Buildings and Bridges An Overview Prof M T R Jayasinghe Senior Professor Department of Civil Engineering University of Moratuwa Moratuwa, Sri Lanka (Power point slides used for a lecture conducted on 14 th of June, 2019 at The Surveyor’s Institute of Sri Lanka )
An over view of the presentation • Introduction to Sri Lanka • Tall reinforced concrete buildings in Sri Lanka • The role of surveyors in tall buildings • Summary on concrete buildings • Steel framed buildings in Sri Lanka • Summary on steel buildings • The concrete bridges • Summary on bridges • Acknowledgement
Introduction to Sri Lanka Total area – 64000 square km Population – 22 million and more than 2.5 million live in other countries Hence, a very significant influx of foreign exchange Demand to move to city centers and hence modern buildings and apartments Sri Lanka can be promoted as an ideal destination for retirement due to tropical climatic conditions
Introduction to Sri Lanka • Carbon footprint of USA (17 tons), Canada (14 tons), Germony (9 tons), France (5 tons), South Korea (12 tons), China (8 tons), Malaysia (8 tons), Thailand (4.5 tons), India (1.6 tons) • Sri Lanka – 0.8 tons – hence one of the greenest economies • Hydro-power – 30-40%, coal 30-40%, diesel or heavy oil 10%- 30% • Renewable 10% with wind and solar but fast increasing the share; this has a ceiling of about 500 MW unless pumped storage is used along with battery storage • Many houses are generating own electricity with solar with 6-8 kw installed capacity and hence carbon neutral or negetive • 1 kw can give 4 to 6 kWhours per day – much higher than Europe • Most houses with solar may prefer to have an electric first car • Solar with battery storage has a very high potential in Sri Lanka with clustered roof mounted systems
Introduction to reinforced concrete tall buildings • Tall buildings can be considered as vertical cantilevers fixed to the ground. • Therefore, tall buildings must be provided with a strong foundation. • One of the key requirements is the accurate setting out of the building foundations • The foundation could be a raft or a thick reinforced concrete slab • In Sri Lanka, due to the bed-rock being located at reasonable depths, pile foundations also could be economically used • The locations of the piles must be carefully selected and accurately established at the site
BG 30 from Baur – up to 2.5 m diameter, easily 30 m or more
Importance of maintaining the verticality • The columns in a tall building can be subjected to very heavy loads • Thus, in the structural design, the design engineers will find the forces in the vertical members using 3D mathematical modelling • If the setting out is incorrect and the verticality is not maintained very accurately, the vertical load carrying members (columns and walls) can be subjected to heavy additional effects • Such effects can adversely affect the building and there can be many serviceability issues like excessive deflections and vibrations
A typical mathematical model
Main components of a tall building At each floor level, a slab is needed One requirement is that slab must be a horizontal plate at the correct floor level This shall be achieved with axial shortening effects due to loads and shortening of concrete columns The beams will support the slabs Columns are needed to support the beams If the grid of upper part of the building is different to the car park area arrangement, “Transfer beams” or “Transfer Plates” will be used
An example of transfer beams in tall buildings
An example of transfer plates in a tall building
Crescat Monarch in Colombo Crescat Monarch building with 30 floors was originally designed as an office building, but subsequently changed to become an apartment building
Cellular transfer plate in Fairway Sky Garden – Rajagiriya due to the building turning by 45 degrees over the car park area
Cellular transfer floors Cellular transfer plates look almost like thick slab However, it is a grid of beams acting with top and bottom slabs can simulate the behaviour of a thick plate but using less concrete and steel while having more robustness
The car park areas and pile caps
Pile foundations with single and multiple piles
Tall Buildings with very special shapes Under construction Computer generated 69 storey Altair
The architect and the team Structural Design Engineer – Predrag Error – an engineer from former Yugoslavia and now practicing in Middle East after gaining experience in Australia and Europe Check and Certifying Engineer – Thishan Jayasinghe – A chartered engineer can certify only up to four floors and beyond that needs a special permit. Only the experienced members of Institution of Engineers, Sri Lanka with post graduate degree in structural engineering can certify tall building having more than 20 floors – needs a special permission and name on the directory of structural engineers published annually and used by the Urban Development Authority for approval Coordinating Engineers – Deepal Wickramasinghe and Bimal Fernando
Other tall apartment buildings – Clearpoint Vertical garden needed cantilevers up to 4.8 m to plant trees not obstructed by columns – made possible with PT Price – Rs 35 to 40 million or Will be affordable only if having property in a more expensive country Run by a management committee one year after the sale of more than 80% of the apartments
Fairmount Urban Oasis and Fairway Skygarden
The 26 storey, 3 star city hotel with five star facilities and an “Infinity” swimming pool at the roof top with panoramic view
Midas Gen was the main software for the Kingdom tower and ETABS was used for checking
Structural forms for tall buildings
Transfer floors with large beams supporting walls above and supported by few columns below The locations are very critical for stability
Extruded view of transfer beams and indicate that beams may not be loaded symmetrically
Summary on reinforced concrete tall buildings • With the proposed Colombo International Financial Center (Port City) project, we can expect more than 100 tall buildings from 2020 to 2040 • Surveyors will have a major role to play in these projects with respects to implementation at macro level for master plans and location of buildings • The services of surveyors will be needed for the location of grid lines, location of piles, maintaining verticality, establishment of grids on transfer floors and beams, etc. • All these will need a good understanding in the way that tall buildings behave to appreciate the great deal of responsibility resting on the surveyors dealing with buildings at micro level
Introduction to steel framed buildings • Steel framed buildings are often used for warehouses • The usual structural form is portal frames • Instead of UB sections, it is possible to use steel trusses as well • Some of these buildings can be pre-fabricated type • Since the foot print is large, accurate setting out of the grid lines is essential • Foundation construction may pose problems since these light weight structures are often constructed on grounds with poor soil conditions
Alternative systems has resulted in much shorter construction times At Negambo hospital – the progress at 6 th of July
Progress – 16 th July – the buildings with 3.0 m long eaves to ensure adequate shading
Precast prestressed concrete panels made continuous with an innovative method to reduce vibrations in thin panels
Use of precast prestressed concrete panels of 90 mm thickness, 1.0 m width and up to 6.0 m length for concrete floors - Panels connected with 40 mm thick reinforced chip concrete screed Pre-cast Pre-tensioned slabs spanning on steel beams with a reinforced in-situ topping on top
Upper precast concrete floor completed with ceramic tiles and the ceiling erected rapidly with Durra panle – the walls with flexi-board mounted Durra Panels to have water resistance
A/C ducts of air conditioning system mounted under the structural members
23 rd of July – Two storey buildings that can resist cyclones of probable magnitude and also an earthquake up to 7 on Richter scale
Three story building – the same concept can be used even in a tall building once adequate attention is paid to detail and the lateral stability
Summary on Steel Buildings • Steel framed buildings are very useful in sites with lower soil bearing capacity due to lower weight • These can be massive and the tolerances for erection of the buildings could be low • Hence, it is essential to be very accurate in setting out and installation of foundations
Concrete bridges • The cost of 1 m 2 area of a bridge can be 5-10 times the cost of a similar area in a building • The reason for this difference is that bridges are designed for massive loads that can be due to heavy vehicles • The concrete bridges can be out of reinforced concrete or PT based • The bridges can be straight or may have deviations as can be seen in the elevated highways • There is no room for errors in setting out of bridges
Simple reinforced concrete bridges
The arrangement
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