Mohammadsina Sharifi Ghalehnoei, Nima Noormohammadi
Abstract In this study, numerical investigation of reinforced concrete (RC) beams strengthened with prestressed CFRP sheets is presented via the finite element (FE) analysis. Due to the high expenses of experimental tests, especially for large real-scale structures, numerical modeling could be an effective replacement. The main achievement of the present study is to give an insight into the flexural behavior of large RC beams retrofitted by prestressed CFRP sheets. The FE model is first verified by recently published experimental results and then implemented for the analysis of large-scale specimens, which are normally seen in RC structures. The effect of mesh size, width and length of CFRP sheets, ductility and stiffness, and the failure modes are investigated for 13 large specimens. Two recently developed reinforcement techniques, namely the externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) will be probed for the specimens. Based on the results, prestressing the CFRP sheets attached via the EBROG technique considerably enhances the ultimate load, stiffness and ductility of the RC beam in flexure. Besides, it tends to the failure mechanism to the desirable mode of concrete face separation and spreads the cracks along the beam.
Systems of building construction. Including fireproof construction, concrete construction
Abstract This study investigates the corrosion characteristics of prestressing strands and reinforcing bars using mold specimens. These components such as prestressing strands and reinforcing bars are critical for the durability and structural safety of prestressed and reinforced concrete structures, as they bear loads in tensile regions. Prestressing strands, which are constantly under high tensile stress, are particularly susceptible to corrosion. The presence of poorly compacted grout or the infiltration of de-icing agents from an upper girder can accelerate corrosion in these strands, potentially leading to their failure and significantly compromising structural safety. The extent of corrosion in the prestressing strands and reinforcing bars was quantitatively evaluated based on the charge transmitted through a specified circuit over a specified period, following Faraday's law. The methodology proposed in this study offers an accurate assessment of the corrosion characteristics observed in the prestressing strands and reinforcing bars. This study provided predictions of corrosion amount and depth for both types of reinforcements, depending on variations in the accelerated corrosion experiments. These findings are expected to aid in modeling corrosion in full-sized specimens, setting environmental parameters, and forecasting corrosion rates relative to the service life of the structures
Systems of building construction. Including fireproof construction, concrete construction
This article presents an analysis of the risk of accidents at the diesel fuel hydrotreating process plant of the LK-6U primary oil refining complex. The probability of accident scenarios was modeled using a «bow-tie» diagram that combines fault trees and event trees. The main causes of accidents and their consequences are assessed, and measures to effectively reduce their frequency and possible consequences using an emergency and fire protection system are proposed. The results of the study showed the possibility of significant reduction of fire risk level with the introduction of modern technical solutions and automatic control system.
Systems of building construction. Including fireproof construction, concrete construction
Abstract The durability and structural performance of reinforced concrete (RC) structures decrease over time owing to various factors such as environmental deterioration and increased service loads. Therefore, as the service life of RC structures increases, it is important to derive objective and quantitative evaluation results on their durability and structural performance. However, most previous studies have analyzed only the individual impacts of multiple factors that reduce the durability of RC structures and have not considered the combined effects of these factors. In addition, the durability and structural performance evaluation methods for RC structures proposed by domestic and international institutions are based on the subjective judgments of experts in structural diagnostics, and the evaluation results are generally expressed as grades, posing significant limitations on the effective maintenance of RC structures. Therefore, this study conducted a detailed field investigation on the factors that reduce the durability of 21 RC structures. Based on field investigation data, a remaining service life evaluation model reflecting combined deterioration was developed using an adaptive neuro-fuzzy inference system. In addition, the structural reliability theory was introduced into the proposed model to reflect the failure probability of structural members and the importance of each member, block, and floor. An evaluation procedure was developed to objectively evaluate the safety level of RC structures by comprehensively considering both the durability and structural performance. The procedure is expected to be widely utilized in the field of structural safety diagnostics as it provides a quantitative estimate of the remaining service life.
Systems of building construction. Including fireproof construction, concrete construction
Sergey M. Dymov, Maxim V. Vishchekin, Roman A. Kislyakov
et al.
The article discusses some methods for measuring the temperature on a person's head in personal protective equipment against wind loads and low temperatures. Sample data from field tests are presented. Diagrams of air gaps in a firefighter's helmet and the passage of air flows through them are shown. The need for instrumental temperature control in the engine compartment and possible criteria for a subjective assessment of the protective properties of a fire helmet is stated.
Systems of building construction. Including fireproof construction, concrete construction
Vadim V. Zykov, Konstantin V. Domrachev, Andrey N. Gladkikh
et al.
The article provides an analytical activities review aimed at the development of documents for the preliminary planning of actions for fire service units of territorial fire and rescue garrisons of the Russian Federation. Issues of development of fire extinguishing plans for Federal districts, distribution of their number by objects of development and types of fire service were considered. The article offers a structure of an electronic database project for ordering storage, accounting and organization of operational access to plans developed for objects of protection to extinguish fires in fire and rescue garrisons.
Systems of building construction. Including fireproof construction, concrete construction
Abstract To investigate the response of post-installed rebar connectors in steel frame retrofitted concrete structures under combined shear and tension, seven shear-and-tensile tests were conducted. The bearing capacity, stiffness, and hysteresis behavior of the connectors were investigated during the tests. Both Monotonic and cyclic load regimes were applied in the loading process. The results show that with the increase of the loading angle, the deformation capacity, the yield force, ultimate tensile force, and tensile stiffness of the specimen decrease, while the maximum shear force and shear stiffness of the specimen increase. The bearing capacity, stiffness, and energy dissipation performance of the specimen under a monotonic load is greater than that under the coupled shear-and-pull load. The bearing capacity, stiffness, hysteresis curve, and failure status of the specimens are not affected by different loading regimes. At the end, the design formula of anchor bolt for this type of connectors from the design code of China, United States, and Japan were compared. Formulas to calculate the shear strength under combined shear and tension is developed.
Systems of building construction. Including fireproof construction, concrete construction
Hyun-Seop Shin, Sung-Wook Kim, Jae-Heum Moon
et al.
Abstract In an explosion test using a shock tube, the behavior of pressure waves can be reproduced with high reliability. However, the explosion in a shock tube occurs in a confined space. It is difficult to predict the behavior of pressure waves and its effect on various concrete specimens by using the research findings related to free-field explosions. Moreover, few studies have focused on explosive-driven shock tubes. In this study, the behavior of pressure waves in a shock tube was numerically analyzed using a finite-element analysis program. The explosive used to generate the pressure waves was an ammonium nitrate fuel oil (ANFO), which exhibits non-ideal explosion characteristics. The Jones–Wilkins–Lee (JWL) and ignition-and-growth (I&G) equations of state were used for blast-pressure calculation. The analysis results were affected by factors such as the release rate of explosive energy and the development of the pressure waves in the confined explosion. The blast behaviors, such as the low release rate of explosive energy and the resulting increase in the impulse, were analyzed using the ignition-and-growth equation. The impulse produced during the development of waves reflected by the block installed at the tube inlet exceeded that produced by the tube wall. Such behaviors that occurred at the beginning of a blast affected the process of wave propagation along the shock tube and the wave reflection due to the test specimen at the outlet of the shock tube. In this study, the blast behavior in the shock tube, which could be referenced for the analysis of blast overpressure and its effect on concrete specimens, was numerically analyzed. Further research on the structural behaviors of concrete specimens due to blast overpressure is needed.
Systems of building construction. Including fireproof construction, concrete construction
Djarir Yahiaoui, Abdelaziz Boutrid, Mohamed Saadi
et al.
Abstract The concept of external glass FRP composite confinement is a current process for strengthening concrete beams subjected to static loads. End anchorage glass FRP composites of 80 mm width and 90–130 mm length with different thicknesses (2.4 and 4.8 mm) have been fixed at the bottom of beams with bolts of various diameters (6 and 10 mm). For this purpose, the behavior of beams strengthened with bolt-end anchoring glass fiber polymer composites (BEGFPC) has been analyzed. It is concluded that the load capacity of the BEGFPC beams is improved by increasing the end-anchorage glass FRP composite thickness (about 98–188%). In addition, the BEGFPC system with bolts of 6 mm diameter has significantly improved the flexibility of beams. In contrast, the 10 mm bolts in diameter give a high ultimate load, whatever their quantity. Therefore, combining bolts with diameters of 6 and 10 mm would be the best solution for increasing the ultimate load and ductility of the retrofitted beams. Depending on the number and bolts' arrangement, there is also an enhancement in the crack patterns by changing from intermediate flexural failure to shear failure in beams.
Systems of building construction. Including fireproof construction, concrete construction
Abstract To prevent damage to shaft walls in mines due to uneven loading, the mechanical properties of a shaft wall structure made of hybrid-fiber-reinforced concrete were studied. First, through orthogonal testing, the optimal mix proportion of the hybrid-fiber-reinforced concrete was obtained. Subsequently, a numerical calculation model of the shaft wall structure under uneven loading was established. The calculation results showed that the structure exhibits a tensile stress under the action of uneven loading and that its bearing capacity can be improved using the hybrid-fiber-reinforced concrete. Based on the numerical simulation results, a calculation formula for the bearing capacity of the shaft wall was obtained by regression. Finally, a model test was conducted on the shaft lining structure. The results obtained were consistent with those obtained using the numerical simulation regression formula, confirming the reliability of the numerical simulation results. This study showed that a hybrid-fiber-reinforced concrete shaft wall structure can better withstand uneven loads and has improved brittle failure characteristics. Hybrid-fiber-reinforced concrete is an excellent material for deep shaft wall structures.
Systems of building construction. Including fireproof construction, concrete construction
Abstract Recent years have witnessed that the prefabricated concrete structure is in the widespread use of building structures. This structure, however, still has some weaknesses, such as excessive weight of components, high requirements for construction equipment, difficult alignment of nodes, and poor installation accuracy. In order to handle the problems mentioned above, the prefabricated component made of lightweight concrete is adopted. At the same time, this prefabricated component is beneficial to reducing the load of the building structure itself and improving the safety and economy of the building structure. Nevertheless, it is rarely found that the researches and applications of lightweight concrete for stressed members are conducted. In this context, this paper replaces ordinary coarse aggregate with lightweight ceramsite or foam based on the C60 concrete mix ratio so as to obtain a mix ratio of C40 lightweight concrete that meets the engineering standards. Besides, ceramsite concrete beams and foamed concrete beams are fabricated. Moreover, through three-point bending tests, this paper further explores the mechanical properties of lightweight concrete beams and plain concrete beams during normal use conditions. As demonstrated in the results, the mechanical properties of the foamed concrete beam are similar to those of the plain concrete beam. Compared to plain concrete beams, the density of foamed concrete beams was lower by 23.4%; moreover, the ductility and toughness of foamed concrete were higher by 13% and 3%, respectively. However, in comparison with the plain concrete beam, the mechanical properties of the ceramsite concrete beam have some differences, with relatively large dispersion and obvious brittle failure characteristics. Moreover, in consideration of the nonlinear deformation characteristics of reinforced concrete beams, the theoretical calculation value of beam deflection was given in this paper based on the assumption of flat section and the principle of virtual work. The theoretically calculated deflection values of ordinary concrete beams and foamed concrete beams are in good agreement with the experimental values under normal use conditions, verifying the rationality and effectiveness of the calculation method. The research results of this paper can be taken as a reference for similar engineering designs.
Systems of building construction. Including fireproof construction, concrete construction
Leonid P. Vogman , Vladimir A. Zuykov, Aleksandr V. Zuykov
et al.
There is carried out the comparative analysis of the fire and explosion hazard of liquefied and compressed gases that are currently used and are promising as fuels for compressed gas vehicles. There are investigated the conditions of frequent emergencies in compressed gas vehicles. The violation of rules for installation and operation of compressed gas equipment of vehicles is one of the main causes of fires.
Systems of building construction. Including fireproof construction, concrete construction