The Burj Khalifa benefited from a temporary real time monitoring program and network before a permanent program ensued.
The temporary program was developed and installed in cooperation with Notre Dame University to monitor: 1) the building acceleration level during construction, which was also used for the tower system identification; 2) a complete GPS system, consisting of the rover at level 138 and a fixed station at the office annex, to measure the building real time displacement with time; and 3) a weather station to measure the temperature, humidity, wind speed and direction at level 138. The detailed configuration of the temporary real time monitoring system is shown in Figure 14.
While the building movement from wind loads remained relatively small throughout the construction period, on Sept. 10, 2008 the tower was subjected to the influence of a remote earthquake that occurred in Bandar Abbas, Iran, approximately 850 miles south of Tehran. During this event the earthquake was observed and felt across the GCC states and many buildings were evacuated. Figure 14 shows the measured motion of the tower at level 139. The peak accelerations observed were 2.76milli-g and 3.82milli-g in the x and y directions, respectively. Since the tower did not have an accelerometer at the base, a real time history analysis was not performed. During this event, the tower had the highest acceleration ever recorded since the installation of the monitoring system.
In addition to the recorded building acceleration and displacements depicted in Figure 14, a complete system identification was performed for the tower and included the estimation of the tower’s natural frequencies and damping. Predicted natural frequencies from the 3-D FEAM and the measured frequencies were within a 2 to 3 percent range, including the higher modes. The temporary real-time monitoring program was conceptualized, funded, and installed by Samsung in cooperation with Notre Dame University (Kareem, Kijewski, and Kwon) – serving as a seed program for expansion of the monitoring system into a state-of-the-art full scale structural health monitoring program.
Detailed summary of the temporary real time monitoring program configuration and building movement during construction (due to Sept. 10, 2008 earthquake in Iran)
Permanent full scale real time structural health monitoring program and network
The final chapter in monitoring the structural system at Burj Khalifa included the development and installation of a comprehensive full scale structural health monitoring (SHM) program consisting of: 1) three pairs of accelerometers at the foundation level of the tower to capture base accelerations; 2) six pairs of accelerometers at levels 73, 123, 155 (top of concrete), 160M3, Tier23A, and top of the pinnacle to measure the tower acceleration simultaneously at all levels; 3) a GPS system to measure the building displacement at level 160M3; 4) 23 sonimometers at all terrace and setback levels, including the top of the pinnacle at over 828 meters above ground, to measure wind speed and direction; and 5) a weather station at level 160M3 to measure wind speed and direction, relative humidity and temperature. This final SHM program was an extension to the already existing temporary SHM system developed to monitor the building behavior during construction in cooperation between Samsung C &T, The University of Notre Dame, and the wind tunnel testing facility at Cermak Peterka Petersen. (See Figure 15 for the detailed configuration of the SHM program concept developed by the author for Burj Khalifa.)
Detailed summary of the permanent real-time Structural Health Monitoring (SHM) program concept developed by the author for Burj Khalifa
Since completion of the installation of the SHM programs at Burj Khalifa, the tower’s structural system characteristics have been identified and included measuring the tower’s: 1) acceleration at all levels; 2) displacements at level 160M3; 3) wind speed direction at all terraces; 4) building frequencies, including higher modes; 5) estimated building damping ratio at low amplitude due to both wind and seismic events; and 6) time history records at the base of the tower due to seismic events.
Comparison between the predicted building behavior and the in-situ measured response has been excellent. While these findings cannot be shared fully here because of confidentiality restrictions, Figure 16 provides samples of the data measured in real time at Burj Khalifa during an earthquake of M5.8 magnitude that occurred in southern Iran on July 20, 2010. While the magnitude of this earthquake was diminished when it reached Dubai and was relatively small (less than 1milli-g at the Burj Khalifa site), the earthquake had frequency content that matched the pinnacle frequencies, thus setting the pinnacle in resonance. The acceleration time history record captured at the lowest basement level was used to perform the time history analysis of the tower and a summary of the measured accelerations and the predicted displacements (not to scale) of the tower is shown in Figure 16 at all monitored levels.
Sample of measured acceleration at all levels (not to scale) and predicted displacement at all levels due to an earthquake event that occurred in southern Iran on July 20, 2010.
Historically, tall building design and construction relied solely on minimum building code requirements, fundamental mechanics, scaled models, research, and experience. While many research and monitoring programs have been employed in tall buildings, these programs had very limited research and scope to be systematically validated and/or holistically integrated.
The development of the comprehensive SHM programs at Burj Khalifa provided immediate and direct feedback on the actual structural performance of the tower from beginning of construction and throughout its lifetime, and includes the following:
- Testing all concrete grades to confirm the concrete mechanical properties and characteristics (strength, modulus of elasticity, shrinkage and creep characteristics, split cylinder, durability, heat of hydration, etc.)
- Survey monitoring programs to measure the foundation settlement, column shortening, and tower lateral movement from the early construction stage until the completion of the structure.
- Strain monitoring program to measure the actual strains in the columns, walls, and near the outrigger levels to confirm the load transfer into the exterior mega columns.
- Survey program to measure the building tilt in real time and the utilization of GPS technology in the survey procedure.
- Temporary real-time SHM program to measure the building acceleration and displacement, and to provide real-time feedback on tower dynamic characteristics and behavior during construction.
- Permanent real-time SHM program to measure the building acceleration, movement, dynamic characteristics (frequencies, mode shapes), acceleration time history records, wind velocity and direction along the entire height, and fatigue behavior of the spire/pinnacle.
The data collected from the survey and SHM programs were found in good agreement with Samsung predicted structural behavior. The survey and SHM programs developed for Burj Khalifa have:
- Validated the design assumptions and parameters used in the design, analysis, and construction techniques.
- Provided real-time information on the structural system response and allowed for potential modification to construction techniques to ensure the expected performance during construction and through the building’s lifetime.
- Identified anomalies at early stages and allowed for means to address them.
- Generated very large amount of in-situ data for all concrete materials used for the tower.
- Provided full feedback on the foundation and structural system behavior and characteristics since the start of construction.
The survey and SHM programs developed for Burj Khalifa will certainly pioneer the use of such concepts as part of the fundamental design of building structures and will be benchmarked as a model for future monitoring programs for all critical and essential facilities. However, advancements in computer and IT technologies, innovative advancement in fiber optic sensors, nanotechnologies, dynamic monitoring devices, new GPS system technologies, and wireless monitoring techniques will be used as a base for future survey and SHM programs and will become an integral part of building design and intelligent building management systems.
Ahmad Abdelrazaq, S.E., M.ASCE, is the senior executive vice president and head of Highrise & Complex Building Division, Samsung C&T Corporation. Prior to joining Samsung C&T, he was an associate partner and senior project structural engineer for projects, including Burj Khalifa, during his tenure at SOM. He is also an adjunct professor at Seoul National University, School of Engineering. Contact him at email@example.com.