Abstract The use of natural fibre reinforcement in polymer and concrete composites has in recent ... more Abstract The use of natural fibre reinforcement in polymer and concrete composites has in recent years attracted significant research interest. When coconut fibre reinforced concrete (CFRC) is confined by flax fibre reinforced polymer (FFRP), the strength of FFRP-CFRC composite is significantly enhanced. While researchers have studied the effect of FFRP confinement on compressive strength, their work has mainly focussed on the outside confinement of CFRC. In contrast, this study considers a double confinement, i.e. CFRC is confined respectively by large and small FFRP tubes both externally and internally. The experimental results show that in comparison with single confinement, double confinement enhances the axial compressive strength and strain of the FFRP-CFRC composite, even though less concrete is used.
Flax fibre reinforced polymer (FFRP) has been heavily studied in terms of static properties. To s... more Flax fibre reinforced polymer (FFRP) has been heavily studied in terms of static properties. To study its dynamic behaviour, experimental work also needs to be carried out. This study presents the tensile properties of flax fibre reinforced polymer (FFRP) composite under static and dynamic loadings. Experiments and Weibull distribution analysis were performed to investigate the strain rate effect on the dynamic properties of FFRP composites. In total, 45 specimens were considered. Dynamic tensile tests were performed by using a high-speed servo-hydraulic testing machine with a strain rate ranging from 0.764 s-1 to 135.68 s-1. Empirical formulas of dynamic increase factor (DIF) were derived at various strain rates. Weibull distribution analysis was applied to quantify the variability of tensile strength at different strain rates. Failure process and failure modes of FFRP were discussed via analysing high-speed camera recording. The results show that the tensile strength, failure strain, DIF and energy absorption of FFRP increased with the strain rate when it was higher than 79.12 s-1 .
Abstract The seismic vulnerability of skewed bridges has been known since the past few decades. P... more Abstract The seismic vulnerability of skewed bridges has been known since the past few decades. Previous research has found that skewed bridges are more prone to girder unseating than a straight bridge due to the in-plane rotations of the bridge girder which were found to be aggravated by pounding between adjacent spans and abutments. A good understanding of the pounding between girder and abutments of a skewed bridge is crucial for the integrity of the bridge. Most of the past research was performed mainly numerically and without considering movable abutments. Very limited experimental work has been done, and none has incorporated movement of abutments as the surrounding ground moves during earthquakes (movable abutments), influence of girder-abutment pounding, and skew angle at the same time. This study aims to close the knowledge gap through a series of shake table tests performed on a straight bridge, 30° and 45° skewed bridge with abutments on either side of the bridge structure. Abutment movement was considered by subjecting the bridge-abutment model to uniform ground excitations. The results show that ignoring pounding effects could significantly underestimate the bending moments at the piers by up to 1.94 times and the transverse relative displacements by up to 3.43 times. The NZTA recommendation for the seat length was severely inadequate to accommodate for the large displacements of skewed bridges, especially in the transverse direction.
Journal of Reinforced Plastics and Composites, Aug 5, 2016
Impact properties of flax fibre-reinforced polymer composites were investigated using two differe... more Impact properties of flax fibre-reinforced polymer composites were investigated using two different impact test methods, i.e. drop-weight test and Charpy test. The drop-weight impact tests were conducted with varying drop height. For the drop-weight tests, the perforation energy and the energy absorbed by a specimen are used to study the impact response of the flax fibre-reinforced polymer composite. In a series of Charpy tests, the energy absorbed per unit width of the specimen was investigated. Impact force and Hertzian force were analysed and were found to increase with composite thickness. The ductility index decreased as the composite thickness increased. The failure of flax fibre-reinforced polymer composites started as micro-cracks, progressed to larger cracks and perforation occurred at last. However, the damage to flax fibre-reinforced polymer composites differed with the thickness of the specimens.
Impact behaviour of a novel natural coconut fibre reinforced concrete was investigated. Dynamic i... more Impact behaviour of a novel natural coconut fibre reinforced concrete was investigated. Dynamic increase factor of CFRC was studied by experiments and theoretical method. Impact damage mechanisms of the CFRC cylinders have been described. Both single and repeated impact tests have been studied. The relationship between impact height and maximum impact stress was examined.
... simultaneous ground excitations on the structural responses are often limited to the two-dime... more ... simultaneous ground excitations on the structural responses are often limited to the two-dimensional problems (eg Hachem & Mahin, 2000 ... Three-dimensional study with soil-structure interaction is often restricted to the foundation-soil systems (eg Karabalis & Mohammadi, 1998 ...
Coconut fibre-reinforced concrete (CFRC) is widely used in the construction of house walls, espec... more Coconut fibre-reinforced concrete (CFRC) is widely used in the construction of house walls, especially in rural areas, but its impact resistance has rarely been studied. This paper investigates the dynamic compressive behaviour of CFRC by conducting high-speed servo-hydraulic tests under different strain rates ranging from 0·2 to 30 s−1. To study the strain rate effects on compressive strength, failure pattern, failure processes and energy absorption, CFRC cylindrical specimens with different coconut fibre contents – that is, 1, 3 and 5% of cement mass – were prepared and tested. The results showed that compressive strength increased with the strain rate, but decreased when the coconut fibre volume exceeded 3%. This paper discusses the relationship between the fibre-content-dependent dynamic increase factor and the strain rate for CFRC composites. In addition, it studies the failure process of CFRC via an analysis of the effect of the fibre content. The result of this research should be helpful in designing high-speed, impact-resistant, natural fibre-reinforced composites.
Earthquake Engineering & Structural Dynamics, Aug 12, 2021
The influence of soil on the dynamic response of soil‐structure systems is usually studied on a s... more The influence of soil on the dynamic response of soil‐structure systems is usually studied on a stand‐alone (SA) structure, even though closely adjacent structures form the vast majority of the population, especially in large cities. When structures are closely adjacent to each other, the wavefield in the soil, generated by the vibration of the footings, produces a complex interaction between them. Scant attention, especially by physical experiments, has been paid to this interaction. This work addresses the seismic response of a single degree‐of‐freedom structure (structure of focus) considering the influence of one and two closely adjacent neighbours. Experiments were performed using a large laminar box filled with sand sitting on a shake table. Results from utilising four recorded ground motions from the 2010–2011 Canterbury earthquake sequence are analysed. The effect of adjacent structures on the acceleration and displacement of the top mass of each structure, as well as the uplift of the footings, are discussed. Changes in the fundamental frequency due to the presence of neighbouring structures are identified. The use of the SA system, without consideration of closely adjacent structures, may result in a significant error in the estimation of the response of the structure of focus. In general, acceleration, lateral displacement and uplift reduced in comparison with that of the corresponding SA case. A footing settlement mechanism, resulting from uplift of the system that reflects the influence of adjacent structures, is also revealed.
Structure and Infrastructure Engineering, Feb 13, 2019
Skewed bridges are bridges with longitudinal axes at an angle to the abutments. They are more sus... more Skewed bridges are bridges with longitudinal axes at an angle to the abutments. They are more susceptible to damage during seismic events due to in-plane rotations of the girders induced, especially when pounding occurs. Most current design standards do not consider many factors that could significantly affect the response of skewed bridges, such as the skew angle and effect of the supporting soil. A bridge-abutment model with 0 , 30 , and 45 skew angles were subjected to shake table tests. Ground motions were simulated based on the New Zealand design spectra for Class C and E soil conditions. The effects of the different characteristics of ground motions on the seismic response of skewed bridges considering presence of pounding and the supporting soil were investigated. The results were also used to evaluate the recommendation of girder seat lengths specified in design specifications, e.g. the New Zealand Transport Agency (NZTA) Bridge Manual. It was found that the NZTA recommendation for seat length could potentially significantly underestimate the out-of-plane movements of the girders. In the worst case, the displacement of the skewed bridge was up to 3.48 times that of the straight bridgemuch larger than the recommended value of 1.25 times.
Skewed bridges are prone to large in-plane rotations of the girders, especially when seismically-... more Skewed bridges are prone to large in-plane rotations of the girders, especially when seismically-induced pounding with the abutments occur. These rotations have been associated with increase in relative displacements, leading to potential unseating or permanent dislocation of the girders, especially in the transverse direction. The approach adopted in current design specifications for the seat lengths of skewed bridges is oversimplified and could potentially underestimate the relative displacements. Shake table tests were performed on a 1:20 scale bridge-abutment model with 0°(straight), 30°, and 45°skew angles. The effects of pounding, supporting soil, and ground motions simulated based on different soil conditions were considered. The bridge segment and abutments experienced spatially uniform excitations. The results were used to develop empirical formulae for estimation of the relative displacements of skewed bridges. Normalisation of the responses means that the proposed approach can be incorporated into design specificationsas an amplification or reduction compared to that calculated for a straight bridge. It was found that the empirical formulae proposed in this study are able to provide more conservative estimates of the expected relative displacements of the girders of skewed bridges.
Four scaled one-storey single-bay steel plate shear wall (SPSW) specimens with unstiffened panels... more Four scaled one-storey single-bay steel plate shear wall (SPSW) specimens with unstiffened panels were tested to determine their behaviour under cyclic loadings. e shear walls had moment-resisting beam-to-column connections. Four different vertical loads, i.e., 300 kN, 600 kN, 900 kN, and 1200 kN, representing the gravity load of the upper storeys were applied at the top of the boundary columns through a force distribution beam. A horizontal cyclic load was then applied at the top of the specimens. e specimen behaviour, envelope curves, axial stress distribution of the infill steel plate, and shear capacity were analyzed. e axial stress distribution and envelope curves were compared with the values predicted using an analytical model available in the literature.
Abstract The use of natural fibre reinforcement in polymer and concrete composites has in recent ... more Abstract The use of natural fibre reinforcement in polymer and concrete composites has in recent years attracted significant research interest. When coconut fibre reinforced concrete (CFRC) is confined by flax fibre reinforced polymer (FFRP), the strength of FFRP-CFRC composite is significantly enhanced. While researchers have studied the effect of FFRP confinement on compressive strength, their work has mainly focussed on the outside confinement of CFRC. In contrast, this study considers a double confinement, i.e. CFRC is confined respectively by large and small FFRP tubes both externally and internally. The experimental results show that in comparison with single confinement, double confinement enhances the axial compressive strength and strain of the FFRP-CFRC composite, even though less concrete is used.
Flax fibre reinforced polymer (FFRP) has been heavily studied in terms of static properties. To s... more Flax fibre reinforced polymer (FFRP) has been heavily studied in terms of static properties. To study its dynamic behaviour, experimental work also needs to be carried out. This study presents the tensile properties of flax fibre reinforced polymer (FFRP) composite under static and dynamic loadings. Experiments and Weibull distribution analysis were performed to investigate the strain rate effect on the dynamic properties of FFRP composites. In total, 45 specimens were considered. Dynamic tensile tests were performed by using a high-speed servo-hydraulic testing machine with a strain rate ranging from 0.764 s-1 to 135.68 s-1. Empirical formulas of dynamic increase factor (DIF) were derived at various strain rates. Weibull distribution analysis was applied to quantify the variability of tensile strength at different strain rates. Failure process and failure modes of FFRP were discussed via analysing high-speed camera recording. The results show that the tensile strength, failure strain, DIF and energy absorption of FFRP increased with the strain rate when it was higher than 79.12 s-1 .
Abstract The seismic vulnerability of skewed bridges has been known since the past few decades. P... more Abstract The seismic vulnerability of skewed bridges has been known since the past few decades. Previous research has found that skewed bridges are more prone to girder unseating than a straight bridge due to the in-plane rotations of the bridge girder which were found to be aggravated by pounding between adjacent spans and abutments. A good understanding of the pounding between girder and abutments of a skewed bridge is crucial for the integrity of the bridge. Most of the past research was performed mainly numerically and without considering movable abutments. Very limited experimental work has been done, and none has incorporated movement of abutments as the surrounding ground moves during earthquakes (movable abutments), influence of girder-abutment pounding, and skew angle at the same time. This study aims to close the knowledge gap through a series of shake table tests performed on a straight bridge, 30° and 45° skewed bridge with abutments on either side of the bridge structure. Abutment movement was considered by subjecting the bridge-abutment model to uniform ground excitations. The results show that ignoring pounding effects could significantly underestimate the bending moments at the piers by up to 1.94 times and the transverse relative displacements by up to 3.43 times. The NZTA recommendation for the seat length was severely inadequate to accommodate for the large displacements of skewed bridges, especially in the transverse direction.
Journal of Reinforced Plastics and Composites, Aug 5, 2016
Impact properties of flax fibre-reinforced polymer composites were investigated using two differe... more Impact properties of flax fibre-reinforced polymer composites were investigated using two different impact test methods, i.e. drop-weight test and Charpy test. The drop-weight impact tests were conducted with varying drop height. For the drop-weight tests, the perforation energy and the energy absorbed by a specimen are used to study the impact response of the flax fibre-reinforced polymer composite. In a series of Charpy tests, the energy absorbed per unit width of the specimen was investigated. Impact force and Hertzian force were analysed and were found to increase with composite thickness. The ductility index decreased as the composite thickness increased. The failure of flax fibre-reinforced polymer composites started as micro-cracks, progressed to larger cracks and perforation occurred at last. However, the damage to flax fibre-reinforced polymer composites differed with the thickness of the specimens.
Impact behaviour of a novel natural coconut fibre reinforced concrete was investigated. Dynamic i... more Impact behaviour of a novel natural coconut fibre reinforced concrete was investigated. Dynamic increase factor of CFRC was studied by experiments and theoretical method. Impact damage mechanisms of the CFRC cylinders have been described. Both single and repeated impact tests have been studied. The relationship between impact height and maximum impact stress was examined.
... simultaneous ground excitations on the structural responses are often limited to the two-dime... more ... simultaneous ground excitations on the structural responses are often limited to the two-dimensional problems (eg Hachem & Mahin, 2000 ... Three-dimensional study with soil-structure interaction is often restricted to the foundation-soil systems (eg Karabalis & Mohammadi, 1998 ...
Coconut fibre-reinforced concrete (CFRC) is widely used in the construction of house walls, espec... more Coconut fibre-reinforced concrete (CFRC) is widely used in the construction of house walls, especially in rural areas, but its impact resistance has rarely been studied. This paper investigates the dynamic compressive behaviour of CFRC by conducting high-speed servo-hydraulic tests under different strain rates ranging from 0·2 to 30 s−1. To study the strain rate effects on compressive strength, failure pattern, failure processes and energy absorption, CFRC cylindrical specimens with different coconut fibre contents – that is, 1, 3 and 5% of cement mass – were prepared and tested. The results showed that compressive strength increased with the strain rate, but decreased when the coconut fibre volume exceeded 3%. This paper discusses the relationship between the fibre-content-dependent dynamic increase factor and the strain rate for CFRC composites. In addition, it studies the failure process of CFRC via an analysis of the effect of the fibre content. The result of this research should be helpful in designing high-speed, impact-resistant, natural fibre-reinforced composites.
Earthquake Engineering & Structural Dynamics, Aug 12, 2021
The influence of soil on the dynamic response of soil‐structure systems is usually studied on a s... more The influence of soil on the dynamic response of soil‐structure systems is usually studied on a stand‐alone (SA) structure, even though closely adjacent structures form the vast majority of the population, especially in large cities. When structures are closely adjacent to each other, the wavefield in the soil, generated by the vibration of the footings, produces a complex interaction between them. Scant attention, especially by physical experiments, has been paid to this interaction. This work addresses the seismic response of a single degree‐of‐freedom structure (structure of focus) considering the influence of one and two closely adjacent neighbours. Experiments were performed using a large laminar box filled with sand sitting on a shake table. Results from utilising four recorded ground motions from the 2010–2011 Canterbury earthquake sequence are analysed. The effect of adjacent structures on the acceleration and displacement of the top mass of each structure, as well as the uplift of the footings, are discussed. Changes in the fundamental frequency due to the presence of neighbouring structures are identified. The use of the SA system, without consideration of closely adjacent structures, may result in a significant error in the estimation of the response of the structure of focus. In general, acceleration, lateral displacement and uplift reduced in comparison with that of the corresponding SA case. A footing settlement mechanism, resulting from uplift of the system that reflects the influence of adjacent structures, is also revealed.
Structure and Infrastructure Engineering, Feb 13, 2019
Skewed bridges are bridges with longitudinal axes at an angle to the abutments. They are more sus... more Skewed bridges are bridges with longitudinal axes at an angle to the abutments. They are more susceptible to damage during seismic events due to in-plane rotations of the girders induced, especially when pounding occurs. Most current design standards do not consider many factors that could significantly affect the response of skewed bridges, such as the skew angle and effect of the supporting soil. A bridge-abutment model with 0 , 30 , and 45 skew angles were subjected to shake table tests. Ground motions were simulated based on the New Zealand design spectra for Class C and E soil conditions. The effects of the different characteristics of ground motions on the seismic response of skewed bridges considering presence of pounding and the supporting soil were investigated. The results were also used to evaluate the recommendation of girder seat lengths specified in design specifications, e.g. the New Zealand Transport Agency (NZTA) Bridge Manual. It was found that the NZTA recommendation for seat length could potentially significantly underestimate the out-of-plane movements of the girders. In the worst case, the displacement of the skewed bridge was up to 3.48 times that of the straight bridgemuch larger than the recommended value of 1.25 times.
Skewed bridges are prone to large in-plane rotations of the girders, especially when seismically-... more Skewed bridges are prone to large in-plane rotations of the girders, especially when seismically-induced pounding with the abutments occur. These rotations have been associated with increase in relative displacements, leading to potential unseating or permanent dislocation of the girders, especially in the transverse direction. The approach adopted in current design specifications for the seat lengths of skewed bridges is oversimplified and could potentially underestimate the relative displacements. Shake table tests were performed on a 1:20 scale bridge-abutment model with 0°(straight), 30°, and 45°skew angles. The effects of pounding, supporting soil, and ground motions simulated based on different soil conditions were considered. The bridge segment and abutments experienced spatially uniform excitations. The results were used to develop empirical formulae for estimation of the relative displacements of skewed bridges. Normalisation of the responses means that the proposed approach can be incorporated into design specificationsas an amplification or reduction compared to that calculated for a straight bridge. It was found that the empirical formulae proposed in this study are able to provide more conservative estimates of the expected relative displacements of the girders of skewed bridges.
Four scaled one-storey single-bay steel plate shear wall (SPSW) specimens with unstiffened panels... more Four scaled one-storey single-bay steel plate shear wall (SPSW) specimens with unstiffened panels were tested to determine their behaviour under cyclic loadings. e shear walls had moment-resisting beam-to-column connections. Four different vertical loads, i.e., 300 kN, 600 kN, 900 kN, and 1200 kN, representing the gravity load of the upper storeys were applied at the top of the boundary columns through a force distribution beam. A horizontal cyclic load was then applied at the top of the specimens. e specimen behaviour, envelope curves, axial stress distribution of the infill steel plate, and shear capacity were analyzed. e axial stress distribution and envelope curves were compared with the values predicted using an analytical model available in the literature.
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