Column Reinforcement Research Articles

The shearing performance of a beam-column joint in a reinforced concrete frame subjected to bidirectional loading

The anti-seismic capability of beam-column joints in reinforced concrete frame structures undergoing bidirectional loading may be lower than the designed capability for unidirectional earthquake action. To date, detailed calculation methods for the shear capability and shearing performance for joints in reinforced concrete frames subjected to bidirectional loading have not been reported. In this work, the shear mechanism of the beam-column joint in a reinforced concrete frame under bidirectional loading is analyzed. The study shows that when a synthetic shear force is imposed on the joint, the oblique compression zone comes into being at the corner of the joint, and the oblique compression strut is formed in the core area of the joint, which is different from the shear mechanism of the joint under unidirectional loading. A shear capacity calculation model is established based on the strut-and-tie model. Through the testing of reinforced concrete frame joints under bidirectional monotonous loading, the combined shear and deformation in the joint are obtained, the mechanical properties in each principal plane and in the combined shear action plane are analyzed, the shearing performance of the joints in a reinforced concrete frame under bidirectional loading is defined, and the shear contributions of hoop and column reinforcement are verified. The predicted values of the shear capability in this work are in good agreement with the reported experimental results.

Durable Bridge Columns using Stay-In-Place UHPC Shells for Accelerated Bridge Construction

Ultra-high performance concrete (UHPC) is a durable material that allows the construction of innovative structural elements and conforms with accelerated bridge construction (ABC) goals. The main idea of this research is to utilize UHPC to prefabricate a shell that acts as a stay-in-place form for bridge columns. The prefabricated shell eliminates the conventional formwork while reducing the on-site construction time and acting as a durable protective layer for the normal concrete inside the shell against environmental attacks. In addition, the UHPC shell provides additional confinement to the column concrete, which improves the column’s structural performance. During construction and after completing the column reinforcement work onsite, based on the conventional construction methods, the prefabricated UHPC shell is placed around the column reinforcement, followed by casting a portion of UHPC for a column-to-footing connection, which improves the capacity of the connection and shifts the plastic hinge zone above the connection. Once the UHPC portion hardens, normal concrete is placed inside the shell, forming a permanent concrete-filled UHPC shell. The construction process is finalized by placing and connecting a prefabricated cap beam to the column through the same developed connection as that in this research. This technical note presents the development of two test specimens using an UHPC shell in lieu of a conventional formwork with the advantage of improving the column performance and durability.

Experimental investigation of the performance of diagonal reinforcement and CFRP strengthened RC short columns

In this study, quasi-static seismic performances of CFRP wrapped and diagonal reinforcement reinforced concrete (RC) short columns are presented. RC short columns have been tested experimentally under constant axial load and cyclic lateral load. In the scope of this study, the performance of eighteen RC short columns, which consist of six CFRP wrapped, six diagonal reinforcement and six reference (Ref) columns, have been examined. Ref columns are the perfect columns produced in accordance with the regulation requirements. Therefore, it is aimed to examine the proposed diagonal rebar and CFRP applications as an alternative to the design in the earthquake regulations. The use of Ø10 and Ø12 reinforcements as a shear reinforcement for Ref columns and columns with diagonal reinforcement has also been examined for the contribution of the diameter of shear reinforcement to performance. Besides the difference in the diameters of the shear reinforcement and the applied methods, the aspect ratio (αs) is another parameter. Eighteen test columns were divided into three series and tested with αs = 2, 1.5 and 1 aspect ratio in order to examine the effectiveness of the applied methods by increasing the effect of shear dominant behaviour. The experimental results showed that columns with diagonal reinforcement and CFRP wrapped columns succeeded in exceeding the performances of perfect Ref columns and could be an alternative to the existing design.

Impact Response of Reinforced Concrete Columns with Different Axial Load under Low-Velocity Impact Loading

Building collapses from the seismic pounding of two adjacent buildings have been found in many past earthquakes. For the two buildings with different story height, the pounding induces impact load and local stress at column mid-height where the provided column reinforcement is normally lesser than the column’s edge. This paper aims to investigate the impact responses of reinforced concrete columns with different axial load and shear capacity by using numerical simulation method. Sixteen reinforced concretes columns were subjected to an impact load created by dropping 300 kg hammer at the height of 1,200 mm above the mid-span of the column. Every specimen has an identical cross section of 220 mm by 220 mm, with 3,000 mm of clear span length. Both ends of the column were fully restrained. The magnitude of the axial load varies from 0% to 40% of the ultimate axial capacity of the concrete section. Shear reinforcement spacing varies from @200 mm to @60 mm. It is found that the axial loads have a great effect on the impact responses of the RC columns. The specimens with high axial load yield higher peak impact force value and less mid-span deflection. Shear cracks were observed on the specimens with low axial force, but the cracks were relatively decreased when increasing the axial load.

Comparison between cyclic response of RC columns transversely reinforced with FRP strips and carbon steel

This study investigates the effects of different confinement methods for longitudinal reinforcement bars in reinforced concrete, RC columns. Comparison is made between three RC columns; two were transversely reinforced with carbon steel in single tie and continuous spiral form, and the third sample were transversely reinforced with Fibre Reinforced Polymer, FRP strips in continuous spiral form. Numerical simulation is conducted using validated numerical models. All three RC column models were subjected to a constant axial load and cyclic loading. Hysteresis curves and backbone curves were used to analyse cyclic behaviour of each samples. Comparisons between the RC columns were made based on the ultimate load capacity and energy dissipation capacity ratio. Results show that, RC column transversely reinforced with FRP strips exhibits the highest ultimate load and energy dissipation capacity. The ultimate load capacity is 15% and 10% higher than the RC column transversely reinforced with carbon steel in single tie and continuous spiral form respectively. The FRP strips also increases the energy dissipation capacity up to 35% and 22% compared to the one transversely reinforced with carbon steel in single tie and spiral form respectively. It can be concluded that the usage of FRP strips as transverse reinforcement in RC column is able to improve the cyclic responses of the conventional RC columns.

Structural behaviour of self-compacting concrete columns reinforced by steel and glass fibre-reinforced polymer rebars under eccentric loads

Glass fibre-reinforced polymer (GFRP) rebars are preferable alternatives to steel bars for minimizing corrosion problems. In this study, experimental and analytical work are carried out to investigate the behaviour of GFRP reinforcement versus traditional steel reinforcement in self-compacting concrete columns under eccentric loads. The GFRP-reinforced columns have lower carrying capacities than the steel-reinforced columns, with a difference of ∼24%. Furthermore, the two confining materials (of the tube and spirals) improve this reduction. The analytical results show good agreement with the experimental results for steel-reinforced columns, whereas the GFRP-reinforced columns report a noteworthy contrast.

Investigation on steel-concrete composite frame in Chinese traditional style buildings by pseudo-dynamic test

A series of pseudo-dynamic tests of a 1/2-scale 1-story 3-bay Chinese traditional style frame using steel - concrete composite columns was performed. During the test, the input ground motions were chosen from El Centro wave, Taft wave and Lanzhou wave. And peak ground acceleration (PGA) were 35 gal (minor earthquake of 7 degrees), 100 gal (precautionary earthquake of 7 degrees), 220 gal (major earthquake of 7 degrees) and 400 gal (major earthquake of 8 degrees), respectively. The failure modes, displacement and acceleration time history curves, hysteretic loops of restoring force- displacement, energy dissipation capacity and deformability, inter - story drift ratio of the test model were analyzed. It is shown that the typical failure modes of the model are concrete cracking at the connection between hypostyle column and penetrating tie as well as yield of longitudinal reinforcement of hypostyle column and peristyle column. And also, the model has better plastic deformation capacity. With a larger PGA, natural frequencies and dynamic amplification factors decreased, but its energy dissipation capacity increased. The energy dissipation of the model subjected to El Centro wave was largest with the same PGA. Based on the experimental results, the modal analysis and dynamic elasto-plastic analysis of the test model was performed using finite element software SAP2000. The results showed that under the action of horizontal earthquake, the 1st mode was translation of the model, and the plastic hinges of the model first formed on the ends of penetrating tie and successively developed at the root of hypostyle column, peristyle column, CRST-2 and CRST-3 and CRST-1 and CRST-4. And the inter-story drift ratios of the model subjected to 700 gal El Centro was close to the limited value in Chinese Code for Seismic Design of Buildings (GB50011-2010), indicating that the frame had a higher safety margin.

Experimental Study on Reinforcement and Chloride Extraction of Concrete Column with MPC-CFRP Composite Anode

In this research, Magnesium Phosphate Cement (MPC) was innovatively used to bond with Carbon Fiber Reinforced Plastic (CFRP) in order to form the MPC-CFRP as a composite material, adopted both for chloride ions extraction and reinforcement of concrete columns. First of all, a series of tests were conducted to evaluate the feasibility of the MPC-CFRP as anode of Electrochemical Chloride Extraction (ECE) system, including chloride ions concentration, Scanning Electron Microscope (SEM) and tensile strength. Then, the MPC-CFRP was used to wrap around reinforced concrete column for the sake of reinforcement and extraction of chloride ions. The test results indicated that the chloride extraction efficiency and the tensile resistance of the MPC-CFRP electrode were superior to the control group. The ECE process can decrease the interface bonding strength between the concrete and the steel rebar while the compression resistance of the columns could be increased remarkably. Therefore, the MPCCFRP composite material is capable of achieving the dual functions of strengthening and repairing the reinforced concrete construction.

Experimental testing of medium scale GFRP reinforced concrete frames

Fibre reinforced polymers (FRP) have been used as strengthening for existing RC structures for many decades. Lately, there has been a lot of interest in using FRP as internal reinforcement in beams, slabs and columns. One potential area of application could be reinforced concrete frames internally reinforced with GFRP bars. With limited research in this direction, the objective of this publication is to assess the behaviour of glass FRP (GFRP) reinforced concrete frames under reversed cyclic lateral in plane loading and to analyse the seismic performances of such elements. For the purpose of this paper, experimental testing of two 1/3 scaled down frames is conducted in displacement-controlled mode with the loading history according to ACI 374.1-05. The control sample is reinforced with conventional steel reinforcement and the results obtained are compared with the sample reinforced with GFRP bars. In summary, observations on the sample behaviour at specified drift ratio such as load-displacement behaviour, envelope curves and energy dissipation are presented.

Совершенствование технологии усиления бетонных колонн при реконструкции каркасных зданий

Совершенствование технологии усиления бетонных колонн при реконструкции каркасных зданий

Axial compressive behavior of square concrete columns confined with CFRP strip ties using wet lay-up technique

Pultruded fiber-reinforced polymer (FRP) bars used as confining reinforcement in concrete columns provide limited ductility and confinement efficiency due to the drastic reduction of strength at bend portions and premature bond slip failure at overlapping regions. In this study, complete close-type CFRP strip ties (C-S) with rectangular cross-section and fabricated using wet lay-up technique were proposed to overcome the shortcomings of pultruded FRP ties. Ten square concrete columns (300 × 300 × 900 mm), longitudinally reinforced with steel bars and confined with different types of ties such as steel, pultruded CFRP (C-P), and CFRP strip (C-S) ties, were tested to investigate their axial compressive behavior. Test results depicted that the columns confined with C-S ties exhibited improved confined concrete strength and ultimate axial strain in comparison with the columns confined with steel and C-P ties. Confined concrete strength and ultimate axial strain were increased up to 1.16 times and 3.5 times, respectively, by the replacement of C-P ties with the equal volumetric ratio of C-S ties.

Improvement of Structural and Technologies Solutions for Erection of Flat Slab Buildings

The object of this research is frame systems with concealed girders and flat floor slabs. The research helped identify the main advantages and disadvantages of precast/cast-in-situ frame systems for the construction of flat slab buildings using modular elements. The key methods used in the research were the analysis of the existing domestic and foreign technologies and the development of a new structural system differing from the systems discussed in the paper in terms of its technological intensity, versatility of application and rational design.The authors suggest a precast/cast-in-situ frame building system with concealed girders and flat floor slabs where the volume of modular precast elements drastically exceeds that of the cast-in-situ part of the frame. This allows for considerable saving in assembly and erection time due to a reduced number of process operations and modular assembly units. In order to identify the key benefits, the suggested frame system was compared with a KUB 3-V multi-purpose beamless frame system, which has been popular in Russia in recent years. Apart from a smaller number of process operations, the new system allows reducing the scope of welding and removing embedded parts connecting shells of drop panels with the bare part of column reinforcement. It also eliminates the needs for additional installation fixtures for columns and floor slabs, such as: support brackets and conductors for each column. The envelope of a building using the suggested frame system may consist of semi-integral thermopanels offered by domestic and foreign producers.

The Audit and Assessment of Building Structural Strength (Case Study of Mataram Islamic State University Rectorate Building)

Rectorate building of Mataram Islamic State University was designed of four story building and startedunder construction on 2008. However, the construction was aborted due to lack of administrationmanagement and left the building under incomplete condition with only foundation and the first floorerected. Ten years afterward, the management decided to continue construct the building. This studyaimed to investigate the condition of existing building whether can be rebuilt properly corresponding tothe previous design. The investigation included structural cracks that happened on structural element aswell as the deflection of structural beams. The conditions of existing structural column have also beeninvestigated.The assessment process was conducted both on field and laboratory testing. The field testing was run withSchmidt Rebound Hammer test to know the compressive strength of structural concrete and its quality.The waterpass, theodolite, and tape measurement were used to measure the building geometric. SAP2000 computer package was used to analyze the structure. Loading test was carried out base on the totalmeasurement test which was required in SNI 03-2847-2002. The total measurement load of 700 kg/m2was employed representing U = 85% (1,4D + 1,7L), where D was dead load and L was live load. In thisstudy, the loading test was conducted on 300/700 and 200/500 size beams.Test result indicated that the qualities and the concrete compressive strengths on the buildingconstruction elements were varied. Steel reinforcement of structural columns was good enough towithstand the load, but, the column concrete strength should be improved. On the beam of 300/700 in thefirst floor, the deflection did not exceed the maximum deflection based on the code. However, themaximum deflection on 200/500 beam was 6.92 mm > 5.85 mm (maximum allowable deflection) andpermanent deflection after loading of 2.31 mm > 1.46 mm (maximum allowable permanent deflection).Therefore, rehabilitation and retrofitting of structural columns and 200/500 mm beam are essential.

Experimental study on seismic behaviour of shear wall with reinforcement of column form,concrete-filled steel tubular frames and diagonal bars

In order to reasearch and develop more efficient anti-seismic system of high-rise building structures, a new shear wall with reinforcement of column form, concrete-filled steel tubular frames and diagonal bars was put forward in this paper. Three shear wall specimens with different structural form were designed and made, and then tested by the low-cycle loading experiment. According to the test results, anti-seismic behaviour indexes such as failure characteristics, bearing capacity, ductility, and stiffness degradation of three specimens were analized. The ABAQUS model of new shear walls was established. The experimental results show that, compared with other specimens, the anti-seismic energy dissipation capacity and bearing capacity of the shear wall specimen with reinforcement of column form, concrete-filled steel tubular frames and diagonal bars is enhanced significantly, and the process of stiffness degradation is more slow. The column-form reinforcement can improve ductility, and the concrete-filled steel tubular frames can guarantee the lateral stiffness.

Simplified empirical model for shear strength of RC beam–column joints

In this study, a simplified empirical model is proposed to estimate the shear strength of reinforced concrete beam–column joint. For development of proposed model, various governing parameters affecting the joint shear strength have been identified and evaluated. The identified parameters, namely, concrete compressive strength, width of beam and column, depth of beam and column, column axial load, longitudinal reinforcement of beam and column, yield strength of reinforcement, and joint shear reinforcement, are considered. The influence of aforementioned parameters is determined from the statistical evaluation of collected 326 experimental results of interior and exterior beam–column joints from the literature. The database consists of specimens with wide range of above-mentioned parameters. Proposed model is suitable for the beam–column joints reinforced with vertical, horizontal and diagonal (X-cross) type of reinforcement. Based on experimental database, the efficacy of proposed model is compared with various joint shear strength models. Comparison shows that proposed model predicts more accurate joint shear strength than other considered models. The proposed model is simple in use and can be used for the design purpose.

Shaking table tests on braced reinforced concrete frame structure across the earth fissure under earthquake

SummaryA series of shaking table tests on a scaled model were conducted to investigate the effect of steel braces on reinforced concrete frame structure across earth fissure under earthquake. In the test, a 1/15 scaled model structure taking into account soil–structure interaction was designed on the basis of similarity theorem. Seismic response data, including acceleration responses, displacement responses, shear force distributions, and strain amplitudes of column reinforcement were obtained and analyzed by comparing the results of unbraced and braced structure. Results show that with the peak ground acceleration of input motions increased, maximum of inter‐story drifts, shear forces, and strain amplitudes increased, whereas the acceleration amplification factors decreased. Steel braces could obviously reduce the seismic response of the structure, indicating that this retrofit method is an effective control measure for structures across the earth fissure under earthquake. These results are significant for studying the effect of earth fissure on seismic responses of structures.

Analysis of the influence of column reinforcement anchorage length in a concrete two-pile cap

Abstract This paper describes the parametric analysis applied to assess the influence of column anchorage-reinforcement length on concrete two-pile caps under uniform compression. The non-linear numerical analysis was conducted with the bi-dimensional elements of ATENA 2D software, considering perfect adherence between steel and concrete. Simulation was based on the experimental reference model by Munhoz [1], which was the parameter adopted to validate the numerical modeling. From the validated model, four different anchorage reinforcement lengths were adopted, 34,0 cm, 20,0 cm, 10,0 cm e 3,0 cm, in order to compare pile caps behavior after these changes. Pile cap simulations presented similar behavior, i.e., column anchorage reinforcement length is not a preponderant factor for the internal mechanisms that regulate the function of these elements.

Severely Damaged Reinforced Concrete Circular Columns Repaired by Turned Steel Rebar and High-Performance Concrete Jacketing with Steel or Polymer Fibers

A new strategy that repairs severely damaged reinforced concrete (RC) columns after an earthquake is proposed as a simpler and quicker solution with respect to the strategies currently available in the literature. The external concrete parts are removed from the column surface along the whole plastic hinge region to uncover the steel reinforcement. The transverse steel is cut away, and each longitudinal rebar is locally substituted by steel rebar segments connected by welding connections to the original undamaged rebar pieces outside the intervention zone. The new rebar segments have a reduced diameter achieved by turning to ensure plastic deformation only in the plastic hinge, protecting the original rebar and the welding connections. The connection is specifically designed to be effective and simple, and is directly realized on column reinforcement. Finally, the removed concrete is restored by a jacket built with high-performance concrete with steel or polymer fibers. The use of concrete with high volume fraction of polymer fibers to repair the column is investigated for the first time in this paper. This concrete was characterized by compression and flexural tests in the laboratory and its mechanical characteristics were compared with those of the concrete with steel fibers, which are being increasingly used in construction. The repair strategy was applied to two RC columns (1:6 scaled bridge piers), tested by asymmetric cyclic tests. The results show that the column strength, stiffness, and ductility were restored, and the energy dissipation capacity improved. The experimental evidence was investigated by fiber models in OpenSees.

Fragility functions and floor spectra of RC masonry infilled frames: influence of mechanical properties of masonry infills

A wide number of experimental studies conducted in latest years pointed out the high influence of the mechanical properties of masonry units and mortar bed joints on lateral strength and stiffness of masonry panels. This feature significantly modifies the global response of infilled frames under seismic actions as well as the local interaction phenomena. Despite a wide investigation on the influence of the infills on global behaviour of reinforced concrete (RC) frames has already been provided, different features characterizing the seismic performances of buildings suggest the need of accurately evaluating local interaction phenomena as well as the influence of the panel on specific and relevant aspects, as the accelerations transferred to non-structural components. This study provides a parametrical analysis of the influence of shear strength and elastic modulus of masonry infills on the seismic behaviour of RC frames originally designed for gravity loads. Regular buildings with different height were analysed using the Incremental Dynamic Analysis in order to provide fragility curves, investigate on the collapse mechanisms and define the floor spectra depending on the properties of the infills. Results obtained pointed out the high influence of the considered parameters on the fragility of existing RC frames, often characterized by inadequate transversal reinforcement of columns, which may lead to brittle failure due to the interaction with the infills. Floor response spectra are also significantly affected by the influence of masonry infills both in terms of shape and maximum spectral accelerations. Lastly, on the basis of the observed failure mechanisms, a parameter defining the ductility of the frames depending on the properties of the infills was also provided (Capacity Design Factor). The correlation between the mechanical properties of the infills and this parameter suggests its reliability in the simplified vulnerability analysis of existing buildings as well as for the design of new buildings.

Exploratory study of adopting longitudinal column reinforcement details as a design-controllable tool to seismic behavior of exterior RC beam-column joints

This study presents the test results of seven exterior beam-column joints with different longitudinal reinforcement details for the columns. The test program included a beam-column joint designed to serve as a control specimen, in which column reinforcement was continuous ribbed steel bars. The other six specimens were divided into two groups, three specimens for each group. In the first group, the longitudinal column reinforcement was detailed with well-confined lap-splice longitudinal bars: two specimens were reinforced with lap-splice deformed steel bars and the later was with lap-splice plain steel bars. The same reinforcement details were used for the second group but additional longitudinal basalt fiber reinforced polymer (BFRP) rebars were placed at the joint and extended to the upper and lower columns. The test results showed that splicing the longitudinal column reinforcement successfully reduced the contribution of the joint to the deformability of the beam-column joint. Furthermore, adding BFRP rebars to the beam-column joint could be applied as damage controllable bars reducing both the damage level at the serviceability state and the shear deformability of the joint up to failure. A sole strut resistant mechanism was realized by the joints of all test specimens detailed with lap-spliced longitudinal column reinforcement. Ultimately, the test results point to a probability to the renunciation of the ACI 318-11 requirements for splicing longitudinal column reinforcement at column mid-height.