Oh, people of Nairobi. I am heartbroken about your building collapse. If you look at the photos of the remaining rubble, there was clearly no or almost no reinforcing steel bars (rebars) used in the construction of these buildings.
Reinforcing steel provides a cage that the concrete can be layered onto.
If the reinforcing steel had failed, you would see long, twisted metal noodles all over.
I don't see any metal except what looks like an iron gate in the first photo.
And in this photo, there is nothing but what looks like a balcony on an uncollapsed building. I don't even see any columns at all. If there were any, they simply failed.
It appears that the builders used only a material that strongly resists the forces of compression (concrete--which you could squeeze all day between your hands and it wouldn't crush) but not the forces of shear, or twist. (That's what the steel is for--you could try to twist steel reinforcing bar all day and get nowhere.) Another important point for engineering is the footing--what actually supports the building. If they are by a river--and Nairobi was originally built on marshland--then the footing and how it is engineered is all important, along with how everything is fastened together.
What seems to be the cause of this collapse is a classic case of money being put before lives. This latest collapsed building was undermined by flooding at a nearby river. It's hard to find the collapsed building on the map, but I think it's the Nairobi River. Part of the land underneath must have given way, leading to the sheer forces that collapsed those supporting walls.
And this is only one of several collapsed buildings in Kenya over the last few years. These are not accidents. This are negligence. It is not hard to build for structural integrity. It just costs more in material and takes a little longer. It requires hiring an experienced engineer and following their directions. Carefully.
This is not likely to happen in Kenya, which also has an earthquake risk. In 2014, a report was given to the government stating that four out of five buildings in Nairobi would not be safe in a minor earthquake.
The government dismissed the report.
Kenya is a gorgeous country. Nairobi is huge--6.5 million in the greater Nairobi area--and facing explosive growth. Where I live, building inspectors are an irritation. They take their sweet time getting to your site. They seem to require detail after detail, and they must be obeyed.
Still, I'm grateful for them. I hope the people of Kenya can get their government to provide proper building inspections and enforce safe buildings.
And I'm praying for the people of Nairobi whose lives have been crushed--both literally and figuratively--by someone saving money through shoddy construction.