Image: Supplied.

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The prototype being reassembled in the grounds of the university. It came through the February earthquake undamaged and proved the technology worked.

Image: Stephen Dickens. The prototype showcases the technology behind post-tensioned LVL timber buildings. Post-tensioned timber framed buildings — an idea born twenty years ago — has now become a commercial reality. He is Christchurch born and bred and did his first degree in engineering at the University of Canterbury in the late s. It was while he was studying at Columbia he moved away from steel and concrete and developed a keen interest in wood as a structural material and that interest ultimately led him to sell his shares in his company, and join the University of Canterbury.

He is now Professor of Timber Design at the university, where he teaches and researches structural design. That meant that back then research into earthquake engineering tended to take a back seat and instead he did a lot of work in other areas like fire safety and structural engineering. He says the severity of the February earthquake in particular was exceptional. The horizontal and vertical accelerations were some of the highest ever recorded anywhere in the world.

We design for accelerations of around 1G and the vertical acceleration was near 2Gs.

seismic design of timber structures

The buildings that fared best in the earthquakes were ones that had seismic design features and wooden buildings, in particular, engineered timber buildings, he says. Another solution, he says, is rocking frames and walls where buildings move in an earthquake then snap back into position with no damage.

Importantly, both these buildings were able to be used right after the quakes, providing medical assistance to those who required it. Business continuity is a happy outcome of seismic design.

The story goes that colleague and associate professor Stefano Pampinin — who is managing the research programme and is currently on the advisory board for the Canterbury Earthquakes Royal Commission — had long used a timber model to teach students the concept behind PRESSS. So they did. The university started research in earnest and sourced funding from the Ministry of Science and Innovation and set up a research consortium. Professor Buchanan is taking a few of us on a tour of the labs.

I see testing machines, pulleys, chains and lots of equipment. Looking around I see what he means. Huge, crumbled lumps of reinforced concrete litter the lab.

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Professor Buchanan points to a large blue structure with steel chained to it. So our long-term plan is to build something much better than that. The building proved the technology works and has suffered no damage through the February earthquake and the numerous aftershocks since.In the eurocode series of European standards EN related to constructionEurocode 8: Design of structures for earthquake resistance abbreviated EN or, informally, EC 8 describes how to design structures in seismic zoneusing the limit state design philosophy.

Its purpose is to ensure that in the event of earthquakes:. The random nature of the seismic events and the limited resources available to counter their effects are such as to make the attainment of these goals only partially possible and only measurable in probabilistic terms. The extent of the protection that can be provided to different categories of buildings, which is only measurable in probabilistic terms, is a matter of optimal allocation of resources and is therefore expected to vary from country to country, depending on the relative importance of the seismic risk with respect to risks of other origin and on the global economic resources.

Special structures, such as nuclear power plants, offshore structures and large dams, are beyond the scope of EN EN contains only those provisions that, in addition to the provisions of the other relevant Eurocodes, must be observed for the design of structures in seismic regions. It complements in this respect the other EN Eurocodes. Eurocode 8 comprises several documents, grouped in six parts numbered from EN to EN EN applies to the design of buildings and civil engineering works in seismic regions.

It is subdivided in 10 Sections, some of which are specifically devoted to the design of buildings.

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EN covers the seismic design of bridges in which the horizontal seismic actions are mainly resisted through bending of the piers or at the abutments; i. It is also applicable to the seismic design of cable-stayed and arched bridges, although its provisions should not be considered as fully covering these cases. In ENprinciples and application rules for the seismic design of the structural aspects of facilities composed of above-ground and buried pipeline systems and of storage tanks of different types and uses, as well as for independent items, such as for example single water towers serving a specific purpose or groups of silos enclosing granular materials are addressed.

EN establishes the requirements, criteria, and rules for the siting and foundation soil of structures for earthquake resistance. It covers the design of different foundation systems, the design of earth retaining structures and soil-structure interaction under seismic actions. EN establishes requirements, criteria, and rules for the design of tall slender structures: towers, including bell-towers, intake towers, radio and TV-towers, masts, chimneys including free-standing industrial chimneys and lighthouses.

From Wikipedia, the free encyclopedia. Its purpose is to ensure that in the event of earthquakes: human lives are protected; damage is limited; structures important for civil protection remain operational.

European Standards EN. European Commission - European Committee for Standardization. Basis of structural design 1: Actions on structures 2: Design of concrete structures 3: Design of steel structures 4: Design of composite steel and concrete structures 5: Design of timber structures 6: Design of masonry structures 7: Geotechnical design 8: Design of structures for earthquake resistance 9: Design of aluminium structures. Categories : Bridge design EN standards Eurocodes. Namespaces Article Talk.

Views Read Edit View history. Help Learn to edit Community portal Recent changes Upload file. Download as PDF Printable version.The WFCM includes design and construction provisions for connections, wall systems, floor systems, and roof systems.

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A range of structural elements are covered, including sawn lumber, structural glued laminated timber, wood structural sheathing, I-joists, and trusses. The design example uses plans from a 2-story residence as the basis for a structural design to resist wind, seismic and snow loads. This webinar provides an overview of the prescriptive and engineered provisions, tabulated values, design examples, and requirements for installation per the SDPWS and WFCM.

The WFCM has recently been updated and contains both a prescriptive and engineering design approach. Although the prescriptive design will tend to provide more conservative results than the more efficient engineered design, designers may arrive more readily at a solution. This seminar includes examples of seismic and wind shear wall designs for segmented and perforated shear walls, utilizing the WFCM and the SDPWS along with a comparison of the results.

On completion of this course, participants are able to:.

Seismic Design Principles

Equivalencies: 1. Both code-referenced standards provide procedures for designing diaphragms for wood construction.

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This presentation will demystify diaphragm design by providing wind and seismic design examples for in-plane lateral design of wood- and gypsum-sheathed diaphragms including high-load diaphragms. This presentation will provide an overview of the significant changes in the WFCM relative to the previous edition. The WFCM provides code officials and designers with time-saving tools based on engineered and prescriptive solutions based on structural engineering principles for wood structures to resist anticipated lateral and gravity loads.

Using plans from a 2-story residence, a structure is prescriptively designed to resist high wind, seismic, and typical residential gravity loads.

This webinar will deal specifically with design of roof systems, and appropriate connections between roof, floor, wall, and foundations to maintain load path for wind uplift. New shear wall aspect ratio limits for wind will also be examined. Main Menu Main Menu Pulldown. Publication Year: Choose an Edition This webpage is also available for viewing as Text-Only.

What's Changed? The WFCM includes the following publication. Other Resources. Free Printable Download. Expand all Collapse all. Understand the differences between segmented and perforated shear wall design. Understand hold down design and special conditions that pertain to seismic hold downs. Analyze wood- and gypsum-sheathed diaphragms using prescriptive and engineered procedures. Evaluate special inspection requirements as required for high-load diaphragms.This section describes some of the design and construction techniques and devices commonly used to create a low-damage building using timber.

Overseas, commercial and multi-unit residential buildings have been built as high as 10 storeys, and taller buildings are planned. The tallest timber building in New Zealand is 6 storeys, and most are less than 3 storeys high. Compare this with houses built according to NZS Timber-framed buildingswhich limits residential timber construction to 2.

While timber technologies are continually improving and taller timber structures are being designed, they have yet to be built in this country. In practice, factors such as wind and gravity loads, fire safety and acoustics limit the height of timber structures more than concerns about their rigidity and seismic performance. Nevertheless, many of the concepts covered in the sections on concrete and steel also apply to multi-storey commercial timber structures, and this section looks at a few of them.

As with the other materials, some techniques in timber work best when combined with other systems. Others can provide a stand-alone resilient solution or be retrofitted into an existing building to improve seismic performance. Elements of a timber structure designed to resist earthquake forces. Timber moment frames are most often used in single-storey buildings, but they are suitable for any large buildings with few internal walls, such as industrial buildings or multi-storey open-plan offices.

Timber moment frames must be designed and constructed with enough rigid connections to resist lateral seismic forces. Because of the additional expense of these moment-resisting connections, moment frames are generally not as common as traditional nailed light-timber frames. Structures that use timber moment frames also tend to have much greater flexibility than designs that use shear panels.

A multi-storey office building that uses a moment frame, for example, may need to be designed with stiffer shear panels around the lift shafts or stairwells to control lateral deflections. A variant of the moment frame, known as a portal, is a two-dimensional frame that consists of two upright columns supporting a rigidly connected cross beam or pitched rafters.

A portal frame is a continuous type frame, and several portal frames can be connected together to create a stable three-dimensional space. The lateral strength of the structure is derived from the stiffness of the members and the rigidity of the connections between them. Therefore, timber portal frames are commonly prefabricated using engineered wood products, such as laminated veneer lumber LVL or glue-laminated timber glulam.

seismic design of timber structures

Portal frames are generally suitable for single-storey construction because they allow long spans and open interiors, making then suitable for many commercial and industrial building applications. Historically, many schools, public buildings and industrial complexes in Christchurch use this technology, and they generally performed very well in the and earthquakes.

Portal frames are also very widely used in steel construction, but their performance in timber is noteworthy. Timber may be strengthened with diagonal concentric or eccentric braces made from timber or steel.

seismic design of timber structures

Timber frames often use a series of steel diagonal braces as a horizontal load -transferring element at roof level in place of a diaphragmalthough rigid wood-based sheet elements are also commonly used. In timber buildings with pitched roofs, braces are usually located in the plane or space of the roof, but they may also be placed in the ceiling plane.

In this case, the bracing acts as a horizontal truss, transferring seismic forces from the horizontal framing members to the vertical elements and down to the foundations. Prestressed laminated timber buildings, or Pres-Lamis a relatively new technique that uses post-tensioned technology in timber.

The system uses the same principle as the post-tensioned techniques described for concrete and steel. Pres-Lam uses a series of timber beam and columns members connected together with high-strength post-tensioning tendons or steel bars to create a moment frame.

The tendons run inside internal ducts in the beams for the full length of the structure, passing through holes in the columns and providing moment-resistance at each beam-column joint.

The columns are usually prefabricated from flat panel sections made from laminated veneer lumber LVLglue-laminated timber glulam or similar. In a Pres-Lam system, tensioning tendons are usually enclosed inside internal ducts formed using timber sections. During a minor earthquake, the additional frame stiffness provided by the tensioning reduces movement of the structure.

When exposed to larger lateral seismic forces, the structure will oscillate as the elastic action of the tendons allows gaps to open and close between individual members within the frame rocking joints. The tendons pull the structure back into its original position as the shaking subsides.

Post-tensioned systems are usually combined with dissipation devices to limit the amplitude of the displacement and dampen the rocking oscillations as quickly as possible.This resource page provides an introduction to the concepts and principles of seismic design, including strategies for designing earthquake-resistant buildings to ensure the health, safetyand security of building occupants and assets.

World's Largest Earthquake Test

The essence of successful seismic design is three-fold. First, the design team must take a multi-hazard approach towards design that accounts for the potential impacts of seismic forces as well as all the major hazards to which an area is vulnerable. Second, performance-based requirements, which may exceed the minimum life safety requirements of current seismic codes, must be established to respond appropriately to the threats and risks posed by natural hazards on the building's mission and occupants.

Third, and as important as the others, because earthquake forces are dynamic and each building responds according to its own design complexity, it is essential that the design team work collaboratively and have a common understanding of the terms and methods used in the seismic design process.

In addition, as a general rule, buildings designed to resist earthquakes should also resist blast terrorism or wind, suffering less damage. Blast Protection. About half of the states and territories in the United States—more than million people and 4. In the U. Earthquakes are the shaking, rolling, or sudden shock of the earth's surface. Basically, the Earth's crust consists of a series of "plates" floating over the interior, continually moving at 2 to millimeters per yearspreading from the center, sinking at the edges, and being regenerated.

Friction caused by plates colliding, extending, or subducting one plate slides under the other builds up stresses that, when released, causes an earthquake to radiate through the crust in a complex wave motion, producing ground failure in the form of surface faulting [a split in the ground], landslides, liquefaction, or subsidenceor tsunami.

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This, in turn, can cause anywhere from minor damage to total devastation of the built environment near where the earthquake occurred. In order to characterize or measure the effect of an earthquake on the ground a. If the level of acceleration is combined with duration, the power of destruction is defined. Usually, the longer the duration, the less acceleration the building can endure. A building can withstand very high acceleration for a very short duration in proportion with damping measures incorporated in the structure.

Intensity is the amount of damage the earthquake causes locally, which can be characterized by the 12 level Modified Mercalli Scale MM where each level designates a certain amount of destruction correlated to ground acceleration. Earthquake damage will vary depending on distance from origin or epicenterlocal soil conditions, and the type of construction. Seismic Terminology For definitions of terms used in this resource page, see Glossary of Seismic Terminology.

The aforementioned seismic measures are used to calculate forces that earthquakes impose on buildings. Ground shaking pushing back and forth, sideways, up and down generates internal forces within buildings called the Inertial Force F Inertialwhich in turn causes most seismic damage.

The greater the mass weight of the buildingthe greater the internal inertial forces generated.High winds, hurricanes and earthquakes are a harsh reality for much of the U. Building in these unpredictable climates requires special consideration of wind- and seismic-resistive construction materials. Wood-frame buildings can be designed to stand up to high winds and earthquakes given these characteristics:.

Lightweight Wood-frame buildings typically weigh less than those made of concrete and steel, reducing inertial seismic forces. Ductile Connections The ability to yield and displace without fracturing under abrupt lateral or horizontal stresses is an attribute of wood-frame construction, which features several nailed connections that allow it to respond to seismic and high-wind events without critical failure.

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Redundant Load Paths The numerous fasteners and connectors used in wood-frame construction offer multiple, often redundant, load paths for extreme forces, reducing the chance the structure will collapse if some connections fail. Heavy bracing for shear walls can resist lateral distortion common in earthquakes. Resilience Not easily swayed. Wood Meets Seismic Design Requirements.

Resilience resources. Back to top. Get wood innovation in your inbox. Sign Up!For more on Sam, see his bio here.

Shearwalls that are too flexible may prevent the structure from meeting drift limitations even if the shearwall design has adequate strength. For seismic load applications, section For light-frame buildings, the maximum permitted drift is 2. This limitation is put in place not merely for serviceability reasons, but is an inherent effect of current seismic design provisions that is required to be checked to ensure life safety. Current seismic design provisions do not use the Maximum Considered Earthquake MCE response, but instead design procedures are in place to allow for a much smaller seismic force to be utilized based on the ability of the lateral resisting system to absorb and dampen the energy during the seismic event.

This process requires the structure to deflect under each cycle of loading, but not deflect enough for a collapse to occur, so this method relies heavily on ductility inherent in the chosen lateral resisting system.

More ductile systems can undergo larger deflections when loaded and the benefit is a lower seismic design force. A simple steel frame and yield curve is shown below to further clarify the definition of ductility. An increase in the lateral resisting system ductility means a lessened seismic design force for the structure see graph below.

On a separate note, the reliance on ductility for seismic design is one reason seismic detailing and limitations must be followed even when wind controls the design. Okay, back to our original discussion. Since the amount of deflection the lateral system will undergo is not just a serviceability issue, the required deflection check is even more critical than for gravity loaded systems due to P-Delta effects.

Although deflection checks including P-Delta effects are included in most structural analysis software, this design check is often omitted in structures analyzed by hand.

Traditionally, for high wind design, we used the actual pressures the building is expected to experience. The building was expected to perform well not just for life safety, but also to sustain minimal cosmetic damage and protect the contents and belongings. Currently ASCE requires all building envelope openings be protected from flying debris in wind-borne debris regions, allowing the designer to use a much smaller internal pressure 3x less than when not protecting the openings.

This measure was put in place in ASCE and was a result of losses realized when the building envelope is penetrated during the wind event and significant damage occurring from water intrusion.

One of the most popular methods used to protect openings is to use impact-resistant glazing systems. There are racking limitations for this type of opening protection in order for them to work properly and maintain their structural integrity. In my opinion, this issue is addressed in section 4. The only way for a design to be in conformance with these wind or seismic requirements is for the designer to check building drift and ensure that the components within the lateral force-resisting system are all compatible and do not exceed the allowable drift.

If they are not compatible or have excessive drift, then additional considerations must be made, just as we would increase the depth of a beam to comply with serviceability deflection requirements.


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