Initial crack detection in concrete plate and shell structures using concept of earthquake ground motions

Many methods and sensors have been developed for crack detection in concrete structures and for earthquake ground motion detection, respectively. In a previous study, a seismo-accelerometer based on spring-mass strong motion seismo-accelerograph has been developed for the purpose of detecting earthquake waves travelling through the earth crust from the epicenter at faultline. This study aims to apply the method developed in previous study to detect wave from crack initiation point on the surface of plate and shell concrete as a new alternative for initial crack detection method. This study focused on the development of a downscaled seismo-accelerometer of previous study for better ease of use. Concrete plate and shell specimens were selected in this study as the travel of wave from crack initiation point in the specimen mimic to that of earthquake waves travelling through the earth crust from the epicenter at the faultline. Magnetometer technology and spring-mass system formed the fundamental design aspect of the seismo-accelerometer. In Objective 1, the seismo-accelerometer was designed using Finite Element Modelling to attain natural period of 1 second, required for spring-mass based strong motion accelerograph. The modelling yield natural period of 0.99475 second and verified experimentally with Harmonic Shake Table test yielding 1.2 seconds, which is in the acceptable range. Ground motion test was carried out at Ranau Meteorological Station and the results were compared with international earthquake database. Earthquakes detected are in Sabah and nearby regions. Crack induction tests on factory-ready concrete plate and shell specimens were carried out in Objective 2, where the results shown that the concept of ground motion detection can be used for crack detection purposes. The crack detection equations for factory-ready concrete plate and shell are Mcrack,plate = log10A + 0.6919 and Mcrack,shell = log10A + 0.7115, respectively. Objective 3 provides the proof that the ground motion detection can be applied for crack detection based on crack wave attenuation on structures such as concrete plate and shell which have the same configuration as earth crust, where the earthquakes occur. Thus, the seismo-accelerometer developed in the study can be used for earthquake ground motion detection if placed on the bedrock or ground, and can be used for crack detection if placed on structures with similar configuration to earth crust such as concrete plate and shell structures. This contributes towards both Structural Health Monitoring and Seismic Monitoring apart from providing an alternative method to existing methods in both fields

Shear capacity evaluation of reinforced concrete beams: finite element simulation

The shear performance of reinforced concrete beams with rectangle cross-section and two different continuous rectangular spiral shear reinforcement under monotonous loading is numerically evaluated. Further, the behaviour of two continuous shear reinforcement systems named, “Single Square Spring Shear Resistance System” (SSSSRS) and “Double Square Spring Shear Resistance System” (DSSSRS) as transverse reinforcements are compared with conventional discontinuous system “Stirrups”. The finite element study includes three (3) beams. The results clearly show that the application of continuous shear reinforcement system delivered improved shear behaviour and enhanced bearing capacity in beams. Beams with Single Square Spring Shear Resistance System (SSSSRS) and Double Square Spring Shear Resistance System (DSSSRS) exhibited 14.4% and 19.8% increased shear performance in comparison with conventional control beam. It was concluded that under the same deflection higher forces was achieved for “Single Square Spring Shear Resistance System” (SSSSRS) and “Double Square Spring Shear Resistance System” (DSSSRS) compared to control specimens

One-way transnational magnetic mass damper model for structural response control against dynamic loadings

Structural responses should be reduced to minimize the consequent structural damage caused by dynamic excitation. The one-way translational magnetic mass damper model is developed as a new type of damper for the purpose of structural response control. The damper utilizes the concept of repulsive force between magnets with same poles to create a magnetic force to stabilize or bring the structure back to its original position. The dynamic performance of the structure was tested using a harmonic shaking table. In this study, the three parameters used are excitation speeds: 2.5V (low), 6.0V (medium) and 8.5V (high); strength of magnets: weak (N35), medium (N45) and strong (N52); and the mass in the damper: 40 g, 101 g and 162 g. The correlations of the parameters towards the structural displacement are verified in the testing. The displacement is highly reduced up to 100% at the first level and 85.2% at the fifth level. The most optimum structural response control was attained when a strong magnetic strength and mass of 162 g are used. When tested with three excitation speeds; 2.5V, 6.0V and 8.5V, the damper with this setting provides the optimum damping effect towards the structure in terms of displacement

Development Of A tri-axial Seismo-Accelero-Crackometer for earthquake ground motion and structural damage detection

Monitoring of earthquake ground motions required separate use of seismometer and accelerometer, to measure magnitude and distance, and intensity of the earthquake respectively. However, systems currently available are expensive, limiting user’s monitoring capability. This paper presents the development of tri-axial Seismo-Accelero-Crackometer for earthquake ground motion and structural damage detection. The system which consists of a spring-mass damper with sinusoidally forced eight identical linear springs, is developed such that the mass absolute motions and motion relative to base can be measured when force arising from base excitation imposed to the system. Similar concept of ground motion detection is applied locally to detect the wave or force released by the crack, indicating initiation of structural damage. Apart from measuring the three components of ground motions, Seismo-Accelero-Crackometer would also able to detect structural damage, hence providing economically practical solution for structural monitoring against earthquakes and damages, currently not practiced in most developing countries

The mechanical properties of steel-polypropylene fibre composites concrete (HyFRCC)

This paper discusses the experimental results on the mechanical properties of hybrid fibre reinforced composite concrete (HyFRCC) containing different proportions of steel fibre (SF) and polypropylene fibre (PPF). The mechanical properties include compressive strength, tensile strength, and flexural strength. SF is known to enhance the flexural and tensile strengths, and at the same time is able to resist the formation of macro cracking. Meanwhile, PPF contributes to the tensile strain capacity and compressive strength, and also delay the formation of micro cracks. Hooked-end deformed type SF fibre with 60 mm length and fibrillated virgin type PPF fibre with 19 mm length are used in this study. Meanwhile, the concrete strength is maintained for grade C30. The percentage proportion of SF-PPF fibres are varied in the range of 100-0%, 75-25%, 50-50%, 25-75% and 0-100% of which the total fibre volume fraction (Vf) is fixed at 0.5%. The experimental results reveal that the percentage proportion of SF-PPF fibres with 75-25% produced the maximum performance of flexural strength, tensile strength and flexural toughness. Meanwhile, the percentage proportion of SF-PPF fibres with 100-0% contributes to the improvement of the compressive strength compared to that of plain concrete

Earthquake Vulnerability Index of Buildings in Kota Kinabalu, Sabah, Malaysia

Sabah has experienced an increasing number of low to moderate seismic events throughout the years, owing to the presence of certain moderately active fault lines in the region. A significant earthquake struck in Ranau in 2015. Central and eastern Sabah, including Kota Kinabalu, were affected by the earthquake. Around 300 moderate magnitude earthquakes have occurred in this region during the last 150 years, ranging from MW 2.5 to MW 6.9. The majority of existing structures in Kota Kinabalu are based on wind and gravity loads, notably those built between the 1970s and 2000s. As a result, the inspection stages for building vulnerabilities are somewhat limited. The purpose of this study was to establish an earthquake vulnerability index for existing buildings in the city. The building databases contain information on the locations, structural and geometric properties of 247 structures that have been collected and analyzed. The obtained data is used to conduct an empirical assessment of the seismic vulnerability of existing buildings. Furthermore, this will be performed by employing a seismic vulnerability assessment with a score assignment, which is useful for analyzing a large number of buildings. Out of the total sampled buildings, the majority are classified as grade 3 and 4, suggesting a risk of severe structural damage. In comparison, only 5% of the population suffers from minor to no structural damage. In conclusion, the anticipated vulnerability index can be used to plan and carry out repair, reinforcing, and adaptation actions on existing structures that were designed and built without respect for earthquake loads. Such estimates may reveal weaknesses that should be avoided during the design and construction of new structures to avoid future earthquake damage

Seismic performance of ductility classes medium RC beam-column connections with continuous rectangular spiral transverse reinforcements

The seismic performance of RC columns can considerably be improved through the use of continuous spiral reinforcement in terms of ductility and energy dissipation capacity. Since the beam-column connections were subjected to brittle failure after earthquakes, the simultaneous application of this method in both beams and columns could greatly improve the seismic behaviour of such connections. In this investigation, a new proposed detail for beam to column connection introduced as "twisted opposing rectangular spiral" was investigated both experimentally and numerically and its seismic performance was verified through comparison with normal rectangular spiral and conventional shear reinforcement systems. In this research, three full scale beam to column connections were first designed according to Eurocode (EC8-04) for Medium ductility classes and then tested by quasi-static cyclic loading suggested by ACI Building Code (ACI 318-08). Finally, numerical methods were hired to validate the experimental results. The results indicated that the ultimate lateral resistance, ductility and energy dissipation capacity of the connection could be improved using the new proposed connection

Ground motion prediction equations for far field earthquake considered by strike slip fault mechanism

The ground motion prediction equation (GMPE) was developed using regression analysis. This estimation process needs to use a GMPE which provides peak ground acceleration (PGA) estimates incorporating a number of earthquake magnitude, distance and other seismic parameters. The database consisting of more than 35 PGA dataset from different earthquakes recorded by Seismology Station in Malaysia have been used to develop the relationship for this paper. This study aims to investigate the new relationship attenuation to gain exact peak ground acceleration at the location on site. In the Southern Asia region (Indonesia, Philippine and Malaysia) for example, there is significant hazard from earthquake along the strike slip fault

One-way translational magnetic mass damper model for structural response control against dynamic loadings

Structural responses should be reduced to minimize the consequent structural damage caused by dynamic excitation. The one-way translational magnetic mass damper model is developed as a new type of damper for the purpose of structural response control. The damper utilizes the concept of repulsive force between magnets with same poles to create a magnetic force to stabilize or bring the structure back to its original position. The dynamic performance of the structure was tested using a harmonic shaking table. In this study, the three parameters used are excitation speeds: 2.5V (low), 6.0V (medium) and 8.5V (high); strength of magnets: weak (N35), medium (N45) and strong (N52); and the mass in the damper: 40 g, 101 g and 162 g. The correlations of the parameters towards the structural displacement are verified in the testing. The displacement is highly reduced up to 100% at the first level and 85.2% at the fifth level. The most optimum structural response control was attained when a strong magnetic strength and mass of 162 g are used. When tested with three excitation speeds; 2.5V, 6.0V and 8.5V, the damper with this setting provides the optimum damping effect towards the structure in terms of displacement