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Topic 19: Bracing theory, terms and elements.© Unitec New Zealand

Construction Systems 1

Topic introduction, overview and threshold concepts.

>>FACULTY OF TECHNOLOGY AND BUILT ENVIRONMENT

Intention of this short overview.

Students will be introduced to the fundamentals and basics of the topic area content.

Words and terms used in designing bracing in accordance with NZS3604 will be defined and explained including the units employed to measure bracing requirements.

Typical elements used in providing bracing to the sub- floors , walls and roofs of a typical timber framed dwelling to NZS3604 will be identified using photos , images and drawings .

>>FACULTY OF TECHNOLOGY AND BUILT ENVIRONMENT

Timber Framing and Loadbearing Masonry.

“Timber framing pretty good in EQ, load bearing brick not so much”

P Etherington , UNITEC.

Definition:

Any method employed to provide lateral support to a building .

Bracing theory. What is meant by BRACING anyway ?

© Unitec New Zealand

The two main lateral forces that we have to be concerned with are -:

WIND and EARTHQUAKE.

Bracing theory. What are we actually bracing against ?

Bracing theory. What are we actually bracing against ?

WIND and EARTHQUAKE.

Bracing theory. What parts of a typical house have to be braced?

What’s to brace?– Roof:

• Sheets• Metal strapping• Timber framing

– Walls :• Sheets• Metal strapping• Proprietary steel frame inserts

( Gamma etc ) • Diaphragms

– Sub-floor :• Brace or anchor piles• Cantilevered piles• Concrete block walls• Exterior Cladding or framing

© Unitec, Mushtak Dawood

Bracing theory. What is meant by bracing DEMAND?

BRACING DEMAND. -: The horizontal forces resisted by a whole buildingor by an element within a building.

These horizontal forces are a resultof wind or earthquake action. Bracing demand forces are measured inbracing units (BUs).

They shall be determined as set out in 5.2 (wind) or5.3 (earthquake

Demand is measured in Bus for Wind

Demand is measured in BU’s / Sq m for Earthquake.

Demand is what we actually work out from the tables in NZS3604:2011

Bracing theory. What is meant by bracing CAPACITY?

BRACING CAPACITY. -: Strength of bracing of a whole building or ofelements within a building. Bracing capacity is measured in bracing units(BUs), and shall be determined from section 5.

Source- GAMMA bracing systems .

Capacity is what we actually build into the project or house to strengthen it against the lateral forces of Wind and Earthquake.

Bracing theory. ALONG and ACROSS ? Whats’ that all about ?

ALONG and ACROSS refer to WIND demand.

The key element to identify here is the RIDGE.

ALONG is parallel to the ridge .

ACROSS is at right angles to the ridge.

HIP ROOFS -: Use the across values from the tables to work out demand in both directions

WALL BRACING / WALL BRACING ELEMENT : A section of wall above theground floor level that performs a bracing function.

Bracing theory. What is meant by a bracing ELEMENT?

Bracing theory. What are BRACING LINES ?

BRACING LINE. A line along or across a building for controlling the distribution of wall bracing elements.

Bracing lines are only seen on plans .They are not something we build. Just a design aid.

Bracing theory. What does NZS3604 mean by BRACING DISTRIBUTION?

Wall bracing elements shall be located as close as possible to the corners of external walls and evenly throughout the building.

Bracing elements shall be evenly distributed along each line as far as is possible.

Don’t put all your reinforcements in the one place !

Bracing theory. What does NZS3604 mean by BRACING DISTRIBUTION?

Christchurch.New set of three storey of townhouses (row houses) where the main floor completely collapsed .

Squished car poking out of the bottom.

This was before the rule about 50% of the total bracing demand / no. brace lines so there was very little bracing on the front where the car ports were on the ground floor and it rocked back and forth a couple times and came straight down.

Bracing theory. What is a DIAPHRAGM and its effect on bracing?

DIAPHRAGM. A building element such as a floor or ceiling capable oftransferring loads in its own plane to boundary members.

Bracing theory. What is a DRAGON TIE and how does it affect bracing?

Dragon ties don’t contribute to the bracing capacity but, like diaphragms, let us space the bracing lines further apart .

Bracing theory. What do BRACING PLANS look like ?

>>FACULTY OF TECHNOLOGY AND BUILT ENVIRONMENT

© Unitec New Zealand

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END

“Next session we will be exploring the principles of Bracing Design in accordance with NZS 3604:2011.

Image sources-:

Slide 1- Unitec, Phil Etherington. Slide 2- Unitec, R Kelly, MmcGarrigle 2014Slide 3 - Unitec, Phil Etherington. Slide 4-Renovate.org.nz. E architect.co.uk, Gamma BracingSlide 5- GIB living .co.nzSlide 6Slide 7- Clipart, M Dawood.Slide 8- NZS 3604 2011. Slide 9- GIB Bracing manual, Gamma Bracing. Slide 10- NZS 3604 2011. Slide 11- Carter Holt Harvey, Gamma Bracing products. Slide 12-Lifesun.info , R Packard, Unitec.Slide 13- LaSalle.edu, R Packard, Unitec. Slide 14- Unitec, Phil Etherington. Slide 15- Wood solutions Australia.Slide 16-NZS 3604, Ted CarpentrySlide 17- Rohan Packard Unitec, Doc 1. 2013