Wei Loo - Academia.edu (original) (raw)
Papers by Wei Loo
Multi-storey platform cross laminated timber (CLT) structures are becoming progressively desirabl... more Multi-storey platform cross laminated timber (CLT) structures are becoming progressively desirable for engineers and owners. This is because they offer many significant advantages such as speed of fabrication, ease of construction, and excellent strength to weight ratio. With platform construction, stories are fixed together in a way that each floor bears into load bearing walls, therewith creating a platform for the next level. The latest research findings have shown that CLT platform buildings constructed with traditional fasteners can experience a high level of damage especially in those cases where the walls have adopted hold-down brackets and shear connectors with nails, rivets or screws. Thus, the current construction method for platform CLT structures is less than ideal in terms of damage avoidance. The main objective of this study is to develop a low damage platform timber panelised structural system using a new configuration of slip friction devices in lieu of traditional c...
In terms of seismic performance, timber structures have been observed to perform well, in spite o... more In terms of seismic performance, timber structures have been observed to perform well, in spite of timber being an inherently non-ductile material. This is due mainly to the ductility of the steel-to-timber connections, and the way in which they interact with the timber material. If these connections are detailed to deform plastically, while keeping the timber members elastic, the overall structure achieves ductility. For nailed sheathing-to-framing shear walls and floor diaphragms, the New Zealand structural timber code, NZS3603:1993 [1] allows ductilities of up to four to be assumed. The issue with such an approach is that in a design level earthquake, the deformations required to achieve ductility often renders the structure irreparable, or at least requiring expensive repairs. Recent developments in engineered lumber products have seen the availability of mass timber panels of tremendous strength and stiffness. These include CLT (cross laminated timber) and LVL (laminated veneer lumber) panels. Under typical loading conditions these panels are essentially rigid, and the experiments of Popovski and Karacabeyli [2] demonstrate that the hysteretic behaviour is largely governed by the plastic deformations in the steel bracket connections attaching the walls to the floor. The hysteretic loops bear some resemblance to those of sheathing to framing shear walls, the main difference being they are more tightly pinched. The seismic performance of such walls is adequate, however, damage is still a consequence after an earthquake
IOP Conference Series: Materials Science and Engineering, 2019
The Initial Evaluation Procedure, conducted as part of Initial Seismic Assessment, is the main to... more The Initial Evaluation Procedure, conducted as part of Initial Seismic Assessment, is the main topic of this paper. An overview is provided of the eight key steps which define this procedure, and how they are used to determine ratio of New Building Standard (%NBS). The key steps are encapsulated in a programmed EXCEL worksheet (developed and current used in New Zealand) which takes into account various parameters and applies an algorithm to arrive at a preliminary assessed value. Actual examples of various buildings assessed using this procedure in recent years by authors are presented, and the results and some areas of interest are discussed.
IOP Conference Series: Materials Science and Engineering, 2019
In earthquake design philosophy non-linear inelastic damage is concentrated at predetermined loca... more In earthquake design philosophy non-linear inelastic damage is concentrated at predetermined locations in a structure, with the aim being to keep structural members critical for collapse avoidance, elastic. Non-linear elements can include the beam column joints in steel and reinforced concrete moment resisting frames, the nail connections of timber sheathing-to-framing shear walls, and the hold-down connectors of shear walls. To numerically model the seismic behaviour of these structures, it is critical to be able to quickly and simply model their respective hysteretic behaviours. It is particularly important to identify the parameters that will allow for the accurate replication of the degrading and pinching qualities of the force-displacement relationships. The authors summarise the use of a proprietary multi-linear plastic link, available in most finite element packages, in order to achieve this. A step-by-step process to model the links, from previous research, is described. Thi...
Earthquakes and Structures, 2015
In conventional seismic design, structures are assumed to be fixed at the base. To reduce the imp... more In conventional seismic design, structures are assumed to be fixed at the base. To reduce the impact of earthquake loading, while at the same time providing an economically feasible structure, minor damage is tolerated in the form of controlled plastic hinging at predefined locations in the structure. Uplift is traditionally not permitted because of concerns that it would lead to collapse. However, observations of damage to structures that have been through major earthquakes reveal that partial and temporary uplift of structures can be beneficial in many cases. Allowing a structure to move as a rigid body is in fact one way to limit activated seismic forces that could lead to severe inelastic deformations. To further reduce the induced seismic energy, slip-friction connectors could be installed to act both as hold-downs resisting overturning and as contributors to structural damping. This paper reviews recent research on the concept, with a focus on timber shear walls. A novel approach used to achieve the desired sliding threshold in the slip-friction connectors is described. The wall uplifts when this threshold is reached, thereby imparting ductility to the structure. To resist base shear an innovative shear key was developed. Recent research confirms that the proposed system of timber wall, shear key, and slip-friction connectors, are feasible as a ductile and lowdamage structural solution. Additional numerical studies explore the interaction between vertical load and slip-friction connector strength, and how this influences both the energy dissipation and self-centring capabilities of the rocking structure.
Structural Engineering and Mechanics, 2012
ABSTRACT
The use of rigid engineered timber panels, such as cross-laminated-timber, in construction is inc... more The use of rigid engineered timber panels, such as cross-laminated-timber, in construction is increasing around the world, particularly in Europe and Australasia. Typically the panels rely on nailed or screwed steel plates for hold-downs and shear keys. However, this can mean the level of ductility is difficult to quantify. Furthermore ductile wall behaviour will inevitably be associated with permanent damage to the connections. There have been calls from designers for a solution in which the level of ductility can be predicted and achieved with confidence. The authors propose a novel, yet simple, slipfriction device that limits activated forces on a structure during an earthquake by allowing it to slightly rock. An experimental LVL wall was fitted with these devices acting as hold-downs. The shear key consisted of steel rods bearing against upright steel plates along the base of the wall. Under cyclic displacement tests, the wall demonstrated excellent elasto-plastic behaviour. The predicted wall strength from theory, matched, in general, the forces measured, while ductility levels can be as large as the designer desires, within obvious limits. Even under only self-weight, the wall readily descended at one end, while uplifting at the other. The results suggest that structures of engineered lumber can perform with reliable levels of ductility and remain free from damage.
Journal of Constructional Steel Research, 2014
In recent decades, there has been increasing interest in the use of slip-friction connectors (or ... more In recent decades, there has been increasing interest in the use of slip-friction connectors (or slotted-bolt connectors) to dissipate energy in earthquake resistant structures. These devices, which rely on the friction controlled sliding of steel plates, have already seen implementation in buildings with steel moment resisting frames, with the intention that non-linear behaviour is concentrated at the connectors themselves, thereby protecting the structure from damage. The sliding mechanism of slip-friction connectors can be either symmetric or asymmetric. In the case of symmetric connectors, brass shims have, up until now, been required to ensure stable elastoplastic behaviour. However brass can be expensive, and sometimes difficult to procure. A new type of symmetric connector that entirely eliminates the need for shims of any kind is proposed. The centre-plate of the connector consists of abrasion resistant steel that is in direct contact with the mild steel plates between which it slides. From experimental testing, the performance of the proposed connector is found to be equal, if not superior, to that of traditional symmetric connectors with brass shims. The proposed connector maintains strength and stiffness over a large number of cycles of loading, and although minor pre-conditioning of the sliding surfaces may be required in order to improve behaviour, is nevertheless simpler, and likely to be cheaper, than its current equivalent with brass shims. The potential for galvanic corrosion is also avoided.
Engineering Structures, 2012
In the event of seismic overloading, timber shear walls have normally been designed to yield by a... more In the event of seismic overloading, timber shear walls have normally been designed to yield by allowing inelastic distortion of the sheathing-to-framing nail connections, thereby reducing the likelihood of brittle failure of timber chords or plywood sheathing. A new concept in shear wall design is presented. It involves the use of slip-friction connectors in lieu of traditional hold-down connectors. Slip-friction connectors, originally developed for the steel framing industry, rely on the mobilisation of friction across steel plates to resist loading up to a predetermined threshold. Upon this threshold being exceeded, relative sliding between the steel plates allows the shear wall to displace in an inelastic manner. This paper discusses the results of numerical analyses of timber shear walls which utilise slip-friction connectors. The results suggest that slip-friction connectors hold the promise of being able to effectively protect sheathing, framing, and nail connections from excessive stresses and deformations during earthquake events of design level intensity or higher. Walls with appropriately adjusted slip-friction connectors are highly ductile, are efficient dissipaters of seismic energy, and have a tendency to self-centre after an earthquake.
Construction and Building Materials, 2017
h i g h l i g h t s Abrasion resistant steel on mild steel produces stable sliding when surfaces ... more h i g h l i g h t s Abrasion resistant steel on mild steel produces stable sliding when surfaces are in the clean mill-scale condition. Where faying surfaces are polished so that bright steel is visible, severe frictional behaviour invariably arises. In one instance of polished on polished sliding, the test was terminated due to the surfaces friction welding together. The observed sliding behaviours of various surface types can be explained in the context of the adhesion theory of friction. The clean mill-scale condition should be specified in the design and implementation of slip-friction connectors.
Earthquake Engineering & Structural Dynamics, 2014
ABSTRACT
Multi-storey platform cross laminated timber (CLT) structures are becoming progressively desirabl... more Multi-storey platform cross laminated timber (CLT) structures are becoming progressively desirable for engineers and owners. This is because they offer many significant advantages such as speed of fabrication, ease of construction, and excellent strength to weight ratio. With platform construction, stories are fixed together in a way that each floor bears into load bearing walls, therewith creating a platform for the next level. The latest research findings have shown that CLT platform buildings constructed with traditional fasteners can experience a high level of damage especially in those cases where the walls have adopted hold-down brackets and shear connectors with nails, rivets or screws. Thus, the current construction method for platform CLT structures is less than ideal in terms of damage avoidance. The main objective of this study is to develop a low damage platform timber panelised structural system using a new configuration of slip friction devices in lieu of traditional c...
In terms of seismic performance, timber structures have been observed to perform well, in spite o... more In terms of seismic performance, timber structures have been observed to perform well, in spite of timber being an inherently non-ductile material. This is due mainly to the ductility of the steel-to-timber connections, and the way in which they interact with the timber material. If these connections are detailed to deform plastically, while keeping the timber members elastic, the overall structure achieves ductility. For nailed sheathing-to-framing shear walls and floor diaphragms, the New Zealand structural timber code, NZS3603:1993 [1] allows ductilities of up to four to be assumed. The issue with such an approach is that in a design level earthquake, the deformations required to achieve ductility often renders the structure irreparable, or at least requiring expensive repairs. Recent developments in engineered lumber products have seen the availability of mass timber panels of tremendous strength and stiffness. These include CLT (cross laminated timber) and LVL (laminated veneer lumber) panels. Under typical loading conditions these panels are essentially rigid, and the experiments of Popovski and Karacabeyli [2] demonstrate that the hysteretic behaviour is largely governed by the plastic deformations in the steel bracket connections attaching the walls to the floor. The hysteretic loops bear some resemblance to those of sheathing to framing shear walls, the main difference being they are more tightly pinched. The seismic performance of such walls is adequate, however, damage is still a consequence after an earthquake
IOP Conference Series: Materials Science and Engineering, 2019
The Initial Evaluation Procedure, conducted as part of Initial Seismic Assessment, is the main to... more The Initial Evaluation Procedure, conducted as part of Initial Seismic Assessment, is the main topic of this paper. An overview is provided of the eight key steps which define this procedure, and how they are used to determine ratio of New Building Standard (%NBS). The key steps are encapsulated in a programmed EXCEL worksheet (developed and current used in New Zealand) which takes into account various parameters and applies an algorithm to arrive at a preliminary assessed value. Actual examples of various buildings assessed using this procedure in recent years by authors are presented, and the results and some areas of interest are discussed.
IOP Conference Series: Materials Science and Engineering, 2019
In earthquake design philosophy non-linear inelastic damage is concentrated at predetermined loca... more In earthquake design philosophy non-linear inelastic damage is concentrated at predetermined locations in a structure, with the aim being to keep structural members critical for collapse avoidance, elastic. Non-linear elements can include the beam column joints in steel and reinforced concrete moment resisting frames, the nail connections of timber sheathing-to-framing shear walls, and the hold-down connectors of shear walls. To numerically model the seismic behaviour of these structures, it is critical to be able to quickly and simply model their respective hysteretic behaviours. It is particularly important to identify the parameters that will allow for the accurate replication of the degrading and pinching qualities of the force-displacement relationships. The authors summarise the use of a proprietary multi-linear plastic link, available in most finite element packages, in order to achieve this. A step-by-step process to model the links, from previous research, is described. Thi...
Earthquakes and Structures, 2015
In conventional seismic design, structures are assumed to be fixed at the base. To reduce the imp... more In conventional seismic design, structures are assumed to be fixed at the base. To reduce the impact of earthquake loading, while at the same time providing an economically feasible structure, minor damage is tolerated in the form of controlled plastic hinging at predefined locations in the structure. Uplift is traditionally not permitted because of concerns that it would lead to collapse. However, observations of damage to structures that have been through major earthquakes reveal that partial and temporary uplift of structures can be beneficial in many cases. Allowing a structure to move as a rigid body is in fact one way to limit activated seismic forces that could lead to severe inelastic deformations. To further reduce the induced seismic energy, slip-friction connectors could be installed to act both as hold-downs resisting overturning and as contributors to structural damping. This paper reviews recent research on the concept, with a focus on timber shear walls. A novel approach used to achieve the desired sliding threshold in the slip-friction connectors is described. The wall uplifts when this threshold is reached, thereby imparting ductility to the structure. To resist base shear an innovative shear key was developed. Recent research confirms that the proposed system of timber wall, shear key, and slip-friction connectors, are feasible as a ductile and lowdamage structural solution. Additional numerical studies explore the interaction between vertical load and slip-friction connector strength, and how this influences both the energy dissipation and self-centring capabilities of the rocking structure.
Structural Engineering and Mechanics, 2012
ABSTRACT
The use of rigid engineered timber panels, such as cross-laminated-timber, in construction is inc... more The use of rigid engineered timber panels, such as cross-laminated-timber, in construction is increasing around the world, particularly in Europe and Australasia. Typically the panels rely on nailed or screwed steel plates for hold-downs and shear keys. However, this can mean the level of ductility is difficult to quantify. Furthermore ductile wall behaviour will inevitably be associated with permanent damage to the connections. There have been calls from designers for a solution in which the level of ductility can be predicted and achieved with confidence. The authors propose a novel, yet simple, slipfriction device that limits activated forces on a structure during an earthquake by allowing it to slightly rock. An experimental LVL wall was fitted with these devices acting as hold-downs. The shear key consisted of steel rods bearing against upright steel plates along the base of the wall. Under cyclic displacement tests, the wall demonstrated excellent elasto-plastic behaviour. The predicted wall strength from theory, matched, in general, the forces measured, while ductility levels can be as large as the designer desires, within obvious limits. Even under only self-weight, the wall readily descended at one end, while uplifting at the other. The results suggest that structures of engineered lumber can perform with reliable levels of ductility and remain free from damage.
Journal of Constructional Steel Research, 2014
In recent decades, there has been increasing interest in the use of slip-friction connectors (or ... more In recent decades, there has been increasing interest in the use of slip-friction connectors (or slotted-bolt connectors) to dissipate energy in earthquake resistant structures. These devices, which rely on the friction controlled sliding of steel plates, have already seen implementation in buildings with steel moment resisting frames, with the intention that non-linear behaviour is concentrated at the connectors themselves, thereby protecting the structure from damage. The sliding mechanism of slip-friction connectors can be either symmetric or asymmetric. In the case of symmetric connectors, brass shims have, up until now, been required to ensure stable elastoplastic behaviour. However brass can be expensive, and sometimes difficult to procure. A new type of symmetric connector that entirely eliminates the need for shims of any kind is proposed. The centre-plate of the connector consists of abrasion resistant steel that is in direct contact with the mild steel plates between which it slides. From experimental testing, the performance of the proposed connector is found to be equal, if not superior, to that of traditional symmetric connectors with brass shims. The proposed connector maintains strength and stiffness over a large number of cycles of loading, and although minor pre-conditioning of the sliding surfaces may be required in order to improve behaviour, is nevertheless simpler, and likely to be cheaper, than its current equivalent with brass shims. The potential for galvanic corrosion is also avoided.
Engineering Structures, 2012
In the event of seismic overloading, timber shear walls have normally been designed to yield by a... more In the event of seismic overloading, timber shear walls have normally been designed to yield by allowing inelastic distortion of the sheathing-to-framing nail connections, thereby reducing the likelihood of brittle failure of timber chords or plywood sheathing. A new concept in shear wall design is presented. It involves the use of slip-friction connectors in lieu of traditional hold-down connectors. Slip-friction connectors, originally developed for the steel framing industry, rely on the mobilisation of friction across steel plates to resist loading up to a predetermined threshold. Upon this threshold being exceeded, relative sliding between the steel plates allows the shear wall to displace in an inelastic manner. This paper discusses the results of numerical analyses of timber shear walls which utilise slip-friction connectors. The results suggest that slip-friction connectors hold the promise of being able to effectively protect sheathing, framing, and nail connections from excessive stresses and deformations during earthquake events of design level intensity or higher. Walls with appropriately adjusted slip-friction connectors are highly ductile, are efficient dissipaters of seismic energy, and have a tendency to self-centre after an earthquake.
Construction and Building Materials, 2017
h i g h l i g h t s Abrasion resistant steel on mild steel produces stable sliding when surfaces ... more h i g h l i g h t s Abrasion resistant steel on mild steel produces stable sliding when surfaces are in the clean mill-scale condition. Where faying surfaces are polished so that bright steel is visible, severe frictional behaviour invariably arises. In one instance of polished on polished sliding, the test was terminated due to the surfaces friction welding together. The observed sliding behaviours of various surface types can be explained in the context of the adhesion theory of friction. The clean mill-scale condition should be specified in the design and implementation of slip-friction connectors.
Earthquake Engineering & Structural Dynamics, 2014
ABSTRACT