Search Results (14)

To facilitate the disassembly and recycling of structural components, this study proposes a novel demountable reinforced-concrete column–steel beam (RCS) joint. Numerical simulations were conducted to analyze the performance of this new RCS joint using finite element software ABAQUS 2021. Simultaneously, to expand the parametric analysis of the finite element model, further validating aspects such as concrete strength, the flange strength of the steel beam, the strength of the gusset plates, and the longitudinal reinforcement ratio were studied. The finite element analysis results demonstrate that the proposed demountable RCS joint exhibits superior bearing capacity and ductility compared to conventional cast-in-place joints. To further investigate the seismic behavior and influencing rules of this joint, analyses were carried out focusing on aspects such as hysteresis curves, skeleton curves, ductility, energy dissipation, residual deformations, and strength degradation. The findings reveal that gusset plate strengths, steel beam strength, beam-end connecting plate strength, longitudinal reinforcement ratio, and concrete strength have significant impacts on the strength and failure modes of the RCS joints. In addition, the life cycle analysis of four different material structures shows that the demountable RCS joints have the smallest carbon emission during the life cycle, which is conducive to the reuse of resources. Finally, the development of demountable RCS joints is proposed for China’s construction industry. Full article

To investigate the effects of parameters on the seismic performance of slender T-shaped RC walls subjected to a biaxial seismic action, a numerical model was established using a fiber-based cross-section and displacement-based beam–column element. The axial load ratio, shear span ratio, flange width to web height ratio, concrete strength grade, stirrup ratio, and longitudinal reinforcement ratio were selected for the parametric study, and the effects of these parameters on the performance degradation under biaxial loading were investigated. Furthermore, a sensitivity analysis of various parameters for the decrease was conducted. The results showed that the bearing and deformation capacities under biaxial loading were both decreased, and the total energy consumption was greater than that under uniaxial loading. The impacts of different parameters and loading paths on the decrease extent were significantly different, and the overall reduction was greater in the flange direction than in the web direction. Under the square loading path, the T-shaped wall had the greatest reduction in its seismic performance, followed by the eight-shaped and cruciform loading paths. The changes in the axial load ratio, shear span ratio, and concrete strength significantly affected the performance degradation under biaxial loading. Accordingly, it is recommended to reasonably consider the values of these three parameters in a multidimensional seismic design to maintain safety redundancy. Full article

Structurally deficient bridges are commonly retrofitted using conventional methodologies, including reinforced concrete, steel jackets, and fiber-reinforced polymers. Although these retrofit methods aim to improve structural performance, exposure to aggressive environments may undermine the durability performance of the retrofit material. More recently, ultra-high-performance concrete (UHPC) has provided an alternative to conventional construction methods, with its superior material characteristics favoring its use in retrofit applications. In this study, a large-scale reinforced concrete (RC) T-beam is constructed and artificially damaged. The T-beam is then retrofitted with an external envelope of UHPC on all faces. Sandblasting is introduced to the surface, providing partially exposed reinforcement in the T-beam to simulate material deterioration. Additional reinforcement is placed in the web and flange, followed by casting the enveloping layer of UHPC around the specimen. The feasibility of this method is discussed, and the structural performance of the beam is assessed by subjecting the beam to cyclic and ultimate flexural loading. This paper presents the results of cyclic and ultimate testing on the RC-UHPC composite T-beam regarding load–displacement, failure mode, and strain responses. The retrofitted T-beam specimen is subjected to a cyclic loading range of 131 kN for 1.576 million cycles. Despite no visible cracks in the cyclic testing, the specimen experiences a 12.22% degradation in stiffness. During the ultimate flexural testing, the specimen shows no relative slip between the two concretes, and the typical flexural failure mode is observed. By increasing the longitudinal reinforcement ratio in the web, the failure mode can shift from localized cracking, predominantly observed in the UHPC shell, toward a more distributed cracking pattern along the length of the beam, which is similar to conventional reinforced concrete beams. Full article

Beam–column connection zones are high regions of interest in reinforced concrete (RC) structures, which are expected to respond elastically to seismic loads. Using carbon fiber-reinforced polymers (CFRP) to improve these connections, performance is critical in retrofitting deficient RC frames because existing slabs may pose numerous limitations in the design and wrapping of CFRP sheets in joints. The main aim of this research is to develop a new design for flange-bonded CFRP retrofit of frames, including slabs, for the relocation of plastic hinges of the connection area toward the beam and to develop beam–column joint capacity and building stability in cases of subjection to dynamic loads. The performance of these proposed retrofittings was explored both experimentally and numerically. Two full-scale fabricated interior RC joints of a real moment-resisting frame with moderate ductility were subjected to monotonic loads before and after retrofitting, and the results were used to detail the numerical progress and verify of the beam–column connection. Moreover, a parametric study was conducted on CFRP sheets’ optimal thickness to examine its influence on plastic hinge relocation in the connection region. Results show that the retrofitting method can efficiently relocate the plastic hinge to the mid-span of the beam, which, in turn, leads to improved capacity and achievement of the RC frame and guarantees better structural safety a lower cost. Full article

Compared to more complex structures, simply configured reinforced concrete column–steel beam (RCS) composite structures have more promising application prospects, especially in regions with moderate–high seismic levels, due to their ease of construction. However, the current understanding of the seismic performance of simplified RCS joints is not sufficient. Validated by experimental results, a nonlinear finite element analysis (FEA) model was developed in this study to reveal the seismic behavior of simplified RCS joints. Six vital design parameters, namely axial load ratio, concrete strength, yield strengths of steel webs and flanges, and diameters of transverse and longitudinal reinforcements, were comprehensively studied. Research has shown that the axial compression ratio has a significant impact on the failure mode and bearing capacity of joints. When the concrete strength increases, the load-bearing capacity of the joints significantly increases, while the brittleness of high-strength concrete leads to a decrease in its deformation capacity. In addition, when the steel beam strength is constant, higher flange and web yield strengths have a limited influence on crack propagation and strain development. The stirrup reinforcement ratio and longitudinal reinforcement ratio play a significant role in inhibiting crack propagation and improving the bearing capacity, respectively. With the help of the numerical results, six theoretical models introduced by national codes and other researchers were compared. Among them, the modified model proposed by Kanno demonstrated the highest accuracy and was the most suitable for simply configured RCS joints. Full article

Uplift-restricted and slip-permitted (URSP) connectors have been demonstrated to effectively enhance the anti-cracking performance of RC slabs in negative moment areas. While their efficacy is recognized, studies of composite frames utilizing URSP connectors remain scarce, limiting their application in construction. This research undertakes a numerical analysis of the seismic performance of steel–concrete composite frames that employ URSP connectors. The influence of key design parameters on seismic behavior is scrutinized. Leveraging prior tests on composite frames with URSP connectors carried out by the authors’ group, a sophisticated three-dimensional FEM model is crafted. This model, built using the ABAQUS software (2016), accounts for the intricate mechanical behaviors of shear connectors. The fidelity of the FEM model is validated through a juxtaposition of numerical and test outcomes, assessing strain distribution, damage patterns, and load–displacement curves. This numerical model serves as a basis for the study, exploring the impacts of three crucial design parameters on structural seismic performance. The findings suggest that the arrangement length of URSP connectors should be constrained to less than half of the frame beam’s span to optimize mechanical performance during seismic events. Additionally, enhancing both the flange thickness and the steel beam’s height is recommended to further bolster structural integrity. Full article

In this study, three new types of demountable connections, consisting of reinforced concrete columns and steel beams, are proposed, and their seismic performance is investigated through the use of cyclic loading tests. The test results reveal that these three demountable RCS joints show good seismic performance, in which the ductility coefficients of specimens RCS-1 and RCS-2 are improved by 69% and 109%, respectively, compared with the reference group of RCS-0 specimens. Various parameters, such as the beam flange thickness, bolt strength, and connecting steel strength, were analyzed using the finite element software ABAQUS 2021 to determine the effect of these parameters on the seismic performance and behavior of the connections. The results also show that the three demountable RCS joints are very sensitive to the variation in beam flange steel thickness, while the connector steel strength and bolt type have very little effect on the joint load-carrying capacity. In addition, different current theoretical approaches for calculating the shear bearing capacity in the panel zone of joints are discussed. Full article

Shape memory alloy (SMA) is a material that can change shape in response to external stimuli such as temperature, stress, or magnetic fields. SMA types include nitinol (nickel-titanium), copper-aluminum-nickel, copper-zinc-aluminum, iron-manganese-silicon, and various nickel-titanium-X alloys, each exhibiting unique shape memory properties for different applications. Reinforced concrete (RC) T-beams strengthened and pre-stressed with Fe-SMA bars are numerically investigated for their flexural response under the influence of various parameters. The bars are embedded in a concrete layer attached to the beam’s soffit. Based on the numerical results, it was found that increasing the compression strength from 30 to 60 MPa slightly improves the beam’s strength (by 2%), but it significantly increases its ductility by approximately 45%. As opposed to this, the strength and ductility of the pre-stressed T-beam are considerably improved by using a larger diameter of Fe-SMA bars. Specifically, using 12 mm Fe-SMA bar over 6 mm resulted in 65% and 47% greater strength and ductility, respectively. Furthermore, this study examines the importance of considering the flange in the flexural design of pre-stressed beams. It is seen that considering a 500 mm flange width enhanced the ductility by 25% compared to the rectangular-section beam. The authors recommend further experimental work to validate and supplement the calculations and methodology used in the current numerical analysis. Full article

Steel–concrete composite box beams are widely used in bridge engineering, which might bear transverse and longitudinal bending moments simultaneously under vehicle loads. To investigate the fatigue performance of joints between the steel girders and the top reinforced concrete (RC) slabs under transverse bending moments, a reduced scale joint between the weathering steel girder with the corrugated steel web (CSW) and the top RC slab was designed and tested under constant amplitude fatigue loads. Test results show that the joint initially cracked in the weld metal connecting the CSW with the bottom girder flange during the fatigue loading process. The initial crack propagated from the longitudinal fold to the adjacent inclined folds after the specimen was subjected to 7.63 × 10⁵ loading cycles and caused the final fatigue failure. Compared with the calculated fatigue lives in the methods recommended by EC3 and AASHTO, the fatigue performance of the details involved in the joint satisfied the demands of fatigue design. Meanwhile, finite element (FE) models of joints with different parameters were established to determine their effect on the stress ranges at the hot spot regions of the joints. Numerical results show that improving the bending radius or the thickness of the CSW helps to reduce the stress ranges in the hot spot regions, which is beneficial to enhance the fatigue resistance of the investigated fatigue details accordingly. Full article

The existing literature mainly focuses on the research of reinforced concrete (RC) beams under a single load such as blast or impact. In this paper, the slab–rib–slab RC beam, a new type of structure widely used in bridge structures, was taken as the research object. The explicit dynamic analysis software LS-DYNA was used to numerically analyze the dynamic response and failure behavior of I-shaped RC beams under combined blast and impact loads. For this reason, an effective numerical analysis model was obtained by carrying out experiments on I-shaped RC beams under contact explosion. The key factors affecting the dynamic response of the structure under combined loads were numerically analyzed. Numerical results showed that different load application sequences have important effects on the dynamic response of the structure. When the impact load was first applied to the structure, more severe concrete damage and deformation occured in the depth direction of the beam. However, when the blast load was first applied to the structure, the concrete at the lower flange was damaged in the span direction of the beam due to tension, and no large-scale concrete spallation occurred in the depth direction. This was mainly due to the different mechanisms of blast and impact loads. In addition, the vulnerability of the I-shaped RC beams varied with some structural parameters, including span, depth, and configuration of reinforcement. At the same time, the results showed that the structure is more sensitive to changes in structural parameters when it is first subjected to impact loads. Full article

As is well known, in the current design codes, the shear strength of beams is calculated based on the modified truss theory, which does not consider the effects of the flange area of T-beams. The main objective of this paper was to gain a better understanding and enhance the experimental database of the shear behavior of RC T-beams and illustrate the contribution of the flange to the shear capacity of T-beams. To accomplish this aim, a specially designed experimental program was executed, and its test results were analyzed. The main investigated variables were flange dimensions (thickness and width) and its reinforcement (longitudinal and/or vertical). Nineteen simply supported beam specimens were tested to failure under a load configuration made of two concentrated loads. Eighteen specimens had T-shaped cross-sections, while one specimen had a rectangular cross-section for comparison purposes. The items monitored during testing included the development of diagonal cracks, concrete strains, reinforcement strains, maximum loads, and deflections. Test results showed a notable increase in the shear strength of T-beams compared to rectangular beams with the same web size. For the range of variables investigated, increasing the flange thickness-to-beam depth ratio (ρ_t) from 0.3 to 0.5 increased the shear capacity by up to 54%. In addition, increasing the flange width-to-web width ratio (ρ_b) from 3 to 5 increased the shear capacity by up to 19%. It was also shown that the results of three-dimensional finite element (FE) analyses using ANSYS compared reasonably well with the test results for all specimens. Finally, based on the test and FE results, a simplified method that accounts for the contribution of the flange to shear capacity was proposed. Full article

In this paper, experimental investigations for strengthening reinforced concrete (RC) continuous beams were performed. Eighteen T-beams were cast, twelve of which were inverted T-beams where the flange portion of the T-beam was subjected to positive flexure to represent the support region of a continuous beam. Six of the T-beams were non-inverted where the web is subjected to positive flexure. Carbon fiber reinforced polymer (CFRP) sheets with different widths were considered, and different strengthening configurations with the same area of CFRP were investigated. The use of one-layer, multiple layers, or multiple strips of CFRP were evaluated to investigate the effect of these configurations on the ultimate capacity and ductility of the strengthened beams. From the experimental observation of the non-inverted beams, it was found that the ultimate load capacities of the CFRP-strengthened beams were enhanced by 4% to 90% compared to the control beam. Using multiple layers of CFRP sheets enhanced the stiffness of the beams by 4% to 46%, depending on the CFRP area and configurations. The debonding of CFRP before the ultimate failure provided additional ductility to the tested beams. For the strengthening of the inverted beams, it was found that the addition of CFRP strips did not increase the strength of the beams when the width of CFRP to beam width ratio was less than 0.25, but the ductility of the beam was enhanced slightly. The use of multiple strips was found to be a more effective way for the strengthening of the negative moment region than using multiple layers. This can also provide more desirable modes of failure than when applying CFRP in multiple layers. Ductility was found to be lower if multiple layers were used compared to other configurations. Moreover, it was observed that as the compressive strength of concrete increased the addition of the CFRP improved the beams ductility. Full article

Recently, an analytical model called the generalized softened variable angle truss-model (GSVATM) aimed to predict the full behavior of reinforced concrete (RC) rectangular beams under torsion. In this article, such a model is used to compute the full torsional behavior of RC flanged beams, namely T- and L-shaped beams. The calculation procedure to include the influence of the flanges is described. A comparative analysis between the predictions from the GSVATM and some experimental results, related with RC flanged beams under torsion and found in the literature, is also presented. From this comparative analysis and for high loading levels, the GSVTM is reliable. Yet, for low loading levels, the theoretical model still needs to be refined. Full article

The effectiveness of a new retrofitting technique to upgrade the structural behaviour of reinforced concrete (RC) deep beams without steel stirrups using carbon fibre-reinforced polymer (CFRP) ropes as the only transverse shear reinforcement is experimentally investigated. Five shear-critical beams with rectangular and T-shaped cross-section are tested under monotonic loading. The strengthening schemes include (a) one vertical and one diagonal single-link CFRP rope that are internally applied through the web of the rectangular beam using an embedded through-section (ETS) system and (b) two vertical U-shaped double-link ropes that are applied around the perimeter of the web of the flanged beam using a near-surface-mounted (NSM) system. In both cases, the free lengths of the CFRP ropes have been properly anchored using epoxy bonded lap splices of the rope as NSM at (a) the top and the bottom of the web of the rectangular beam and (b) the top of the slab of the T-beam. Promising results have been derived, since the proposed strengthening technique enhanced the strength and altered the brittle shear failure to a ductile flexural one. The experimental results of this study were also used to check the validity of an analytical approach to predict the strength of shear strengthened deep beams using FRP ropes as transverse link reinforcement. Full article