• Steel and Composite Structures
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• v.26 no.6
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.

• Computers and Concrete
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• v.34 no.4
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• pp.379-391
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• 2024

The ultra-high performance concrete (UHPC) mixed with hybrid fibers has excellent mechanical properties and durability, and the hybrid fibers have a certain impact on the bearing capacity, deformation capacity, and crack propagation of beams. Many scholars have conducted a series of studies on the bending performance of prestressed UHPC beams, but there are few studies on prestressed UHPC beams mixed with hybrid fibers. In this study, five bonded post-tensioned partially prestressed UHPC beams mixed with steel fibers and macro-polyolefin fibers were poured and subjected to four-points symmetric loading bending tests. The effects of different prestressing degrees and prestressing levels on the load-deflection curves, crack propagation, failure modes and ultimate bearing capacity of beams were discussed. The results showed that flexural failure occurred in the prestressed UHPC beams with hybrid fibers, and the integrity of specimens was good. When the prestressing degree was the same, the higher the prestressing level, the better the crack resistance capacity of UHPC beams; When the prestressing level was 90%, increasing the prestressing degree was beneficial to improve the crack resistance and ultimate bearing capacity of UHPC beams. When the prestressing degree increased from 0.41 to 0.59, the cracking load and ultimate load increased by 66.0% and 41.4%, respectively, but the ductility decreased by 61.2%. Based on the plane section assumption and considering the bridging effect of short fibers, the cracking moment and ultimate bearing moment were calculated, with good agreement between the test and calculated values.

• Advances in concrete construction
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• v.10 no.1
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• pp.81-92
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• 2020

Flexural and splitting strength behavior of conventional concrete can significantly be improved by incorporating the fibers in it. A significant number of research studies have been conducted on various types of fibers and their influence on the tensile capacity of concrete. However, as an important property, tensile capacity of fiber reinforced concrete (FRC) is not modelled properly. Therefore, this paper intends to formulate a model based on experiments that show the relationship between the fiber properties such as the aspect ratio (length/diameter), fiber content, compressive strength, flexural strength and splitting strength of FRC. For the purpose of modeling, various FRC mixes only with steel fiber are adopted from the existing research papers. Automated neural network search (ANS) is then developed and used to investigate the effect of input parameters such as fiber content, aspect ratio and compressive strength to the output parameters of flexural and splitting strength of FRC. It is found that the ANS model can be used to predict the flexural and splitting strength of FRC in a sensible precision.

• Steel and Composite Structures
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• v.9 no.5
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• pp.397-418
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• 2009

Eight panel specimens were tested in one-way bending to study the behaviour and capacity of composite slab joists consisting of cold-formed steel C-sections and concrete. Various shear transfer mechanisms were implemented on the C-section flange embedded in the concrete to provide the longitudinal shear resistance. Results showed that all specimens reached serviceability limit state while in elastic range and failure was ductile. Shear transfer achieved for all specimens ranged from 42 to 99% of a full transfer while specimens employed with shear transfer enhancements showed a greater percentage and therefore a higher strength compared with those relying only on surface bond to resist shear. The implementation of pre-drilled holes on the embedded flange of the steel C-section was shown to be most effective. The correlation study between the push-out and panel specimens indicated that the calculated moment capacity based on shear transfer resistance obtained from push-out tests was, on average, 10% lower than the experimental ultimate capacity of the panel specimen.

• Steel and Composite Structures
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• v.14 no.4
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• pp.313-333
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• 2013

The web-encased steel-concrete composite (WESCC) beam is a new developed steel-concrete composite beam. Experiments of six simply supported WESCC beam specimens were conducted. The effects of the shear-span ratio and steel section type were all investigated on the static behaviors such as failure modes, failure mechanism and bearing capacity. The experimental results denoted that all specimens failed in bending mode and the degree of combination between the bottom armor plate of steel shape and concrete were very well without any evident slippage, which demonstrated that the function of bottom armor plate and web were fully exerted in the WESCC beams. It could be concluded the WESCC beams have high stiffness, high load carrying capacity and advanced ductility. The design methods are proposed which mainly consist the bearing capacity calculation of bending and flexural rigidity. The calculation results of the bearing capacity and deflection which take the shear deflection into account are in agreement with the experimental results. The design methods are useful for design and application of the innovative composite beams.

• Steel and Composite Structures
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• v.13 no.3
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• pp.295-308
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• 2012

This paper experimentally investigated the buckling capacity of built-up steel columns mainly, Cruciform Columns (CC) and Side-to-Side (SS) columns fabricated from two Universal Beam (UB) sections. A series of nine experimental tests comprised of three UB sections, three CC sections and three SS sections with different lengths were tested to failure to measure the ultimate axial capacity of each column section. The lengths used for each category of columns were 1.8, 2.0, and 2.2 m with slenderness ratios ranging from 39-105. The measured buckling loads of the tested specimens were compared with the predicted ultimate axial capacity using Eurocode 3, AISC LRFD, and BS 5959-1. It was observed that the failure modes of the specimens included flexural buckling, local buckling and flexural-torsional buckling. The results showed that the ultimate axial capacity of the tested cruciform and side-by-side columns were higher than the code predicted design values by up to 20%, with AISC LRFD design values being the least conservative and the Eurocode 3 design values being the most conservative. This study has concluded that cruciform column and side-to-side welded flange columns using universal beam sections are efficient built-up sections that have larger ultimate axial load capacity, larger stiffness with saving in the weight of steel used compared to its equivalent universal beam counterpart.

• 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.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.78-86
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• 2003

Reinforced concrete beams are often retrofitted with various FRP composite sheets. This paper is focused on the comparison of structural performance of various FRP sheets and proposal of the retrofitting design formula. Effects of the FRP kinds(AFRP, GFRP, CFRP) and the reinforcing steel ratio on behavior of the retrofitting beams are tested and analyzed with particular emphasis on the maximum load capacity, stiffness, and ductility. The experimental work included 4 point flexural testing of 3.2m span reinforced concrete beams with bonded external reinforcements. The results show that the difference of FRP kinds is not large and the flexural load capacity is mainly affected by stiffness of the retrofitting materials. This paper also proposes the design formula on the retrofitting reinforced concrete flexural members and checks with this experimantal work and previous research results.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.466-475
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• 2001

The potential shear strength of reinforced concrete beams decreases after flexural yielding due to the decrease of the effective compressive strength of concrete in plastic hinge zone. A truss model considering shear deterioration in the plastic hinge zone was proposed in order to evaluate the ductile capacity of reinforced concrete beams failing in shear after flexural yielding This model can determine the potential shear strength of the beam by using a truss model. The potential shear strength gradually decreases as the increase of the axial strain of member. When the calculated potential shear strength decreases up to the flexural yielding strength, the corresponding rotation angle is defined as the ductile capacity of the beam. The predicted ductile capacity of reinforced concrete beams is shown to be in a good agreement with experimental results.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.2
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• pp.11-18
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• 2012

This study proposes flexural failure design criteria of continuous slabs enhanced by a hybrid system of fiber reinforced polymer (FRP) and ultra high performance concrete (UHPC). The proposed hybrid retrofit system is designed to be placed at the top surface of the slabs for flexural strengthening of the sections in both positive and negative moment zones. The enhancing mechanisms of the proposed system for both positive and negative moment regions are presented. The neutral axis of the enhanced sections in positive moment zone at flexural failure is enforced to be in UHPC overlay for preventing the compression in FRP. From this condition, a relationship between design parameters of FRP and UHPC is established. Although the capacity of the proposed retrofit system to enhance flexural strength and ductility is confirmed through experiments of one-way RC slabs having two continuous spans, the retrofitted slabs failed in shear. To prevent this shear failure, a design criteria of flexural failure is proposed.