Research Report

Well, with about 4 weeks until I have to hand in my report to my english teacher, I have been able to get my first chapter finished. I still dont have any graphics to put in yet but at least I have something done. I still have a lot of work to go though, I just have to keep finding sometime to work on it between the other assignments and things to do. Anyway I better get back atter!

Proposed Outline

 I have created an outline for my Technical Report. I found that this was a good way to get my ideas together and decide which section needs more work. Feel free to leave some advice or any hints on how I can improve my outline.

1.0 Introduction
    •    1.1 Thesis Question
    •    1.2 Introduce Topic
    •    - Provide some background info about my topic
    •    - Cite the BC Building code showing new code provisions
2.0 Seismic Activity
    •    2.1 Overview
    •    - Brief explanation of earthquakes and what causes them
    •    2.2 Forces associated with earthquakes
    •    - Provide insight into the dynamic forces associated with earthquakes
    •    2.3 How structures react to seismic forces
    •    - Show how buildings react when a seismic load is applied to them
    •    - Illustrations will be created to show damages from earthquakes
3.0 Wood
    •    3.1 Types of wood used in construction
    •    - Wood selection
    •    - Grades of wood
    •    3.2 Strengths
    •    - Determine best species of wood to use
    •    - Determine the strongest species of wood
    •    3.3 Loading
    •    - Determine the forces from each storey acting on the floors below it
4.0 Shear Walls
    •    4.1 What is a shear wall
    •    - Explain what a shear wall is
    •    - Why shear walls are needed
    •    4.2 Performance of a Shear wall
    •    - What makes a shear wall so strong
    •    - Components of a shear wall
    •    4.3 Structural Analysis of a Shear Wall
    •    - Work with James Gu to design a shear wall
    •    - Complete a structural analysis of my design

5.0 Seismic Response
    •    5.1 Performance of  Wood
    •    - Will apply the seismic forces to the wood and shear wall I designed
    •    5.2 Structural Analysis
    •    - Determine if my building survived the earthquake
6.0 Conclusions
    -Answer my thesis question: Is it in fact practical to build 6 storeys with wood?

Progress Report

Introduction:

This memo describes the progress I have made to date on my independent-study
project to write a report on The Seismic Response of Mid-Rise Wood-Framed
Construction. In this memo, I review and describe work I have completed, work I am
currently engaged in, and work I plan to complete by the end of the project. This project
will result in a technical report which will provide insight into the performance of wood
structures durning seismic activity.

Completed Work:

Starting in February 2010 I started researching and gathering information for my report.
I started off by gathering research about seismic activity and the forces associated with
it. I then moved on to research shear walls, which are an integral part in the strength of
buildings, especially in seismic regions. The final step of my research was to research
the performance of wood. I looked at different species and strengths of wood, which will
aid in choosing the right wood for not only the frame of the building but also the shear
walls.

Present Work:

I am currently in the process of determining the strengths of different species of wood.
Choosing the strongest wood that also preforms well under seismic conditions will be a
challenge, but is integral to building in seismic areas.

Future Work:

Next, I will be designing a shear wall which will give the building most of its structural
support. During this process I will also be doing wood design calculations to determine
whether or not the structure will withstand the forces caused by the seismic activity. I
hope to compare a building without shear walls to a building with shear walls to
determine how safe and structurally sound they are.

Potential Problems/Solutions:

During the course of my research I have run into various problems. The biggest issue
that I will have is that I do not know how to design shear walls. The solution to this
problem is to work with James Gu, who is a structural engineer that specializes in wood
applications. Two other problems are that I don’t know structural design nor do I know
wood design. However I am taking ARET 3620 and 3600 which are teaching us wood
and structural design. I am taking what I learn in class and apply it to my report.

Next Steps:

Once I complete my present and future work, I will be compiling the information that I
have gathered into a logical sequence and create an outline of what my report will
contain. I hope to have this portion done by October 4th. I will then go ahead and create
that graphics that I require throughout my report. If everything goes according to plan I
hope to have my first and second drafts done before November 1st. The final report wil
be ready for review during the second week of November.

Conclusion:

So far, the project is proceeding well. I have not run into any major problems, nor do I
anticipate any in the remaining work. With the help of James and the information that I
will be learning in the ARET 3620 and 3600 courses I am well on my way.

Abstract

The seismic response of mid-rise wood-frame construction

In April of 2009 new provisions in the BC Building Code came into effect allowing the maximum height of residential wood-framed construction to increase from four storeys to six. This change was brought on by a successful test of a 6 storey wood-framed structure that was placed on a shake table in Japan. The shake table is the largest in the world and accounts for the three dimensional forces that are present during an earthquake. Testing took place on a building constructed of primarily of wood and was fully furnished at the time of the test. Surprisingly the structure withstood a full minute of a magnitude 7.3 earthquake. Once the test was completed the engineers deemed the building had suffered no structural damage and was safe to be occupied. You may wonder how just a simple wood structure can stand up to the forces of an earthquake but it all comes down to the overall design of a shear wall and type of bracing system that can be used.

The shear wall is basically a structural member that is designed to withstand the lateral loads associated with wind and earthquakes. Shear walls are usually constructed of typical framing members, sheathing and fasteners. The framing members are usually 2” x 4” or 2” x 6” wood studs and plates. In most cases the studs are spaced either 16” or 24” on centre. Because the frame must support the vertical loads, two or three studs are typically nailed together at the perimeter of the wall to provide the extra support to keep the frame rigid. Sometimes diagonal braces are used within the frame to increase the overall stiffness of the frame. This stiffness is small compared to the stiffness of of what the sheathing offers. Sheathing for load bearing walls is usually 4’ x 8’ sheets of ply wood or OSB (oriented strand board). The interior walls may be sheathed with GWB (gypsum wall board). The plywood or OSB sheathing is connected to the framing members with nails and sometimes staples.

When the lateral loads of seismic activity is applied to the wall, the fasteners work with the rigid sheathing panels and the flexible frame of the shear wall to carry the load. The fasteners are the most important components in determining shear wall performance, influencing both stiffness and strength. Creating as solid hold down system is no easy task. Since buildings are always moving, shear walls tend to shrink over time causing causing the wall to loose its strength. However using the proper methods and equipment, shrinkage can be combated. Hold down systems are typically anchored in a concrete slab or right onto the foundation wall creating a rigid frame. Then the right fasteners are used to keep the shear wall, one continuous structural member. The placement of the fasteners are crucial to keep movement and shrinkage to a minimum.

Since 2009 wood-frame construction has been applied in buildings of up to 6 storeys in height and of irregular shape. Since it is very expensive to test large scale models of buildings to determine the seismic response of them, the investigation of how a shear wall is to perform is an important analytical method. Therefore it is of great importance to develop the proper design and study the performance of shear walls in mid-rise wood-frame construction to ensure continued safety during seismic events.

Auto Tight Hold Down System

I was doing some further research into shear wall design and I though, what kind of bracing system will keep a shear wall rigid? Turns out there are many ways to brace a shear wall but this method caught my eye. Its called the Auto Tight Hold Down System. What happens over time, as the wood structure shrinks and settles, up to one half inch (½) per floor or more, the excessive looseness will lead to shear wall failure. Tests have shown that as little as three-sixteenths of an inch (3/16) of looseness can reduce the strength of a wood shear wall by 40%. I though wow, for a location that experiences a high amount of earthquakes a year, these buildings keep getting weaker every year. Now this product is designed to compensate for the shrinkage and automatically tighten to keep the shear wall rigid. I have some pictures below of how the product is placed in a shear wall that I have taken from their website.




















Auto Tight Hold Down Website

Thesis Statement

Topic: Seismic Response of Mid-Rise Wood-Framed Construction.

Thesis Question: How does a mid-rise wood-framed building withstand the 3 dimensional forces applied by seismic activity?

Application: Strength and design of a shear wall and placement with respect to the shape of a building.

Location of Shear Walls

Im adding some further info regarding shear walls. Tony brought up a good point asking where you would place shear walls in irregular shaped buildings to account for the three dimensional forces brought about by an earthquake. Well heres my answer:

-Shear walls should create a box.
-Shear walls should be located on each level of the structure including the crawl space.
-Shear walls should create a box structure
-To be effective, shear walls should be equal length and placed symmetrically on all four exterior walls of the building.

For irregular shaped buildings the shear walls should be placed at regular intervals along the length of the wall on every storey. Or a whole wall can act as a shear wall extending up through multiple floors. Heres an interesting article of a curved shear wall if anyone is interested.

http://livebuilding.queensu.ca/building_systems/structural_design/shear_wall_loading