• Earthquakes and Structures
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• v.15 no.2
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• pp.113-122
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• 2018

This study presents a new beam-column model comprising material nonlinearity and joint flexibility to predict the nonlinear response of reinforced concrete structures. The nonlinear behavior of connections has an outstanding role on the nonlinear response of reinforced concrete structures. In presented research, the joint flexibility is considered applying a rotational spring at each end of the member. To derive the moment-rotation behavior of beam-column connections, the relative rotations produced by the relative slip of flexural reinforcement in the joint and the flexural cracking of the beam end are taken into consideration. Furthermore, the considered spread plasticity model, unlike the previous models that have been developed based on the linear moment distribution subjected to lateral loads includes both lateral and gravity load effects, simultaneously. To confirm the accuracy of the proposed methodology, a simply-supported test beam and three reinforced concrete frames are considered. Pushover and nonlinear dynamic analysis of three numerical examples are performed. In these examples the nonlinear behavior of connections and the material nonlinearity using the proposed methodology and also linear flexibility model with different number of elements for each member and fiber based distributed plasticity model with different number of integration points are simulated. Comparing the results of the proposed methodology with those of the aforementioned models describes that suggested model that only uses one element for each member can appropriately estimate the nonlinear behavior of reinforced concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.197-200
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• 2008

An analytical model for predicting the shear strength of prestressed concrete beams was developed, applying the previously proposed strain-based shear strength model. In flexure-compression member without shear reinforcement, compression zone of intact concrete primarily resist to the shear force rather than tension zone. The shear capacity of concrete at the compression zone was defined based on the material failure criteria. The shear capacity of the compression zone was evaluated along the inclined failure surface considering interaction with the normal stress. Since the distribution of normal stress varies due to the flexural deformation of member, the shear capacity was defined as a function of the flexural deformation. Finally, the shear strength was determined at the intersection of the shear capacity curve and the shear demand curve. As a result of the comparisons to prior test data, the proposed model accurately predicted the shear strength of specimens.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.1 s.47
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• pp.41-49
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• 2006

Through the 1982 Urahawa-ohi and the 1995 Kobe earthquakes, a number of bridge columns were observed to develop a flexural-shear failure due to the bond slip as a consequence of premature termination of the column longitudinal reinforcement. Because the seismic behavior of RC bridge piers is largely dependent on the performance of the plastic hinge legion of RC bridge piers, it is desirable that the seismic capacity of RC bridge pier is to evaluate as a curvature ductility. The provision for the lap splice of longitudinal steel was not specified in KHBDS(Korea Highway Bridge Design Specification) before the implementation of 1992 seismic design code, but the lap splice of not more than 50%, longitudinal reinforcement was newly allowed in the 2005 version of the KHBDS. The objective of this research is to investigate the distribution and ductility of the curvature of RC bridge column with the lap splice of longitudinal reinforcement in the plastic hinge legion. Six (6) specimens were made in 600 mm diameter with an aspect ratio of 2.5 or 3.5. These piers were cyclically subjected to the quasi-static loads with the uniform axial load of $P=0.1f_{ck}A_g$. According to the slip failure of longitudinal steels of the lap spliced specimen by cyclic loads, the curvatures of the lower and upper parts of the lap spliced region were bigger and smaller than the corresponding paris of the specimen without a lap splice, respectively. Therefore, the damage of the lap spliced test column was concentrated almost on the lower part of the lap spliced region, that appeared io be failed in flexure.

• Structural Engineering and Mechanics
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• v.59 no.5
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• pp.853-866
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• 2016

This paper examines a methodology for computing the probability of structural failure of reinforced concrete beams subjected to fire. The significant load variables considered are dead load, sustained live load and fire temperature. Resistance is expressed in terms of moment capacity with random variables taken as yield strength of steel, concrete class (or grade of concrete), beam width and depth. The flexural capacity is determined based on the design equations recommended in Indian standard IS456:2000. Simplified method named $500^{\circ}C$ isotherm method detailed in Eurocode 2 is incorporated for fire design. A transient thermal analysis is conducted using finite element software ANSYS$^{(R)}$ Release15. Reliability is evaluated from the initial state to 4h of fire exposure based on the first order reliability method (FORM). A procedure is coded in MATLAB for finding the reliability index. This procedure is validated with available literature. The effect of various parameters like effective cover, yield strength of steel, grade of concrete, distribution of reinforcement bars and aggregate type on reliability indices are studied. Parameters like effective cover of concrete, yield strength of steel has a significant effect on reliability of beams. Different failure modes like limit state of flexure and limit state of shear are checked.

• Structural Engineering and Mechanics
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• v.74 no.6
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• pp.809-819
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• 2020

For the first time, the influence of in-plane magnetic field on wave propagation of Graphene Nano-Platelets (GNPs) polymer composite nanoplates is investigated here. The impact of three- parameter Kerr foundation is also considered. There are two different reinforcement distribution patterns (i.e. uniformly and non-uniformly) while the material properties of the nanoplate are estimated through the Halpin-Tsai model and a rule of mixture. To consider the size-dependent behavior of the structure, Eringen Nonlocal Differential Model (ENDM) is utilized. The equations of wave motion derived based on a higher-order shear deformation refined theory through Hamilton's principle and an analytical technique depending on Taylor series utilized to find the wave frequency as well as phase velocity of the GNPs reinforced nanoplates. A parametric investigation is performed to determine the influence of essential phenomena, such as the nonlocality, GNPs conditions, Kerr foundation parameters, and wave number on the both longitudinal and flexural wave characteristics of GNPs reinforced nanoplates.

• Computers and Concrete
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• v.17 no.3
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• pp.353-386
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• 2016

Realistic assessment of the performance of reinforced concrete structural members like columns is needed for designing new structures or maintenance of the existing structural members. This assessment requires analytical capability of employing proper material models and cyclic rules and considering various load and displacement patterns. A computer application was developed to analyze the non-linear, cyclic flexural performance of reinforced concrete structural members under various types of loading paths including non-sequential variations in axial load and bi-axial cyclic load or displacement. Different monotonic material models as well as hysteresis rules, were implemented in a fiber-based moment-curvature and in turn force-deflection analysis, using proper assumptions on curvature distribution along the member, as in plastic-hinge models. Performance of the program was verified against analytical results by others, and accuracy of the analytical process and the implemented models were evaluated in comparison to the experimental results. The computer application can be used to predict the response of a member with an arbitrary cross section and various type of lateral and longitudinal reinforcement under different combinations of loading patterns in axial and bi-axial directions. On the other hand, the application can be used to examine analytical models and methods using proper experimental data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.39-48
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• 2015

Reinforced concrete (RC) structures strengthened with FRP materials would cause the loss of the reinforcing effect and the sudden failure of the structure due to the debonding of FRP. The debonding fracture strength of the FRP-strengthened concrete structures has been evaluated using the same strength method as applied in RC structures based on the debonding strain of FRP. However, the values of the FRP debonding strain are different according to design guidelines. Thus, this study carried out an experimental study on RC beams reinforced with GFRP and evaluated the debonding fracture strength of the strengthened beams from each design guideline. Since the debonding failure occurs prior to reaching the ultimate value of concrete compressive strain, this study accounts for the nonlinear stress distribution of concrete. This study also proposed equations that can evaluate the debonding strength of GFRP-strengthened RC beams with similar safety to the ultimate flexural strength of non-strengthened RC beams.

• Structural Monitoring and Maintenance
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• v.10 no.4
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• pp.315-337
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• 2023

During the design phase, it is crucial to determine the interface stresses between the reinforcing plate and the concrete base in order to predict plate end separation failures. In this work, a simple theoretical study of interface shear stresses in beams reinforced with P-FGM and E-FGM plates subjected to an arbitrarily positioned point load, or two symmetrical point loads, was presented using the linear elastic theory. The presence of pores in the reinforcing plate distributed in several forms was also taken into account. For this purpose, we analyze the effects of porosity and its distribution shape on the interracial normal and shear stresses of an FGM beam reinforced with an FRP plate under different types of load. Comparisons of the proposed model with existing analytical solutions in the literature confirm the feasibility and accuracy of this new approach. The influence of different parameters on the interfacial behavior of reinforced concrete beams reinforced with functionally graded porous plates is further examined in this parametric study using the proposed model. From the results obtained in this study, we can say that interface stress is significantly affected by several factors, including the pores present in the reinforcing plate and their distribution shape. Additionally, we can conclude from this study that reinforcement systems with composite plates are very effective in improving the flexural response of reinforced RC beams.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.13-22
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• 2011

In this study, ultimate strengths of 51 continuous reinforced concrete deep beams were evaluated by the ACI 318M-08's strut-tie model approach implemented with the presented indeterminate strut-tie model and load distribution ratio of the companion paper. The ultimate strengths of the continuous deep beams were also estimated by the shear equations derived based on experimental results, conventional design codes based on experimental and theoretical shear strength models, and current strut-tie model design codes. The validity of the presented strut-tie model and load distribution ratio was examined through the comparison of the strength analysis results classified according to the primary design variables of shear span-to-effective depth ratio, flexural reinforcement ratio, and concrete compressive strength. The present study results of ultimate strengths obtained using the indeterminate strut-tie model and load distribution ratio of the continuous deep beams agree fairly well with those obtained using other approaches. In addition, the present approach reflected the effect of the primary design variables on the ultimate strengths of the continuous deep beams consistently and accurately. Therefore, the present study will help structural designers to conduct rational and practical strut-tie model designs of continuous deep beams.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1065-1079
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• 2014

The ultimate behavior of reinforced concrete corbel is complicated due to the primary design variables including the shear span-to-effective depth ratio a/d, flexural reinforcement ratio, load condition, and material properties. In this study, a simple indeterminate strut-tie model reflecting all characteristics of the ultimate strength and complicated structural behavior is proposed for the design of the reinforced concrete corbels with shear span-to-effective depth ratio of $a/d{\leq}1$. A load distribution ratio, defined as the fraction of applied load transferred by horizontal truss mechanism, is also proposed to help structural designers perform the design of reinforced concrete corbels by using the strut-tie model approaches of current design codes. For the development of the load distribution ratio, numerous material nonlinear finite element analyses of the proposed indeterminate strut-tie model were conducted by changing primary design variables. The ultimate strengths of reinforced concrete corbels tested to failure were evaluated by incorporating the proposed strut-tie model and load distribution ratio into the ACI 318-11's strut-tie model method. The validity of the proposed model and load distribution ratio was examined by comparing the strength analysis results with those by the ACI 318-11's conventional design method and strut-tie model methods of current design codes.