Many of the 1,400 timber bridges in Minnesota do not meet present day standards. Some of these bridges can be improved rather than replaced. When the desired service level can be attained by widening a bridge six feet or less, the bridge can be retrofitted by placing a second, wider, transverse deck onto the existing deck and substructure. Bridge components must be carefully inspected prior to a retrofit project. The retrofit of Bridge #6641 in Sibley County is a good example. First, the bituminous surface was removed. A longitudinal beam supported the extended deck. Grout was poured and leveled and then nail-laminated panels were laid transversely. A bituminous surface was laid over the full width of the new deck. The cost of the project was $51,632. (Replacing the bridge was estimated to take 2-3 years and cost $215,000.) The county quantified the strength change and load distribution characteristics by performing static and dynamic load tests before and after the retrofit. Adding a second deck effectively decreased the static deflections and improved the transverse load distribution. Nail-laminated timber bridge #2642, also in Sibley County, was retrofitted in 1992 and load-tested again in 1995. All dynamic deflections were lower than those of the post-retrofit tests in 1992. This improvement can be explained in part by the drying of the moisture that was introduced into the bridge deck during grouting. A retrofitted timber bridge is expected to last an additional 20-40 years.
Timber construction has become completely modernized. It has gained considerably in market share with respect to competing building materials and is dominated by systems such as frame and solid timber construction.
Every timber construction is determined by its structure. Hence it is essential to know the connections and relationships from the design stage right through to the construction phase. Systems in Timber Engineering takes a whole new approach to this subject. It is a comprehensive, analytical, and visually organized treatment, from the simple single-family house to the large-scale multistore structure. It includes the building envelope, which is so important for saving energy, and systems for ceilings and interior dividing walls, which are so essential from the vantage point of construction.
This work uses plans, schematic drawings, and pictures to show the current and forward-looking state of the technology as applied in Switzerland, a leading country in the field of timber construction.
The main sources of lateral loads on buildings are either strong winds or earthquakes. These lateral forces are resisted by the buildings’ Lateral Load Resisting Systems (LLRSs). Adequate design of these systems is of paramount importance for the structural behaviour in general. Basic procedures for design of buildings subjected to lateral loads are provided in national and international model building codes. Additional lateral load design provisions can be found in national and international material design standards. The seismic and wind design provisions for engineered wood structures in Canada need to be enhanced to be compatible with those available for other materials such as steel and concrete. Such design provisions are of vital importance for ensuring a competitive position of timber structures relative to reinforced concrete and steel structures.
In this project a new design Section on Lateral Load Resisting Systems was drafted and prepared for future implementation in CSA O86, the Canadian Standard for Engineering Design in Wood. The new Section was prepared based on gathering existing research information on the behaviour of various structural systems used in engineered wood construction around the world as well as developing in-house research information by conducting experimental tests and analytical studies on structural systems subjected to lateral loads. This section for the first time tried to link the system behaviour to that of the connections in the system. Although the developed Section could not have been implemented in CSA O86 in its entirety during the latest code cycle that ended in 2008, the information it contains will form the foundation for future development of technical polls for implementation in the upcoming editions of CSA O86.
Some parts of the developed Section were implemented in the 2009 edition of CSA O86 as five separate technical polls. The most important technical poll was the one on Special Seismic Design Considerations for Shearwalls and Diaphragms. This technical poll for the first time in North America includes partial capacity design procedures for wood buildings, and represents a significant step forward towards implementing full capacity-based seismic design procedures for wood structures. Implementation of these design procedures also eliminated most of the confusion and hurdles related to the design of wood-based diaphragms according to 2005 National Building Code of Canada. In other polls, the limit for use of unblocked shearwalls in CSA O86 was raised to 4.8 m, and based on the test results conducted during the project, the NLGA SPS3 fingerjoined studs were allowed to be used as substitutes for regular dimension lumber studs in shearwall applications in engineered buildings in Canada.
With the US being the largest export market for the Canadian forest products industry, participation at code development committees in the field of structural and wood engineering in the US is of paramount importance. As a result of extensive activities during this project, for the first time one of the AF&PA Special Design Provisions for Wind and Seismic includes design values for unblocked shearwalls that were implemented based on FPInnovations’ research results. In addition, the project leader was involved in various aspects related to the NEESWood project in the US, in part of which a full scale six-storey wood-frame building will be tested at the E-Defense shake table in Miki, Japan in July 2009. Apart from being built from lumber and glued-laminated timber provided from Canada, the building will also feature the innovative Midply wood wall system that was also invented in Canada. The tests are expected to provide further technical evidence for increasing the height limits for platform frame construction in North America.
Building construction - Design
Earthquakes, Effect on building construction
Glued joints - Finger
Grading - Lumber
In October 2007 a series of seismic tests were carried out on a 7-storey building made of cross laminated (XLam) wooden panels in natural scale on a shaking table E-Defence in Japan within the SOFIE project. The paper presents calculation procedure, prediction of dynamic behaviour of the tested structure excited by the earthquake record "Kobe JMA 1995" and comparison between predicted, that means calculated and measured response. Due to blind prediction approach some construction details were not known before dynamic time history response calculation. Therefore some assumptions, engineering judgment and rough static analyses were needed to define all construction parts which were in modelling approach assumed as important and could have had influence on dynamic response of the analyzed structure. The most important assumptions related to the definition of the stiffness and load bearing capacity of mechanical connections, types of anchors and their positions in each floor level, were determined on the basis of static analysis where the structure was loaded with equivalent horizontal seismic forces and then were used in dynamic analysis. A mathematical model was developed in program SAP2000 where modal and time history analyses were carried out. Comparison of calculated and measured results is described and evaluated on the basis of the model assumptions and its simplification.
The general objective of this study is to gain a better knowledge on the shear strength of glulam subjected to predominant shear loading and with different boundary conditions. Specific objectives include the following:
- Propose a practical setup for testing glulam in shear which does not generate too large secondary stresses in the specimen, e.g. perpendicular to the grain stresses.
- Investigate the shear strength of glulam specimens both with I-cross section and with rectangular cross section.
- Investigate the influence of growth ring orientation on the shear strength of glulam.
This paper illustrates a research project about the calculation and design of Cross Laminated Timber (CLT) elements stressed by concentrated loads. Its focus lies on the shear design of CLT-elements next to punctual supports including reinforcements with self-tapping screws with continuous threads in areas of high shear stresses. Different influencing parameters on the distribution of shear forces next to a punctual support were evaluated by using comparative FEM-analyses. In the course of laboratory tests material-mechanical principles were determined to consider the interaction of rolling shear stresses and compression perpendicular to the grain. In addition to FEM simulations several experimental tests were carried out to describe the load bearing behaviour and the strengthening effect of CLT-elements reinforced by self-tapping screws. The investigations aim at developing a design concept including the effects mentioned above.
Characteristics of the Radio-Frequency/Vacuum Drying of Heavy Timbers for Post and Beam of Korean Style Housings Part II: For Korean Red Pine Heavy Timbers with 250 × 250 mm, 300 × 300 mm in Cross Section and 300 mm in Diameter, and 3,600 mm in Length
This study examined the characteristics of radio-frequency/vacuum dried Korean red pine (Pinus densoflora heavy timbers with 250 × 250 mm (S), 300 × 300 mm (L) in cross section and 300 mm in diameter, and 3,600 mm in length, which were subjected to compressive loading after a kerf pretreatment. The following results were obtained : The drying time was short and the drying rate was high in spite of the large cross section of specimens. The moisture gradient inall specimens was gentle in both longitudinal and transverse directions owing to dielectric heating. The shrinkage of the width in the direction perpendicular to was 21 percent ~ 76 percent of that of the thickness of square timbers in the direction parallel to the mechanical pressure. The casehardening for all specimens was very slight because of significantly reduced ratio of the tangential to radial shrinkage of specimens and kerfing. The surface checks somewhat severely occurred although the occurrence extent of the surface checks on the kerfed specimens was slight compared withthat on the control specimen.
Light-frame shearwall assemblies have been successfully used to resist gravity and lateral loads, such as earthquake and wind, for many decades. However, there is a need for maintaining the structural integrity of such buildings even when large openings in walls are introduced. Wood portal frame systems have been identified as a potential alternative to meet some aspects of this construction demand. The overarching goal of the research is to develop wood portal frame bracing systems, which can be used as an alternative or in combination with light-frame wood shearwalls. This is done through investigating the behavior of wood portal frames using the MIDPLY shearwall framing technique. A total of 21 MIDPLY corner joint tests were conducted with varying bracing details. Also, a finite element model was developed and compared with test results from the current study as well as studies by others. It was concluded from the corner joint tests that the maximum moment resistance increased with the addition of metal straps or exterior sheathings. The test results also showed a significant increase in the moment capacity and rotational stiffness by replacing the Spruce-Pine Fir (SPF), header with the Laminated Veneer Lumber (LVL) header. The addition of the FRP to the standard wall configuration also resulted in a significant increase in the moment capacity. However, no significant effect was observed on the stiffness properties of the corner joint. The FE model was capable of predicting the behavior of the corner joints and the full-scale portal frames with realistic end-conditions. The model closely predicted the ultimate lateral capacity for all the configurations but more uncertainty was found in predicting the initial stiffness.The FE model used to estimate the behavior of the full-scale portal frames constructed using the MIDPLY framing techniques showed a significant increase in the lateral load carrying capacity when compared with the traditional portal frame. It was also predicted using the full-scale FE model that the lateral load carrying capacity of the MIDPLY portal frame would increase with the addition of the metal straps on exterior faces. A parametric study showed that using a Laminated Strand Lumber (LSL) header increased the lateral load carrying capacity and the initial stiffness of the frames relative to the SPF header. The study also showed that there was an increase in the capacity if high strength metal straps were used. Doubling of the nail spacing at header and braced wall segment had a considerable effect on the lateral capacity of portal frame. Also, the initial stiffness was reduced for all the configurations with the doubling of the nail spacing at the header and braced wall segment in comparison with the reference frame.
This paper reports the results of experimental push-out tests on three different types of timber–concrete composite (TCC) connections, including normal screw, SFS and bird-mouth. The load-slip diagrams obtained from lab tests are employed to calculate the slip modulus of the connections for serviceability, ultimate and near collapse cases based on Eurocode 5 recommendations. Additionally, four full-scale TCC beams with normal screw, SFS and bird-mouth are constructed and tested under four-point bending within the serviceability load range to verify the slip modulus of connections which derived from the push-out tests. Further, based on the experimental results and using nonlinear regression, an analytical model each one of the connections is derived which can be easily incorporated into nonlinear FE analyses of TCC beams.
This thesis presents a state of the art on moisture induced stresses in glulam, complemented with own findings. These are covered in detail in the appended papers. The first objective was to find a suitable model to describe moisture induced stresses, in particular with respect to mechanosorption. A review of existing models led to the conclusion that the selection of correct material parameters is more critical to obtain reliable results than the formulation of the mechanosorption model. A series of laboratory tests was thus performed in order to determine the parameters required for the model and to experimentally measure moisture induced stresses in glulam subjected to one dimensional wetting/drying. Special attention was paid to using glulam from the same batch for all the experimental measurements in order to calibrate the numerical model reliably. The results of the experiments confirmed that moisture induced stresses are larger during wetting than during drying, and that the tensile stresses could clearly exceed the characteristic tensile strength perpendicular to grain.