Residential and Multi-rise buildings
When designing structural engineering components for Residential structures, for the most part the most cost effective option is often standard 700x350 concrete strip footings, with Y12 rebar top and bottom, or possibly just bottom depending on how well the soil conditions in the area hold out. Strip or spread footings are generally built underneath each designed ground floor wall, following only the path of walls to be built on top of them, except where a stiffening strip is required to tie the structure together as a whole in large open spans (if any). See example of strip footings in the pictures attached below:
Whereas raft foundations consist of arrays of ribs with a floor slab over it, tying the entire structure together as a “boat” or a “float” like the name suggests, in some cases expansion joints are added for irregular shape buildings or long continuous buildings, where multiple of these rafts are tied together by means of slightly movable joints in order to prevent serviceability cracks etc. The main function of a float or raft foundation is to literally “float” the loaded structure and to evenly distribute the load over the underlying “unreliable/unstable” soil, whereas a spread footing is either used to build straight onto bedrock (without much required reinforcement) or to build on soil with reliably high bearing capacities.
Developing in clay and dolomite affected areas bring just such factors to design considerations, the most popular and probably cheapest solution for this is using a raft foundation with 750mm deep ribs. A raft foundation is sometimes also called a waffle foundation because it resembles the shape of a waffle. As can be seen in the pictures below:
This little article is just for FAQ purposes, but note that spread footings and rafts are a collective concept of a vast variety of foundation types and sizes, raft foundations can have ribs ranging to 10’s of meters below the ground for high rise buildings in some areas, each and every project is handled as an individual and should never be fitted with a “template” designing approach.
On residential projects depending obviously from one project to the next, and a variety of factors. Rib and block slabs seem to be the most popular on simple residential projects, and also the cheapest in most cases ranging from 300rands to 400rands per square meter. This is also at times preferred as a roofing option on more modernized designs.
Rib and block slabs (seen in attached pictures below) consists of “lintel-like” ribs also called lintels by some, spaced 440mm apart and filled with hollow ash and cement type brick-blocks to take up space and lighten the slab, then covered with 50mm of concrete and plastered to finish under the slab and exposed sides. This option is probably the cheapest, although not the most time effective as it is quite labor intensive in comparison to prefabricated slab options. Rib/block spans are obviously limited to maximum spans as they are nothing more than pre-stressed lintels with tensioned wire in them, however rib and block slabs can be used on almost any project, with large and extra-large slab spans the lintel spans can be shortened by means of reinforced concrete beams or even steel beams cast into the concrete, rib and block slabs don’t by any means limit creative design, in fact in some cases they even aid some creative and aesthetic freedom to building projects. Solid reinforced concrete slabs are preferred in projects with high level of floor traffic, or even high intensity floor loads, as a rib and block slab would preferably be avoided in large commercial and industrial spaces, they could work beautifully for residential or office spaces.
This is but a nutshell explanation of the engineering consulting service offered by us. All concrete or steel design, for residential, commercial or industrial projects are handled with care and confidence, where each and every projects structural requirements are assessed and discussed with clientele in order to get the best combination of cost effectiveness and serviceability from your structures.
Also we were recently required by local municipalities on certain commercial projects to do stormwater attenuation plans, where the stromwater runoff post and pre development needed to be calculated and attenuated according to municipal requirements. We also offer these deliverables loosely for other structural engineering firms that don’t do their own stromwater reports.
If you have any further queries or questions on building your home, office or whatever structures you need consulting on. Please use our contact form on the home page, and the relevant professional will get back to you as soon as possible.
With the ever increasing human population, and the earth's natural resources that is dwindling by a thread, the need for sustainable energy usage in buildings have become top priority. In South Africa alone, the population grew from 47mil (according to the 2001 National Census) to 53mil (according to the 2011 National Census).
Energy Efficiency in buildings is now a voluntary standard to which all new buildings must comply. These new regulations was written into law in September 2011 and was made applicable as of 11 November 2011. These are the new SANS 10400-XA: Energy Usage in Buildings, and SANS 204: Energy Efficiency in buildings. The only exception, as with the other new building regulations, is that where the architectural work on a project had commenced prior the publishing of the standard, an application may be submitted to the Local Authority within 6 months of the standard’s publication date, requesting that the application be dealt with in accordance with the prior regulations. The new SANS 10400 part XA refers in many areas to the SANS 204 guidelines, which have been available in draft format since 2008.
Manfred Braune, Technical Executive at the Green Building Council of South Africa explains that SANS 10400 part XA essentially tackles how buildings are architized and built by addressing and providing guidelines for minimum requirements for things such as glazing, insulation, shading, orientation and building processes, including air-conditioning, hot water and lighting.
Regulations like these transformed the built environment in countries like Germany, where such standards was first introduced in 1975. All though these regulations only came into action in 2011 in South Africa, is there no doubt that the South African building industry will catch up fast and maybe leapfrog countries like Germany in this specific field.
The new standards cover a broad spectrum that will ensure a greener, cleaner tomorrow in South Africa’s building industry. Below are some examples of the types of specification requirements:
Author: Riscali Architecture Building Plans & Engineering
The standards can be purchased from :
New building regulations now apply, 2011, http://www.property24.com/articles/new-building-regulations-now-apply/14367
Energy Efficiency: Understanding the new Building Regulations in South Africa, 2012, http://timberdesign.co.za/energy-efficiency-understanding-the-new-building-regulations-in-south-africa/
GREEN BUILDING LEGISLATION IN SOUTH AFRICA, 2012, http://www.greenbusinessguide.co.za/green-building-legislation-in-south-africa/
Energy Efficiency – Overview, 2012, https://www.sabs.co.za/Sectors-and-Services/Services/Energy/index.asp
We all like that natural feeling of swimming in a farm dam, surrounded by all the healthy natural elements en plant growth. Well now you can swim in a natural environment from the comfort of your own back yard. Riscali introduces Eco-pools. An Eco-pool is a natural recreation of pristine ponds and mountain pools found in nature. The water is circulated through an ecosystem of natural elements and water plants, which keeps it clean and sparkling… so clean that you can drink the water from your pool. The result is a natural tranquil feeling that creates a lush indigenous aquatic garden. The water is clear, soft on the skin and infused with natural healing powers. No salt, no chemicals and no sterilization.
The wonderful thing about an Eco-pool is the low level of maintenance. Eco-pools are naturally self-sustainable and self-regulating. This is because the pool is designed to reach a stage where it completely operates as a natural and balanced aquatic ecosystem. The only maintenance that is required is to keep the water plants in shape and trim them from time to time and emptying the leaf trap. Twice a year the water need to be tested by professionals where it is analyzed in a laboratory. The treatment of the water is biological only, and no harmful chemicals will be added to the water.
The water in an Eco-pool is soft, clean and “delicious”…both literally en figuratively. No more burning eyes, no more dry hair or itchy skin. The water is pure and clean, and even drinkable, so you can drink water as you take a dive. It has been tested that the water quality from an Eco-pool is even better than municipal drinking water.
According to recent studies, some traditional pool products are a health hazard, linking it to cancer, allergies and asthma. An Eco-pool eliminates pollution and allergies.
Now you can enjoy a natural swimming sensation, for even a longer period of time than summer gives us. The shallow aquatic garden serves as a natural solar heater. Every day of the year you will be treated with a glorious natural “pond”, filled with flowers, dragon flies, frogs and birds.
Author: Riscali Architecture Building Plans & Engineering