Journal of Civil Engineering Researchers
Volume:4 Issue: 3, Summer 2022

One of the problems of common bracing system is their buckling against compressive loads, which reduces the amount of energy loss of the structure. Buckling Restrained Brace (BRB) have solved the problem of conventional braces by eliminating the overall buckling of thebrace under pressure. Buckling Restrained Braced Frame (BRBF) is a new type of bracing system that has been widely used in recent years. Nowadays the use of buckling restrainedbraces, due to having more advantages compared to conventional steel braces, have received the attention of researchers and engineers that these advantages include: high ductility, more energy loss, no overall and local buckling, andalso having a symmetrical cyclic curve. This type of bracing is considered as one of the effective systems for dealing with lateral loads caused by the earthquake.Disadvantages in the seismic behavior of conventional braces, such as ductility and low energy loss, general and local buckling, as well as having an asymmetric cyclic curve, have provided grounds for its modification or exclusion from the seismic design process. Buckling restrainedbraces are a type of energy loss system that, in addition to providing high lateral stiffness, increase the formability and energy loss of the structure. The use of this type of braces is allowed in the regulations of some countries. But in some other countries, including Iran, it has not been mentioned. According to the seismicity of the country and the increasing use of these structures in the world, the use and localization of this type of bracing system in Iran is inevitable, and the entry of this lateral bearing system into the design regulations, especially the earthquake regulations of Iran, is mandatory. The results of the analysis show that the energy loss capacity of the buckling restrainedbrace is about 5 times the energy loss capacity of the normal brace.

The importance of evaluating the performance of structures against earthquakes is not hidden from anyone. It is important to have an overview of the resistance level of the structure to achieve a safe and economical design against the potential input forces. Therefore, a lot of research is always done in this areain different ways.This article contains the method and results of the study of seismic vulnerability for WFP connection which is widely used and pre-approved connection for steel moment frames that Has been introduced in the tenth section of the Iranian building code. The purpose is to draw the fragility curve using numerical methods.Due to the fact that this connection is pre-approved just for medium moment frames, it is necessary to check its reliability if want to use it in a special moment frame. Theprobability of structural damage caused by seismic force can be presented as a function of ground motion characteristics and various design parameters Using fragility curves. In this study, seven records of earthquake accelerograms were used for incremental nonlinear dynamic analysis (IDA) those most consistent with the site intended for this structure.

Since the parameters affecting the strengthening of cracked beams and their failure behavior after strengthening are very important, this research is devoted to the numerical investigation of the failure behavior of cracked concrete beams reinforced with steel sheet. The investigated beams have an initial crack in the middle of the span and are reinforced with a steel layer under the beam. Using the finite element method and non-linear static analysis, the bearing capacity of the samples, the growth and opening of the crack opening have been evaluated. First, in order to evaluate the accuracy of the modeling, the results obtained with the data obtained from the existing laboratorywork were compared, and after ensuring the correctness of the modeling, the effect of changing various parameters, including sheetthickness, mechanical characteristics of concrete, initial crack length, was investigated. The results show that the load-opening diagrams of the crack openings have two maximum load points, the first and second maximum points increase with the increase of concrete strength and sheet thickness, and due to the increase in the initial crack length, the first maximum point decreases, while the maximum point The second remains almost unchanged.

Cement production hasalways been associated with environmental challenges due to carbon dioxide emissions. On the other hand, cement production is an energy-intensive process and leads to the consumption of abundant fossil fuels. In order to solve this problem, the productionof geopolymer concrete is on the agenda. The researchers decided to reduce the negative effects of cement production and have superior properties than ordinary concrete. In the current study, slag-based geopolymer concrete was used with 0-2% polyolefin fibers and 0-8% nano-silica to improve its structure. After curing the specimens under dry conditions at a temperature of 60°C in an oven, they were subjected to compress strength, tensile strength and Drop weight hammertests to evaluate their mechanical properties, as well as Permeability test to assess their durability. tests were performed at 7 and 90 days of ageat ambient temperature (20°C). The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete.Increasing the curing age improved the results of all tests. The results of all tests in geopolymer concrete showed the superiority of the results over conventional concrete. At the 28-day curing age, the addition of up to 8% nanosilica to the geopolymer concrete composition improved the compressive strength test results by 19.01%, water permeability by up to 35% and impact strength by up to 36.36%. Addition of up to 2% of polyolefin fibers in the composition of geopolymer concrete resulted in a 28.95% decrease in compressive strength but a 20% improvement in water permeability and an 8.26-fold increase in impact strength. In the following, by conducting the SEM test, a microstructure investigation was carried out on the concrete samples. In addition to their overlapping with each other, the results indicate the geopolymer concrete superiority over the regular concrete. Besides, it demonstrated the positive influence of nano-silica addition on the concert microstructure.

When an earthquake occurs in a region, it causes structural damages to buildings. Retrofitting these damaged structures before earthquakes to happen reduces the potential hazards and minimizes future casualties. In this paper, the seismic assessment of Reinforced Concrete (RC) structures inadequately to withstand seismic loads due to changing demands, and their retrofitting is studied. After a brief introduction of seismic retrofit described for existing structures, methods of assessing the seismicvulnerability of existing buildings are presented. To show the effect of the selected retrofit approach on the seismic behavior of RC buildings, an existing hospital building was selected as the case study. Since the use and occupancy of the selected RCbuilding designed as a residential building had changed, a seismic assessment was carried out using Opensees software to show whether the building needs seismic retrofit or not. After macro modeling to assess the seismic behavior of the structure, the dynamic analysis was conducted by applying 7 earthquake records on soil type B based on Iranian seismic code. Selecting the retrofit approach, which contains using Lead Rubber Bearing (LRB), was performed based on Iranian codes. To consider the uncertainties related to the ground motion, 27 ground motion time histories were utilized and results showed that the building needs seismic retrofit because of the increasing demands. Furthermore, the performed reliability study illustrated an effective role in improvingthe seismic behavior of the buildings under earthquake loads by the retrofit method.

The subject of evaluating the vulnerability and strengthening of structures against various natural and artificial factors such as earthquake, wind, fire and explosion, etc., has been the focus of most civil engineering researchers in recent years. However, the engineering profession is generally not well aware of the design of static or dynamic structures to resist the explosion. In this research, it has been done by presenting materials about the introduction of explosion and the components of this type of loading, and by examining the parameters in explosive loading and the relationshipbetween them, Review and presentation of comprehensive information in this regard has been discussed.