• Earthquakes and Structures
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• v.24 no.5
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• pp.353-364
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• 2023

In this study, a method has been proposed for the static and dynamic nonlinear analysis of multi-storey buildings, which takes into account the contribution of axial deformations in vertical load-bearing elements, which are especially important in tall and narrow structures. Shear deformations on the shear walls were also taken into account in the study. The presented method takes into account the effects that are not considered in the fishbone and flexural-shear beam models developed in the literature. In the Fishbone model, only frame systems are modeled. In the flexural shear beam model developed for shear wall systems, shear deformations and axial deformations in the walls are neglected. Unlike the literature, with the model proposed in this study, both shear deformations in the walls and axial deformations in the columns and walls are taken into account. In the proposed model, multi-storey building is represented as a sandwich beam consisting of Timoshenko beams pieced together with a double-hinged beam. At each storey, the total moment capacities of the frame beams and the coupled beams in the coupled shear walls are represented as the equivalent shear capacity. On the other hand, The sums of individual columns and walls moment at the relevant floor level are represented as equivalent moment capacity at that floor level. At the end of the study, examples were solved to show the suitability of the proposed method in this study. The SAP2000 program is employed in analyses. In a conclusion, it is observed that among the solved examples, the proposed sandwich beam model gives good results. As can be seen from these results, it is seen that the presented method, especially in terms of base shear force, gives very close results to the detailed finite element method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.6
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• pp.399-405
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• 2023

This study presents an optimal seismic design method based on genetic algorithms to induce beam-hinge collapse mechanisms in reinforced concrete moment frames. Two objective functions are used. The first minimizes the cost of the structure and the second maximizes the energy dissipation capacity of the structure. Constraints include strength conditions of columns and beams, minimum conditions for column-to-beam flexural strength ratio, and conditions for preventing plastic hinge occurrence of columns. Linear static analysis is performed to evaluate the strength of members, whereas nonlinear static analysis is carried out to evaluate energy dissipation capacity and occurrence of plastic hinges. The proposed method was applied to a four-story example structure, and it was confirmed that solutions for inducing a beam-hinge collapse mechanism are obtained. The value of the column-beam flexural strength ratio of the obtained design was found to be larger than the value suggested by existing seismic codes. A more robust strategy is needed to induce a beam-hinge collapse mode.

• Geomechanics and Engineering
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• v.38 no.2
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• pp.139-155
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• 2024

The piled raft foundations are subjected to lateral loading under the action of wind and earthquake loads. Their bearing behavior and flexural responses under these loadings are of prime concern for researchers and practitioners. The insufficient experimental studies on piled rafts subjected to lateral loading lead to a limited understanding of this foundation system. Lateral load sharing between pile and raft in a laterally loaded piled raft is scarce in literature. In the present study, lateral load-displacement, load sharing, bending moment distribution, and raft inclinations of the piled raft foundations have been discussed through an instrumented scaled down model test in 1 g condition. The contribution of raft in a laterally loaded piled raft has been evaluated from the responses of pile group and piled raft foundations attributing a variety of influential system parameters such as pile spacing, slenderness ratio, group area ratio, and raft embedment. The study shows that the raft contributes 28-49% to the overall lateral capacity of the piled raft foundation. The results show that the front pile experiences 20-66% higher bending moments in comparison to the back pile under different conditions in the pile group and piled raft. The piles in the piled raft exhibit lower bending moments in the range of 45-50% as compared to piles in the pile group. The raft inclination in the piled raft is 30-70% less as compared to the pile group foundation. The lateral load-displacement and bending moment distribution in piles of the single pile, pile group, and piled raft has been presented to compare their bearing behavior and flexural responses subjected to lateral loading conditions. This study provides substantial technical aid for the understanding of piled rafts in onshore and offshore structures to withstand lateral loadings, such as those induced by wind and earthquake loads.

• Korean Journal of Construction Engineering and Management
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• v.5 no.6 s.22
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• pp.212-217
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• 2004

Carbon fiber reinforced plastic(CFRP) plate Is one of the alterative materials for soengthening of reinforced and prestressed connote members due to excellent strength and light weight In this paper, the behavior of beams strengthened with CFRP plate and CFS(Carbon fiber sheet) is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear lone appear in same position. The main failure mode is a peeling-off of the CFRP plate near the loading points due to flexural-shear crack, Because of this failure mode, failure load is not linearly proportional to the thickness of CFRP plates. When beam is wrapped with CFS around oかy loading point it does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When line moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened beam and moment of unstrengthened beam is proposed 1.5-2.0. In order to use the plate of thicker than 6mm, CFS may be extended to the location which moment of strengthened beam is 1.5 times than moment of unstrengthened beam.

• Smart Structures and Systems
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• v.15 no.4
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• pp.997-1018
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• 2015

Structural health monitoring along with damage detection and assessment of its severity level in non-accessible reinforced concrete members using piezoelectric materials becomes essential since engineers often face the problem of detecting hidden damage. In this study, the potential of the detection of flexural damage state in the lower part of the mid-span area of a simply supported reinforced concrete beam using piezoelectric sensors is analytically investigated. Two common severity levels of flexural damage are examined: (i) cracking of concrete that extends from the external lower fiber of concrete up to the steel reinforcement and (ii) yielding of reinforcing bars that occurs for higher levels of bending moment and after the flexural cracking. The purpose of this investigation is to apply finite element modeling using admittance based signature data to analyze its accuracy and to check the potential use of this technique to monitor structural damage in real-time. It has been indicated that damage detection capability greatly depends on the frequency selection rather than on the level of the harmonic excitation loading. This way, the excitation loading sequence can have a level low enough that the technique may be considered as applicable and effective for real structures. Further, it is concluded that the closest applied piezoelectric sensor to the flexural damage demonstrates higher overall sensitivity to structural damage in the entire frequency band for both damage states with respect to the other used sensors. However, the observed sensitivity of the other sensors becomes comparatively high in the peak values of the root mean square deviation index.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.99-116
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• 2014

The American Concrete Institute (ACI) 318-11 permits the use of the moment magnifier method for computing the design ultimate strength of slender reinforced concrete columns that are part of braced frames. This computed strength is influenced by the column effective length factor K, the equivalent uniform bending moment diagram factor $C_m$ and the effective flexural stiffness EI among other factors. For this study, 2,960 simple braced frames subjected to short-term loads were simulated to investigate the effect of using different methods of calculating the effective length factor K when computing the strength of columns in these frames. The theoretically computed column ultimate strengths were compared to the ultimate strengths of the same columns computed from the ACI moment magnifier method using different combinations of equations for K and EI. This study shows that for computing the column ultimate strength, the current practice of using the Jackson-Moreland Alignment Chart is the most accurate method for determining the effective length factor. The study also shows that for computing the column ultimate strength, the accuracy of the moment magnifier method can be further improved by replacing the current ACI equation for EI with a nonlinear equation for EI that includes variables affecting the column stiffness and proposed in an earlier investigation.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.1
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• pp.29-37
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• 2020

This study is to investigate the effect of a retrofitted reinforced concrete frame with non-seismic details strengthened by embedded steel moment frames with an indirect joint, which mitigates the problems of the direct joint method. First, full-scale experiments were conducted to confirm the structural behavior of a 2-story reinforced concrete frame with non-seismic details and strengthened by a steel moment frame with an indirect joint. The reinforced concrete frame with non-seismic details showed a maximum strength of 185 kN at an overall drift ratio of 1.75%. The flexural-shear failure of columns was governed, and shear cracks were concentrated at the beam-column joints. The reinforced concrete frame strengthened by the embedded steel moment frames achieved a maximum strength of 701 kN at an overall drift ratio of 1.5% so that the maximum strength was about 3.8 times that of the specimen with non-seismic details. The failure pattern of the retrofitted specimen was the loss of bond strength between the concrete and the rebars of the columns caused by a prying action of the bottom indirect joint because of lateral force. Furthermore, methods are proposed for calculation of the specified strength of the reinforced concrete frame with non-seismic details and strengthened by the steel moment frame with the indirect joint.

• Structural Engineering and Mechanics
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• v.54 no.1
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• pp.35-54
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• 2015

The performance of a newly generated steel connection known as SidePlateTM moment connection for seismic loading and progressive collapse phenomenon has been investigated in this paper. The seismic evaluation portion of the study included a thorough study on of interstory drift angles and flexural strengths based on 2010 AISC Seismic Provisions while the acceptance criteria provided in UFC 4-023-03 guideline to resist progressive collapse must be satisfied by the rotational capacity of the connections. The results showed that the SidePlate moment connection was capable of attaining adequate rotational capacity and developing full inelastic capacity of the connecting beam. Moreover, the proposed connection demonstrated an exceptional performance for keeping away the plastic hinges from the connection and exceeding interstory drift angle of 0.06 rad with no fracture developments in beam flange groove-welded joints. The test results indicated that this type of connection had strength, stiffness and ductility to be categorized as a rigid, full-strength and ductile connection.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.93-103
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• 2009

The concept of the effective moment of inertia has been generally used for the deflection estimation of reinforced concrete flexural members. The KCI design code adopted Branson's equation for simple calculation of deflection, in which a representative value of the effective moment of inertia is used for the whole length of a member. However, the code equation for the effective moment of inertia was formulated based on the results of beam tests subjected to uniformly distributed loads, which may not effectively account for those of members under different loading conditions. Therefore, this study aimed to verify the influences of moment shapes resulting from different loading patterns by experiments. Six beams were fabricated and tested in this study, where primary variables were concrete compressive strengths and loading distances from supports, and test results were compared to the code equation and other existing approaches. A method utilizing variational analysis for the deflection estimation has been also proposed, which accounts for the influences of moment shapes to the effective moment of inertia. The test results indicated that the effective moment of inertia was somewhat influenced by the moment shape, and that this influence of moment shape to the effective moment of inertia was not captured by the code equation. Compared to the code equation, the proposed method had smaller variation in the ratios of the test results to the estimated values of beam deflections. Therefore, the proposed method is considered to be a good approach to take into account the influence of moment shape for the estimation of beam deflection, however, the differences between test results and estimated deflections show that more researches are still required to improve its accuracy by modifying the shape function of deflection.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.67-79
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• 2010

Severe flexural vibration of the rotor shaft of a Francis turbine runner was experienced in the past. It was shown that the vibration was caused by the fluid forces and moments on the backshroud of the runner associated with the leakage flow through the back chamber. The aim of the present paper is to study the self-excited rotor vibration caused by the fluid force moments on the backshroud of a Francis turbine runner. The rotor vibration includes two fundamental motions, one is a whirling motion which only has a linear displacement and the other is a precession motion which only has an angular displacement. Accordingly, two types of fluid force moment are exerted on the rotor, the moment due to whirl and the moment due to precession. The main focus of the present paper is to clarify the contribution of each moment to the self-excited vibration of an overhung rotor. The runner was modeled by a disk and the whirl and the precession moments on the backshroud of the runner caused by the leakage flow were evaluated from the results of model tests conducted before. A lumped parameter model of a cantilevered rotor was used for the vibration analysis. By examining the frequency, the damping rate, the amplitude ratio of lateral and angular displacements for the cases with longer and shorter overhung rotor, it was found that the precession moment is more important for smaller overhung rotors and the whirl moment is more important for larger overhung rotors, although both types of moment due to the leakage flow can cause self-excited vibration of an overhung rotor.