations have been proposed. These relations can be utilized to estimate the performance levels of structures from damage indices. Finally, tables are represented for determination of the structural damage index values for assumed performance levels of the ZBF structures based on static and dynamic damage analysis.

Nanosilicas have been known as super-pozzolanic materials and compared to silica fume, these materials have higher purity of silica and finer particles. However, in contrast to silica fume, nanosilicas are produced by various methods, leading to different morphologies and agglomeration statuses in their initial form. On the other hand, due to several mechanisms such as the bridging effect of calcium ions between particles, double layer compression at a high ionic concentration, and dehydration of silica surfaces, nanosilica particles are destabilized in the pore solution environment of cement mixtures. Thus, the behavior of these materials is different from that of silica fume. In this research, considering the recent studies, a comprehensive investigation has been carried out on the influence of nanosilicas on the mechanical, durability and microstructural characteristics of cement composites. This study investigates the mechanisms that influence the performance of nanosilica in cement-based materials. Based on these mechanisms, several applications have been suggested and discussed. Some of these applications include viscosity-modifying agent in self-compacting concrete, enhancing the cohesion of cement composites, increasing the adhesion capacity of repair mortars and shotcrete to the substrate surface, accelerating the cement hydration, developing low-alkali cements and fast early-strength cements.

A practical Bridge Management System has been developed by the author, which is referred to as the Japanese Bridge Management System (J-BMS) for existing concrete bridges. This paper introduces a newly developed bridge management system for the prestressed concrete (PC) bridges (J-BMS PC version) which is integrated with the PC bridge rating expert system (PC-BREX). The proposed system is able to predict the deterioration process of the existing PC bridge superstructure components as well as assess a broad array of optional corrective strategies. The system also has the capability to search and retrieve from a J-BMS database system (J-BMS DB), the necessary information, carry out suitable analyses to arrive at some recommendations that would help users to optimize their decisions based on engineering aspects, cost and economic issues and bridge management policies. A comparison of the results of applying the system to some actual in-service PC bridges with a special designed survey form to experts shows that optimal maintenance planning as well as bridge rating can be predicted accurately by using the system.

In this research, Performance-Based Plastic Design (PBPD) method has been modified according to the proposed method for considering Soil–Structure Interaction (SSI) effects. In the proposed modified method, based on the existing relationships and in order to maintain the simplicity of the PBPD design method, two important parameters have been modified in the PBPD design method. These two parameters include the modification of the vibration period of the structure due to the effect of SSI and the lateral target displacement modification, which is a key parameter in the evaluation of the structural performance. Efforts have been made to refine the modifications to maintain the simplicity and robustness of the PBPD equations. Finally, design base shear force of the PBPD method has been corrected due to the SSI effect regarding the modified relationships. By making the modifications, in order to better understand this method, structures with a number of different floors, including the 4, 8, 12, and 20 spatial space moment frames, are designed and compared with the results of designing the method without the effect of SSI and design method based on the capacity.