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CONTENTS
Volume 59, Number 6, June 25 2026
 

Abstract
Butterfly-shaped steel plate dampers (BSPDs) have been proposed as innovative replaceable structural fuses in building frames and bridge piers to concentrate damage and dissipate seismic energy, thereby protecting main gravity-load-bearing members. However, their post-buckling energy dissipation capacity—a massive potential seismic energy reserve—is often neglected in current designs. To systematically investigate this behavior, an individual energy dissipating rib was first simplified as a cantilever beam, and theoretical calculation formulas for key mechanical parameters at the pre-buckling, post-buckling, and failure stages were derived using the principle of virtual work. Subsequently, 14 full-scale BSPD specimens were tested under quasi-static cyclic loading to evaluate the effects of key geometric parameters (end width b, middle width a, rib height H, number of ribs n, plate thickness t, and number of plates N) on the damper's mechanical performance. The experimental results agreed well with the theoretical analyses, showing a minimum error of 3.04%. To compensate for the limited number of physical tests, an extended parametric analysis comprising 82 finite element models was conducted using ABAQUS to comprehensively investigate the parametric effects on post-buckling energy dissipation. The results demonstrate that BSPDs exhibit remarkable energy dissipation capacity. The hysteretic curves show a plump "spindle" shape before buckling and transition to a pinched "bow" shape after buckling. Notably, the post-buckling energy dissipation accounts for a significant proportion of the total energy dissipation, reaching up to 88% at maximum, highlighting its crucial, yet previously underestimated, contribution to the overall seismic resilience of structures.

Key Words
butterfly-shaped steel plate dampers; energy dissipation; hysteretic performance; numerical simulations; quasi-static tests

Address
Yu Yang:School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China

Lueqin Xu:School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China

Ruihua Pan:School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China

Dong Xie:School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China

Guangyang Yan:School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China

Abstract
This study investigates the strength and stiffness of column base plate connections supporting damping devices for seismic retrofit. The connection consists of a base plate and high-tension anchor bolts placed on both sides of the column, which penetrate the slab. Four column specimens incorporating these base plate connections were tested under monotonic lateral loading. Test results demonstrate that the strength and stiffness of the connections are significantly affected by the plate thickness and anchor details (i.e., anchor diameter and distance from the column). The yield mechanism and post-yield hardening behavior of the base plates were further investigated through finite element analysis. The stiffness and strength of the connections were evaluated using the elastic bending theory and yield line theory, respectively. The validity of the proposed methods was verified by comparing the results with experimental and finite element analysis data. Based on these findings, design and detailing considerations are recommended.

Key Words
base plate; base connection; rotational stiffness; yield line theory; seismic retrofit

Address
Tae-Sung Eom:School of Architecture, Dankook University,
152 Jukjeon-ro, Yongin-si, Gyeonggi-do 16890, Republic of Korea

Han-Tae Ryu:School of Architecture, Dankook University,
152 Jukjeon-ro, Yongin-si, Gyeonggi-do 16890, Republic of Korea

Jinwoo Kim:Seismic Safety Center, Korea Conformity Laboratories, 73 Yangcheong 3-gil, Cheongju-si, Chungcheongbuk-do 28115, Republic of Korea

Abstract
Partially concrete-filled steel tubular (PCFST) beams are a modified version of concrete-filled steel tubular (CFST) beams, where the concrete filling in the tension zone is optimised while still maintaining the structural integrity of the beam. Research on PCFST has primarily focused on their flexural behaviour, yet there remains a scarcity of understanding their shear behaviour. This paper aims to address this gap by numerically investigating the shear behaviour of PCFST beams and compare it with the shear behaviour of CFST. A finite element model is developed using the ABAQUS software and the main parameters varied in the present paper are shear span-to-depth ratio, concrete compressive strength, steel yield strength, and depth-to-thickness ratio of the steel tube. From the parametric study, it is observed that the influence of concrete compressive strength on the shear behaviour of PCFST beams is not significant compared to the steel yield strength. Additionally, specimens with a shear span-to-depth ratio of less than 0.5 exhibited shear failure which is similar to a CFST beam. To check the applicability of the plastic moment resistance for a PCFST cross-section in a high shear condition, a limiting shear demand-to-capacity ratio is proposed. Furthermore, the shear force obtained from the numerical study is compared with the existing code specifications. The code predictions are found to be very conservative for specimens that had a shear-predominant failure. This is because these codes do not consider the enhancement in the concrete shear strength and the composite action between the steel tube and concrete infill.

Key Words
CFST; numerical study; PCFST; shear behaviour; shear demand-to-capacity

Address
M. Surya Prasanth:Department of Civil Engineering, Vignan's Lara Institute of Technology & Science, Vadlamudi, India

U. Mashudha Sulthana:Department of Civil Engineering, National Institute of Technology Tiruchirappalli, Thuvakudi, India

Abstract
This paper investigates the eccentric compression behavior of multi-limb (9-limb) light steel concrete T shaped composite column in an ultra-low energy modular wall prefabricated building system. Nine groups of T-shaped composite column specimens were subjected to static eccentric loading tests. The effects of eccentricity, steel thickness, slenderness ratio, and eccentricity angle on structural performance were systematically analyzed. The results showed that all specimens mainly exhibited yielding of the steel on the compression side, concrete crushing, and overall bending failure in medium (MC) and long (LC) columns. The load-displacement curves indicated that eccentricity had a significant influence on the peak bearing capacity: higher eccentricity reduced strength but improved ductility. Under eccentric loading, the strain distribution across the section was generally consistent with the plane section assumption.

Key Words
cold-formed thin-walled steel; eccentric compression static test; local buckling; special-shaped composite column; ultra-low energy prefabricated building

Address
Weichao Li:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China

Haodong Zhang:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China

Wentao Qiao:1)School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China
2)Key Laboratory of Roads and Railway Engineering Safety Control (Shijiazhuang Tiedao University),
Ministry of Education, Shijiazhuang, Hebei Province ,050043, China

Chenlei Wang:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China

Haiying Zhang:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China

Bing Yan:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, China

Abstract
This study proposes an analytical procedure for predicting the ultimate axial strength of short, compact circular concrete-filled steel tubes (CFTs) by explicitly considering the nonlinear Poisson's ratio of concrete and the associated confinement interaction with the steel tube. The procedure incrementally evaluates axial strain, lateral expansion, and confinement pressure, enabling strain-dependent coupling between the concrete core and the steel tube. The confined concrete strength and strain are determined using established confined concrete models, while the steel tube response is evaluated using a von Mises yield criterion. The proposed method is validated against 99 experimental results collected from the literature. Comparisons with existing design codes and prediction models demonstrate improved accuracy within the applicable range of short, compact circular CFTs with conventional concrete and steel strength levels, particularly for cases where confinement effects are significant.

Key Words
composite structure; concrete-filled steel tube (CFST); geometric nonlinearity; load displacement behavior; material nonlinearity; nonlinear analysis; structural prediction; ultimate bearing capacity

Address
Ying-Chiang Cho: 1)International Joint Institute of Tianjin University, Fuzhou, Fujian, China
2) School of Physics and Information Engineering, Minnan Normal University, Fujian, China

Abstract
This paper investigates the flexural performance of Carbon Fiber-reinforced Polymer (CFRP) reinforced circular sea-sand seawater concrete (SSC) filled steel tube (CFRP-SSCFST) members. Six specimens were tested under different bending conditions, with key variables including the number of CFRP layers, the CFRP bonding method, and the shear span ratio. The results indicate that all specimens demonstrated bending failure mode. The external CFRP members underwent peeling failure, while the internal CFRP members underwent longitudinal tension failure. CFRP significantly improved the failure mode and the mechanical performance of the CFST members. One layer of internal CFRP reinforcement significantly enhances the flexural performance of the specimens compared to one layer of external CFRP, with the ultimate bending moment increased by 10.92%, the residual bending moment increased by 17.28%, and energy ductility improved by 24.19%. Both initial and serviceability-level stiffness demonstrated no significant difference between the two configurations. Adding an external layer of CFRP to specimens with internal CFRP did not significantly enhance their overall mechanical performance of the specimens. Based on the existing design codes and experimental results, a flexural stiffness calculation method for CFRP-SSCFST members considering CFRP enhancement and a predictive model for the ultimate bending moment are proposed, providing data support and practical guidance for engineering applications.

Key Words
CFRP; CFST; flexural stiffness; SSC; ultimate bending moment

Address
Yushun Xu:Petro China Guangxi Marketing Company, Nanning 530022, P.R. China

Yan Liang:College of Civil and Architectural Engineering, Guangxi University, Nanning 530004, P.R. China

Zhifei Zhou:College of Civil and Architectural Engineering, Guangxi University, Nanning 530004, P.R. China

Zongping Chen:College of Civil and Architectural Engineering, Guangxi University, Nanning 530004, P.R. China

Yunsheng Pang:College of Civil and Architectural Engineering, Guangxi University, Nanning 530004, P.R. China

Fan Ning:College of Civil and Architectural Engineering, Guangxi Vocational Normal University, Nanning 530007, P.R. China

Jianbo Ye:Petro China Guangxi Marketing Company, Nanning 530022, P.R. China

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