• Earthquakes and Structures
• /
• v.22 no.2
• /
• pp.109-120
• /
• 2022

Older or damaged structures can require significant retrofit to ensure they perform well in subsequent earthquakes. Supplemental damping devices are used to achieve this goal, but increase base shear forces, foundation demand, and cost. Displacement reduction without increasing base shear is possible using novel semi-active and recently-created passive devices, which offer energy dissipation in selected quadrants of the force-displacement response. Combining these devices with large, strictly passive energy dissipation devices can offer greater, yet customized response reductions. Supplemental damping to reduce response without increasing base shear enables a net-zero base shear approach. This study evaluates this concept using two incremental dynamic analyses (IDAs) to show displacement reductions up to 40% without increasing base shear, more than would be achieved for either device alone, significantly reducing the risk of response exceeding the unaltered structural case. IDA results lead to direct calculation of reductions in risk and annualized economic cost for adding these devices using this net-zero concept, thus quantifying the trade-off. The overall device assessment and risk analysis method presented provides a generalizable proof-of-concept approach, and provides a framework for assessing the impact and economic cost-benefit of using modern supplemental energy dissipation devices.

• Journal of Korean Association for Spatial Structures
• /
• v.22 no.2
• /
• pp.29-37
• /
• 2022

The collapse of reinforced concrete (RC) frame buildings is mainly caused by the failure of columns. To prevent brittle failure of RC column, numerous studies have been conducted on the seismic performance of strengthened RC columns. Concrete jacketing method, which is one of the retrofitting method of RC members, can enhance strength and stiffness of original RC column with enlarged section and provide uniformly distributed lateral load capacity throughout the structure. The experimental studies have been conducted by many researchers to analyze seismic performance of seismic strengthened RC column. However, structures which have plan and vertical irregularities shows torsional behavior, and therefore it causes large deformation on RC column when subjected to seismic load. Thus, test results from concentric cyclic loading can be overestimated comparing to eccentric cyclic test results, In this paper, two kinds of eccentric loading pattern was suggested to analyze structural performance of RC columns, which are strengthened by concrete jacketing method with new details in jacketed section. Based on the results, it is concluded that specimens strengthened with new concrete jacketing method increased 830% of maximum load, 150% of maximum displacement and changed the failure modes of non-strengthened RC columns.

• Smart Structures and Systems
• /
• v.29 no.3
• /
• pp.485-498
• /
• 2022

In near-fault earthquake prone areas, the velocity pulse-like seismic waves often results in excessive horizontal displacement for structures, which may result in severe structural failure during large or near-fault earthquakes. The recently developed isolator-gap damper (IGD) systems provide a solution for the large horizontal displacement of long period base-isolated structures. However, the hysteresis characteristics of the IGD system are significantly different from the traditional hysteretic behavior. At present, the hysteretic behavior is difficult to be reflected in the structural analysis and performance evaluation especially under random earthquake excitations for lacking of effective analysis models which prevent the application of this kind of IGD system. In this paper, we propose a mathematical hysteretic model for the IGD system that presents its nonlinear hysteretic characteristics. The equivalent linearization is conducted on this nonlinear model, which requires the variances of the IGD responses. The covariance matrix for the responses of the structure and the IGD system is obtained for random earthquake excitations represented by the Kanai-Tajimi spectrum by solving the Lyapunov equation. The responses obtained by the equivalent linearization are verified in comparison with the nonlinear responses by the Monte Carlo simulation (MCS) analysis for random earthquake excitations.

• Structural Engineering and Mechanics
• /
• v.83 no.4
• /
• pp.563-576
• /
• 2022

This study aimed to evaluate the progressive collapse potential of buildings designed using conventional design codes for the merchant occupancy classification and subjected to a sudden column failure. For this purpose, three reinforced concrete buildings having different story numbers were designed according to the seismic design recommendations of TSCB-2019. Later on, the buildings were analyzed using the GSA-2016 and UFC 4-023-03 to observe their progressive collapse responses. Three columns were removed independently in the structures from different locations. Nonlinear dynamic analysis method for the alternate path direct design approach was implemented for the design evaluation. The plasticity of the structural members was simulated by using nonlinear fiber hinges. The moment, axial, and shear force interaction on the hinges was considered by the Modified Compression Field Theory. Moreover, an existing experimental study investigating the progressive collapse behavior of reinforced concrete structures was used to observe the validation of nonlinear fiber hinges and the applied analysis methodology. The study results deduce that a limited local collapse disproportionately more extensive than the initial failure was experienced on the buildings designed according to TSCB-2019. The mercantile structures designed according to current seismic codes require additional direct design considerations to improve their progressive collapse resistance against the risk of a sudden column loss.

• Steel and Composite Structures
• /
• v.46 no.5
• /
• pp.621-635
• /
• 2023

The combination of replaceable and repairable properties in structures has introduced new approach called "Low Damage Design Structures". These structural systems are designed in such a way that through self-centering, primary members and specific connections neither suffer damage nor experience permanent deformations after being exposed to severe earthquakes. The purpose of this study is the seismic assessment of steel moment resisting frames with the aid of rigid rocking cores. To this end, three steel moment resisting frames of 4-, 8-, and 12-story buildings with and without rocking cores were developed. The nonlinear static analysis and incremental dynamic analysis were performed by considering the effects of the vertical and horizontal components of 16 strong ground motions, including far-fault and near-fault arrays. The results reveal that rocking systems benefit from better seismic performance and energy dissipation compared to moment resisting frames and thus structures experience a lower level of damage under higher intensity measures. The analyses show that the interstory drift in structures equipped with stiff rocking cores is more uniform in static and dynamic analyses. A uniform interstory drift distribution leads to a uniform distribution of the bending moment and a reduction in the structure's total weight and future maintenance costs.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.17 no.1
• /
• pp.28-35
• /
• 2021

The flow accelerated corrosion (FAC) is one of significant aging and degradation mechanism and can affect structural integrity of CANDU feeder pipes. Pipe burst can occur under normal operation pressure (min. 10 MPa) if wall-thinning of the feeder pipe due to FAC is accumulated. Previous studies considered simple shapes of feeder pipe with local wall-thinning in order to conservatively assess structural integrity of wall-thinned feeder pipe. In this paper, a new FE model is developed, having an actual shape of the feeder pipe (double bent) as well as the actual wall-thinning shape and location based on the in-service inspection result. Then, the burst pressure assessment of the wall-thinned feeder pipe is performed using lower bound limit load analysis considering elastic-perfectly plastic material. In addition, an improved formulation to predict the burst pressure of the wall-thinned feeder pipe is presented and the safety margin is compared with an existing assessment method.

• International conference on construction engineering and project management
• /
• 2009.05a
• /
• pp.747-753
• /
• 2009

Planning the construction for a system of bored piles in building foundation engineering is (1) to predict the time duration required to complete all the bored piles with due consideration of relevant engineering factors and site constraints; then (2) to predict the total project time generally by aggregating the predicted working duration for construction of each bored pile. The duration for construction of an individual bored pile results from analyzing various working sequences and different activity duration (such as predrilling, excavation, steelfixing, air-lifting, and concreting, etc.), which is informed by experiences and site records of previous projects. However, determining the project duration for constructing many bored piles on one site is much more complicated than adding up the time duration for individual piles. In practice, project schedules are often found to be unrealistic and incorrect during the construction stage. This is because construction planning is not based on a exhaustive and comprehensive evaluation of site factors, such as site layout plan, site constraints, quality control, environmental control, safety control and logical relationships between different trades. In this paper, we identify those factors based on a foundation engineering site in Hong Kong with ninety-seven bored piles and address their effects on uncertainties in activity time and project time.

• Earthquakes and Structures
• /
• v.25 no.3
• /
• pp.209-221
• /
• 2023

The Mw=7.7 (Pazarcık-Kahramanmaraş) and Mw=7.6 (Elbistan-Kahramanmaraş) earthquakes that occurred in Türkiye on 06.02.2023 with 9 hours' intervals, caused great losses of life and property as the biggest catastrophe in the instrumental period. The earthquakes affecting an area of 14% of the country were enormous and caused a great deal of loss of life and damage. Numerous buildings have collapsed or damaged at different levels, both in the city centers and in rural areas. Within the scope of this study, masonry structure damage built from different types of materials in the earthquake region was taken into consideration. In this study, the damage and causes of such masonry structures that do not generally receive engineering services were examined and explained in detail. Insufficient interlocking between wall-wall and wall-roof, inadequate masonry, lack of horizontal and vertical bond beams, usage of low-strength materials, poor workmanship, and heavy earthen roof are commonly caused to structural damages. Separation at the corner point and out-of-plane mechanism in structural walls, and heavy earthen roof damages are common types of damage in masonry structures.

• Wind and Structures
• /
• v.37 no.2
• /
• pp.79-94
• /
• 2023

This paper traces the drafting of the new EN 1991-1-4 Eurocode 1 - Actions on structures - Part 1-4: General actions - Wind actions within Mandate M/515 of the European Commission to CEN, for the evolution of structural Eurocodes towards their Second Generation. Work of the Project Team started in August 2017 and ended in April 2020, with delivery of a final draft for public enquiry. The revised document contains several modifications with respect to the existing 2005 version, and new sections were added, covering aspect not dealt with in the previous version. It has a renovated structure, with a main text limited in size and containing only fundamental material; all the remaining information, either normative or informative is arranged into thirteen annexes. Common to other Eurocode Parts, general requests from CEN were those of reducing the number of Nationally Determined Parameters and of enhancing the ease of use. More specific requests were those of (a) the drafting of a European design wind map, (b) improving wind models, (c) reviewing force and pressure coefficients, (d) reviewing the procedures for evaluation of the dynamic response, as well as (e) making editorial improvements aimed at a more user friendly document. The author had the privilege to serve as Project Team member for the drafting of the new document, and this paper brings his personal view concerning some general aspects of wind code writing, and some more specific aspects about the particular document.

• Nuclear Engineering and Technology
• /
• v.55 no.9
• /
• pp.3472-3484
• /
• 2023

The objective of this research is to assess the seismic performance of different types of electrical cabinets in nuclear power plants. The cabinets under investigation are: (a) Case 1: a short single cabinet; (b) Case 2: a tall single cabinet; (c) Case 3: separated cabinets; and (d) Case 4: a combined cabinet with coupling effects. To accurately capture the real behavior of the cabinet, three-dimensional finite element models are developed using ANSYS with connection non-linearity. Frequency domain decomposition (FDD) is used to determine the dynamic properties of the cabinets from shaking table testing data, and these results are utilized to validate the numerical model. The close match between the experimental and numerical results obtained from the modal analysis demonstrates the accuracy of the numerical model. Subsequently, transient structural analysis is performed on the validated models to explore seismic performance. The results show that the acceleration response of the combined cabinet is lower than the single cabinet and the separated cabinet. This observation suggests that top anchors used to combine two different types of cabinets play a crucial role in assessing the efficiency and seismic resistance of electrical cabinets in a nuclear power plant.