Civil Engineering March 2022 | Vol 30 No 2

38 March 2022 Civil Engineering The client provided TAP with details of the existing antennae for modelling purposes. These were verified against the point clouds and suitable assumptions were catered for in the analysis. The loading on each tower was devel- oped by investigating the importance of the tower and the location with respect to its surroundings. The structural analysis was performed for both serviceability and ultimate loading with the results shown in Figure 4. The outcome from the structural analysis was utilised to generate recom- mendations for each tower, along with the necessary scope of work for refurbishment where applicable. The connection of each tower to the foundation, either surface mounted or embedded steel stubs, was evaluated above ground level for condition assessment and possible refurbishment. Intrusive investiga- tion of the foundations was excluded from the scope due to the project schedule and it was proposed that it be conducted when a contractor is on site. CHALLENGES AND INNOVATIONS The project posed various challenges. With the structural integrity of the towers in question, the client could not guarantee that the towers were safe to climb for the measurement of the tower members to generate drawings. To address this chal- lenge, ground-based LiDAR systems along with drone technology was utilised to scan the towers. However, the weather impacted the use of the drones. The effect of wind on the sturdiness of the drones was mitigated by utilising different sized drones as well as flying at times of the day when weather conditions were most suitable. To improve the accuracy of the LiDAR scans, multiple scans were performed at different positions around the tower. Verification of angle member sizes and thickness was also done using physical measurements on certain points on the towers. This allowed for an accuracy of up to 2 mm and, when utilising standard da- tabases of steel sizes, allowed for suitable structural models to be developed. Another challenge was that PLS TOWER only caters for version G of the standard. However, the latest version of the design standard for telecommunica- tion towers was version H at the time of performing the project, although Eskom utilises version G of the standard due to the structural analysis software available to it. The differences between the versions were compared to see if there would be any impact on the structural analysis. Due to time constraints, steel samples could not be taken from the towers for material testing. The age of the towers and the steel and bolt grades utilised in the industry at that time of construction were used to estimate the material and bolt grades on the towers. The development of structural draw- ings utilised a database of steel sections, but the towers under investigation were designed with imperial and metric units. The database of section sizes was there- fore conservatively estimated to select section sizes for analysis purposes. CONCLUSION The project was completed with the analysis of the five towers showing four different outcomes: 1. Towers 1 and 2 were found to have failed sections and required urgent replacement, with no further climbing allowed. 2. Tower 3 was over-utilised with the existing loads but also had climbing load violations. Refurbishment techniques would be more costly than replacement and replacement of the tower was therefore recommended. 3. Tower 4 was over-utilised with the existing loads but required some minor refurbishment work to be able to perform emergency maintenance on the antennae. 4. Tower 5 only had over-utilised bolts (these could be replaced one at a time) and required minor refurbishment to be able to carry 30% additional loading. The proposals for each tower have been submitted to the client for the next phase.  Project Team Chief structural engineer: Rishen Moodley Chief civil engineer: Siyabonga Dubazana Senior Engineer: Imraan Ally Technician: Siyabonga Sentile Engineering manager (KZN): Jay Hiralal Sub-contractor: Thyssenkrupp Figure 4 Existing tower utilisation Tower 1 Tower 2 Tower 3 Tower 4 Tower 5