By Engr. Thaung Htut Aung
For people, cities have been priority destinations to explore their opportunities in education and business. This influx of people coming into cities led to the constraint of space. To address this constraint a solution that was explored and is still being practiced is vertical expansion i.e. construction of high-rises and tall buildings. These vertical expansion accommodates offices as well as residences, hotels, and shopping malls. But this leads to increase in population density, which in an event of a disaster is a public safety issue as well as a concern for economic continuity. The impact of disasters to the public cannot be underestimated, for which design professionals need special considerations in their designs and incorporate state-of-the-art technologies and tools.
Considering the impact of disasters especially earthquakes to tall buildings, experts at the Asian Institute of Technology (AIT) carried out research as well as collaborated with partners to provide technical support in the area of Performance-based Seismic Design of Tall Buildings. This support is currently being offered through AIT Solutions, which is an outreach center established by AIT to connect with industry and community partners to spread AIT’s expertise in engineering, technology, infrastructure, and knowledge transfer activities.
AIT Solutions has worked with partners and collaborators in over 130 tall buildings in the Asian region, wherein its team has carried out PBD for different types of structural systems, some of which do not strictly conform to all prescriptive provisions of building codes and verify that the structure meets the stated performance objectives and provide a level of public safety and overall building ductility requirements equivalent to that of a building that follows the prescriptive building code requirements.
With the experience in working on several tall building projects, one aspect that stands out in successfully achieving PBD implementation is the timing and collaboration between the design professionals. The timing and collaboration between the design professionals (architect, structural design consultant, PBD consultant, PBD reviewer, site-specific probabilistic seismic hazard assessment consultant, wind tunnel consultant, and geotechnical engineer) is important to complete the design on time as well as minimize multiple design iterations. PBD peer reviewer should be engaged at an early stage of the project, PBD peer reviewer should review the work of structural design and PBD consultants phase by phase from the early stage of the design process. Upon substantial completion of the structural design by the structural design consultant, PBD consultant evaluates the performance of the building using the seismic input provided by the PSHA consultant. PBD consultant then provides the evaluation results and recommendations to the structural design consultant to modify and update the design.
In initial assessment of analysis results, global responses of the building, i.e. base shear, transient drifts, residual drifts, lateral displacements, are checked for different levels of earthquakes. Transient drift is the maximum drift that occurs within the entire duration of oscillation of the building while the residual drift is the permanent story drift when the excitation stops. Residual drift is checked to prevent excessive post-earthquake deformations which will pose potential hazards to surrounding buildings and lead the censure from building authorities. Lateral displacements are checked to prevent the pounding with adjacent buildings. Each structural component in lateral force resisting system, i.e. foundation, columns, shear walls, coupling beams, diaphragms, beams and columns in moment resisting frames, is evaluated in terms of strength capacity and ductility requirements to prevent the deleterious effects on components to carry gravity loads. Since the performance of the building is explicitly evaluated in PBD to resist the strongest earthquake ever likely to occur, marginal analysis is carried out in design optimization without large safety margins, for the use of construction materials, and for cost effectiveness and sustainability of limited natural resources while meeting the performance objectives of the design.
To know more about how we support our partners and collaborators during the Performance-based Seismic Design evaluation of buildings, contact us at: firstname.lastname@example.org.