Abstract
This paper presents a novel method to safety assessment, considering the deterministic characteristics of existing structures. Initially, the concept of disposable resistance is introduced, stemming from the deterministic attributes of the existing structure, leading to the formulation of the limit state expression. Subsequently, a rational value for the ratio of the permanent action effect to resistance is derived, serving as the foundation for optimizing the partial factors within the limit state expression. The rating principles for the safety assessment of existing structural members are established. Finally, a systematic study of safety assessment methods for existing masonry structures is conducted. The findings indicate that in evaluating the safety of existing masonry structures: (1) the resistance partial factor (rR) is set at 2.1; (2) the permanent action partial factor (rG) is assigned a value of 1.0; (3) for variable action factors (rQ), values of 1.3, 1.4, and 1.5 are applied, respectively, for subsequent working years of 30a, 40a, and 50a. The assessment method proposed in this paper is more in line with the reality of existing structures and can effectively avoid over-strengthening of structures.
Key Words
deterministic characteristics; existing structures; limit state expression partial factors; rating principle; structural safety assessment
Address
Lele Wu: State Key Laboratory of Building Safety and Built Environment, Beijing 100013, China;
School of Civil Engineering, Tianjin Chengjian University, Tianjin 300384, China;
Tianjin Key Laboratory of Structural Protection and Reinforcement, Tianjin Chengjian University,
Tianjin 300384, China
Tao Yang and Hongcheng Guan: China Academy of Building Research, Beijing 100013, China
Caoming Tang: China Academy of Building Research, Beijing 100013, China;
Research Center for Disaster Prevention, Ministry of Housing and Urban-Rural Development,
Beijing 100013, China
Youshan Zhao: State Key Laboratory of Building Safety and Built Environment, Beijing 100013, China
Abstract
Concrete's heterogeneous structure makes it a highly dispersive medium for wave propagation, affecting ultrasonic test measurements. Aggregate grain size is a major source of heterogeneity, influencing wave characteristics. To have a clear understand of the effect of grain size on wave properties, it is essential to eliminate variability from aggregate-mortar interface and concrete mixture design; this requires examining specimens made of identical aggregates. Coupling also influences wave measurements significantly. While ultrasonic immersion testing provides consistent coupling, it isn't suitable for in-situ testing. Laser vibrometers (LV) have the potential to offer a reliable non-contact alternative for in-situ measurements. This study investigates the influences of aggregate content and coupling on ultrasonic measurements. Immersion and LV tests are performed on homogeneous (acrylic, nylon) and heterogeneous (concrete, mortar with varying glass bead content) specimens. Material properties, including wave velocities, acoustic impedance, elastic moduli, and attenuation, are determined using both methods. Wave signals are analyzed in time and frequency domains to identify optimal material characterization method. Results indicate that attenuation primarily originates from the irregular shape of aggregates compared to the smooth surface of glass beads. Furthermore, LV measurements of P-wave velocity and attenuation strongly agree with immersion tests, suggesting LV as a viable alternative.
Key Words
aggerate grain size; cementitious materials; laser vibrometer; mechanical properties; NDT; ultrasonic immersion test
Address
Sabah H.L. Fartosy: College of Engineering, Mustansiriyah University, Baghdad, Iraq
Edward Ginzel and Giovanni Cascante: Department of Civil Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada
Ahmet S. Kirlangic: School of Computing, Engineering, and Digital Technologies, Teesside University,
Middlesbrough TS1 3PX, United Kingdom
Abstract
Masonry, one of the oldest construction materials, has a historical significance in building structures. However, unreinforced masonry (URM) structures frequently exhibit poor performance in the face of seismic events, strong winds, shocks and impacts, often failing in a brittle manner. The primary objective of reinforcing URM structures is to enhance their resilience against lateral loads and tension forces. Recent decades have witnessed a concentrated effort on seismic retrofitting and strengthening methods, employing composite and mesh-type materials. This comprehensive review focusses on the practical applications of various reinforcement types for masonry walls, emphasizing three commonly used systems: external surface reinforcement, near surface reinforcement and internal surface reinforcement. The main goal is to evaluate the effectiveness of these techniques, providing a thorough overview of their advantages and limitations. Additionally, an in-depth exploration of the literature examines how different reinforcement systems impact the mechanical properties of distinct categories of masonry walls, including clay brick, concrete blocks, and autoclaved concrete blocks (AAC) blocks. This systematic review not only provides valuable insights for researchers and engineers but also highlights current research trends and suggests potential avenues for future exploration.
Key Words
external surface; internal surface; masonry; near surface; retrofitting; review; strengthening
Address
Teiborlang Warjri, Richard Badonbok Lyngkhoi,
Gregoria Kyntunamlang Langstang and Comingstarful Marthong: Department of Civil Engineering, National Institute of Technology Meghalaya, Shillong 793003, India
Abstract
Gearbox is an integral part of wind turbine (WT) design and timely fault detection can reduce unexpected downtime and maintenance costs. This study presents a method to detect turbine gear faults that combines Envelope analysis combines with Gated Recurrent Units (GRUs). Envelope analysis extracts high-frequency fault features from vibration signals, while GRUs excel in recognizing temporal patterns, making this combination particularly powerful for early fault detection in gears. This method aims to enhance diagnostic accuracy, offering significant advantages over traditional methods that rely primarily on human inspection and basic signal processing. Its ability to detect and localize issues early ensures a direct and impactful contribution to optimizing maintenance strategies. The results, based on the analysis of signals from a planetary gearbox, demonstrate a marked improvement in diagnostic capabilities.
Address
Said Djaballah and Abdelhak Belahcene: Department of Mechanical Engineering, Faculty of Technology, University of Chlef, Algeria
M'hamed Beriache: Rheology and Mechanics Laboratory, Faculty of Technology, University of Chlef, Algeria
Abdelmoumene Hechifa: Department of Mechanical Engineering, Faculty of Technology, University of Skikda, Algeria
Kamel Meftah: LGEM, Department of Mechanical Engineering, Faculty of Technology, University of Batna 2, Algeria
Abstract
This paper investigates the effects of micro-steel fibers (MSF) and macro-polyolefin fibers (MPF) on the flexural behavior and impact resistance of high-strength concrete (HSC). For this purpose, eleven mix compositions with four different volume fractions of MPF (0.25%, 0.5%, 75% and 1%), four volume fractions of MSF (0.25%, 0.5%, 75% and 1%), and also three mixes with the combination of micro-steel and macro-polyolefin fibers at a total fiber volume fraction of 1.0% were designed. The compressive strength, post-crack behavior, flexural behavior, and impact resistance were studied. The highest equivalent flexural strength ratios were achieved in hybrid mixes combining MSF and MPF, reaching up to 79.1% for the M25-75 mix, indicating the synergistic benefits of fiber hybridization. Moreover, the flexural performance test indicated that the energy absorption capacity was significantly larger for the hybrid mixes. The results showed that while MPF mixes exhibited higher impact resistance at the first crack for a given fiber volume fraction, the hybrid fiber mixes displayed the best overall impact resistance at failure.
Key Words
flexural behavior; high strength concrete; impact resistance; macro-polyolefin fibers; micro-steel fiber
Address
Oveys Afzali-Naniz, Arash Ashouri-Seynaki and Moosa Mazloom: Department of Structural and Earthquake Engineering, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, I. R. Iran
