Full-scale Columns Research Articles

Seismic Performance of GFRP-Reinforced Concrete Rectangular Columns

AbstractThis paper presents an assessment of the seismic performance of concrete columns internally reinforced with glass-fiber-reinforced polymers (GFRP) bars. Eight full-scale column prototypes with 1,650-mm shear span and 350-mm square cross-section were constructed and tested under combined lateral cyclic quasi-static and constant axial loading. The test specimens represent the lower portion of first-story columns between the footing and the contra-flexure point. The test parameters included longitudinal reinforcement type and ratio, level of axial load, and stirrup spacing. Test results showed that the drift capacity of GFRP-reinforced concrete (RC) rectangular columns at failure ranged between 8.5 and 12.5%, which exceeds the limitations of North American building codes. This indicates that the deformability of GFRP-RC column prototypes successfully replaced the ductility in steel–RC columns in dissipating the seismic energy in the presence of constant axial load. Furthermore, there was insignifican...

Experimental behavior of SFRC columns under uniaxial and biaxial cyclic loads

The use of Steel Fiber Reinforced Concrete (SFRC) was experimentally evaluated with the aim of verifying its effectiveness in reducing the damage and improving the ductility as well as the energy dissipation of seismic resistant columns with special emphasis to the base regions where plastic hinges develop.Sixteen full-scale cantilever columns were tested under reversing cyclic lateral loading and constant axial load. Both unidirectional (uniaxial) and bidirectional (biaxial) lateral displacements were imposed in order to better simulate the actual response of a column during an earthquake.A volume fraction of 1.0% of steel fibers was adopted together with different percentages of transverse reinforcement; the latter was adopted with two steel grades having different ductility performance in order to evaluate their influences on the column behavior.The results of the experimental campaign confirmed that SFRC may reliably reduce the columns damage by preventing the concrete cover to spall out at earlier stages and increase their initial stiffness and energy dissipation, especially for uniaxial loads that resulted less severe than the biaxial ones.

Experimental behavior of precast HSFRC columns in steel socket foundation under cyclic loads

The present paper aims to investigate the influence of steel fibers on the behavior of high strength precast concrete columns in steel socket foundation under cyclic loading. The experimental program was mainly defined to study the effects of the volume fraction and the type of fibers on the behavior of full-scale precast columns subjected to reversed cyclic horizontal loading under constant axial load. Experimental parameters under investigation were: the transverse reinforcement ratio, the axial load, the fiber type and content as well as the effect of steel-to-concrete bond of rebars in the critical region. The latter was investigated since it could considerably govern the local ductility in terms of curvature and of global displacement of the precast column, especially in presence of fibrous reinforcement.Experimental results highlight the importance of the stirrup spacing in the critical region as well as the positive effect of fibers on the crack development, by preventing the concrete cover to spall-out at earlier stages. Steel Fiber Reinforced Concrete (SFRC) tends to enhance the structural stiffness, the strength and the dissipated energy.

Influence of base-plate connection stiffness on the design of low-rise metal buildings

The objective of this research is to evaluate the influence of column base-plate connection rotational stiffness on the design of low-rise metal building systems. Currently, low-rise metal buildings are designed based on a zero rotational stiffness (pinned connection) assumption at the column-bases. Although prior research indicates that the assumption of zero rotational stiffness of the column base-plate connection could result in a significant underestimation of the overall lateral stiffness of horizontally loaded moment frames (leading to less economical designs), there has been no systematic study to investigate this issue. This paper first presents the details of an experimental research program that was conducted to quantify the rotational stiffness of “pinned” column base-plate connections that are commonly used in the low-rise metal building industry. Eight full-scale column base-plate connections with varying base-plate dimensions, numbers of anchor rods, anchor rod diameters, and gage distances were tested. Then, the data obtained were used to investigate the reduction in the total weight of gabled frames used in metal building construction. Finally, a piecewise nonlinear spring model was fitted to the test data to represent the rotational stiffness of the joints beyond the elastic range. Analyses of example frames indicate that consideration of the rotational stiffness of the pinned connections reduces frame deflections between 11 and 67% and has the potential to make metal building systems more economical by decreasing the frame weight between 0 and 12%, which is considered a substantial cost saving for the metal building industry where profit margins are relatively low.

Effects of Detailing on the Cyclic Behavior of Steel Baseplate Connections Designed to Promote Anchor Yielding

AbstractThis paper presents the results from an experimental investigation into the role that anchor selection, setting arrangement, and stretch length have on the post-yield behavior, rotation capacity, and ultimate strength of column baseplate connections. Eight full-scale column baseplate connections were designed to promote anchor yielding and tested under quasi-static, reversed cyclic loading. The connections utilized cast-in headed bolts, adhesive anchors, undercut anchors, two different types of setting arrangements, and a range of stretch lengths. The performance of the connections was evaluated by comparing their cyclic moment-rotation behavior, kinematics, and physical damage to the connection components. Anchor type, material selection, and the method used to level the column were found to have pronounced impact on the strength and rotation capacity of the connection. Increased stretch length was associated with only moderate increases in connection rotation capacity. In addition, a numerical m...

Behavior of Rectangular Reinforced-Concrete Columns under Biaxial Cyclic Loading and Variable Axial Loads

AbstractThe behavior of reinforced-concrete (RC) elements subjected to axial loading variation in conjunction with cyclic biaxial bending is recognized as a very important research topic with a reduced number of experimental results available. Six full-scale RC rectangular columns were tested and analyzed to study the effects of variable axial load on the hysteretic behavior of RC building columns under biaxial horizontal loading. The experimental results are presented and discussed in terms of damage evolution, global hysteretic behavior, stiffness degradation, columns’ capacity, and energy dissipation. The global findings revealed the significant effects of the axial load variation on the hysteretic behavior of RC columns.

Conditional Probabilistic Analysis of Cement-Treated Soil Column Strength

AbstractThe quality of cement-treated soil columns is usually assessed by examining the strength of cored samples. This paper presents a finite-element analysis approach with random field theory for assessing the quality of a cement-treated soil column from which cored samples are retrieved. Monte Carlo simulations with conditional distribution (conditional simulation) were conducted to generate spatial dependence random fields with the data known at some locations. Simulations without the known data (unconditional simulation) were also performed for comparison. Using the random field samples generated from the Monte Carlo simulations, finite-element analysis was performed to simulate the compression behavior of a full-scale column in which material properties vary with a presence of spatial autocorrelation. Finite-element analysis with conditional simulation predicts the overall strength of a targeted cement-treated soil column appropriately, and the overall strength variability obtained with the conditi...

Behavior of ultra-high performance fiber reinforced concrete columns under blast loading

This paper presents the results of a study examining the blast load performance of ultra-high performance fiber reinforced concrete (UHPFRC) columns. As part of the experimental program nine full-scale columns constructed with compact reinforced composite (CRC), a proprietary UHPFRC, were tested under simulated blast loading and exposed to varying blast pressure–impulse combinations using a shock-tube. Parameters considered in this study include concrete type, fiber content, fiber properties, transverse reinforcement spacing and longitudinal reinforcement ratio. The results demonstrate that the use of UHPFRC significantly improves the blast performance of reinforced concrete columns by reducing maximum and residual displacements, enhancing damage tolerance, and eliminating secondary blast fragments. The results also indicate that fiber content, fiber properties, seismic detailing and longitudinal reinforcement ratio are important factors that can affect the blast load behavior and failure mode of UHPFRC columns. The analytical investigation examines the suitability of using single-degree-of-freedom (SDOF) analysis to predict the blast response of the UHPFRC columns tested in the research program.

Nonlinear numerical simulation of RC columns subjected to cyclic oriented lateral force and axial loading

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Loading (CL), Cyclic Oriented Lateral Force and Axial Loading (COLFAL), Monotonic Loading (ML) or Oriented Pushover Force and Axial Loading (OPFAL) in any direction. In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of RC columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE) in general cases of CL, COLFAL or ML and are discretized into Variable Oblique Finite Elements (VOFE) in the particular cases of ML or OPFAL. For pushover particular case, a fairly fast converging and properly accurate nonlinear simulation method is proposed to assess the behavior of RC columns. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns.

Experimental cyclic behaviour of RC columns with plain bars and proposal for Eurocode 8 formula improvement

A significant number of existing reinforced concrete building structures were designed and built before 1970, prior to the enforcement of modern seismic design codes. The response of these structures when subjected to cyclic loads, such as that induced by earthquakes, is strongly influenced by the bond properties between the reinforcing bars and the surrounding concrete. This paper describes the results of a testing campaign composed of seven unidirectional cyclic tests and one monotonic test performed on full-scale columns built with plain bars, without adequate reinforcement detailing for seismic demands. An additional unidirectional cyclic test was carried out on a specimen with deformed bars for reference. The influence of bond properties, a cold joint at the base, lapping of longitudinal reinforcing bars, amount of reinforcing steel, cross-section dimensions and imposed loading history (monotonic or cyclic) is discussed. Finally, a correction coefficient to the expressions of EC8-3 for the calculation of ultimate rotation capacity of columns with plain reinforcing bars is proposed.

High-strength RC columns subjected to high-axial and increasing cyclic lateral loads

This experimental investigation was conducted to examine the behavior and response of high-strength material (HSM) reinforced concrete (RC) columns under combined high-axial and cyclic-increasing lateral loads. All the columns use high-strength concrete (<TEX>$f_c{^{\prime}}$</TEX>=100MPa) and high-yield strength steel (<TEX>$f_y$</TEX>=685MPa and <TEX>$f_y$</TEX>=785MPa) for both longitudinal and transverse reinforcements. A total of four full-scale HSM columns with amount of transverse reinforcement equal to 100% more than that required by earthquake resistant design provisions of ACI-318 were tested. The key differences among those four columns are the spacing and configuration of transverse reinforcements. Two different constant axial loads, i.e. 60% and 30% of column axial load capacity, were combined with cyclically-increasing lateral loads to impose reversed curvatures in the columns. Test results show that columns under 30% of axial load capacity behaved much more ductile and had higher lateral deformational capacity compared to columns under the 60% of axial load capacity. The columns using closer transverse reinforcement spacing have slightly higher ductility than columns with larger spacing.

Advancing behavioral understanding and damage evaluation of concrete members using high-resolution digital image correlation data

The capabilities of a high-resolution Digital Image Correlation (DIC) system are presented within the context of deformation measurements of full-scale concrete columns tested under reversed cyclic loading. The system was developed to have very high-resolution such that material strains on the order of the cracking stain of concrete could be measured on the surface of full-scale structural members. The high-resolution DIC system allows the measurement of a wide range of deformations and strains that could only be inferred or assumed previously. The DIC system is able to resolve the full profiles of member curvatures, rotations, plasticity spread, shear deformations, and bar-slip induced rotations. The system allows for automatic and objective measurement of crack widths and other damage indices that are indicative of cumulated damage and required repair time and cost. DIC damage measures contrast prevailing proxy damage indices based on member force-deformation data and subjective damage measures obtained using visual inspection. Data derived from high-resolution DIC systems is shown to be of great use in advancing the state of behavioral knowledge, calibrating behavioral and analytical models, and improving simulation accuracy.

Confinement Model for Concrete Columns Internally Confined with Carbon FRP Spirals and Hoops

AbstractRecent years have seen valuable research work and widespread applications of fiber-reinforced polymer (FRP) bars as flexural and shear reinforcement for concrete structures. Nonetheless, the axial compression behavior of FRP reinforced concrete (RC) columns has not yet been defined. This study introduces equations and a confinement model to predict the stress-strain envelope responses of RC columns reinforced with carbon-FRP bars (CFRP) and confined by CFRP spirals or hoops. The model takes into account the effect of many parameters such as transverse reinforcement configuration, longitudinal reinforcement ratio, volumetric ratio, and the size and spacing of spirals or hoops. Results of analysis using the proposed confinement model were verified by means of a series of experiments with full-scale circular CFRP-RC columns. The proposed equations have been shown to predict accurately confined concrete core stress, corresponding concrete strain, and prepeak and postpeak stress-strain relationships fo...

Damping and frequency changes induced by increasing levels of inelastic seismic demand

The objective in this research is to determine the feasibility of using changes on the dynamic properties of a reinforced concrete (RC) structure to identify different levels of seismic induced damage. Damping ratio and natural frequency changes in a RC bridge column are analyzed using different signal processing techniques like Hilbert Transforms, Random Decrement and Wavelet Transforms. The data used in the analysis was recorded during a full-scale RC bridge column shake table test. The structure was subjected to ten earthquake excitations that induced different levels of inelastic demand on the column. In addition, low-intensity white noises were applied to the column in-between earthquakes. The results obtained show that the use of the damping ratio and natural frequency of vibration as damage indicators is arguable.

Behavior of Rectangular Columns Constructed with SCC and Steel Fibers

Extensive research has shown that properly detailed and closely spaced transverse reinforcement in reinforced concrete columns can ensure ductile behavior during earthquakes. However, in regions of high seismicity, detailing requirements can result in heavily congested sections; the use of self-consolidating concrete (SCC) can facilitate construction in these situations. Although extensive research exists on the axial load behavior of traditional concrete columns, only limited research exists on the behavior of columns constructed with SCC. Research over the past two decades has also shown that use of steel fiber-reinforced concrete (SFRC) can improve the strength and ductility of columns by delaying cover spalling and improving core confinement. Recent research has also shown that the combined use of SCC and steel fibers can ease problems associated with the workability of traditional fiber-reinforced concrete. This paper presents the results from an experimental program that was conducted to study the axial behavior of reinforced concrete columns constructed with SCC and SFRC. Full-scale columns having rectangular cross sections were tested under pure axial compressive loading. The columns were detailed with varying amounts of transverse reinforcement in accordance with the requirements of the Canadian Standards Association. The results confirm that increasing confinement with closely spaced transverse reinforcement in rectangular SCC columns results in improvements in behavior and ductility. In addition, the results demonstrate that the use of SFRC in rectangular columns results in improvements in performance and ductility.

Fire Performance of Steel Reinforced Concrete Columns

Performance of steel reinforced concrete (SRC) columns under fire is investigated in this paper. A three-dimensional finite-element analysis (FEA) modeling is developed for sequentially coupled heat transfer and structural analysis, in which the classical creep strain and the transient strain of concrete together with thermal strain are included explicitly by subroutines. Four SRC columns with H-shaped steel and cross-shaped steel are experimentally investigated, and the test results are adopted to verify the FEA modeling. The FEA modeling is then used to construct the model of a typical full-scale SRC column and perform analysis to the behavior of the column in fire. Extensive parametric studies are performed to investigate the fire resistance of the SRC column, and the key influencing parameters are identified. Finally, a simplified calculation method is proposed to predict the fire resistance of the SRC column.

Mechanical behaviour of FRP-confined masonry by testing of full-scale columns

The vulnerability of masonry constructions under seismic forces, or more generally under the mechanical actions during the centuries, has been highlighted in the last years by several events that caused the loss of significant heritage buildings. Faced with this difficulty, the use of composite materials, fiber reinforced polymers (FRP) may be a solution for mitigating the vulnerability of masonry buildings. This solution has been tested in the laboratory by researchers in the last decade. In particular, studies regarding elements such as walls, arches and vaults, strengthened with FRP materials are available. A few numbers of studies are known for columns, which have been tested only as small or middle scale samples. The current state of the art does not report studies on FRP-confined masonry columns tested in real scale. The research presents the results of an experimental program performed on full-scale masonry columns strengthened with different composite systems. The same kind of study had been previously performed by the authors on medium scale masonry columns, using the same materials for both the masonry core and for the FRP system. Prismatic columns with a square cross section were subjected to compression tests according to the following test schemes: two control unconfined columns; column with continuous wrapping by using unidirectional glass FRP (GFRP) sheets; column with discontinuous wrapping by using GFRP unidirectional sheets; column with continuous GFRP wrapping and internal carbon FRP bars bonded in the transverse directions; column wrapped with continuous alkali resistant GFRP grid and steel spikes bonded together in lime based matrix. The experimental results are presented and discussed in the paper along with the comparison with the results obtained from the experimental tests on medium scale specimens. The comparison between experimental data and theoretical predictions provided by the analytical model found in the guidelines of the CNR technical document is also illustrated.

Pilot and full scale applications of sulfur-based autotrophic denitrification process for nitrate removal from activated sludge process effluent

Sulfur-based autotrophic denitrification of nitrified activated sludge process effluent was studied in pilot and full scale column bioreactors. Three identical pilot scale column bioreactors packed with varying sulfur/lime-stone ratios (1/1–3/1) were setup in a local wastewater treatment plant and the performances were compared under varying loading conditions for long-term operation. Complete denitrification was obtained in all pilot bioreactors even at nitrate loading of 10 mg NO3−–N/(L.h). When the temperature decreased to 10 °C during the winter time at loading of 18 mg NO3−–N/(L.h), denitrification efficiency decreased to 60–70% and the bioreactor with S/L ratio of 1/1 gave slightly better performance. A full scale sulfur-based autotrophic denitrification process with a S/L ratio of 1/1 was set up for the denitrification of an activated sludge process effluent with a flow rate of 40 m3/d. Almost complete denitrification was attained with a nitrate loading rate of 6.25 mg NO3−–N/(L.h).

The Strain Change Rules of Full-Scale High Strength Concrete Frame Columns with High Axial Compression Rations

Based on experimental study of 9 full-scale high-strength concrete(HSC) rectangular frame columns with high axial compression ratios, high-strength longitudinal reinforcements and transverse reinforcements and rectangular interlocking ties, their strain change rules of longitudinal reinforcement, stirrups and concrete were discussed and analyzed. The main results indicate as follows. The maximum tensile strain of longitudinal reinforcement decrease and the tensile strain of concrete increase quickly as the axial compression ratios and the strength grades of concrete are higher; the strains of outer stirrups are all the time greater than those of inner stirrups; the single brace stirrups have the same action with the closed stirrups.

Control of cracking in full-scaled columns made of ultra-high-strength concrete

Experiments have shown that autogenous shrinkage and elevated temperature due to hydration in reinforced concrete members composed of ultra-high-strength concrete, such as concrete that has a design strength of over 120 MPa cause surface cracks, internal cracks, and cracks around rebar. Since ultra-high-strength concrete is generally used in Japan as cast-in-place concrete or precast concrete, the mitigation of these cracks is a crucial issue because the concrete is expected to have high durability. In the present study, expansive additive, shrinkage reducing agent, combined use of expansive additive and shrinkage reducing agent, thermal insulation to control temperature differences within a member, and combined use of thermal insulation and expansive additive were evaluated by placing full-scale columns and cutting out specimens in order to observe the crack patterns in the columns. Ways to mitigate the cracks were found and characterized. Although thermal insulation generally suppressed surface cracks, the peak temperature increased and consequently so did the risk of internal cracks due to the higher peak temperature and the resultant increase in autogenous shrinkage. Partial replacement of binder with expansive additive reduced cracks around rebar and surface cracks, but the soundness of the bond increased the risk of internal cracks. Addition of shrinkage reducing agent reduced surface cracks and internal cracks. Combined use of expansive additive and shrinkage reducing agent appeared to give a combination of these advantages. The best way to mitigate cracking was combined use of thermal insulation and expansive additive. This method reduced all types of cracks.