Points for Consideration

• Our posts and footings are designed in accordance with British Standards. Soil conditions, terrain, climatic, geographic and topographic changes all impact on the final design. Can you trust other businesses to consider these elements and provide a structure that is designed appropriately?
• We could apply a worst case scenario to all sites and design footings and posts accordingly, in which case design sizes reached by different engineers should be relatively similar. Any significant differences should be easily explained within the design criteria and assumptions. However, any installation supported by smaller posts or footings will not have the same inherent strength as a structure with larger ones.
• We are in the business of selling "peace of mind". Our structures are designed to withstand severe weather. Some people think that if a structure behaves well in light wind conditions it can resist anything. This is plainly not the case and hence very risky to disregard.
• Post and footing sizes vary depending upon the number of shade panels connecting to them and the direction of the resultant force. If a competitor thinks that the height of the post is the only factor to be considered in the design of these items our suggestion is to preclude that company from any future involvement in your project.
• Uplift is the major design consideration for these types of structures. As wind passes over the structure, negative pressure causes a suction effect on the fabric from above which in effect billows the fabric upward. The major resistance to this is the dead mass of the footings. If they are under-designed the post and footing can be torn out of the ground.
• The size of a foundation must take into account wet soil conditions which make it easier for the footing to rotate or move than when hard and dry. A rule of thumb used by engineers when designing bored pier foundations, is to disregard a depth of the soil from the top of the foundation. They assume the soil for a certain depth offers no resistance to the rotational moment caused by a force at the top of the post. The rule is to disregard a depth equivalent to 1.5 x the diameter of the pier. For example a 450mm diameter pier equates to a 675mm depth to be disregarded. If the design depth of the footing is 1m then by this method the design is for 325mm depth of soil is resisting the load. It’s difficult to imagine anyone accepting a panel of 100sq.m supported by 4 posts 2.4m high each sitting on footings with a design depth of just 325mm (around 1 foot) is it. Well let’s hope not anyway!
• Posts can deflect a maximum allowable distance determined by the design. The smaller the deflection, the larger the post section must be. In other words if you wish to have the smallest possible post sizes you must be prepared to accept posts which deflect more. Some companies hide the post deflection by leaning them backward dramatically to prevent the "banana" in the post being noticed too easily. So it may be that customers are not aware that posts bend under load which may cause them concern.
• Any structure can be designed to the slimmest of safety margins. Our design has appropriate factors of safety to ensure adequate levels of protection exist for circumstances beyond what can be regarded as "right on the upper limit".
• Risking children's and people's safety in general is not in our interest. If company's involved in the construction of shaded areas don't fully understand the potential for personal injury when they specify post and footing sizes then they shouldn't be in the business.