• Steel and Composite Structures
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• v.51 no.3
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• pp.225-241
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• 2024

For several reasons, cold-formed steel (CFS) beams are often manufactured with holes. Nevertheless, because of holes, the reduction in the web area causes a decrease in the bending strength. Edge stiffeners are presently added around the holes to improve the bending strength of flexural members. Therefore, this research studies CFSZ-beams with stiffened holes and investigates how edge stiffener affects bending strength and failure modes. Nonlinear analysis was carried out using ABAQUS software and the developed finite element (FE) model was verified against tests from previous studies. Using the verified FE model, a parametric study of 104 FE models was conducted to investigate the influence of key parameters on bending strength of Z- sections. The results indicated that the effect of holes is less noticeable in very thin Z-sections. Moreover, adding edge stiffeners around the holes improves the flexural capacity of Z-beams and sometimes restores the original bending capacity. Because the computational techniques used to solve the CFS buckling mode with stiffened holes are still unclear, a numerical method using constrained and unconstrained finite strip method (CUFSM) software was proposed to predict the elastic distortional buckling moment for a wide variety of CFSZ-sections with stiffened holes. A numerical method with two procedures was applied and validated. Upon comparison, the numerical method accurately predicted the distortional buckling moment of CFS Z-sections with stiffened holes.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.733-738
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• 2000

This paper was aimed to evaluate the structural performance of flexural members repaired by polymer cement and epoxy mortar at soffit. Main test variables were repair materials, ratio of reinforcement and additional reinforcing bars. Test results shows that the repaired beams could change flexural capacity by materials and additional reinforcing bars. In polymer cement, the section repaired can carry same load, cracking moment and the flexural stiffness of the monolithic beams with same size. In epoxy mortar, all data were greater than the shotcrete. However, note that epoxy mortar may conduct member into brittle failure mode.

• Structural Engineering and Mechanics
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• v.40 no.4
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• pp.541-562
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• 2011

In the design of earthquake resistant reinforced concrete (RC) structures, both flexural strength and deformability need to be considered. However, in almost all existing RC design codes, the design of flexural strength and deformability of RC beams are separated and independent on each other. Therefore, the pros and cons of using high-performance materials on the flexural performance of RC beams are not revealed. From the theoretical results obtained in a previous study on flexural deformability of RC beams, it is seen that the critical design factors such as degree of reinforcement, concrete/steel yield strength and confining pressure would simultaneously affect the flexural strength and deformability. To study the effects of these factors, the previous theoretical results are presented in various charts plotting flexural strength against deformability. Using these charts, a "concurrent flexural strength and deformability design" that would allow structural engineers to consider simultaneously both strength and deformability requirements is developed. For application in real construction practice where concrete strength is usually prescribed, a simpler method of determining the maximum and minimum limits of degree of reinforcement for a particular pair of strength and deformability demand is proposed. Numerical examples are presented to illustrate the application of both design methods.

• Steel and Composite Structures
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• v.23 no.4
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• pp.473-481
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• 2017

Steel plate shear wall (SPSW) system has been increasingly used for lateral loads resisting system since 1980s when the utilization of post-buckling strength of SPSW was realized. The structural response of SPSWs largely depends on the behavior of the surrounded beams. The beams are normally required to behave in the elastic region when the SPSW fully buckled and formed the tension field action. However, most modern design codes do not specify how this requirement can be achieved. This paper presents theoretical investigation and design procedures of manually calculating the plastic flexural capacity of the beams of SPSWs and can be considered as an extension to the previous work by Qu and Bruneau (2011). The reduction in the plastic flexural capacity of beam was considered to account for the presence of shear stress that was altered towards flanges at the boundary region, which can be explained by Saint-Venant's principle. The reduction in beam web was introduced and modified based on the research by Qu and Bruneau (2011), while the shear stress in the web in this research is excluded due to the boundary effect. The plastic flexural capacity of the beams is given by the superposition of the contributions from the flanges and the web. The developed equations are capable of predicting the plastic moment of the beams subjected to combined shear force, axial force, bending moment, and tension fields induced by yielded infill panels. Good agreement was found between the theoretical results and the data from previous research for flexural capacity of beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.93-100
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• 2008

The use of fiber reinforced polymer (FRP) composites is significantly growing in construction and infrastructure applications where durability under harsh environmental conditions is of great concern. In order to examine the applicability of FRP rebar as a reinforcement in flexural member, flexural tests were conducted. 12 beams with different FRP materials such as CFRP, GFRP and Hybrid FRP and reinforcement ratio were tested and analyzed in terms of failure mode, moment-deflection, flexural capacity, ductility index and sectional strain distribution. The test results were also compared with the theoretical model represented in ACI 440.1R06. Test results indicate that the flexural capacity of the beams reinforced by FRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the deflection overestimates the actual deflection of GFRP series and underestimates the deflection of CFRP series.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.1
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• pp.114-123
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• 2013

This study was performed to verify the structural reinforcing effect of recycled polyethylene terephthalate (PET) fiber. In order to verify the structural reinforcing capacity of RPET fiber, recycled PET fiber added RC slab specimens were prepared to examine the flexural capacity while those of plain concrete and those of added with PP fiber, and the behavior of the specimens were also evaluated. The result shows that the compressive strength reduces as the fiber volume fraction increases, and the rate of reduction varies from 2% to 7%. The result of the flexural capacity shows that the ultimate capacity of plain specimens is the highest compare to those fiber reinforced specimens, but it has shown that specimens reinforced by 5% PET fiber has the highest energy absorption and the ductility index. In the application of PET fiber in slab specimens has shown that ductility capacity have increased where the ultimate capacity decreasing. That is the different tendency of beam specimens, which the ultimate capacity and the ductility of those have both shown the improvement compare to plain concrete specimens, which means the reinforcing effect of PET fiber in slab is less strong than in beam. Therefore, the application of PET fiber in slab structures as reinforcement needs the proper mix proportion of concrete and volume fraction of PET fiber with deep consideration of the structures.

• KCI Concrete Journal
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• v.12 no.2
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• pp.73-84
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• 2000

A new form of construction utilizing structural steel as the boundary elements in ductile flexural concrete walls is proposed to solve the bar congestion problems in such a heavily reinforced region, while maintaining the ductility and energy absorption capacity comparable to their traditional form. Two wall specimens containing rectangular hollow structural sections (HSS) and channels at their ends respectively, and one companion standard reinforced concrete wall specimen with concentrated end reinforcement were constructed and tested under reversed cyclic loading to evaluate the construction process as well as the structural performance. Initially, all three specimens were chosen and detailed with some caution to have approximately the same flexural capacity without change of the original shape and dimension of a rectangular cross section correction. Analysis and comparison of test results indicated that the reversed cyclic responses of three walls showed similar hysteretic properties, but in those with steel boundaries, local buckling of the corresponding steel webs and flanges following significant yielding was a dominant factor to determine the hysteretic response. The monotonic and cyclic responses predicted based on a sectional approach was also presented and found to be in good agreement with measured results. Design recommendations considering local instability of the structural steel elements and the interaction between steel chords and a concrete web member in such a composite wall are presented.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.2
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• pp.203-210
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• 2002

In these days, High-strength steel prevails throughout the construction fields for the benefit of structural and economical aspects. But high-strength steel is used by the simple calculation of flexural capacities for the purpose of reducing flexural reinforcement. So, this paper is mainly focused on the shear behavior of high-strength steel reinforced concrete beams without stirrups comparing with normal-strength steel reinforced concrete beams. Specimens were made and tested with the experimental parameters, such as steel yield strength, reinforcement ratios and minimum shear reinforcement. The main result was that not only area but also the yield strength of flexural reinforcement should be considered to predict the shear capacities of concrete beams. In addition, the experimental results were simulated by modified compression field theory analysis program, RESPONSE 2000. A good agreement was achieved between the test results and program analyses.

• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.545-566
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• 2009

Bridge columns are subjected to combined actions of axial force, shear force and bending moment during earthquakes, caused by spatially-complex earthquake motions, features of structural configurations and the interaction between input and response characteristics. Combined actions can have significant effects on the force and deformation capacity of RC columns, resulting in unexpected large deformations and extensive damage that in turn influences the performance of bridges as vital components of transportation systems. This paper evaluates the seismic response of three prototype reinforced concrete bridges using comprehensive numerical models that are capable of simulating the complex soil-structural interaction effects and nonlinear behavior of columns. An analytical approach that can capture the shear-flexural interacting behavior is developed to model the realistic nonlinear behavior of RC columns, including the pinching behavior, strength deterioration and stiffness softening due to combined actions of shear force, axial force and bending moment. Seismic response analyses were conducted on the prototype bridges under suites of ground motions. Response quantities of bridges (e.g., drift, acceleration, section force and section moment etc.) are compared and evaluated to identify the effects of vertical motion, structural characteristics and the shear-flexural interaction on seismic demand of bridges.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.325-335
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• 2006

In this paper, flexural test, girder-connection test and barrier-connection test for the pultruded composite bridge deck of hollow section, were carried out and its structural characteristics were evaluated. In the flexural test specimen, deflection was measured at center of the span and strains were measured at various locations to see the structural behavior up to the failure. In addition, finite element analysis was performed for the flexural test specimen and the results were compared with experiments, and load carrying capacity was evaluated. Also, field load test was conducted for the demonstration plate girder bridge and other field applications were described.