The paper presents the design and modelling of Cathedral Hill 2, a 15-storey timber building, planned for construction in Canada. The building is a 59-metre tall office-use construction with an all-timber structure where the lateral-load-resisting system consists of segmented Pres-Lam walls. The paper firstly presents the design philosophy, and the motivations for the use of the Pres-Lam system, which was mainly driven by serviceability limit-state wind loading. The final part of the paper shows the verification of the building’s dynamic behaviour using non-linear time-history analysis, showing that, although the lateral-load design is governed by serviceability limit-state wind deflections, earthquake demand must not be overlooked due to higher-mode amplifications.
Controlled rocking heavy timber walls (CRHTW) were originally developed in New Zealand as a lowdamage seismic force resisting system using Laminated Veneer Lumber (LVL). This paper examines one way of adapting them to regions of low-to-moderate seismicity in North America, using Cross-Laminated Timber (CLT) composed of Canadian timber species. In particular, the adaptation simplifies the CRHTW by omitting supplemental energy dissipation and minimizing the potential for long-term damage to the timber from the post-tensioning. Key assumptions that are used in the design and analysis stages are evaluated with regard to the difference between timber products, and the structural performance of a prototype CRHTW design is confirmed by nonlinear time history analysis. Despite the lack of supplemental energy dissipation, the prototype design performs well with negligible residual drifts and a median peak roof drift of 0.63%. Future research is identified for the continued development of the adapted CRHTW.
This study proposes an iterative direct displacement based design method for a novel steel-timber hybrid structure. The hybrid structure incorporates Cross Laminated Timber (CLT) shear panels as an infill in steel moment resisting frames. The proposed design method is applied to design 3-, 6-, and 9-story hybrid buildings with three bays and CLT infilled middle bay. Nonlinear time history analysis, using twenty earthquake ground motion records, is carried out to validate the performance of the design method. The results indicate that the proposed method effectively controls the displacements due to seismic excitation of the hybrid structure.
This thesis discusses a novel timber-steel core wall system for use in multi-storey buildings in high seismic regions. This hybrid system combines Cross Laminated Timber (CLT) panels with steel plates and connections to provide the required strength and ductility to core walled buildings. The system is first derived from first principles and validated in SAP2000. In order to assess the feasibility of the system it is implemented in the design of a 7-storey building based off an already built concrete benchmark building. The design is carried out following the equivalent static force procedure (ESFP) outlined by the National Building Code of Canada for Vancouver, BC. To evaluate the design bi-directional nonlinear time history analysis (NLTHA) is carried out on the building using a set of 10 ground motions based on a conditional mean spectrum. To improve the applicability of the hybrid system an energy based design methodology is proposed to design the timber-core walled building. The methodology is proposed as it does not rely on empirical formulas and force modification factors to determine the final design of the structure. NLTHA is carried out on the proposed methodology using 10 ground motions to evaluate the suitability of the method and the results are discussed and compared to the ESFP results.
New Zealand Society for Earthquake Engineering Conference
April 27-29, 2017, Wellington, New Zealand
With the increasing acceptance and popularity of multi-storey timber buildings up to 10 storeys and beyond, the influence of higher mode effects and diaphragm stiffness cannot be overlooked in design. Due to the lower stiffness of timber lateral load resisting systems compared with traditional construction materials, the effect of higher modes on the global dynamic behaviour can be more critical. The presence of flexible timber diaphragms creates additional vibration modes, which have the potential to interact with each other, increasing the seismic demand on the whole structure. This paper uses a parametric non-linear time-history analysis on a series of timber frame and wall structures with varying diaphragm flexibility to study their dynamic behaviour and to determine diaphragm forces. The analyses results showed that although higher mode effects play a significant role in the structural dynamic response, this increased demand can be successfully predicted with methods available in literature. The parametric analyses showed that the diaphragm flexibility did not significantly increase the shear and moment demand; however, stiff wall structures with flexible diaphragms experienced large inter-storey drifts measured at diaphragm midspan compared with the drift of the wall alone. As expected, the diaphragm forces observed from the time-history analyses were significantly higher than the forces derived from an equivalent static analysis, leading to a potentially unsafe design. The paper presents a simplified approach for evaluating these amplified peak inertial diaphragm forces.
Seismic torsional responses in buildings is a result of eccentricity in mass and stiffness distribution. Torsional irregularity is one of the major causes of severe damage and collapse of structures during an earthquake. In this study, effect of torsion on the structures is reviewed, the definition of torsional irregularity and the characteristic of the structure that leads to this type of irregularity is elaborated. The evolution of the methods to consider the effect of torsion in the National Building Code of Canada (NBCC) is reviewed and different methods to prevent torsional irregularity in the structures are discussed. Hybridization with Cross-Laminated Timber (CLT) is suggested as a new method to rectify the effect of torsional irregularity for different performance levels. Accordingly, the definition of hybridization and hybrid structure seismic behavior, CLT material specifications and CLT seismic performance is discussed. In order to evaluate the effect of CLT hybridization on buildings with torsional irregularity, a four-storey reinforced concrete (RC) structure with torsional irregularity is considered for Vancouver seismicity condition. SAP2000 software is used to conduct Linear Dynamic Analysis (LDA) and Non-Linear Time History Analysis (NLTHA) using eight different ground motion scaled to Vancouver design spectra. The effect of the CLT wall panel as shear wall on the in plane seismic base shear and inter-storey drift is shown using the linear and non-linear dynamic analysis. The result from the analysis compared to the code static values. The literature of Performance Based Seismic Design (PBSD) is reviewed. PBSD is used to determine the performance level of the original and hybrid building. The inter-storey drifts criteria defined in FEMA 356 guidelines is used for the purpose of NLTHA.
New Zealand Society for Earthquake Engineering Conference
April 27-29, 2017, Wellington, New Zealand
Pres-Lam is a post-tensioned rocking timber technology that has been developed over the last decade at the University of Canterbury. Pres-Lam overcomes a major challenge in timber construction, the development of a high strength moment connection, by tying mass timber elements together with high-strength steel post-tensioned tendons. In seismic areas, additional reinforcing can be added to the system increasing capacity as well as providing hysteretic damping. In 2010 Pres-Lam moved from laboratory testing to onsite implementation and has now been used in the construction of numerous building in New Zealand and around the world. This paper will present the lateral load design of the first Pres-Lam structure to be built in the United States: the Peavy Building at Oregon State University, Corvallis, Oregon. Peavy is a three-storey mass timber building within the College of Forestry. A glulam and CLT gravity structure support the timber-concrete-composite floor, which is made up of CLT panels spanning between glulam beams. The lateral load carrying capacity is provided in the two orthogonal directions by Pres-Lam walls fabricated from Cross Laminated Timber (CLT). The paper will present an overview of the design philosophy and the main motivations for the use of the Pres-Lam system, discuss the requirements for U.S. code compliance, and review the nonlinear time-history analysis of the Pres-Lam structure.
This paper presents the seismic design and analysis of a 20-storey demonstration wood building, which was conducted as a part of the NEWBuildS tall wood building design project. A hybrid lateral load resisting system was chosen for the building. The system consisted of shear walls and a shear core, both made of structural composite lumber, connected with dowel-type connections and heavy-duty HSK (wood-steel-composite) system. The core and the shear walls were linked with horizontal steel beams at each floor. The wood-based panel-to-panel interface was designed to be the main energy dissipating mechanism of the system. A detailed finite element model of this building was developed and non-linear time history analyses were performed using 10 earthquake motions. The results showed that the seismic response of the 20-storey demonstration building met the various design criteria and the design details are appropriate.
This paper presents a study on the seismic design of hybrid multi-storey wood buildings made of CLT and Light-Frame shear walls acting at the same level. Within the framework of the force-based method, the aim of this study is to propose a simple formulation in order to establish the value of the q-factor of the hybrid system which could be also implemented in seismic design codes such as Eurocode 8. This was achieved by analysing the results of nonlinear dynamic (time-history) analyses performed on a four storey case-study building with different combinations of CLT and Light-Frame shear walls.
Steel-timber hybrid structural systems offer a modern solution for building multi-story structures with more environmentally-friendly features. This paper presents a comprehensive seismic performance assessment for a kind of multi-story steel-timber hybrid structure. In such a hybrid structure, steel moment resisting frames are infilled with prefabricated light wood frame shear walls to serve as the lateral load resisting system (LLRS). In this paper, drift-based performance objectives under various seismic hazard levels were proposed based on experimental observations. Then, a numerical model of the hybrid structure considering damage accumulation and stiffness degradation was developed and verified by experimental results, and nonlinear time-history analyses were conducted to establish a database of seismic responses. The numerical results further serve as a technical basis for estimating the structure's fundamental period and evaluating post-yielding behavior and failure probabilities of the hybrid structure under various seismic hazard levels. A load sharing parameter was defined to describe the wall-frame lateral force distribution, and a formula was proposed and calibrated by the time-history analytical results to estimate the load sharing parameter. Moreover, earthquake-induced non-structural damage and residual deformation were also evaluated, showing that if designed properly, desirable seismic performance with acceptable repair effort can be obtained for the proposed steel-timber hybrid structural system.