• Steel and Composite Structures
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• v.51 no.5
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• pp.563-573
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• 2024

This research experimentally evaluated the local stress distribution along the cross-section of composite beams under both positive and negative moments. The experiment utilized a large-scale, two-story, two-by-three bay steel gravity frame with a concrete on metal deck floor system. The composite shear connections, which are nominally assumed to be pinned under gravity loading, can develop non-negligible moment-resisting capacity when subjected to lateral loads. This paper discusses the local stress distribution, orshear lag effects, observed near the beam-to-column connections when subjected to combined gravity and lateral loading. Strain gauges were used for measurements along the beam depth at varying distances from the connection. The experimental data showed amplified shear lag effects near the unconnected region of the beam web and bottom flange under the applied loading conditions. These results indicate that strain does not vary linearly across the beam cross-section adjacent to the connection components. This insight has implications for the use of experimental strain gauge data in estimating beam demands near the connections. These findings can be beneficial in informing instrumentation plans for future experimental studies on composite beams.

• International Journal of Concrete Structures and Materials
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• v.2 no.2
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• pp.115-122
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• 2008

Ductility is important in the design of reinforced concrete structures. In seismic design of reinforced concrete members, it is necessary to allow for relatively large ductility so that the seismic energy is absorbed to avoid shear failure or significant degradation of strength even after yielding of reinforcing steels in the concrete member occurs. Therefore, prediction of the ductility should be as accurate as possible. The principal aim of this paper is to present the basic data for the ductility evaluation of reinforced high-strength concrete beams. Accordingly, 23 flexural tests were conducted on full-scale structural concrete beam specimens having concrete compressive strength of 40, 60, and 70MPa. The test results were then reviewed in terms of flexural capacity and ductility. The effect of concrete compressive strength, web reinforcement ratio, tension steel ratio, and shear span to beam depth ratio on ductility were investigated experimentally.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.963-974
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• 2005

This paper presented four shear test results from experimental tests of two large prestressed concrete beams cast with high strength concrete. In particular, this experiment investigated the effects of draped strands on shear behavior of these full-scaled beams. This study indicated that the use of draped strands increased the ultimate shear capacity as well as the web-shear cracking load. The test results also showed that draped strands reduced strand slip at ends of beams, which represented that these strands were effective to relieve the anchorage stresses. The test results were compared to predictions by two major codes; ACI 318-02 Building Code and AASHTO LRFD(2002). The shear design provisions in these codes provided conservative results on the shear strengths of all test specimens with reasonable margins of safety, and these provisions were particularly more conservative for test specimens having draped strands.

• Advances in nano research
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• v.12 no.5
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• pp.515-527
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• 2022

The application of fibers in concrete obviously enhances the properties of concrete, also the application of natural fibers in concrete is raising due to the availability, low cost and environmentally friendly. Besides, predicting the mechanical properties of concrete in general and shear strength in particular is highly significant in concrete mixture with fiber nanocomposite reinforced concrete (FRC) in construction projects. Despite numerous studies in shear strength, determining this strength still needs more investigations. In this research, Adaptive Neuro-Fuzzy Inference System (ANFIS) have been employed to determine the strength of reinforced concrete with fiber. 180 empirical data were gathered from reliable literature to develop the methods. Models were developed, validated and their statistical results were compared through the root mean squared error (RMSE), determination coefficient (R²), mean absolute error (MAE) and Pearson correlation coefficient (r). Comparing the RMSE of PSO (0.8859) and ANFIS (0.6047) have emphasized the significant role of structural parameters on the shear strength of concrete, also effective depth, web width, and a clear depth rate are essential parameters in modeling the shear capacity of FRC. Considering the accuracy of our models in determining the shear strength of FRC, the outcomes have shown that the R² values of PSO (0.7487) was better than ANFIS (2.4048). Thus, in this research, PSO has demonstrated better performance than ANFIS in predicting the shear strength of FRC in case of accuracy and the least error ratio. Thus, PSO could be applied as a proper tool to maximum accuracy predict the shear strength of FRC.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.57-60
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• 2005

The objective of this paper is to investigate and analyze the behaviour of prestressed I section structural members constructed with ultra high perfomance steel fiber reinforced cementitious concrete (SFR-UHPC). This material is known as reactive powder concrete (RPC) mixed with domestic materials and its compressive strength is over 150MP. The parameters of test specimens were span to depth ratio, prestressing force, prestressing wire placement and web width. Most influential parameter to determine the failure mode between shear and flexural action was proved to be shear span ratio. The characteristics of ultra high-strength concrete is basically brittle, but due to the steel fiber reinforcement behaviour of this structure member became ductile after the peak load. As a result of the test, the stress block of compressive zone should be redefined. The proposed analytical calculation of internal force capacity based by plastic analysis gave a good prediction for the shear and flexural strength of specimens. The numerical verification of the finite element model which constitutive law developed for Mode I fracture of fiber reinforced concrete correctly captured the overall behaviour of the specimens tested.

• Structural Engineering and Mechanics
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• v.57 no.6
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• pp.1051-1064
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• 2016

Link-to-column connections in Eccentrically Braced Frames (EBFs) have critical role in their safety and seismic performance. Accordingly, in this study, contribution of supplemental stiffeners on hysteretic behavior of the link-to-column connection is investigated. Considered stiffeners are placed on both sides and parallel to the link web between the column face and the first stiffener of the link. Hysteretic behaviors of the link beams with supplemental stiffeners are numerically investigated using a pre-validated numerical model in ANSYS. It turned out that supplemental stiffeners can change energy dissipation mechanism of intermediate links from shear-flexure to shear. Both rectangular and trapezoidal supplemental stiffeners are studied. Moreover, optimal placement of the supplemental stiffeners is also investigated. Obtained results indicate a discrepancy of less than 9% in maximum link shear of the numerical and experimental specimens. This indicates that the numerical results are in good agreement with those obtained from the test. Trapezoidal supplemental stiffeners improve rotational capacity of the link. Moreover, use of two supplemental stiffeners at both ends of the link can more effectively improve hysteretic behavior of intermediate links. Supplemental stiffeners would also alleviate the imposed demands on the connections. This latter feature is more pronounced in the case of two supplemental stiffeners at both ends of the link.

• Computers and Concrete
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• v.27 no.2
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• pp.153-162
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• 2021

This paper aims to simulate the isotropic elastic damage theory of Liu Jun (2012) using the self-programmed UMAT subroutine in the interface of ABAQUS. Liu Jun (2012)'s method based on the mechanic theory can not be used interactively with the currently commonly used finite element software ABAQUS. The advantage of this method in the paper is that it can interact with ABAQUS and provide a constitutive program framework that can be modified according to user need. The model retains the two scalar damage variables and the corresponding two energy dissipation mechanisms and damage criteria for considering the tensile and compressive asymmetry of concrete. Taking C45 concrete as an example, the relevant damage evolution parameters of its tensile and compressive constitutive model are given. The study demonstrates that the uniaxial tensile stress calculated by the subroutine is almost the same as the Chinese Concrete Design Specification (GB50010) before the peak stress, but ends soon after the peak stress. The stress-strain curve of uniaxial compression calculated by the subroutine is in good agreement with the peak stress in Chinese Concrete Design Specification (GB50010), but there is a certain deviation in the descending stage. In addition, this paper uses the newly compiled subroutine to simulate the shear bearing capacity of the shear key in a new structural system, namely the open-web sandwich slab. The results show that the damage constitutive subroutine has certain reliability.

• Journal of Korean Society of Steel Construction
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• v.27 no.5
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• pp.423-433
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• 2015

A double split tee connection, which is a beam-column moment connection, shows different behavioral characteristics under the influences of the thickness of a T-stub flange, a high-strength bolt gauge distance, and the number and diameter of a high-strength bolt. A double split tee connection is idealized and designed that a flexural moment normally acting on connections can be resisted by a T-stub and a shear force by a shear tap. However, where a double split tee connection is adopted to a low-and medium-rise steel structure, a small-sized beam member can be adopted. Then, a shear tab may not be bolted to the web of a beam. This study was conducted to suggest the details of a connection to secure that a double split tee connection with a geometric shape has a sufficient capacity to resist a shear force. To verify this, this study was conducted to make a three-dimensional nonlinear finite element analysis on a double split tee connection.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.615-623
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• 2015

The previous strut-and-tie models (STMs) to evaluate the shear strength of squat shear walls with aspect ratio less than 2.0 do not consider the axial load transfer of concrete strut and individual shear transfer contribution of horizontal and vertical shear reinforcing bars in the web. To overcome the limitation of the existing models, a simple STM was established based on the crack band theory of concrete fracture mechanics. The equivalent effective width of concrete strut having a stress relief strip was determined from the neutral axis depth and effective factor of concrete strength. The shear transfer mechanism of shear reinforcement at the extended crack band zone was calculated from an internally statically indeterminate truss system. The shear transfer capacity of concrete strut and shear reinforcement was then driven using the energy equilibrium in the stress relief strip and crack band zone. The shear strength predictions of squat shear walls evaluated from the current models are in better agreement with 150 test results than those determined from STMs proposed by Siao and Hwang et al. Furthermore, the proposed STM gives consistent agreement with the observed trend of the shear strength of shear walls against different parameters.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.3
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• pp.69-77
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• 2003

This paper presents test results on eight reduced beam section(RBS) steel moment connections. The testing program addressed bolted versus welded web connection and panel zone(PZ) strength as key variables, Specimens with medium PZ strength were designed to promote energy dissipation from both PZ and RBS regions such that the requirement for expensive doublet plates could be reduced. Both strong and medium PZ specimens with a welded web connection were able to provide satisfactory connection rotation capacity for special moment-resisting frames. On the other hand, specimens with a bolted web connection performed poorly due to premature brittle fracture of the beam flange of the weld access hole. If fracture within the beam flange groove weld was avoided using quality welding, the fracture tended to move into the beam flange base metal of the weld access hole. Plausible explanation of a higher incidence of base metal fracture in bolted web specimens was presented. The measured strain data confirmed that the classical beam theory dose not provide reliable shear transfer prediction in the connection. The practice of providing web bolts uniformly along the beam depth was brought into question. Criteria for a balanced PZ strength improves the plastic rotation capacity while reduces the amount of beam distortion ore also proposed.