In any structural engineering project, the design concepts and technology used need to provide robust health and long service life to generate assured revenue. Modern Architecture, advances in computations, advances in construction materials & machines, studies on post construction behavior reflecting in National Codes have resulted into more vibrant modern cities.
The success of structural design depends on possible failure analysis rather than safe design. A small technical snag at any stage of construction result into serious instability in structure. After 9\11 incident, Industry related structural engineering compels to predict probable worst load combinations which may act momentarily on any one time during the entire life of the structures and incorporate adequate deign strengths. Simultaneously the cost, duration of construction, availability of specific materials and feasibility of construction needs to be harmonized before approving the release of ‘GOOD FOR CONSTRCTION’ drawings.
Every country has developed and framed many design codes on different natural and accidental loads to be considered while designing any structure. The codes also provide adequate design guidelines for materials, construction methodology, long term behaviors of materials and to account such things in the designs before constructions. During February 2023 Turkey- Syria earthquakes, the structures designed as per the national codes have withstood seismic forces nicely and have performed very well.
Many international construction projects around the world are based on the lessons drawn from mother nature. A coconut tree is very slender, but its roots are nearly one third the height to allow large deflections and yet be ductile. This concept is used in all tall building and skyscraper designs. A Banyan tree with large base has many branches supporting its stability ,are compared to multi storey building structure. Slender members subjected to small lateral dynamic loads due wind, earthquake, tsunamis etc. experience huge instabilities. The beehive bracing system widely used in such slender structures of tall building and skyscrapers around the world has drawn its inspiration from Beehive (one of the stable structures of nature) made by arranging several hexagons equal to story height in a unique way as in Beehive.
Structural Health Monitoring (SHM) is an emerging multidisciplinary engineering field to monitor health of structures in real time and formulate remedies based on the present health and thus protect the useful life of the structures. SHM programs are normally custom designed for every infrastructure to monitor continuously real time variation of different internal stresses & strains, loads applied relative to their inbuilt strengths, degradation of materials, accidental loads, timely detection of micro cracks, deflections and rotations of structural components, architectural aspects like internal sound, light and shade, temperatures, humidity, air quality assessment etc. These data provide accurate and precise information on present health level of structure for customized health inspection and optimized maintenance services to protect normal life. Repairs, rehabilitations and retrofitting of the structures need less time.
Megastructures need accelerometers at foundation and different level to record the time history of seismic disturbances and long gage length optic sensor system to evaluate the post-earthquake ground settlements. A well-planned GPS system records displacements of entire structure due to lateral loads, sonimometers /weather stations record wind speeds and their directions, relative humidity, and temperatures. The SHM programs will start right from foundation stage to real working life for knowing and monitoring foundation settlement, non-verticality and shortening of structural members due to immediate and long-term elastic shrinkage and creep effects, fatigue characteristics. SHM programs supports the correlation between predicted behavior with actual behavior during gust wind speeds and seismic excitements. Tuned Mass Damping (TMD) and Base Isolation (BI) techniques are used in SHM programs to control the response of the structure during most of the seismic disturbances. In these methods the structure will move opposite to the direction of seismic force and there by bringing the structures to equilibrium. Image processing, scanning technique, thermal scanning help on larger scale to monitor the structural health of most of large engineering projects. The programs include web-based reporting and a SMS alert system for real time responses. The SHM program are best when they are self-powered, maintenance free and eco- friendly.
With the increase in population and urbanization, cities are expected to grow vertically with new satellite towns. More than 50% of the world tall structures are built in ASIA and application of SHM technology is to grow rapidly in ASIA with the economic growth. UN predicts by 2050, 70% of world population will be migrated to urban areas and most of the cities turning into smart cities with popular SHM programs for every infrastructure.
This compels all engineering community to start planning for cost effective and popular SHM programs for every infrastructure for a healthy city and for a better normal life. The job market in these segments demand huge number of interdisciplinary engineers.
Dr. Mahantesh N B
Dr. Sumeet Chakraborty
Department of Civil Engineering. – ACED