Civil Engineering Infrastructures Journal
Volume:53 Issue: 2, Dec 2020

A new macroscopic four node reinforced concrete shear wall element is presented. The element is capable of considering the effect of wall opening without any divisions in the element. Accordingly, the opening may be located arbitrary inside the element. Furthermore, three degrees of freedom are suggested here at each node, totally compatible with the surrounding frame elements. The element is considered only for in-plane stiffness of the wall. Therefore, the surrounding frame elements are assumed to be assembled separately which provides a suitable modeling condition. The element consists of vertical springs, horizontal springs and a shear membrane shell. No rigid element is used in the assembly for imposing the bending action; however, the compatibility is achieved using the definition of shape functions. The element is developed and evaluated in linear applications. The results indicate that some major defects of other macroscopic shear wall elements are removed by the proposed element.

FRC concretes with high strength are practical material for strengthening existing particularly damaged concrete structures and able to dissipate seismic energy. The main purpose of this paper was to using high strength-FRC concrete for strengthening the damaged and undamaged frames. The five experimental specimens were loaded laterally and vertical gravity loads, simultaneously. The first specimen was a reference without strengthening, but the second same specimen was strengthened. The other three specimens were initially were loaded up to 55, 75, and 100% of the maximum capacity of the reference specimen and prepared as damaged specimens. The damaged specimens were laterally and vertically loaded. The test results showed that ductility of the undamaged strengthened frame was 2.2 times that of the reference specimen, while these amounts for three strengthened specimens (55, 75, and 100%) were up to 110, 60, 15 increase compared to the reference.  The maximum lateral capacity of second undamaged, third fourth, and fifth damaged specimens were 38 and 35, 16, 9% more than that of reference; while the significant increase of energy absorption from 1.28 to 2.37 times reference was observed.

This research aimed to use response surface methodology (RSM) for investigating the Marshall Stability (MS), flow and Voids in Mineral Aggregates (VMA) of asphalt concrete containing different percentages of Reclaimed Asphalt Pavement (RAP) and rejuvenated by different percentages of waste cooking and engine oil. Variables of RAP content in 3 different levels of 25, 50 and 75% (by the weight of total aggregates) and waste oils content in 3 different levels of 5, 10 and 15% (by the weight of total binder) were selected. Quadratic and linear two factor interaction models were well fitted to the experimental results. Analysis of variance showed that the models were capable to well predict the MS, flow and VMA of the mixtures, and the terms of oil and RAP content and type of oil are significant. MS, flow and VMA increased with increasing RAP content and decreased with increasing oil content. Results also reveal that higher MS, flow and VMA values are resulted by using WEO than using WCO. Some interaction effects were found between RAP content, oil content and type of oil on the responses. Optimization analysis showed that using 10.6% of WCO and 15% of WEO, allows a maximum RAP incorporation of 75 and 51.77%, respectively, by which the properties are similar to control mix. Use of the rejuvenators allows using high RAP content without sacrificing the properties of the mixtures.

The long-term effects of scour have been identified as one of the primary reasons for bridge failure. To evaluate the performance of the bridges against scour, it is essential to assess the conditions of the bridge foundation including the depth of the piles.  Sonic Echo (SE) has been a favorable nondestructive method to evaluate the condition of unknown bridge foundations in the recent decades. Previous studies have shown that the results obtained from SE tests can be affected by a variety of factors such as the pile-to-soil stiffness ratio, length-to-diameter ratio of the pile, presence of defects and anomalies near the pile head, striking method, and hammer type. Although previous studies have discussed such affecting factors, there is a lack of comprehensive investigation regarding the effect of striking method and hammer tip type specific to wood piles supporting bridge decks. In the current study, the effect of striking method and hammer type on the success of SE tests conducted on wood piles has been scrutinized by investigating various options of striking methods and hammer tip types. After comparing different options, superior ones were identified and recommendations for better conducting the SE tests on unknown wood bridge foundations were presented. Numerical simulations were also performed to support some of the conclusions.

One of the aims of earthquake engineering is to build secure structures against random loads and also various damage types under lateral loads. Progressive collapse, a word that has attracted attention of many researches after the failure of the World Trade Center, can occur under abnormal loads such as explosion or natural causes like earthquakes. Resistance to progressive collapse is expressed by a parameter called Robustness. The purpose of this study is to survey various methods of calculating robustness index under lateral loads, especially seismic loads, in steel moment frames. So three steel structures with 4, 8 and 15-story and intermediate moment frames were designed and analyzed subsequently. Different methods of measuring the robustness indexes were compared and eventually presented a simple method to assess robustness index based on nonlinear dynamic analysis. Robustness index introduced using this method, which is based on the types of Pancake and Zipper collapses and energy parameters, tries to express an appropriate standard for structural strength against earthquakes.

In large civil engineering structures, the output-only modal identification is the most applicable technique for estimating the modal parameters such as damping. However, due to no measurement and control of excitation force, the identified parameters obtained by output-only technique have more uncertainty than those derived from the input-output technique. Given the different nature and uncertainties of the two modal identification techniques, in the present study, the damping related to the first 12 modes of a double-layer grid developed from the ball joint system were identified via the two techniques and compared with each other. For this purpose, a double-layer grid was constructed by pipes and balls with free-free boundary conditions provided for both input-output and output-only experiments. Exciting the grid, its acceleration response was measured at appropriate degrees of freedom. Then, by using these data and performing modal analysis, involving four different methods of input-output and five different methods of output-only, the natural frequencies and damping ratios of the desired modes were extracted. The results indicated that despite the good agreement between the modal damping of the grid, as identified by different methods of input-output together and by different methods of output-only together, the results of input-output and output-only methods were different with each other. The damping values through the input-output modal identification methods were on average 65% higher than the corresponding values of the output-only modal identification methods.

The cosine integral transform method is applied to find the expressions for spatial variations of displacements and stresses in the Westergaard continuum under vertical concentrated loading, and distributed loadings acting over lines and geometric areas on the surface. The half-space is considered to be horizontally inextensible and the displacement field reduces to the vertical displacement component. The paper derives a displacement formulation of the equation of equilibrium in the vertical direction. Cosine integral transformation is applied to the formulated equation and the Boundary Value Problem (BVP) is found to simplify to Ordinary Differential Equation (ODE). The general solution of the ODE is obtained in the cosine integral transform space. The requirement of bounded solutions is used to obtain one integration constant. Inversion of the bounded solution gave the solution in the real problem domain space. The stress fields are obtained using the stress-displacement equations. The requirement of equilibrium of the vertical stress fields and the vertical point loading at the origin is used to determine the remaining integration constant, and thus the vertical deflections and the stresses. The solutions obtained are kernel functions employed to derive the expressions for solutions for line, and uniformly distributed loads applied over given geometric areas such as rectangular and circular areas. The vertical stresses are expressed in terms of dimensionless vertical stress influence factors and tabulated. The vertical displacements and stresses obtained are identical with Westergaard solutions obtained by stress function method. The solutions agree with results obtained by Ike using Hankel transform method.

The creep of earth slopes is an important challenge of the long-term stability of slopes. This paper develops a limit equilibrium method (LEM)-based analytical approach for calculating the shear displacement of creep-induced failure surface in 2D state for all slices where both force and moment equilibrium equations are simultaneously satisfied as a new research. The relation between shear displacement and creep time is obtained with regard to visco-elastoplastic creep model. The overall safety factor is first calculated for the slip surface using Spencer method. Then, the shear displacements of all slices are obtained based on vertical displacement of crown and using displacement compatibility relation exists between slices. By combining force and moment equilibrium equations and assuming a zero resultant for inter-slice forces, the vertical displacement at crown is determined using visco-elastopastic creep model. A numerical model was developed to calculate slope displacement by the proposed method. Force and moment equilibrium equations are simultaneously satisfied by iteration technique. The proposed method is verified through two numerical examples comparing the new approach and conventional finite element method.

Panel zone is a part of a column web where surrounded by the continuity plates and the column flanges. Panel zone plays a vital role in the connection behavior. Despite the upward tendency of using cruciform section in many seismic regions, few studies have focused on the behavior of these columns, and especially on the behavior of their panel zone. As well, some recent studies have shown that axial load has a remarkable effect on the yielding process of the panel zone. In this research, a mathematical model is presented to consider the effect of axial force on the behavior of the panel zone in the cruciform columns. The model included the shear stiffness of the panel zone in the elastic and non-elastic region, the yield shear and the ultimate shear capacity of the panel zone. Consequently, 432 Finite Element Models (FEM) in a wide range of dimensions are performed and a parametric study has been done. The comparisons of the results of proposed mathematical model with the results of all Finite Element models demonstrate that the average and maximum deviation for yield and ultimate shear strength of the panel zone are respectively 5.32%, 8.12%, 6.2%, and 8.44%. This matter exhibits the accuracy and efficiency of the proposed mathematical relations.

This paper investigates the composite beam with bolt shear connectors. Composite beams are usually used as secondary beam in buildings. It is clear that studying the torsion in side beams in buildings such as balconies is of great importance. The composite beam was loaded under three different loading conditions including a pure flexural loading, and simultaneous flexural loading with two alternative torsional loading modes. The obtained results from the analysis were compared with each other by three-dimensional non-linear finite element model using ABAQUS. The obtained results, including the mid span deflection, the rotation and slip of composite beams under different loading conditions were investigated. The effect of the type and number of shear connectors on slip of composite beam was studied, too. The results indicated that the slip between the steel beam and the concrete slab along the composite beam increased due to flexure loading, but the torsional loading had a slight effect on the slip.

In this paper, the artificial intelligence is employed to design a Fault-Tolerant Controller (FTC) for structural vibrations. The FTC is designed to reduce the probability of damage considering sensor fault. For this purpose, Neural Networks (NNs) are used as fault detection and accommodation and fuzzy logic is used as a controller. This control strategy requires two groups of neural networks. The first group of neural networks finds the faulty sensor by estimating the structural responses and comparing them with the responses obtained from the sensors. The second group has the task of estimating the response of the faulty sensor using data obtained from healthy sensors. To evaluate this method, the time history analysis of a 3-story benchmark building equipped with accelerometers and active actuators has been used. This evaluation is based on determining the probability of structural damage and the generation of fragility curves under forty ground motions. To develop fragility curves, the criteria specified in the FIMA 356 (IO, LS and CP) for the moment frame based on the inter-story drift are used. This study show that in the absence of the neural networks, sensor fault reduces the performance of the fuzzy controller and it is even possible to increase the structural responses compared to the structure without the controller. In addition, results demonstrate that the proposed control strategy can rectify the deterioration of sensor faults and decrease the probability of failure.

Soil-cement is a mixture of Portland cement, soil and water, which are bonded together due to the cement hydration and compaction. It have durability, low permeability and resistance against wear. Water to cement ratio, cement content and type have been commonly investigated as the most effective factors on the compressive strength of soil-cement. This study aims at the investigation of the effects of some other factors, such as Sand Equivalent (SE), Plasticity Index (PI), and gradation of the soil on the compressive and flexural strength of soil-cement. Results show that the compressive and flexural strength of soil-cement increases with increasing the sand equivalent and decreasing the plasticity index of the soil.