Drift Capacity Research Articles

Impact of reinforcing ratio and fiber volume on flexural hardening behavior of steel reinforced UHPC beams

The gradual hardening failure of steel reinforced UHPC beams is desirable for high drift capacity and resilient structural design. However, the occurrence sequence of the crack localization and steel yield needs to be clarified. The investigation on the load-drift capacity response after the crack localization in the hardening failure is warranted. The present study conducts flexural tests on the steel reinforced UHPC beams with different fiber volumes and reinforcing ratios. All the beams show gradual hardening failure, and crack localization and steel yield occur simultaneously from the experimental observations and neutral axis height changes. The relative change - the fiber bridging capacity loss and steel strain hardening capacity after the crack localization dominates the hardening length of the load-drift capacity response. High fiber volume tends to extend the hardening length; while high reinforcing ratio tends to first extend the hardening length, then shortens the hardening length due to more and quick fiber bridging capacity loss. The ductility loss and residual tensile UHPC contribution reduction at high reinforcement ratio of 2.83% support this proposal. Moreover, increasing fiber volume is effective to enhance flexural cracking resistance at the initial stage, while increasing reinforcing ratio leads to greater improvement at the later crack development stage, which provides new design path for steel reinforced UHPC beams.

Seismic Performance of Reinforced Concrete Beams Susceptible to Single-Crack Plastic Hinge Behavior

Following the 2010/2011 Canterbury and 2016 Kaikoura earthquakes, a number of reinforced concrete (RC) beams in high-rise structures developed a single primary crack at the beam-column interface without the formation of distributed secondary cracks along the beam length. Detailed assessments showed that these beams have conforming longitudinal steel ratios and the single-crack mechanism may be due to design and/or construction practices for beam-column joints in the 1980s. In order to investigate the seismic behavior of reinforced concrete beams with detailing that inhibited the spread of flexural yielding, an experimental program was carried out on RC beam specimens, having similar reinforcement detailing to that of beams that developed a single crack at their ends during the Kaikoura earthquake to understand their seismic behavior, postearthquake repairability, and residual low-cycle fatigue life. Experimental results showed that the beams were able to undergo significant inelastic drift demands without loss of lateral resistance and have sufficient residual drift capacity following moderate and large earthquake demands. The response of the beam specimens was dominated by hinge rotation via the bond-slip mechanism. Comparisons showed that the measured drift capacities of the beams exceeded the predicted drift capacities computed using state-of-the-practice procedures.

Predicting the drift capacity of precast concrete columns using explainable machine learning approach

Accurately and reliably predicting the drift capacity (DC) of concrete columns is crucial for the seismic design and damage evaluation of structures. Despite precast concrete columns (PCCs) being applied to seismic zone, the method for predicting the DC of PCCs is still scarce owing to its high complexity. This study aims to develop a machine learning-based model for predicting the DC of PCCs using eXtreme Gradient Boosting (XGBoost) algorithm. A DC database of PCCs was assembled from existing literature which involves 177 flexural-dominant specimens with 44 features. A model establishment procedure was carried out to develop XGBoost models, including data cleaning, feature selection, and hyperparameter optimization. The models with and without feature selection were then validated by test results, and the former as the proposed model was further compared with existing empirical formulas and explained by global interpretation, individual interpretation, and feature dependency using SHapley Additive exPlanations (SHAP). Results show that XGBoost algorithm can develop adequate models to predict the DC of PCCs with high accuracy and great reliability. The feature selection method is effective to identify 11 dominant features and delete the rest for the proposed model. The empirical formulas are not suitable to directly predict the DC of PCCs. Global interpretation presents the influence of the 11 dominant features on the DC of PCCs. Feature dependency proves that there are high dependencies between these features. This study firstly develops special models for predicting the DC of PCCs using a machine learning approach, as well as systematically identifies and discusses the effects of various features on the DC of PCCs.

Experimental Investigation on the Performance Levels and Drift Capacity of SRC Columns

To promote the performance-based seismic design and assessment of steel-reinforced concrete (SRC) structures, 27 SRC columns, varying axial load ratio n, steel ratio ρss, and shear span ratio λ, were tested under quasi-static cyclic loadings. The failure modes, hysteretic response, performance levels (PLs), damage states and drift limits of the SRC columns were reported and discussed. The results showed that the failure mode shifted gradually from flexural to shear as λ decreased, but the deformability was not weakened obviously. Six PLs were defined based on the backbone curve of the SRC columns. Each PL was correlated to a damage state that represents a specific macroscopic damage extent. The relative error of drift limits between performance levels and damage states was less than 9% on average. Parametric analysis showed that n and ρss were the most influential factors for drift limits, whereas λ had an ignorable effect. Then, practical regression formulas were established in terms of n and ρss for drift limits of three key PLs (PL1, PL5, and PL6) of the SRC columns, and they were in good agreement with the experimental results. Finally, the average damage indices of PL1 to PL6, calculated using the model proposed in this paper, were 0.26, 0.45, 0.65, 0.83, 0.95, and 0.99, respectively.

Numerical Model Calibration and a Parametric Study Based on the Out-Of-Plane Drift Capacity of Stone Masonry Walls

Failure under seismic action generally occurs in the form of out-of-plane collapses of walls before reaching their in-plane strength in historical stone masonry buildings. Consistent finite element (FE) macro modeling has emerged as a need for use in seismic assessments of these walls. This paper presents the numerical model calibration of U-shaped multi-leaf stone masonry wall specimens tested under ambient vibrations and out-of-plane (OOP) load reversals. The uncertain elastic parameters were obtained by manual calibration of the numerical models based on ambient vibration test (AVT) data of the specimens. To obtain nonlinear calibration parameters, static pushover analyses were performed on FE models simulating quasi-static tests. The calibrated numerical models matched well with the experimental results in terms of load–drift response and damage distribution. As a result, the modulus of elasticity and tensile and compressive degrading strength parameters of masonry walls were proposed. A parametric study was conducted to examine the effects of different materials and geometric properties (tensile strength, aspect ratio, slenderness ratio, and geometric scale) on the OOP behavior of stone masonry walls. A quite different strain distribution was obtained in the case of a large aspect ratio, while it was determined that the geometric scale had no effect on the strain distribution. Tensile strength was the dominant parameter affecting the load–drift response of the models. Within the presented work, a practical tool for out-of-plane seismic assessment has been proposed for the structures covered in this paper.

Seismic behavior of reinforced concrete beam-column joints with unstressed steel strands fully or partially used for beam longitudinal reinforcement

Five beam-column joint specimens: three exterior and two interior specimens were subjected to cyclic loading to investigate the effectiveness of using unstressed Grade 1860 MPa steel strands as full/partial replacement for the conventional Grade 420 MPa deformed bars as beam longitudinal reinforcement. The study also developed a special hooked anchorage detail to anchor the steel strands in the joint region. The test specimens failed by beam plastic hinge formation near the column face as intended in design, with drift capacities between 5.12% and 7.57%. However, the full (100%) and partial (50%) replacement of deformed bars by strands led to a 58% and 28% decrease in average relative energy dissipation. Despite this, the full/partial replacement of deformed bars by strands as beam longitudinal reinforcement resulted in enhanced reentering capabilities. Fracture of longitudinal steel strands observed in the beam plastic hinge region at the end of the test indicated the effectiveness of the special hooked anchorage detail in allowing steel strands to develop their capacity. Further, the flexural strength of the beams of test specimens was evaluated through a detailed moment-curvature analysis, which predicted the beam flexural strength with high accuracy and less variation (mean = 1.01, standard deviation = 0.02). After that, beam flexural strengths were evaluated following the ACI 318–19 procedure modified to include the proposed bilinear strand model, which produced conservative estimates of beam flexural strength (mean = 1.15) suitable for design. Also, the procedure to estimate the beam's probable flexural strength is presented. Finally, required modifications to the conventional seismic design procedure were proposed to incorporate the use of strands as beam longitudinal reinforcement.

Experiment study on seismic behavior of squat UHPC shear walls subjected to tension-shear combined cyclic load

Five squat UHPC shear walls with high axial tension ratio ranging from 0.5 to 0.6 were tested under tension-shear combined cyclic load to replicate seismic performance of bottom shear walls in high-rise buildings. All specimens exhibited shear-sliding failure mode characterized by multiple shear-related cracks distributed in a dense array and full-length localization of horizontal crack along the end of anchorage rebars. The seismic behaviors were comprehensively evaluated by hysteretic responses, energy dissipation capacity, strength and stiffness degradation. Additionally, detailed analysis on the strain development of vertical reinforcement and web horizontal rebars were carried out to study their shear resistance contribution. It was found that, with the assistance of steel fibers providing an efficient shear resistance consistent with the varying direction of principal tensile stress, the shear capacity of UHPC shear wall was slightly improved even when axial tension ratio increased to 0.6. The ultimate drift capacity of UHPC specimens reached 3.3% drift with an excellent strength retention ability of more than 500kN in this test. Besides, the accumulated energy consumption of UHPC specimen after crack localization improved by 38% compared with the normal concrete shear wall. Results of strain analysis demonstrated that vertical reinforcement provided an effective clamping force in the shear-sliding resistance. A modified design formula considering efficient tension resistance offered by UHPC was proposed with adequate safety concerns and accuracy.

In-plane shear strengthening of traditional unreinforced masonry walls with near surface mounted GFRP bars

In this study, the effectiveness of Near Surface Mounted (NSM) method, for in-plane shear strengthening of traditional and historical Unreinforced Masonry (URM) walls, is investigated through a comprehensive experimental study. For this purpose, square solid clay brick masonry wallettes (42 samples) with three different types of traditional mortars including gypsum mortar, lime-cement-sand mortar and lime-sand mortar are prepared and retrofitted with NSM Glass Fiber Reinforced Polymer (GFRP) bars. Then, diagonal shear tests are conducted to evaluate the in-plane shear behavior of the masonry wallettes. The effects of some key variables such as wall thickness, the retrofitted face of the wall, reinforcement ratio, and the type of paste for mounting the reinforcing bars, on the effectiveness of the retrofitting method are investigated. The results of the tests are presented in terms of the failure modes and the lateral shear stress-drift curves of the test specimens. Accordingly, the retrofitting method can enhance the in-plane shear strength, and the ultimate lateral drift capacity of the URM wallettes. According to the test results, the type of filler paste and reinforcement ratio influence the strength enhancement of the test specimens. Furthermore, in specimens retrofitted with the one-side retrofitting scheme, due to the asymmetry of walls under in-plane loads, an unexpected out-of-plane deformation is induced in the walls under in-plane load which adversely affects its global behavior.

A methodology for the calibration of partial safety factors accounting for knowledge level, in pushover-based seismic assessment of URM buildings according to the new draft of Eurocode 8

The current draft of the revised version of Eurocode 8 introduces significant modifications regarding the global seismic assessment of existing masonry buildings via nonlinear static analysis, particularly when dealing with building knowledge. The approach is still based on the selection of discrete knowledge levels, although partial safety factors are now consistently applied to global displacement capacity. This paper firstly describes the main new aspects introduced by the considered code revision. Among these, new strength criteria for the single masonry elements are introduced, together with a Bayesian approach to update the knowledge on material properties, exploiting the availability of experimental results. To better explore the code approach, the seismic assessment procedure is applied to a case study building, made of clay bricks, considering different knowledge levels. In particular, a distribution of displacement capacities is obtained for each knowledge level by considering residual uncertainties and properly sampling material properties and local drift capacities of masonry structural members. A statistical procedure for defining partial safety factors reducing the global displacement capacity resulting from the analysis is then presented.

Estimation of ultimate capacities of Moment-Resisting Frame’s subassemblies with Mid-Storey Pin connection based on elastoplastic local buckling

This research proposes a novel method of Mid-Storey Pin Moment-Resisting Frames’ (MSP MRFs) ultimate capacity estimation. Shell and solid numerical models with initial imperfections are defined and calibrated against the experimental results. Parametric studies are conducted, presenting the influence of structural parameters on the performance and failure mode of the frame dictated by the elastoplastic local buckling of members. It is shown that commonly used control over column-to-beam plastic moment ratio is insufficient; the need for column-to-beam stiffness ratio consideration is highlighted. Finally, innovative yet simple equations are proposed to estimate the frame’s storey drift capacity and ultimate strength ratio.

Improving seismic capacity of dry stacked interlocking masonry structure through confinement at corners

Interlocking dry stacked masonry is an emerging building material and has a project wining future due to its sustainable and affordable housing aspects. The aim of this research work is to study the improvement in seismic parameters of self-interlocking mortarless masonry by the provision of confinement at the corners. To fulfill the aim, a full-scale structure was fabricated by using locally prepared self-interlocking stabilized earth blocks and evaluated by testing through quasi-static test. Damaged patterns and different seismic parameters have been assessed, which include lateral load carrying capacity, energy dissipation, displacement ductility, structural stiffness, response modification factor and performance levels. On the basis of test data, the corners confinement of dry stacked masonry enhanced the ultimate lateral load and drift capacity by 64% and 288% respectively.

Strengthening of historical earthen constructions with steel plates: Full-scale test of a two-story wall subjected to in-plane lateral load

The Spanish conquerors that came to Latin America built earthen dwellings (one- and two- stories). In this way, construction with earthen materials was introduced in the history and the cultural heritage of the Northern South American territory. Unfortunately, past earthquakes have shown that historic earthen buildings are highly vulnerable. Research on this subject has focused on the evaluation of seismic retrofitting alternatives, especially in one-story earthen walls without openings, or studying reduced-scale earthen models. According to the scientific literature consulted, few pseudo-static tests have been conducted on full-scale earthen walls with openings. For this reason, in this research, a full-scale two-story earthen wall specimen with dimensions of 5.95 m long, 6.20 m high, and 0.65 m thick (both floors with openings) was subjected to cyclic lateral loads (in-plane shear load). Based on the authors’ knowledge, this is the largest full-scale two-story earthen wall tested to date in a structures laboratory. After inducing repairable damage to the unreinforced wall, a rehabilitation strategy based on steel plates (conforming to a grid) was installed on both sides of the wall. The steel plates were connected (welded) with pass-through steel rods. Subsequently, the repaired and reinforced wall was retested and the experimental results showed that the in-plane stiffness was improved or at least restored. In addition, the lateral load capacity increased by 208 % on average compared to the unreinforced wall test results. Lastly, the unreinforced wall had a drift capacity of 0.5 % while the reinforced wall reached a maximum drift of 1.8 %. Therefore, it was found that the proposed reinforcement with steel plates significantly improves the seismic performance of two-story historic earthen walls.

Effect of Inadequate Lap Splice Length on the Collapse Probability of Concrete wall Buildings in Malaysia

Background: In recent decades, Malaysia has shown a significant increase in the number of constructed high-rise buildings due to rapid urbanization and an increase in its population. However, due to the country's low seismicity, the majority of such tall buildings and infrastructures have not been designed against seismic actions. Therefore, they do not comply with the required seismic detailing and often suffer from inadequate lap splice length. After the 2015 Sabah earthquake that imposed significant damage to public buildings, the seismic vulnerability of buildings in Malaysia received increasing attention. As a result, researchers have tried to quantify the seismic vulnerability of buildings in Malaysia through the development of fragility curves. Objectives: In Malaysia, most developed seismic fragility curves for buildings have not taken into account the effect of inadequate lap splice length. Therefore, this study investigates to what extent an inadequate lap splice length can alter the concrete wall buildings’ probability of collapse. Methods: Two 25-story concrete wall buildings with an identical plan but different parking levels were selected. Fifteen natural far-field earthquake records were used in the incremental dynamic analysis to calculate the inter-story drift demand and capacities. The inelastic response of beams and columns was simulated through the lumped plasticity model, and that of concrete walls and slabs was taken into account through the fiber-based distributed plasticity model. The effect of inadequate lap splice length in columns was simulated in the finite element models using the proposed method in ASCE/SEI 41-17 code. The developed fragility curves were compared with those established by other researchers for the same buildings. Results: It was observed that seismic-induced damage mostly concentrated on the columns of parking levels while the concrete walls remained in the elastic region. The obtained inter-story drift capacities were all less than 2%. Besides, the inter-story drift capacities of interior frames were less than half of exterior frames. The exterior frame of the building with three parking levels exhibited a larger probability of exceeding the CP limit state than the interior frame. A similar observation was made for the building with five parking levels when the PGA was more than 0.25g. Moreover, the probability of exceeding the CP limit state of the exterior frame with three parking levels was significantly more than that of the exterior frame with five parking levels. A similar observation was made for the interior frames when the PGA was larger than 0.2g. Furthermore, the conducted comparison showed that an inadequate lap splice length could increase the concrete wall buildings’ probability of collapse between 38 to 89%. The increase in the collapse probability of the interior frame with five parking levels was almost twice that of the exterior frame. Conclusion: It was concluded that the inadequate lap splice length could significantly reduce columns’ rotational capacity and result in brittle failure mode and limited residual strength. Besides, the inadequate lap splice length of columns reduced the inter-story drift capacity of investigated buildings and significantly increased their probability of collapse. Therefore, it was strongly suggested to include the effect of inadequate lap splice length in the finite element models when conducting seismic vulnerability studies.

A finite element study on the ultimate lateral drift capacity of interior reinforced concrete flat slab-column connections

Reinforced concrete (RC) flat slabs may be a part of the lateral load resisting system or may only serve as a gravity load bearing element in RC structures. In both cases, RC slab-column connections have a crucial role in the global seismic performance of RC buildings. Punching shear failure in flat slabs concentrated in the slab-column connection region is a common brittle failure mode which can adversely affect the global seismic behavior of structures. However, few studies have been done on the numerical simulation of brittle shear failure in slab-column connections under simultaneous gravity and lateral loads. In this paper, to evaluate the behavior of RC slab-column connections under simultaneous gravity and lateral loads and to examine the effects of various influential parameters on the lateral drift capacity of the connections, a numerical study is conducted on interior slab-column connections. The investigated influential variables are the flexural reinforcement in the slab, slab thickness, and the dimensions of the supporting column. The numerical study is implemented in the finite element software ABAQUS. First, the numerical model is verified through modeling three interior RC slab-column connections tested in other experimental studies. Then, all the connections are analyzed under the simultaneous effects of gravity and lateral loads and their lateral load-drift curves are determined. According to the analysis results, in addition to the gravity load intensity, other variables such as flexural reinforcement ratio, slab thickness, and the size of the supporting column affect the lateral behavior of the connection.

Pseudo-Dynamic Test on Composite Frame with Steel-Reinforced Recycled Concrete Columns and Steel Beams

Pseudo-dynamic tests were conducted on a 2/5-scaled, three-story, two-span frame with steel-reinforced recycled concrete (SRRC) columns and steel beams. The El-Centro earthquake waves, Taft earthquake waves, and Lanzhou artificial earthquake waves were considered as the main loads to study the seismic behavior. The failure modes, displacement and acceleration time history curves, hysteretic characteristics, energy dissipation, stiffness degradation, and inter-story drift capacity of the composite frame were analyzed. Results showed that the composite frame did not show plastic deformation during the whole test process, and the steel beams and columns basically did not yield. Under the action of three seismic waves, the displacement response, acceleration response, and restoring force response of the composite frame were increased with seismic intensity, while the hysteretic curves and energy dissipation were different as the seismic wave changed. The seismic response of the composite frame was greatly affected by the spectral characteristics of the loading ground motion and the hysteretic energy mainly consisted of recoverable elastic deformation energy. Under the action of Taft wave with the input peak acceleration of 400 gal (rare earthquake), the stiffness degradation of composite frame was the largest, which reduced to 47% of the initial stiffness. This indicated that the composite frame had good energy dissipation performance in the elastic and elastic-plastic stages, and still possessed good rigidity after a rare earthquake, fully achieving the design purpose of “no collapse in major earthquake”.

Cyclic behavior of reinforced concrete columns with five-spiral reinforcement

Multi-spiral transverse reinforcement has been shown to provide superior seismic performance than conventional rectilinear tie reinforcement. This research intends to investigate the flexural behavior of the five-spiral transverse reinforcement configuration for square concrete columns. Large-scale flexure-critical five-spiral columns and counterpart conventional tied columns were tested under low (0.1fca′Ag) and high (0.3fca′Ag) constant axial load and subjected to double-curvature lateral cyclic loading. Test results showed that with 16%–29% less transverse reinforcement, the five-spiral columns displayed superior flexural strength, higher ductility, and larger drift capacities than the counterpart conventional tied columns. The five-spiral columns also showed improvements in the seismic capacity of the column in terms of energy dissipation. Furthermore, it was determined that the nominal moment strength could conservatively compute the actual moment strength of five-spiral columns. However, the five-spiral columns showed a higher flexural overstrength from the nominal moment than the counterpart tied columns. From the existing code methods examined in calculating the expected maximum moment, the Caltrans SDC 2019 method provided the best prediction of the maximum flexural strength of the columns, followed by the AASHTO 2017 method, then the ACI318-19 method. All three methods, however, could not fully capture the superior confinement effect of the five-spiral reinforcement.

A novel seawater and sea sand concrete-filled CFRP-carbon steel composite tube column: Seismic behavior and finite element analysis

The seismic behavior of a novel seawater and sea sand concrete (SSC)-filled carbon fiber-reinforced polymer (CFRP)-carbon steel composite tube (SFSCT) column under combined axial compression and reversed cyclic loadings was studied in this paper. This structure makes use of seawater and sea sand resources, and CFRP was adopted to isolate the corrosion by chloride ions on the steel tube. Tests of eight composite columns were carried out. The test parameters include the axial compression ratio, the number of CFRP layers and the bonding direction. The test results revealed that all of the specimens displayed superb seismic performance with a drift ratio over 4%. The failure of the SFSCT column exhibits a typical compressive-flexural failure mode. Compared with the results of the SSC-filled steel tube columns, the hoop strain of the specimen under additional CFRP confinement is reduced by 1.6 times, and the flexural strength and drift capacity increase by 22% and 17%, respectively. A fiber model was created by finite element analysis, and parametric studies of the main design parameters were performed. The effects of the steel tube and CFRP on the seismic performance were evaluated. Using experiments and finite element analysis, the relationships among the drift capacity, axial compression ratio and confinement level were investigated. A design method for predicting the drift capacity of SFSCT columns was proposed.

Rational use of HPFRC in slab – column connections under reversed horizontal cyclic loading

Slab – column connections that are subjected to combined gravity and horizontal loading during an earthquake are prone to premature failure due to punching shear. Traditional solutions to avoid punching failure and to increase the displacement capacity of this type of connection include using stirrups and double-headed studs as shear reinforcement. The use of High-Performance Fiber Reinforced Concrete (HPFRC) in a small region of the slab around the column as a substitute for traditional solutions is investigated in this paper, because this material has the potential to reduce labor and material costs. To fulfill this objective, four slab specimens with a thickness of 150 mm were tested under combined gravity and reversed horizontal drifts. The results are discussed in detail. The experimental variables considered were the top flexural reinforcement ratio, the size of the HPFRC zone and the intensity of the gravity load. Previously published tests that serve as reference specimens are used to compare the results. The behavior of the specimens with HPFRC was substantially improved compared to the reference specimens in terms of drift capacity: from only 1.0% drift to above 5.5%, even though a very small quantity of HPFRC was used, extended up to only 1.5 times the effective depth of the slab from the face of the column. Specimens with HPFRC also behaved better when compared to specimens with High-Strength Concrete (HSC). Side effects of using HPFRC in the slab in the vicinity of the column include an increase of the unbalanced moment transfer capacity and lateral stiffness, as well as a reduction of the deflections of the slab.

A Numerical Investigation on the Limitations of Design Equations for Steel Plate Shear Walls

In previous studies various design issues on steel plate shear wall (SPSW) systems under lateral loading were investigated using analytical and experimental methods. However, these studies tried to examine the interactive effect of only a few of design parameters, such as panel aspect ratio, column flexibility parameter, axial load ratio on the boundary frame columns, web plate thickness, stiffness of horizontal and vertical boundary elements and top anchor beam, etc., on the drift capacity and shear force distribution among frame and panel components of SPSWs at a time. This study investigates the effect of all of these parameters in the same framework. A parametric study is conducted on finite element models of 292 3-story SPSWs with rigid beam-to-column connections and designed for specified parameters. By evaluating failure forms from finite element analyses, the limiting (undesired) cases resulting from different combinations of specified geometric properties are identified. A column flexibility factor of 2.2 is proposed instead of the current limit value of 2.5 for satisfactory column performance, improved drift capacity and balanced strength distribution among frame and panel of SPSW. The value of 0.75 for the ratio of plate shear force to total shear force has emerged as a critical threshold value for the strength distribution among plate and frame components in order to conform capacity design principles. This study provides a comprehensive look on the behavior of SPWS for determining the most suitable combination of various parameters in the design of SPSW structures.

Cyclic Behavior of Reinforced Concrete Columns with Unstressed Steel Strands as Longitudinal Reinforcement

The use of unstressed Grade 1860 MPa seven-wire steel strands as longitudinal reinforcement has the potential to reduce steel congestion in reinforced concrete members. However, no studies which use unstressed steel strands as the longitudinal reinforcement in concrete columns have been reported in the literature. Thus, in this study, five large-scale column specimens: four of which used unstressed steel strands and one which used conventional Grade 420 MPa deformed bars as longitudinal reinforcement were subjected to cyclic loading under constant axial load to investigate the effectiveness in using strands. Columns with unstressed steel strands as longitudinal reinforcement exhibited drift capacities ranging between 4.96% and 5.70%, which is well over the conventional expectation of 3.50% drift requirement for columns in special moment frames. Also, the specimens exhibited lower energy dissipation but enhanced recentering capability owing to the fact that the strands have significantly higher tensile yield capacity compared to deformed bars. A reduction in effective elastic stiffness was also observed as the postcracking stiffness of specimens with strands dropped due to the low longitudinal reinforcement ratio of 0.78% provided. The test results indicated the relative ineffectiveness of strands in compression than in tension, where the strand bulged and unwound once the surrounding confinement deteriorated. Despite this, strands did straighten up and continued to sustain tensile stresses under load reversal. Based on the experimental observations, two constitutive models, one which considers strain hardening and the other which assumes an elasto-perfectly plastic response in tension was proposed for strands. The constitutive model with strain hardening was able to produce reasonably accurate estimates of flexural strength when used in a detailed moment-curvature analysis. Both constitutive models when used in a simplified analysis, which used equivalent stress block for concrete, was able to consistently produce conservative estimates of flexural strength, which is suitable for design purpose.