• Computers and Concrete
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• v.10 no.4
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• pp.331-347
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• 2012

This paper describes the varying material model, the analysis method and the software development for reinforced concrete circular columns confined by spiral or hoop transverse steel reinforcement and subjected to eccentric loading. The widely used Mander model of concentric loading is adapted here to eccentric loading by developing an auto-adjustable stress-strain curve based on the eccentricity of the axial load or the size of the compression zone to generate more accurate interaction diagrams. The prediction of the ultimate unconfined capacity is straight forward. On the other hand, the prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. This nonlinear procedure is programmed using C-Sharp to build efficient software that can be used for design, analysis, extreme event evaluation and forensic engineering. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.2469-2475
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• 2014

In 1990s, with the increase of domestic building renovation but also increase the amount of anchor. The 45-degree cone failure theory has been used in concrete anchor bolts design, but the CCD (concrete capacity design) method was adopted as a new design method since 2000. However, the method has some problems because it is based on the experimental results of pre-installed concrete anchor bolts. In this study, the objective is to investigate the effects of anchor edge distance, anchor interval and concrete strength on pullout characteristics of post-installed concrete set anchor embedded in plain concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.47-54
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• 2016

In this study, the flexural capacity of fiber reinforced concrete floor slabs were evaluated using main design loads, racking and moving loads. Based on design standards and guidelines, the magnitude and loaded area of each load were determined, and its relationship was assessed. For the application of a single load, flexural capacity should be evaluated in the edge of a floor slab. In addition, the slab with thickness and concrete strength, greater than 180mm and 35MPa, respectively, sufficiently satisfied flexural capacity with a minimum of equivalent flexural strength ratio. The combination of racking loads required the largest equivalent flexural strength ratio to satisfy the flexural capacity of the floor slab. The combination of racking and moving loads showed equivalent flexural strength ratio smaller than the case of combination of racking loads, but larger than the application of single racking or moving loads. The results of this study indicated that the flexure of fiber reinforced concrete floor slabs should be designed using the combination of design loads.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.207-211
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• 2006

This paper presents an experimental study on the repair performance of sprayed engineered cementitious composites(ECC) serving as a repair material. Sprayable ECC, which exhibit tensile strain-hardening behavior in the hardened state and maintain sprayable properties in the fresh state, have been developed by using a parallel control of micromechanical design and rheological process design. The effectiveness of sprayable ECC in providing durable repaired structures was assessed by spraying the ECC and testing them for the assessment. The experimental results revealed that, when sprayed ECC were used as a repair material, both load carrying capacity and ductility represented by the deformation capacity at peak load of the repaired flexural beams were obviously increased compared to those of commercial prepackaged mortar(PM) repaired beams. The significant enhancement in the energy absorption capacity and tight crack width control of the ECC repair system treated with wet-mix spraying process suggests that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

• Steel and Composite Structures
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• v.16 no.2
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• pp.187-201
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• 2014

A new through-beam connection system for a concrete filled steel tube column to RC beam is proposed. In this connection, there are openings on the steel tube while the reinforced concrete beams are continuous in the joint zone. The moment and shear force at the beam ends can be transferred to column by continuous rebar and concrete. The weakening of the axial load and shear bearing capacity due to the opening of the steel tube can be compensated by strengthening steel tube at joint zone. Using this connection, construction of the joint can be made more convenient since welding and hole drilling in situ can be avoided. Axial compression and reversed cyclic loading tests on specimens were carried out to evaluate performance of the new beam-column connection. Load-deflection performance, typical failure modes, stress and strain distributions, and the energy dissipation capacity were obtained. The experimental results showed that the new connection have good bearing capacity, superior ductility and energy dissipation capacity by effectively strengthen the steel tube at joint zone. According to the test and analysis results, some suggestions were proposed to design method of this new connection.

• Advances in concrete construction
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• v.11 no.2
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• pp.111-126
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• 2021

Concrete cracking due to brittle tension strength significantly prevents fully utilization of the materials for "flexural-shear failure" type shear walls. Theoretical and experimental studies applying fiber reinforced concrete (FRC) have achieved fruitful results in improving the seismic performance of "flexural-shear failure" reinforced concrete shear walls. To come to an understanding of an optimal design strategy and find common performance prediction method for design methodology in terms to FRC shear walls, seismic performance on shear walls with PVA and steel FRC at edge columns and plastic region are compared in this study. The seismic behavior including damage mode, lateral bearing capacity, deformation capacity, and energy dissipation capacity are analyzed on different fiber reinforcing strategies. The experimental comparison realized that the lateral strength and deformation capacity are significantly improved for the shear walls with PVA and steel FRC in the plastic region and PVA FRC in the edge columns; PVA FRC improves both in tensile crack prevention and shear tolerance while steel FRC shows enhancement mainly in shear resistance. Moreover, the tensile strength of the FRC are suggested to be considered, and the steel bars in the tension edge reaches the ultimate strength for the confinement of the FRC in the yield and maximum lateral bearing capacity prediction comparing with the model specified in provisions.

• Computers and Concrete
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• v.2 no.1
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• pp.79-96
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• 2005

The use of high-strength concrete (HSC) has significantly increased over the last decade, especially in offshore structures, long-span bridges, and tall buildings. The behavior of such concrete is noticeably different from that of normal-strength concrete (NSC) due to its different microstructure and mode of failure. In particular, the shear capacity of structural members made of HSC is a concern and must be carefully evaluated. The shear fracture surface in HSC members is usually trans-granular (propagates across coarse aggregates) and is therefore smoother than that in NSC members, which reduces the effect of shear transfer mechanisms through aggregate interlock across cracks, thus reducing the ultimate shear strength. Current code provisions for shear design are mainly based on experimental results obtained on NSC members having compressive strength of up to 50MPa. The validity of such methods to calculate the shear strength of HSC members is still questionable. In this study, a new approach based on artificial neural networks (ANNs) was used to predict the shear capacity of NSC and HSC beams without shear reinforcement. Shear capacities predicted by the ANN model were compared to those of five other methods commonly used in shear investigations: the ACI method, the CSA simplified method, Response 2000, Eurocode-2, and Zsutty's method. A sensitivity analysis was conducted to evaluate the ability of ANNs to capture the effect of main shear design parameters (concrete compressive strength, amount of longitudinal reinforcement, beam size, and shear span to depth ratio) on the shear capacity of reinforced NSC and HSC beams. It was found that the ANN model outperformed all other considered methods, providing more accurate results of shear capacity, and better capturing the effect of basic shear design parameters. Therefore, it offers an efficient alternative to evaluate the shear capacity of NSC and HSC members without stirrups.

• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.25-42
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• 2023

This paper presents a finite element (FE) simulation of eccentrically loaded lightweight aggregate concrete-encased steel (LACES) columns with H-shaped steel sections, analytical equations are also established to estimate the columns' axial and bending moment interaction capacities. The validity of the proposed models is checked by comparing the results with experimental data. Good agreements between the test and proposed models' results are found with acceptable agreements. Moreover, design parameters, including the lightweight aggregate concrete (LWAC) strength, eccentricity, column slenderness ratio, and confinement, are studied using the FE analysis, and their efficiency factors are discussed. The results show that the ultimate axial capacity of the LACES composite columns subjected to eccentric loading is negatively affected by the increase in the columns' height, but it is positively affected by the increase of the confinement. Increasing the eccentricity and columns' height reduced the columns'stiffness. In addition, the ultimate capacity of the LACES column is significantly influenced by the LWAC strength and eccentricity, where the ultimate capacity of the LACES column is significantly increased by increasing LWAC strength, and it is remarkably decreased by increasing the eccentricity. When the eccentricity changed from zero to 70 mm, the ultimate axial capacity and stiffness decreased by 67.97% and 63.56%, respectively.

• Steel and Composite Structures
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• v.51 no.2
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• pp.117-126
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• 2024

There are many challenges in the construction of large-section tunnels, such as extremely soft rock and fractured zones. In order to solve these problems, the confined concrete support technology is proposed to control the surrounding rocks. The large-scale laboratory test is carried out to clarify mechanical behaviours of the combined confined concrete and traditional I-steel arches. The test results show that the bearing capacity of combined confined concrete arch is 3217.5 kN, which is 3.12 times that of the combined I-steel arch. The optimum design method is proposed to select reasonable design parameters for confined concrete arch. The parametric finite element (FE) analysis is carried out to study the effect of the design factors via optimum design method. The steel pipe wall thickness and the longitudinal connection ring spacing have a significant effect on the bearing capacity of the combined confined concrete arch. Based on the above research, the confined concrete support technology is applied on site. The field monitoring results shows that the arch has an excellent control effect on the surrounding rock deformation. The results of this research provide a reference for the support design of surrounding rocks in large-section tunnels.

• Steel and Composite Structures
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• v.22 no.3
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• pp.613-625
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• 2016

The joints of the new prefabricated concrete assemble beam-column joints are put together by the hybrid joints of inserting steel under post-tensioned and non-prestressed force and both beams and columns adopt prefabricated components. The low cyclic loading test has been performed on seven test specimens of beam-column joints. Based on the experimental result, the rotation capacity of the joints is studied and the $M-{\theta}$ relation curve is obtained. According to Eurocode 3: Design of steel structures and based on the initial rotational stiffness, the joints are divided into three types; by equivalent bending-resistant stiffness to the precast beam, the equivalent modulus of elasticity $E_e$ is elicited with the superposition method; the beam length is figured out that satisfies the rigid joints and after meeting the requirements of application and safety, the new prefabricated concrete assemble beam-column joints can be regarded as the rigid joints; the design formula adopted by the standard of concrete joint classification is theoretically derived, thereby providing a theoretical basis for the new prefabricated concrete structure.