Case Study of Injaka Bridge Collapse

The Injaka Bridge project was in a small town called Bushbuckridge in South Africa. It was proposed to be a seven-span 300m steel structure. In July 1998 it was being constructed using the incremental launching method when disaster struck, and the bridge collapsed. The bridge collapsed for many reasons which were mainly due to lack of qualification and experience of the engineers involved in the project. Their lack of experience and negligence essentially led to the death od 14 people and the injury of 19 others on site that day.

Introduction

Background

The Injaka Bridge is a bridge that was proposed to be built in over the Ngwaritsane River in Bushbuckridge, Mpumalanga, which is a province in eastern South Africa. The bridge was proposed to be a seven-span continuous prestressed steel structure with a full construction length of 300 m and was designed to be constructed using a method known as the incremental launching method. This method involves building a section of the bridge, attaching a nose to that section and then pulling the two units forward. This process is then repeated until the bridge has reached its desired length. The steel nose attached to the leading end of the first segments function was to reduce the cantilever moment, the corresponding shear force and bearing reactions during launching. To allow the bridge units to slide across the top of the bridge supports during the process, both temporary sliding bearings were used in conjunction with the permanent bearings.

Parties Involved

“The owner of the works was the Department of Water Affairs and Forestry. VKE Consulting Engineers were appointed by the owner to design the bridge to span the Ngwaritsane River, near Bosbokrand. The contractor, Concor Holdings (Pty) Limited, was appointed to design the temporary works from design information obtained from VKE and to build the structure. ”

Collapse of Bridge

On the 6th July 1998 the Injaka Bridge collapsed abruptly during the construction process. The bridge was being constructed using the incremental launching method which if managed and supervised correctly should be a straight forward process. Unfortunately, on this day for several simple reasons, as the bridge section was being launched both the bridge section and the nose section experienced failure and collapsed. The event that triggered the collapse of the Injaka Bridge was a knock through the bottom slab of the bridge deck by one of the bearings from below which was caused by the incorrect positioning of the slide path. When the bridge collapsed there were many people present on the platform (including the designer of the bridge, Ms M Gouws) which unfortunately led to the deaths of 14 people and the injury of at least 19 others.

Reasons for Collapse

The Injaka bridge collapsed due to several basic mistakes which could have easily been avoided had normal design and project management principles been applied. The causes of the collapse resulted from a long list of shortcomings and can be summarized as follows:

• Insufficient experienced personnel and supervision
• Launch Nose not structural sound
• Deck slab poorly designed
• Incorrectly placement of bearings
• Incorrect temporary works slide path

“The design of the bridge was assigned by VKE Consulting to M Gouws, under the direct supervision of Bischoff (The head of Structural Engineering in VKE). To all intents and purposes the design of the bridge was left to Gouws, who could not have been considered to have sufficient experience in incrementally launched bridges. ” [4] The design of the bridge was left completely to Gouws, who could not have been considered to have enough knowledge in this method of bridge construction. During the construction process cracks began to appear in the longitudinal direction along the bridge which were completely ignored by everybody on site. Mr. Bischoff was informed of these cracks which he thought could be very serious at first but after carrying out a few calculations believed everything was reasonably correct. The engineer gave permission for operations to proceed but any contractor should have seen that it was not the correct decision to make considering all the damage on the bridge section regardless of an engineer’s recommendation.

Major Engineering Lessons Learnt

After this bridge collapsed it was discussed by the authorities involved what measures must be taken to prevent future failures. Firstly, it was stated that as a given anybody who undertakes the design of a structure is to be fully qualified and have appropriate experience to do so. It was also decided that regardless of the designer of the structure there must always be a design review stating that even the best engineers can make mistakes.

These organisations also stated that the contractor and engineer should accept the same responsibility to ensure compatibility between the temporary and permanent works on site. Finally, a precaution which could have saved numerous of lives on the day was introduced which states that nobody should, for safety reasons, be allowed on top of the deck of the bridge or the nose section while launching takes place, except for the construction personnel required to perform their work on the bridge deck or nose section.

Conclusion

In conclusion the Injaka Bridge collapse in South Africa was a terrible disaster which occurred due to the negligence of the engineers and personnel on site. The lack of experience and qualification of the people involved with this project along with some poor errors of judgement were the main reasons those 14 people lost their lives on site that day. If proper design and project management principles were adhered to along with the use of qualified and experienced engineers, then all the deaths and injuries could have easily been prevented. It really shows us just how important the engineer’s job is and how catastrophic a small mistake can be.

Recommendations

From studying the Injaka bridge collapse in depth I have developed several recommendations which I feel would have made life changing differences during the construction process of this bridge.

• Every engineer involved with the project should be suitably qualified and experienced to do so.
• Every engineers’ work should always be subject to a design review.
• There should be specially equipped and experienced teams in place during the launch procedure when using the incremental launch method.
• There should be a safety team ready on the ground on site in case of emergencyissues for engineers.

When televisions and computers were introduced to society at the end of the 20th century the great effect it would have on future generations was not initially realised. Both these pieces of technology have allowed society to relax, further their education and many other benefits but they have also led to much more negative issues such as depression and obesity. This is a prime example of how engineers have improved society with the introduction of new technology but from another angle have also had negative effects on certain areas within that society.