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.
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.
... 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.
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.
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.
... 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.
Uploads
Papers by Nawawi Chouw