The high performance in-plane of cross laminated timber (CLT) panels has created a potential for the use of CLT members act as diaphragms in steel structures. The behaviour of this diaphragm system depends strongly on the connections involved in linking the panels together and to the steel members. A study of the connections at both locations was made using experimental testing of two connection designs for the panel-to-panel case, and the development of a staggered lag screw connection for the panel-to-steel beam case. The results showed good performance for the double spline and fully-threaded inclined screws panel-to-panel connections. The lag screw connection showed high strength, stiffness, and ductility. The CSA Standard O86-09 was found to best predict the strength of both types of connections. Characteristic design stiffness values were presented for the stiffness at low levels of displacement and the initial, elastic stiffness.
In this paper, we discuss the structural design of one of the tallest timber-based hybrid buildings in the world: the 18 storey, 53 meter tall student residence on the campus of the University of British Columbia in Vancouver. The building is of hybrid construction: 17 storeys of mass wood construction on top of one storey of concrete construction. Two concrete cores containing vertical circulation provide the required lateral resistance. The timber system is comprised of cross-laminated timber panels, which are point supported on glued-laminated timber columns and steel connections between levels. In addition to providing more than 400 beds for students, the building will serve as an academic site to monitor and study its structural performance, specifically horizontal building vibration and vertical shrinkage considerations. We present the challenges relating to the approval process of the building and discuss building code compliance issues.
Recent years have seen more architects and clients asking for tall timber buildings. In response, an ambitious timber community has been proposing challenging plans and ideas for multi-storey commercial and residential timber buildings. While engineers have been intensively looking at gravity-load-carrying elements as well as walls, frames and cores to resist lateral loads, floor diaphragms have been largely neglected.
Complex floor geometries and long span floor diaphragms create stress concentrations, high force demand and potentially large deformations. There is a lack of guidance and regulation regarding the analysis and design of timber diaphragms so structural engineers need a practical alternative to simplistic equivalent deep beam analysis or costly finite element modelling.
This paper proposes an equivalent truss method capable of solving complex geometries for both light timber framing and massive timber diaphragms. Floor panels are discretized by equivalent diagonals, having the same stiffness as the panel including its fasteners. With this method the panel unit shear forces (shear flow) and therefore fastener demand, chord forces and reaction forces can be evaluated. Because panel stiffness is accounted for, diaphragm deflection, torsional effects and transfer forces can also be assessed.
Project contact is Christopher Higgins at Oregon State University
This project will optimize the strength, stiffness, vibration characteristics, acoustic qualities and fire resistance of cross-laminated floor systems utilizing a composite concrete and cross-laminated timber product. This project includes development, testing and optimization of an economical shear connector (to connect the CLT panel to the concrete slab) that will be compared with existing screw and steel plate solutions. The resulting prototype floor system will be tested at full scale.
Cross Laminated Timber (CLT) is a lightweight construction material with a strength and stiffness comparable to Reinforced Concrete (RC). A crucial aspect of fully realizing the potential of CLT as a structural material is ability to interconnect it to similar and dissimilar materials. A study of connections was made through in-plane shear and tension tests on half-lapped and single-spline connections that make edge-toedge jointing between CLT panels using screws. A novel aspect of the study is investigation of how placing washers under screw heads alters stiffness and strengths of connections. Subsidiary axial load tests on screws assisted explanation of the shear and tension test results. Conclusions include the importance of accounting for large displacement effects on how screws transfer forces across joint-planes, and need to improve current generation connection design methods so that they account for effects of eccentricities that result from construction arrangement and detailing decision.
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.
The structural use of wood in North America is dominated by light wood-frame construction used in low-rise and – more recently – mid-rise residential buildings. Mass timber engineered wood products such as laminatedveneer-lumber and cross-laminated timber (CLT) panels enable to use the material in tall and large wood and woodbased hybrid buildings. The prospect of constructing taller buildings creates challenges, one of them being the increasein lateral forces created by winds and earthquakes, thus requiring stronger hold-down devices. This paper summarises the experimental investigation on the performance a high-capacity hold-down for resisting seismic loads in tall timberbased structural systems. The connection consists of the Holz-Stahl-Komposit-System (HSK)™ glued into CLT with the modification that ductile steel yielding was allowed to occur inside the CLT panel. The strength, stiffness, ductility and failure mechanisms of this connection were evaluated under quasi-static monotonic and reversed cyclic loading. The results demonstrate that the modified hold-down-assembly provides a possible solution for use in tall timber-based structures in high seismic zones
Mass timber is emerging as a viable form of construction around the world in new markets for wood buildings. The entrance into these markets has driven the demand for more knowledge to enable designs alongside other structural materials such as steel and reinforced concrete. Large, in-plane tests on cross-laminated timber (CLT) diaphragms (4570 mm x 4570 mm [15 ft x 15 ft]) are used to quantify ductility through the diaphragm force reduction factor (Rs) from ASCE 7-16, m-factors from ASCE 41-17, and validate common methodologies of mass timber design currently implemented in structural engineering practice. The tests demonstrate that cross-laminated timber can function well as a diaphragm with a mean Rs value of 1.19 at indicate a ductility like precast concrete diaphragms with R_s=0.7-1.4. Like precast concrete systems, cross-laminated timber diaphragms depend heavily on the inter-panel connections for a ductile design and will require several categories to classify the types of CLT systems. Analysis methods from ASTM E455 validate the assumptions that a CLT diaphragm is shear-controlled in its behavior for purposes of determining Rs. M-factors are an indirect measurement of the nonlinear deformation capacity of a component and are used as a multiplier to the expected strength of a component. The m-factors observed (0.46 to 1.9 for Immediate Occupancy to Collapse Protection performance levels, respectively) resulted in lower than values from previous studies on similar panel-to-panel connections. The initial stiffness of the large diaphragm panel-to-panel connections, 6.86 kN/mm (39.8 kip/in), were lower than the spline stiffness estimates of 11.5 kN/mm (65.7 kip/in) based on individual fastener tests. The hysteretic loading resulted in lower spline stiffnesses 4.37 kN/mm (24.9 kip/in) while the monotonic testing showed a mean spline stiffness of 9.04 kN/mm (52.5 kip/in). Calculating CLT diaphragm displacement based on NDS methods proved to be conservative compared to test results for the purposes of determining ASCE 7-16 diaphragm flexibility status.
Recently, Canadian building regulations have allowed construction of light-frame wood buildings up to six storeys. Even though equivalent static force procedure (ESFP) is generally used for the seismic design of such buildings, in cases of irregular structures and in high seismic zones a linear dynamic analysis (LDA) is required by the code. However, commercial software has not yet been adapted to the dynamic analysis of this type of structures. In this paper, a design procedure for light-frame wood shear walls using a braced frame model and LDA is proposed and the potential for design optimisation is presented for a six-storey light-frame wood building located in Quebec City in the Eastern Canada. Comparisons between the proposed LDA procedure and ESFP based on the shear distribution, overturning moments, interstorey drifts and total inelastic deflections are shown. Structural advantages of using the proposed LDA are demonstrated.
The cross laminated timber (CLT) technology is nowadays a well-known construction system, which that can be applied to several typologies of residential and commercial buildings. However some critical issues exist which limit the full development of the CLT construction technology: problems in handling, difficulty in assembling...