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CONTENTS
Volume 29, Number 5, November 2025
 

Abstract
Electrical switchboards are essential in power plants for managing, distributing, and converting high-voltage electricity. However, seismic events can cause structural and functional damage, leading to severe secondary failures in critical infrastructure. Conventional reinforcement methods, such as anchoring and base strengthening, are widely used but often fail to prevent rocking and uplifting, resulting in localized deformations and impact damage. This study assesses the impact of seismic reinforcement on switchboards using shaking table tests. Initial tests revealed that standard anchoring methods were insufficient to prevent structural damage, causing significant stress and deformation around anchoring points. To address this, two alternative reinforcement strategies were examined: (1) increasing the number of connecting bolts between the switchboard and the base channel and (2) reinforcing the switchboard's bottom panel with a welded steel grid. Numerical simulations and additional tests validated their effectiveness. Results showed that increasing the connecting bolts significantly improved structural stiffness, reducing acceleration responses and deformation by up to 20%. However, welded grid reinforcement enhanced localized stiffness but failed to mitigate impact acceleration effectively. The findings emphasize anchoring reinforcement as a practical and cost-effective solution for improving seismic resilience in electrical switchboards, offering valuable insights for optimized seismic retrofitting in power plants.

Key Words
earthquakes; electrical switchboard; impact assessment; seismic retrofit; shaking table tests

Address
Sang-Moon Lee: Institute for Smart Infrastructure, Gangneung-Wonju National University, 7 Jukheon-gil, Gangneung-si,
Gangwon-do, Republic of Korea
Bub-Gyu Jeon and Sung-Wan Kim: Seismic Research and Test Center, Pusan National University, 49, Busandaehak-ro, Mulgeum-eup, Yangsan-si, Gyeongsangnam-do, Republic of Korea
Woo-Young Jung: Department of Civil and Environmental Engineering, Gangneung-Wonju National University, 7 Jukheon-gil, Gangneung-si, Gangwon-do, Republic of Korea

Abstract
Conventional seismic analyses of buildings primarily focus on horizontal earthquakes, while vertical seismic motions have received less consideration. However, vertical earthquakes can sometimes be more severe than horizontal earthquakes. This study aims to compare the response of buildings to vertical earthquakes, considering ASCE 7-16, IS 1893:2016, and NBC 105:2020. It also investigates the variations in the responses of the structures with variations in height and plinth area. Furthermore, it compares the graphs and results of quasi-static pushover analyses with response spectrum analyses. It was found that ASCE 7-16 has a lower impact on vertical earthquakes, while IS 1893:2016 has a more significant effect than NBC 105:2020. Similarly, buildings of varying heights and plinth areas were modeled in ETABS. Normalised displacements were calculated from top-story maximum vertical displacements, and pushover curves were generated. Both procedures imply that the effect of vertical earthquakes increases with a decrease in the plinth area and height of the building. Additionally, a lower output time step size in quasi-static pushover analysis revealed yielding at lower displacements, and a lower load scale factor resulted in lower damage measures in the building.

Key Words
ETABS; maximum roof vertical displacement; normalised displacement; quasi-static pushover analysis

Address
Sagar Giri and Sulav Sigdel: Department of Civil Engineering, Pulchowk Campus, Tribhuvan University, Pulchowk, Lalitpur, Nepal
Ashish Poudel: Department of Civil Engineering, Oxford College of Engineering and Management, Pokhara University, Gaindakot, Nawalpur, Nepal

Abstract
This work aims to study the natural frequencies of functionally graded beams by applying the higher-order shear deformation theory (HDT). The study focuses on the variation of mechanical properties across the beam's thickness. A new model of FGM beams is proposed, in which the material properties are governed by a novel power-law distribution of the volume fraction, varying from the exterior to the interior of the beam. By applying Hamilton's principle, the governing equations are derived using the state-space method. The accuracy of this method is demonstrated for the classical beam model, and the obtained results are validated through comparisons with previous studies. A comprehensive analysis is carried out to evaluate the impact of key parameters, such as the power-law index and the slenderness ratio, on the natural frequencies of functionally graded beams under various boundary conditions.

Key Words
boundary conditions; HDT; natural frequencies; new model of FG beam; state space method

Address
Radim Ghelamallah and Tlidji Youcef: 1) Department of Civil Engineering, University of Tiaret, Algeria, 2) Materials and Structures Laboratory, Civil Engineering Department, University of Tiaret, Algeria
Benferhat Rabia and Hassaine Daouadji Tahar: 1) Department of Civil Engineering, University of Tiaret, Algeria, 2) Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria

Abstract
As of now, the load-bearing systems in reinforced concrete structures differ for aesthetic reasons. Inclined columns are typically employed in building design for various configurations. The literature indicates that the limited research conducted primarily uses response spectrum analysis about inclined columns. The current research uses multi-modal pushover and time-history nonlinear analytic approaches to comparatively evaluate the effects of real earthquakes on structural behavior. This work aimed to examine the performance of reinforced concrete structures with inclined columns affected by earthquake loads via nonlinear analysis. A total of four distinct 17-storey building models were developed, comprising one reference and three inclined column buildings. For modeling, columns located on the outside axes were constructed with an inclination. The different angles of column inclinations (79o and 84o), the storeys where the inclined columns end (9 and also 17), and nonlinear analytical methods were evaluated as parameters. Linear and nonlinear assessments were performed to ensure that the building design complies with the standards set out by the Türkiye Building Earthquake Code (TBEC). The inclined column design was discovered to reduce effective relative storey drift values, increase stiffness, and reduce ductility demand. It also altered the region where the damage was concentrated. As the inclination angle of the columns increased, the displacement capacities enhanced, the load-bearing capacity decreased, and the formation of plastic hinges diminished. Building models with inclined columns demonstrated superior performance relative to standard column building models. In the multi-mode pushover analysis, buildings with inclined columns up to the ninth story met the advanced performance target, whereas other models failed. None of the building models evaluated by non-linear time history analysis have satisfied the performance criteria. TBEC indicates that both methodologies are applicable in performance analysis. Nonetheless, it is evident that disparate results were yielded by the two analytical methods. Consequently, it was determined that all analytical methodologies must be considered regarding safety when assessing building performance.

Key Words
inclined column; multi-mode pushover analysis; non-linear time history analysis; reinforced concrete

Address
Department of Civil Engineering, Karabük University, 78050 Karabük, Türkiye

Abstract
One-dimensional site response analyses have been widely employed to estimate the amplification of ground motions as the motions propagate from the bedrock to the ground surface. The two primary approaches for site response analysis are equivalent-linear and nonlinear analyses. The former is commonly utilized in practice because of its simplicity and low computational cost, whereas the latter is more complex, but better at capturing realistic soil behaviors under strong ground motions. Thus, the results of equivalent linear and nonlinear site response analyses are expected to diverge under high-intensity ground motions. This study aimed to compare the seismic demands of bridge columns subjected to free-field motion generated using the two site response analyses. To this end, a series of nonlinear dynamic analyses of a bridge system was performed using 319 ground motions obtained from each site response analysis method. Subsequently, the maximum and residual drift ratios of the bridge column were compared, and their fragility curves were developed in terms of the maximum drift ratio. For site classes D and E, the average maximum drift ratios of the bridge column under the ground motions obtained from the equivalent linear analysis were approximately 1.40-1.49 times higher than those from the nonlinear approach. Similarly, the average residual drift ratios obtained using equivalent-linear-based ground motions were approximately 1.53-3.77 times higher than those obtained using nonlinear-based ground motions. Column fragility curves subjected to equivalent-linear-based ground motions showed 7%-12% higher exceedance probabilities compared with the nonlinear-based ground motions.

Key Words
bridge; equivalent-linear and nonlinear site response analysis; fragility curve; nonlinear dynamic analysis; seismic demand

Address
Yewon Park and Jong-Su Jeon: Department of Civil and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea
Minsun Kim: Safety Innovation and Disaster Prevention Research Division, Korea Expressway Corporation Research Institute, Hwaseong, Gyeonggi-do, 18489, Republic of Korea

Abstract
In this paper, a new damage detection method for shear structure based on substructure method and dynamic photogrammetry is proposed. The presented substructure method can identify the damage in shear structure using the absolute acceleration responses of structure measured by acceleration sensors. However, because of the iterative measurement of each substructure, a considerable amount of sensor installation and cabling work are still needed to be done and it would be difficulty or dangerous to install sensors and wiring on some parts of structure. Fortunately, as a non-contact measurement method, the dynamic photogrammetry can provide displacement response of measurement points conveniently and quickly. In order to reduce the impact of camera movement or the difficulty in selecting external reference points, the relative displacement responses are adopted in this paper. Therefore, the substructure algorithm and damage indices corresponding to relative displacement responses are need to be studied. In this paper, the adopted substructure algorithm and the relative displacement responses are introduced. And then, the ARMAX model (i.e., autoregressive moving average with extra input model) of each substructure is used to construct the damage indices using the relative displacements. The derivation of the relationship between the relative displacements of each substructure is also a novelty of this paper. Finally, the dynamic photogrammetry is introduced to obtain the relative displacement responses of each substructure. Based on the proposed damage indices and dynamic photogrammetry, the new damage detection method for shear structure is established. The proposed method is verified using a six-degree-of-freedom system and a laboratory plane frame. The results show that the proposed method can effectively identify the damage in shear structure.

Key Words
autoregressive moving average with extra input model; dynamic photogrammetry; relative displacements; shear structure; structural health monitoring

Address
Jun Luo: 1) School of Civil Engineering and Architecture, Chongqing University of Science and Technology, No. 20, East University Town Road, Shapingba District, Chongqing 401331, China, 2) Chongqing Zhiruiyuan Traffic Engineering Technical Consulting Co., Ltd, Chongqing, China, 3) Chongqing Bureau of Geology and Minerals Exploration, Chongqing, China
Chenming Gou, Yuan Hu and Liping Wang: School of Civil Engineering and Architecture, Chongqing University of Science and Technology, No. 20, East University Town Road, Shapingba District, Chongqing 401331, China

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