• Computers and Concrete
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• v.31 no.3
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• pp.207-221
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• 2023

In this investigation, the interaction between opening space and neighboring joint has been examined by experimental test and Particle flow code in two dimension (PFC2D) simulation. Since, firs of all PFC was calibrated using Brazilian experimental test and uniaxial compression test. Secondly, diverse configurations of opening and neighboring joint were provided and tested by uniaxial test. 12 rectangular sample with dimension of 10 cm*10 cm was prepared from gypsum mixture. One quarter of tunnel and one and or two joint were drilled into the sample. Tunnel diameter was 5.5 cm. The angularities of joint in physical test were 0°, 45° and 90°. The angularities of joint in numerical simulation were 0°, 30°, 60°, -30°, -45°, -60° and its length were 2cm and 4cm. Loading rate was 0.016 m/s. Tensile strength of material was 4.5 MPa. Results shows that dominant type of crack which took place in the model was tensile cracks and or several shear bands develop within the model. The Final stress is minimum in the cases where oriented angle is negative. The failure stress decrease by decreasing the joint angle from 30° to 60°. In addition, the failure stress decrease by incrementing the joint angle from -30° to -60°. The failure stress was incremented by decreasing the number of notches. The failure stress was incremented by decreasing the joint length. The failure stress was incremented by decreasing the number of notches. Comparing experimental results and numerical one, showed that the failure stress is approximately identical in both conditions.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.3-10
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• 2010

This study evaluates the seismic performance of reinforced concrete (RC) flat plate structures relation to the gravity shear ratio. For this purpose, 3 and 7 story framed buildings were designed for gravity loads only. Subsequently, a nonlinear static pushover analysis and a nonlinear time history analysis for the prototype buildings were carried out. In the nonlinear analysis, newly propose analytical slab-column joint model was utilized to capture punching shear failure and fracture mechanism in the analysis. The analytical results showed that seismic performance of RC flat plate frame is strongly influenced by the gravity shear ratio. In particularly, in the RC flat plate frame with a large gravity shear ratio the lateral strength and maximum drift capacity decreased significantly.

• Computers and Concrete
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• v.32 no.3
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• pp.339-349
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• 2023

Fast-built construction is a key feature for successful applications of precast concrete (PC) moment frame system in recent construction practices. To this end, by introducing some unique splicing details in precast connections, especially between PC columns including panel zones, use of temporary supports and bracings can be minimized based on their self-sustaining nature. In addition, precast wide beams are commonly adopted for better economic feasibility. In this study, three self-sustaining precast concrete (PC) wide beam-column connection specimens were fabricated and tested under reversed cyclic loadings, and their seismic performances were quantitatively evaluated in terms of strength, ductility, failure modes, energy dissipation and stiffness degradation. Test results were compared with ASCE 41-17 nonlinear modeling curves and its corresponding acceptance criteria. On this basis, an improved macro modeling method was explored for a more accurate simulation. It appeared that all the test specimens fully satisfy the acceptance criteria, but the implicit joint model recommended in ASCE 41-17 tends to underestimate the joint shear stiffness of PC wide beam-column connection. While, the explicit joint model along with concentrated plastic hinge modeling technique is able to present better accuracy in simulating the cyclic responses of PC wide beam-column connections.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.473-480
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• 2016

The purpose of this study is to provide analytical method to reasonably evaluate the complicated failure behaviors of shear friction of reinforced concrete shear wall specimens using grade 500 MPa high-strength bars. A total of 16 test specimens with a variety of variables such as aspect ratio, friction coefficient of interface in construction joint, reinforcement details, reinforcement ratio in each direction, material properties were selected and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the modified shear friction constitutive equation in interface based on the concrete design code (KCI, 2012) and CEB-FIP Model code 2010. The mean and coefficient of variation for maximum load from the experiment and analysis results was predicted 1.04 and 17% respectively and properly evaluated failure mode and overall behavior characteristic until failure occur. Based on the results, the analysis program that was applied modified shear friction constitutive equation is judged as having a relatively high reliability for the analysis results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.293-308
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• 2012

The shear behavior at the particle/surface interface such as rock joint can determine the mechanical behavior of whole structure. Therefore, a fundamental understanding of the mechanisms governing its behavior and accurately estimation of the interface strength is essential. In this paper, PFC, a numerical analysis program of discrete element method was used to investigate the effects of the surface roughness on interface strength. The surface roughness was characterized by smooth, intermediate, and rough surface, respectively. In order to investigate the effects of particle shape and crushing on particle/surface interface behavior, one ball, clump, and cluster models were created and their results were compared. The shape of particle was characterized by circle, triangle, square, and rectangle, respectively. The results showed that as the surface roughness increases, interface strength and friction angle increase and the void ratio increases. The one ball model with smooth surface shows lower interface strength and friction angle than the clump model with irregular surface. In addition, a cluster model has less interface strength and friction angle than the clump model. The failure envelope of the cluster model shows non-linear characteristic. From these findings, it is verified that the surface roughness and particle shape effect on the particle/surface interface shear behavior.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.555-562
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• 2016

The objective of the present study is to evaluate the shear transfer capacity of transverse reinforcement at the concrete interfaces with smooth construction joint. The transverse reinforcing bars were classified into two groups: V-type for the arrangement perpendicular to the interface and X-type for inclined-crossing arrangement. The transverse reinforcement ratio at the interface varied from 0.0045 to 0.0135 for V-type and 0.0064 to 0.0045 for X-type. The mechanism analysis proposed for monolithic concrete interface, derived based on the upper-bound theorem of concrete plasticity, was modified to evaluate the shear friction capacity of concrete interfaces with smooth construction joint. Test results showed that the specimens with X-type reinforcement had lower amount of relative slippage at the interface and higher shear friction capacity than the companion specimens with V-type reinforcement. This observation was independent of the unit weight of concrete. The mean and standard deviation of the ratios between the experimental shear friction strength of smooth construction joints and predictions obtained from the proposed model are 1.07 and 0.14, respectively.

• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.59-69
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• 2015

This study examined the magnitude and distribution of earth pressure on the support system in a jointed rock mass due to the different joint sets as well as varying the rock type and joint condition (joint shear strength and joint inclination angle). Based on a physical model test and its numerical simulation, a series of numerical parametric analyses were conducted using a discrete element method. The results showed that the induced earth pressure was affected significantly by a joint set depending on the inclusion of the joint inclination angle, which induces a joint sliding condition, but the number of joint sets alone was not important, even though the earth pressure could be increased slightly as the number of joint sets is increased. In addition, the study results were compared with Peck's earth pressure for soil ground, which indicated that the earth pressure in a jointed rock mass could be considerably different from that in soil ground. The study suggests that the effects of joint sets as well as rock type and joint condition are important factors affecting the earth pressure in a jointed rock mass and they should be considered when designing a support system in a jointed rock mass.

• Steel and Composite Structures
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• v.23 no.4
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• pp.409-420
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• 2017

This paper theoretically studies the cyclic behavior of hybrid connections between steel coupling beams and concrete shear walls with embedded steel columns. Finite element models of connections with long and short embedded steel columns are built in ABAQUS and validated against the test results in the companion paper. Parametric studies are carried out using the validated FE model to determine the key influencing factors on the load-bearing capacity of connections. A close-form solution of the load-bearing capacity of connections is proposed by considering the contributions from the compressive strength of concrete at the interface between the embedded beam and concrete, shear yielding of column web in the tensile region, and shear capacity of column web and concrete in joint zone. The results show that the bond slip between embedded steel members and concrete should be considered which can be simulated by defining contact boundary conditions. It is found that the loadbearing capacity of connections strongly depends on the section height, flange width and web thickness of the embedded column. The accuracy of the proposed calculation method is validated against test results and also verified against FE results (with differences within 10%). It is recommended that embedded steel columns should be placed along the entire height of shear walls to facilitate construction and enhance the ductility. The thickness and section height of embedded columns should be increased to enhance the load-bearing capacity of connections. The stirrups in the joint zone should be strengthened and embedded columns with very small section height should be avoided.

• Steel and Composite Structures
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• v.36 no.5
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• pp.533-551
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• 2020

A finite element analysis (FEA) model is established to investigate the concrete-encased concrete-filled steel tubular (CFST) column to reinforced concrete (RC) beam joints under cyclic loading. The feasibility of the FEA model is verified by a set of test results, consisting of the failure modes, the exposed view of connections, the crack distributions and development, and the hysteretic relationships. The full-range analysis is conducted to investigate the stress and strain development process in the composite joint by using this FEA model. The internal force distributions of different components, as well as the deformation distributions, are analyzed under different failure modes. The proposed connections are investigated under dimensional and material parameters, and the proper constructional details of the connections are recommended. Parameters of the beam-column joints, including material strength, confinement factor, reinforcement ratio, diameter of steel tube to sectional width ratio, beam to column linear bending stiffness ratio and beam shear span ratio are evaluated. Furthermore, the key parameters affecting the failure modes and the corresponding parameters ranges are proposed in this paper.

• Earthquakes and Structures
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• v.20 no.2
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• pp.133-148
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• 2021

The paper presents a simplified force-based seismic design procedure for the preliminary design of steel haunch retrofitting for the seismic upgrade of deficient RC frames. The procedure involved constructing a site-specific seismic design spectrum for the site, which is transformed into seismic base shear coefficient demand, using an applicable response modification factor, that defines base shear force for seismic analysis of the structure. Recent experimental campaign; involving shake table testing of ten (10), and quasi-static cyclic testing of two (02), 1:3 reduced scale RC frame models, carried out for the seismic performance assessment of both deficient and retrofitted structures has provided the basis to calculate retrofit-specific response modification factor Rretrofitted. The haunch retrofitting technique enhanced the structural stiffness, strength, and ductility, hence, increased the structural response modification factor, which is mainly dependent on the applied retrofit scheme. An additional retrofit effectiveness factor (ΩR) is proposed for the deficient structure's response modification factor Rdeficient, representing the retrofit effectiveness (ΩR=Rretrofitted /Rdeficient), to calculate components' moment and shear demands for the retrofitted structure. The experimental campaign revealed that regardless of the deficient structures' characteristics, the ΩR factor remains fairly the unchanged, which is encouraging to generalize the design procedure. Haunch configuration is finalized that avoid brittle hinging of beam-column joints and ensure ductile beam yielding. Example case study for the seismic retrofit designs of RC frames are presented, which were validated through equivalent lateral load analysis using elastic model and response history analysis of finite-element based inelastic model, showing reasonable performance of the proposed design procedure. The proposed design has the advantage to provide a seismic zone-specific design solution, and also, to suggest if any additional measure is required to enhance the strength/deformability of beams and columns.