Craig's building truth: building science

An Explanation on Building Science.

Loads on Structures.

Loads can come from gravity wind, or earthquakes or possible weight loads and collision

Gravity:

There are 2 types of downward loads a dead load ie: the weight of the building. And a live load like people or furniture.

Sometimes snow on a roof can be a load that needs to be designed for.

Loads can be transferred down the studs and into the foundations. This is referred to as a load path. ON commercial buildings steel portals transfer most of the load

Wind:

Wind speed and direction can have a big impact on buildings, wind hitting a building creates pressure on one side and a vacuum on the other side (lee)

The 3 main types of pressures on buildings are

Uplift:

Caused by negative pressure on the roof this can be resisted by the connectors that connect the bottom plate to the foundations ie: straps, hold down bolts, and other fixings or hardware.

Torsion:

This is when the pressure is trying to push the building out of square, causing the building to "rack" this can be resisted by bracing elements such as strapping gib systems ceiling diaphragms and connectors.

Overturning:

Pushing the building off its foundation - can be resisted by the weight of the building itself, the foundations like anchor piles, or connectors.

Seismic effects:

Can be resisted by shear walls or base isolators.

I have put shear walls up in commercial places under bridges and at the wellington airport.

I have also done retro work in Wellington doing earthquake strengthening by running 30 mil reo between the under floors and locking it in the idea was this would slow the concrete floor failing by allowing the whole building to move as one. This building was already operational and an older building, the bottom floor was a food court so we did all the work at nighttime and got out before opening.

A good example of a base isolator can be seen at Te Papa in front of the entrance they have a stairwell that goes down and you can see one of the isolators and read about how it works.

https://www.tepapa.govt.nz/discover-collections/read-watch-play/science/halting-jolts-how-te-papa-resists-earthquakes

The types of forces that transfer through a building are

Designing for loads.

Buildings are designed to withstand loads.

Loads get transferred through designed load paths, vertical loads get transferred from the top of the building to the foundations.

Horizontal loads are transferred by introducing rigidity.

https://www.youtube.com/watch?v=W_KZ7cZmxO8

3604 has all the specs for vertical loads and horizontal structural loads for buildings up to 3 storeys high.

a lot of the work can be used with connectors like cyclone straps.

Bracing elements.

Mostly achieved these days with gib systems or plywood walls. The architect will have specified plans sometimes it will be engineered. The first port of call is 3604.

Ground stability

A building site must be inspected for stability.

Things to think about are:

evidence of flooding and slips

where water comes from and where it goes.

what soil is there.

excavations

the LIM will have information.

good ground is said by 3604 to have a bearing capacity of 300kpa a geo-tech engineer can test the soil with a scala penetrometer.

liquefaction and a high water table can also cause problems for building plans.

At the retirement village The Oaks in Warkworth there is an underground river, the building foundation was covered with waterproofing, there was also a full-time pump in the bottom of the lift shaft that was constantly removing groundwater the piles must have been driven really deep. At a demolition job at the ford car yard in Whangarei I worked on they did not have an adequate footing in the original building for the ground, it was next to a tidal stream, the concrete slab had dropped 300 mil and the building was written off

Whangarei ford

Waterproofing penetrating structures.

Keeping water out of a building is one the most important aspects of construction design.

There are many ways water can enter a building

through

Gravity - prevented with slopes and flashings

pressure - prevented with air seals.

surface tension - prevented with breaks and drip grooves.

capillary attraction - prevented with gaps in weatherboards channels.

water vapour is usually created inside the house - use an HRV system or ventilation system to stop.

Weathertightness principles.

the 4 ds

Deflection: keep the water out like roofs and overhangs and cladding.

Drainage: cavity systems

Drying: the perforated strip on the cavity allows leftover moisture

Durability: fixings, materials, timber treatment, steel treatment.

bad building practices and poor plans plus bad products can lead to massive problems like the leaky building problem we had. Which we may be facing again now

https://www.youtube.com/watch?v=QOHYiD3ILMg

Chemical properties of materials.

Thought needs to be given to where materials are used, how they are used and what they interact with. Metals in particular have limits of where and how they can be used, DPC can be used sometimes to separate non-conforming items.

Durability

thought needs to be given to the durability of materials for example brass can look good but are very soft and easily damaged so cannot be easily reused

Malleability

means a product can be compressed and deform without fracturing. Lead was often used for this reason but is now considered toxic other products perform the same function.

Flammability

A highly flammable product is not considered suitable for building, volatile products can be used during construction safety and harm sheets should be considered,

Energy efficiency

https://www.youtube.com/watch?v=YK7G6l_K6sA

Sound Transmission

https://www.youtube.com/watch?v=gVjyV-thkM4

Examples of building science in my work