Openings are usually required to allow services like plumbing, sewage pipes and electrical
wiring to run through beams. This prevents an extra depth of the floor/ceiling, while preserving architectural considerations. The introduction of large opening causes additional tension perpendicular to grain in timber beams. The low tensile strength perpendicular to grain of wood allows crack formation. Crack propagation around the hole considerably decreases the load-carrying capacity of the beam. However, in most cases, crack formation and propagation around
the hole can be prevented by the use of an appropriate reinforcement. Screw, glued-in rods, and plywood are alternative options for the reinforcement. Design of the reinforcement requires that the working mechanism of the reinforcement is fully understood and properly addressed. In addition, reinforcement should be designed for actions produced in the section of the beam weakened by the hole. The current paper uses a simple truss model around the opening to calculate the tensile force in the reinforcement. Two simple formulations for design of the reinforcement are derived and compared with numerical and experimental results, showing an overall good correspondence. The proposed truss model can be considered for incorporation in future codes of practice.
This paper presents a numerical study conducted on a seven-story timber building made of cross-laminated (X-lam) panels, equipped with a linear translational tuned mass damper (TMD). The TMD is placed on the top of the building as a technique for reducing the notoriously high drifts and seismic accelerations of these types of structures. TMD parameters (mass, stiffness, and damping) were designed using a genetic algorithm (GA) technique by optimizing the structural response under seven recorded earthquake ground motions compatible, on average, with a predefined elastic spectrum. Time-history dynamic analyses were carried out on a simplified two-degree-offreedom system equivalent to the multistory building, while a detailed model of the entire building using two-dimensional elastic shell elements and elastic springs for modeling connections was used as a verification of the evaluated solution. Several comparisons between the response of the structure with and without TMD subjected to medium- and high-intensity recorded earthquake ground motions are presented, and the effectiveness and limits of these devices for improving the seismic performance of X-lam buildings are critically evaluated.
The paper presents a numerical study conducted on a seven storey cross-laminated (X-lam) buildings equipped with translational Tuned Mass Dampers (TMD’s), as a technique for reducing the notoriously high drifts and maximum seismic accelerations of these types of structures. The building was modelled in the finite element software package Abaqus using 2D elastic shell elements and non-linear springs, which were implemented as an external user subroutine and properly calibrated to simulate the cyclic behavior of connectors in X-lam buildings. The used TMD device is linear, and placed on the top of the building. Time-history dynamic analyses were carried out under natural earthquake ground motions. Several comparisons between the response of the structure with and without TMD are presented, and the effectiveness and limits of these devices to improve the seismic performance of X-lam buildings are critically discussed.
This paper describes the structural design of low-rise multi-storey timber buildings using a new and exciting structural system. This system, originally developed for use with pre-cast concrete, combines un-bonded post-tensioning and additional energy dissipaters, providing a recentering capability after the earthquake, while greatly reducing the structural damage. This new structural system can be used in multi-storey buildings, with large structural timber members made from laminated veneer lumber (LVL) or glulam timber, with lateral loads resisted by prestressed timber frames or walls, separately or in combination. A case study of a six storey timber office building in a moderate seismic area is analysed and a virtual design is carried out, allowing investigation of different methods of structural analysis, and development of many construction and connection details for rapid construction. Total building cost is compared to equivalent steel and reinforced concrete options.
This paper describes the design of a novel semi-prefabricated LVL-concrete composite floor that has been developed in New Zealand. In this solution, the floor units made from LVL joists and plywood are prefabricated in the factory and transported to the building site. The units are then lifted onto the supports and connected to the main frames of the building and to the adjacent units. Finally, a concrete topping is poured on top of the units in order to form a continuous slab connecting all the units. Rectangular notches cut from the LVL joists and reinforced with coach screws provide the composite action between the concrete slab and the LVL joists. This system proved to be an effective modular solution that ensures rapid construction. A design procedure based on the use of the effective flexural stiffness method, also known as the “gamma method” is proposed for the design of the composite floor at ultimate and serviceability limit states, in the short and long term. By comparison with the experimental results, it is shown that the proposed method leads to conservative design. A step-by-step design worked example of this novel semi-prefabricated composite floor concludes the paper.
The aim of this document is to report the state of the art in terms of research and practice of Timber-Concrete Composite (TCC) systems, in order to summarize the existing knowledge in the single countries and to develop a common understanding of the design of TCC.
This report was made within the framework of WG4-Hybrid Structures within COST Action FP1402. It intends to reflect the information and studies available around the world, but especially in Europe through the active contribution and participation of experts from various countries involved in this Action.
The paper discusses experimental and numerical seismic analyses of typical connections and wall systems used in cross-laminated (X-Lam) timber buildings. An extended experimental programme on typical X-Lam connections was performed at IVALSA Trees and Timber Institute. In addition, cyclic tests were also carried out on full-scale single and coupled X-Lam wall panels with different configurations and mechanical connectors subjected to lateral force. An advanced non-linear hysteretic spring to describe accurately the cyclic behaviour of
connections was implemented in ABAQUS finite element software package as an external subroutine. The FE model with the springs calibrated on single connection tests was then used to reproduce numerically the behaviour of X-Lam wall panels, and the results were compared with the outcomes of experimental full-scale tests carried out at IVALSA. The developed model is suitable for evaluating dissipated energy and seismic vulnerability of X-Lam structures.
With the increased usage of Cross Laminated Timber (CLT) in the United States, research efforts have been focused on demonstrating CLT as an effective Seismic Force Resisting System (SFRS). Presented in this paper are the findings of full-scale shake table tests of a two-story 223 m2 (2400 ft2) building with two sets of CLT shear walls on the first and second story. The testing consisted of three phases, each with a unique wall configuration, but only the first phase is presented herein, which consisted of a shear wall with 4:1 aspect ratio CLT panels. The structure was subjected to ground motions scaled to intensities that correspond to a Service Level Earthquake (SLE), Design Base Earthquake (DBE), and Maximum Considered Earthquake (MCE) respectively. In all phases and motions the structure performed well and was in accordance with FEMA collapse prevention requirements for each motion intensity.
Notched connections are extensively used in timber-concrete (TC) composite beams and floors. Their main advantage is a significantly higher shear strength and stiffness compared to mechanical fasteners. Several mechanical and geometrical aspects, however, should be properly taken into account for design optimization of notched connections, as they strongly affect their structural performance and the corresponding failure mechanisms. In this paper, a preliminary Finite-Element (FE) numerical investigation is carried out by means of full 3D numerical models. The mechanical behaviour of each connection component (e.g. the reinforced concrete topping, the steel coach screw, the timber beam) is properly implemented. Shear or crushing failure mechanisms in the concrete, possible plasticization of the coach screw, as well as longitudinal shear or tension perpendicular to the grain failure mechanisms in the timber beam are taken into account using cohesive elements, damage material constitutive laws and appropriate surface-tosurface interactions. The results of parametric FE studies are compared to experimental data derived from literature, as well as to the results of simplified analytical models, demonstrating that the FE model is capable to capture the experimental behaviour of the connection including the failure mechanisms.
16th European Conference on Earthquake Engineering
Research Status
Complete
Summary
The NHERI TallWood project is a U.S. National Science Foundation-funded four-year research project focusing on the development of a resilient tall wood building design philosophy. One of the first major tasks within the project was to test a full-scale two-story mass timber building at the largest shake table in the U.S., the NHERI at UCSD’s outdoor shake table facility, to study the dynamic behaviour of a mass timber building with a resilient rocking wall system. The specimen consisted of two coupled two-story tall post-tensioned cross laminated timber rocking walls surrounded by mass timber gravity frames simulating a realistic portion of a building floor plan at full scale. Diaphragms consisted of bare CLT at the first floor level and concrete-topped, composite CLT at the roof. The specimen was subjected to ground motions scaled to three intensity levels representing frequent, design basis, and maximum considered earthquakes. In this paper, the design and implementation of this test program is summarized. The performance of the full building system under these different levels of seismic intensity is presented.
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