Distilled Wisdom
Wind
Forces on a structure increase as the square of the wind speed. That is, doubling of the wind speed increases the forces by 4 times. You can’t normally choose a less exposed site but you can design the building to have a lower drag coefficient by changing its shape and/or reducing the area that is presented to the wind. Then you may save costs in simpler connections and cheaper members.
Flood
Some structures are partly or fully submerged in a flood or tidal flow. Again the forces increase as the square of the fluid velocity. Compounding this, the structure may catch debris which further increases the area acted upon by the water pressure. Forces can be lowered by reducing the area exposed to the flow or by reducing the potential to catch debris. While the actual characteristics of a rain catchment vary, very often raising a bridge over a creek by only a modest amount may place it above the design flood so the only flood forces to be resisted are those on the piers (if any).
Connection Forces
When dealing with high forces tending to dislodge structural components, it can be worthwhile to space elements closer together so the force per fixing is reduced. Then cheaper fixings may be more easily installed. Of course this may present a QA problem in ensuring that all fastenings have been installed on site.
In prefabricated frames in heavy timber or structural steel, the converse may be true. Then we often find that larger capacity members are more appropriate.
Roofs
An effective eaves overhang contributes to the thermal efficiency of a house in summer while reducing rain impacts on open windows and extending the life of the cladding and its finishes. In stick construction in timber, the rafters are usually notched over the external wall. This is fine for small overhangs. For wide overhangs, a larger rafter size is sometimes required but can be reduced if notching is reduced or eliminated altogether.
Bracing
Wall bracing is simply a way of taking lateral wind loads from the top plate down to the floor of the next storey. This continues all the way down the building until the load is taken out to the foundations. It is simply done by using thin plywood panels strategically placed throughout the building. Many-a-time some building professionals think that by placing extra bracing in the roof plane it may somehow compensate for a lack of walls available for bracing. Nothing could be further from the truth. All that extra reinforcing the ceiling diaphragm does is allow these bracing walls to be spaced further apart.
Barriers & Railings
Currently (2009) railings on pedestrian bridges have to be a minimum of 1.1m high while buildings require barriers only 1.0m high. There are some current discussions that are likely to lead to higher barriers to prevent falls. One of the arguments is that that the average Australian’s centre of gravity is increasing. Of course facilities for cyclists require an even higher barrier to achieve the same result.
For pedestrians with mobility problems, the location and frequency of rest platforms on ramps can present some architectural challenges. It is worth noting, if the gradient can be reduced to 3% then the see-saw nature of the vertical alignment can be eliminated. Then it is classified as a walkway and, at that slope or less, landings are not mandatory.