Calibration of CSCM model for numerical modeling of UHPCFTWST columns against monotonic lateral loading

doi:10.1016/j.engstruct.2021.112396

Engineering Structures

Volume 240, 1 August 2021, 112396

https://doi.org/10.1016/j.engstruct.2021.112396 Get rights and content

Highlights

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CSCM model was calibrated to simulate UHPCFTWST column under monotonic lateral load.
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Properties of UHPC were obtained by uniaxial and triaxial compression tests.
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A 3D finite element model based on the calibrated CSCM model was developed.
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The sectional response of UHPCFTWST column was investigated.

Abstract

The objective of this study is to calibrate continuous surface cap model (CSCM) for ultra-high-performance concrete (UHPC), and then to investigate the structural behavior of UHPC filled thin-walled steel tubular (UHPCFTWST) column against monotonic lateral loading via numerical simulation of nonlinear pushover analysis. The parameters of CSCM model for UHPC were derived via fitting experimental data of a series of tests on UHPC under uniaxial/triaxial states. Subsequently, a detailed 3D FE (finite element) model of UHPCFTWST column against monotonic lateral loading was developed and validated. After that, the effect of main design parameters, including steel ratio, steel grade, axial compression ratio, dosage of steel fiber, and bonding strength, on the structural behavior of UHPCFTWST column against monotonic lateral loading was investigated via a parametric study based on the FE model. Eventually, the axial pressure-moment (P-M) interaction diagram of a specified UHPCFTWST column was derived to illustrate the sectional response. Comparisons of the lateral behavior of UHPCFTWST column with that of normal strength concrete (NSC) filled steel tubular (NSCFST) column were also made for better illustrations. It indicates that the lateral load capacity and ductility were both improved with the increase of steel ratio, whereas the increase of steel grade improved the lateral load capacity but reduced the ductility owing to the increase of yield drift ratio. Moreover, the increase of axial compression ratio improved the lateral load capacity but significantly degraded the ductility. Although the increase of the dosage of steel fiber improved the lateral load capacity and ductility, but a suitable volume ratio should be specified in consideration of the cost. The comparisons with NSCFST column indicated the advantage and potential of UHPC application to concrete filled steel tubular (CFST) column with a thinner steel tube and a higher grade of steel. The P-M interaction diagram of UHPCFTWST column exceeds that of NSCFST column by a large extent, which indicates a greater safety redundancy.

Introduction

Composite members fabricated with a combination of steel and concrete enjoy the advantages of both materials [1], specifically the high tensile strength and ductility of steel, the high compressive strength of concrete and its ability to prevent buckling of steel tube. CFST column is the most commonly used steel–concrete composite member. Many investigations [2], [3], [4] show that CFST column presents excellent seismic-resistance performance, including high strength, high ductility, and large energy dissipation capacity. Furthermore, HSC (high strength concrete) filled steel tubular (HSCFST) column has been employed worldwide in the construction of modern engineering structure over the last two decades owing to its positive effect on the increase of available space and decrease in the self-weight of structures. The brittle nature of HSC, however, becomes more significant with the increase of compressive strength. When the confinement effect of steel tube is reduced, the brittle nature of HSC adversely affects the ductile performance of HSCFST column [5], [6]. Varma et al. found that the cyclic curvature ductility of square HSCFST column was reduced significantly by increasing the steel tube b/t (width-to-thickness) ratio [7], [8]. Since column ductility has a great effect on the seismic performance of the whole structure, further investigation is needed for ductility improvement of HSCFST column with less confinement effect (thin-walled steel tube).

Previous studies indicate that the ductility of CFST column can be enhanced by improving the properties of core concrete, as investigated in Refs. [9], [10], [11], [12], [13]. As an innovative cementitious composite material, UHPC is a construction material with excellent mechanical properties, including super-high strength (compressive strength ≥ 150 MPa and tensile strength ≥ 8 MPa) and excellent toughness and energy absorption capacity [14], [15], [16]. Therefore, UHPC is a more appropriate filling material to improve the ductility of HSCFST column with less confinement effect, especially in HSCFTWST (HSC-filled thin-walled steel tubular) column [17], [18], [19], [20]. Investigations on the structural behavior of UHPC filled steel tubular (UHPCFST) columns under axial/eccentric compression loading have been carried out [21], [22], [23], [24]. Chen et al. [21] found that steel tube and UHPC worked well together, and the ductility was improved with the increase of confinement. An et al. [22] concluded that all UHPC columns confined with steel tube exhibited very good ductility with a large shortening in the post-peak stage. Xiong et al. [23] figured out that the replacement of ultra-high strength concrete with UHPC would improve the ductility of the CFSTs. Zhang et al. [24] investigated the structural behavior of UHPCFST column under eccentric loading and it was found that the specimens exhibited ductile characteristics as the initial eccentricity and slenderness ratio increase. Xiong et al. [25] observed that all slender UHPCFST columns under eccentric loading exhibited an overall buckling mode. In addition to the axial performance, the structural behavior of columns under lateral loading is also critical in seismic performance [26], [27]. As a typical component that can be equivalent to a single degree of freedom system, the lateral behavior of bridge pier-type column under monotonic lateral loading has been widely investigated. Dawood et al. [27] developed a FE model to reproduce the lateral force–displacement skeleton curves with good accuracy. Wang et al. [28] proposed an equivalent plastic-hinge model to evaluate the lateral behavior of precast segmental UHPC bridge column and validated it by comparing with experimental lateral force–displacement relationship. Bu et al. [29] figured out that empirical formulas established based on results of the current FE models can be effective to assess the lateral behavior. However, such investigations on UHPCFTWST column remain limited. Hence, more investigation is needed on the structural behavior of such UHPC component under monotonic lateral loading to guide engineering practices.

Physical experimentation is an intuitive and effective approach to evaluate the structural behavior of UHPCFTWST column. However, this approach has shortcomings, including time requirements, cost, implementation difficulty, and reliability problems. Thus, numerical simulation is an alternative approach to study the structural behavior of UHPC members [30], [31], [32], [33]. Nevertheless, the accuracy of numerical results is critically influenced by the calibration of the material model. Many material models have been developed for concrete in the general finite element software LS-DYNA, such as Mat_16 (Pseudo tensor model), Mat_72R3 (KCC model), Mat_84 (Winfrith model), Mat_111 (JHC model), Mat_159 (CSCM model), Mat_272 (RHT model), etc. Bohara et al. [34] recommend CSCM model (Mat_159) for numerical simulation of RC column under cyclic loading based on the numerical results obtained by comparing different concrete material models, including the KCC, Winfrith, and CSCM model. However, the approach of reflecting behavior of UHPC through adjustment of the auto-generated parameters of CSCM model may not be appropriate, since these parameters are derived from the properties of conventional concrete. This emphasizes the accuracy and reliability of the constitutive model when utilized in numerical simulations (especially the finite element simulations) to describe behavior of UHPC.

Accordingly, the present study aims to calibrate CSCM model for investigating the structural behavior of UHPCFTWST column against monotonic lateral loading via numerical simulation of nonlinear pushover analysis. A brief overview was firstly introduced in CSCM model. After that, the parameters of CSCM model for UHPC were derived via fitting experimental data obtained from a series of tests on UHPC under uniaxial/triaxial states. Meanwhile, the derived parameters of CSCM model were validated through a series of single element analysis. Subsequently, a detailed 3D FE model of UHPCFTWST column under monotonic lateral loading based on the calibrated CSCM model was developed and validated. Furtherly, the effect of main design parameters, such as steel ratio, steel grade, axial compression ratio, dosage of steel fiber, and bonding strength on the structural behavior of UHPCFTWST column against monotonic lateral loading was investigated by a parametric study based on the FE model. Eventually, the sectional response of a specified UHPCFTWST column is investigated via the P-M interaction diagram. Comparisons of the lateral behavior of UHPCFTWST column with that of NSCFST column were also made for better illustrations.

Section snippets

Overview of model theory

CSCM model includes failure surface, hardening surface, damage formulations reflecting strain softening and modulus reduction, and viscoplastic strain rate-effect modeling the dynamic behavior of concrete. Three stress invariants, the first invariant of stress tensor (I₁), the second invariant of stress deviator tensor (J₂), and the third invariant of stress deviator tensor (J₃), combined with the cap hardening parameter, are exploited to express the failure surface, shown as Eq. (1): $f (I_{1}, J_{2}, J_{3}, κ)$

Mixture proportion of UHPC

Table 1 lists the mixture proportion of the investigated UHPC. Ordinary Portland cement grade 52.5 was used as the binder material, and 35.6% silica fume was also included. Nano-CaCO₃ was employed to further accelerate the hydration process. Polycarboxylic-based superplasticizer was adopted to achieve the desired workability (slump = 210 mm). Based on the previous experimental results obtained by the authors, a 2% volume ratio of smooth steel fiber at 10 mm length and 0.12 mm diameter (Fig. 2)

Numerical model validation and parametric study

Previous research indicates that the lateral load-deformation envelope curves under cyclic lateral loading are basically coincident with the curves under monotonic lateral loading for CSFT columns [50]. Moreover, Dawood et al. [27] presented a detailed 3D FE model of segmental precast post-tensioned bridge piers and validated it by comparing the numerical lateral force–displacement relationship with the skeleton curve resulting from experiments. Tong et al. [30] developed a 3D FE model and

Summary and conclusions

This study calibrated and validated CSCM model in detail through TXC and TXE tests. A detailed 3D FE model to estimate the structural behavior of UHPCFTWST column against monotonic lateral loading was developed based on the calibrated CSCM model. Nonlinear pushover analysis was utilized to carry out a parametric study to investigate the effect of the main design parameters, such as steel ratio, steel grade, axial compression ratio, dosage of steel fiber, and bonding strength, on structural

CRediT authorship contribution statement

Shenchun Xu: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Pengtao Wu: Investigation, Data curation. Zhongxian Liu: Methodology, Project administration. Chengqing Wu: Conceptualization, Methodology, Resources, Writing - review & editing, Visualization, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The research presented herein is supported by the National Natural Science Foundation of China (Grant Nos. 51908155 and 51978186).

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