Number Of Stirrups Research Articles

Numeričko ispitivanje učinka uvjeta oslanjanja na posmično ponašanje grede u armiranobetonskim gredama realnih veličina

In studies on beams in the literature, the beam elements are designed and tested as simply supported. Therefore, in this study, the behaviour of reinforced concrete (RC) beams under fixed support conditions was numerically investigated using ANSYS finite element software. The variables used in the study are the shear span/effective depth ratio (a/d) and stirrup spacing of the analysed specimens. In this study, 16 RC beams on a 1/1 scale were analysed in 4-point bending protocol. The a/d ratios were assumed to be 1.0, 2.0, and 3.0, in the test members produced. In addition, as another variable, the lateral reinforcement amount was designed and analysed at f8/75, f8/150 and f8/300 mm spacings without stirrups. Load-displacement and stiffness graphs are drawn based on the numerical results. The numerical results were interpreted and compared based on the graphs drawn for each analysis, stress distribution, and damage occurrence in the experiments. The results indicated that the a/d ratio and number of stirrups had strong effects on the behaviour of the fixed supported beams. The results of the beam analyses obtained using ANSYS finite element software were consistent with the experimental results.

Seismic performance of reinforced concrete beam-column joints with diagonal bars wrapped by steel tubes: experimental, numerical and analytical study

Diagonal bars can be used as joint reinforcement to address the congestion problem, yet a certain number of stirrups are still required for joint confinement. In this study, diagonal bars wrapped by steel tubes are proposed as joint reinforcement to fully replace the stirrups. Three interior beam-column joint specimens reinforced by conventional stirrups, debonded diagonal bars wrapped with plastic or steel tubes, are tested. The results indicate that replacing the plastic tubes with steel tubes can prevent shear failure in the joint without stirrups, increase the ductility, and reduce the joint distortion. However, it decreases the deformation capacity and increases the peak beam curvature. Compared to the stirrup-reinforced specimen, the specimen reinforced by the steel tube-wrapped diagonal bars has higher loading capacity and lower peak beam curvature without compromising the energy dissipation, stiffness, and joint distortion. Results from finite element analysis indicate that increasing the column axial load ratio to 0.4 leads to higher early stiffness and slower degradation of loading capacity. It should be noted that a sufficient area of steel tubes is required to avoid joint shear failure and sudden loss of loading capacity. The anchorage segments are recommended to be installed at the same depth as the beam longitudinal reinforcement to maximize their efficiency. Finally, an analytical model for predicting the failure mode and loading capacity is also developed, and a good agreement between predicted and tested results is obtained.

Behavior of RC Beam–Column Joints Strengthened with Modified Reinforcement Techniques

Using a significant number of transverse hoops in the joint’s core is one recognized way for achieving the requirements of strength, stiffness, and ductility under dynamic loading in a column joint. The shear capacity of a joint is influenced by the concrete’s compressive strength, the anchoring of longitudinal beam reinforcement, the number of stirrups in the joint, and the junction’s aspect ratio. Seismic motion on the beam may produce shear capacity and bond breaking in the joint, causing the joint to fracture. Furthermore, due to inadequate joint design and details, the entire structure is jeopardized. In this study, the specimens were divided into two groups for corner and interior beam–column joints based on the joint reinforcement detailing. The controlled specimen has joint detailing as per IS 456:2000, and the strengthened specimen has additional diagonal cross bars (modified reinforcement technique) at the joints detailed as per IS 456:200. The displacement time history curve, load-displacement response curves, load-displacement hysteretic curve, and load cycle vs. shear stress were used to compare the results of the controlled and strengthened specimens. The findings show that adding diagonal cross bars (modified reinforcing techniques) to beam–column joints exposed to cyclic loads enhances their performance. The inclusion of a diagonal cross bar increased the stiffness of the joint by giving an additional mechanism for shear transfer and ductility, as well as greater strength with minimum cracks.

Finite Element Method Analysis Applied to the Study of a Corner Joint in Reinforced Concrete Structures

The principal objective for this work was to extend the field of application of FEM to space frame beam-column connections under static loading and with lateral displacements. A four-storey building was modelled under static load condition. Horizontal and vertical structural elements were designed according to Eurocode 2. In order to understand the behavior of the external node made by under column, two beam and upper column, two models using correct boundary condition and nonlinear behavior of materials have been done using Abaqus Software The analysis was performed on an interior and an exterior joint models each in two conditions: unconfined and confined joint varying the distributions of number of stirrups for the beam reinforcement and the column reinforcement .A sup structural model to submit to numerical analysis have been performed, the Concrete Damage Plasticity model (CDPM) has been chosen for fit the nonlinear behavior for the concrete and the elastoplastic model has been adopted for the nonlinear behavior for the reinforcement (stirrups, longitudinal and vertical bars). The models were then verified against already existing and validated analytical results and results of experiments conducted on specimens.

A Structural Design Comparison Between Two Reinforced Concrete Regular 6-Level Buildings using Soil-Structure Interaction in Linear Range

Structural engineers commonly design superstructures as fixed at the base and transmit the reactions to the infrastructure in order to design the foundation system and estimate the displacement of the soil while disregarding the change in seismic response that this induces. In this article, the foundation system was transformed into equivalent springs, and the seismic response in the linear range was compared and quantified, obtaining results such as increased periods, increased amounts of steel reinforcement in beams (between 7% and 25%) and columns (between 29% and 39%), an increase in the number of stirrups per linear meter (between 3% and 11% in columns and between 5% and 45% in beams) and drifts (between 1% and 14%), and a decrease in basal shear (up to 20%), which directly affects the design of the structure. This study concludes that the inclusion of the soil-structure interaction is necessary for structural design in the linear range.

Mechanical Behavior of ECC and ECC/RC Composite Columns under Reversed Cyclic Loading

Engineered cementitious composite (ECC) is an advanced composite material with strain-hardening and multiple-cracking behaviors. The substitution of conventional concrete with ECC can significantly improve the deformation and energy dissipation ability of reinforced concrete (RC) columns. This paper reports on the mechanical behavior of ECC/RC composite columns. An ECC/RC composite column can be obtained by substituting concrete with ECC in the column bottom. The material composition, transverse reinforcement ratio, and axial load level were considered as experimental parameters. Experimental results from reversed cyclic load tests on nine scaled columns are presented. The results indicate that ECC and ECC/RC composite columns have better ductility, better energy dissipation capacity, and slower stiffness degradation than RC columns. The increase in axial load on the ECC/RC composite column negatively affects the ductility but can considerably improve the load capacity and maintain the structural integrity. The results also indicate that the number of stirrups can be properly reduced in ECC and ECC/RC composite columns because of the high-shear strength of ECC.

Ultimate-Load Behavior of RC Structural Systems Designed according to Eurocodes

AbstractVarious circumstances influence the behavior of reinforced concrete (RC) structures, some of which may increase the risk of a brittle failure for the whole system caused by shear forces. This paper presents a wide probabilistic investigation on the ultimate load behavior of RC structural systems designed according to Eurocodes. A full probabilistic model is derived and different structural systems are studied through material and geometric nonlinear analysis via Monte Carlo simulations. The resistance model is consistent with a current Eurocode and considers different failure modes (axial, bending, and shear). Results show that the ultimate failure load of RC structural systems designed according to Eurocodes may vary depending on the combination of three factors: (1) structural configuration; (2) load distribution; and (3) number of stirrups.

Steel-CFRP composite and their shear response as vertical stirrup in beams

An experimental study was conducted for the effectiveness of steel-CFRP composite (CFRP laminates sandwiched between two steel strips) as stirrups in concrete beam to carry shearing force and comparison was made with conventional steel bar stirrups. A total numbers of 8 concrete beams were tested under four point loads. Each beam measured 1,600 mm long, 160 mm width and 240 mm depth. The beams were composed of same grade of concrete, with same amount of flexural steel but different shear reinforcements. The main variables include, type of stirrups (shape of stirrups and number of CFRP layers used in each stirrup) and number of stirrups used in shear spans. After getting on an excellent closeness between the values of ultimate shear resistance and ultimate tensile load of steel-CFRP stirrups, it could be concluded that the steel-CFRP stirrups represent the effective solution of premature failure of FRP stirrups at the bends.

Numerical simulation for seismic performance evaluation of fibre reinforced concrete beam–column sub-assemblages

In the present study, performance of exterior beam–column sub-assemblages designed using normal concrete (NC) and steel fibre reinforced concrete (SFRC) is investigated. Nonlinear finite element method is adopted to analyse the sub-assemblages under reverse cyclic loading. To suit the material models for SFRC, available concrete model is judiciously modified. Cyclic behaviour of reinforcement, concrete (both normal and fibre reinforced) modeling based on fracture energy, bond–slip relations between concrete and steel reinforcement have been incorporated. The study also includes numerical investigation of crack and failure patterns, ultimate load carrying capacity, strain comparisons and formation of plastic hinges, load displacement hysteresis, energy dissipation and ductility. Experimentally validated numerical models are used to study the influence of various parameters on the performance of the beam–column sub-assemblage. Results obtained from experimental investigation were used for numerical validation. The influence of several parameters such as concrete strength, number of stirrups in the joint and amount of steel fibres on joint shear behaviour and strength of beam–column sub-assemblages are investigated. It is found that the failure mode cannot be favourably changed by adding fibres, if the compressive strength of the matrix is too low. It is also observed that the influence of fibre contribution to improve the residual tensile strength and fracture energy is significant and inter-dependent. Further, increase in residual tensile strength of FRC is found to be linear with increase in joint shear strength. In the present study, relationship for strength degradation depending on joint shear deformation for FRC has been established.

Effectiveness of concrete confinement on lap splice performance in concrete beams under reversed inelastic loading

Proposals from Cornell University for seismic design of lap splices, where the strength provided to the lap splice by the concrete confinement is considered insignificant, were evaluated. The concrete confining the splice length is assumed to deteriorate after high-intensity (inelastic) reversed load cycling so that the performance is mainly dependent on the amount of transverse reinforcement provided to confine the lap splice. Lap lengths of 30–40 bar diameters are proposed, along with heavy transverse reinforcement. Longer lap lengths are considered to be less effective. By contrast, for static loading the concrete confining the splice is known to play a major role in transferring load between the bars along the splice.The current program consisted of testing six reinforced concrete beams under fully reversed cycled loading. The three similar beams in each of the two series contained equal stirrup confinement (number of stirrups) along the lap length to satisfy the Cornell University recommendations for seismic loading for the measured reinforcing yield strength, while the splice length was varied. Splices were located in the bottom face of the test beams and were positioned in a region of maximum moment to ensure severe stressing. Each series of specimens exhibited only small strength gains with increasing splice lengths; however, the performance, when evaluated on the basis of the ductility achieved and the hysteretic energy absorbed prior to failure, was superior with long splices. Since the main reinforcement in the test beams was loaded past yielding, large increases in deformation capacity resulted in only small increases in load.Full reversal inelastic load cycling is very detrimental to the concrete that confines the splice region when compared to static (monotonic) loading or one-directional repeated loading to failure. Splice failure loads under reversal loading in the current study were below predicted static strengths for the same beam configurations, and with the longer lap lengths, static failure would have been flexural rather than in the splice. Key words: reinforced concrete, beams, splices (lap), confinement, seismic design, cycled loading, ductility, strength.