Elasto-plastic behaviour of a rigid timber shear wall with slip-friction connectors (original) (raw)
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A numerical study of the seismic behaviour of timber shear walls with slip-friction connectors
Engineering Structures, 2012
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.
Seismic behaviour of timber shear walls with load limiting slip-friction connectors
In the event of seismic overloading, timber shear walls have normally been designed to yield by allowing inelastic distortion of the sheathing to timber frame nailed connections, thereby reducing the likelihood of brittle failure of timber chords or plywood sheathing. A new concept in shear wall design involves the use of slip-friction connectors in lieu of standard hold-down connectors. Slip-friction connectors, originally developed for the steel framing industry, rely on the mobilization 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-but with minimal material yielding of nails or timber. Thus post-earthquake residual damage in the shear wall is expected to be significantly mitigated. This paper discusses the results of the numerical investigation of two types of timber shear wall with slip-friction connectors, standard and Midply. Results from a preliminary numerical analyses carried out by the authors are presented. The advantages of the shear wall incorporating slip-friction connectors are highlighted.
Experimental testing of a rocking timber shear wall with slip-friction connectors
Earthquake Engineering & Structural Dynamics, 2014
Allowing a structure to uplift and rock during an earthquake is one way in which activated forces can be capped and damage to the structure avoided or minimised. Slip-friction connectors (also known as slotted-bolt connectors) were originally developed for use in steel construction, but for this research have been adapted for use as hold-downs in an experimental 2.4 m 2.4 m rigid timber shear wall. A novel approach is used to achieve the desired sliding threshold in the connectors, and the wall uplifts when this threshold is reached. From a series of quasi-static cyclic tests, it is shown that slip-friction connectors can impart ductile and elasto-plastic characteristics to what would otherwise be essentially brittle structures. Because forces on the wall were capped by the slip-friction connectors to levels well below the design level, no damage to the wall was observed. Self-centring potential was also found to be excellent. The slip-friction connectors themselves are of a unique design and have proven to be robust and durable, adequately performing their duty even after almost 14 m of cumulative travel under high contact pressures. To resist base shear without unduly affecting rocking behaviour, a new type of shear-key is proposed and implemented, and a procedure developed to quantify its influence on overall wall behaviour.
A low damage and ductile rocking timber wall with passive energy dissipation devices
Earthquakes and Structures, 2015
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.
2014
In conventional design, structures are assumed to be fixed at the base. To reduce the impact of earthquake loading and to provide an economically feasible structure, minor damage is tolerated in the form of controlled plastic hinge development at predefined locations in the structure. Uplift is avoided, because it is considered to be the first stage of eventual collapse. However, observations of structural damage following major earthquakes reveal that partial and temporary uplift of structures have proven beneficial in many cases. Allowing a structure to move as a rigid body will limit seismic forces activated in the structure that lead to serious inelastic deformations. To further reduce the induced seismic energy, slip-friction connectors can be installed to act as hold-downs and as a significant contributor to energy dissipation. This paper provides a review of recent research on the concept, with a focus on timber shear walls. A novel approach is used to achieve the desired sli...
Seismic resistant rocking coupled walls with innovative Resilient Slip Friction (RSF) joints
Multi-story hybrid timber-steel structures are becoming progressively desirable owing to their aesthetic and environmental benefits and also to the relatively higher strength to weight ratio of timber. Moreover, there is an increasing public pressure to have low damage structural systems to minimize the destruction after severe earthquakes. A recent trend in the timber building industry is the use of cross laminated timber (CLT) wall systems. CLT is a relatively novel engineered wood based product well suited for multi-story structures. Latest research findings have shown that CLT buildings constructed with traditional steel connectors can experience high damage mainly because of stiffness degradation in the fasteners. It has been proven that friction joints can provide a perfectly elastoplastic behaviour and a stable hysteretic response. Up until now, the main disadvantage of the friction joints has been the undesirable residual displacements after an earthquake. This study presents a hybrid damage avoidant steel-timber wall system using the innovative Resilient Slip Friction (RSF) joint. The proposed system includes coupled timber walls and boundary steel column as the main lateral load resisting members. RSF joints are used as ductile links between the adjacent walls or between the walls and the steel boundary columns. The efficiency of the system has been investigated by experimental joint component tests on the RSF joint followed by reversed cyclic numeral analyses and dynamic non-linear time-history simulations on the wall system. The results confirmed that the proposed system has the potential to be recognised as an efficient lateral load resisting system.
Reliability assessment of timber shear walls under earthquake loads
2000
A modified version of the BRANZ procedure for lateral capacity rating of bracing walls was used to determine the sustainable lateral mass of a 910-mm wide '2x4' timber shear wall. The key modifications involve: (1) the use of a multi-criteria system identification method to determine a structural model that fits test data from both cyclic testing and pseudo-dynamic testing; and (2) probabilistic treatment of ground motions (i.e., using suites of site-specific earthquake records with 2%, 10% and 50% exceedance probability in 50 years as input loads in Monte Carlo simulation). Then the reliability index for the wall system that was rated according to the modified BRANZ procedure was estimated when subjected to a range of earthquake intensities in Tokyo. For this particular wall, we obtained reliability indices (at the safety limit state) ranging from 0.94 to 5.20, depending on the displacement capacity determined from the static cyclic test, and the suite of earthquakes from which the sustainable mass was calculated from. Thus, it is desirable to quantify and include the inherent uncertainty in displacement capacity and ground motions in the analysis. The method presented herein is general and can be applied to allow the direct use of laboratory data, from cyclic or pseudo-dynamic testing, for dynamic and seismic reliability analyses of lateral resisting systems with no distinct yield point.
Experimental and Numerical Analyses of New Massive Wooden Shear-Wall Systems
Buildings, 2014
Three innovative massive wooden shear-wall systems (Cross-Laminated-Glued Wall, Cross-Laminated-Stapled Wall, Layered Wall with dovetail inserts) were tested and their structural behaviour under seismic action was assessed with numerical simulations. The wall specimens differ mainly in the method used to assemble the layers of timber boards composing them. Quasi-static cyclic loading tests were carried out and then reproduced with a non-linear numerical model calibrated on the test results to estimate the most appropriate behaviour factor for each system. Non-linear dynamic simulations of 15 artificially generated seismic shocks showed that these systems have good dissipative capacity when correctly designed and that they can be assigned to the medium ductility class of Eurocode 8. This work also shows the influence of deformations in wooden panels and base connectors on the behaviour factor and dissipative capacity of the system.
Ductile Behavior of Timber Structures under Strong Dynamic Loads
Wood in Civil Engineering, 2017
Due to their comparatively low mass that implies reduced horizontal dynamic loads even during strong earthquakes, wood-made buildings might be a good choice in seismic prone regions. To meet the modern design philosophy requirements, however, such structures should be able to behave in a ductile way under exceptional events. By presenting a brief review of the latest developments in the field, this chapter investigates on when and to what extent historical and modern timber buildings may exhibit a ductile and dissipative behavior. A special focus is given to the crucial role of connections and to the difficulties involved by their mechanical model when carrying out codebased non-linear dynamic analyses. Although a ductile behavior is typically required under strong earthquakes, it is to note that a well-designed ductile structure may also be able to withstand other exceptional events as, for instance, tornadoes or blasts.