Journal of Rehabilitation in Civil Engineering
Volume:9 Issue: 3, Summer 2021

In order to design buildings against earthquakes, it is necessary to get comprehensive information about their behavior against the forces induced by earthquakes. According to the structural codes, the designed structures should not be damaged against light or moderate earthquakes so that the members should have sufficient strength and safety while they should be a ductile complex with a proper structural configuration against sever earthquakes to dissipate the forces caused by ground motions. In the design of steel buildings, use of moment-resisting frames in combination with braces is a seismic-resistant system. One of these system is the dual steel moment-resisting frames with zipper braces. In this research, the seismic performance of the moment-resisting frame with zipper brace system has been studied and its performance has been compared to the performance when the chevron bracing system is used. Three 4-story, 8-story and 12-story buildings have been selected as representatives for low-rise, mid-rise and high-rise buildings, respectively and then they have been modeled by SAP2000 software and finally, their seismic performances have been evaluated using time history analysis. The structural responses have been compared as comparing the relative displacement of the stories (story drift), the maximum displacement of roof, and the formation of plastic hinges in the members. The results of current study show that using a zipper member decreases both overall displacement of the structure and the damage index so that it directs formation of plastic hinges from horizontal and vertical members toward diagonal members.

In the current experimental work, the simultaneous effect of fineness modulus, water-to-cementitious materials [W/(C+M)], and also micro silica content were investigated on workability, mechanical and physical properties of high strength concrete. For this purpose, 45 mix-designs were made by selecting five different ratios of micro-silica, three W/(C+M) ratios, and three distributions of particle size and then the slump, compressive strength, elastic modulus, and split tensile strength of each designed concrete mixture were determined. Findings showed that increasing the micro-silica content up to 10 wt% improves the mechanical properties of concrete and then leads to a reduction in strength parameters, so that the effect of changes in the micro-silica content on mechanical parameters of concrete becomes more prominent with increasing and decreasing the fineness modulus of aggregate and W/(C+M) ratio, respectively. It was also observed that increasing the micro-silica content leads to reducing the slump and unit weight of concrete so that this reduction is more noticeable in the low fineness modulus of aggregate and water-cement ratio.

Nowadays, Reinforced Concrete (RC) wall-slab systems are being used more extensively due to their effective performance seen in past earthquakes. Progressive collapse is a phenomenon in which all or part of a structure is damaged due to damage or collapse of a small relevant part. The majority of research done in the field of progressive collapse has been on frame-shaped structures. Further, the performance of RC wall-slab structural systems, especially against progressive collapse, has been less studied. In this study, at first, nine concrete buildings of five, ten and fifteen stories with wall-slab structural systems, with the ratio of spans length to the story height (L/H) of 1, 1.5 and 2 and a structural height of 2.75 meters in each story, were designed by the ETABS V16 software. Then, using the SAP2000 software and nonlinear shell-layered elements, nonlinear static analysis was performed by the Alternative Load Path (ALP) method on the models and the results were evaluated. The results demonstrated the relatively high strength of buildings with wall-slab structural systems in withstanding progressive collapse. The rate of vertical displacement of the removal location, the maximum von Mises stress in rebar, the maximum compressive stress and strain in concrete in the interior wall removal scenarios were less extensively compared to the corner wall removal scenarios. In contrast, progressive collapse potential increased significantly with increasing number of stories and the L/H ratio. Also, it was found that, buildings with the wall-slab structural system may exhibit brittle failure behavior influenced by progressive collapse.

The object of this research is to compare the behavior of floating and end bearing stone columns made of recycled aggregates of building debris with natural aggregate. To do so, both types of stone columns were constructed by crushed concrete and crushed brick as recycled aggregates and compared with the same models made of gravel as natural aggregates. All the columns were constructed with the same size, density, and grading in a clay bed. To evaluate the initial quality of materials of the stone columns, the index tests were performed. The results of such tests illustrated the less resistance of recycled materials in comparison to the natural materials; On the contrary, according to the results of the index tests, crushed bricks are not recommended to construct stone columns. Despite the index tests, results of loading on a floating column filed with natural and recycled aggregate were approximately the same, but the bearing capacity of the end bearing column made of natural aggregates was higher than the same model made of recycled aggregates.

In this paper the effect of axial load on dynamic behavior of a simple frame, subjected to harmonic, seismic and earthquake excitation is investigated. The equations of motion are considered for two types of small and large deformations. The method of multiple scales is applied to solve the differential equations of motion with harmonic loading and for small and large deformations. Then, the steady state response near one-to-one resonance condition is studied. The results show that the dynamic behavior of the frame under axial load is completely different in resonance and non-resonance cases. The equations of motion with earthquake loading is also considered and the effect of axial load in the frame behavior under the time history and the response spectrum of the model is studied. Although white noise as a stochastic loading is applied to the model and, the results are approximated using the method of stochastic differential equations so, the mean value and covariance are calculated and the effect of axial force on them is investigated.

In most road pavements design methods, a solution is required to transform the traffic spectrum to standard axle load with using equivalent axle load factor (EALF). The EALF depends on various parameters, but in existing design methods, only the axle type (single, tandem, and tridem) and pavement structure number were considered. Also, the EALF only determined for experimental axles and axle details (i.e., axle weight, length, pressure), wheel type (single or dual wheel) plus pavement properties were overlooked which may cause inaccuracy and unusable for the new axle. This paper presented a developed model based on Artificial Neural Network (ANN) for calculation of EALFs considering axle type, axle length, contact area, pavement structure number (SN), tire pressure, speed, and final serviceability. Backpropagation architecture was selected for the model for the EALF prediction based on fatigue criteria. Finally, among all reviewed ANN configuration, a network with 7-13-1 was selected for the optimum network.

In this paper, by using direct modeling of the soil-pipe line system using finite element modelling (FEM) in OpenSEES software and integration with the particle swarm optimization (PSO) algorithm which is provided in MATLAB software in the reciprocating method, which is repeated in enough epochs, the optimal intervals of the anchor blocks has been gained and the effect of different parameters of pipe diameter, pipe length, burial depth, different soils and different earthquake stimuli on the seismic behavior of pipes having anchor blocks investigated.The results show that the change in the depth of the burial and the diameter of the pipe has no effect on the anchor block optimal intervals. Also, increasing the length of the pipe will cause to increase the proposed optimal distance between the anchor blocks. The levels of earthquake hazard and soil type, as well as the length of the pipe, are factors affecting on the distance between the anchor blocks. The simultaneous effect of softening the soil and increasing the level of the earthquake hazard increases the distance between the anchor blocks.

Concrete is a heterogeneous, complex composite construction material. Fresh property of concrete is a critical property with significant effect on quality , cost of construction, strength, and durability. Even to this day the workability of fresh concrete is measured by empirical test, notably by slump test in spite of its drawbacks and sometimes with misleading results with less practical significance. There is an urgent need to characterize the flow of fresh concrete b y its rheological properties based on material science approach to overcome the inadequacies of the empirical test methods.Fluid rheology approach is the most fundamental one and describes the concrete flow by at least two parameters namely yield stress and plastic viscosity by considering fresh concrete as a Bingham fluid. Understanding and controlling the two fundamental fresh properties of concrete allow for more economical and better performing concrete mixes with the use of wide range of ingredients.This paper brings out the importance of rheology and advocates the use of fundamental science approach with two parameter tests along with advantages and limitations of using rheometers. Also highlights the use of concrete shear box static tests for wide range of workability requirements with the use of new and marginal materials in concrete industry.