Based on the upper bound kinematic approach of the yield design theory, this paper presents a simplified approach for evaluating the shear capacity of reinforced concrete (RC) beams in fire ...conditions. The proposed method assumes rigid-block velocity fields of a beam under 4-point bending loading, and accounts for fire-induced strength reduction of materials as a function of temperature distribution across the beam cross-section. At first, to determine the shear capacity using a general velocity field in the beam, a simple convex optimization problem is numerically solved. Then, simplified analytical expressions corresponding to steel-yielding or concrete crushing velocity fields are provided, using two particular velocity fields, thus giving closed-form expressions in those particular cases. Such an approach allows for a direct and quick evaluation of the shear capacity of RC beams from the thermal analysis of their cross-section and is further compared to available experimental results.
•The shear strength of RC beams subject to fire is evaluated by a yield design method.•Semi-analytical solutions are obtained by using simplified failure mechanisms.•The proposed approach is favorably compared to available experimental results.
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In this study, two methods of CFRP applications were utilized to strengthen the shear deficient beams with circular holes and a comprehensive experimental program consisting of 11 ½ ...scaled specimens was undertaken. The beams with hole diameter (D)/beam height ratio (H) of 0.30, 0.44, 0.64 ratios, symmetrically drilled in shear span were tested under vertical loading. D/H ratio of 0.30 did cause not only a decrease in load carrying capacity but also increased the ductility of the beam. However, significant decreases in load carrying capacities were observed as the hole diameters increase. The load carrying capacity and ductility were significantly improved owing to different CFRP configurations. The fact that the hole diameter and CFRP strengthening method are very important parameters for strengthening is observed. No CFRP strengthening alternative was successful in the beams with a D/H ratio of 0.64. A detailed macro and micro damage analyses are presented.
Engineering design problems are often multi-objective in nature, which means trade-offs are required between conflicting objectives. In this study, we examine the multi-objective algorithms for the ...optimal design of reinforced concrete structures. We begin with a review of multi-objective optimization approaches in general and then present a more focused review on multi-objective optimization of reinforced concrete structures. We note that the existing literature uses metaheuristic algorithms as the most common approaches to solve the multi-objective optimization problems. Other efficient approaches, such as derivative-free optimization and gradient-based methods, are often ignored in structural engineering discipline. This paper presents a multi-objective model for the optimal design of reinforced concrete beams where the optimal solution is interested in trade-off between cost and deflection. We then examine the efficiency of six established multi-objective optimization algorithms, including one method based on purely random point selection, on the design problem. Ranking and consistency of the result reveals a derivative-free optimization algorithm as the most efficient one.
•Multi-objective optimization (MOO) approaches in general and in Reinforced Concrete (RC) structures are reviewed.•A novel multi-objective model is developed for the optimal design of RC beams.•A set of algorithms are examined and compared through numerical testing.•This paper enlightens the merits of advanced MOO methods in structural engineering problems.
In this article unlike existing linear models, a nonlinear differential model is used to describe the nonlinear heat distribution in a reinforced concrete beam using a heating wire. The results of ...experiments carried out under different heating modes are adequately described with good approximation by the analytical results obtained using the methods of group analysis of differential equations.
In this paper, six concrete beams reinforced with a combination of GFRP (glass fiber reinforced polymer) bars and steel bars, and three concrete beams reinforced only with steel bars were designed ...and tested. Several flexural behaviors of the tested beams were analyzed and compared with theoretical models. The experimental and analytical results showed that under the designed service loads, the crack width and deflection that appeared in the GFRP-steel reinforced concrete beams developed faster than those shown by the steel-reinforced concrete beams. With the same total reinforcement amount of GFRP and steel bars, the ultimate flexural capacity of GFRP-steel reinforced concrete beams was nearly 91–97% of that of steel-reinforced concrete beams, but the deflection and maximum crack width were obviously larger than those of steel-reinforced concrete beams under the same service load levels. The beam deformability coefficient approximately decreased with increasing nominal reinforcement ratio ρnom,F. The area ratio of GFRP bars to steel bars Af/As had a great influence on the flexural behaviors of GFRP-steel reinforced concrete beams. Comparisons showed that the data obtained for flexural capacity, deflection, deformability and crack width of GFRP-steel reinforced concrete beams were consistent with the predictions calculated by the proposed models.
To investigate the blast resistance of steel reinforced concrete (SRC) beams under contact explosion, contact explosion tests on four SRC beams were carried out. The damage modes and dynamic response ...of SRC beams and the effect of structural steel and studs were analyzed. Finite element models of SRC beams and the corresponding RC beams were established to compare and analyze the different stress wave propagation in the middle-span cross-section and stress-time history curves of critical nodes in the section to reveal the damage mechanism of SRC beams. The results show that under contact explosion, U-shaped craters were formed on the blasting surface of the SRC beams, and the depth of the crater center was the distance from the top surface of the beam to the top surface of structural steel. The cover concrete on upper half side surfaces and bottom surface was spalled off. However, the concrete protected by structural steel flanges was not damaged, and comparing with RC beams, the setting of structural steel reduced the compressive stress in concrete protected or shielded by structural steel flanges and tension stress waves in concrete near the side and bottom surfaces of SRC beams. So, the concrete spalling on the side and bottom surfaces suffered less severe damage, and concrete protected by structural steel flanges was not damaged for SRC beams. Besides, when larger structural steel was used, the effects were more significant.
•Four SRC beams with different structural steel and studs were tested under contact explosion.•The damage of SRC beams with different structural steel and studs arrangement differed greatly.•Structural steel reduced the compressive or tension stress in critical regions of SRC beams.•The structural steel protected the concrete between and below the two flanges effectively.•SRC beams were less severely damaged compared to the corresponding RC beams.
•Pre-damaged RC beam specimens are prepared to represent seismic damages.•Natural FRP made with jute is applied to repair damaged RC beams.•Strengthening shear behaviour of pre-damaged RC beams are ...investigated.•Predicted shear strengths suggested by Japanese design codes are calculated.
This paper examines the use of natural jute fabric reinforced polymer (JFRP) composite sheets as external strengthening material of reinforced concrete (RC) beams. Pre-damaged RC beam specimens are prepared to represent seismic damage. The shear behaviour of pre-damaged deep RC beams strengthened with JFRP sheets are investigated subjected to non-reversed cyclic three-point bending load test. The JFRP strengthening ratio and the pre-damaged level of RC beam are considered in this study. The test results revealed that JFRP can significantly improve the shear strength capacity of beams. All strengthened beams show a similar failure mode which is a rupture on JFRP sheets. The shear enhancement of JFRP strengthened pre-damaged beams are comparable to that of non-damaged beams strengthened with conventional FRPs, proving the applicability of JFRP strengthening in pre-damaged shear-deficient beams. In addition, the experimental results are compared with the predicted values by the Japanese design codes.
In this research, it is studied the crack and flexural behavior of reinforced concrete beams with various bottom ash ratios (BARs) considered as fine aggregate in an experimental and numerical ...investigation. For experimental purposes, different concrete series are considered varying aggregate sizes ranging from 0 to 25 mm. To supplement concrete, bottom ash is put to use in conjunction with material from 0–5 mm in size aggregate particles as replacement for fine aggregates with ratios of 25%, 50%, 75%, and 100%. Experiments were done to investigate the behavior of the beams and how flexural and fracture behaviors are represented. 75% BARs gave optimum results in terms of displacement capacity. Increasing BAR to 100% decrease deflection capacity of the beam. Also, ANSYS software is used to build 3D finite element models (FEMs) of beams to compare with experiment data. Experimental and 3D numerical tests show exceptionally tight flexural and fracture behaviors. Following this, a computer-generated structure is made by running SAP 2000, and the strength of the beams is then utilised in an RC structural model. Every stage of the building’s construction is thoroughly assessed utilizing multiple types of seismic testing, employing the SAP2000 program, with the resulting analysis providing significant findings on how the seismic force of 75% BAR affects horizontal displacement of each floor. The results showed that the weight of the structure dramatically decreases as the number of columns and RCBs are raised while also increasing the number of BARs. Moreover, the magnitude of earthquake and BAR have a significant effect on the horizontal displacement behavior of reinforced concrete structures. The strength of the concrete structure varies between close- and far-fault earthquakes, and for close-fault earthquakes, concrete strength is stronger than for far-fault earthquakes. This brings us to the second disadvantage of BAR which is the 75% strain produces a severe displacement of reinforced concrete structures. Besides, it was seen that the simulations and experiments yield tiny cracks with very identical configurations.
The aim of this study is to apply acoustic emission (AE) technique and study the damage mechanism of the reinforced concrete (RC) beams under four-point bending. Laboratory experiments are performed ...on three types of RC beams of grade M30 with 42, 64 and 93% of longitudinal steel against balanced section. The damage in the beams are classified into four zones symbolizing formation of micro cracks, visible cracks, steel yielding and concrete crushing. The AE parameters such as amplitude, rise time, count, duration and average frequency are quantified in each damage levels and a parametric analysis is performed between average frequency and RA value. The results showed that as the level of damage increased, the values of AE parameters such as count, hits, rise time, acoustic emission energy and duration increased except for average frequency. This results coincided with the visual observation results according to crack modes. The adequacy of the crack classification is also evaluated by Gaussian mixture modelling (GMM), a probabilistic based approach. GMM is used as a parametric model to overcome the randomness found in the data set generated by AE testing. The results of the present investigation can be utilized in health monitoring of concrete structures subjected to flexural load.
•Self-sensing and structural behavior of reinforced concrete beams were assessed.•CF and CNT were used to improve electrical properties.•Self-sensing of shear damage under four-point bending was of ...particular focus.•Structural behavior and failure mode of CF- and CNT-based beams were quite different.•Damage in shear was successfully self-sensed with superior performance of CF.
Self-sensing property of concrete is mostly assessed using small specimens without reinforcement, which may be misleading for real-time structures. To better simulate the actual field conditions, this study examined self-sensing of damage in large-scale reinforced concrete beams tested under four-point bending. During flexural testing, special attention was paid to the self-sensing capability of shear failure, since this type of failure occurs suddenly and catastrophically. Inadequate shear reinforcements were used to increase shear failure possibility of 100 × 150 × 1000 mm3 (width × height × length) reinforced large-scale beams and beams were produced with a high shear span (a = 350 mm) to effective depth (d = 125 mm) ratio of 2.8. To increase the electrical conductivity of large-scale beams, chopped carbon fibers (CF) and multi-walled carbon nano tubes (CNT) were used. Instantaneous self-sensing recordings were made using brass electrodes embedded in different shear spans of beams. In addition to conducting self-sensing evaluations, researchers also investigated the effects of CF and CNT particles on the mechanical properties/structural behavior of large-scale beam specimens with the proposed reinforcement configuration. Results showed that compared to CNT, CF usage significantly improved the load carrying capacity and ductility, resulting in bending mode of failure even with indaquate shear reinforcement. Shear damage was successfully self-sensed in all tested beams, although all CF-based specimens started self-sensing from the beginning of loading with significantly higher changes in electrical resistivity results, unlike CNT-based specimens. Conductive network of CF-based specimens seemed to be disturbed more easily at high load levels. CF usage seems like a better option compared to CNT given its lower cost and easier mixability.
