Seismic resistant rocking coupled walls with innovative Resilient Slip Friction (RSF) joints (original) (raw)

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.

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.

Determination of the seismic performance factors for post-tensioned rocking timber wall systems

Earthquake Engineering & Structural Dynamics, 2016

Post-tensioned technologies for concrete seismic resistant buildings were first developed in the 1990s during the PREcast Seismic Structural Systems program. Among different solutions, the hybrid system proved to be the most resilient solution providing a combination of re-centering and energy dissipative contributions respectively by using post-tensioned tendons and mild steel reinforcement. The system, while providing significant strength and energy dissipation, reduces structural element damage and limits post-earthquake residual displacements. More recently, the technology was extended to laminated veneer lumber (LVL) structural members, and extensive experimental and numerical work was carried out and allowed the development of reliable analytical and numerical models as well as design guidelines. On the basis of the experimental and numerical outcomes, this paper presents the evaluation of the seismic performance factors for posttensioned rocking LVL walls using the FEMA P-695 procedure. Several archetype buildings were designed considering different parameters such as the building and story height, the type of seismic resistant system, the magnitude of gravity loads and the seismic design category. Lumped plasticity models were developed for each index archetype to simulate the behavioral aspects and collapse mechanisms. Non-linear quasistatic analyses were carried out to evaluate the system over-strength factor; moreover, non-linear time history analyses were performed using the incremental dynamic analysis concept to assess the collapse of each building. From the results of quasi-static and dynamic analyses the response modification factor, R, system over-strength factor, Ω 0 , and deflection amplification factor, C d , values of, respectively, 7, 3.5 and 7.5 are recommended.

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.

Seismic Behaviour of Cross-Laminated Timber Structures

2012

FPInnovations has undertaken a multi-disciplinary project on determining the structural properties of a typical CLT construction. One of the important parts of the project is quantifying the seismic resistance of structures with CLT panels. In this paper, results from a series of quasi-static monotonic and cyclic tests on CLT wall panels are presented and discussed. CLT wall panels with various configurations and connection details were tested. Wall configurations include single panels without openings with three different aspect ratios, panels with openings, as well as multi-panel walls with step joints and fasteners between them. Connections for securing the walls to the foundation include off-the-shelf steel brackets with annular ring nails, spiral nails, and screws, a combination of steel brackets and hold-downs, and custom made brackets with timber rivets. In addition, results from two storey configurations that include two walls and a CLT slab in between are presented and disc...

Elasto-plastic behaviour of a rigid timber shear wall with slip-friction connectors

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.

Monotonic Tests on Beam-To-Column Joint with Steel Link for Timber Seismic Resistant Structures

2023

For the design of dissipative heavy timber frame structures, in the context of modern seismic design approach based on the mechanical triad of strength, stiffness and ductility, brittle timber failure modes can be avoided by integrating modern timber connection technology into hybrid timber-steel system. The overall seismic performance can be improved, entrusting the dissipation function to ad hoc conceived devices, as an alternative to connections. Steel links located at the ends of the beams are very promising solutions, which can develop plastic hinges, thus providing a ductile behaviour, with a significant dissipative capacity. Besides timber members, as well as connections, to be designed with an adequate over-strength, can remain in elastic field. In this perspective, the paper illustrates the mechanical characterisation through monotonic tests of two different configurations of timber beam-to-column joint with steel link for heavy timber frames, consisting of a timber element connected to a steel link by means of a steel end-plate and gluedin steel rods. The experimental results indicate a satisfactory agreement with the theoretical ones, therefore the suitability of the system and of the design criteria.

Lateral Performance of Cross-laminated Timber Shear Walls: Analytical and Numerical Investigations

Modular and Offsite Construction (MOC) Summit Proceedings

Cross-laminated timber (CLT) is becoming a viable option for mid-rise buildings in North America. CLT walls are very effective in resisting lateral forces resulting from wind and seismic loads, yet no standard provisions are available to estimate the resistance of CLT shear walls under lateral loading. The present research investigated CLT shear wall’s performance by evaluating the preferred kinematic rocking behaviour. An analytical procedure was proposed to estimate the resistance of CLT shear walls in a platform type construction. Finite element models of CLT shear with various brackets and hold-downs connections were developed. The models were validated against experimental results. Furthermore, a parametric study on CLT shear walls with the variation of type and number of connectors was conducted. The resistance estimated from parametric study and against analytical were compared. The proposed formulas can be useful tool for the design of CLT platform-type buildings, however, r...

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.