Top Longitudinal Reinforcement Research Articles

Optimization and experimental study on seismic performance of precast dry-wet hybrid beam-column joint with local prestressing

In order to improve the seismic performance, a novel dry-wet hybrid beam-column joint was optimized based on the findings of the preliminary experiment. Four full-scale prefabricated specimens were tested under cyclic loading to further investigate their seismic behavior and explore the various factors, including the connection methods for beam top longitudinal reinforcement in the joint core, magnitude of prestressing force, forms of hoop reinforcement at beam ends, and types of grouting material used in corrugated steel ducts. The results indicate that the new joint failed in the flexural mode, and its experimental bearing capacity value was consistent with the theoretical value, indicating a good safety margin. Additionally, it exhibited remarkable ultimate deformation capacity and displacement ductility coefficient exceeding 3, comparable to cast-in-place structures. The performance indicators of post-tensioned (PT) bar specimens were similar to those of cast-in-place structures and superior to PT rod specimens. The energy dissipation of PT rod specimens accounted for approximately 80 % to 90 % of that of the PT bar specimen. The viscous damping ratios of specimens with PT bars and PT rods were approximately 20 % and 15 %, respectively. Two methods of connecting beam top longitudinal bars by grouting or couplers, accompanied by a local unbonded treatment, could both fulfill anchorage requirements. However, the later one resulted in loosening of steel bars within the connector during late loading stages. The anchoring performance of prestressed grouting material could satisfy the anchoring requirements of PT bars, but still failed to meet the slippage resistance requirements of PT rods. Increasing the prestressing force can enhance the initial stiffness, significantly reduce yield displacement, and improve ductility coefficient, while having minimal impact on strength and energy dissipation. The open composite stirrups at beam ends do not significantly impact overall performance of the joint. The optimal details for the novel joint involves a combination of high-strength PT bars, grouting in corrugated ducts with local debonding treatment, and open composite stirrups at beam ends.

Experimental and analytical investigation of the behaviour of reinforced concrete beam under pure torsion

An experimental investigation and FE analysis are conducted on utilising basalt fibre-reinforced polymer (BFRP) fabric to increase the resistance of RC beams against torsion. A total of 4 no. of beams were cast with the same concrete batch mix M20. One beam was used as a control specimen, i.e. unstrengthened beam, and the other three beams were strengthened using BFRP laminates for different configurations, which includes one beam of Full U-Wrapping, one beam of strip wrapping of 150 mm width and 150 mm spacing between two strips and one beam of strip wrapping of 300 mm width and 150 mm spacing between two strips. Under purely torsion conditions, all of the beams were tested. All these beams have 150 mm × 250 mm c/s dimensions and 2100 mm in length. The beam contains bottom longitudinal reinforcement of 12 mm dia. and top longitudinal reinforcement of 10 mm dia. Stirrups used are of 8 mm diameter with 100 mm spacing; at support, it is 40 mm spacing for the length of 150 mm.The torsion test setup, loading frame and special end supports were fabricated for applying torsional load on beam specimens. The beams were subjected to pure torsional loading and twisting moment, and strains and twist angles were recorded. The experimental investigation results were validated using FEM-based ANSYS software. The model of the beams was created in SOLIDWORKS software and then imported into ANSYS for FE analysis. The simulations of beams were carried out in ANSYS Workbench. The effectiveness of U-wrapped beams was found to be better than the other strip-wrapping techniques.

Single-side yielding precast concrete slotted beam-column connection with replaceable energy dissipation bars: Experimental investigation and finite element analysis

A new type of rebar coupler, non-slipping combined threaded sleeve (NCTS), is proposed, and based on this, replaceable energy dissipation (ED) connector is assembled. An innovative single-side yielding slotted beam-column connection with replaceable ED bars (SYSC-REDB) was developed by placing the ED connector in the beam end bottom of prefabricated concrete frame. Four quasi-static tests were conducted to evaluate the seismic behavior, such as the damage distribution, failure characteristics, hysteretic response, ED capacity, and deformation pattern. The hysteretic curves were stable and full without pinching, indicating excellent seismic performance. The deformation pattern of single-side yielding can enhance the ED capacity of connectors, concentrate damage and failure on the ED bars, and significantly reduce the deformation of the top beam and beam elongation. The joint could be repaired by replacing the ED bars via the inner space of the NCTS. The seismic behavior of the repaired specimens was similar to those of the original specimens. In addition, the finite element models of ED connector and SYSC-REDB joint were established by ABAQUS respectively, and their accuracy were verified by comparing with the test phenomena and results. Furthermore, parametric finite element analysis was executed for some key factors, including the top-hinge area depth, ED bar area, and top longitudinal reinforcement bar area. Theoretical and parametric study of bending moment capacity is also performed.

Corrosion Crack Morphology and Creep Analysis of Members Based on Meso-Scale Corrosion Penetration.

In this paper, to study the development of load-carrying capacity and long-term creep performance of reinforced concrete beams under different corrosion patterns, the rate-dependent model of concrete is used as the basis to consider the creep development process from the meso-scale level. The porosity mechanics method is used to simulate the generation and penetration process of corrosion products. Three corrosion conditions are set: bottom longitudinal reinforcement corrosion, top longitudinal reinforcement corrosion and all reinforcement corrosion. The corrosion rate is used as the variable in each corrosion condition. The results show that: (1) the greater the corrosion rate in all conditions, the lower the bearing capacity. In addition, the corrosion of top longitudinal reinforcement causes the damage form of the beam to change to brittle damage; (2) the creep coefficient decreases with the increase in corrosion rate in all working conditions, but the main factor for this phenomenon is the obvious increase in initial deformation. Consequently, it is not suitable to follow the conventional creep concept (deformation development/initial deformation) for the development of plastic deformation of damaged members. It is more reasonable to use the global deflection to describe the long-term deformation of corrosion-damaged members.

Experimental investigation on progressive collapse resistance of precast concrete frame structures with different beam-column connections

In this paper, twelve 1/4-scale precast concrete (PC) substructural specimens with different beam-column connections under progressive collapse scenario were tested and the results were compared with that of the corresponding conventional reinforced concrete (RC) subassemblies. For assembled monolithic concrete (AMC) specimens, the top longitudinal reinforcement bars of beam passed though the beam-column joint continuously. However, the bottom longitudinal reinforcement bars of beam were either anchored as a 90° bend or lap spliced in the cast-in-place joints. Moreover, the flange effects as well as the effects of transverse beam and slab were also investigated according to spatial subassemblies with or without precast composite slabs. For fully assembled concrete (FAC) specimens, dowel bars and corbel connections, as well as steel plates and hidden corbel connections were used in the beam-column joints. Test results showed that the AMC specimens with or without precast composite flanges (slabs) exhibited almost the same progressive collapse resistance as RC specimens in the literatures, except for the peak value of the vertical load at the compressive arch action (CAA) stage for the AMC specimen with lap-splice of bottom rebars in the joints. Significant CAA at small deformation stage and subsequent tensile catenary action (TCA) at large deformation stage developed in the laminated beams under column removal scenarios. Furthermore, the transverse beam and composite slab effects could obviously increase the capacity of an AMC two-span beam. However, unlike RC specimens, CAA and TCA were not completely developed in the FAC specimens due to pull-out failure of the rebars in the beam-column joints or premature failure of the welding points between steel plates and rebars.

Prediction of Catenary Action Capacity of RC Beam-Column Substructures under a Missing Column Scenario Using Evolutionary Algorithm

Catenary action plays crucial role in resisting the applied vertical load at large deformations stage in reinforced concrete (RC) structures. This paper aims to predict the catenary action capacity of RC beam-column substructures by utilizing the distinctive properties of gene expression programming (GEP). The input parameters selected for the modelling are: double-beam span-to-depth ratio, relative axial restraints stiffness, relative rotational restraints stiffness, bottom and top longitudinal reinforcement ratios, and yield strength of longitudinal rebars. A comprehensive and reliable database was collated from internationally published research articles to develop and verify the model. The GEP-based model was assessed by comparing its performance with regression based model. Various statistical indicators and external validation criteria suggested in literature proved that the model is accurate and possess high prediction and generalization capacity. Sensitivity analysis was carried out to show the contributions of the input parameters, while parametric analysis was performed to show that the proposed model is not merely a combination of the input parameters but can accurately represent the given physical system. The proposed formulation from GEP is found to be simple, robust, and easy to utilize for pre-design purposes.

Influence of the top reinforcement detailing in the behaviour of flat slabs

This paper studies the influence of different longitudinal top reinforcement detailing on the behaviour and punching capacity of flat slabs. Experimental and numerical studies were carried out. The experimental campaign consisted in testing three reinforced concrete slabs 2.20 m wide with a thickness equal to 0.15 m. The numerical study was conducted using the non-linear finite element software ATENA 3D. Using numerical models, which were calibrated using the experimental tests, a parametric study was carried out to include other design solutions beyond the tested ones. The parameters that were changed in this parametric study were the steel reinforcement ratio, the concrete strength and the detailing of the top steel reinforcement, namely using a solution with uniform distribution and other with a higher concentration of reinforcement near the column. Finally, the results were compared with predictions obtained using some of the existing codes (Eurocode 2 and Model Code 2010). From this study it can be concluded that concentrating the top flexural reinforcement, keeping the same total amount of top longitudinal reinforcement, results in a stiffer response, an increment in the punching resistance, and a decrease in the maximum vertical displacement.

Progressive collapse resistance of precast beam–column sub-assemblages with engineered cementitious composites

This paper addresses the experimental investigation on the behaviour of precast concrete beam–column sub-assemblages with engineered cementitious composites (ECC) in structural topping and beam–column joints under middle column removal scenarios. Sub-assemblages comprising of a double-span beam and a middle beam–column joint were laterally connected to a rigid frame on one side and a reaction wall on the other side through load cells. Quasi-static vertical loading was imposed onto the middle column. Compressive arch action (CAA) and catenary action developed sequentially in the bridging beam with increasing middle joint displacement. Unlike conventional concrete, structural topping made of ECC exhibited multi-cracking behaviour with limited crack width and compatible deformations with embedded reinforcement at the initial stage of CAA. However, beyond the tensile strain capacity of ECC, major cracks formed near the face of the end column stub, causing severe strain localisation of the top longitudinal reinforcement in the beam. Besides, at large deformations, high tensile strain capacity of ECC actually hindered the development of flexural cracks in the beam, in particular, at the curtailment point of the top longitudinal reinforcement near the end column stub, thereby substantially reducing the deformation capacity of sub-assemblages. Eventually, fracture of beam longitudinal reinforcement at the face of end column stub led to failure of beam–column sub-assemblages. Through linear variable differential transducers mounted in the plastic hinge region, rotation capacity of plastic hinge could be calculated at the catenary action stage. Finally, the effectiveness of ECC on mitigating progressive collapse was examined to gain a better insight into its potential structural applications.

Behaviour of precast concrete beam–column sub-assemblages subject to column removal

Under column removal scenarios, initiation of alternate load paths via adjacent bridging beams to redistribute vertical loads requires certain level of ductility and continuity in beam–column joints. Although this approach does not consider the magnitude of the blast event, it is threat-independent and offers a minimum level of robustness against column removal scenarios. This paper studies the behaviour of precast concrete sub-assemblages which comprised two precast beams and a precast column joining together by cast-in-place concrete topping above the two beams and the beam–column joint. The top longitudinal reinforcement in the structural topping of precast beams passed through the beam–column joint continuously. However, the bottom beam longitudinal reinforcement was either lap-spliced or anchored as a 90° bend within the cast-in-place joint. Due to discontinuity of bottom beam longitudinal reinforcement, the ability of such an assemblage to develop compressive arch action (CAA) and subsequent catenary action has to be investigated, in particular, the effect of the top and bottom beam longitudinal reinforcement ratios. Test results show that significant CAA and catenary action developed in the beams under column removal scenarios, with pull-out failure of the bottom beam reinforcement in the joint. The enhancement of CAA and catenary action to structural resistance greatly depends on joint detailing and beam reinforcement ratio. Furthermore, the effectiveness of horizontal shear transfer between concretes cast at different times is examined at large deformation stage. Finally, practical suggestions are given to enhance structural resistance of a similar type of precast concrete sub-assemblages.