I suspected a potential train accident when I was informed of extra carriages to be added to Ballore trains. I am also expecting a re-collapse of the bridge which is under construction. Please do not be too spiritual here. I am using technical knowledge to make my argument. Like someone said, I was just being smart by using my small knowledge and insight when I made that prediction. I am not a prophet.
I do not know if the container used at that bridge is temporary or not. But I would like to assume that it is temporal. For you to easily grasp where I am coming from, it would be good for me to start by talking about temporary structures.
In construction, a temporary structure is a means or method which provides support, access, enhancement or facilitates the construction of permanent structures like a bridge at a given or a short period of time. TEMPORARY STRUCTURES normally form the interface of design and construction. The fact that temporary structures are often used in construction projects does not mean anything should be used as a temporary structure.
In some types of works or projects, such as urban tunnels and bridges, the use of temporary structures involves significant risks. Hence, we must design, analyse and assess such projects. I would, therefore, expect the contractors responsible for building the bridge to take into the intermediate stages of construction and their sequences.
What I would like Cameroonians to understand is that failures and collapses in construction take place during the construction phase and in most cases on temporary structures. The reason for this is because temporary structures are most often neglected in the construction project risk management process.
For your information, temporary structures are used to facilitate the construction of buildings, bridges, tunnels, and other above-and-below-ground facilities so as to provide access, support, and protection for the facility that is under construction (the bridge in our case) and must assure the SAFETY of the workers and the public. Does that container assure PUBLIC SAFETY? I strongly doubt it.
It has been proven by researchers and experts that during the planning stage in construction management, most builders do not consider analysing temporary structures. Temporary structures are often neglected and that temporary structures only feature as AFTER-THOUGHTS in their agenda. Fellow Cameroonians, I am afraid, that seems to be the case here. A proper analyse of the use of the container seems to have been neglected. Based on careful studies by experts, most tragic failures occur during construction because temporary structures were not properly designed, constructed or/and maintained. I am afraid; the container to hold the bridge was not designed for the purpose it has now been used for. Faulty bridge launching, uncompleted bridges, poor digging techniques, soil solidity, missing bracings, poor supervision, design change, faulty sequence and instability are some of the causes of construction accidents and failures. Unfortunately, this seems to be what is happening in Cameroon today.
HOW DANGEROUS IS THE BRIDGE JUDGING FROM THE PHOTOS
Looking at the pictures above, I actually wonder if a dynamic, multi-scale and multi-perspective methodology to manage risk emerging from that container (which I am thinking is a temporary structure) was used and developed. I am referring to Risk Breakdown Structures (RBSs).
A structure (for example, a building/house) comprises of many things amongst which are floor(s), walls, ceilings and a roof.
In construction, there is a terminology known as load-bearing. The container in our case could be described as a load-bearer. It is supposed to be a dead load as well. A dead load in construction refers to objects that are fixed (they do not move), while life loads would refer to anything that can be moved (for example chairs, tables and people using the facility.
The rectangular walls of the container will be covered by soil. For the container to remain fixed without being able to move, it would require that the soil holds both sides of the container tightly. The container must not move at any time during the usage of the bridge. However, the danger is that the soil would in time have to force the container walls to move inward towards each other. Do I need to explain the outcome of this? What is most scary and so surprising to me is the absence of cross bracing.
Look at the entrance structure of the container. I would describe this in simple language. What you see are two poles and a flap (bar). You might want to call it the door but we can’t say it’s a door because there is no structure that covers the entrance into the container. Let’s just call the frames; (pillars/poles). The entrance of the container should have been ‘’blocked/protected’’ by a cross-bracing. A strong metal structure of this shape (x) that would be holding the poles together, to prevent the container from shrinking if being pushed by the soil that surrounds the container. So, a strong metal would have been placed across the entrance running from top left to down right and from down left to top right. The absence of the cross-bracing tells it all. It’s unsafe. The potential risk of a collapse over time is high.
Unfortunately, from the picture, it does not seem the container is standing on a concrete floor. If that is the case, let us expect another collapse of this bridge. The foundation of a building or any load bearer must be extremely solid, with the ability of being able to carry any object without having the floor sinking. If the container is standing directly above the soil or on a floor with weak concrete components, then we should expect another disaster. The foundation of a building suffers the most. It carries all the weight. Hence, it must be extremely solid.
How solid is the roof of the container? To prevent a roof from collapsing, roofs must be supported by vertical and or horizontal beams/frames. In this case, if you look inside the container, you see a completely empty container with no vertical frames; what we often call in Cameroon as pillars. When it comes to a structure that carries life loads like (cars, trains, people, trucks, etc), I would expected to see some frames (pillars), running from the floor of the container to the ceiling of the container, in order to support the container from either sinking or to prevent the roof from falling. However, I do not support the use of the container in the first place. If you look inside the container, you see no such frames.
Water can be very dangerous in construction. A porous surface/object/structure is damaging to construction projects. If water is able to pass through the soil and remains in the soil, it has the potential of causing damages to properties. The soil can easily erode for holding water for too long. The consequence of this is that the bridge again would likely collapse. From our pictures, it shows that no adequate measure has been taken by the contractors to devise a means of preventing water from getting into the surrounding soil. It also seems there is no device to collect water and to direct water from rainfall to another direction. This is extremely important. All of my mates with civil engineering background, including my lecturers, have laid strong emphasis on this (water)
Part 2 later: PROTECTING THE CONTAINER, RISK OF ANOTHER COLLAPSE, IMPORTANT ISSUES, CALCULATION
By Callistus Funjong