Buildings and Bridges An Overview

Prof M T R JayasingheSenior Professor

Department of Civil EngineeringUniversity of Moratuwa

Moratuwa, Sri Lanka

(Power point slides used for a lecture conducted on 14th 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 countriesHence, a very significant influx of foreign exchange Demand to move to city centers and hence modern buildings and apartmentsSri 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 buildingAt each floor level, a slab is neededOne requirement is that slab must be a horizontal

plate at the correct floor levelThis shall be achieved with axial shortening effects

due to loads and shortening of concrete columnsThe beams will support the slabsColumns are needed to support the beamsIf 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 – Rajagiriyadue to the building turning by 45 degrees over the car park

area

Cellular transfer floorsCellular 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

Computer generated 69 storey Altair

Under construction

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 EuropeCheck 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 approvalCoordinating Engineers – Deepal Wickramasinghe and Bimal Fernando

Other tall apartment buildings – ClearpointVertical garden needed cantilevers up to 4.8 m to plant trees not obstructed by columns – made possible with PTPrice – Rs 35 to 40 million or

Will be affordable only if having property in a more expensive countryRun 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 6th of July

Progress – 16th 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

23rd 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 m2 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

The concrete bridge with minimum carbon foot print – cost is only Rs 2000 per sq ft, 300ft long and 10 ft wide

Bridge must assure that cultural pageants with elephants can use the bridge so as construction vehicles can cross it – hence designed for 25 units of HB as for BS5400: Part2: 1978

Other bridges in the Eastern Province with precast prestressed concrete beams

Shape of PT beams

Y-beams

Cross section with Y beams

Deck supporting beams of Orugodawatta flyover

Modern Plate Girder Steel Bridges

Incorrect setting out details at Rajagiriya flyover

Computer modelling to rectify the mistake –hence no room for mistakes

PT concrete 4 lane bridge at Orugodawatta on A4 highway

The bridge looks like a continuous bridge

Inspiration for such cantilevers came from bridge capping beams having 5.5 m cantilevers and constructed with post

tensioned prestressed concrete

During construction – Pier capping beams supporting the precast beams of 30 m span having a weight of over 100 tonnes

After completion with 5.5 m cantilevers supporting heavy loads from the weight of the beams and vehicles using the bridge

In use after completion of the 4 lane flyover with a total length of 560 m

DEF in Southern Highway bridge pile caps in Sri Lanka – The British consultant and the Japanese contractor underestimated the potential and

portland lime cement was allowed when specification clearly indicated only Portland cement and also too much optimization of pile caps

Summary on concrete bridges

• Concrete bridges have a very good durability record if adequate attention has been paid to the details

• The setting out shall be done very accurately• Otherwise, there can be costly alterations• When the bridges are curved, curve setting

principles shall be used to get the accurate path envisaged by the designer

Acknowledgement

• Academic staff of University of Moratuwa who gave me a solid start• Prof Chris Burgoyne, my mentor and a brilliant engineer who showed me

the way forward when reading for Ph.D.• All my very good friends in Sri Lanka and United Kingdom who have

helped me in numerous ways• The staff at University of Moratuwa for all the support and

encouragement for career development• The Sri Lankan construction industry that allow us almost any wish we

have to be fulfilled • All my co-researchers for their hard work• The office bearers and staff of The Surveyors Institute of Sri Lanka

Key words for searching on Intenet to learn about Sri Lanka

• Altair Sri Lanka• Fairmount Rajagiriya• Skygarden Rajagiriya• Clearpoint Rajagiriya• Elements Rajagiriya• Crescat Monarch• Heritanc, Kandalama, Cinnamon Bay, Beruwala Earl’s Regency, Kandy

Citrus, Wadduwa Magampura holiday resort Blue waters – WadduwaRest house, Polonnaruwa Jetwing Blue, Negambo

• Ruins of Anuradhapura, Ruins of Polonnaruwa, Galle Fort,• Yala Safari, Udawalawe Safari• MAS Intimates Thurulie, Nelung Art Center• The clothing factory in Sri Lanka - Thurulie• Architect Moshe Safdie• ICSECM 2017

Straw panels as a walling material

Testing on Durra panels (compressed straw panels)

Construction with Durra panels

Method used to convince the general public of the load carrying capacity of compressed straw panels by the

manufacturing company

Rapid construction with alternative materials

The two storey house with the walls, floors and the ceiling all out of Durraincluding bathroom areas

Two storey house with light weight panels – the structure to be completed in 20 days for a two stoery house with living, dining, pantry, a bed room in ground floor, a toilet and bath, a store room, three bed rooms in the

upper floor with one study room and a balcony and a roof top garden at the second floor level with a water tank located over the staircase, floor to floor height of 3.0 m – cost of the structure to be 15 GB pounds per sq ft

and also using a lot of waste materials

Staircase out of lightweight panels

Precast prestressed concrete beams used for slabs

Placing of precast beams for the upper floor slab