1. Introduction

Forensic engineering (in the field of structural engineering) is the detailed study of a failed structure conducted to investigate the reasons for the failure. It is usually called the science that combines engineering with law and justice. Forensic engineering has multiple objectives such as finding the reasons behind failures of structures, the parties responsible for the failures, methods ofrepairing and rehabilitation and methods to improve structures through research. Forensic engineering research in a way led to the development of high rise buildings and marvellous bridges around the world.

Forensic engineering investigations usually do not have specific sequence of activities or procedures. Most of the forensic investigations include visual inspections, measurements, materials testingand structural analysis. Interviewswith people related to the structure,incidents happened in an around the structure, records related to the structure and photographs etc., are also included in the investigation depending on the failure. Someimportant aspectsof forensic investigations are;

1. cause of a failure is determined after the analysis of all information gathered, reviewed and verified,
   
   
2. information is gathered from independent and reliable sources using scientific methods,
   
   
3. widerange of information about the failure is collected without limiting to a narrow and limited set of data, and
   
   
4. the investigation is opened to all possible paths during the analysis without prejudice and predeterminations.

Some of the important qualifications of a forensic engineer are,being an expert in the subjectto technically determine the failure reasons and having fair, impartial and ethicalpersonal qualities to avoid any conflicts of interest.

2. Failure of structures in the resent past

With the rapid development, structural failures are also increasing around the world. Therefore, the importance of forensic engineering has become more important than ever. Failure reasons of structures collapsed in the resent past give enough evidences to emphasise the need for forensic engineering investigations. The lessons learnt from these failures can then be used to avoid such failures in the future. In this section, several failures of structures occurred in 2017 and 2018in Sri Lanka and around the world are discussed.

Pedestrian bridge collapse at Miami, USA on 17th March 2018: The collapse of a pedestrian bridge at the USA before open for public killing at least six people and injuring few others is the most resent failure of a structure in a developed country (Figure 1). Although the failure reasons are still underway, it has been reported that cracks have been observed two days before,but the designers have not considered any safety concerns. When the collapsed happened, workers were in the process of strengthening this new bridge.

Figure 1: Collapsed pedestrian bridge in USA (CNN, 17/03/2018)

Building collapse at Grandpass, Colombo on 14th February 2018: The most resent building collapse in Sri Lanka is a single storey old masonry building that collapsed killing 7 people and injuring many othersat Colombo(Figure 2). It is suspected that the influence of construction activities of a nearby site caused this failure apparently due to an accident due to negligence. Regarding the failure, reports on forensic investigations have not been released yet for the public.

Figure 2: Collapsed building at Grandpass, Colombo (Daily Mirror, 14/02/2018)

Bridge collapse at Chirajara, Colombia on 16thJanuary 2018: The second structure selected to discuss is a 446 m long cable stayed reinforced concrete bridge collapsed during the construction at Chirajara, Colombia (Figure 3). As reported on 16th January, 10 people were killed, several people were injured and 11 people were missing as a result of this bridge failure. Exact reasons for the failure are not revealed yet; however, the suspected reasons for this failure which occurred during the construction under normal weather conditions are improper design and construction.

Figure 3: Collapsed cable stayed bridge, Colombia (Reuters, 16/01/2018)

Building walkway collapse, Jakarta, Indonesia on 15th January 2018: A different failure is selected as the third example which is the collapse of themezzanine walkway of the stock exchange building at Jakarta, Indonesia (Figure 4). This failure injured more than 70 peopleand likely no deaths were reported. The investigation revealed that the suspension cable connections of the 20 years old walkway failed due to concentration of weight of about 100 people at one location of the walkway. The possible reasonswere loose or corroded bolts, failures at shearing joints and wear & tear of connection parts. Accordingly, the failure is directly related to inadequate maintenance of the walkway.

Figure 4: Collapsed walkway, Indonesia (Reuters, 16/01/2018)

Building collapse at Negambo on 17th August 2017: The next failure incident discussed here is the collapse of part of a reinforced concrete building at Negambo (Figure 5). The building was under construction when the failure occurred. Several workers were injured due to this collapse. Maturity of the structure below and problems associated with the formwork are the suspected reasons for this failure that highlights the effects of incorrect construction practices. However, results of forensic investigations of this failure have not been released to the public yet.

Figure 5: Collapsed part of the building in Negambo (Daily News, 17/08/2017)

Building Collapse at Wellawatta, Colombo on 18th May 2017: The last failure incident discussed in this section is the collapse of a reinforced concrete floor slab of a hotel building in Colombokilling 2people and injuring more than 27 people (Figure 6). The building was in use while a new construction is going on at the time of the collapse. Several investigations carried out on the collapse pointed out that the structure was not strong to carry the loads at the time of the failure. It was reported that the building had been modified heavily adding two new floors without getting the consent of the designer or the approval of the Municipal Council. The reasons for this failure have been highlighted in investigation reports as the violation of building codes during the design and construction, improper alterations and use of bad materials and workmanship.

Figure 6: Collapsed building in Wellawatta, Colombo (NBRO, http://www.nbro.gov.lk)

The main reasons for the collapses of five structures discussed in this section are negligence, improper design, incorrect construction practices, inadequate maintenance, improper alterations, bad materials and workmanship. Many lives of people and millions of money could have been saved if proper engineering practices were used.

3. Forensic Investigations – Case studies

Forensic investigations are not common in Sri Lanka. The reasons may be the lack of experts, high cost, lack of tools and equipment, lack of confidence in engineers to takeover such investigationsand lack of need of such investigations after a failure. In order to encourage forensic engineering, threeselected forensic investigations carried out in Sri Lanka are discussed here.

Investigation on Steel Bridge failure at Paragastota in 1999: Paragastota bridge is a steel truss bridge originally constructed in 1906 at Anuradhapura over Kala Oya. This bridge was brought to Peragastota in 1966 and a major repair was carried out in 1990. The bridge collapsed on 10th July 1999 when a truck carrying about 25 tons of metal was crossing the bridge (Figure 7).An investigation was carried out to find reasons for the failure that included visual observations, taking measurements, materials testing, finite element modelling and structural analysis. It was revealed that the failure was due to overloading of the bridge that triggered the yielding of bottom chord members, resulting large deformation with consequent fracture of diagonal members of the bridge. It was also found that the overloading is not only due to the truck but due to the reinforced concrete deck laid on the bridge replacing the original timber deck in 1990 without any structural design.Provided that proper structural design had carried out prior to the laying of the reinforced concrete deck, the failure could have been avoided.

Figure 7: Paragastota bridge after failure

Figure 8: Cement grinding plantbuilding before improvements		Investigation of partial failure of cement grinding plant structure at Galle in 2013: Four storey reinforced concrete building,designed to install a cement grinding plant, completed in 2013 had observable bending and shear cracks on some of its main beams (Figure 8). Reasons for these cracks were not clear as there were no imposed loads on the structure and no any accidental events happened during the construction. Therefore, an investigation was carried out to find the reasons for these cracks and to decide improvement methods. An extensive series of tests were first carried out to examine the strength of concrete and steel used in the structure. The tests showed that the strength of concrete was slightly less than the required strength but this was not the reason for such critical cracks. Then, a structural analysis was carried out using a finite element model. This analysis revealed that the structure was under designed and the amount of reinforcement provided in beams that have been failed was inadequate. The structure was strengthened by adding several shear walls and retrofitting using steel and FRP on failed beams.

Investigation of failure of telecommunication tower at Nuwara Eliya in 2014: A recently built 60 m tall self-supported telecommunication tower was collapsed after heavy winds occurred on 12th July 2014 (Figure 9). An investigation was carried out as per the request of the telecommunication authority that included visual inspections, study on the original design drawings, materials testing, finite element modelling and structural analysis. The forensic investigation revealed that the failure had been caused by a fatigue crack of a major steel leg member initiated from a bolt hole at a joint located about 20 m above the ground level that led to the collapse of the entire tower during the gusty winds. As a result, all the towers with the similar configuration were recommended to be improved.

Figure 9: Telecommunication tower after the collapse

4. Conclusions

The resent failures of structures point to the fact that most of them were the result of design faults, construction faults (improper practices, materials & workmanship), improper alterations or modifications, accidents, negligence & carelessness or a combination of these. This study revealed that the improvements made as a result of forensic investigations made the failed structures usable again. The failures of structures also show that theengineers (as consultants and contractors) have not adequately performed their role at the design, construction and service phases, thus being partly responsible for the failures.

Application of proper engineering practices is the way to avoid collapse of structures. The attention of engineers is essential in all three phases: design, construction and service for safe and efficient performance of a structure.The performance should be monitored throughout its service life (structural health monitoring), regular maintenance should be done and structural weaknesses should be improved as soon as they are identified. Although it is not yet an essential requirement, forensic engineering investigations should be carried out for both partial and complete failures of structures in the country. Then, justice can be brought to the victims, partially failed structures can be improved while totally failed structures can be used to learn lessons so that loss of livesand waste of money can be minimized.

Prof. Ranjith Dissanayake and Dr. Chaminda S Bandara
Department of Civil Engineering,
Faculty of Engineering,
University of Peradeniya.

References:

1. K. L. Charper, Forensic Engineering, 2nd Edition, 2001, CRC Press, p. 407.
2. U. I. Dissanayake, (2000), Failure of Paragastota steel bridge, Proceedings of Annual Sessions, IESL Central Province.
3. M. P. Ranaweera and P. B. R. Dissanayake, (2005), Consultant’s role in the construction phase of a building project, Proceedings of Annual sessions, IESL Central Province.
4. P. B. R. Dissanayake, C. Bandara and G. Dissanayake, Review of critical reinforced concrete elements and reasons for failure, RCW cement grinding plant, Holcim Lanka Ltd., Galle, March 2014.
5. P. B. R. Dissanayake and C. S. Bandara, Report for investigation of failure reasons of Mobitel tower at Boragas, NuwaraEliya, August 2014.