Why the Mwiki,Kasarani Building collapsed and how to prevent this.
In February 2012, a building collapsed while under construction in Mwiki,Kasarani.
Following a visit to the site, the causes can be deduced as follows:
1. Lack of proper consultancy from the design team. Local Authority bye-laws require that any site in construction should display publicly the name of the Architect, Engineer, Contractor and Owner at the plot entrance. This was not done. This means that if the owner got approval to construct from the local authority, he opted not to display the project team names .This happens in most projects whereby the owner does not employ and maintain the relevant consultants during the construction period.
Buildings without this public display of consultants in most cases are not designed and supervised by registered Architects and Engineers, hence posing a risk to the general populace in-case of collapse.
Where there is a public display of the Architect, Engineer and Contractor, they tend to naturally make sure nothing goes wrong since the responsibility lies with them.
Local Authorities do not have the capacity to police and make sure all sites display this. The best solution for them is to embrace online portal solutions .
This ensures that once construction commences, the owner is required to erect the billboard display of consultants and contractor, take a picture/video and upload to the specific building plan approval page which displays a log of events from date of approval, all through to the current building status. This way, minimal personnel stationed at the Local authority offices can easily visit the web portal, check for updated billboard images and give their comments. In some instances, the bill board displays have unregistered consultants and contractors hence not effective.
Spacing of Columns.
From the pictures, it’s rather obvious to someone in the buildings industry that something was not right in the way the columns were spaced. Towards the far end, columns are spaces 2 to 3 meters apart, which is too close. This is the area that was left intact. This is over-design of structural capacity. Towards the area that collapse, i.e. the front side, the columns are spaces 6 to 8 meters apart. This is under-design of structural capability.
Owners are supposed to send pictures of different construction stages then the Local Authority Engineers can deduce from the pictures as to the quality of workmanship and any other input. In this case, the Local Authority engineers could have noticed the anomaly in terms of column spacing and raised an issue for the project to be physically visited for closer scrutiny.
Y 20 on Beams.
The beam that joins the large over 6m spans seems to have been over-designed with heavy Y20 thick steel reinforcement.
Normally, this reinforcement overhangs and crosses over to the canopy. In this case, the Y20 steel reinforcement reaches the columns at the plot boundary next to the road and end there. The canopy cantilever is reinforced with smaller diameter of steel-y10 or y12. This shows that the steel structural design was not concluded.
2. Lack of proper consultancy advice in terms of Building Technology.
Hollow Pot Technology.
The building floor slab was constructed using clay brick hollow pot technology. This technology introduces hollow clay bricks into the slab .The hollow parts reduce the volume of the concrete hence reduces the cost as compared to the usual reinforced concrete slab which is usually 150mm thick.
Hollow pot technology requires a keener structural engineering since most funds, foremen and small-time contractors are not used to this method hence do not understand it.
The Langata Southern Bypass opposite Carnivore building that collapse also had utilized the same hollow pot floor slab technology.
It’s not a surprise that both buildings collapsed since in both cases, consultancy was wanting.
The Local Authority engineers could then have seen the hollow pot slab technology being used and raised a red flat for the need for a physical visit.
Ministry of Local Authority Role:
The Ministry of Local Authorities is tasked with the responsibility to police and ensure that all buildings constructed in Kenya are safe.
The Engineers required to assist the Local Authority to do this are few compared to the number of projects being constructed all over the country.
Pictures/videos of the site works in progress, site bill board and specific tasks such as steel structural reinforcement, concrete mix should be required to be updated regularly so that buildings which seem to be obvious cases of danger can then be followed up with a physical site visit.
Building types that pose greatest danger.
Buildings that pose the greatest danger in terms of similarity of buildings that have collapsed in the recent past are:
a. Buildings that have not employed registered architects and engineers for supervisory roles, in most cases, the information is not displayed publicly at the building entrance. All buildings that have collapsed in Kenya fall in this category.
b. Buildings that have the ground floor designed to be a hall e.g. supermarket, parking space. The Kiambu and Mwiki buildings that collapsed had such a design whereby the ground floor is not braced and held by stone walling. Such designs are good and save space but care should be taken so that building owners are not left to try such construction designs without the input and supervision of registered architects and engineers.
c. Buildings that use hollow-pot technology and the owners have not retained registered architects and engineers to offer supervisory services during construction. Such cases can be seen in the Langata and the Mwiki buildings.
The inability of Local Government to be able to police all construction projects in Kenya has resulted to building owners constructing without using specified supervisory personnel under law.
Specific tasks such as reinforced concrete works are then taken pictures or videos and uploaded to the project’s page .
The Local Authority engineers can then be able to view and advice on many projects at the comfort of their offices.
New projects coming up without approval can then be easily noticed and identified through Google maps features enabled in the portal.
Next to the collapsed building is a building that was not appropriately built and the Government has partially demolished the columns holding the front part. This has left the first floor hanging dangerously, posing great danger to citizens. Again, since the Local Authority cannot police 100% of the construction in Kenya, use of Google maps within the web portal would have reminded the Local Authority personnel while scrutinizing the Collapsed building approvals that there is a building next to it that was ear marked for demolition, a few columns demolished but the owner has not yet remedied the building as required by law.
Architect Francis Gichuhi Kamau.
B.Arch. Nrb. MA.A.K[A]