19-11-2012-SUMMARY OF E-CONFERENCE ON TALL BUILDING

Moderator- Prof. Dr.Swaminathan Krishnan

High rise buildings have to be planned, designed, constructed, and maintained properly.He emphasized that even though alanysis can be carried out using available softwaretackling of the wind load and seismic loads by choosing right configuration of thebuildings is very important. Also other aspects like DETAILING, TRANSPORTATIONconstruction materials in and around the building during execution also need to bethought of.

Moderator- Prof. Dr.CVR.MURTHY.

Dr.CVR.Murthy in his welcome address informed that

Tall Buildings seek higher level of engineering and architecture services. In particular,the attention is focused for the first time on formalizing some of the important buildingconstruction items, like MEP, utilities, services, facades, false ceilings/floors, buildingphysics, building services automation, and maintenance.

He stated that India needs to strengthen three of its existing systems.

1.A strong technology base with

(a)A Focused Research and Development on all aspects of Tall Buildings, especiallyGeotechnical and Geophysical Investigations, Wind Tunnel Studies, Structural Behaviourunder near-field earthquake ground motions and strong wind actions, and MEP servicesand other utilities;(b)A Trained Manpower of Academics and Practioners (including Architects, Engineersand Contractors);(c) A Proven construction materials (especially new materials, - curves of highstrength concrete, lateral inplane response of structural glazing) and technologies; and(d)A Code of Practice for Tall Building in India (which guides professionals onGeophysical and Geotechnical, Architectural, Structural, MEP, Fire and Constructionalaspects);

(2) A legally empowered body of regulators of Tall Buildings, with wings in every cityand town interested in constructing Tall Buildings. Currently only Mumbai city has a TallBuilding Committee, even though Tall Buildings are mushrooming across the country;and

(3) A change in the mental approach to designing and constructing such buildings. Forinstance, the usual construction practice needs to be halted of starting constructionwithout designing the building. Unless the planning and designing of Tall Building iscompleted, even approvals for construction should not be issued by local municipalbodies.

He is interested to participate as one among us by sharing his knowledge with us.

Dr.N.SUBRAMANIAN,:

I call him the GURU of sefi forum since he explained even a small postwithout any hesitation with what he learned.

Dr.Subramanian in his welcome address stressed the importance of Building Tallbuildings due to reasons stated in his address. He pointed out the growth of Tallbuildings in India specially in Mumbai, Delhi, and Kolkata. He also pointed out thatbuilding Tall Buildings is not taking place in India but all over the world but at greatertrend than India.

Dr.N.S has pointed out maintenance of the buildings in additions to instrumentations ofhigh raise buildings for the determination of wind/ EQ/ other loads is to be done in afew cases. I learnt that about 400 buildings in Singapore are instrumented- see thenews item at the end. Has any building in India instrumented like that?

He also narrated the instrumentation as being conducted in Singapore.

MODERATOR Alpha Seth:

As Madam Alpha seth in her welcoming mail has given some note as Econferenceprotocol in which members are advised to restrict their posting to 2 in a single e mail.Also advised to exercise utmost civility while expressing your disagreement.

Listed the various topics for discussions from a to v (22 topics) including subdivisions.

Er.Suraj has listed ways and means to

Accessing construction materials to higher floors by listing 21 items likepumping of RMC.

Under Urbanisation of Metropolis Surrounding Areas-General Discussion–HighRise topic he again listed 42 points for the above.

Siting Tall Buildings Considerations –Once again Er.Suraj has suggested 17valid notes for this topic.

Er.P.K.Mallick has sought a clarification on the shuttering details for concretingof floor beams and slabs in highrise building subjected to sudden gust wind ?

Er.Hemant Gor has attached a pdf file from CTBHU Committee on Seismic Design ofTall Buildingswww.ctbhu.org

A KIND NOTE TO ALL WHO ATTACH OR ADD ANY MATERIALS SHOULD CHECKSO THAT THEY ARE NOT COPY RIGHTED ONE.

BJReddy also attached on document from CTBUH, which will basically explain"Criteria for the Defining and Measuring of Tall Buildings”.

Er.V.P. AgarwalISHA CONSULTANTS (P) LTDNEW DELHI 110074

Has voiced his concern over the improvement in preparation of the drawings andcareful checking of Building designs and detailed drawings. Informed about theshortage of trained manpower for checking and the errors involved by many CADdraftsmen.

He also cautioned that due to the clients urgency or due to the pressure from othersproper checking can not be carried out and need special care in SOIL INVESTIGATIONSAND TH REPORTS.

Er.Suraj has again posted the Fire Water Provision For Tall Buildings topicfor which he has summorised 20 notes.

Er.JEET SINGH:

Some of the points that come to his mind are listed below:1) Terrorist/Blast attacks:

In response to this Dr.N.Subramanian has sent the reply as :

Reg. measures to mitigate the effects of Terrorist attacks on buildings. I wish to bringto your notice a nice booklet authored by Prof. Murty of IITK(now he is in IITM) onthe above title and published by IITK and Gujarat State disaster Management Authorityin 2007, which may be obtained from NICEE. Though it is not meant specifically for Tallbuildings, the principles are same. You may also note that the detailing is similar to EQdesign as the main aim is to prevent progressive collapse.

Note also that this document is based on the extensive literature made available byFEMA(FEMA 426, 427,428,429 & 452). FEMA 426 may be downloaded fromhttp://www.accem.org/pdf/mitigatebuildings.pdf

For other FEMA documents visit: http://www.fema.gov/library/

A document titled Building Design for Homeland Security, is interesting as itfamiliarizes students with assessment methodologies available to identify the relativelevel of risk for various threats, including explosive blast and chemical, biological, or

radiological agents. The students will be introduced to publications FEMA 426 and FEMA452 and will be asked to provide mitigation measures for a range of manmade hazards.The primary target audience for these courses includes engineers, architects, andbuilding officials. A number of PPP slides explain the concepts.

For Tsunami loads see the PPP at escweb.wr.usgs.gov/share/mooney/SriL.V6.ppt

2) Tsunami loads:

3) Seismic reoccurance:

3) Seismic reoccurance:

He pointed out the importance of the above not only with respect to high rise buildingsbut also other types of buildings.

Er. BMR has sought clarifications for the followings:

What are the basic possible structural arrangements for tall structures in terms oflocation of shear walls? eg. core, peripherial, etc. and what should be the basic for thechoice of arrangement?

Is prestressed pre-tensioned better or post-tensioned. If pre tensioned is employedthen please provide some reference for design & detailing of connections and are thereany tolerance limits for the same?

Response to the above Dr.N.S has given the explanations as:

Location of shear walls should be at the extreme boundaries, so that we will get a goodleaver arm for resisting the lateral loads, and hence the forces induced will be less.Many engineers adopt core walls, as it is easy to locate them around the stairs and lifts.Also such walls will have box configuration instead of the simple rectangular walls;hence provide much stability- However, much care should be exercised in designing thelink beams around openings in the shear walls- Read the book by Smith & Coull, TallBuildings Structures-Analysis and Design, Wiley, 1991, which still remains as anexcellent book on this topic.

Are you talking about pre-tensioned slabs in Tall buildings. Most of these slabs areexecuted by proprietary firms and you need to consult them. However visit thefollowing sites, which may be useful:

http://www.vsl.net/Portals/0/vsl_techreports/PT_Slabs.pdf

http://www.post-tensioning.org/pti_journal.phphttp://www.pci.org/publications/journal/index.cfm

Geotech Consultant Mr.Jaydeep Wagh : has sent his views as follows salientpoints are highlighted :

SITING OF TALL BUILDINGSHigh rise buildings can generally be constructed almost any site with any subsurfaceconditions. However, certain difficult or complex subsurface conditions at some sitesmay render construction of high rise buildings impractical with respect to time andcost. These difficult subsurface conditions may include presence of competent strata atrelatively deep depths (>60m) or due to presence of miscellaneous fill with boulders,which make it difficult for piling equipment to penetrate to competent strata. Acomprehensive geotechnical engineering program combined with extensivegeotechnical experience of high rise buildings is essential in arriving at safeand cost effective foundation design.

GEOTECHNICAL INVESTIGATION PROGRAM:A complete geotechnical investigation program is an essential pre-requisite to arrive atdesign spring constants and/or foundation design of high rise buildings. A propergeotechnical investigation program may also help in significantly reducing foundationcosts along with ensuring safe foundations.

An universal detailed geotechnical investigation program cannot be prescribed for ahigh rise building site as it will obviously depend on the type of building, number offloors, number of basements (if any), and subsurface conditions. Typically,boreholes for a high rise building are spaced at every 25m to 30m and areextended to 1.5 times the width of foundation or 5m into relativelyincompressible strata and atleast 5 times pile diameters in case of pilefoundations. At a minimum SPT tests are generally conducted in soil and softrock, while rock coring operations are conducted in hard rock. A detailedcustom geotechnical program can be chalked out after initial boreholes are availableand a foundation system type has been selected. Detailed tests includingpressuremeter tests, plate load tests, or pile load tests can then be conducted. If localexperience is available, a detailed geotechnical investigation program may be specifiedright from the beginning. However, it is prudent to still study initial borehole logs tosee if any modification to the geotechnical investigation program is required.

PILED RAFT FOUNDATION :A piled raft foundation can be considered in lieu of a complete pilefoundation, if relatively competent strata but not totally adequate, isencountered at raft founding level. The efficiency of a piled raft foundation woulddepend on the relative stiffness of the soil/rock at raft founding level in comparison tothe soil/rock near pile tip level. It may be important to note that some degree ofresistance is always provided by the soil/rock beneath the pile cap or the piled raft.However, the effort required in analyzing this available resistance may not be justified ifthe soils at pile cap/raft level are relatively much softer. A typical example of this isa building constructed in soft marine clay areas when the pile tip is extendedto underlying hard rock. The contribution of a pile cap or raft portion of the piledraft in carrying loads may range from negligible (as mentioned above) to even 90% insome cases.

Typical allowable deformations are generally governed by the permissible differentialsettlement of the structure. Differential settlements limits as specified in severalcountry codes for raft foundations can also be applied to piled rafts. Typical permissiblelimits range from L/660 for spread foundations to L/400 for raft foundations. Somecountry codes also specify a permissible for total maximum deformations, for eg. 75mmin IS1904.

A more aggressive form of piled raft design, which has become quite popular in recenttimes due to development of geotechnical finite element programs is settlementreducing piles. This specific application can be used where a conventional raft onlyfoundation would have adequate factor of safety against shear failure, but cannot beutilized as it does not meet the permissible total/differential settlement criteria. Fewpiles are then added beneath the raft at strategic locations solely to reduce thetotal/differential settlements to within permissible limits.

A pile load test is absolutely essential for design of a piled raft system. A pile loadtest not only provides ultimate pile capacity, but also provides the pattern of pile loadv/s. pile settlement, which is essential in deformation analysis of a piled raft. Test pileshould be conducted using same equipment and methods as for final working piles.

Manual design methods can be utilized for geotechnical analysis of conventionalbuildings with relatively uniform loading patterns and uniform homogeneous typicallysingle layer soil type. However, finite element softwares are often a must forhigh rise building piled raft analysis, and are also considered moreaccurate.

In response to Mr. Geotech Consultant Mr.Jaydeep Wagh Er. Suraj has put 22notes regarding the Soil Investigation & Reporting .

Er.drferozkottamal has posted the question for clarification.

How to check safety against overturning, what should be the height aspect ratio,geometric proportioning...

Er.R L DINESH:

Has a doubt about the proposed of Tall building whether it will have effecton the adjacent structures due to wind.

In response Dr.N.S has the following :

IS 875 is very old, developed in 1987 and needs revision. Please visit the NICEE website(http://www.nicee.org/IITK-GSDMA_Codes.php). Down load the documentsIndian Code for Wind Loads IS: 875 (Part 3)

IS: 875(Part 3): Wind Loads on Buildings and Structures - Proposed Draft &Commentary

Wind Storms, Damage and Guidelines for Mitigative Measures A Commentary on Indian Standard Code of practice for design loads (other

than earthquake): For buildings and structures: Part 3 Wind Loads (SecondRevision)

An Explanatory Handbook on Proposed IS 875 (Part 3) Wind Loads onBuildings and StructuresThey discuss the provisions to consider wind interference effects. Similar clausesmay be found in ASCE 7-2010.

A reply from Er. Sureshkumar_Kumaresan( I hope he is an expert in WindEngg) is :

(1) When new structures are coming nearby, the wind loads on the existingstructures can increase/decrease depending on many factors such as thespacing between them, dimensions/geometry of the structures, oncoming turbulence,structural properties etc. Note that this influence will exist only for a few angles ofattack and generally the built-in factor of safety will cover if any increase in loading.

(2) In another sense, over the years the city is going to get build and then thecrowded cities will essentially protect the new upcoming buildings from the full forcewind. This means typically upcoming new structures may experience less loadthan a similar structure getting constructed now.

Er.B.V.Harsoda, A Bronze Sponsor has attached 2 papers from

The 14th World Conference on Earthquake Engineering held on October 12-17, 2008,Beijing, China1. Study of Structural RC Shear Wall System in a 56-Story RC Tall Building.

2. AMBIENT VIBRATION MEASUREMENT AND EARTHQUAKE RESISTANT BEHAVIORANALYSIS ON A TWOTOWER TALL BUILDING WITH ENLARGED BASE.

The above papers can be downloaded from the links as appeared in his postings.

In addition he has provided a YOUTUBE on Tall building design which can be viewed bypressing PLAY button.

Er.u.mukesh has put the posting:

How do we define tall buildings? For this Er. RangaRajan has given the link where hecan find the definition for Tall buildings.

http://www.sefindia.org/forum/viewtopic.phpt=13016&postdays=0&postorder=asc&start=20

In addition Madam Alpa Sheth has given some more explanation regarding the Tallbuilding definition in the context of Indian scenario as 70m, China as 28 m, IBC ~50m.

After how many stories or height "Wind load" would be governing than "Earthquakeload"?

She clarified on the boundary limit of WIND and Seismic of Tall building. In this contextshe explained the drift limit of h/500 and h/250 for wind and seismic forces where h isthe total height of the building.

Prof.Swaminathan has raised the limit of minimum stiffness requirement for whichMadam Alpa sheth has commented as:

Typically, we seem to link stiffness with max allowable deformation under the designseismic loads of say h/500 and up to elastoplastic inter story limit of h/120 for shearwalls (say h/100 or frame-shear walls and so on) under such loads.

She raised the question to Prof.Swaminathan as my question is- should we have someother way of defining stiffness- either as you say ratio of area of the shear walls/verticalelements to total floor area or max fundamental period of a building with relation to itsheight or ....as in India she came across buildings with 220 to 230 m high havefundamental period of as high as 9 seconds.

Er. Chinmayrshah has asked permission for presenting research project on“Stability Aspects of Tall Commercial Buildings in Earthquake and Recent Practices".

Hope moderator can reply to this.

Today:

No.of posting: 23

No. of replies: 29

T.RangaRajan.

E-Confer. Raconteur